阅读说明：本技术 天线 (Antenna with a shield ) 是由 艾伯塔斯·雅克布斯·比勒陀利乌斯 亚伯拉罕·格特·威勒姆·杜普洛伊 艾哈迈德·托哈·莫巴舍 康 于 2018-03-21 设计创作，主要内容包括：公开了一种用于通信装置的天线。该天线具有包括地平面和盖组件的结构。盖组件是导电的,大体上平坦并且具有平面形状,该平面形状在第一盖组件尺寸(L<Sub>1</Sub>)中比其在垂直于第一盖组件尺寸(L<Sub>1</Sub>)的第二盖组件尺寸(L<Sub>2</Sub>)中小。地平面是导电的并且大体上平坦的,而且地平面的大小大于盖组件的大小。盖组件导电地连接至地平面,而且与地平面间隔开,从而使得盖组件与地平面之间存在空间,并且该天线是中心馈电的。(An antenna for a communication device is disclosed. The antenna has a structure including a ground plane and a cover assembly. The lid assembly is conductive, substantially planar and has a planar shape that is within a first lid assembly dimension (L) 1 ) Perpendicular to the first cover assembly dimension (L) 1 ) Second cover assembly size (L) 2 ) Medium and small. The ground plane is conductive and substantially planar, and the size of the ground plane is greater than the size of the cover assembly. The cover assembly is conductively connected to the ground plane and spaced apart from the ground plane such that a space exists between the cover assembly and the ground plane, and the antenna is center fed.)

1. An antenna for a communication device, the antenna having a structure including a ground plane and a cover assembly, wherein:

the lid assembly is conductive, substantially planar, and has a planar shape that is within a first lid assembly dimension (L)₁) Perpendicular to the first cover assembly dimension (L)₁) Second cover assembly size (L)₂) The medium-small size is small and medium-sized,

the ground plane is electrically conductive, substantially planar, and has a planar shape with a first ground plane dimension (G)₁) And a second ground plane size (G)₂) Wherein

Said first and second ground plane dimensions (G)₁And G₂) Parallel to the first and second cover assembly dimensions (L), respectively₁And L₂)，

The ground plane has a first ground plane dimension (G)₁) Is greater than the cap assembly dimension (L) in the first cap assembly₁) And the ground plane has a size in the second ground plane dimension (G)₂) Is greater than the cap assembly dimension (L) of the second cap assembly₂) The size of (1); and

the cover assembly is conductively connected to the ground plane and spaced apart from the ground plane such that a space exists between the cover assembly and the ground plane, an

The antenna is center fed.

2. An antenna for a communication device, the antenna having a structure including a ground plane and a cover assembly, wherein:

the cover assembly is electrically conductive, substantially planar, and has a planar shape that is within a first cover assembly dimension (L)₁) Perpendicular to the first cover assembly dimension (L)₁) Second cover assembly size (L)₂) The medium-small size is small and medium-sized,

the ground plane is electrically conductive and substantially planar,

the size of the ground plane is larger than that of the cover assembly;

the cover assembly is conductively connected to the ground plane and spaced apart from the ground plane such that a space exists between the cover assembly and the ground plane, an

The antenna is center fed.

3. An antenna as claimed in claim 1 or 2, wherein the cover assembly is spaced from and parallel to the ground plane.

4. An antenna according to any of the preceding claims, wherein energy/radiation radiated/emitted by the antenna emanates from between the cover assembly and the ground plane.

5. The antenna according to any of the preceding claims, wherein the energy/radiation radiated/emitted by the antenna is radiated from the ground plane and the cover assembly along the second cover assembly dimension (L)₂) Is emitted between the edges extending in the direction of (a).

6. An antenna as claimed in claim 5, wherein no energy/radiation is emitted therefromThe ground plane and a dimension (L) of the cover assembly along the first cover assembly₁) Is radiated/emitted between the edges extending in the direction of (a).

7. An antenna as claimed in any one of the preceding or following claims, wherein the communications device is an RFID reader operable for use in applications involving road vehicle detection and/or identification, and wherein, in components and assemblies of the RFID reader, at least the ground plane of the antenna is operable to be mounted on a surface of the road.

8. An antenna as claimed in any preceding claim, wherein the cover assembly is of dimension L₁×L₂Is substantially rectangular.

9. The antenna of claim 8, wherein energy/radiation radiated/emitted by the antenna is radiated from the ground plane and the generally rectangular cover assembly along the second cover assembly dimension (L)₂) Is emitted between the long edges extending in the direction of (a).

10. The antenna of claim 9, wherein no energy/radiation is emitted from the ground plane and the substantially rectangular cover assembly along the first cover assembly dimension (L)₁) Is radiated/emitted between the short edges extending in the direction of (a).

11. An antenna as claimed in any one of claims 1 to 6 or 8 to 10 when dependent on at least claim 7, wherein the ground plane extends substantially all the way through the road, or through a lane of the road.

12. An antenna as claimed in any one of the preceding claims being or being able to be understood as directly or indirectly dependent on claim 1, wherein the ground plane is at the first ground plane size (G)₁) Is not necessarily the same size as the ground plane at the second ground plane dimension (G)₂) Middle and large size phaseAnd, said ground plane having said first and second ground plane dimensions (G)₁And G₂) Is at least five times larger than the wavelength (λ) of the operating signal of the antenna.

13. The antenna of claim 12, wherein the road or lane of the road is about 4m wide and at the first ground plane dimension (G)₁) Is dimensioned to extend substantially all the way through the road or a lane of the road, and in a second ground plane dimension (G)₂) In the direction of (a), the ground plane extends approximately 1.5 m.

14. The antenna of any one of the preceding claims, wherein the planar shape of the cover assembly is in the first cover assembly dimension (L)₁) Is smaller than the second cover assembly size (L)₂) And f is a medium and small factor f, wherein f is more than or equal to 0.3 and less than or equal to 0.75.

15. The antenna of any one of the preceding claims, wherein the second cover assembly dimension (L)₂) Is about half of the operating signal wavelength (λ) of the antenna plus or minus a matching factor (x) of up to 20%.

16. The antenna of claim 14 or 15, wherein the frequency of the operating signal of the antenna is about 800MHz to 1GHz and the second cover component size (L₂) In the direction of (a), the cover assembly extends between about 90mm and 260 mm.

17. The antenna of claim 14, 15 or 16, wherein the frequency of the operating signal of the antenna is about 800MHz to 1GHz and the size (L) of the first cover component₁) In the direction of (a), the cover assembly extends between approximately 27mm and 195 mm.

18. The antenna of claim 14, 15, 16 or 17, wherein the operating signal of the antenna is largeAbout 920MHz, in the first lid assembly dimension (L)₁) In the direction of (a), the cover assembly extends approximately 75mm and is in the second cover assembly dimension (L)₂) In the direction of (a), the cover assembly extends for about 180 mm.

19. The antenna as claimed in any one of the preceding claims being or being understood as referring to claim 8, wherein the antenna is fed at a position on the cover assembly where the cover assembly is at the first cover assembly dimension (L)₁) And is the lid assembly dimension (L) midway between the sides of₂) Halfway between the ends of (a).

20. The antenna of claim 8 or any one of claims 9 to 19 when dependent on at least claim 8, wherein the shape of the cover assembly is L in overall dimension₁×L₂While having one or more sides or edges that are serpentine.

21. An antenna as claimed in any preceding claim, wherein the cover assembly is supported at a location spaced from the ground plane by one or more conductive support members.

22. An antenna as claimed in claim 21 when read as dependent on at least claim 8, wherein there are four conductive support members, one conductive support member being positioned between each of the four corners of the rectangular cover assembly and the ground plane.

23. An antenna as claimed in claim 21 or 22, wherein the distance by which the cover assembly is spaced from the ground plane is defined by the length of the support member.

24. The antenna of claim 23, wherein the support member supports the cover assembly spaced from the ground plane by a distance of approximately an operating signal wavelength (λ) of the antenna divided by a factor h, where 10 ≦ h ≦ 35.

25. The antenna of any of claims 22 to 24, wherein the support members are between the second cover assembly dimension (L |)₂) Is about half the operating signal wavelength (λ) of the antenna minus about 1% to 10%.

26. The antenna of any of claims 22 to 25, wherein the support members are between the first cover assembly dimension (L |)₁) With the first cover assembly dimension (L)₁) Approximately the same minus approximately 1% to 10%.

27. An antenna as claimed in any preceding claim, wherein the ground plane comprises a chassis and the cover assembly is spaced from and parallel to the chassis such that the space between the cover assembly and the ground plane is the space between the cover assembly and the chassis.

28. The antenna of claim 27, wherein the cover assembly and the chassis are both formed of a substantially rigid and electrically conductive material.

29. An antenna as claimed in claim 27 or 28, wherein the chassis is substantially planar and has a planar shape which is larger than that of the cover assembly but smaller than that of the ground plane.

30. An antenna as claimed in any of claims 27, 28 or 29 when dependent on at least any of claims 21 to 26, wherein the cover assembly is supported at a location where it is spaced from the chassis by the one or more support members.

31. An antenna as claimed in any preceding claim, wherein a filler or support material is provided in the space between the ground plane and the cover assembly.

32. An antenna as claimed in claim 31 when dependent on claim 21 or any claim dependent directly or indirectly on claim 21, wherein the filler or support material substantially fills the space between the ground plane and the cover assembly between the support members.

33. An antenna according to claim 31 or 32, wherein the filler or support material is a pressure resistant material and preferably also has a low dielectric constant and substantially constant dielectric properties at least at the operating signal frequency of the antenna.

34. An antenna as claimed in any preceding claim, further comprising a protective cover.

35. The antenna of claim 34, wherein the protective cover is in contact with the ground plane and extends over the cover assembly to protect the cover assembly.

36. The antenna of claim 35, wherein the protective cover is in contact with the ground plane all the way around a cover assembly, and the cover assembly and a space between the ground plane and the cover assembly are enclosed within the ground plane and the protective cover.

37. An antenna according to any of claims 34 to 36, wherein the protective cover acts as a radome.

38. An antenna as claimed in any of claims 34 to 37, wherein the protective cover is operable to assist the ground plane in reducing the radiation pattern of the antenna.

39. An antenna as claimed in any one of claims 34 to 38, wherein the protective cover has one or more edges which extend from the ground plane to the level of the cover assembly and the one or more edges of the protective cover have at least a portion which is sloped to help reduce the impact or shock on vehicle tyres or the like which contact or roll over the protective cover (or a portion thereof).

40. The antenna of claim 39, wherein one or more edges of the protective cover are straight along its length.

41. An RFID reader comprising an antenna as claimed in any preceding claim or operable for use with the antenna.

Technical Field

The present invention relates to an antenna, and more particularly to an antenna having particular design and performance characteristics, among other things.

In some specific (though infinite) example applications, the antenna may be located on the surface of a road, lane, etc., and can be used to perform Radio Frequency Identification (RFID) with radio frequency identifiable tags (RFID tags) located on the front and/or rear of a passing vehicle. In this application (or a similar application), the antenna would be a component of (or associated with) an RFID reader operable to communicate with the RFI tag. Preferably, the RFID tag will be located on (or integrated as a component of) a license plate of a vehicle. More specifically, for vehicles with license plates on the front and rear, the RFID tag will preferably be placed on (or integrated as part of) one or both of the license plates of the vehicle, or for vehicles with only one license plate, the RFID tag will preferably be placed on (or integrated as part of) that single license plate.

Notwithstanding the foregoing, it should be clearly understood that no specific limitation is implied from any of the above-mentioned or below-discussed example applications or uses. Thus, the antenna may also be used in a wide range of other areas and/or applications. By way of example, the antenna may instead find its use on, for example, goods or products moving past the antenna (e.g., goods or products carried past the antenna by a machine or on a conveyor belt, like in a factory or manufacturing facility, airport baggage handling system, etc.), rather than being used in road applications to detect RFID tags placed on the front and/or rear of a registered road traveling vehicle (or on the license plate of the vehicle).

However, for convenience, the invention will be described hereinafter with reference to and in the context of the above road application in which an antenna communicates with an RFID tag located on (or integrated as part of) a vehicle license plate.

Background

For background and introduction to the present invention, reference is hereby made to the following earlier patent applications, namely:

■ International patent application No. PCT/AU215/050161 (hereinafter "patent application' 161");

■ International patent application No. PCT/AU215/050384 (hereinafter "patent application' 384");

and

■ Australian patent application No. 2016101994 (hereinafter "patent application' 994").

The entire contents of the earlier patent applications listed above are hereby incorporated by reference herein. Moreover, features, components, assemblies, design features, methods, procedures, acts, alternatives, possible substitutions, and the like described in the earlier patent applications listed above may also be used in the invention or as part thereof, even if not specifically stated or illustrated herein. However, in the event of any inconsistency or discrepancy (or to the extent of any of the disclosures in the present specification and the disclosures in any of the earlier patent applications listed above, the present specification prevails and is covered. Moreover, the mere incorporation of the teachings of the above-listed earlier patent applications herein does not imply that any express or implied limitation or definition of any invention disclosed in any of those earlier patent applications, or any express or implied limitation or definition of any other disclosure given herein, must also be applied to the present invention or disclosed herein.

In the context of road vehicle detection and identification through the use of RFID, the ' 161, ' 384, and ' 994 patent applications (to varying degrees of specificity) illustrate that there are a number of significant benefits and advantages arising from the following: placing the RFID tag on the vehicle rather low (i.e. very close to ground/road height), preferably placing the tag on one or both of the vehicle license plates (or embedding the tag within one or both of the vehicle license plates, thereby making the license plate a "smart" license plate); and also to enable the RFID tag to be read by an RFID reader, the antenna of which is (at least) placed on or in the road.

It should be noted that the proposals in the preceding paragraphs, i.e. placing the RFID tag low on the vehicle (preferably with the tag on or embedded in the license plate) and enabling the tag to be read by an RFID reader (at least) with its antenna placed on or within the road, represent a major departure from the design and ideas behind conventional RFID systems for vehicle detection, identification and/or surveillance. Indeed, in most conventional RFID-based vehicle detection, identification and/or surveillance systems, RFID tags are mounted on the inside of the windshield of the vehicle (i.e., at a fairly high location on the vehicle), and the RFID tags on the vehicle are read by RFID readers mounted (often) "high" (typically on an overhead gantry or the like). These conventional systems, which include windshield mounted RFID tags and overhead or gantry based RFID reader placements, suffer from a number of disadvantages, as discussed more particularly in patent application ' 161, but also in patent applications ' 384 and ' 994. However, among the many drawbacks, the most significant one is the very pure costs associated with the overhead gantry, not only in terms of the costs of producing the gantry itself (which are large metallic constructions), but also in terms of the costs associated with erecting the gantry above the road and installing the RFID reader devices and the like thereon, as well as any subsequent maintenance or repair of the gantry and/or reader devices thereon, all of which usually require partial or complete closure of the road (which in turn is extremely destructive and expensive, not to mention the real costs associated with maintenance or repair).

The patent applications referenced to the above aspects describe the design and configuration of certain antennas and RFID readers incorporating the antennas, which can be installed or deployed on or in roads, and which may also be adapted (when installed/deployed on or in roads) to read RFID tags on the license plates of passing vehicles, including on expressways or other roads having high (or potentially high) vehicle speeds. The antennas and RFID readers described in those patent applications, and other associated disclosures therein, thus provide a possible alternative to conventional RFID systems, including particularly in highway and open road scenarios that rely on elevated gantries and the like. The use of the antennas described in those patent applications thus allows for a number of major drawbacks associated with overhead gantries or the like, including (among other things) avoiding or reducing their cost, while still allowing for vehicle detection and identification using RFID, etc.

For the purposes of the present description, it should be noted that in the case of antennas mounted/deployed on or in roads and used to read RFID tags on the license plates of passing vehicles, particularly on highways or other roads having high (or potentially high) vehicle speeds (and it is generally believed that certain antennas described in the above patent applications are suitable/capable of being used in such high speed applications), there is a necessary read zone for the antenna to be fairly well defined in its size and shape in practice. In other words, there is an area of fairly well-defined size and shape near the RFID reader antenna, which requires that the RFID reader inside the RFID reader antenna is able to communicate with the license plate mounted RFID tag of the vehicle if (or whenever) the vehicle tag is within the area. The reason for this necessary read zone (area) being rather well defined in terms of its size and shape is due to a number of factors, including: the placement and orientation of the license plate on the vehicle, the lane size (particularly width), the typical maximum travel speed of the vehicle (particularly on highways and other high speed (or potential highway) roads), and the time required for the RFID reader to reliably "read" (i.e., detect and unambiguously identify) the vehicle's (license plate-mounted) RFID tag. This is explained below.

(Note: the immediately following section is cited from the '384 patent application however, the following section has been abbreviated where necessary to make sense in the context of the present introductory discussion and reference is made to the drawings in this specification, rather than the (substantially equivalent) figures in the' 384 patent application:

under normal conditions, it is generally considered that vehicle identification using passive UHF RFID requires about 80ms to reliably exchange 512 bits of identification data, in consideration of radio characteristics, interference, the need for data loss retries, and the like. In this regard, it is generally considered that 512 bits of data are sufficient to identify the vehicle and perform at least a preliminary off-line verification of its identity. A vehicle traveling at 36km/h will travel 0.8m within 80ms, and a vehicle traveling at 180km/h will travel 4m within 80 ms. Thus, for the purposes of the present discussion [ and as also applicable herein ], the 4m of vehicle travel will serve as [ and also be assumed to be ] the minimum exposure required to reliably read the RFID tag on a moving vehicle. The skilled person will recognise that this is based on the assumption of a maximum vehicle speed of 180km/h, which seems reasonable considering that the vehicle will rarely (almost never) travel faster on public roads than this.

[ see the' 384 application, paragraph [0081]

Fig. 5 shows an … … read zone [ adjacent to the RFID reader antenna, within which ] vehicles are equipped with RFID enabled license plates [ that must be "read", i.e., detected and identified ]. The RFID enabled license plate [ lane width and hence license plate width ] travel path in fig. 5] is 4m wide with a read zone starting 5m in front of the reader antenna and ending 5m beyond the reader antenna (the reader in this example is located at the center of the lane … …). The space in front of the reader antenna 1m to more than 1m is excluded from the read zone to reduce the blinding effect of radiation reflections [ as discussed further in the' 384 application, from the underside of the vehicle when passing directly over the antenna ], and also because of angle reading problems that may arise in this area, particularly for vehicles (and their license plates) moving close to the side of the lane (rather than directly in line with the reader along the center of the lane).

… … [ depicted in FIGS. 1 and 5] typical values for the parameters are: l is 1m, Lx is 4m, Ly is 2m, and h is more than or equal to 200mm and less than or equal to 1200mm [ or more than or equal to 300mm and less than or equal to 1300mm ].

Figure 5 shows that the active read zone for RFID tags 9 … … is located on the vehicle license plate using an in-road RFID reader reading … …. The required read zone [ or required read region 2, also shown in fig. 1] covers a typical lane width [2Ly ═ 4m and the required 4m "in-beam" travel path (Lx) … …. The (width and plane) "dropped doughmut" shaped radiation pattern of the RFID reader (which is a highly preferred shape of the radiation pattern [ as shown in fig. 2 ]) is represented in fig. 5 with a circle denoted 3; it should be understood that even though this radiation pattern shape … … is indicated as being just as large as the circle [3] in [ fig. 5], this circle [3] in fig. 5 actually represents a falling-ring-like or extruded-ring-like radiation pattern, which preferably has a shape approximating that shown in [ fig. 2 ]. In summary, the radiation pattern [3] of the RFID reader has a front reading range of about 6m, combined with the reading angle effect on the RFID tag of the license plate, resulting in the shown effective … … reading zone [9 ]. The active … … read zone [9] is the area where the RFID tag on/in the vehicle license plate is located, which will receive sufficient power from the RFID reader to turn on and effectively reflect the modulated signal. As shown in fig. 5, the effective read zone 9 is substantially in the shape of a "figure 8", where the center of the figure 8 is located at the location of the RFID reader and the two circular portions of the "figure 8" project on either side of the vehicle's direction of travel. (it will of course be recalled that the antenna … … of the RFID reader is non-directional, so the orientation of the "figure 8" shaped effective read zone [9] -i.e., consistent with the direction of vehicle travel-results from the geometry of the requisite read zone [2], and convergence of the "figure 8" circle near the reader results from read angle issues.

[ see the' 384 patent application, [00124] - [00126] paragraphs ]

The '384 and' 994 patent applications thus explain (at least) the necessary read zone (i.e. the area close to the RFID reader antenna, within which the RFID reader within the RFID reader antenna needs to be able to communicate with the vehicle RFID tag if said tag is within said area):

■ are approximately 4m wide (2 m laterally on either side of the antenna) -this generally corresponds to the maximum width of most of the roadway,

■ occupy a space of about 5m to about 1m in front of the antenna in a given direction (i.e. in the direction of travel in the lane) and also a space of about 1m to about m behind the antenna (in the same direction) — 1m immediately in front of and behind the antenna is not included in the necessary reading area because of potential blindness and difficulty in reading the angle in this area, whereas the range of the first 5m to 1m and the second 1m to 5m of the antenna allows "reading" of tags within 4m of the travel of vehicles on both sides of the front and rear of the antenna, and if the vehicle is traveling at the maximum assumed vehicle speed (180km/h), 4m is the distance traveled in the time required to perform the "reading", and

■ extend in height, at least within the horizontal area defined in the foregoing, from between about 0.2-0.3m and about 1.2-1.3m above ground (road) level, this height range corresponding to the height range of the license plate (and therefore the RFID tag contained therein or provided thereon) above the ground at which the license plate (and therefore the RFID tag contained therein or provided thereon) is mounted on most road-going vehicles.

In particular, the gap between moving vehicles on the road is typically at least one vehicle length, on average about 6 m. The gap between vehicles is very difficult and is typically less than 4m only in very slow moving scenes. This provides sufficient time to read the front license plate of the following vehicle as well as the rear license plate of the preceding vehicle. Note that: these respective license plates are not simultaneously in the read zone. This geometry limits the number of RFID tags in the read zone. It should also be noted that RFID tags are now used to identify vehicle components and other items, such as pallets, containers, gas tanks … …. All of these tags and the objects to which they are attached are placed on the vehicle. These tags will also be within the radiation of the overhead gantry reader and the side readers. Where an overhead gantry reader and a side reader are used, they can therefore interfere with the reading of the tags on the license plate. However, these tags are generally not in the beam of the reader on/in the road. The on/in road readers are thus less disturbed by other tags in and on the vehicle.

For further illustration and to avoid any doubt, the necessary read zones described in the points in paragraph [0012] above are shown in FIG. 1. In fig. 1, the necessary read zone is again indicated with reference numeral 2. It should be noted that the dimensions of the essential read zones given in paragraph [0012] above may not exactly match the essential read zones discussed in the ' 161, ' 384, and ' 994 patent applications. However, those earlier patent applications clearly disclose a necessary read zone that is at least similar to the one given above, even if the cited zones differ slightly in size.

In order to achieve an effective read zone that covers or encompasses the necessary read zone just described, one approach previously thought desirable (as discussed in the ' 161, ' 384, and ' 994 patent applications) is through the use of an omnidirectional, vertically polarized radiation pattern, and thus through the use of an RFID reader antenna capable of providing such a radiation pattern.

More specifically, as explained in the ' 161, ' 384, and ' 994 patent applications, it was previously thought desirable that the radiation pattern 3 of the RFID reader antenna should preferably have a shape that may be described as a "drop ring" or "squeeze ring" -i.e., a shape as illustrated in fig. 2.

RFID tag antennas, such as those used particularly for RFID tags on vehicle license plates (which may often be simple slot antennas or the like, but a range of other antenna types may also be used), typically have a highly directional radiation pattern. (see fig. 5 and 6). More specifically, the radiation pattern of the RFID tag antenna on the vehicle license plate will almost invariably be directed generally in a direction 6 that is parallel to the "front" direction of the license plate, although directed away from the vehicle/license plate, as depicted in fig. 4. The direct radiation communication path 8 between the RFID tag antenna on the license plate and the RFID reader antenna (on/in the road) thus has an elevation (i.e. height/vertical) offset 5 from the front direction of the license plate and may also have a direction (horizontal) offset 7. The presence or absence of a directional (horizontal) offset 7 depends on the path of travel of the vehicle, in particular whether the RFID tag antenna on the license plate of the vehicle passes directly over the antenna or is offset to one side. Both elevation and directional offset (especially directional offset) can contribute to reading angle issues.

As will be apparent from the above, fig. 5 is a plan (i.e., "top-down") view of a road that includes three lanes. All three lanes carry vehicles in the same direction in this example, all three lanes are approximately 4m wide. In the middle of the center lane there is an RFID reader antenna placed on/in the road. Fig. 5 shows the following aspects superimposed on a three-lane road:

■ must read zone 2 (square area indicated by hatching);

■ Omnidirectional radiation Pattern 3 of an RFID reader antenna-recall that "omni-directionality in azimuth" is a radiation pattern shape characteristic previously thought to be most desirable for an RFID reader antenna; and

■ effective read zone 9, which in the two-dimensional "top-down" view in fig. 5 has the shape of the "number 8" (as a result of the overall geometry, including the geometry/shape of the requisite read zone 2 and the radiation pattern 3, which in this example is omnidirectional (circular).

FIG. 6 is generally similar to FIG. 5, except that only a single lane is shown, and the direction of vehicle travel in the lane is exactly opposite to the direction of vehicle travel shown in FIG. 5. However, one situation shown in fig. 6, which is not shown in fig. 5, is the approximate general shape of the radiation pattern of the antenna on the RFID tag on the license plate of the vehicle (or at least a plan geometric illustration of the shape of the radiation pattern of the tag antenna of this license plate). The radiation pattern shape of the antenna on the RFID tag (i.e., the "tag antenna radiation pattern") is indicated by reference numeral 4 in fig. 6. Although not the focus of the present invention (and indeed separate and independent from the present invention), the shape of the radiation pattern of the license plate tag antenna is still very important in the practical implementation of a system using RFID for road vehicle detection and identification, since it is the interaction between the radiation from the tag antenna and the radiation from the RFID reader antenna (and the radiation pattern shapes of the two respective antennas have a great influence on this interaction) that facilitates the exchange of information and thus the "reading" of the license plate RFID tag by the RFID reader. In summary, it is evident from the radiation pattern 4 shown in fig. 6 that the RFID tag antenna used on the license plate of a vehicle will typically, if not invariably, be highly directional, pointing forward in (or parallel to) the direct "frontal" direction of the license plate (this is also explained above and shown in fig. 4).

Next, for purposes of the present description, it should now be understood that for "open road" and highway applications, it is generally desirable to be able to detect and identify vehicles that may potentially be anywhere within a lane, including perhaps even across or across multiple lanes (if the road has more than one lane). This means that in these kinds of "open road" and highway applications there is a need (or likely to frequently be) to be able to detect and unambiguously identify passing vehicles despite the fact that there is often considerable uncertainty as to the actual position of the vehicle (i.e. the position of the vehicle actually relative to the antenna) as it passes the antenna. This is at least in part because, for a particular RFID reader antenna for a particular lane, the necessary read zone extends across the full width of the lane, as depicted in fig. 5 and 6. There is also a need to be able to detect vehicles moving in different directions relative to the antenna, for example if the antenna is placed at an intersection or intersection where different vehicles may pass over or past the antenna as they travel in different directions. As a result of these things, RFID reader antennas that can be placed on/in roads and that are adapted to read RFID tags on the license plates of passing vehicles on highways or other open road applications should generally have (or at least be desirable for them to have) a radiation pattern that "points" in the radiation direction around most, if not all, of the antennas. In other words, it is generally believed that the radiated energy of the RFID reader antenna should propagate to some extent in all radial directions (i.e., all horizontal directions parallel to the road surface-in other words, in all directions within the azimuth plane). Indeed, it was previously considered preferable to propagate the radiated energy of the antenna equally in all radiation directions (i.e. in all horizontal directions parallel to the road surface-or in other words equally in all directions within the azimuth plane). Thus, it was previously believed (and this was suggested in the ' 161, ' 384, and ' 994 patent applications) that the RFID reader antenna should preferably be omni-directional in the azimuth plane. However, this has now been somewhat reconsidered, as discussed further below.

Another important consideration is that the amount of energy radiated by the RFID reader antenna in the "up" direction (i.e., the amount of energy directed vertically upward perpendicular to the road surface-or in other words, the amount of energy directed at an upward angle relative to the azimuth plane) should be limited. There are many reasons for this, including limiting the potential for "blinding" energy reflections from the underside of the vehicle over the top of the antenna.

Further practical problems have been identified and are believed to be likely not adequately addressed by the various antenna designs set forth in the ' 161, ' 384, and ' 994 patent applications, which are challenges as follows: governments and regulatory agencies etc. and in particular those responsible for approving installation and/or use of any form of equipment (or any kind of object) on (or near) public roads are often very conservative and thus not ready for approval (or at least hesitant and highly prudent to allow) for installation and/or use of new types or forms of equipment (like for example RFID reader antennas on or in roads) that have not been used before on public roads, especially if the form (i.e. size and/or shape and/or general configuration and appearance etc.) of the new equipment is unfamiliar, not customary or different from the types and forms of equipment that have been previously approved for use on public roads and have actually been used on public roads, and in particular if the form of the new device is perceived to pose a potential risk or danger (even if only minimal or minimal stealthy potential risk).

Another problem has been identified and is believed to be potentially not adequately addressed by the various antenna designs proposed in the ' 161, ' 384 and ' 994 patent applications, which is associated with the directionality of the RFID reader antenna used on the vehicle license plate. For the avoidance of doubt, it is well known that the nature of most, if not all, of the types of antennas used (or likely used) for RFID tags on the license plates of vehicles (which may often be simple slot antennas, but a range of other antenna types may also be used) is highly directional (inherent to their design, placement and configuration). In other words, these kinds of antennas emit radiation mainly in a direction directly away from (i.e. perpendicular to) the ground plane of the antenna (which is parallel to the plane of the license plate), and the "spread" of radiation in a direction perpendicular/transverse to this "straight ahead" direction, in particular in a direction perpendicular to the "straight ahead" direction and parallel to the road surface, is relatively low. Thus, these kinds of antennas typically (due to their inherent configuration) have a narrow and forward pointing radiation pattern shape, like the radiation pattern shape 4 shown in fig. 6.

However, it has been identified that when these kinds of RFID tag antennas are used on license plates and especially on license plates that are in turn mounted on vehicles with large (or steep) metal fronts (like for example buses, trucks, some military vehicles, and even some vans and 4WD/SUV, etc.), the radiation emitted by the tag antennas on the license plates may sometimes become more directional in terms of efficiency. Thus, the radiation pattern shape 4 generated using an RFID tag antenna mounted on a license plate of such a vehicle having a large (or steep) metal front face may actually become narrower and more forwardly directed/focused. (incidentally, it is generally believed that the reason for this, at least in part, is that the large (or steep) metal vehicle front face acts at least slightly as an actual ground plane (or extension/enlargement of the actual ground plane) of increased size for the RFID tag antenna on the license plate.) in any case, this increased directivity of tag radiation on the license plate may in turn have the following consequences: for example, if the radiation pattern of the RFID reader tag antenna that is to "read" the RFID tag of the license plate has a completely omnidirectional shape (3) (i.e. extends equally in all radiation directions, as proposed in the ' 161, ' 384 and ' 994 patent applications), the combined effect of each of these geometries of the narrower RFID tag antenna radiation pattern and the RFID reader antenna radiation pattern and the interaction between them can be as follows: the effective read zone 9 can sometimes no longer extend all the way through the lane and therefore (where this occurs) may not completely cover the entire necessary read zone 2, as shown in fig. 7 (i). Thus, at the location where this occurs, the valid (i.e. actual) reading zone 9 may not cover all of the necessary reading zone 2 (i.e. there may be portions of the necessary reading zone 2 that are not covered by the actual reading zone 9, in particular portions near its edge/periphery (near the lane edge)), which means that it is assumed that: a passing vehicle may avoid detection/identification (or miss detection/identification) if the RFID tag antenna on the license plate passes through one of these peripheral areas of the requisite reading area 2, or the RFID tag antenna on the license plate does not have sufficient time within the active/actual reading area 9 to achieve a complete "read".

To help accommodate this, it has now been recognized that it may be desirable (at least in some environments/situations) to have the radiation pattern shape of the RFID reader antenna extend further than in other directions than in one or some horizontal directions, or in other words, to have the range of the radiation pattern of the RFID reader antenna be greater in one or some directions in the azimuth plane (i.e., the plane parallel to the road surface that radiates around the antenna) than in other directions. It is desirable that the present invention can provide a method that makes this possible. In particular, despite the increased directivity of the tag antenna radiation, it may sometimes be desirable to have the radiation pattern 3' of the RFID reader antenna extend even further through the road (or more in a direction perpendicular to the direction of travel of the vehicle on the road), which has the following effect: the effective read zone 9' again covers the full lane (and thus the full required read zone 2) (as a result of the respective geometries of the RFID tag antenna radiation pattern and the RFID reader antenna radiation pattern (discussed above) and as a result of the interaction between these two parties), as shown in fig. 7 (ii).

Another possible reason for desiring to extend the radiation pattern shape of the RFID reader antenna further in one or some horizontal directions than in other directions (and particularly to expect the radiation pattern to extend further in a direction perpendicular to the direction of travel of the vehicle on the road than in a direction parallel to the direction of travel of the vehicle) is that it is more difficult for vehicles (and their drivers) to avoid detection by "winding" the antenna (or by driving along a path/track that is a sufficient lateral distance from one side or the other of the antenna), as shown in fig. 7(ii) (albeit in an exaggerated and simplified two-dimensional manner), the drivers may attempt to do so and avoid having sufficient time within the radiation pattern of the antenna to achieve a complete/successful "read".

Yet another problem with using an RFID reader antenna that provides a radiation pattern that is omnidirectional in azimuth (i.e., like the "ring-down" radiation pattern depicted in fig. 2), especially when multiple such antennas are used at the same location, is that RFID tags on the car can be subject to crosstalk. This crosstalk may occur when the vehicle is driving between lanes (i.e., between two reader antennas), as depicted in fig. 3. In an arrangement such as this, the effective read zones of the various readers/antennas may often be designed to overlap to detect vehicles driving between lanes that avoid detection. However, in this setting, it is possible that two readers will transmit the same data message, which can cause confusion for a single tag (i.e., within a single vehicle) that is at an equal (or approximately equal) distance from the two antennas. See fig. 3 (i). If an RFID reader antenna is still to be used that provides a radiation pattern that is omnidirectional in azimuth (i.e., like a "ring-down" radiation pattern), one possibility for solving (or reducing) this problem is to stagger the antennas to try and establish sufficient separation to avoid crosstalk. Such a staggered separation may cause a diagonal separation of the driving path, so that lane dividers (vehicles driving between lanes) may still be detected, as shown in fig. 3 (ii).

Furthermore, a possible alternative to deal with or solve the problem discussed above with reference to fig. 3(i) may be to have the radiation pattern shape of the RFID reader antenna extend further in one or some horizontal directions than in other directions, or in other words to have the range of the radiation pattern shape of the RFID reader antenna be larger in one or some directions than in other directions in an azimuth plane (i.e. a plane parallel to the road surface that radiates around the antenna). In particular, in this case (and this in contrast to the case described with reference to fig. 7(ii) above), it may be desirable for the radiation pattern 3 "of the RFID reader antenna to extend (at least slightly) further along the road (or at least more in a direction parallel to the direction in which the vehicle is travelling on the road). Where this is done (and it is generally believed that the invention or variations thereof potentially suggest a method by which this may be achieved, or to which the method may be advanced), it is more likely to use selective feeding (potentially including non-centre feeding) to thereby cause the long axis of the radiation pattern shape (in azimuth plane) to point diagonally to the left or right, as shown in figure 8 (i). The tags can then be found using intelligent time division multiplexing to point the beam diagonally left or right (in a fast switching manner). Multiplexing can further lock the tags (once detected) until the tags are sufficiently interrogated and then multiplexing is resumed. Multiplexing requires synchronization between multiple nearby RFID reader antennas (see fig. 8 (ii)). In fact, different readers are able to detect the multiplexing of neighboring readers, even though the signal strength from the neighboring readers may be very low.

As mentioned above (although not limiting), for design purposes it is generally assumed that on motorways and open roads, the vehicle may travel up to (or almost) 180km/h, or at least at speeds of this order. As a result of potentially high vehicle speeds on highways and open roads, this is often the case: a vehicle passing an RFID antenna on a highway or open road and whose license plate-mounted RFID tag must be read by an RFID reader associated with the antenna will only be within the "read zone" of the antenna for a very short period of time (due to the speed at which the vehicle moves past the fixed antenna). The above explanation is: it is generally accepted that it takes (substantially) 80ms to "read" a license plate-mounted RFID tag; the vehicle running at 180km/h runs for 4m within 80 ms; and therefore a necessary read zone of 4m is required to enable successful "reading" of the RFID tags on the vehicle, assuming that the vehicle may pass the RFID reader antenna at speeds up to 180km/h (which is the maximum speed assumed for design purposes, although in reality the vehicle speed is almost never so high). In fact, as explained above, the necessary read zone should include the front 4m and back 4m of the antenna, but not the front 1m and back 1m regions immediately following the antenna (where blinding and/or read angle issues may prevent reliable reading). Therefore, in the direction of vehicle travel, the necessary read zone should cover 5m to 1m in front of the RFID reader antenna and 1m to 5m behind the RFID reader antenna. In order for the radiation pattern of the RFID reader antenna to "cover" these necessary areas, the power to radiate energy from the RFID reader antenna should be high enough to do so.

It has also been mentioned above that it has now been recognised that it is desirable to have the radiation pattern shape assume to extend further across the road than the radiation pattern 3 of the RFID reader antenna shown in figure 5. From the discussion in paragraph [0029] above, it may initially be thought that extending the radiation pattern shape further across the road may simply be a matter of increasing the power supplied to the RFID reader antenna (which may actually increase the range/size of the radiation pattern in all directions). However, simply increasing the power supplied to the RFID reader antenna is not always possible or allowed. On the one hand, there may be a limit on the amount of power that can be supplied to the antenna, for example due to a limit on the power that can be easily transmitted to a location on or within the road of the antenna, or may be due to a limit on the amount of power that can be supplied by the battery (if the battery has a lifetime or a less short recharge interval, etc.). Also, in many jurisdictions, there are laws or regulations that set limits on the amount of power that a wireless antenna (including an RFID antenna set for vehicle detection/identification purposes) can transmit. For example, these situations therefore typically set limits on the amount of power that can be supplied to the on-road/in-road antennas. However, even in addition to the above, there are practical reasons as to why it is undesirable to increase the power supplied to an RFID antenna (particularly an RFID antenna located on or in a road and used for vehicle detection and identification). For example, it was mentioned above that the amount of energy radiated in an "upward" direction from an on-road or internal antenna (i.e., the amount of energy vertically upward perpendicular to the road surface) should be limited, primarily to limit "blinding" reflections from the underside of the vehicle. Simply increasing the amount of power supplied to an on-road or in-road RFID antenna for vehicle detection/identification not only increases the size of the antenna radiation pattern in the radiation direction (parallel to the ground), but also increases the intensity (or power density) of the radiation pattern directed in a vertically upward direction (perpendicular to the ground) (i.e., increases the amount of radiated power), which would have the opposite effect, as this would (among other things) increase the likelihood of undesirable "blinding" reflections from the underside of the vehicle. Moreover, increasing the amount of power supplied to an RFID antenna is also likely to increase the amount of heat generated not only by the antenna itself, but also (and often more) by the associated RFID reader device supplying power to the antenna (among other devices). The heat generated by the antenna and associated RFID reader device can be extremely important, especially in the "in-road" scenario where the RFID reader (or its components/assemblies) are installed, as the possibilities for ventilation or other methods of heat dissipation are often very limited due to the location and environment in these installation scenarios. It is therefore important to minimize the heat generated by the antenna and any associated RFID reader (or other) electronics in the first place, as ventilation or heat dissipation difficulties mean that if excessive heat is generated in the first place, there may be a risk of overheating the antenna and/or electronics (which may in turn lead to damage or an anti-overheating shutdown, if not truly overheating or damage).

The '384 and' 994 patent applications disclose certain antenna designs having configurations intended to help overcome, among other things, a number of challenges associated with variable (and often substantially and dynamically variable) wireless Radio Frequency (RF) transmission conditions/environments existing in the vicinity of the antenna, including challenges due to the "near-ground effect". In fact, it is specifically explained in the' 384 patent application:

... "near-ground effect" is the ground (part of the earth) or surface-induced ground effect on which the antenna is mounted closest to the antenna (e.g., about 6m or about one typical vehicle length from the antenna). This "near-ground effect" (i.e., the ground effect from "near-ground") … … may be highly variable and even substantially variable (i.e., subject to changes over time and/or due to changes in conditions, etc.) in particular

While discussing … … the ability of the antenna to help compensate/address ground effects (particularly near ground effects), it is also useful to emphasize … … about the antenna and some other/relevant points … … that are important within its operating range in [ currently considered on/in-road ] applications. The first point is that when the antenna … … is positioned [ on/within the roadway ] for use in, for example, vehicle detection and/or RFID vehicle identification applications, the antenna can be considered to be effectively used in a manner generally similar or analogous to the antenna in the RADAR transmitter/sensor. Indeed, … … RADAR essentially comprises a wireless signal that is first transmitted by a sensor; the wireless signal is then reflected by the object to be observed, and the reflected signal is received and interpreted by the sensor (e.g., in order to detect the presence of an object, and/or its position and/or movement relative to the sensor, etc.). In the case of RFID, a signal may be transmitted by an RFID reader (including antenna … …), and a "reflected" signal may then be sent back to the RFID reader from, for example, an RFID tag on the vehicle. In RFID, both signals (i.e., the signal transmitted by the RFID reader and also the "reflected" signal sent back from the RFID tag to the RFID reader) may be modulated to carry information/data (this data modulation on the signal is at least part of distinguishing the RFID from conventional RADAR where the signal is not modulated). In other words, in RFID, information may be modulated onto a signal transmitted by an RFID reader so that information is transmitted from the reader back to the tag, and similarly, information may be modulated onto a signal transmitted (reflected) back to the RFID tag so that information is transmitted from the tag back to the reader. In the presence of such a bidirectional data exchange, and in particular in RFID vehicle identification applications, the exchange of information may be used to perform (it may in fact be that this enables to perform) an [ unambiguous ] identification (i.e. ID detection/recognition) of a specific vehicle. … …, alternative arrangements or situations are also possible in which the signal transmitted by the RFID reader and the "reflected" signal sent from the RFID tag back to the RFID reader (or one of them) are not modulated so that there is therefore no two-way data exchange as just described above. However, even in this alternative situation where the signal transmitted by the RFID reader and/or the "reflected" signal transmitted from the RFID tag back to the RFID reader is not modulated, the signal transmitted by the RFID tag is still received and interpreted by the reader, which (among other things) is still available for vehicle detection. Indeed, when such a reflected signal transmitted (reflected) back from the RFID tag is received by the reader, this signal (even if an unmodulated signal) may immediately indicate the presence of the RFID tag (and thus the vehicle) within the read range of the reader (although in this case which particular vehicle-i.e. the particular vehicle identity/ID-may not be determinable, at least not solely from the signal transmitted by the RFID tag). Moreover, the way the signal changes over time (i.e. the way the signal is sent from the RFID tag over time and received by the reader, even if it is an unmodulated signal) can be used (interpreted by the reader) to determine information about the (unidentified) vehicle (except just its presence). In practice, the position and movement of the vehicle, such as the distance and position relative to the reader, its speed of travel (and possibly direction), etc., may be determined. It will be appreciated that this last unmodulated signal scenario is somewhat more similar to a traditional RADAR [ compared to a two-way data exchange scenario in which explicit vehicle identification is achieved using RFID ].

Another point to emphasize is that when the antenna … … is used in, for example, vehicle detection and/or RFID vehicle identification applications, it may be used in a manner similar or analogous to a conventional RADAR antenna (see above), while at the same time the area in which [ RFID reader antennas used in on/in road applications currently under consideration ] need to operate, as well as the necessary transmission range, radiation pattern shape, and even physical location of the antenna (and thus the physical location in which and from which the antenna signal is transmitted) may be substantially different from antennas used in conventional RADARs. Indeed, for reasons explained in detail in the '161 and' 384 patent applications, the RFID reader antenna used in the presently considered on/in-road applications generally needs to be located at ground level, typically on or in the ground surface (i.e. on or in the surface of the earth) -for example on or in the surface of a road. The antenna would then generally need to be configured to be positioned at (and thus have its signal radiation radiate from) a ground plane on earth. This is very different from conventional RADAR, which is almost always located at a fairly high position above ground level, typically at least 2 wavelengths above ground (i.e., conventional RADAR antennas typically operate at a height of at least twice the wavelength of the RADAR signal they emit). Thus, conventional RADAR antennas are generally not required to accommodate many, if any, changes in signal transmission propagation conditions due to "near-ground effects". Of course, for them the influence of earth [ especially varying conditions/environments on earth ] causing propagation of signal transmissions may often be assumed to be negligible or at least constant, e.g. regardless of time and/or weather or environmental conditions or various changes of position in ground conditions, etc. This is very different from the RFID reader antenna used in the currently considered on/in-road applications, where the effect on the signal transmission propagation caused by the ground (especially the close ground) on/in which the RFID reader antenna has to be operated at present and where the antenna is located on or in (and especially the varying conditions/environments) can vary widely … … between different locations and also at the same location [ for example ] the signal transmission propagation conditions can vary widely over time even at a single location, for example as the surface conditions change due to nearby surface water versus dry, wet soil versus dry, [ and so on ]. [ Signal Transmission propagation conditions can also vary widely between different locations, possibly due to, for example, the presence or absence of metal or other conductors in the road bed, substances of different conductivity on the road, like paint or oil, etc. ] … …

Moreover, conventional RADAR antennas generally have a very concentrated/directional radiation pattern, which is intended to transmit over large or very large transmission distances (typically in a broadcast manner). Therefore, not only are conventional RADAR antennas generally positioned quite high above the ground plane, they have narrow concentrated/directional radiation patterns and transmit over large distances (i.e., they operate in what is commonly referred to as the far field — also known as the Fraunhofer region). In contrast, [ RFID reader antennas used in currently considered on-road/in-house applications ] may [ and typically will ] need to transmit over and within a very close range to the antenna, possibly even within the radiating near field (also known as the Fresnel region) of the antenna. Moreover, an antenna according to embodiments of the present invention may [ and typically will ] need to provide a non-concentrated radiation pattern, and which extends further in a direction parallel to the plane of the ground plane of the antenna than it does in a direction perpendicular to the plane of the ground plane of the antenna [ as discussed above and also in the '161 and' 384 patent applications ]. By way of illustrative example … …, [ for ] a … … antenna configured to operate at a signal frequency of about 1GHz (and thus at a signal wavelength of about 300 mm), an antenna that is a component of an RFID reader located on/within a road surface may be used, so to speak, to "radar" detect and/or identify one or more vehicles within a radius of about 5 or 6m around the antenna, where the RFID tags on the vehicles are at a height of about 2m or less.

In summary, the '384 and' 994 patent applications refer to certain antenna designs (and antenna design methodologies) which are intended to help overcome many of the problems and challenges just described in the above-referenced sections, particularly where (modulated and/or unmodulated) RADAR or similar RADAR transmission is the data transfer method used and utilizes a transmitting antenna above ground and a reflecting antenna within about 6m and below 6 m.

Furthermore, as already explained earlier, in the context of RF road vehicle detection/identification applications, there are many advantages arising from the placement of an RFID reader or at least its antenna on or in the road surface. However, as has been further explained immediately above, the placement of the antenna on or within the road surface (especially where the necessary read range is within 6m of the antenna) limits (or possibly prevents altogether) the use of conventional radar radiation methods in which the earth is typically quantized (i.e. assumed to be) in particular to a single RF element that is homogeneous and stable/unchanged/non-time-varying (or nearly so).

Those skilled in the art of antenna design will recognize that conductivity (including but not limited to road surface conductivity) is not the only relevant parameter when it is one of the important parameters affecting the radiation pattern of an antenna on or in a road. For example, as another example, in a road building, some different types of aggregate may be used. The manner in which these different types of aggregates age, change, combine, compact, etc. varies over time. Many of the potential effects of these (including different material compositions, densities, porosities, surface shapes, texture of the road surface, etc.) can also significantly affect the radio frequency transmission conditions/environment on the road, and thus the radiation pattern of the antenna on/in the road.

It is generally recognized that the following methods and/or appropriate antenna hardware/apparatus may be desirable if present: the method and/or suitable antenna hardware/arrangement can accommodate potentially wide and dynamically varying radio frequency transmission conditions/environments that may exist on a road at different times or at different times, different locations on different roads, so that an antenna placed on/within a road or an antenna capable of being placed at different locations on/within a road can achieve a consistent (or at least an acceptable degree of consistency) desired antenna radiation pattern at all locations, under all conditions. It may be particularly desirable if the following conditions exist: the tuning of the in-or on-road antenna can be made (or can become) more "sophisticated science" -that is-the antenna tuning can be performed as follows: tuning variations in the size, design, configuration, etc. of the antenna (or certain components of the antenna) result in more predictable and reliable effects on the radiation pattern of the antenna, and thus less reliance on pure "trial-and-error" tuning.

Even though a number of introductory discussions and background information are provided above, it should be clearly understood that the present specification is only a reference to any previous or existing antenna design, apparatus, device, product, system, method, practice, disclosure or indeed any other information or any matter or problem that does not constitute an admission or admission that: any of those matters, either individually or in any combination, form the common general knowledge of a person skilled in the art or are admitted to be prior art. Moreover, the mere fact that something is mentioned or discussed in the background section above does not necessarily mean that it is well known (or fully understood) prior to the present invention. Indeed, the above background section may also contain explanations, features, characteristics, possible embodiments, possible choices, alternatives or modifications, uses thereof, etc. related to the present invention, including something that may or may not be repeated anywhere else in this specification.

Disclosure of Invention

In one form, the present invention broadly resides in an antenna for a communication device, the antenna having a structure including a ground plane and a cover assembly, wherein:

the lid assembly is electrically conductive, substantially planar, and has a planar shape (i.e., a shape when viewed in orthographic projection) that is at a first lid assembly dimension (L)₁) Perpendicular to the first cover assembly dimension (L)₁) Second cover assembly size (L)₂) Medium to small (i.e., L)₁⊥L₂And L is₁<L₂)，

The ground plane is electrically conductive, substantially planar, and has a planar shape (i.e., a shape when viewed on an orthographic projection) with a first ground plane dimension (G)₁) And a second ground plane size (G)₂) Wherein

Said first and second ground plane dimensions (G)₁And G₂) Parallel to the first and second cover assembly dimensions (L), respectively₁And L₂)，

The ground plane has a first ground plane dimension (G)₁) Is greater than the cap assembly dimension (L) in the first cap assembly₁) And the ground plane has a size in the second ground plane dimension (G)₂) Is greater than the cap assembly dimension (L) of the second cap assembly₂) Of (a) and

the cover assembly is conductively connected to the ground plane and is spaced apart from the ground plane such that a space (also referred to as a "cavity") exists between the cover assembly and the ground plane, and

the antenna is center fed. (in this regard, a center feed means (or at least includes) a feed (i.e., like a feed cable, conductor, or the like) connected at the geometric center of the planar cover assembly, which corresponds to a position in the cover assembly corresponding to a null or virtual null).

In another, slightly different form, the present invention broadly resides in an antenna for a communication device, the antenna having a structure including a ground plane and a cover assembly, wherein:

the cover assembly is electrically conductive, substantially planar, and has a planar shape that is within a first cover assembly dimension (L)₁) Perpendicular to the first cover assembly dimension (L)₁) Second cover assembly size (L)₂) Medium to small (i.e., L)₁⊥L₂And L is₁<L₂)，

The ground plane is electrically conductive and substantially planar, wherein

The size of the ground plane is larger than that of the cover assembly;

the cover assembly is conductively connected to the ground plane and is spaced apart from the ground plane such that a space (also referred to as a "cavity") exists between the cover assembly and the ground plane, and

the antenna is center fed. (again, center feed means (or at least includes) a feed (i.e., like a feed cable, conductor, or the like) connected at the geometric center of the planar cover assembly).

The cover assembly is not only spaced apart from the ground plane, but also (at least approximately) parallel to the ground plane.

It has been mentioned in connection with the two forms of the invention described above that the cover assembly is in particular electrically conductive. However, it is generally, if not always, the case that the cover assembly is (at least in large part) non-radiating when the antenna is in operation. In other words, it is generally, if not always, the case that little, if any, electromagnetic radiation EMR (which is typically radio frequency RF given the present "RFID" application) generated from the operating antenna is radiated by the cover assembly. Instead, the manner in which energy is radiated by the antenna will be described in detail below.

Continuing from the above, it is generally believed that in most, if not all embodiments of the invention, the energy/radiation (EMR, which is typically RF for the present RFID application) radiated/emitted by the antenna emanates from between the cover assembly and the ground plane. More specifically, it is believed that in most, if not all embodiments of the invention, the energy radiated/emitted by the antenna(s)A quantity/radiation from the ground plane and the cover assembly along the second cover assembly dimension (L)₂) Is emitted between the edges extending in the direction of (at least to some extent). (thus, it is generally considered to be the case that it is the ground plane and the cover assembly dimension (L) along the second cover assembly₂) Is generated at least to some extent by the open sides of the space/cavity between the edges extending in the direction of (and these thus form a virtual cavity resonator).

It is also generally believed that in most, if not all, embodiments no (or at least a very small amount) of energy/radiation will be from ground level and along the first cover assembly dimension (L)₁) Is (at least to some extent) extended between the edges. (thus, it is generally considered that along the first cover assembly dimension (L)₁) The open end face of the space/cavity between the (at least to some extent) extended ground plane and the edge of the cover will generally effectively function as a recess for the space/cavity along the second cover assembly dimension (L)₂) The virtual ground planes of the (at least to some extent) extended virtual cavities, and these virtual ground planes will thus (generally be considered) function as virtual waveguides).

The above-mentioned communication device may be an RFID reader operable for use in applications involving road vehicle detection and/or identification, and at least the ground plane of the antenna of components and assemblies of the RFID reader is operable to be mounted on a surface of the road.

The cap assembly may be of size L₁×L₂Is substantially rectangular. Wherein in this case, energy/radiation radiated/emitted by the antenna (RF MER) may be radiated/emitted from the ground plane and the substantially rectangular cover assembly along the second cover assembly dimension (L)₂) Is emitted between the long edges extending (at least substantially). (thus, in these embodiments, it is generally considered that these two open sides of the space/cavity (i.e. between the ground plane and the long edge of the cover) are created on both sides of the cover, and that they thus form a virtual cavity resonator).

And, the dimension in the cap assembly is L₁×L₂In principle ofIn the case of a rectangular shape, no (or at least a very small amount of) energy/radiation may be emitted from the ground plane and the substantially rectangular cover assembly along the first cover assembly dimension (L)₁) Is (at least substantially) extended between the short edges. (thus, it is generally believed that in these embodiments, the two open end faces of the space/cavity (i.e. between the ground plane and the short edge of the cover) are created on both sides of the cover, which in fact act as virtual ground planes, and these may thus (generally) act as virtual waveguides).

The ground plane may extend substantially all the way through (the width of) the road, or all the way through (the width of) the lane of the road.

Reference is made to the form of the invention first described above under the heading of the invention "summary of the invention", said ground plane being at said first ground plane size (G)₁) Is not necessarily the same size as the ground plane at the second ground plane dimension (G)₂) But the ground plane has the same size in the first and second ground plane dimensions (G)₁And G₂) Is at least five times larger than the wavelength (λ) of the operating signal of the antenna. (i.e., { G)₁,G₂}≥5λ)

In some particular embodiments, the road or lane of the road may be about (or at least) 4m wide and at the first ground plane dimension (G)₁) Is dimensioned to extend substantially all the way through the road or a lane of the road, and in the second ground plane dimension (G)₂) In the direction of (a), the ground plane extends about (or at least) 1.5m or more.

The planar shape of the cap assembly is within the first cap assembly dimension (L)₁) May be larger than it is in the second cover assembly size (L)₂) And f is a medium and small factor f, wherein f is more than or equal to 0.3 and less than or equal to 0.75. (i.e., L)₁＝f L₂(or L)_across＝f L_along) Wherein f is more than or equal to 0.3 and less than or equal to 0.75-the length of the short side [ L ]_across]The cut-off frequency of the waveguide, which can be selected to be at the desired signal frequencyThe ratio is lower. This short side gap may thus almost become part of the ground plane and the cavity package).

Generally, in at least most embodiments of the present invention, the second cover assembly dimension (L)₂) Is about half of the operating signal wavelength (λ) of the antenna plus or minus a matching factor (x) of up to 20%. (thus, the cover assembly of the antenna may have a length along its longest dimension that produces a resonance at the operating signal frequency of the antenna). Thus, by way of example, and not limitation, if the operating signal frequency of the antenna is approximately 800MHz to 1GHz, then the second cover assembly dimension (L) is₂) May extend between about 90mm and 260mm and is within the first cap assembly dimension (L)₁) The cover assembly may extend between about 27mm and 195mm in the direction of (a). In a more specific (but again non-limiting) example, the operating signal of the antenna may be about 920MHz, and in this case, at the first cover assembly size (L)₁) In the direction of (a), the cover assembly may extend approximately 75mm and in the second cover assembly dimension (L)₂) In the direction of (a), the cover assembly extends for about 180 mm.

It was mentioned above that the antenna is center fed, and it is also mentioned that the cover assembly may be of size L₁×L₂Is substantially rectangular. More specifically, the antenna may be fed at a position on the cover assembly where the cover assembly is at the first cover assembly size (L)₁) And is the lid assembly dimension (L) midway between the sides of₂) Halfway between the ends of (a). (the antenna will typically be fed by a 50 ohm coaxial cable matched to the antenna impedance, as is conventional, but no strict limitation is implied in this regard).

With reference to the planar shape of the lid assembly, this may be in the overall dimension L₁×L₂While generally rectangular, the shape may also have one or more sides or edges that are serpentine (i.e., made at least somewhat curved or undulating to thereby increase the sides or edges in L, respectively₁Or L₂The length or distance traversed between the corners). This edge meandering may have the effect of increasing the bandwidth of the antenna.

The cover assembly may be supported at a location spaced apart from (e.g., vertically above) the ground plane by one or more conductive support members. (in this regard, the height and long sides of the cavity [ L ] are generally considered_along]Or possibly the height of the cavity and the length of the long side gap between the support members on the long sides determines the resonant frequency of the antenna. It is further generally believed that the selection of an ideal height of the cavity involves a balance or trade-off between desirable but competing needs for a low antenna profile on the one hand (which may be achieved at least in part by reducing the height of the cavity) and for at least a smaller footprint of the lid assembly on the other hand (which may be achieved at least in part by increasing the height of the cavity), but at the expense of a lower antenna profile/lid height).

In the case of a rectangular cover assembly, there are four conductive support members, one positioned between each of the four corners of the rectangular cover assembly and the ground plane, as discussed above.

The distance that the cover assembly is spaced apart from the ground plane is defined by the length (height) of the support member. It is generally recognized that in some embodiments, the support member supports the cover assembly spaced apart from (or above) the ground plane by a distance of approximately the operating signal wavelength (λ) of the antenna divided by a factor h, where 10 ≦ h ≦ 35.

At the second cover assembly size (L)₂) May be about half of the operating signal wavelength (λ) of the antenna minus about 1 to 10% (preferably minus about 5%) of the distance between the support members (i.e., in the case of a rectangular cover assembly, which is the distance between two support members at one of the short ends of the cover assembly and the other two support members at the other short end of the cover assembly). (it is generally considered that there may be a ground plane and open sides of the space/cavity with the long edges of the lid on both sides of the lid (i.e. two support members)In between) to generate resonance and thereby form a virtual cavity resonator).

In the first cover assembly dimension (L)₁) Is a distance between the two support members at one of the long sides of the cover assembly and the other two support members at the other long side of the cover assembly in the case where the cover assembly is rectangular, and the first cover assembly size (L)₁) Approximately 1% to 10% (preferably 5%) less is about the same.

The ground plane may comprise (or include) a chassis (which may initially be formed separately from other parts of the ground plane, but which should be included into the ground plane and which should form an integral part of the ground plane when the antenna is fully assembled and mounted (e.g. on a road), and the cover assembly is spaced from and (at least substantially) parallel to the chassis such that the space between the cover assembly and the ground plane (the "cavity") is the space between the cover assembly and the chassis. The cover assembly and the base plate are both formed of a substantially rigid and electrically conductive material. This will typically be a metal, but other substantially rigid and sufficiently conductive materials (e.g. carbon) may also be used. The materials used to form the lid assembly and the base plate need not be the same material.

The base plate may be substantially planar and have a planar shape that is larger than the planar shape of the lid assembly but smaller than the planar shape of the ground plane (the base plate of which in fact forms an integral part).

The lid assembly may be supported at a position where it is spaced apart from (vertically above) the base plate by one or more support members referenced above.

A filler or support material may be provided in a space between the ground plane and the cover assembly. This filler or support material may be used to provide additional structural reinforcement or support between the ground plane and the cover assembly. However, the presence of such a filling or support material is not necessarily critical, and wherein the antenna is likely to be unexposedExposed to a load (or only a light load) which can be neglected. However, in the presence of a filler or support material (e.g., to better enable the antenna to better withstand significant, repeated loads), this may give the overall antenna structure a configuration that may be described as "wafer-like", i.e., like a cookie having a relatively soft filler (support material) between two more rigid layers (the backplane/ground plane and the cover assembly). Also, as explained above, the first cap assembly mentioned above with L₁Is smaller (preferably much smaller) than the second cover assembly dimension L₂The length of the middle antenna (and the cover assembly). The cover assembly is also smaller (preferably much smaller) than the ground plane. Thus, the overall configuration of the antenna may be described as asymmetric, even "massively asymmetric". For this reason, at least this particular antenna of which the applicant is concerned is a "massive asymmetric wafer antenna" or "MAMA". Also, for reasons already explained, this large scale asymmetric wafer antenna can be considered to be actually or at least functionally/theoretically similar to a combination of a modified waveguide antenna and a modified cavity antenna).

The filler or support material may substantially fill the space (cavity) between the ground plane and the cover assembly between the support members.

The filler or support material may be a pressure resistant material and it also has a low dielectric constant and/or substantially constant dielectric properties at least over the operating signal frequency of the antenna (and preferably).

The antenna structure may further comprise a protective cover. The protective cover may be in contact with the ground plane and it may extend over the cap assembly to protect (at least) the cap assembly. The protective cover may be in contact with the ground plane all the way around the cover assembly, and the cover assembly and a space between the ground plane and the cover assembly are enclosed within the ground plane and the protective cover.

The protective cover may (at least partially) serve as a radome. Alternatively or in addition, the protective cover may also be operable to (assist the ground plane) reduce the radiation pattern of the antenna (i.e. reduce the elevation angle of the maximum gain path and direct most of the radiation to the region between the maximum gain path and the ground plane).

The boot may have one or more edges that extend from the ground level to (or above) the level of the cover assembly and have (upwardly and inwardly) at least one portion that is sloped to help reduce the impact or shock on a vehicle tire or the like that contacts or rolls over the boot (or a portion thereof). (the thickness and shape of the sides of the cover may also help, at least in part, to concentrate the radiation of the antenna below the path of maximum gain).

One or more edges of the shield may be straight (i.e. not curved or serpentine) along its length (i.e. along the sides and ends where the overall planar shape of the shield is rectangular).

In another form, the invention broadly resides in an RFID reader including an antenna as described above or operable for use with the antenna.

Drawings

Preferred features, embodiments and variants of the invention can be determined from the following detailed description, which provides the person skilled in the art with sufficient information to carry out the invention. The detailed description is not to be taken in any way as limiting the scope of the foregoing summary. The detailed description will follow with reference to a number of the accompanying drawings:

FIG. 1 is a schematic diagram of the necessary read zones for an RFID reader antenna on a roadway.

Fig. 2- "drop-ring" (or "squeeze-ring") shaped antenna radiation patterns that are omnidirectional in azimuth and have previously been considered desirable for road RFID reader antennas.

FIG. 3-schematic illustration of the manner in which an RFID tag for a vehicle may produce "cross talk," in which multiple RFID reader antennas are used, each providing an omnidirectional radiation pattern.

Fig. 4-elevation/height and directivity/horizontality offset of the radiated communication path between the RFID tag of the vehicle license plate and the on-road RFID reader antenna with respect to the "frontal" direction of the license plate.

FIG. 5-plan (top) view of a three lane road with an RFID reader antenna placed in the middle of the center lane on the road. Note that: the figure shows only a single RFID reader antenna located in the center lane for clarity of illustration only. Generally, it is practical to have an RFID reader antenna placed in the middle of each lane-see fig. 1. Also note: reference numeral 3 in the figure represents the radiation pattern of the RFID reader antenna, wherein the radiation pattern is omni-directional in azimuth (i.e. equal in all radiation directions), as has previously been considered desirable.

FIG. 6-plan view of a single lane roadway (i.e., when viewed from a top down perspective) with an RFID reader antenna placed in the middle of the roadway on the roadway. Note that: reference numeral 3 in this figure again represents the radiation pattern of the RFID reader antenna, wherein the radiation pattern is omnidirectional in azimuth (i.e. equal in all radiation directions), as has previously been considered desirable.

Fig. 7 — (i) a schematic illustration of the potential reduction in the width of the effective read zone 9 due to the increased directivity of the RFID tag antenna radiation on the license plate (e.g. due to the vehicle having a large and steep front); and (ii) a potentially preferred RFID reader antenna radiation pattern shape (or at least a preferred shape when viewed in plan) 3' that may help accommodate this.

FIG. 8- (i) a schematic diagram of a possible alternative for addressing the potential reduction in the width of the effective read zone, as depicted in FIG. 7(i), where the radiation pattern shape is made to switch between pointing obliquely left and obliquely right using time division multiplexing; and (ii) the need for multiplexing synchronization when between nearby antennas.

FIG. 9 is a perspective view of a typical conventional retroreflective ("cat-eye") pavement marker.

FIG. 10-perspective view of a typical conventional retroreflective ("cat-eye") pavement marker installed on a roadway (between two lines separating adjacent lanes).

FIG. 11-side view of an RFID reader structure (or portion thereof that includes a reader antenna structure) according to one possible embodiment of the invention. Note that: in this figure, the floor is shown (which is part of the ground plane), but the ground plane is not shown around the rest of the floor. The ground plane (including/containing the floor visible in this figure) is located directly above the roadway (not shown).

Fig. 12-perspective view of an RFID reader structure (or portion thereof that includes a reader antenna structure) according to the same embodiment. In fig. 12 and 13, the floor is shown (which is part of the ground plane), but the ground plane is not shown around the rest of the floor. The ground plane (including/containing the floor visible in these figures) is located directly above the roadway (not shown).

Fig. 13-an exploded perspective view of an RFID reader structure (or a portion thereof that includes a reader antenna structure) according to the same embodiment.

Fig. 14-side view of an RFID reader (antenna) structure located on and above a road surface according to the same embodiment, but also showing (by way of non-limiting example) other electronics that may be associated with the RFID reader and that may (at least in this particular installation, although they need not always be) be located in the road (i.e. buried under the road surface and under the antenna, etc.).

Fig. 15-dimension schematic of ground plane and antenna cover assembly with respect to a single lane. It should be noted that this figure shows the entire ground plane and also the cover assembly, but does not show other components, such as the protective cover, the bottom plate, etc.

Fig. 16-a graphical representation of the shape and intensity/power of the radiation pattern produced by an antenna according to one possible embodiment of the invention.

Fig. 17-a graphical representation of the shape and intensity/power of the radiation pattern produced by an antenna according to another possible embodiment of the invention, which differs from the embodiment of the radiation pattern represented in fig. 16 and whose (in particular) cover has a different length-to-width dimension compared to the embodiment of the radiation pattern represented in fig. 16.

Fig. 18 — (i) a and (i) b are diagrammatic representations of the shape of the radiation pattern produced by an antenna (wafer antenna) according to another possible embodiment of the invention, and (ii) and (iii) are diagrammatic representations of the shape of the radiation pattern produced by the same (wafer) antenna compared to the shape of the radiation pattern produced by an alternative type of (mushroom) antenna, the latter being of the type described in patent application' 994.

Detailed Description

According to another possible embodiment of the invention, fig. 11, 12, 13 and 14 all show an RFID reader structure, or at least all of them show a part comprising an RFID reader antenna. As shown in these figures, the RFID reader structure (or the portion thereof containing the antenna) includes a backplane 61 (which is a self-part of the ground plane of the antenna-see below), a protective cover 62 (in this case in the form of a transparent, preferably transparent or translucent, rectangular "dome" made of a sturdy/structural (preferably transparent or translucent) material such as polycarbonate, engineering plastics like acetal (also variously referred to as such as Delrin, Celcon, Ramtal, and others), etc.), a four-corner support member or "post" 63, a cover assembly (hereinafter simply "cover") 64, a block 66 of support or filler material ("support" 66), and a feed conductor/pin 67. These various components and assemblies of the RFID reader antenna structure will be discussed in more detail below.

This particular embodiment of the invention will be described with reference to its use in roadway applications and its background in which an RFID reader antenna communicates with an RFID tag located on (or integrated as part of) a vehicle license plate. This embodiment of the invention will also be explained below with reference to the following cases: the RFID reader antenna is mounted on the road (and commissioned and used) in a manner that causes the radiation pattern of the reader antenna to extend further across the road than it does along the road (i.e. to extend more in a direction perpendicular to the direction in which the vehicle is travelling on the road), as shown in fig. 7 (ii). However, it should be clearly understood that this and other embodiments or variants of the invention can also be installed (and commissioned and used) on the road in the following manner: the long dimension that causes the radiation pattern of the reader antenna (or its ability) extends at least slightly more along the road than simply straight through, and it may have the additional ability to switch quickly (i.e., between oblique left and oblique right) with multiplexing, as discussed above with reference to fig. 8. However, this will not be explained in detail at the end.

Referring to the chassis 61, as mentioned above, this is (or it becomes) an integral part of the overall ground plane of the antenna when the antenna is fully assembled and mounted. The ground plane is entirely conductive (at least at the operating frequency of the antenna) and therefore the bottom plate 61, which is part of the flat ground, is also made of a conductive material. Typically, the base plate 61 will be made of a substantially rigid and electrically conductive material, such as aluminum (or some other substantially rigid, electrically conductive material), although other materials (e.g., carbon) may also be used. Because the base plate 61 is made of a substantially rigid material in addition to being electrically conductive, the base plate 61 thus provides a structural substrate on which other components of the antenna structure can be mounted, including the posts 63, the cover 64, the block 66 between the base plate 61 and the cover 64, and the protective cover 62.

The manner in which the base plate 61 is made integral (or made as an integral part of an integral larger ground plane) is not critical and any means for achieving this can be used. Typically, the chassis 61 is made of an electrically conductive material, and at least the other surrounding parts of the overall ground plane that contact the edges of the chassis 61 are also electrically conductive (at least at the operating frequency of the antenna), which is sufficient to ensure that the overall ground plane (including the chassis 61 and other parts of the ground plane surrounding it) is electrically conductive. In any event, it should be emphasized (and clearly understood) again that the backplane 61 depicted in fig. 11, 12, 13, and 14 is not itself a ground plane (or is not the entire ground plane — the entire ground plane is shown in fig. 15). Conversely, the chassis 61 is a conductive component that becomes an integral part of a larger overall ground plane when the antenna is assembled and mounted, and the chassis 61 forms a rigid structural component on which other components of the antenna structure may be mounted. Further explanation regarding the specific features and functions of the base plate 61 will be provided below.

The overall ground plane of the antenna (including the chassis 61 and the portion of the ground plane surrounding it) should be applied to the surface of the road (or mounted directly thereon). The actual size of the ground plane (in terms of its length and width on the road, and also its overall shape) will be discussed below, but it should again be noted that only the floor 61 is shown in figures 11, 12, 13 and 14, rather than the entire ground plane. The entire ground plane is shown in fig. 15.

In general terms, the ground plane as a whole (and in particular its portion surrounding the baseplate 61) forms a rather thin layer, which is typically applied directly on the road surface or on top of it (the thickness of the ground plane is not necessarily critical to the invention, and it may vary from embodiment to embodiment or depending on how the ground plane is made, but by way of indication (though without limitation) the thickness of the ground plane may range from a few millimetres up to several centimetres). Typically, the portion of the ground plane surrounding the backplane 61 will be formed as discussed below, and the backplane 61 will then be mounted somewhere within its boundaries. Typically, the bottom plate 61 will be mounted at the geometric center of the ground plane, however this is not necessarily critical and it is often sufficient if not at the exact geometric center to have the bottom plate 61 located towards the center or somewhere in the middle of the ground plane. But the bottom plate 61 should generally not be very close to the periphery of the overall ground plane, otherwise other parts of the antenna may not be sufficiently covered by the ground plane-see below.

In this embodiment, once the chassis is mounted on the road or possibly even before the chassis is mounted on the road or relative to other parts of the ground plane, the remaining antenna structure is located directly on (or mounted on) the upper side/surface of the chassis 61. In this particular embodiment (see in particular fig. 13), a slightly thinner or concave depression 65 is provided in the middle of the upper surface of the bottom plate 61. The short vertical walls extending around the recess 65 in the bottom plate 61 and defining the recess 65 are practically identical in shape to the outer periphery of the base of the protective cover 62. Thus, when the protective cover 62 is mounted to the base plate 61 (along with other components contained beneath the cover 62 and between the cover 62 and the base plate 61), the peripheral edge of the recess 61 provides external support for the peripheral base portion of the cover 62. This may help to strengthen the base portion of the cover 62 and prevent it from deforming or bending outwardly, which may otherwise tend to squeeze the cover 62 and deform it outwardly, for example in the event that a car or vehicle is driven through the antenna thereby imposing a downward force. Reinforcing the base of the cover 62 in this manner and helping to prevent it from deforming or bending outwardly also helps to reinforce the overall cover 62 (including its upper portion) in the vertical direction. This is because preventing outward deformation or bending of the cover 62 also thereby helps prevent the upper portion of the cover 62 from being forced downwardly towards the surface of the roadway. In other words, it helps prevent the overall cover 62 from being "squashed" and this, in turn, can help provide additional protection to the components (e.g., the cover 64 and the posts 63) housed between the cover 62 and the base plate.

As already mentioned, the overall ground plane should be electrically conductive. For the avoidance of doubt, unless the context clearly dictates otherwise, references herein to a "conductive" ground plane or to the word "conductive" should generally be understood to mean (include) fully conductive, as well as partially conductive, but effectively sufficiently conductive at the operating frequency of the antenna (typically about 1Ghz, although other operating frequencies are possible), even though other frequencies do not necessarily have to be.

The ground plane as a whole must generally be of a certain size, or at least of a certain minimum size. One important reason that ground planes should be generally dimensioned is that: to help ensure that it (i.e., the ground plane) operates to adequately shield other portions of the antenna structure (especially conductive and radiating portions) from potentially wide and dynamically variable radio frequency effects of the underlying path, other "near-ground" effects, and the like. Another reason that the ground plane should generally be of a certain size is that: to help ensure that it operates to adequately shield any cables, electronics, etc. that may be located below ground level from potentially very strong magnetic fields generated by electric vehicles that are becoming increasingly prevalent on public roads.

The overall ground plane may have virtually any shape, provided that its dimensions (in all directions along the ground) are sufficient to provide adequate shielding for other parts of the antenna. And as mentioned above, the other conductive and radiating components of the antenna should be positioned sufficiently towards the middle of the ground plane and away from the periphery of the ground plane to be sufficiently shielded.

In certain embodiments described herein, and as shown, for example, in fig. 15, the overall ground plane has a planar shape (i.e., a shape when viewed in orthographic projection), a first ground plane dimension (G) thereof₁) Than perpendicular to the first ground plane dimension (G)₁) Of a second ground plane size (G)₂) Large (i.e., G)₁⊥G₂And G₁>G₂). However, as already mentioned, the ground plane may potentially be shaped in other ways.

The ground plane should preferably be mounted on the road surface (as discussed above), and in this particular example, its second ground plane size (G)₂) Oriented parallel to the direction of travel of the vehicle on the road (i.e., G2 ═ G_along)。

In the particular embodiment presently described, the ground plane is substantially flat (i.e., is a thin layer on a road) and its planar shape is of dimension G₁(or G)_across)×G₂(or G)_along) Wherein G is as mentioned above₁(or G)_across)>G₂(or G)_along). More specifically, in certain preferred versions of the present embodiment, and where the reader and other portions of the antenna structure have certain dimensions discussed below, the ground plane should be a generally thin, flat rectangle with a G₁4m (or thereabouts) and G₂3m (or thereabouts). It should be noted that with respect to the first ground plane dimension G₁(or G)_across) This corresponds to the full width of a single lane on most roads, 4m (ca). For roads with lanes wider than this, it may be the first ground plane dimension G₁(or G)_across) Larger than 4m to extend all the way through the roadway (although this may not always be necessary). It should however be clearly understood that in other embodiments, in particular if the size and dimensions of the other parts of the reader and/or antenna structure are different from the size or dimensions of the other parts of the reader and/or antenna structure of this particular embodiment (which may happen, for example, if the day is not the same)The wires operate at different signal frequencies), or perhaps in other operational examples, the absolute and relative dimensions of the ground plane may also be changed from that just described.

Without other limitations, which have been discussed elsewhere herein, in order for the ground plane to adequately shield other portions of the antenna structure from potentially variable radio frequency effects of the underlying road (and from other "near-ground" effects), the ground plane (and thus the material or substance from which it is formed) may need to have the lowest conductivity (at least when "finished" and ready). Or in other words, the ground plane may (when completed/installed and ready) need to have a resistivity below a certain maximum. For the particular antenna structure proposed herein, as well as given antenna power, desired radiation pattern shape, antenna gain, antenna reflection losses, etc., it is generally believed that the ground plane (and thus the materials and substances forming it) should preferably (when installed, completed and ready) have a value of about 10³S/m or higher (i.e., the conductivity should preferably be approximately equal to or higher than 1000 siemens/m). In other words, it is generally believed that the electrically conductive ground plane (and thus the material/substance from which it is formed) should preferably (when completed) have a thickness of less than about 10^-3A resistivity of Ω m (i.e. the resistivity should preferably be equal to or less than 0.001 ohm-meter).

Regarding the establishment/formation/installation/deployment of the electrically conductive ground plane, and in particular of those parts thereof other than the soleplate 61, the establishment/formation/installation involved on the ground plane itself should preferably be as economical and non-destructive as possible (in terms of time, cost, complexity, etc.), also taking into account that the road (or at least a section of the road or lane) will generally have to be closed when this occurs.

It is mentioned above that the ground plane may need to have the lowest conductivity (or in other words a resistivity below a certain maximum value), and it is also mentioned that for the specific antenna structure, given antenna power, desired radiation pattern shape, etc. as proposed herein, the conductivity should preferably be about 10³S/m or higher. If the conductivity of the ground plane is greater than about 10⁶S/m, which may in fact be considered "fully" conductive, and which may in fact be suitable or even more desirable for providing shielding in the present antenna application; this is of course not a requirement, however, and embodiments of the invention may still operate very efficiently with ground planes in which the conductivity is much lower than "fully" conductive.

If the ground plane (or its parts other than the bottom plate 61) is made solely or mainly of a mesh made of, for example, stainless steel, copper, aluminum or some other suitable electrically conductive metal alloy, or possibly of steel wool or metal cloth, a conductivity of more than about 10 can be established⁶An S/m conductive ground plane. However, the practicality and difficulty associated with applying such a metal mesh to the road surface (at least or especially if the mesh is a separate, independent object and is not embedded in or part of some other object or substance that can be more easily applied to the road) means that: portions that establish a ground plane around the floor 61 with only such a metal alloy mesh (or slightly more than this) may be less attractive than other possible alternatives, some of which are discussed below. Furthermore, the formation of the ground plane (around the floor) with only the metal mesh (or a little more than this) may also have a certain associated risk/danger, especially if the mesh is lifted off the road surface, for example due to improper or incomplete installation, or as a result of wear and tear, etc. Thus, when using a ground plane (other than the backplane) made of only metal alloy mesh (or slightly more than this), it may be very effective in its ability to shield the antenna structure from potentially variable radio frequency effects of the road lying below (and from other "near-ground" effects), and at the same time embodiments of the invention may operate well with a ground plane (other than the backplane) made of such simple metal alloy mesh, although for practical reasons it is generally considered to be less likely (or likely less likely) to be used than other possible alternatives to form a ground plane (other than the backplane).

Alternatively, the ground plane (other than the floor) may instead be formed and applied as, for example, paint (or as a liquid applied to the road in a manner similar to paint), or as an epoxy applied to the road, or even as a polymer that can melt onto the road surface. To achieve the required minimum level of conductivity (see above), the electrical conductor or some form of conductive component or substance may be mixed in an appropriate amount (in the case of a conductive substance) or otherwise incorporated into any of these prior to installation.

Another consideration that may affect the method selected to form the ground plane (in addition to the backplane) is: the road surface generally expands, contracts and changes shape slightly over time. For example, when a road is loaded by the wheels pressing on the road as they pass, the road surface will temporarily compress/change shape slightly below due to the pressure imposed by the wheels. Also, due to temperature fluctuations (e.g., between the day and night, or with seasonal changes, etc.), expansion and contraction of the road surface may occur. This often repeated/cyclic shape expansion and contraction and changes may thus create cyclic loads/stresses and thereby fatigue in the structure to which it is connected or bonded. This may in turn lead to fatigue-related failures, such as failure of any ground plane (or ground plane layer) provided thereon, especially if the ground plane (or ground plane layer, except the backplane) is in the form of a rigid or fragile structure. On the other hand, if the ground plane is formed of a substance that has, or if its structure allows or provides (at least to some degree) elasticity, toughness, "stretchability" (give), etc., the ground plane (or ground plane layer, except for the bottom plate) will generally be less susceptible to fatigue.

In view of the foregoing, one approach that is generally considered potentially suitable (including because the required electrical conductivity can be provided, but also because it can potentially be economically manufactured to minimize destructive application on roads, and to provide a degree of resilience once formed) to provide a ground plane (other than the backplane) is: using a substance that may be applied as a paint, or as an impregnated epoxy cloth that can be placed on the road, or as a polymer that can be melted onto the road, and any of these when used, the conductive component/substance may be in the form of, for example, graphite powder (or possibly particulate)Aluminum or other metal, etc.) into a paint, epoxy, or polymer. Of course other conductive components/substances (i.e. other than graphite powder) may be used. However, referring to a ground plane (or a ground plane layer, in addition to a floor) formed, for example, from an epoxy/graphite mixture, as a comparative example of the hardness of a ground plane/layer formed in this way, epoxy/graphite mixtures are also commonly used for load bearing structures and surfaces in the manufacture of yachts. Furthermore, the epoxy/graphite mixture may have up to about 10⁴S/m conductivity (it will be noted that it readily meets the objects of the present invention).

Another method that may be considered suitable for forming a ground plane (in addition to the backplane) is: carbon cloth (which may have more than 10 a) sprayed on or glued with epoxy onto the road surface⁵Conductivity of S/m). Such carbon cloth may alternatively be embedded in a polymer sheet which itself may be melted onto the road surface. In other applications and industries, such as ship and yacht manufacturing and repair, etc., it has been shown that maintenance and repair of carbon cloth layers/surfaces/structures and similarly epoxy/polymer layers/surfaces/structures can be relatively easy, cost and time efficient, and effective using readily understood methods and techniques, none of which require detailed explanation herein.

When a ground plane (or layer) is applied/formed/installed on a road, the components, substances or elements within the ground plane (other than the backplane) provide electrical conductivity, which should preferably be close (ideally as close as possible) to the upper surface of the ground plane. In other words, once the ground plane (except the bottom plate) has been applied/formed/mounted on the road, the component, substance or element providing the electrical conductivity should preferably be as close to the top as possible within the vertical thickness of the structure/layer of the ground plane. This is because the closer the component, substance or element providing the electrical conductivity is to the upper surface, the better it will provide shielding for other parts of the antenna structure. Of course, this may also often need to be balanced with the need to provide a conductive component, substance, or element to be covered to protect the vehicle from exposure to the element, damage, wear, etc. while it is being driven.

Another method that may be considered suitable for forming a ground plane (in addition to the backplane) is: a pre-manufactured "patch" type product is used that can be applied to roads. These may be similar in many respects to road repair/modification Products produced by, for example, south Africa corporation AJ BroomRoad Products (Pty) Ltd, and are referred to as BRP road patches. It is then possible to manufacture the ground plane (except for the bottom plate) with something similar to a BRP road patch; that is, it is possible to establish a ground level (in addition to the floor) with a pre-formed product that is manufactured on paper (or some other suitable substrate or base material) and a bitumen rubber binder (or some other similar binder) that holds the bitumen pre-coated aggregate thereon. The prefabricated product thus produced may be supplied in thin sheets (i.e. prefabricated sheets) sized to suit the intended application (see above for dimensions of ground level). The backplane 61 may potentially be installed before, after or simultaneously with the patch being installed on the road to form the other part of the ground plane.

Still referring to the possibility of forming a ground plane (in addition to the floor) with a pre-patch-like product as described above, the particle/granule/pebble size of the aggregate bound in the asphalt rubber binder may also be selected to fit; for example to resemble or match the particle/grain/pebble size of the aggregate in the roadway to which the patch is applied. The overall color of the patch (including or due to the color of the aggregate) may be made (or the aggregate may be blended) to substantially match the color of the roadway to which the patch is applied, such that the patch appears to be purely a part of the roadway (i.e., unique from the roadway) when applied. Alternatively, the patch may be colored, or it may have markings (e.g., border or edge markings) or the like, to make the patch clearly visible or easily visually distinguishable from other portions/areas of the roadway. The latter can be used in the following situations: in order for the vehicle operator/driver to be able to see when they are about to pass the area/location containing the antenna that will detect and/or identify their vehicle (and therefore they can know), this is preferable or there is a requirement by them that this is important for privacy reasons and/or for system transparency requirements used in compliance with law enforcement and evidence collection (for providing evidence collected in a legal and unambiguous way, etc.). The aggregate and the "particulates" that make up the aggregate may also include an appropriate number or proportion of particulates that are lighter in color or are reflective, or may be particularly reflective to light in a particular spectral range (e.g., the infrared spectrum). These lighter and/or reflective particles are not necessarily intended to simply illuminate the overall color of the patch surface (which may also have some effect, although they may not, depending on the manner and proportion of bonding with the aggregate) -rather, the portions of the spectrum that are lighter in color, or reflective in certain parts of the spectrum (e.g., infrared in particular), are intended to help reduce heating and heat retention and may provide some degree of radiant heat reflection. Given that the antenna is located directly on top of the ground plane and the road material below it, it may often be important to reduce heating and heat retention in the ground plane (and in the road material below it) in order to prevent possible heating or overheating of the electronics associated with and located with the antenna.

A pre-patch like that described above may be adhered to the road surface to form the ground plane (except for the floor) in any suitable manner or using any suitable technique. By way of example, such patches may be adhered using a cationic emulsion or an anionic emulsion.

In order to provide sufficient electrical conductivity to a pre-patch like that described above, an electrical conductor or some form of conductive component or substance may be included (along with aggregate, etc.) in the mixture bound within the asphalt rubber binder. Alternatively, an aluminium alloy or other metallic conductive mesh may be incorporated therein (or as part of a patch) so that the conductive metallic mesh (rather than being applied to the road solely as a separate mesh) is applied to the road as part of (or within) the patch product. As another alternative, particulate or granular aluminum (or other metal) may in fact be included within (i.e., as part of) the aggregate, which was coated in the asphalt during initial patch formation/manufacture. The resulting patch will then potentially have the necessary electrical conductivity due to the aluminum (or other metal) contained within and as part of the aggregate. This also has the benefit of providing a useful option of recycling scrap aluminum (or other metals) from other sources.

In addition to providing shielding, the conductive ground plane may also contribute to one or more of the following: concentrating the radiation emitted by the antenna into a desired azimuth area (which is preferably an elliptical shape or other shape as discussed below); the elevation angle of the maximum gain path within the colon (colon) is reduced and the radiation pattern below the maximum gain path is concentrated.

The overall ground plane of the RFID reader antenna structure (which is a component of the RFID reader structure) has been explained above. It has also been explained that the components of the reader antenna (and the reader) other than the ground plane are located or mounted on top of the ground plane, in particular on top of the bottom plate 61. It has been further explained that the conductive ground plane may need to have a certain minimum size, for example in order to sufficiently shield the antenna structure. In case a single antenna (corresponding to a single RFID reader) is used only at a given location (e.g. installed in a road), the antenna structure will have its own associated ground plane. However, there may be the following: multiple RFID reader antennas are used at a given location. To help visualize this, consider fig. 5. Fig. 5 shows in fact the following: at the depicted location, on the road surface in the middle of the center lane, only a single RFID reader antenna is used. However, in other cases, multiple antennas may be used, for example in a straight line through a road. For example, the following may be the case: an antenna is mounted centrally on each lane of the road so that the antennas together define a straight line through the road. In this case, the multiple antenna structures do not necessarily need to each have their own unique ground plane separate from the ground plane of any other antenna. Instead, a single conductive area may potentially be provided and shared by some or all of the antennas, such that the single area operates as a ground plane for two or more separate antennas. As a possibility, a single partially conductive area shared by all antenna structures, wherein the plurality of antenna structures form a straight line through the road, may be provided as a wide strip extending across all lanes of the road (i.e. across the total width of the road). This is depicted in fig. 1.

It should be noted, however, that where multiple antennas are used at a given location (e.g., as just discussed), each (or one or more of them) may still have its own associated (i.e., unique and unshared) ground plane separate from the ground plane of any other antenna. This may occur assuming that if the reader antenna in one lane is positioned slightly further along the road than the reader antenna in an adjacent lane, such that only the portion of the conductive strip extending vertically through the road (i.e., as shown in fig. 1) does not provide sufficient coverage around each antenna. However, from a practical perspective, the time, cost, effort, etc. associated with installing or establishing separate ground planes for each antenna structure may be greater than installing or establishing a single, larger partially conductive region (e.g., a wide strip extending through the roadway as mentioned above) that is shared by some or all of the antennas and operates as the ground plane for those antennas, so providing a common/shared ground plane for multiple reader antennas is desirable where possible. Another possible benefit is that such a strip may be coloured, or it may have markings (e.g. edge markings extending across the road before and after the antenna structure in the direction of vehicle travel), or it may have a different surface texture or stone/particle size or the like, to make the strip clearly visible (or possibly audible when driving past), which (as described above) may be used in the following cases: vehicle operators need to be able to see (or at least know or alert when this occurs) when they are about to pass through the area/location where their vehicle will be detected and/or identified. Also, as noted above, the strips may incorporate lighter colored or reflective particles to help minimize heat generation and heat retention, among other things.

Returning again to consider the general RFID reader antenna structure, as already explained, this also includes a cover assembly (cover) 64. The cover has a planar shape (i.e., a shape when viewed in orthographic projection from above),its first size (L)₁) Less than it is perpendicular to the first dimension (L)₁) Second dimension (L)₂) (i.e., L)₁⊥L₂And L is₁<L₂). In at least this embodiment, the cover 64 is substantially thin, generally flat and rectangular, and has a dimension L₁(or L)_across)×L₂(or L)_along) In a planar shape of (2), wherein L₁(or L)_across)<L₂(or L)_along) As mentioned above. More specifically, the planar shape of the cover 64 is in the first dimension (L)₁) Preferably in the second dimension (L) thereof₂) A medium and small factor f, wherein f is more than or equal to 0.3 and less than or equal to 0.75 (i.e., L)₁＝f L₂(or L)_across＝f L_along) Wherein f is more than or equal to 0.3 and less than or equal to 0.75). L is₂(or L)_along) Should be approximately half the operating signal wavelength (λ) of the antenna plus or minus a matching factor (x) of up to 20%. (i.e., L)_alongλ/2 ± x, x ≦ 20%). In the particular embodiment presently described and shown in fig. 11, 12, 13, 14 and 15, the cover is in the second dimension (L)₂) Extend approximately 90mm to 260mm (i.e., L)₂90mm to 260 mm). Indeed, it is conceivable that the depicted embodiment of the antenna may be implemented in practice with an operating frequency of 920MHz, which implies a wavelength of about λ 0.326 m. This means that if L is_along137mm, which is currently considered to be most desirable for (and which is the most desirable operating frequency for) an operating frequency of 920MHz, then x is-0.026 or about 19%. Wherein L is_along＝137mm，L_acrossAnd may be any value within the range from about 40mm to about 110 mm. But in another example, for an operating frequency of 1GHz (which means λ ═ 0.3m), this means that if L were to be equal_along180mm, then x is 0.03 or about 16%. Wherein L is_along＝180mm，L_acrossAnd may be any value within the range from about 54mm to about 135 mm. For a given length of the cover (i.e., L)_alongWhich is determined by reference to the operating frequency), the width of the cover (i.e., L)_across) May be varied or adjusted to tune the antenna or to adjust the shape of the radiation pattern, as discussed below。

The cover 64 is made of a thin conductive sheet (and preferably of a fairly rigid and resilient material), typically metal (although other non-metallic conductive materials are also potentially possible). It is believed that a range of conductive metals are potentially suitable, including silver, aluminum, copper, and other metals known for their conductivity. However, while it is quite possible to use metals (and alloys thereof) known, for example, for their electrical conductivity, it is generally believed that it is in fact desirable for the cover 64 to be made of metals that are more known for their strength, but also have a high (or sufficiently high) electrical conductivity, such as, for example, steel or titanium. Steel or titanium (or other metals or alloys that may have properties substantially similar to these) are considered potentially quite suitable for reasons: not only because they are sufficiently conductive, but they are also strong and highly elastic (i.e., they "spring back" if deformed, of course assuming that the deforming force does not cause the material to reach or exceed its elastic deformation or yield stress limit). These metals (i.e., steel, titanium, etc.) also have high fatigue resistance, meaning that repeated elastic deformation should not quickly cause metal fatigue (i.e., weakening). The reasons why these properties (i.e., strength, elasticity and fatigue resistance) are considered potentially important are: because in road applications where the antenna is used, the antenna will frequently be run over by vehicles (including large and heavy vehicles such as trucks) and this will therefore cause some (even relatively small) deformation of the various components of the antenna (including the cover 46, even if the cover 64 is received and protected within the enclosure 62), including the cover 64.

Cover 64 at L₁(or L)_across) And L₂(or L)_along) The dimensions in terms of dimensions have already been discussed above. In terms of thickness, as also mentioned above, the cover 64 is (or will generally be) a generally thin plate. However, the actual thickness of the cover 64 is not critical. In fact, as already mentioned elsewhere, the cover 64 is not a radiating component of the antenna. Thus, the thickness of the cover 64 is likely to vary or vary (e.g., depending on the material used) without affecting the wireless/signal transmitting properties/function/operation of the antenna. Nonetheless, depending on the material from which it is formed (strength, resilience, etc., among other properties), the cover 64 will typically have from less than 1 millimetreMeters to thicknesses in the range up to several millimeters. However, as already mentioned, it is intended to imply no limitation on the actual thickness of the cover 64. Because the cover 64 will generally be quite thin, it may be considered very susceptible to bending/deforming beyond the yield stress of the material. However, as will be explained below, the cover 64 is supported below (also protected below the cover 62) by the supports 66, which prevents the cover 64 from (plastically) deforming beyond the yield stress of the material.

As best shown in fig. 13, there is a conductive feed pin 67 associated with (and connected to) the cover 64. As will be understood by those skilled in the art, the feed pin 67 carries current to the cover 64. It is important to understand, however, that the antenna in this embodiment (and in general the invention) is not a patch antenna (or the like). Thus, although the feed pin 67 carries current to the cover 64, the cover 64 does not radiate the energy emitted by the antenna. Instead, as explained elsewhere, it is generally believed that what resonates is the open side of the cavity on both sides of the cover, i.e., along the long side of the cover (L) between the ground plane (floor 61) and the edge of the cover 64₂) And (4) extending. It is therefore believed that these long side gaps between the cover 64 and the base plate 61 form a virtual cavity resonator and that they therefore radiate the energy emitted by the antenna.

In the particular embodiment shown in the drawings, the feed pin 67 is connected to the cover 64 at the following locations (from the underside): this position is exactly half way between the short ends of the rectangular cover (i.e., along the L of the cover 64)₂One half of the size) and also exactly half-way between the long sides of the rectangular cover (i.e., L through cover 64)₁One half of the size). The cover 64 and antenna are thus typically "center fed" or "center fed" in the particular embodiment shown.

As shown in fig. 11 and 12, particularly when the RFID reader antenna structure is assembled, the cover 64 is mounted relatively above, but parallel to the base plate 61 and supported in this position by four posts 63. The pillars 63 are electrically conductive and they thus serve to conductively connect the conductive base plate 61 (and thus the ground plane) to the conductive cover 64. In terms of the material from which the posts 63 are made, the materials are generally contemplated as discussed above with respect to the cover 64, and the same materials may potentially be used (although it is generally clear that the material used for the posts 63 need not necessarily be the same as the material used for the cover 64). One post 63 is provided for each corner of (and below) the rectangular cover 64. Each strut 63 is in fact made up of three sub-struts, as can be best understood from figure 13. In the case of each pillar 63, three sub-pillars constituting the pillar are provided:

one of the sub-pillars is exactly in the corner, i.e. forming a corner sub-pillar;

second subsidiary strut edge L₁The orientation is immediately adjacent (i.e., very close, if not in direct contact with) the corner sub-pillar on the inside of the corner sub-pillar; and

third subsidiary strut edge L₂The direction is immediately adjacent (i.e., very close, if not in direct contact with) the corner sub-pillar on the inside of the corner sub-pillar.

Thus, on each post 63, the three sub-posts together define corners (in particular right-angled corners), and these corners help to accurately and securely position the support 66, which support 66 is a rectangular prism and has a dimension L₁And L₂The orientation is designed to fit snugly (i.e., closely) between the posts 63 such that the corners of the rectangular support 66 are inset into the corners defined by the posts 63. The support 66 will be discussed further below.

As will be appreciated, it is simply the height of the posts 63 that defines the size of the vertical separation between the ground plane (floor 61) and the cover 64. The height of the struts 63 thus plays a significant role in defining (and adjusting their height can be used to tune by varying) the size of the gap vertical dimension (both along the long and short sides of the cover assembly) between the cover assembly 64 and the ground plane (the chassis 61). It should also be borne in mind, however, that at least in this particular embodiment, the base plate 61 has a recessed portion 65, and the post 63 is located within this recessed portion 65. In fact, the pillar is located on a very slightly raised platform, which itself is formed in the base of the recess 65. Thus, the posts 63 extend between the upper surface of the base plate 61 and the underside of the cover 64, the posts 63 being connected to the base plate 61 at the upper surface of the base plate 61, the upper surface of the base plate 61 being on a slightly raised platform portion within the recessed portion 65. Thus, it is possible to state that in this embodiment, the vertical height of the posts 63, together with the depth of the recess 65 in the base plate 61 (and the raised platform height), define the "effective" vertical dimension/size of the long side (and short side) gap, i.e., the gap between the long side and the short side of the cover 64 between the upper surface of the base plate 61 and the portion of the base plate surrounding the recess 65.

Indeed, it is generally believed that the recess 65 in the base plate 61 not only provides structural external support for the enclosure 62, but also has some effect on the radiation properties of the antenna. In particular, it is believed that the depth of the depression 65 (and more particularly, the forward height of the short vertical perimeter wall of the depression 65) can affect how much of the radiation of the antenna is concentrated below the elevation angle of the maximum gain path (all around the antenna in the azimuth plane). For reasons already explained previously, it is advantageous to concentrate the radiation of the antenna lower down (including below the elevation angle of the maximum gain path). It is generally believed that if the depth of the recess is greater (deeper) so that the height of the peripheral wall of the recess is greater (higher), this may have the effect of concentrating more of the antenna radiation below the elevation angle of the maximum gain path. Conversely, if the depth of the recess is relatively small (shallower), so that the height of the peripheral wall of the recess is smaller (lower), it is believed that this may have the effect of causing less antenna radiation to be concentrated below the elevation angle of the maximum gain path. As a further possible alternative, instead of (or possibly in addition to) making the depth of the recess 65 deeper in the bottom plate 61 to increase the height of the peripheral wall of the recess and thus concentrate the radiation pattern of more antennas lower down below the maximum gain path, it is instead (or also possible to incorporate one or more further components or conductive elements into the antenna structure, which act as "wall extensions" (i.e. height extensions of the peripheral wall of the recess 65). A single such component or element may be, for example, a narrow strip of metal (or conductive material) forming a "ring" that is placed on the base plate 61 immediately above the perimeter wall of the recess 65 and extends around and immediately above in the shape of the perimeter wall of the recess 65, such that the inner surface of this ring effectively forms an extension of the perimeter wall of the recess 65 itself (i.e., it increases the effective height of the perimeter wall). Alternatively, because it may not be necessary or important to provide a height extension for those portions of the recess perimeter wall at (or below) the short end gap (i.e., below the short end edge of the lid), because the short end gap is non-radiating, it may be possible to provide a metal (or conductive material) assuming a pair of narrow strips that are placed on the floor 61 immediately above those portions of the recess perimeter wall at (or below) the long side gap (i.e., below the long side edge of the lid), and that extend along and immediately above the long edge length of the perimeter wall of the recess 65, such that the inner surfaces of these strips effectively form an extension of the long edge length of the perimeter wall of the recess 65 (i.e., they increase the effective height of the long edge length). Such components or elements may be provided as separate, further components of the antenna structure, or alternatively it/they may be incorporated into one of the other components, for example by being incorporated into the cover 62, so that the components are accurately positioned relative to the peripheral wall of the recess 65 when the cover 62 is mounted. In any event, providing such components/elements (or something similar) may help to effectively increase the height of (the relevant portion of) the perimeter wall of the recess 65, without necessarily increasing the actual depth of the recess 65 itself (or by not effectively increasing the height of (the portion of) the wall as much as possible), and thereby help to cause more antenna radiation to be concentrated at an elevation angle below the maximum gain path.

It will also be appreciated, however, that the extent to which the depth of the recess 65 can be increased (i.e. deeper) or effectively increased by the introduction of further components/elements may be limited due to the very limited overall height of the antenna structure and its components, in which case only limited variability/adjustment may in fact be permitted. Furthermore, it should also be remembered that because it is generally considered long side gap resonances and because it is generally considered that the resonant nature of these is not solely by the L of the lid₂Length of dimension (or at L)₂The distance between dimensionally-sized pillars 63), and also at least partially by a ground plane (floor 61) and a cover 64 (as discussed above)Essentially defining the effective height of the long side gap). Thus, because it is also generally believed that the height of the long-side gap is important in determining (and providing) the resonant properties of the antenna, the degree of change affecting this height (i.e., the height or effective height of the long-side gap) may be further limited, as it is necessary or desirable not to unduly hinder or compromise these resonant properties for antenna tuning.

On each of the four posts 63, there is a small circular detent or lug on the top of each of the three sub-posts. Furthermore, in each corner of the cover 64, there are three holes, all of which have a diameter corresponding to the diameter of the lugs on the tops of the sub-posts, and the three holes in each corner of the cover 64 are formed in an arrangement corresponding to the arrangement of the lugs on the tops of the sub-posts on each respective post 63. Thus, when the cover is placed on top of the posts 63, the lugs on the top of each post are inserted into the holes in the respective corners of the cover, thereby accurately positioning the cover 64 relative to the posts 63 (and relative to the recesses 65, etc. in the base plate 61). It should be noted that the corners of the cover, where the posts are connected to, are the locations of ground potential (or zero position) in the cover, and it is important that the posts are connected at the locations of ground potential or zero position.

The antenna struts 63 (or one or more of them, or one or more sub-struts of one or more antenna struts 63) may be hollow along their length. For example, there may be a through-hole extending axially through (or each) associated sub-strut. This hollow interior extending through one or more sub-struts may provide one or more conduits for cables, wires, etc. to extend from below the floor 61 (or otherwise below ground level) and connect to any electronic components and/or equipment that may be positioned in the hypothetical space that may be provided above the cover 64 but below the underside of the protective cover 62. It is also possible or alternatively to provide space for other electronic components and/or devices, provided that the space is adjacent to but just outside or beyond the short side gap on one or both ends of the cover 64, but still within the confines of the cover 62 when the cover is installed. Or indeed the electronic components and/or devices may be located in a range of other locations as well, which do not substantially interfere with the radiation properties of the primary antenna. These electronic components and/or devices may include any electronics associated with the RFID reader (such as, for example, a modem or filter or amplifier, etc.), or a communication device (such as an accessory Wi-Fi or bluetooth antenna, etc.), or a lighting assembly as discussed elsewhere herein.

The above mentions that the RFID reader antenna structure comprises a support 66. It is also explained that such supports are sized to fit closely between the corners defined by the respective posts 63. When the antenna structure is assembled, the supports 66 are under the cover, and the supports 66, along with the struts 63, help provide structural support for the cover 64. Because the supports 66 are positioned below the cover 64, the supports 66 must of course be mounted on the base plate 61 between the posts 63 before the cover 64 is mounted on top of the posts 63. In fact, when the antenna structure is assembled, after the base plate 61 has first been mounted on the road and the pillars 63 have been mounted on the base plate 61, the supports 66 can then be inserted between the pillars 63, as discussed above. The thickness of the support 66 in the vertical dimension is such that the support 66 fills (in the vertical direction) the space between the underside of the cover 64 and the upper surface of the base plate 61 (a slightly raised platform within the recess 65).

Thus, as mentioned above, the posts 63 and supports 66 together help to provide structural support in their location for the cover 64 that is mounted above and parallel to ground level. As mentioned above, the posts 63 will typically be made of metal, and they therefore provide a fully ridged support under each of the four corners of the cover 64. The support 66 fills the entire space within the corner defined by the posts 63 and between the undersides of the base plate 61 and the cover 64, and thus contacts the undersides of the base plate 61 and the cover 64, which may be made of a wide range of different materials. The support 66 is not a conductive or radiating component of the antenna, and it should therefore be substantially non-conductive (or at least substantially non-conductive at the frequencies at which the antenna operates). Preferably, the support should be made of a material with suitable dielectric properties (preferably, with a low dielectric constant, with consistent dielectric properties over the bulk material). Also, to help support the cover 64 above, and in particular to help support the interior portion of the cover 64 inwardly from the four (rigid/stiff) corner posts, from downward deformation (as may occur when a large load is applied from above, like when a vehicle runs over an antenna, etc.), the support 66 should be made of some solid material. However, the support 66 need not necessarily be a highly rigid material (i.e., not necessarily like a solid material or the like that forms the boot 62). Instead, the support 66 may (and indeed may be desired to) be made of a material that is solid and has a reasonable degree of elasticity or "stretch". Possible examples of such materials include closed cell foam like styrofoam or the like, or paper or cardboard formed in a cell (or honeycomb) like configuration, or indeed a range of other materials of the kind commonly used as liners in packaging around articles, consumer appliances and the like in transit. It will be appreciated that materials such as this solid but also having a reasonable degree of stretchability or deformability are suitable (or even desirable) because it is first remembered that the cover 64 is a fairly stiff (typically metal) plate. The cover 64 is also directly on top of the support 66 and the underside of the cover 64 contacts the entire (or a majority of) upper surface of the support 66. Thus, when a vertically downward load is applied to the antenna structure, and if the load is large enough to cause deformation of the protective cover 62 and also of the underlying cover 64 (and any object located between the underside of the cover 62 and the upper surface of the cover 64), then if this load causes the cover 64 to deform or bend downwardly, even if the load (after passing through or by the cover 62, etc.) becomes applied only to a small/localized area in the middle of the cover 64 (between the corners supported by the stiff struts 63), the fact that the cover 64 itself is quite stiff will help to spread the localized load and be loaded by a much larger area of the underlying support 66. This will in turn cause a larger area of the support 66 to become compressed, and the compression also expands in the material of the support 66 as follows: having an even greater proportion, if not all, of the support 66 under the cover 64 helps to carry the load (even if the load is applied with a fairly localized load, where the load is transferred onto the cover 64).

It is mentioned above that it may be practical to make the upper support 66 from a material that is preferably solid but also has a reasonable degree of elasticity or "stretch". This is preferred over the assumption of highly rigid materials because: because highly rigid materials (generally by their nature) are less elastic (i.e., less flexible or less deformable). Many are even brittle or subject to breakage. As a result, if a highly rigid material is to be used for the support 66, this may potentially be susceptible to cracking or may fatigue over time. Thus, while not implying any limitation on the materials that may be used for the support 66, it is generally contemplated that the materials that are generally preferred have a degree of elasticity or stretchability, rather than being very highly rigid, as this may in fact perform better when providing support under the cover 64.

As mentioned above, boot 62 takes the form of a transparent, generally flat and rectangular "dome" made of a strong/structural (and transparent or translucent) material such as polycarbonate, which is mounted on top of cover 64, and thus above supports 66, posts 63, etc. located below cover 64. The protective cover or "dome" 62 not only provides a structural protection function, it in fact also functions as a radome (radome). (according to wikipedia: "radome" (a hybrid of radar and dome) is a structural, weather-proof enclosure that protects (e.g., radar) antennas). The radome is constructed of a material that minimizes attenuation of electromagnetic signals transmitted or received by the antenna. Yet still further, the protective cover 62 may also serve (along with the ground plane) to reduce the radiation pattern of the antenna (i.e., reduce the elevation angle of the maximum gain path and direct a significant amount of radiation (i.e., concentrate the radiation) to the area between the maximum gain path and the ground plane, below the maximum gain path).

Incidentally, the maximum gain path in the elevation angle of the radiation pattern of the antenna, and the radiation distribution above and below the maximum gain path, are significantly affected by the height of the long side gap (which has been explained previously), and it is also significantly affected by the ground plane, which is considerably larger in scale than the cover assembly. Yet still further in addition, however, the material thickness and angle of attack (i.e., the angle of the slope) of the long side edges of the shield 62, as well as the dielectric values of the material from which the shield 62 is made, may (generally considered) still further achieve the angle of elevation of the maximum gain path and the radiation distribution above and below the maximum gain path. Thus, these properties (i.e., the slope angle of the long side edges of the cover 62, the thickness of the material of the cover along these long side edges, and the dielectric value of the material from which the cover is made) are further properties that can potentially be altered or modified to tune the antenna or change its radiation pattern. However, again, the extent of possible changes or variations may be generally limited by other considerations. For example, the ability to change or make adjustments to the angle of attack (i.e., the angle of the slope) of the long side edge of the cover 62 may be significantly affected by the need to maintain a slope angle that provides sufficient safety for wheels that may contact and roll over the cover 62, and this may also be affected by the terms of applicable road safety regulations and the like.

For mounting over other components, the protective dome 62 has a generally rectangular prism-like opening formed in its underside. This opening in the underside of dome 62 is itself best seen in fig. 13. The manner in which the other components of the RFID reader antenna are received in this opening in the underside of dome 62 when the dome is mounted thereon is clearly shown in fig. 11, 12, and 14. Thus, when dome 62 is mounted on other components, the outer peripheral portions of dome 62 (i.e., around and between those peripheral portions defining an opening in the underside of dome 62) extend downward and cover the top and sides of the other components. In practice, the dome is mounted in contact with the bottom plate 61 in the following manner: which forms a seal that prevents moisture, dust or other contaminants from entering therein, wherein other components are housed. A suitable sealant or adhesive may be used to form such a seal between the underside of the periphery of dome 62 and the base plate.

The manner in which the outer peripheral base portion of dome 62 is supported by the vertical sides of depression 65 in base plate 61 has been explained above.

An important aspect of the RFID reader antenna design in this particular embodiment is that when the RFID reader antenna is fully assembled (i.e., when the dome 62 has been finally installed to form a protective cover over the other assembled components), the aggregate "true" height of the resulting structure is less than 25mm, preferably about 20 mm. In this regard, "true" height means the vertical distance between the upper surface of baseplate 61 and the top surface of dome 62 in the region immediately surrounding (i.e., on the outside of) dome 62. By way of example, if the "true" height of the assembled antenna structure is 20mm, the actual height of the dome 62 may be a few millimeters greater than it, however, it should be noted that, like the other portions of the antenna structure, the dome 62 is received into the recessed portion 65 in the center of the chassis, so even if the vertical height of the dome 62 is slightly greater than 20mm (perhaps 21-23mm), the "true" height of the overall antenna structure (which is the height that would appear from the vehicle approaching its viewpoint point) will still be only 20 mm.

It is important to limit the height of the overall RFID reader antenna structure to less than 25mm (preferably 20mm) because, as discussed above, governmental and regulatory authorities responsible for approving the installation and/or use of any form of equipment (or any kind of object) on or near public roads are generally very conservative and thus highly prudent in allowing the installation and/or use of new types or forms of equipment that have not previously been used on public roads, particularly if the form (i.e., size and/or shape and/or general configuration or appearance, etc.) of the new equipment is unfamiliar, unconventional, or different than the type or form of equipment that has previously been approved for use. However, in this regard, under most countries/jurisdictions, regulatory authorities responsible for approving the installation and use of equipment on roads have permitted the installation and use of traditional retroreflective ("cat-eye") road signs, like those depicted in fig. 9 and 10, and these are certainly in extremely widespread use. Importantly, these conventional retroreflective pavement markers typically have a height of about 25 mm. Thus, the presently described RFID reader antenna structure will have a height no greater than (or possibly less than) that of conventional retroreflective road signs that are widely approved for use, general acceptance, and use.

It should be noted that the overall length of boot/dome 62, in a direction parallel to the direction of travel of the vehicle along the roadway, is generally much longer (typically several times longer) than the typical length in this direction of a conventional retroreflective ("cat-eye") roadway sign like that shown in fig. 9 and 10. However, in a direction perpendicular to the direction of vehicle travel along the road (i.e., the direction through the road), the overall width of the boot/dome 62 will be about the same as (or possibly less than) the width of a conventional retroreflective ("cat-eye") road sign. It is also important that from the point of view of the oncoming vehicle (or the driver of the vehicle) it is the width (i.e. the dimension in the direction across the road) and the height of the object on the road that determines the apparent dimension of the object (i.e. it is the width and the height of the object on the road that primarily determine how large the object appears from the point of view of the oncoming vehicle). In providing drivers of oncoming vehicles with a size that identifies the object they are approaching on the road, the length of the object in a direction parallel to the direction of travel of the vehicle is generally of less importance, and in fact the driver may not even be able to adequately identify how long the object is in a direction parallel to the direction of travel of the vehicle, given the viewing angle involved when the driver views the object from a distance away from the object. Thus, even though the protective cover/dome 62 of the antenna structure in this embodiment, which determines its apparent size from the point of view of an oncoming vehicle, is longer than a conventional retroreflective road sign, this is not as important (and may not even be noticeable) to a driver who will understand the size of the object (cover 62) based on object width and height, and thus it (cover 62) will appear substantially indistinguishable or indistinguishable in size and shape from a conventional retroreflective road sign (which they are completely accustomed to viewing and driving over).

In other words, in the presently described embodiments, the RFID reader antenna structure is mounted such that one of the short edges of the rectangular RFID reader antenna structure (i.e., L with the cover)₁One of the parallel-sized edges) points along/against/along the road. Thus, depending on the point of view of the vehicle (and its driver) approaching the RFID reader structure, it is the short edge (and in particular the short edge of the cover 62) that the vehicle (and its driver) will "see". For the reasons discussed above, even for the cover 64 given length (L)₂Which is determined according to the antenna operating frequency), the antenna may still be (L)₁) And (4) changing. However, it is contemplated that the width (L) of the cover 64₁) Will typically be less than 100mm and typically less than 90mm (with a width of about 75mm to 80mm being expected to be typical). As can be seen from fig. 12 and 13, L parallel to the lid₁Will be slightly greater than the L of the lid₁And (4) size. This is because dome 62 is at L₁The direction extends beyond and overhangs cover 64 on both sides (in effect dome 62 overhangs the cover on all sides). However, if it is assumed that the width of the cover 64 is 80mm and the dome 62 is at L₁Dimensionally extending over 20mm thereof on either side, which means that the overall width of the RFID reader antenna structure "in view" of the approaching vehicle (i.e. from its viewpoint point) will be about 120 mm. This is again generally the same width as a widely approved, commonly accepted and used conventional retroreflective road sign.

It is also important that the edge of the structure that the vehicle "sees" when approaching (i.e. the forward facing edge of the cover 62) is a straight edge (i.e. this edge extends in a straight line across the road from the point of view of an oncoming vehicle). This is important because: this is in fact very different from alternative RFID reader antennas, such as those previously proposed in the above' 994 patent application, which are RFID reader antenna structures having an overall circular planar shape. As a result, in the case of the RFID reader antenna structure previously proposed in the' 994 patent application, the edges of the structure that the vehicle would "see" when approaching along a roadway are curved, rather than straight edges. Also in practice, in the case of the RFID reader antenna structure proposed before the' 994 patent application, when driving over the antenna structure, the wheel/tire of the vehicle may first also be (naturally) curved rather than straight at the edges of the structure that hit/touch. This is not considered a significant problem for vehicles (e.g., cars, trucks, etc.). However, it is generally at least believed that this may cause difficulties for vehicles such as motorcycles, bicycles, etc., whereby the following risks are perceived: if the front wheel of the vehicle were to strike a curved edge at a slight angle (i.e., at an angle other than exactly "directly on" the edge), this could cause the vehicle front wheel to be knocked off the way, potentially causing accidents and injuries. However, in the antenna structure in the presently described embodiment, this problem is solved or discussed because the structural edge that the vehicle "sees" when approaching (i.e. the forward facing edge of the cover 62) is a perfectly straight edge that extends directly across the road, and so again, it should be considered that the antenna structure in this embodiment no longer creates a hazard on the road as compared to conventional retroreflective road signs of the type that are generally accepted and used (and are not considered to pose an unacceptable risk).

Also, as can be seen in fig. 11, 12, 13, and 14, the sides of domes 62 (although straight along their length) are not merely straight, vertical sides. Instead, there is at least an upper portion on each of the sides of the dome 62 (and this typically extends over half the height of the dome), which slopes inwardly and upwardly. It will generally be the case that the dome 62 extends out and overhangs the other components of the antenna by an amount sufficient to allow these ramp portions to have a slope of about 45 ° or less relative to the plane of the floor/ground plane/road. This (together with limiting to a height of 25mm or less) can help allow the wheels of cars and other road going vehicles to roll through the apparatus without excessive jolts or impacts. Again, the ramp angle of the upper portion on the side of the dome 62 is similar to that commonly accepted and used (and considered not to pose an unacceptable risk) on conventional retroreflective road signs. Also as mentioned above, in addition to helping the wheels of cars and other vehicles roll through the equipment without excessive bumps or impacts, the angle of attack (i.e., the angle of slope) of the sloped portion of the shield 62, particularly the long side edges, and the thickness of the material along the long sides and the dielectric values of the material from which the shield 62 is made, may achieve the elevation angle of the maximum gain path and the radiation distribution above and below the maximum gain path in the radiation pattern of the antenna.

It should be noted that while it is suggested that polycarbonate or acetal, etc. may be particularly suitable materials for use in making boot/dome 62, no absolute limitation is implied in this regard. Indeed, there are potentially a range of other structurally strong and dielectrically suitable materials that could also be used, and indeed any of these could be used.

Without limiting the preceding, the reason why polycarbonate is chosen as one possible material of which the protective cover (dome) 62 is made, has been mentioned, due to the strength of this material (and also its durability, hardness, UV resistance in other substantial degradations), and thus its ability to be therefore the protection of the cover 64 and of the other components of the antenna covered by it. However, there may be additional benefits to using polycarbonate: this material can be made transparent or translucent or at least slightly light-permeable. This may be beneficial because: as there may be one or more components containing lights, LEDs or the like, including among other electronic components or components that may be provided within or as part of the RFID reader, which are visible from outside the RFID reader when illuminated, and even from a distance from the RFID reader, especially at night or in low light conditions. These lamps or LEDs (or indeed other electronic components) may be housed in a small space which may (at times) remain between the upper surface of the cover 64 and the underside of the dome 62, or they may be mounted within a cavity or opening formed in one or more peripheral portions of the dome, i.e. horizontally out of the other antenna components already described. In any case, such lights or LEDs may be used, for example, to provide an indication as to the current operating status of the RFID reader or individual component or its function. For example, as a simple example, a red light/LED may be provided that is "on" in the presence of an error or fault or warning associated with the operation of the RFID reader (i.e., there is a component failure, or a power supply failure or interruption, or a battery or backup battery is "nearly empty," etc.). However, such lights, LEDs or the like, which may be contained within (but visible from outside) the RFID reader, may also be used for a range of other purposes. For example, because the RFID readers in these applications are positioned on a road surface (i.e., a surface on which the vehicle is traveling and which the vehicle driver is in close proximity), the LEDs or lights in the RFID readers may also be used to provide various forms of signals to the vehicle. For example, a red or green light may be used to indicate that a lane is open or closed to vehicle travel, or to indicate the direction of travel allowed in a lane (e.g., where "wet traffic" traffic management is implemented that facilitates vehicles traveling in different directions in different times of day in a given lane, which may ultimately be useful to help accommodate a large volume of traffic flow in one direction or otherwise at different times of day). Other possible uses are possible, for example, a flashing light may be used to alert road users of an impending event or danger further down the road. Alternatively, red, yellow, and green signals may be provided in an RFID reader located just before the intersection with the traffic light, and the red, yellow, and green lights in the RFID reader may be changed instantaneously/synchronously and accordingly with changes in the signal of the traffic light. The illuminated or radiated light signal of any lamp or LED within the RFID reader may also be "visible" and detectable to a camera or other imaging device, such as those located at the side of a road and used for law enforcement or traffic management purposes. It will be appreciated that the possible uses mentioned above for lights, LEDs or the like which may be provided within or as part of an RFID reader are merely examples and that there may be many other uses or applications for this.

Where the cover 62 is instead supported in an acetal like, for example, not necessarily transparent or translucent, a light guide may be provided within the cover 62 to still allow the LEDs and the like to be used in a similar manner as described above.

It should now be noted that fig. 14 is a view of an RFID reader comprising the proposed antenna and other RFID reader devices not shown in fig. 11, 12, and 13. It should also be noted from the outset that fig. 14 depicts a situation in which at least some portions of the RFID reader and other associated equipment are located at or below the level of the road surface, while other portions (particularly the components associated with the antennas that have been described in detail above) are located at or above the level of the road surface. And it will be readily appreciated that fig. 14 is a side sectional view and thus the components of the RFID reader and other associated equipment located above and below the road surface level can be seen. The specific components and electronics of the RFID reader shown in fig. 14 will not be discussed in detail herein; however, these are substantially the same (or at least similar) to the components and electronics associated with the RFID reader described in the earlier' 994 patent application.

While fig. 14 depicts at least some (and in this case most) of the components and electronics associated with the RFID reader as buried below the level of the roadway, below the antenna, it should be clearly understood that there are no implied limitations as to the various components and electronics and how and where they are mounted. Thus, the components and electronics associated with the RFID reader do not necessarily need to be embedded beneath the reader antenna. Indeed, in other embodiments, the electronics associated with the RFID reader may instead be positioned to the side of the (hypothetical) roadway and connected to an antenna positioned in the middle of the roadway (or lane) by wires or cables that are installed into small slots or channels that are initially cut into the roadway and then covered after the cables have been installed.

RFID readers are discussed elsewhere herein, and this includes readers that incorporate the presently proposed antenna structure, which can be used to provide not only "two-way" data exchange but also "one-way" (or RADAR-like) data exchange. Further explained elsewhere are, inter alia, "one-way" data exchanges, which can be used for vehicle detection purposes. The currently proposed RFID reader can take advantage of this, especially because the amount of power required for two-way communication can be much larger than for one-way communication. Thus, vehicle detection using a "one-way" data exchange can be used, for example, to help minimize power consumption by enabling the RFID reader to operate normally in a low-power one-way communication mode, and then only transition to a higher-power two-way communication mode (by turning on the RF communication device needed for this) when the vehicle is in fact detected to be present by the one-way data exchange, and therefore only when a need for actual/real vehicle identification is required. (the duty cycle within the RFID reader device preferably enables the high power RF communication device required for bidirectional data exchange to be turned on within milliseconds, so even if the vehicle is detected only at say 6m from the antenna, the time delay to turn on the high power RF device does not prevent proper vehicle identification via RFID ("bidirectional" data "exchange), especially if the vehicle is moving at normal road speeds). In addition to saving power, using the higher power potential required for two-way communication only when necessary also significantly helps to reduce the risk of heat generation and overheating in the RFID reader.

This may be done in any manner, in terms of providing power to the antenna (and other electronic components incorporated in or associated with the RFID reader). For example, using an electromagnetic coil, or directly connecting one or more current (power) carrying cables to the RFID reader structure. Such current (power) carrying cables may be installed in shallow grooves or trenches formed in the roadway (e.g., cut/dug into the roadway and then covered after laying the cables).

Further, communication and data transfer between the RFID reader and other computers or devices separate from or external to the RFID reader may be accomplished, and again, this may be accomplished in any suitable manner. Due to the rugged environment and the permanent (or at least semi-permanent) nature of installations in "on-road" applications, connecting cables alone (like ethernet cables or the like) may often not be suitable for enabling data transfer. However, other conventional wireless communication methods (e.g., WiFi, bluetooth, etc.) may be used, or if the RFID reader is powered by a power cable, conventional "data-over-power" methods may also be used for communication. In the case of using a wireless communication method (e.g., Wi-Fi or bluetooth), an additional antenna may be required to support this method. Such an antenna may be incorporated somewhere within the vault of the RFID reader.

Turning now to fig. 16 and 17, these provide graphical representations of the "shape" of the radiation pattern produced by an antenna according to an embodiment of the present invention. It should be noted that the radiation patterns represented in fig. 16 and 17 were generated using a mathematical model; however, from the actual measurement values taken from the actual prototype antenna similar to the embodiments depicted in fig. 11 to 15, it was confirmed that the mathematical model according to the embodiments of the present invention represents the accuracy of the actual (real world) antenna.

Referring first to fig. 16(i), this is a graphical representation of the geometry of the nodes used in mathematically modeling a particular antenna (i.e., a "wire frame" visualization image), and the radiation pattern representations in fig. 16(ii) - (vii) are generated from this particular mathematical simulation. Note that in fig. 16(i) is not actually shown to illustrate what represents the ground plane of the antenna; however, this is not intended to suggest that the ground plane is not represented in the mathematical model. In any case, it will be readily understood from fig. 16(i) how the geometry of the nodes in the mathematical model (as represented by the "wire-frame" visualization image) correspond to the rectangles (L) supported on the struts 63 at the four corners, respectively, in the particular antenna being simulated₁×L₂) The geometry of the cover assembly 64.

In the rest of fig. 16:

fig. 16(ii) and 16(iii) are plan views (i.e. views "top down" directly from above) of graphical representations of the radiation patterns of the simulated antennas, and if the simulated antennas in these views are considered to be positioned on the road surface in the center of the lane, the direction of vehicle travel on the lane will be horizontally from right to left (or left to right);

fig. 16(iv) and 16(v) are end-point views of graphical representations of the radiation pattern of the simulated antenna, i.e. as if the radiation pattern of the antenna is seen in the direction along/along the road in the direction of travel of the vehicle; and

fig. 16(vi) and 16(vii) are side views of graphical representations of the radiation pattern of the simulated antenna, i.e. as if the radiation pattern of the antenna were seen in a direction through the road perpendicular to the direction of travel of the vehicle.

As shown in various views in fig. 16, the radiation pattern of the analog antenna has a shape that extends further across the road (or more in a direction perpendicular to the direction in which the vehicle travels on the road) than along/along the road. In other words, the antenna radiates more energy or greater energy density laterally across the roadway than along the roadway. And as explained in the background section above, this may have the effect that as a result of the geometry of the RFID tag antenna radiation pattern and the RFID reader antenna radiation pattern of the vehicle (whose radiation patterns are depicted in these views), and as a result of the interaction between the two, the effective read zone should, for example, cover the full width of the lane (as shown in fig. 7 (ii)), regardless of any increased directivity of the radiation of the tag antenna of the vehicle (again, as discussed above).

Turning now to fig. 17(i), this is a graphical representation of the geometry of the nodes used in mathematically modeling a particular antenna (i.e., a "wire frame" visualization image), similar to fig. 16(i), and the radiation pattern representations in fig. 17(ii) - (iii) are generated from this particular mathematical simulation. However, a very important thing to note with respect to fig. 17(i) is that the actual geometry of the represented nodes is different from the geometry represented in fig. 16 (i). More specifically, in FIG. 17(i), the shape/geometry utilized by the cover assembly 64 (e.g., length: width (i.e., L) of its rectangular shape) is simulated₁：L₂) Defined by the ratio) is different from the shape/geometry utilized to simulate the cover assembly 64 in fig. 16 (i). Thus, fig. 17(i) shows a simulated specific antenna therein, and the radiation thereof is represented in another view, fig. 17 having a different geometry than the antenna represented and represented in fig. 16, and that is why the shape of the radiation pattern depicted in fig. 17(ii) - (iii) differs from the shape of the radiation pattern depicted in fig. 16(ii) - (iii). Also, in fact, a comparison of fig. 16 with fig. 17 provides an example method by which the geometry of the present antenna (and in particular the relative length to width ratio of the rectangular cover assembly of the antenna) can be varied in order to vary the shape of the radiation pattern produced by the antenna. In the particular example given in FIG. 17, the particular antenna simulated therein has a thinner (i.e., L) than the particular antenna simulated in FIG. 16₁Narrower in size) and the result of this geometry change (at least simply) causes the radiation pattern of the antenna to extend even further across the roadway (or more in a direction perpendicular to the direction of travel of the vehicle on the roadway) and less along/along the roadway than.

In the simulation scenario of fig. 16 and 17, one important point to note is that the radiation pattern has a "null" (or at least a virtual/effective null) located above the geometry of the cover assembly — as best seen in fig. 16(ii) and 17 (ii). This is important because, moving inwardly toward the center of the antenna in any radiation direction, the overall shape of the radiation pattern of the antenna effectively "curves" (or the energy density in the radiation pattern is effectively attenuated) as this geometric center/null position is approached. And the effect is that the amount of energy emitted by the antenna in the vertically upward direction is limited, which is important in order to prevent e.g. blinding reflections from the underside of the vehicle (as already discussed elsewhere).

It is noted that the radiation pattern of the antenna may be described as extending further in one direction than in the other (i.e. across the road (or in a direction perpendicular to the direction of travel of the vehicle on the road) than along/along the road), and that the various views in fig. 16 and 17 seem to show that the radiation pattern thus has a substantially elliptical shape, in fact (i.e. in reality) the radiation pattern does not really have any well-defined edges or boundaries. Thus, it is incorrect to say that something is inside or outside the radiation pattern of the antenna. The radiation pattern of the antenna extends (at least in theoretical terms) in virtually all directions and into all spatial areas around the antenna (theoretically to infinity-i.e. the radiation pattern does not theoretically stop or end). However, as the distance from the antenna increases, the intensity (or energy density) of the radiation emitted by the antenna decreases (very rapidly) or becomes lower, and the antenna also does not radiate energy in all directions at the same/equal intensity or density. Conversely, the energy radiated by the antenna is much stronger in some directions and less strong in other directions. Thus, the apparent elliptical shape of the radiation pattern of the antenna is related to (or appears approximately as a result of) a direction extending outward into an area of three-dimensional space surrounding the antenna where the energy density of the antenna radiation is greatest (i.e., the major axis of the ellipse generally corresponds to the direction in which the antenna emits energy at the greatest density-but see further discussion below of the edges/boundaries of the elliptical shape).

Following the above, although theoretically it may be considered that the radiation pattern of the antenna extends infinitely, due to the nature of digital electronics, there are (or can be said to be) edges or boundaries within the radiation pattern of the antenna, which may (in this case) be considered as outer edges or boundaries defining an elliptical shape of the radiation pattern. However, for the reasons discussed above, this edge or boundary is not a feature of the radiation pattern itself. Of course, this edge or boundary becomes defined as a result of the relationship between the energy emitted by the antenna (as an RFID reader antenna) and the operation of the RFID tag and (RFID reader) antenna to exchange information. More specifically, said edge or boundary within the radiation pattern of the (RFID reader) antenna adopts its shape (i.e. an elliptical surface shape, as depicted in the figures in this case for example), and is defined in its three-dimensional space by a locus of points at which the energy density emitted by the (RFID reader) antenna becomes large enough to communicate with RFID tags within the radiation pattern of the (RFID reader) antenna. This may be explained with reference to so-called passive RFID tags for convenience, but it should be clearly understood that the invention is by no means restricted to use with only passive RFID tags (i.e. the invention may also be used with so-called active RFID tags and even any other form of RFID tag). A passive RFID tag is an RFID tag that does not contain its own battery or other power source. Instead, the passive RFID tag itself (i.e., the antenna of the tag and also all of the tag's operating electronics) is powered by the energy emitted by the RFID reader antenna. Now, due to the nature of digital electronics, some minimum amount of power will always be required to operate a given passive RFID tag (e.g., to enable it to power up and transmit a signal back to the RFID reader antenna using its own antenna, etc.). Naturally, however, the amount of power required to operate different passive RFID tags may be different (note that the amount of power required for a passive RFID tag to be powered on and operate is often described as tag sensitivity). Thus, some passive RFID tags with low sensitivity may require more power before they can be powered on and operated, etc., and so these may need to be closer to the RFID reader antenna (where the antenna emits more energy density) to operate and communicate with the RFID reader antenna. On the other hand, other passive RFID tags with higher sensitivity may require lower power to turn on and operate, and therefore they can turn on and operate at a greater distance from the RFID reader antenna. The point is that as a result of this, the above-mentioned edges or boundaries within the radiation pattern (i.e. the surface shape of the ellipse of the radiation pattern in three-dimensional space in this case) are not fixed in practice, which is defined by the locus of points at which the energy density emitted by the antenna becomes large enough for the RFID tag to be able to communicate with the RFID reader antenna. Of course, assuming that the amount of energy emitted by the antenna remains fixed/set, its location (i.e., how far this edge or boundary is from the antenna) depends on the sensitivity of the RFID tag. Thus, in the context of the present invention, assuming a set power output from the RFID reader antenna, the elliptical "size" of the radiation pattern of the antenna (i.e., how "large" the ellipse is relative to the size of the antenna) will be larger for more sensitive tags and smaller for less sensitive tags.

It is also noted, however, that when the present invention is practiced, the RFID tags used on the license plates of automobiles (whether they be passive RFID tags or some other form of tag) should have sensitivity such that the "read-necessary area" (within which the RFID reader must be able to communicate with the license plate-mounted RFID tags of automobiles if the tags of the automobiles are within that area) falls within the ellipse of the radiation pattern of the antenna, the size and shape of which are described above with reference to fig. 1 and 5, etc. In other words, the power output by the RFID reader antenna is such (and in combination with the sensitivity of the RFID tag on the vehicle license plate) that no part of the necessary read zone described above is outside the edges or boundaries of the ellipse of the radiation pattern of the antenna.

In the present specification and claims (if any), the word "comprise", and its derivatives including "comprises" and "comprising", include each of the stated integers but do not preclude the inclusion of one or more other integers.

Reference in this specification to "one embodiment" or "an embodiment" means: the particular features, structures, or characteristics described in connection with the embodiment are included in at least one embodiment of the invention. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

In compliance with the statute, the invention has been described in language more or less specific as to structural or methodical features. It is to be understood that the invention is not limited to the specific features shown or described, since the means herein described comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted by those skilled in the art.