阅读说明：本技术 一种小型超宽带圆极化平面螺旋天线 (Small ultra-wideband circularly polarized planar helical antenna ) 是由 徐友云 李大鹏 蒋锐 于 2020-12-14 设计创作，主要内容包括：本发明公开了一种小型超宽带圆极化平面螺旋天线,包括作为天线的辐射单元的自补型复合螺旋结构和进行馈电的微带渐变巴伦结构；微带渐变巴伦结构为双面结构,由两条不平衡的微带线渐变为平衡的平行双线,渐变过程中实现了阻抗的变换；所述微带渐变巴伦结构的不平衡端向下延伸至反射器。本发明的天线在2-18GHz工作频带内保持着稳定的辐射特性,天线的阻抗带宽达到了150％(2-18GHz),驻波比小于2,天线在工作带宽内(2-18GHz)保持着优秀的圆极化特性,轴比小于3dB。在保证天线辐射特性、阻抗带宽、轴比带宽的基础上,对天线的平面尺寸和剖面尺寸都进行了缩减,达到了小型化的特性。(The invention discloses a small ultra-wideband circularly polarized planar helical antenna, which comprises a self-complementary composite helical structure used as a radiating unit of the antenna and a micro-strip gradient balun structure for feeding; the microstrip gradual change balun structure is a double-sided structure, two unbalanced microstrip lines are gradually changed into balanced parallel double lines, and impedance transformation is realized in the gradual change process; the unbalanced end of the microstrip graded balun structure extends down to the reflector. The antenna of the invention keeps stable radiation characteristic in 2-18GHz working frequency band, the impedance bandwidth of the antenna reaches 150% (2-18GHz), the standing-wave ratio is less than 2, the antenna keeps excellent circular polarization characteristic in the working bandwidth (2-18GHz), and the axial ratio is less than 3 dB. On the basis of ensuring the radiation characteristic, the impedance bandwidth and the axial ratio bandwidth of the antenna, the plane size and the section size of the antenna are reduced, and the characteristic of miniaturization is achieved.)

1. A small ultra-wideband circularly polarized planar helical antenna is characterized by comprising a self-complementary composite helical structure used as a radiating unit of the antenna and a micro-strip gradually-changed balun structure for feeding;

the microstrip gradual change balun structure is a double-sided structure, two unbalanced microstrip lines are gradually changed into balanced parallel double lines, and impedance transformation is realized in the gradual change process; the unbalanced end of the microstrip graded balun structure extends down to the reflector.

2. The small ultra-wideband circularly polarized planar helical antenna of claim 1, wherein said self-complementary composite helical structure has an archimedean helical structure at its center and a sinusoidal helical structure at its outer end for bending the helical antenna arms.

3. The small ultra-wideband circularly polarized planar helical antenna as recited in claim 1, wherein said reflector has a cross-shaped slot in the bottom and a circular reflective cavity around the reflector.

4. The small ultra-wideband circularly polarized planar helical antenna of claim 2, wherein the equation for the Archimedes plus sine function of said self-complementing compound helical structure is:

where ρ represents the radial in a polar coordinate system,the argument of the central archimedean spiral,is the argument r of the outer end sinusoidal helix₀Taking an initial radius, taking an initial value of 2mm, taking a as an Archimedes spiral line growth factor, taking b as a spiral line interval, taking an initial value of 0.8mm, taking c as the amplitude of a loaded sine line, taking an initial value of 1, taking d as the period of the loaded sine line, and taking an initial value of 20; the line width w of the antenna is consistent with the width of the spiral line spacing b.

5. The small ultra-wideband circularly polarized planar helical antenna of claim 4, wherein the Archimedes spiral growth factor a is (2 x w)/pi.

6. The small ultra-wideband circularly polarized planar helical antenna as claimed in claim 1, wherein the diameter of the circular reflector is slightly larger than the diameter of the radiator dielectric plate, and the cross-shaped slot is slightly larger than the cross-sectional dimension of the dielectric plate of the coaxial feed structure.

Technical Field

The invention relates to a small ultra-wideband circularly polarized planar helical antenna.

Background

Wireless communication utilizes the property of electromagnetic waves that propagate freely in space to enable long-distance exchange of information. The antenna exchanges high-frequency current with electromagnetic waves, so that the system can transmit or receive electromagnetic waves in different forms. For a wireless communication system, the performance of an antenna has a great influence on its operation performance, and therefore, the development of the antenna technology is a crucial part of the current development of the wireless communication technology.

With the continuous development of science and technology, radio frequency spectrum is continuously exploited, the bandwidth of a radio system is also continuously expanded, and an Ultra Wide Band (UWB) antenna has its specific advantages in the field of high-speed millimeter wave wireless communication.

The existing ultra-wideband antenna often adopts structures such as a helical antenna, a slot line antenna, a vivaldi antenna, a magnetoelectric dipole antenna and the like. In which only a helical antenna can generate circularly polarized waves, circular polarization has the advantage over linear polarization of being able to reduce the effects of faraday rotation in the ionosphere, without the need to strictly limit the direction between the transmitter and receiver antennas, and is very effective in reducing multipath interference from the ground or other objects. The traditional helical antenna generally adopts a conical logarithmic spiral structure, and the antenna is wound on a cone or a round table to form unidirectional electromagnetic radiation, but the application occasion of the antenna is special due to the complexity of the shape and the size of the antenna. The planar spiral antenna derived from the method adopts a self-complementary spiral structure, the antenna is formed by reversely coiling two metal strip lines with equal length and width to form a planar spiral, and the metal part of the antenna and the blank part present a complementary relationship. The common planar spiral structure comprises an equiangular spiral structure, an Archimedes spiral structure and the like, and the self-complementary structure enables the antenna to achieve approximate non-frequency-variable characteristics, enables the polarization characteristics to achieve near circular polarization characteristics with the axial ratio lower than 3dB, and enables the bandwidth to achieve multi-octave ultra-wideband characteristics.

Due to the uniqueness in features and applications, the design of a planar helical antenna faces a variety of challenging problems, such as circular polarization characteristics, impedance, phase, gain, and directivity pattern, with good characteristics over a very wide bandwidth and small antenna size.

Disclosure of Invention

The invention aims to solve the technical problem that a planar helical antenna in the prior art cannot have extremely wide bandwidth under a small size, and provides a small ultra-wideband circularly polarized planar helical antenna.

In order to solve the technical problems, the invention provides the following technical scheme:

the invention aims to provide a miniaturized ultra-wideband circularly polarized planar helical antenna, the working bandwidth of which is 2-18GHz, and the miniaturized ultra-wideband circularly polarized planar helical antenna mainly comprises but is not limited to a microstrip balun feed structure for converting unbalance into balance, a self-complementary composite helical structure and a reflector structure with a groove at the bottom.

The self-complementary composite spiral structure is used as a radiation unit of the antenna, the composite structure adopts an Archimedes spiral and sine spiral structure, the center adopts the Archimedes spiral structure, the outer end adopts the sine spiral structure to bend the spiral antenna arm, and the size of the spiral antenna is effectively reduced under the condition that the electrical length of the antenna arm in a radiation band is not changed.

The self-complementing type composite spiral structure feeds power through an external microstrip line, and because the structure of the self-complementing type planar spiral antenna is balanced and symmetrical, and the traditional microstrip feeding structure is an unbalanced feeding structure, a balun structure with balance-unbalance conversion is needed. The common balun structure usually adopts a coaxial line structure loaded with a short-circuit metal post as a feeder line of the radiator, and the characteristic impedance of the coaxial line is 50 Ω, but in practice, the characteristic impedance of the planar helical structure radiator is stabilized at 120-. In order to ensure impedance matching of a radiator and a feed structure and realize balun balance characteristics of the feed structure, a microstrip gradual change balun structure is adopted for feeding, the balun structure is a double-sided structure, two unbalanced microstrip lines are gradually changed into balanced parallel double lines, and impedance conversion is realized in the gradual change process. The length of the traditional balun structure is 1/2 of the wavelength corresponding to the lower limit frequency of the antenna operation, which greatly increases the size of the antenna, and reduces the length of the feed line without influencing the in-band characteristic of the antenna in order to reduce the section of the antenna and realize the miniaturization characteristic.

In order to inhibit the characteristic of the bidirectional radiation of the planar helical antenna, a circular reflector structure with a slot at the bottom is provided, a cross-shaped slot is formed in the middle of a circular metal ground, a metal back cavity is loaded on the periphery of the circular metal ground, the downward-radiated left-hand circularly polarized wave is effectively converted into the upward-radiated right-hand circularly polarized wave under the condition of not influencing feed, and the directional gain of the antenna is improved.

In order to further reduce the height of the antenna, the microstrip balun structure is bent, and feeding is carried out in a measuring and feeding mode, so that the section of the antenna is greatly reduced. However, the microstrip line is parallel to the helical line structure, which generates a certain mutual coupling effect, and in order to eliminate the effect, the length of the microstrip line needs to be extended, and the plane size of the antenna is increased.

Has the advantages that:

the antenna of the invention keeps stable radiation characteristic in 2-18GHz working frequency band, the impedance bandwidth of the antenna reaches 150% (2-18GHz), the standing-wave ratio is less than 2, the antenna keeps excellent circular polarization characteristic in the working bandwidth (2-18GHz), and the axial ratio is less than 3 dB. On the basis of ensuring the radiation characteristic, the impedance bandwidth and the axial ratio bandwidth of the antenna, the plane size and the section size of the antenna are reduced, and the characteristic of miniaturization is achieved.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

fig. 1 is a schematic structural diagram of a novel antenna provided by the present invention;

fig. 2 is a top view of an antenna provided by the present invention;

fig. 3 is a return loss diagram of an antenna radiator provided by the present invention in an individual simulation;

fig. 4 is an axial ratio bandwidth diagram of an antenna radiator provided by the present invention simulated alone;

fig. 5 is a schematic diagram of a microstrip balun feed structure of the antenna provided by the present invention;

fig. 6 is a return loss diagram of the microstrip balun feed structure of the antenna provided by the present invention;

fig. 7 is a return loss diagram of an overall simulation of an antenna radiator and a feed structure provided by the present invention;

fig. 8 is an axial ratio bandwidth diagram of an overall simulation of the antenna radiator and feed structure provided by the present invention;

fig. 9 is a 2GH right-hand circularly polarized directional diagram integrally simulated by the antenna radiator and feed structure provided by the present invention;

fig. 10 is a 9GH right-hand circularly polarized pattern simulated by the antenna radiator and feed structure as a whole according to the present invention;

fig. 11 is an 18GH right hand circular polarization pattern for the overall simulation of the antenna radiator and feed structure provided by the present invention;

FIG. 12 is a 2GH right-hand circularly polarized pattern of an antenna loaded reflector cavity provided by the present invention;

FIG. 13 is a 9GH right-hand circularly polarized pattern of an antenna loaded reflector cavity provided by the present invention;

FIG. 14 is an 18GH right hand circular polarization pattern of an antenna loaded reflector cavity provided by the present invention;

the corresponding part names indicated by the numbers in the figures: 1. the self-complementary composite spiral structure comprises a self-complementary composite spiral structure 2, a gradual change microstrip coaxial balun feed structure 3, an FR4 dielectric substrate 4, a reflector 5 and a cross-shaped slotted structure;

Detailed Description

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.

Examples

Referring to fig. 1, a small ultra-wideband circularly polarized planar helical antenna comprises a self-complementary composite helical structure 1 serving as a radiating element of the antenna and a microstrip coaxial gradient balun structure 2 for feeding;

the microstrip coaxial gradual change balun structure 2 is a double-sided structure, two unbalanced microstrip lines are gradually changed into balanced parallel double lines, and impedance transformation is realized in the gradual change process; the unbalanced end of the microstrip coaxial gradual change balun structure 2 extends downwards to a reflector 4, the bottom of the reflector 4 is provided with a cross-shaped groove 5, and an annular reflecting cavity is loaded on the periphery.

The self-compensating composite spiral structure is placed on the upper layer of an FR4 dielectric plate 3 to be used as a radiator of the antenna, and the center of the radiator is loaded with a double-sided parallel gradient microstrip balun structure for feeding.

Specifically, referring to fig. 2, a specific structure of a self-complementary composite spiral can be seen from a top view of the antenna, where the composite spiral adopts a structure of "archimedean spiral + sinusoidal spiral", and an equation of archimedean plus sinusoidal function is:

where ρ represents the radial in a polar coordinate system,the argument of the central archimedean spiral,is the argument r of the outer end sinusoidal helix₀For the starting radius, a is the archimedes spiral growth factor, b is the spiral pitch, c is the loaded sinusoidal line amplitude, and d is the loaded sinusoidal line period.

The wavelength corresponding to the lower limit frequency of the antenna determines the size of the outer diameter of the spiral line, the inner diameter 2r0 of the spiral line determines the upper limit frequency and the impedance matching of the antenna, the theoretical value of the input impedance of the self-complementary structure is 188.5 omega, and the measured value is about 140 omega. The outer diameter of the antenna was taken to be 60mm and the inner diameter was taken to be 4.2mm by calculation. In order to form a self-complementary structure of an antenna to have a good impedance characteristic over a wide frequency band, the line width w of the antenna is uniform with the width of the helical pitch b. The spiral line growth factor a represents the density of the spiral line, the higher the density, the smaller the terminal reflection, but the larger the transmission line loss, the influence on the antenna radiation efficiency, and generally (2 x w)/pi is taken. The sine-line amplitude c determines the coupling between the two complementary spirals, and the period d, like the growth factor a, influences the end reflection coefficient. The composite spiral line structure effectively prolongs the electrical length of the antenna arm in the radiation band and reduces the plane size of the antenna. The entire spiral structure was loaded on FR4 dielectric board (dielectric constant 2.65, loss tangent 0.02) with a thickness of 1 mm.

With reference to figures 3 and 4, simulations of the radiators alone have shown that the lower frequency of the antenna reaches 1.61GHz, which is better than the expected 2GHz result, mainly because the increase in the electrical length of the antenna arms leads to an extension of the lower frequency. The upper limit frequency of the antenna is far higher than 18GHz, and approximate non-frequency change characteristics are achieved at high frequency; the axial ratio of the antenna is lower than 2.25dB in the range of 2-18GHz, and excellent circular polarization characteristics are realized. The excellent performance of the radiator also provides guarantee for the influence caused by impedance matching and balance problems caused by subsequent loading of the feed structure.

Referring to fig. 5, the spiral line is fed by two parallel microstrip lines. On one hand, the two parallel microstrip lines respectively feed the two self-compensating spiral lines, and the unbalanced microstrip lines are converted into two balanced parallel microstrip lines with equal width, so that a balun structure of unbalanced-balanced conversion is realized; on the other hand, the two microstrip lines are subjected to impedance transformation in an exponential gradual change mode. One microstrip line at the unbalanced terminal serves as a transmission line, the input impedance is 50 omega, the other microstrip line serves as a ground line, and the line width is 5 times of that of the transmission line at the unbalanced terminal. The two microstrip lines at the balanced end have the same output impedance, which is 140 Ω. The graded balun microstrip structure is loaded on two sides of an FR4 dielectric slab with the thickness of 1mm (the dielectric coefficient is 2.65, and the loss tangent is 0.02). It is worth noting that the balun structure at the balanced end is slightly higher than the radiator, which is beneficial for welding feeding of the two. The length of a general balun feed structure is 1/2, namely 75mm, of the wavelength corresponding to the lower limit frequency of the antenna operation, and in order to reduce the height of the antenna, the length of the microstrip line is shortened to 30mm on the premise of ensuring that the input impedance and the output impedance of the microstrip line are not changed.

Referring to fig. 6, the shortened feed structure is simulated independently, the reflection coefficient of the feed structure is less than-15 dB in the 2-18GHz working frequency band, and the microstrip line has good transmission characteristics. However, the reduction of the length of the balun structure causes the change of the transmission phase, thereby affecting the balance characteristic of the radiator and having a large influence on the axial ratio of the low-frequency bandwidth and the high-frequency bandwidth of the antenna.

Thanks to the excellent performance of the radiator, as shown in fig. 7 and 8, the planar helical antenna loaded with the balun feed structure still has the return loss lower than-10 dB and the axial ratio lower than 3dB in the working frequency band (2-18GHz), thereby realizing good circular polarization characteristics.

Referring to fig. 9, 10 and 11, it shows that the low, medium and high frequency right-hand circular polarization directional diagrams of the antenna have high equalization degree of the E-plane directional diagram and the H-plane directional diagram of the antenna, and show good right-hand circular polarization characteristics in the antenna radiation direction, and besides the low gain of the antenna at the 2GHz low frequency, the whole gain flatness of the antenna is high, and the gain is about 4.5 dB. The reason why the gain of the low-frequency directional diagram is reduced is mainly that the balun structure is shortened, so that the cut-off frequency at the low frequency is improved, the unbalance at the low frequency is strengthened, and the transmission efficiency is reduced.

The right-hand circularly polarized gain of the antenna is further improved, and the planar helical antenna can generate bidirectional radiation characteristics, and the antenna radiation generates left-hand circularly polarized waves in the opposite direction, so that a slotted circular reflector structure is loaded at the bottom of the antenna. The diameter of the circular metal ground is 60mm, the middle of the circular metal ground is provided with a cross-shaped groove, and the cross-shaped groove is slightly larger than the cross section size of the coaxial feed structure dielectric plate, so that feed grounding short circuit is prevented. The structural characteristic of the centrosymmetry of the cross-shaped groove can convert the reflected left-hand circularly polarized wave into right-hand circularly polarized wave, so that the gain of the antenna is improved.

Referring to fig. 12, 13 and 14, it shows that the antenna low, medium and high frequency right-hand circularly polarized directional diagram loaded with the reflective cavity has the gain increased by about 2dB at the low frequency of the antenna, and the gain at the rest frequency points is increased by about 4dB, so as to realize the characteristic of high gain.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.