阅读说明：本技术 一种基于带状线的同轴馈电微带天线 (Coaxial feed microstrip antenna based on strip line ) 是由 董刚 朱思曈 吴海东 朱樟明 杨银堂 于 2021-09-27 设计创作，主要内容包括：本发明公开了一种基于带状线的同轴馈电微带天线,涉及微波毫米通信技术领域,包括：第一金属层、以及依次位于第一金属层一侧的第一介质层、第二金属层、第二介质层、第三金属层、第三介质层和寄生贴片天线；其中,第一介质层内包括带状线,带状线沿平行于第一金属层所在平面的方向延伸；第二金属层包括第一开口；第二介质层包括过孔和多个第一通孔；沿垂直于第一金属层所在平面的方向,过孔的正投影位于第一开口内；第三金属层包括第二开口,沿垂直于第一金属层所在平面的方向,辐射贴片天线的正投影位于第二开口内；第二金属层通过第一通孔与第三金属层连接；由于带状线通过过孔连接至辐射贴片天线并进行馈电,因而提高了微带天线的增益和带宽。(The invention discloses a coaxial feed microstrip antenna based on strip lines, which relates to the technical field of microwave millimeter communication and comprises the following components: the antenna comprises a first metal layer, a first dielectric layer, a second metal layer, a second dielectric layer, a third metal layer, a third dielectric layer and a parasitic patch antenna, wherein the first dielectric layer, the second metal layer, the second dielectric layer, the third metal layer, the third dielectric layer and the parasitic patch antenna are sequentially positioned on one side of the first metal layer; the first dielectric layer comprises a strip line which extends along a direction parallel to the plane of the first metal layer; the second metal layer comprises a first opening; the second dielectric layer comprises a via hole and a plurality of first through holes; along the direction vertical to the plane of the first metal layer, the orthographic projection of the via hole is positioned in the first opening; the third metal layer comprises a second opening, and the orthographic projection of the radiation patch antenna is positioned in the second opening along the direction perpendicular to the plane where the first metal layer is positioned; the second metal layer is connected with the third metal layer through the first through hole; the strip line is connected to the radiating patch antenna through the via hole and feeds, so that the gain and the bandwidth of the microstrip antenna are improved.)

1. A stripline-based coaxial feed microstrip antenna, comprising: a first metal layer;

the first dielectric layer is positioned on one side of the first metal layer; the first dielectric layer comprises a strip line, and the strip line extends along a direction parallel to the plane of the first metal layer;

the second metal layer is positioned on one side of the first dielectric layer, which is far away from the first metal layer, and comprises a first opening;

the second dielectric layer is positioned on one side of the second metal layer far away from the first metal layer and comprises a through hole and a plurality of first through holes; along the direction perpendicular to the plane of the first metal layer, the orthographic projection of the via hole is positioned in the first opening;

the third metal layer and the radiation patch antenna are positioned on one side of the second dielectric layer, which is far away from the first metal layer; the third metal layer comprises a second opening, and the orthographic projection of the radiation patch antenna is positioned in the second opening along the direction perpendicular to the plane of the first metal layer; the strip line is connected to the radiating patch antenna through the via hole; the second metal layer is connected with the third metal layer through a first through hole;

the third dielectric layer is positioned on one side of the third metal layer far away from the first metal layer;

and the parasitic patch antenna is positioned on one side of the third dielectric layer, which is far away from the first metal layer.

2. The stripline-based coaxial feed microstrip antenna of claim 1, wherein the first dielectric layer further comprises a plurality of second vias through which the first metal layer is connected to the second metal layer.

3. The stripline-based coaxial feed microstrip antenna of claim 2, wherein the orthographic projection of the plurality of first vias encompasses the orthographic projection of the radiating patch antenna in a direction perpendicular to the plane of the first metal layer.

4. The stripline-based coaxially fed microstrip antenna of claim 3, wherein the parasitic patch antenna comprises a third opening and a fourth opening;

and in the direction perpendicular to the plane where the first metal layer is located, the orthographic projection of the radiation patch antenna is positioned between the third opening and the fourth opening, and the third opening and the fourth opening are symmetrically distributed on two sides of the radiation patch antenna.

5. The stripline-based coaxial feed microstrip antenna of claim 1, wherein the first, second and third dielectric layers each comprise a Ferro-A6M low temperature co-fired ceramic material having a dielectric constant of 5.9, a loss tangent of 0.002, and a single layer tile thickness of 0.096 mm.

6. The stripline-based, co-axial fed microstrip antenna of claim 1, wherein the radiating patch antenna and the parasitic patch antenna have a resonant frequency of 80 GHz.

7. The stripline-based coaxial feed microstrip antenna of claim 4, wherein the radiating patch antenna has a width in the first direction of:

where c denotes the propagation speed of light in vacuum, f denotes the operating frequency of the radiating patch antenna, ε_rIs the relative dielectric constant, W, of the substrate material_mFor the calculated width of the radiating patch antenna in the first directionAnd the first direction is the direction in which the third opening points to the fourth opening.

8. The stripline-based coaxial feed microstrip antenna of claim 7, wherein the radiating patch antenna length in the second direction is determined according to the following equation:

in the formula, λ_gIndicating the wavelength of guided waves in the substrate, L_mCalculating the length of the radiation patch antenna in a second direction, wherein the second direction is perpendicular to the first direction, and the first direction and the second direction are both parallel to the plane of the first metal layer;

in the formula, epsilon_eDenotes the effective dielectric constant of the substrate, and h denotes the thickness of the substrate.

9. The stripline-based, coaxially fed microstrip antenna of claim 8, wherein the parasitic patch antenna is dimensioned according to the following equation:

L_p＝L_m

W_p＝2×W_m

in the formula, W_pRepresenting the width of the parasitic patch antenna in the first direction, L_pRepresenting a length of the parasitic patch antenna in the second direction.

10. The stripline-based coaxial feed microstrip antenna of claim 9, wherein the third opening has a length a-W in the second direction_pA/3, a width in the first direction b/10;

the length of the fourth opening is equal to the length of the third opening, and the width of the fourth opening is equal to the width of the third opening.

Technical Field

The invention belongs to the technical field of microwave millimeter communication, and particularly relates to a coaxial feed microstrip antenna based on a strip line.

Background

With the development of modern processing technology, a novel planar antenna represented by a microstrip antenna is gradually formed, and the microstrip antenna has the advantages of low cost, easiness in volume production, small size and low profile, and can be applied to various environments such as dual polarization, multiple frequency bands, multiple beams and the like.

The Package-in-Package (AiP) technology is a technology for integrating a three-dimensional multi-chip module and a radio frequency Antenna based on a Package material and a process, and aims to realize a miniaturized design for system-level communication. The antenna packaging technology can realize the integrated design of the antenna and the radio frequency chip by integrating the packaging cavity around the antenna and internally mounting and pasting the multi-chip assembly, thereby reducing the overall size of the system; the chip signal pin is connected to the PCB through the dielectric substrate, so that the length of an interconnection line is shortened, the system size is reduced on the premise of ensuring the normal work of the antenna and the chip, and the chip signal pin can work together with a radio frequency front-end circuit.

According to the conventional antenna design method in the related art, the size of a patch antenna operating in the W band is generally in the range of 1-2mm, and when such a small-sized antenna is integrated in the application field of AiP, the small-sized antenna is affected by internal large metal parts or large-area scatterers such as a printed circuit board, and the radiation characteristic of the antenna is damaged.

Therefore, how to ensure good radiation characteristics of the antenna or isolate the antenna from the external environment is an urgent technical problem to be solved in the field.

Disclosure of Invention

In order to solve the above problems in the prior art, the present invention provides a stripline-based coaxial feed microstrip antenna. The technical problem to be solved by the invention is realized by the following technical scheme:

the invention provides a coaxial feed microstrip antenna based on strip line, comprising: a first metal layer;

the first dielectric layer is positioned on one side of the first metal layer; the first dielectric layer comprises a strip line, and the strip line extends along a direction parallel to the plane of the first metal layer;

the second metal layer is positioned on one side of the first dielectric layer, which is far away from the first metal layer, and comprises a first opening;

the second dielectric layer is positioned on one side of the second metal layer far away from the first metal layer and comprises a through hole and a plurality of first through holes; along the direction perpendicular to the plane of the first metal layer, the orthographic projection of the via hole is positioned in the first opening;

the third metal layer and the radiation patch antenna are positioned on one side of the second dielectric layer, which is far away from the first metal layer; the third metal layer comprises a second opening, and the orthographic projection of the radiation patch antenna is positioned in the second opening along the direction perpendicular to the plane of the first metal layer; the strip line is connected to the radiating patch antenna through the via hole; the second metal layer is connected with the third metal layer through a first through hole;

the third dielectric layer is positioned on one side of the third metal layer far away from the first metal layer;

and the parasitic patch antenna is positioned on one side of the third dielectric layer, which is far away from the first metal layer.

In an embodiment of the invention, the first dielectric layer further includes a plurality of second through holes, and the first metal layer is connected to the second metal layer through the second through holes.

In an embodiment of the invention, an orthographic projection of the plurality of first through holes surrounds an orthographic projection of the radiation patch antenna along a direction perpendicular to a plane of the first metal layer.

In one embodiment of the present invention, the parasitic patch antenna includes a third opening and a fourth opening;

and in the direction perpendicular to the plane where the first metal layer is located, the orthographic projection of the radiation patch antenna is positioned between the third opening and the fourth opening, and the third opening and the fourth opening are symmetrically distributed on two sides of the radiation patch antenna.

In one embodiment of the invention, the first dielectric layer, the second dielectric layer and the third dielectric layer all comprise Ferro-A6M low-temperature co-fired ceramic materials with the dielectric constant of 5.9, the loss tangent of 0.002 and the thickness of a single-layer ceramic chip of 0.096 mm.

In one embodiment of the present invention, the resonant frequency of the radiating patch antenna and the parasitic patch antenna is 80 GHz.

In one embodiment of the present invention, the width of the radiating patch antenna in the first direction is:

where c denotes the propagation speed of light in vacuum, f denotes the operating frequency of the radiating patch antenna, ε_rIs the relative dielectric constant, W, of the substrate material_mAnd in order to calculate the width of the radiation patch antenna in a first direction, the first direction is a direction in which the third opening points to the fourth opening.

In one embodiment of the present invention, the length of the radiating patch antenna in the second direction is determined according to the following formula:

in the formula, λ_gIndicating the wavelength of guided waves in the substrate, L_mCalculating the length of the radiation patch antenna in a second direction, wherein the second direction is perpendicular to the first direction, and the first direction and the second direction are both parallel to the plane of the first metal layer;

in the formula, epsilon_eDenotes the effective dielectric constant of the substrate, and h denotes the thickness of the substrate.

In one embodiment of the invention, the dimensions of the parasitic patch antenna are determined according to the following formula:

L_p＝L_m

W_p＝2×W_m

in the formula, W_pRepresenting the width of the parasitic patch antenna in the first direction, L_pRepresenting a length of the parasitic patch antenna in the second direction.

In one embodiment of the present invention, a length a of the third opening in the second direction is W_pA/3, a width in the first direction b/10;

the length of the fourth opening is equal to the length of the third opening, and the width of the fourth opening is equal to the width of the third opening.

Compared with the prior art, the invention has the beneficial effects that:

the invention provides a strip line-based coaxial feed microstrip antenna, which comprises a first metal layer, a first dielectric layer, a second metal layer, a second dielectric layer, a third metal layer, a third dielectric layer and a parasitic patch antenna, wherein the first dielectric layer, the second metal layer, the second dielectric layer, the third metal layer, the third dielectric layer and the parasitic patch antenna are sequentially arranged on one side of the first metal layer; the strip line is arranged in the first medium layer and extends along the direction parallel to the plane where the first metal layer is located, the second medium layer comprises a through hole, the side, far away from the first metal layer, of the second medium layer further comprises a radiation patch antenna, and the strip line is connected to the radiation patch antenna through the through hole, so that the gain and the bandwidth of the microstrip antenna are improved.

In addition, the second medium layer comprises a plurality of first through holes, the first medium layer comprises a plurality of second through holes, through introducing the through holes into different medium layers, the influence of an external radiator can be weakened, electromagnetic isolation can be achieved, the antenna can work at five-quarter resonance length, and the coaxial feed microstrip antenna is suitable for application scenarios under AiP technologies.

The present invention will be described in further detail with reference to the accompanying drawings and examples.

Drawings

Fig. 1 is a cross-sectional view of a stripline-based coaxial feed microstrip antenna provided in an embodiment of the present invention;

fig. 2 is a top view of a stripline-based coaxial feed microstrip antenna provided in an embodiment of the present invention;

FIG. 3 is a diagram illustrating simulation results according to an embodiment of the present invention;

fig. 4 is a schematic diagram of another simulation result provided in the embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention are not limited thereto.

Fig. 1 is a cross-sectional view of a stripline-based coaxial feed microstrip antenna according to an embodiment of the present invention. Referring to fig. 1, an embodiment of the present invention provides a coaxial feeding microstrip antenna 100 based on a strip line 3, including: a first metal layer 1;

the first dielectric layer 2 is positioned on one side of the first metal layer 1; the first dielectric layer 2 comprises a strip line 3, and the strip line 3 extends along a direction parallel to the plane of the first metal layer 1;

the second metal layer 4 is positioned on one side of the first dielectric layer 2, which is far away from the first metal layer 1, and the second metal layer 4 comprises a first opening 5;

the second dielectric layer 6 is positioned on one side of the second metal layer 4 far away from the first metal layer 1, and the second dielectric layer 6 comprises a through hole 7 and a plurality of first through holes 8; along the direction vertical to the plane of the first metal layer 1, the orthographic projection of the via hole 7 is positioned in the first opening 5;

a third metal layer 9 and a radiation patch antenna 10 which are positioned on one side of the second dielectric layer 6 far away from the first metal layer 1; the third metal layer 9 comprises a second opening 11, and the orthographic projection of the radiation patch antenna 10 is positioned in the second opening 11 along the direction vertical to the plane of the first metal layer 1; the strip line 3 is connected to the radiating patch antenna 10 through the via 7; the second metal layer 4 is connected with the third metal layer 9 through a first through hole 8;

the third dielectric layer 12 is positioned on one side of the third metal layer 9 far away from the first metal layer 1;

and the parasitic patch antenna 13 is positioned on one side of the third dielectric layer 12 far away from the first metal layer 1.

In the present embodiment, the coaxial feed microstrip antenna 100 based on the strip line 3 includes: the antenna comprises a first metal layer 1, and a first dielectric layer 2, a second metal layer 4, a second dielectric layer 6, a third metal layer 9, a third dielectric layer 12 and a parasitic patch antenna 13 which are sequentially arranged on one side of the first metal layer 1. Specifically, a strip line 3 is arranged in the first dielectric layer 2, the extension direction of the strip line 3 is parallel to the plane where the first metal layer 1 is located, the second dielectric layer 6 comprises a via hole 7, and the third metal layer 9 comprises a second opening 11; along the direction vertical to the plane of the first metal layer 1, the orthographic projection of the via hole 7 is positioned in the first opening 5 of the second metal layer 4, and the orthographic projection of the radiation patch antenna 10 is positioned in the second opening 11; that is, the radiation patch antenna 10 is located in the second opening 11 of the third metal layer 9, and the via 7 realizes the electrical connection between the strip line 3 and the radiation patch antenna 10 through the first opening 5. In the view shown in fig. 1, this design transmits an input electrical signal to a position right under the radiating patch antenna 10, thereby feeding the radiating patch antenna 10.

In this embodiment, the first dielectric layer 2, the second dielectric layer 6 and the third dielectric layer 12 all comprise Ferro-A6M low-temperature co-fired ceramic materials with a dielectric constant of 5.9, a loss tangent of 0.002 and a single-layer ceramic sheet thickness of 0.096 mm. Optionally, the thickness of each dielectric layer is three layers of tile thickness, that is, the height H of the first dielectric layer 2, the second dielectric layer 6 and the third dielectric layer 12 is 0.288 mm.

With reference to fig. 1, the first dielectric layer 2 further includes a plurality of second through holes 14, and the first metal layer 1 is connected to the second metal layer 4 through the second through holes 14.

Specifically, a plurality of vertically metallized second vias 14 may be disposed around the strip line 3 in the first dielectric layer 2, the second vias 14 connecting the first metal layer 1 and the second metal layer 4 to achieve electromagnetic isolation of the strip line 3. Illustratively, in the view shown in fig. 1, 10 second through holes 14 are respectively provided on the left and right sides of the via hole 7, and the distance between the center of each second through hole 14 and the center of the strip line 3 is 0.35 mm.

Fig. 2 is a top view of a stripline 3 based coaxial feed microstrip antenna 100 according to an embodiment of the present invention. Alternatively, referring to fig. 1-2, along a direction perpendicular to the plane of the first metal layer 1, the orthographic projection of the first through holes 8 surrounds the orthographic projection of the radiation patch antenna 10.

Specifically, the first periodic metalized through holes 8 are formed around the radiation patch antenna 10, and the first through holes 8 are connected to the second metal layer 4 and the third metal layer 9, so that the radiation patch antenna 10 is electromagnetically shielded. It can be understood that since the third dielectric layer 12 is located between the third metal layer 9 and the parasitic patch antenna 13, the third metal layer 9 can act as a reflector of the parasitic patch antenna 13.

In this embodiment, the first through hole 8 and the second through hole 14 are made of silver, and the aperture and the height of the two through holes are the same. It should be understood that, the coaxial feeding microstrip antenna 100 based on the strip line 3 performs feeding excitation by using the strip line 3, since the radiation patch antenna 10 and the feeding port are located on different LTCC (Low Temperature Co-fired Ceramic) layers, a metalized via 7, a through hole, a pad, and a back pad are required to implement feeding, however, the through hole may introduce parasitic inductance and parasitic capacitance, and the aperture size of the via 7 may also affect the transmission performance of the feeding network. Illustratively, in the present embodiment, the aperture of the first through hole 8 and the second through hole 14 is 0.1mm, the distance between adjacent first through holes 8/second through holes 14 is 0.2mm, and the height of each first through hole 8 or second through hole 14 for electromagnetic isolation from the component to be isolated is a quarter of the dielectric wavelength.

Alternatively, referring to fig. 1-2, the parasitic patch antenna 13 includes a third opening 15 and a fourth opening 16;

along a direction perpendicular to the plane of the first metal layer 1, the orthographic projection of the radiation patch antenna 10 is located between the third opening 15 and the fourth opening 16, and the third opening 15 and the fourth opening 16 are symmetrically distributed on two sides of the radiation patch antenna 10.

In this embodiment, the parasitic patch antenna 13 includes a third opening 15 and a fourth opening 16, and along a direction perpendicular to the plane of the first metal layer 1, the orthographic projection of the radiating patch antenna 10 is located between the third opening 15 and the fourth opening 16, optionally, the third opening 15 and the fourth opening 16 are both rectangular, and are symmetrically distributed on both sides of the radiating antenna, so as to ensure symmetrical directivity.

It should be noted that the strip-line based coaxial feeding microstrip antenna needs to be placed at a specific angle to make the whole AiP antenna unit operate under 40 ° polarization condition, and fig. 2 is only used to illustrate the tilting state of the antenna, and does not limit the tilting angle.

Optionally, the resonant frequency of the radiating patch antenna 10 and the parasitic patch antenna 13 is 80 GHz.

In the present embodiment, the width W of the strip line 3 is determined as follows_s：

Wherein, W_sDenotes the width of the strip line 3, c denotes the thickness of the medium in which the strip line 3 is located, i.e. the thickness of the first medium layer 2, Z₀Representing the characteristic impedance, ∈_rRepresents the dielectric constant.

Further, the width of the radiating patch antenna 10 in the first direction x is:

where c denotes the propagation speed of light in vacuum, f denotes the operating frequency of the radiating patch antenna 10, epsilon_rIs the relative dielectric constant of the substrate material, the substrate comprises a first dielectric layer 2, a second dielectric layer 6 and a third dielectric layer 12, W_mTo calculate the width of the radiating patch antenna 10 in the first direction x, the first direction x is a direction in which the third opening 15 points to the fourth opening 16.

According to the width W of the radiating patch antenna 10_mDetermining the effective dielectric constant ε of the antenna substrate_e：

Wherein h represents the thickness of the substrate, namely the height of each dielectric layer.

According to the width W of the radiating patch antenna 10_mAnd the effective dielectric constant ε of the antenna substrate_eDetermining equivalent slot radiation length DeltaL_mAnd a guided wave wavelength lambda in the substrate_g：

According to equivalent gap radiation length Delta L_mAnd a guided wave wavelength lambda in the substrate_gDetermining the length of the radiating patch antenna 10 in the second direction y:

in the formula, λ_gIndicating the wavelength of guided waves in the substrate, L_mFor the calculated length of the radiation patch antenna 10 in the second direction y, the second direction y is perpendicular to the first direction x, and the first direction x and the second direction y are both the same as the first direction xThe planes of a metal layer 1 are parallel.

The parasitic patch antenna 13 is then dimensioned:

L_p≈L_m

W_p≈2×W_m

in the formula, W_pRepresenting the width, L, of the parasitic patch antenna 13 in the first direction x_pIndicating the length of the parasitic patch antenna 13 in the second direction y.

Further, the size of the third opening 15 and the fourth opening 16 is determined according to the size of the parasitic patch antenna 13. Specifically, the length a of the third opening 15 in the second direction y is W_pAnd/3, the width b in the first direction x is a/10. In this embodiment, the length of the fourth opening 16 in the second direction y is equal to the length of the third opening 15 in the second direction y, and the width of the fourth opening 16 in the first direction x is equal to the width of the third opening 15 in the first direction x.

Finally, the parameters of the microstrip antenna are determined by the formula: the thicknesses of the first metal layer, the second metal layer and the third metal layer are all 0.01mm, the width Ws of the strip line is 0.07mm, the aperture Rvia hole is approximately equal to 0.25mm, the width Wm of the radiation patch antenna is approximately equal to 1.30mm, the length Lm of the radiation patch antenna is approximately equal to 2.03mm, the width Wp of the parasitic patch antenna is approximately equal to 2.84mm, the length Lp of the parasitic patch antenna is approximately equal to 2.00mm, the lengths a of the third opening and the fourth opening are approximately equal to 0.80mm, the width b of the third opening and the fourth opening is approximately equal to 0.10mm, and the whole microstrip antenna is positioned in a material dielectric layer of 6.4mm multiplied by 6.4 mm. Three-dimensional modeling is carried out on the microstrip antenna by adopting three-dimensional electromagnetic full-wave simulation software HFSS _19.0, the result of the reflection loss S11 is shown in figure 3, two resonance points in a passband are 79.77GHz and 81.81GHz respectively, and the reflection coefficients of the two resonance points are-32.67 dB and-19.95 dB respectively; gain pattern as shown in fig. 4, it can be seen that when the microstrip antenna operates at the center frequency of the pass band, the maximum gain in the E-plane and H-plane radiation directions is 4.90 db.

The beneficial effects of the invention are that:

the invention provides a strip line-based coaxial feed microstrip antenna, which comprises a first metal layer, a first dielectric layer, a second metal layer, a second dielectric layer, a third metal layer, a third dielectric layer and a parasitic patch antenna, wherein the first dielectric layer, the second metal layer, the second dielectric layer, the third metal layer, the third dielectric layer and the parasitic patch antenna are sequentially arranged on one side of the first metal layer; the strip line is arranged in the first medium layer and extends along the direction parallel to the plane where the first metal layer is located, the second medium layer comprises a through hole, the side, far away from the first metal layer, of the second medium layer further comprises a radiation patch antenna, and the strip line is connected to the radiation patch antenna through the through hole, so that the gain and the bandwidth of the microstrip antenna are improved.

In addition, the second dielectric layer comprises a plurality of first through holes, the first dielectric layer comprises a plurality of second through holes, through introducing via holes and through holes in different dielectric layers, the influence of an external radiator can be weakened, electromagnetic isolation can be achieved, the antenna can work at five-quarter resonance length, and the coaxial feed microstrip antenna is suitable for application scenarios under AiP technologies.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations and positional relationships based on those shown in the drawings, and are used only for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be considered as limiting the present invention.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly under and obliquely below the second feature, or simply meaning that the first feature is at a lesser elevation than the second feature.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples described in this specification can be combined and combined by those skilled in the art.

While the present application has been described in connection with various embodiments, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed application, from a review of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.