A low-profile, broadband, low-loss, dual-polarized metasurface antenna

Abstract

The present invention belongs to the field of antenna design, and specifically provides a low-profile broadband low-loss dual-polarization metasurface antenna to solve the problems of narrow working frequency band, high profile, high cross-polarization, etc. of existing dual-polarization antennas. The present invention introduces parasitic patches in the metasurface structure to increase the impedance matching bandwidth; and, through the slit design of the patch, the polarization current is separated, the cross polarization is effectively suppressed, and the resonant frequency is increased to achieve broadband radiation characteristics; in addition, through the optimization design of the patch size and the patch spacing, the matching effect of some frequency points is optimized, and the gain depression of the two polarization directions at high frequencies is weakened; finally, the relative bandwidth of the dual-polarization metasurface antenna in the present invention can reach 61.5%, the isolation within the working frequency band is greater than 37dB, the profile height is only 0.095λ0, and it has stable lateral radiation characteristics; and the antenna also has the advantages of simple structure, easy manufacturing, and low assembly difficulty.

Description

Technical Field

[0001] The invention belongs to the field of antenna design, relates to a dual-polarization antenna, and specifically provides a low-profile, broadband, low-loss dual-polarization metasurface antenna. Background Art

[0002] With the rapid development of wireless communication technology, in order to meet the needs of integrated transmission and reception, antennas not only need to have excellent characteristics such as miniaturization, light weight, wide frequency band, high gain, etc., but also need to have dual-polarization characteristics; on the one hand, dual-polarization antennas can simultaneously transmit or receive two orthogonally polarized electromagnetic waves to improve spectrum utilization; on the other hand, dual-polarization antennas can also effectively combat channel multipath fading and improve the system's anti-interference ability.

[0003] At present, commonly used dual-polarization antennas mainly include cross-dipole antennas, hybrid structure antennas and microstrip patch antennas; among them, the cross-dipole antenna realizes dual-polarization characteristics by feeding two independent ports separately, but the feeding part is large in volume, resulting in a high profile of the entire antenna and is not easy to design; the hybrid structure antenna uses different structures to produce different polarizations, but its structural asymmetry makes it difficult to achieve low cross-polarization; the microstrip patch antenna realizes dual-polarization characteristics by feeding different patches on the same layer of dielectric or on different dielectric layers separately, and has the advantages of low profile, small volume and simple feeding structure, but its bandwidth is generally narrow. Even if the bandwidth is widened by increasing the thickness of the dielectric substrate or adding parasitic units, it is still difficult to meet the wide-bandwidth requirements of modern communication systems for antennas; with the proposal of metasurface antennas, new ideas are provided for the design of dual-polarization antennas; therefore, the present invention proposes a low-profile, broadband, low-loss dual-polarization metasurface antenna. Summary of the invention

[0004] The purpose of the present invention is to provide a low-profile, broadband, low-loss dual-polarization metasurface antenna to solve the problems of narrow operating frequency band, high profile, high cross-polarization, etc. of existing dual-polarization antennas.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A low-profile broadband low-loss dual-polarized metasurface antenna, comprising, from top to bottom, a metasurface structure 1, an upper dielectric substrate 2, a metal floor layer 3, a lower dielectric substrate 4, and a microstrip feeder network 5; wherein the metasurface structure is composed of 4 rectangular A patches 1-1, 4 rectangular B patches 1-2, 4 rectangular C patches 1-3, 4 rectangular D patches 1-4, 4 rectangular E patches 1-5, and 4 rectangular F patches 1-6, wherein the rectangular A patches are arranged in a 2×2 array at a central position, the rectangular B patches are arranged on the outside of the rectangular A patches along the Y-axis direction, the rectangular C patches are arranged on the outside of the rectangular A patches along the X-axis direction, the rectangular D patches are arranged on the outside of the rectangular B patches along the X-axis direction, the rectangular E patches are arranged on the outside of the rectangular B patches along the Y-axis direction, and the rectangular F patches are arranged on the outside of the rectangular C patches along the X-axis direction;

[0007] A slit is opened in the rectangular patch A along the X-axis direction, and the distance between the slit in the rectangular patch A and the edge of the rectangular patch A close to the X-axis is m1, m1<0.5y A ,y A is the size of rectangular patch A along the Y axis; rectangular patch B has a gap along the Y axis, and the distance between the gap in rectangular patch B and the edge of rectangular patch B close to the Y axis is m2, m2<0.5x B , x B is the size of the rectangular patch B along the X-axis direction; the rectangular patch C has two slits along the X-axis direction, dividing the rectangular patch C into three sub-patches; the rectangular patch D has one slit along the X-axis direction and one slit along the Y-axis direction, dividing the rectangular patch D into four sub-patches; the rectangular patch E has one slit along the Y-axis direction, and the distance between the slit in the rectangular patch E and the edge of the rectangular patch E close to the Y-axis is m2, m2<0.5x E , x E is the size of the rectangular E patch along the X-axis direction; the rectangular F patch has two slits along the X-axis direction and one slit along the Y-axis direction, dividing the rectangular F patch into six sub-patches.

[0008] Furthermore, in the metasurface structure, the size of the rectangular A patch is x A ×y A , the spacing between adjacent rectangular A patches is g1; the size of rectangular B patches is x B ×y B , the spacing between adjacent rectangular B patches and rectangular A patches is g0, the spacing between adjacent rectangular B patches is g2; the size of the rectangular C patch is x C ×y C , the spacing between adjacent rectangular C patches and rectangular A patches is g0, the spacing between adjacent rectangular C patches is g1; the size of the rectangular D patch is x D ×y D, the spacing between adjacent rectangular D patches and rectangular B patches is g0, the spacing between adjacent rectangular D patches and rectangular C patches is g0; the size of rectangular E patch is x E ×y E , the spacing between adjacent rectangular E patches and rectangular B patches is g0, the spacing between adjacent rectangular E patches is g2; the size of the rectangular F patch is x F ×y F , the spacing between adjacent rectangular F patches and rectangular E patches is g0, and the spacing between adjacent rectangular F patches is g0; and, x D >x B >x A >x C ,y D >y B >y A , x E ≥x B >y E ,y F ≥y A >x F ,y C = y A , g0>g2>g1.

[0009] Furthermore, in the metasurface structure, the width of all gaps is s.

[0010] Furthermore, the thickness of the upper dielectric substrate is t1, the thickness of the lower dielectric substrate 4 is t2, and t2 <t1。

[0011] Furthermore, three rectangular coupling gaps are opened on the metal floor layer, wherein the first rectangular coupling gap is parallel to the Y-axis and is located directly below the rectangular A patch; the second rectangular coupling gap and the third rectangular coupling gap are parallel to the X-axis, and the second rectangular coupling gap and the third rectangular coupling gap are respectively located below the rectangular B patch outside the rectangular A patch.

[0012] Furthermore, the microstrip feeding network includes: 3 groups of Y-type microstrip transmission lines, wherein the first group of Y-type microstrip transmission lines feeds the metasurface structure through the first rectangular coupling slot to excite vertically polarized current; the second group of Y-type microstrip transmission lines and the third group of Y-type microstrip transmission lines feed the metasurface structure through the second rectangular coupling slot and the third rectangular coupling slot respectively to excite parallel polarized current; and the second group of Y-type microstrip transmission lines and the third group of Y-type microstrip transmission lines are symmetrically distributed and have a feeding phase difference of 180°.

[0013] Based on the above technical solution, the beneficial effects of the present invention are:

[0014] The present invention provides a low-profile broadband low-loss dual-polarized metasurface antenna. First, based on the traditional 4×4 metasurface antenna, two groups of parasitic patches are introduced around the metasurface structure, and one mode is added to each of the two groups of degenerate modes in the vertical polarization direction and the horizontal polarization direction, thereby increasing the impedance matching bandwidth; and, through the slot design of each patch, the slot is used to cut off the current orthogonal to it, so that the polarization currents in the vertical direction and the horizontal direction are separated, and the cross polarization is significantly suppressed; at the same time, for vertical polarization, the strongest current field is distributed on the rectangular A patch located above the central coupling slot, and for horizontal polarization, the strongest current field is distributed on the rectangular B patch located above the coupling slots on both sides. The present invention moves the corresponding slot to the strongest field of the mode, thereby increasing the resonant frequency and realizing broadband radiation characteristics; in addition, the present invention optimizes the patch size and patch spacing that generate the strongest horizontal polarization current, optimizes the matching effect of some frequency points, and effectively weakens the gain depression at high frequencies by increasing the patch size at the four corners;

[0015] In summary, the present invention provides a low-loss dual-polarized metasurface antenna with wide bandwidth. The relative bandwidth of the vertical and horizontal dual polarizations of the antenna can reach 61.5%, the isolation within the working frequency band is greater than 37dB, the profile height is only 0.095λ0 (λ0 is the wavelength in free space relative to the center frequency), and it has stable lateral radiation characteristics. In addition, the antenna also has the advantages of simple structure, easy manufacturing, and low assembly difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the side view structure of the low-profile broadband low-loss dual-polarization metasurface antenna of the present invention, wherein 1 is the metasurface structure, 2 is the upper dielectric substrate, 3 is the metal floor layer, 4 is the lower dielectric substrate, and 5 is the microstrip feeder network; t1 is the thickness of the upper dielectric substrate, and t2 is the thickness of the lower dielectric substrate.

[0017] Figure 2 Schematic diagram of the structure of the super surface structure in the present invention, wherein 1-1 is a rectangular A patch, 1-2 is a rectangular B patch, 1-3 is a rectangular C patch, 1-4 is a rectangular D patch, 1-5 is a rectangular E patch, and 1-6 is a rectangular F patch; x A 、x B 、x C 、x D 、x E 、x F The lengths of the rectangular A patch, rectangular B patch, rectangular C patch, rectangular D patch, rectangular E patch, and rectangular F patch in the X-axis direction, y A ,y B ,y C ,y D ,y E,y F They are the lengths of rectangular A patch, rectangular B patch, rectangular C patch, rectangular D patch, rectangular E patch, and rectangular F patch in the Y-axis direction, g0 is the spacing between adjacent rectangular B patches and rectangular A patches, g1 is the spacing between adjacent rectangular A patches, g2 is the spacing between adjacent rectangular C patches, m1 is the distance between the gap in the rectangular A patch and the edge of the rectangular A patch close to the X-axis, m2 is the distance between the gap in the rectangular B patch and the edge of the rectangular B patch close to the Y-axis, and s is the gap width.

[0018] Figure 3 Schematic diagram of the structure of the metal floor layer in the present invention, wherein w is the side length of the upper dielectric substrate and the lower dielectric substrate, ls1 is the length of the first rectangular coupling gap on the metal floor layer, ws1 is the width of the first rectangular coupling gap on the metal floor layer, ls2 is the length of the second rectangular coupling gap on the metal floor layer, and ws2 is the width of the second rectangular coupling gap on the metal floor layer.

[0019] Figure 4 Schematic diagram of the structure of the microstrip feeder network in the present invention, wherein w is the side length of the upper dielectric substrate and the lower dielectric substrate.

[0020] Figure 5 This is a graph showing the return loss and port isolation results of the low-profile, broadband, low-loss, dual-polarization metasurface antenna in an embodiment of the present invention.

[0021] Figure 6 4 is a gain characteristic diagram of a low-profile, broadband, low-loss, dual-polarization metasurface antenna in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0023] This embodiment provides a low-profile, broadband, low-loss, dual-polarized metasurface antenna, the structure of which is as follows: Figure 1 As shown, from top to bottom, it includes: a metasurface structure 1, an upper dielectric substrate 2, a metal floor layer 3, a lower dielectric substrate 4, and a microstrip feeder network 5;

[0024] The super surface structure 1 is arranged on the upper surface of the first dielectric substrate 2. Figure 2As shown, a plane rectangular coordinate system is established with the center of the upper surface of the first dielectric substrate as the origin, with the left-right direction as the Y axis and the up-down direction as the X axis, and the metasurface structure is an axisymmetric structure about the X axis and the Y axis; the metasurface structure is composed of 4 rectangular A patches 1-1, 4 rectangular B patches 1-2, 4 rectangular C patches 1-3, 4 rectangular D patches 1-4, 4 rectangular E patches 1-5 and 4 rectangular F patches 1-6, wherein the rectangular A patches are arranged in a 2×2 array at the center, and the size of the rectangular A patches is x A ×y A , the spacing between adjacent rectangular A patches is g1; the rectangular B patch is set outside the rectangular A patch along the Y axis direction, and the size of the rectangular B patch is x B ×y B , the spacing between adjacent rectangular B patches and rectangular A patches is g0, and the spacing between adjacent rectangular B patches is g2; the rectangular C patch is set outside the rectangular A patch along the X-axis direction, and the size of the rectangular C patch is x C ×y C , the spacing between adjacent rectangular C patches and rectangular A patches is g0, and the spacing between adjacent rectangular C patches is g1; the rectangular D patch is set outside the rectangular B patch along the X-axis direction, and the size of the rectangular D patch is x D ×y D , the spacing between adjacent rectangular D patches and rectangular B patches is g0, and the spacing between adjacent rectangular D patches and rectangular C patches is g0; the rectangular E patch is set outside the rectangular B patch along the Y axis direction, and the size of the rectangular E patch is x E ×y E , the spacing between adjacent rectangular E patches and rectangular B patches is g0, and the spacing between adjacent rectangular E patches is g2; the rectangular F patch is set outside the rectangular C patch along the X-axis direction, and the size of the rectangular F patch is x F ×y F , the spacing between adjacent rectangular F patches and rectangular E patches is g0, and the spacing between adjacent rectangular F patches is g0;

[0025] Furthermore, in the metasurface structure, x D >x B >x A >x C ,y D >y B >y A , x E ≥x B >y E ,y F ≥y A >x F ,y C = y A, g0>g2>g1; it should be noted that the size parameter x represents the length in the X-axis direction, and the size parameter y represents the length in the Y-axis direction;

[0026] Furthermore, in the metasurface structure, a gap is formed in the rectangular A patch along the X-axis direction, and the distance between the gap in the rectangular A patch and the edge of the rectangular A patch close to the X-axis is m1, m1<0.5y A ; A gap is opened in the rectangular patch B along the Y axis, and the distance between the gap in the rectangular patch B and the edge of the rectangular patch B close to the Y axis is m2, m2<0.5x B ; The rectangular C patch has two slits along the X-axis direction, dividing the rectangular C patch into three sub-patches; the rectangular D patch has one slit along the X-axis direction and one slit along the Y-axis direction, dividing the rectangular D patch into four sub-patches; the rectangular E patch has one slit along the Y-axis direction, and the distance between the slit in the rectangular E patch and the edge of the rectangular E patch close to the Y-axis is m2, m2<0.5x E ; The rectangular F patch has two slits along the X-axis direction and one slit along the Y-axis direction, dividing the rectangular F patch into six sub-patches; further, the width of all slits is s;

[0027] The thickness of the upper dielectric substrate 2 is t1, and the center of the metasurface structure 1 and the center of the upper dielectric substrate 2 are located on the same axis; the thickness of the lower dielectric substrate 4 is t2, and t2 <t1;

[0028] The metal floor layer 3 is arranged on the lower surface of the upper dielectric substrate 2 and is also located on the upper surface of the lower dielectric substrate 4; Figure 3 As shown, three rectangular coupling slots are provided on the metal floor layer 3, wherein the first rectangular coupling slot is parallel to the Y axis and is located directly below the rectangular A patch; the second rectangular coupling slot and the third rectangular coupling slot are parallel to the X axis, and the second rectangular coupling slot and the third rectangular coupling slot are located below the rectangular B patch; the center of the metal floor layer 3 and the center of the metasurface structure 1 are located on the same axis;

[0029] The microstrip feeding network 5 is arranged on the lower surface of the lower dielectric substrate 4, and includes: 3 groups of Y-shaped microstrip transmission lines, such as Figure 4As shown, the first group of Y-type microstrip transmission lines feeds the metasurface structure through the first rectangular coupling slot to excite the vertical polarization current; the second group of Y-type microstrip transmission lines and the third group of Y-type microstrip transmission lines feed the metasurface structure through the second rectangular coupling slot and the third rectangular coupling slot respectively to excite the parallel polarization current; and the second group of Y-type microstrip transmission lines and the third group of Y-type microstrip transmission lines are symmetrically distributed and have a feeding phase difference of 180°; it is also noted that the Y-type microstrip transmission line consists of a main feed line and two parallel branches. In order to ensure equal-amplitude and in-phase feeding, the two branches have feed lines of the same length.

[0030] In terms of working principle, in order to achieve dual-polarization characteristics, the present invention uses a first group of Y-type microstrip transmission lines to excite a vertically polarized current field on the metasurface structure, and uses a second group of Y-type microstrip transmission lines and a third group of Y-type microstrip transmission lines to in-phase excite a horizontally polarized current field on the metasurface structure; on the basis of the traditional 4×4 metasurface structure, a horizontal slit (Y-axis direction) is opened on each of the rectangular B patch, the rectangular D patch, the rectangular E patch, and the rectangular F patch, and the strongest current in the vertical polarization direction is regulated to the rectangular A patch; a vertical slit (X-axis direction) is opened on each of the rectangular A patch and the rectangular D patch, and two vertical slits (X-axis direction) are opened on each of the rectangular C patch and the rectangular F patch, and the strongest current in the horizontal polarization direction is regulated to the rectangular B patch; through the above design, the metasurface structure is Mutually orthogonal strong current modes are separated onto different patches, which can effectively suppress cross polarization, thereby significantly reducing mutual coupling between units and improving the overall performance of the antenna; at the same time, two groups of parasitic patches, namely rectangular E patches and rectangular F patches, are respectively added to the outsides of the rectangular B patch and the rectangular C patch to introduce an additional mode, thereby increasing the matching bandwidth of the antenna and realizing broadband radiation, and, through the size design of the parasitic patches, the current field distributed on them has little effect on the required strong current field; in particular, the present invention effectively improves the matching effect of horizontal polarization on the premise of having little effect on the gain and matching of vertical polarization by increasing the size of the rectangular B patch; and can weaken the gain depression at high frequencies when the antenna radiates on the premise of having little effect on the antenna matching by increasing the size of the rectangular D patch.

[0031] More specifically, in the dual-polarized metasurface antenna provided in this embodiment, the upper dielectric substrate adopts Arlon AD350A, with a dielectric constant of 3.5, a loss tangent of 0.003, and a thickness of t1=4mm; the lower dielectric substrate adopts Neltec NY9260 (IM), with a dielectric constant of 2.6, a loss tangent of 0.002, and a thickness of t2=0.8mm; the upper dielectric substrate and the lower dielectric substrate are both square, with a side length of w, w=85mm; in the metasurface structure, x A =8mm,y A=7.8mm, x B =9.8mm,y B =10mm, x C =7.5mm,y C = y A =7.8mm, x D =8.5mm,y D =11.5mm, x E =9.8mm,y E =8.7mm, x F =7mm,y F =7.8mm, g0=1.3mm, g1=0.8mm, g2=0.9mm, m1=2mm, m2=1.5mm, s=0.3mm; in the metal floor layer, ws1=1.5mm, ls1=16mm, ws2=1mm, ls2=14mm.

[0032] The dual-polarized metasurface antenna in this embodiment is simulated and tested, and the return loss and port isolation results are shown in the figure below: Figure 5 As shown in the figure, its gain characteristic is as follows Figure 6 As shown in the figure, it can be seen that the relative bandwidth of the vertical and horizontal dual polarizations of the antenna can reach 61.5%, the isolation within the working frequency band is greater than 37dB, and a relatively stable gain can be guaranteed within the working frequency band.

[0033] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A low-profile, broadband, low-loss, dual-polarized metasurface antenna, comprising, from top to bottom: A metasurface structure (1), an upper dielectric substrate (2), a metal floor layer (3), a lower dielectric substrate (4), and a microstrip feeder network (5); characterized in that the metasurface structure is composed of 4 rectangular A patches (1-1), 4 rectangular B patches (1-2), 4 rectangular C patches (1-3), 4 rectangular D patches (1-4), 4 rectangular E patches (1-5), and 4 rectangular F patches (1-6), wherein the rectangular A patches are arranged in a 2×2 array at a central position, the rectangular B patches are arranged on the outside of the rectangular A patches along the Y-axis direction, the rectangular C patches are arranged on the outside of the rectangular A patches along the X-axis direction, the rectangular D patches are arranged on the outside of the rectangular B patches along the X-axis direction, the rectangular E patches are arranged on the outside of the rectangular B patches along the Y-axis direction, and the rectangular F patches are arranged on the outside of the rectangular C patches along the X-axis direction; A slit is opened in the rectangular patch A along the X-axis direction, and the distance between the slit in the rectangular patch A and the edge of the rectangular patch A close to the X-axis is m1, m1<0.5y A ,y A is the size of rectangular patch A along the Y axis; rectangular patch B has a gap along the Y axis, and the distance between the gap in rectangular patch B and the edge of rectangular patch B close to the Y axis is m2, m2<0.5x B , x B is the size of the rectangular patch B along the X-axis direction; the rectangular patch C has two slits along the X-axis direction, dividing the rectangular patch C into three sub-patches; the rectangular patch D has one slit along the X-axis direction and one slit along the Y-axis direction, dividing the rectangular patch D into four sub-patches; the rectangular patch E has one slit along the Y-axis direction, and the distance between the slit in the rectangular patch E and the edge of the rectangular patch E close to the Y-axis is m2, m2<0.5x E , x E is the size of the rectangular E patch along the X-axis direction; the rectangular F patch has two slits along the X-axis direction and one slit along the Y-axis direction, dividing the rectangular F patch into six sub-patches; Three rectangular coupling slots are opened on the metal floor layer, wherein the first rectangular coupling slot is parallel to the Y axis and is located directly below the rectangular A patch; the second rectangular coupling slot and the third rectangular coupling slot are parallel to the X axis, and the second rectangular coupling slot and the third rectangular coupling slot are respectively located directly below the rectangular B patch outside the rectangular A patch; the center of the metal floor layer and the center of the metasurface structure are located on the same axis; The microstrip feeding network includes: 3 groups of Y-type microstrip transmission lines, wherein the first group of Y-type microstrip transmission lines feeds the metasurface structure through the first rectangular coupling slot to excite the vertical polarization current; the second group of Y-type microstrip transmission lines and the third group of Y-type microstrip transmission lines feed the metasurface structure through the second rectangular coupling slot and the third rectangular coupling slot respectively to excite the parallel polarization current; and the second group of Y-type microstrip transmission lines and the third group of Y-type microstrip transmission lines are symmetrically distributed and have a feeding phase difference of 180°; the Y-type microstrip transmission line consists of a main feed line and two parallel branches, and the two parallel branches have feed lines of the same length.

2. The low-profile, broadband, low-loss, dual-polarized metasurface antenna according to claim 1, characterized in that: In the metasurface structure, the size of the rectangular A patch is x A ×y A , the spacing between adjacent rectangular A patches is g1; the size of rectangular B patches is x B ×y B , the spacing between adjacent rectangular B patches and rectangular A patches is g0, the spacing between adjacent rectangular B patches is g2; the size of the rectangular C patch is x C ×y C , the spacing between adjacent rectangular C patches and rectangular A patches is g0, the spacing between adjacent rectangular C patches is g1; the size of the rectangular D patch is x D ×y D , the spacing between adjacent rectangular D patches and rectangular B patches is g0, the spacing between adjacent rectangular D patches and rectangular C patches is g0; the size of rectangular E patch is x E ×y E , the spacing between adjacent rectangular E patches and rectangular B patches is g0, the spacing between adjacent rectangular E patches is g2; the size of the rectangular F patch is x F ×y F , the spacing between adjacent rectangular F patches and rectangular E patches is g0, and the spacing between adjacent rectangular F patches is g0; and, x D >x B >x A >x C ,y D >y B >y A , x E ≥x B >y E ,y F ≥y A >x F ,y C = y A , g0>g2>g1.

3. The low-profile, broadband, low-loss, dual-polarized metasurface antenna according to claim 1, characterized in that: In the metasurface structure, the width of all gaps is s.

4. The low-profile, broadband, low-loss, dual-polarized metasurface antenna according to claim 1, characterized in that: The thickness of the upper dielectric substrate is t1, the thickness of the lower dielectric substrate (4) is t2, and t2<t1.

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