Ultra-wideband linear polarization conversion metasurface and metasurface antenna thereof

Abstract

The application discloses an ultra-wideband linear polarization conversion metasurface and a metasurface antenna thereof. The metasurface comprises a metal pattern layer, a dielectric layer one, a dielectric layer two, a metal pattern layer and a metal ground layer in sequence. An air layer is formed between the dielectric layer one and the dielectric layer two. The metal pattern layer comprises rectangular strips and two fan rings with the same shape and independently distributed. The rectangular strips are located on the diagonal lines of the dielectric layer one, and the length of the rectangular strips is less than the length of the diagonal lines. The rectangular strips are symmetrically arranged with the center of the dielectric layer one as the symmetry center, the two fan rings are symmetrically distributed with the long strip as the symmetry axis, and the openings of the two fan rings are opposite to the long strip. The application can realize polarization conversion bandwidth of 6.17 GHz to 19.5 GHz (relative bandwidth of 103.9%), and can also be applied to circularly polarized patch array antenna RCS reduction. The impedance matching bandwidth of the antenna can be widened to 6.2 GHz to 8.4 GHz (30.1%), the axial ratio bandwidth can be widened to 6.75 GHz to 8.32 GHz (20.1%), the peak gain is 11.1 dBi, and the single station RCS of the antenna is reduced by more than 5 dB under the irradiation of x and y polarization plane waves from 6.4 to 18.6 GHz (97.6%).

Description

Technical Field

[0001] This invention relates to an antenna, and more particularly to an ultrawideband linear polarization conversion metasurface and its metasurface antenna. Background Technology

[0002] Metamaterials (MMs) are artificial materials with unique properties not found in natural materials, and have received widespread attention in recent years. As a two-dimensional form, metasurfaces can control electromagnetic wave characteristics in the time domain, spatial domain, and frequency domain. They have been widely used in fields such as superlenses [1] ([1] refers to a reference, the same below, which is introduced in the last part of the specification of this invention), invisibility cloaks [2], holographic imaging [3], orbital angular momentum communication [4], and antenna RCS reduction [5]-[7].

[0003] Polarization conversion metasurfaces (PCMs), as an important branch of metasurfaces, can achieve the control of electromagnetic wave linear polarization to linear polarization, linear polarization to circular polarization, and circular polarization to circular polarization states. Recently, many works have studied PCMs. [8] proposed a double concentric square ring PCM that can achieve linear polarization conversion in the ultra-wideband range of 6.3-20.5 GHz and maintain high incident angle stability. [9] proposed a multifunctional PCM that can achieve linear polarization conversion and circular polarization conversion in multiple frequency bands.

[0004] With the continuous development of national defense science and technology, the stealth technology of aircraft has received widespread attention. As the main contributor to the scattering of aircraft, how to reduce the RCS of the antenna has become an important topic in the research of aircraft stealth. Traditional antenna RCS reduction is mainly achieved through radar absorbing materials, frequency selective surfaces, radomes, etc. However, using radar absorbing materials to reduce the antenna RCS will lead to a significant deterioration in the antenna gain performance, while frequency selective surfaces can only reduce the out-of-band RCS of the antenna. Therefore, how to reduce the antenna RCS while maintaining its radiation performance has become a key research issue. With the proposal of electromagnetic metasurfaces, PCM and phase gradient metasurfaces (PGM) have been applied to antenna RCS reduction. They can scatter the incident electromagnetic waves to other directions to reduce the RCS and maintain the radiation performance of the antenna. Many works have been studied on this topic.

[10] proposed a reflective polarization conversion metasurface antenna, which achieved an RCS reduction of more than 10dB in the broadband frequency range of 9.9-16GHz and achieved broadband impedance matching of 12-15.6GHz. The proposed metasurface antenna consists of a central magnetoelectric dipole antenna and randomly distributed PCM units around it.

[11] proposes a metasurface antenna consisting of a circularly polarized microstrip patch array and a 2.5-dimensional polarization-conversion metasurface located above it. This antenna achieves an RCS reduction of more than 10 dB in the 4-15 GHz broadband range while maintaining the antenna's radiation performance.

[12] proposes a Fabry-Perot resonant cavity antenna consisting of an upper artificial magnetic conductor (AMC), a middle phase gradient metasurface (PGM), and a bottom microstrip patch antenna. This antenna achieves broadband RCS reduction in the 4-13 GHz range while realizing tilted high-gain (11.73 dB) beam radiation.

[13] proposes a hybrid mechanism circularly polarized metasurface antenna. The low-frequency RCS reduction is achieved through the polarization conversion characteristics of the metasurface unit, and the high-frequency RCS reduction is achieved through the phase difference characteristics between the metasurface unit and the ground dielectric layer. This metasurface antenna achieves broadband RCS reduction in the 4.95-15.73 GHz range while widening the antenna's AR bandwidth. Summary of the Invention

[0005] To improve the impedance matching bandwidth (S11), axial ratio (AR), and gain of traditional antennas, this invention provides an ultra-wideband linear polarization conversion metasurface and its metasurface antenna.

[0006] The technical solution provided by this invention is as follows: an ultrawideband linear polarization conversion metasurface, comprising: Dielectric layer one, which is square in shape; The second dielectric layer has the same shape as the first dielectric layer and is arranged in parallel from top to bottom, forming an air layer between the first dielectric layer and the second dielectric layer; The metal pattern layer includes rectangular strips and two fan rings of the same shape that are independently distributed on the side of dielectric layer one facing away from dielectric layer two. The rectangular strips are located on the diagonal of dielectric layer one, and the length of the rectangular strips is less than the length of the diagonal. The rectangular strips are symmetrical about the center of dielectric layer one, and the two fan rings are symmetrically distributed about the rectangular strips as the axis of symmetry, and the openings of the two fan rings face away from the rectangular strips. A metallic grounding layer is fixed on the side of dielectric layer two facing away from dielectric layer one.

[0007] As a further improvement to the above scheme, the first dielectric layer is: = 4.4, loss tangent tan δ = 0.001, FR4 dielectric layer; where, δ is the dielectric constant, and loss tangent tan δ is the loss tangent. And / or, the second dielectric layer is: = 2.2, F4B dielectric layer with loss tangent tan δ = 0.0009.

[0008] As a further improvement to the above scheme, the side length of dielectric layer one is P=9mm; the width of the rectangular strip is w=0.5mm, the length of the rectangular strip is L=10.5mm; the inner ring radius of the fan ring is r=2.5mm, and the width of the fan ring is w1=0.1mm.

[0009] As a further improvement to the above scheme, the thicknesses of the metal pattern layer, dielectric layer one, air layer, dielectric layer two, and metal grounding layer are 0.035mm, 0.5mm, 3.2mm, 0.762mm, and 0.035mm, respectively.

[0010] As a further improvement to the above scheme, both the inner and outer rings of the fan ring are semi-circular rings.

[0011] The present invention also provides a metasurface antenna, which combines multiple of the above-mentioned arbitrary ultrawideband linear polarization conversion metasurfaces with a planar array antenna; Before bonding, each ultrawideband linear polarization conversion metasurface operates in a frequency range of 6.17 GHz to 19.5 GHz with a relative bandwidth of 103.9% and a polarization conversion bandwidth PCR > 0.9. When combined, multiple ultra-wideband linear polarization conversion metasurfaces are fixed in parallel as a whole, and the planar array antenna is set on the side of dielectric layer two facing dielectric layer one. The ultra-wideband linear polarization conversion metasurfaces and the planar array antenna use a common metal grounding layer as the grounding layer.

[0012] As a further improvement to the above scheme, the planar array antenna is a circularly polarized array antenna, a microstrip patch array antenna, or a slot array antenna.

[0013] Furthermore, the circularly polarized array antenna includes a dielectric layer three, multiple circularly polarized patch antennas disposed on the dielectric layer three, and a feeding network; the multiple circularly polarized patch antennas are arranged in an array and fed through the feeding network.

[0014] Furthermore, there are four circularly polarized patch antennas, and the feeding network is a fan-blade sequential rotating feeding network. The number of fan blades corresponds one-to-one with the number of circularly polarized patch antennas and the number of ultra-wideband linear polarization conversion metasurfaces. A circularly polarized patch antenna is arranged between two adjacent fan blades, and each fan blade is electrically connected to a circularly polarized patch antenna. Each circularly polarized patch antenna is located directly below a metal pattern layer.

[0015] Preferably, the thickness of the air layer is adjusted to 3.4 mm, and four metal pillars are used to connect the four ultra-wideband linear polarization conversion metasurfaces to the four circular polarization array antennas respectively, and the four units at the center of the metasurfaces arranged in a checkerboard pattern are mirrored and rotated.

[0016] The ultrawideband linear polarization conversion metasurface (PCM) proposed in this invention consists of a metal patterned layer, an air layer, and a ground dielectric layer, achieving a polarization conversion bandwidth (PCR) of 6.17 GHz to 19.5 GHz (relative bandwidth of 103.9%). Based on the phase cancellation principle, the PCM units and their mirror units are arranged in a checkerboard pattern to form the metasurface. When applied to circularly polarized patch array antennas to reduce RCS, the addition of the PCM widens the antenna's impedance matching (S11) bandwidth from 7.2 GHz to 8.3 GHz (14.2%) to 6.2 GHz to 8.4 GHz (30.1%), the axial ratio (AR) bandwidth from 6.9 GHz to 8.25 GHz (17.8%) to 6.75 GHz to 8.32 GHz (20.1%), and the peak gain is 11.1 dBi. The antenna's monostatic RCS under x and y polarized plane wave illumination is reduced by more than 5 dB from 6.4 to 18.6 GHz (97.6%). The gain improvement was explained using the antenna's current distribution. Finally, a prototype of the proposed metasurface antenna was fabricated and tested. Attached Figure Description

[0017] Figure 1 This is an overall structural diagram of the ultrawideband linear polarization conversion metasurface PCM, where region (a) is the simulation setup diagram and region (b) is the front view and side view of the PCM.

[0018] Figure 2 This is a schematic diagram of the reflection coefficient of PCM and PCR. Region (a) is a schematic diagram of the reflection coefficients of cross-polarization and co-polarization, and region (b) is a schematic diagram of PCR.

[0019] Figure 3These are schematic diagrams of the surface current distribution of the metal pattern layer and the ground layer. Region (a) is a schematic diagram of the surface current distribution at 7.243 GHz, region (b) is a schematic diagram of the surface current distribution at 11.401 GHz, and region (c) is a schematic diagram of the surface current distribution at 17.081 GHz.

[0020] Figure 4 The figures show a comparison of CST and ADS simulation results. Region (a) shows the simulation results under u-polarization, and region (b) shows the simulation results under v-polarization.

[0021] Figure 5 This is a schematic diagram of the scattering performance of the PCM. Region (a) is the PCM and its mirror phase diagram, region (b) is the PCM arrangement diagram, region (c) is the PCM dual-polarization monostation RCS reduction diagram, region (d) is the 11GHz PCM 3D far-field scattering diagram, and region (e) is the 11GHz near-field diagram.

[0022] Figure 6 These are schematic diagrams of a circularly polarized array antenna and a metasurface array. Region (a) is a schematic diagram of the circularly polarized array antenna and the metasurface array, and region (b) is a schematic diagram of the metasurface antenna after the two are combined.

[0023] Figure 7 This is a schematic diagram of the radiation performance of the reference antenna and the proposed antenna. Region (a) is a comparison diagram of the reflection coefficient (S11), and region (b) is a comparison diagram of the axial ratio (AR) and gain (Gain).

[0024] Figure 8 These are schematic diagrams of PCM transmission coefficients and surface current distribution of metasurface antennas. Region (a) is the transmission coefficient diagram, region (b) is the surface current distribution of metasurface antennas at 6.6 GHz, and region (c) is the surface current distribution of metasurface antennas at 8.25 GHz.

[0025] Figure 9 This is a schematic diagram of the scattering performance of a metasurface antenna. Region (a) is the reduced RCS of a dual-polarized monostatic antenna, and region (b) is the reduced RCS of a 12GHz bistatic antenna.

[0026] Figure 10 These are physical fabrication and testing diagrams. Among them, area (a) is a physical diagram of the metasurface antenna and the reference antenna, area (b) is a physical diagram of the vector network analyzer, area (c) is a measurement diagram of the reference antenna in the anechoic chamber, and area (d) is a measurement diagram of the metasurface antenna in the anechoic chamber.

[0027] Figure 11These are schematic diagrams of simulation and measurement results. Region (a) is a schematic diagram of reflection coefficient, region (b) is a schematic diagram of axial ratio, region (c) is a schematic diagram of gain, and region (d) is a schematic diagram of monostatic RCS for the reference antenna and the proposed antenna.

[0028] Figure 12 The diagram shows the radiation patterns of the reference antenna and the proposed antenna in the 8.25 GHz simulation. Region (a) is a schematic diagram in the xoz plane, and region (b) is a schematic diagram in the yoz plane.

[0029] Figure 13 The figure shows a comparison between the test results and simulation results of the LHCP radiation patterns of the proposed antenna and the reference antenna at 8.2 GHz. Region (a) is a schematic diagram under the xoz plane, and region (b) is a schematic diagram under the yoz plane. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] The ultra-wideband linear polarization conversion metasurface proposed in this embodiment can significantly reduce the in-band and out-of-band RCS of circularly polarized array antennas in the frequency range of 6.17 to 19.5 GHz. Furthermore, the impedance matching bandwidth (S11), axial ratio (AR), and gain of the antenna are significantly improved after loading the metasurface. The structure of this embodiment is as follows: 1. The designed metasurface is introduced and the principle of RCS reduction is analyzed; 2. The designed metasurface is applied to a circularly polarized array antenna, and the influence of the metasurface on the antenna's radiation and scattering performance is analyzed; 3. A prototype of the proposed metasurface antenna is fabricated and tested to verify the simulation results; 4. Conclusions are given; 5. References used in this invention are provided.

[0032] I. Structural design of ultrawideband linear polarization conversion metasurface.

[0033] Designed ultrawideband linear polarization conversion metasurface PCM, such as Figure 1 As shown, Figure 1 This is an overall structural diagram of the ultra-wideband linear polarization conversion metasurface (PCM), where region (a) is the simulation setup diagram, and region (b) is the front view and side view of the PCM. The PCM includes: dielectric layer 1 (2), dielectric layer 2 (3), metal pattern layer 1, and metal ground layer 4.

[0034] Dielectric layer 2 is square in shape and can be: = 4.4, loss tangent tan δ = 0.001 for an FR4 dielectric layer, where, δ is the dielectric constant, and tan δ is the loss tangent. Dielectric layer 3 has the same shape as dielectric layer 2 and is arranged parallel to each other vertically. Dielectric layer 3 can be: = 4.4, loss tangent tan δ = 0.001, FR4 dielectric layer. An air layer is formed between dielectric layer 2 and dielectric layer 3. Metal pattern layer 1 includes rectangular strips 11 and two identical fan rings 12, independently distributed on the side of dielectric layer 2 facing away from dielectric layer 3. The rectangular strips 11 are located on the diagonal of dielectric layer 2, and the length of the rectangular strips 11 is less than the length of the diagonal. The rectangular strips 11 are symmetrical about the center of dielectric layer 2, and the two fan rings 12 are symmetrically distributed about the rectangular strips 11 as the axis of symmetry, with the openings of both fan rings 12 facing away from the rectangular strips 11. Metal ground layer 4 is fixed on the side of dielectric layer 3 facing away from dielectric layer 2. Both the inner and outer rings of the fan rings 12 can be semi-circular rings.

[0035] In this embodiment, the metal pattern layer 1 is printed on FR4 (with a thickness of h1). = 4.4, and losstangent tan δ = 0.001) On the dielectric layer, the middle layer is an air layer of thickness h2, and the bottom layer is F4B of thickness h3 ( =2.2, and loss tangent tan δ = 0.0009) dielectric layer, the bottom of the F4B dielectric layer is metal ground layer 4. All metal layer materials, namely metal pattern layer 1 and metal ground layer 4, can be metal copper with a thickness of ts. All simulations and optimizations were completed in CST Studio Suite 2020, and the optimized parameters are as follows: P=9mm, L=10.5mm, W=0.5mm, r=2.5mm, w1=0.1mm, h1=0.5mm, h2=3.2mm, h3=0.762mm, ts=0.035mm.

[0036] Polarization conversion efficiency (PCR) is one of the important factors for measuring the effect of polarization conversion, and it can be expressed by the following formula

[11] : in R xy and R yy These represent the cross-polarization and co-polarization reflection coefficients, respectively. , , The electric field representing the incident wave polarized in either y or x polarization. The electric field representing the y- or x-polarized reflected wave. For example... Figure 2Region (a) in the figure shows the common polarization and cross polarization reflection coefficients of the PCM. It can be seen that, under the incident conditions of x-polarized and y-polarized electromagnetic waves, the common polarization reflection coefficient is less than -10dB from 6.4GHz to 18.8GHz, and the cross polarization reflection coefficient is greater than -1dB. Figure 2 Region (b) in the diagram represents the PCR of the PCM unit, with PCR > 0.9 in the frequency range of 6.17 GHz to 19.5 GHz (103.9%). 103.9% is the relative bandwidth, and the relative bandwidth = 2(f H -f L ) / (f H +f L ), where f H and f L These represent the upper and lower frequency limits, respectively.

[0037] Figure 3 These are schematic diagrams of the surface current distribution in the metal patterned layer and the ground layer. Region (a) shows the surface current distribution at 7.243 GHz, region (b) shows the surface current distribution at 11.401 GHz, and region (c) shows the surface current distribution at 17.081 GHz. Therefore, Figure 3 The surface current distribution diagrams of the three resonant points (7.243 GHz, 11.401 GHz, 17.081 GHz) of the PCM unit are shown. At 7.243 GHz and 11.401 GHz, the currents of the metal pattern layer and the metal ground are parallel to each other in opposite directions, indicating that magnetic resonance occurs at this resonant frequency. At 17.081 GHz, the currents of the metal pattern layer and the metal ground are in the same direction, indicating that electric resonance occurs at this resonant frequency. Under the combined action of multiple resonant points, this structure can achieve ultra-wideband cross-polarization conversion

[14] .

[0038] To further analyze the polarization conversion principle, the equivalent circuit method proposed in

[15] is used to perform equivalent analysis of the designed structure under the uv coordinate axis. The metal arm with the same polarization direction as the current can be equivalent to an inductor, the gap between the metal arms can be equivalent to a coupling capacitor, and the loss of the dielectric layer can be equivalent to a resistor. The basic circuit parameters can be calculated by the formula given in

[16] : and These are the permeability and permittivity in a vacuum. This is the equivalent dielectric constant of the substrate. The calculated equivalent circuit, after fine-tuning in ADS, is compared with the simulation results in CST. Figure 4 The results showed that the two were slightly different but basically similar.

[0039] Figure 5 This is a schematic diagram of the scattering performance of the PCM. Region (a) is the PCM and its mirror phase diagram, region (b) is the PCM arrangement diagram, region (c) is the PCM dual-polarization monostation RCS reduction diagram, region (d) is the 11GHz PCM 3D far-field scattering diagram, and region (e) is the 11GHz near-field diagram. Figure 5 Region (b) is the proposed PCM, arranged in a checkerboard pattern, consisting of 10x10 units, with a total size of 90mmx90mm. The RCS reduction formula for the metasurface can be defined as

[17] : in E S It is the total scattering field of the metasurface. E i This is the total incident field of the incident plane wave. The total scattered field of the PCM can be expressed by the following equation

[18] : E F The reflection field of the PCM unit. AF The array factor is given in

[19] . Detailed calculation and analysis are given, and it is found that when the phase difference between the PCM unit and its mirror unit is 180 degrees (phase difference diagram as shown in Figure 19), the phase difference is calculated as shown in Figure 19. Figure 5 In region (a) of the equation, the RCS reduction of the PCM can be expressed by the following formula: When PCR > 0.9, the RCS reduction of PCM is greater than 10 dB.

[0040] Figure 5 Region (c) in the figure is a comparison diagram of the RCS of PCM and a metal plate of the same size with dual polarization monostation. Compared with the metal plate, PCM reduces the frequency by more than 10 dB in the frequency range of 6.5 to 18 GHz (relative bandwidth 99%) under the incident conditions of x-polarized and y-polarized waves. Figure 5 Region (d) in Figure 5 and region (e) in Figure 6 are 3D far-field and near-field scattering plots at 11 GHz. It can be seen that the PCM scatters the incident electromagnetic wave energy into four undesirable directions, thereby effectively reducing the monostation RCS of the PCM.

[0041] II. Combination of PCM with planar array antennas.

[0042] The planar array antenna can be a circularly polarized array antenna, a microstrip patch array antenna, or a slot array antenna. In this embodiment, a circularly polarized array antenna will be used as an example for detailed description.

[0043] Please see Figure 6The metasurface antenna can be composed of multiple ultra-wideband linear polarization conversion metasurfaces 5 combined with a planar array antenna 6. Before combination, the frequency of each ultra-wideband linear polarization conversion metasurface 5 operates in the frequency range of 6.17 GHz to 19.5 GHz (103.9%), and the polarization conversion bandwidth PCR>0.9. During combination, multiple ultra-wideband linear polarization conversion metasurfaces 5 are fixed in parallel as a whole, and the planar array antenna 6 is set on the side of dielectric layer 2 3 facing dielectric layer 2. The ultra-wideband linear polarization conversion metasurfaces 5 and the planar array antenna 6 use a common metal ground layer 4 as the ground layer.

[0044] The circularly polarized array antenna includes a dielectric layer 61, multiple circularly polarized patch antennas 62 disposed on the dielectric layer 61, and a feeding network 63. The multiple circularly polarized patch antennas 62 are arranged in an array and fed through the feeding network 63. For example, the number of circularly polarized patch antennas 62 can be four, and the feeding network 63 can be a fan-shaped sequential rotating feeding network. The number of fan blades 64 corresponds one-to-one with the number of circularly polarized patch antennas 62 and the number of ultra-wideband linear polarization conversion metasurfaces 5. A circularly polarized patch antenna 62 is arranged between two adjacent fan blades 64, and each fan blade 64 is electrically connected to a circularly polarized patch antenna 62. Each circularly polarized patch antenna 62 is located directly below a metal pattern layer 1.

[0045] The proposed reference antenna is a circularly polarized array patch antenna, such as... Figure 6 As shown in region (a), the antenna consists of four circularly polarized patch antennas and a central sequentially rotating feed network. The dielectric layer material is F4B (…). = 2.2, and loss tangent tan δ = 0.0009), with a thickness of 0.762mm, and a metal grounding layer at the bottom. Other parameters are as follows: P=90mm, L1=16mm, W1=16mm, r=6.3mm. The power supply method is a microstrip line side-feed.

[0046] To reduce the RCS of the reference antenna, the designed PCM is combined with the reference antenna to form a low-RCS metasurface antenna. For example... Figure 6 These are schematic diagrams of a circularly polarized array antenna and a metasurface array. Region (a) shows the schematic diagram of the circularly polarized array antenna and the metasurface array, while region (b) shows the schematic diagram of the metasurface antenna formed by combining the two. Figure 6As shown in region (b), the designed circularly polarized antenna is placed on the second dielectric layer of the PCM, and the PCM and antenna use a common metal plate as a ground layer to minimize the influence of the antenna on the PCM. Simultaneously, the air layer thickness h2 is adjusted to 3.4 mm, and four copper pillars are used to connect the antenna to the PCM. The four central elements of the checkerboard-arranged metasurface are mirrored and rotated to minimize the impact of the PCM on the antenna radiation performance.

[0047] Figure 7 This is a schematic diagram of the radiation performance of the reference antenna and the proposed antenna. Region (a) is a comparison diagram of the reflection coefficient (S11), and region (b) is a comparison diagram of the axial ratio (AR) and gain (Gain). Figure 7 Regions (a) and (b) in the figure show a comparison of the reflection coefficient (S11), axial ratio (AR), and gain of the reference antenna and the metasurface antenna. Compared with the reference antenna, after covering with PCM, the bandwidth of S11 < -10dB is widened from 7.2GHz to 8.3GHz (14.2%) to 6.2GHz to 8.4GHz (30.1%), the bandwidth of AR < 3 is widened from 6.9GHz to 8.25GHz (17.8%) to 6.75GHz to 8.32GHz (20.1%), and the bandwidth of AR < 2 of the metasurface antenna is 6.8GHz to 8.3GHz (19.9%). It can be applied to the field of high-precision mobile communication and is suitable for different transmission environments.

[0048] Figure 7 Region (b) also shows a gain comparison between the reference antenna and the metasurface antenna. It can be seen that after PCM coverage, the gain is significantly improved in the 6.5 to 7 GHz and 7.95 to 8.5 GHz frequency ranges, while the gain is slightly reduced in the 7.2 to 7.5 GHz frequency range, and the gain remains almost unchanged in other frequency bands. The reasons for the gain loss will be analyzed first, such as... Figure 8 As shown, Figure 8 These are schematic diagrams of PCM transmission coefficients and surface current distribution of metasurface antennas. Region (a) is the transmission coefficient diagram, region (b) is the surface current distribution of metasurface antennas at 6.6 GHz, and region (c) is the surface current distribution of metasurface antennas at 8.25 GHz. Figure 8 Region (a) in the diagram shows the common-polarization and cross-polarization transmission coefficients of the PCM. It can be seen that the PCM converts a portion of the x- or y-polarized wave into its cross-polarized wave. This also causes a small portion of the wave radiated by the reference antenna to be scattered as a cross-polarized wave when passing through the PCM, resulting in gain loss in some frequency bands. Finally, current distribution diagrams at 6.6 GHz and 8.25 GHz are given, as shown below. Figure 8As can be seen from regions (b) and (c), most of the PCM elements are effectively excited and act as radiators of the antenna. Therefore, the reason for the enhanced antenna gain is due to the enhanced antenna aperture efficiency and the coherent superposition of far-field energy.

[0049] Figure 9 This is a schematic diagram of the scattering performance of a metasurface antenna. Region (a) is the reduced RCS of a dual-polarized monostatic antenna, and region (b) is the reduced RCS of a 12GHz bistatic antenna. Figure 9 Region (a) in the figure shows the monostatic RCS plots of the reference antenna and the metasurface antenna under x-polarized and y-polarized wave incidence. With x-polarized wave incidence, the addition of the PCM results in a monostatic RCS reduction of over 5 dB compared to the reference antenna in the frequency range of 6.4 to 18.6 GHz (97.6%). With y-polarized wave incidence, the RCS reduction ranges from 6.4 to 18.7 GHz (98%). The proposed metasurface antenna can achieve both in-band and out-of-band monostatic RCS reduction. Figure 9 Region (b) in the figure is a comparison of the bistatic RCS of the reference antenna and the metasurface antenna at 12 GHz. It can be seen that after loading PCM, the bistatic RCS is significantly reduced in the angle range of [-20.20].

[0050] III. Manufacturing and Measurement Please see Figure 10 and Figure 11 , Figure 10 These are physical fabrication and testing diagrams. Among them, area (a) is a physical diagram of the metasurface antenna and the reference antenna, area (b) is a physical diagram of the vector network analyzer, area (c) is a measurement diagram of the reference antenna in the anechoic chamber, and area (d) is a measurement diagram of the metasurface antenna in the anechoic chamber. Figure 11 These are schematic diagrams of simulation and measured results. Region (a) shows the reflection coefficient, region (b) shows the axial ratio, region (c) shows the gain, and region (d) shows the monostatic RCS for both the reference antenna and the proposed antenna. To verify the accuracy of the simulation results for the proposed metasurface antenna, prototypes of both the reference antenna and the metasurface antenna were fabricated. Due to fabrication limitations, a coaxial feeding method was used instead of microstrip side feeding, as shown below. Figure 10 The region (a) is shown in the diagram. A vector analysis network instrument (...) Figure 10 The antenna's reflection coefficient was tested in region (b) of the image, as shown in the figure. Figure 11 As shown in region (a), the bandwidths of the tested reference antenna and metasurface antenna S11 < -10 dB are 7.35 GHz to 8.165 GHz (10.5%) and 6.23 to 8.5 GHz (30.8%), respectively. The axial ratio, gain, and monostatic RCS of the reference antenna and the proposed antenna were measured in a microwave anechoic chamber, as shown in... Figure 10Regions (c) in Figure 10 and (d) in Figure 10 are shown. Comparing the measurement results with the simulation results, the axial ratio and gain bandwidth have shifted to the right overall, with slight differences in values ​​at some frequencies. The measured single-station RCS reduction band is 6.4-18.9 GHz (98.8%), and the overall curve shifts to the left at high frequencies. This may be due to measurement tolerances during the manufacturing process or errors during welding.

[0051] Figure 12 The diagram shows the radiation patterns of the reference antenna and the proposed antenna in the 8.25 GHz simulation. Region (a) is a schematic diagram in the xoz plane, and region (b) is a schematic diagram in the yoz plane. Figure 12 The figures show a comparison of the radiation patterns of the proposed antenna at 8.25 GHz with and without left-hand circularly polarized (LHCP) and right-hand circularly polarized (RHCP) antennas. It can be seen that the proposed antenna's left-hand circularly polarized gain is significantly higher than its right-hand circularly polarized gain in the radiation direction, indicating that this metasurface antenna is a left-hand circularly polarized antenna. Furthermore, the addition of the PCM improves the radiation pattern directivity with almost no impact on the sidelobes and back lobes. Figure 13 The figure shows a comparison between the test results and simulation results of the LHCP radiation patterns of the proposed antenna and the reference antenna at 8.2 GHz. Region (a) is a schematic diagram under the xoz plane, and region (b) is a schematic diagram under the yoz plane. Figure 13 Comparing the simulated and measured radiation patterns at 8.2 GHz, the main lobe gain is basically consistent, while the difference in side lobes may be due to manufacturing tolerances, background noise, and assembly errors in the measurement environment.

[0052] Table 1: Comparison of the proposed metasurface antenna with previous work The radiation and scattering performance of the metasurface antenna proposed in this invention is compared with other literature, as shown in Table 1. It can be seen that the work done in this invention has the widest S11 and 3dBAR bandwidth, and also features high gain and wideband RCS reduction (covering C, X, K). u (band). Although reference

[20] achieved ultra-wideband RCS reduction, the impedance matching and 3dB axial ratio bandwidth were narrow, and the peak gain was low. Reference

[21] achieved high peak gain and wide impedance matching, but the antenna was only linearly polarized, and the RCS reduction effect was poor. Finally, the metasurface antenna proposed in this invention has a simple structure and is easy to process.

[0053] IV. Conclusion.

[0054] This study proposes a metasurface antenna combining a PCM (Polymerized Conduit Array) with a circularly polarized array antenna. The PCM exhibits a PCR (Potential Chance) > 0.9 in the frequency range of 6.17 GHz to 19.5 GHz (103.9%). Combining the PCM with the circularly polarized array antenna not only reduces the monostatic and bistatic RCS of the antenna but also significantly improves the impedance matching (S11) bandwidth, axial ratio (AR) bandwidth, and peak gain of the reference antenna. This PCM can also be used for RCS reduction and radiation performance improvement of other planar antennas such as microstrip patch antennas and slotted antenna arrays. In practical applications, due to its excellent characteristics such as AR < 2, high gain, and wideband RCS reduction in the frequency range of 6.8 GHz to 8.3 GHz (19.9%), this metasurface antenna can be applied to high-precision mobile communications and C-band aircraft stealth applications.

[0055] V. References.

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[12] H. Umair et al ., "Fabry-Perot Antenna Employing ArtificialMagnetic Conductors and Phase Gradient Metasurface for WidebandMonostatic RCSReduction and High Gain Tilted Beam Radiation," in IEEE Access, vol. 9, pp.66607-66625, 2021, doi: 10.1109 / ACCESS.2021.3076913.

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[15] H. B. Wang and Y. J. Cheng, "Single-Layer Dual-BandLinear-to-Circular Polarization Converter With Wide Axial Ratio Bandwidth and DifferentPolarization Modes," in IEEE Transactions on Antennas and Propagation , vol.67, no. 6, pp. 4296-4301, June 2019, doi: 10.1109 / TAP.2019.2905962.

[16] O. Luukkonen et al., "Corrections to “Simple and AccurateAnalytical Model of Planar Grids and High-Impedance Surfaces ComprisingMetalStrips or Patches” [Jun 08 1624-1632]," in IEEE Transactions on Antennas and Propagation , vol. 58, no. 6, pp. 2162-2162, June 2010, doi: 10.1109 / TAP.2010.2047371.

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[21] Y. Zheng et al ., "Wideband Gain Enhancement and RCS Reduction ofFabry–Perot Resonator Antenna With Chessboard ArrangedMetamaterialSuperstrate," in IEEE Transactions on Antennas and Propagation , vol. 66, no. 2, pp. 590-599, Feb. 2018, doi: 10.1109 / TAP.2017.2780896. The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An ultrawideband linear polarization conversion metasurface, characterized in that, It includes: Dielectric layer 1 (2) is square in shape; Medium layer 2 (3) has the same shape as medium layer 1 (2) and is arranged in parallel at the top and bottom, forming an air layer between medium layer 1 (2) and medium layer 2 (3); The metal pattern layer (1) includes rectangular strips (11) and two fan rings (12) of the same shape, which are independently distributed on the side of dielectric layer one (2) facing away from dielectric layer two (3). The rectangular strips (11) are located on the diagonal of dielectric layer one (2), and the length of the rectangular strips (11) is less than the length of the diagonal. The rectangular strips (11) are symmetrical about the center of dielectric layer one (2) and are separated from the two fan rings (12). The two fan rings (12) are symmetrically distributed about the rectangular strips (11) as the axis of symmetry, and the openings of the two fan rings (12) face away from the rectangular strips (11). Metal grounding layer (4) is fixed on the side of dielectric layer two (3) facing away from dielectric layer one (2).

2. The ultrawideband linear polarization conversion metasurface as described in claim 1, characterized in that: Dielectric layer 1 (2) is: =4.4, loss tangent tan δ = 0.001, of which, is the dielectric constant, and loss tangent tanδ is the loss tangent. And / or, dielectric layer two (3) is: = 2.2, F4B dielectric layer with loss tangent tan δ = 0.0009.

3. The ultrawideband linear polarization conversion metasurface as described in claim 1, characterized in that: The side length of the dielectric layer (2) is P=9mm; the width of the rectangular strip (11) is w=0.5mm, and the length of the rectangular strip (11) is L=10.5mm; the inner radius of the fan ring (12) is r=2.5mm, and the width of the fan ring (12) is w1=0.1mm.

4. The ultrawideband linear polarization conversion metasurface as described in claim 1, characterized in that: The thicknesses of the metal pattern layer (1), dielectric layer one (2), air layer, dielectric layer two (3), and metal grounding layer (4) are 0.035mm, 0.5mm, 3.2mm, 0.762mm, and 0.035mm, respectively.

5. The ultrawideband linear polarization conversion metasurface as described in claim 1, characterized in that: The inner and outer rings of the fan ring (12) are both semi-circular rings.

6. A metasurface antenna, characterized in that, The method employs a combination of multiple ultrawideband linear polarization conversion metasurfaces (5) as described in any one of claims 1 to 5 with a planar array antenna (6); Before bonding, each ultrawideband linear polarization conversion metasurface (5) operates in a frequency range of 6.17 GHz to 19.5 GHz with a relative bandwidth of 103.9% and a polarization conversion bandwidth PCR > 0.

9. When combined, multiple ultra-wideband linear polarization conversion metasurfaces (5) are fixed in parallel as a whole, and the planar array antenna (6) is set on the side of dielectric layer 2 (3) facing dielectric layer 1 (2), and the ultra-wideband linear polarization conversion metasurfaces (5) and the planar array antenna (6) use a common metal grounding layer (4) as the grounding layer.

7. The metasurface antenna as described in claim 6, characterized in that: The planar array antenna (6) is a circularly polarized array antenna, a microstrip patch array antenna, or a slot array antenna.

8. The metasurface antenna as described in claim 7, characterized in that: The circularly polarized array antenna includes a dielectric layer three (61) and multiple circularly polarized patch antennas (62) disposed on the dielectric layer three (61) and a feeding network (63); the multiple circularly polarized patch antennas (62) are arranged in an array and fed through the feeding network (63).

9. The metasurface antenna as described in claim 7, characterized in that: There are four circularly polarized patch antennas (62). The feeding network (63) is a fan-shaped sequential rotating feeding network. The number of fan blades (64) corresponds one-to-one with the number of circularly polarized patch antennas (62) and the number of ultra-wideband linear polarization conversion metasurfaces (5). A circularly polarized patch antenna (62) is arranged between two adjacent fan blades (64). Each fan blade (64) is electrically connected to a circularly polarized patch antenna (62). Each circularly polarized patch antenna (62) is located directly below a metal pattern layer (1).

10. The metasurface antenna as described in claim 9, characterized in that: The thickness of the air layer is adjusted to 3.4 mm. Four ultra-wideband linear polarization conversion metasurfaces (5) are connected to four circular polarization array antennas using four metal pillars respectively. The four units at the center of the metasurfaces arranged in a checkerboard pattern are mirrored and rotated.

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