High-frequency-selectivity reflective polarization conversion metasurface with fourth-order response

Abstract

The invention belongs to the technical field of polarization conversion metasurfaces, and particularly provides a high-frequency-selectivity reflective polarization conversion metasurface with fourth-order response, which is used for realizing a polarization converter with high polarization conversion rate. The half-wavelength micro-strip resonator is composed of a frequency selective surface (FSS) and a coupling layer, a coupled half-wavelength micro-strip resonator is composed of an L-shaped micro-strip line of a bottom metal layer and a through hole, response is expanded to a high order, the polarization conversion rate is increased, and the broadening bandwidth is increased; meanwhile, the middle metal layer introduces a polarization conversion zero point, thereby improving the frequency selection characteristics of the two sides of a transmission frequency band. Moreover, the polarization metasurface is rotationally symmetrical in structure, has a dual-polarization conversion characteristic, and has a relatively high application value in the aspect of electromagnetic wave polarization conversion.

Description

Technical Field

[0001] The present invention belongs to the technical field of polarization conversion metasurfaces, and specifically provides a high-frequency selective reflection-type polarization conversion metasurface with a fourth-order response. Background Art

[0002] As a two-dimensional (2-D) artificial material, metasurface plays an important role in the fields of microwaves and optics. Metasurfaces can control the amplitude, phase and polarization of electromagnetic waves. By changing the structure and arrangement of units, metasurfaces with different properties can be designed, including polarization manipulation metasurfaces (PCM). In the past few years, PCM has developed in a multi-layer direction to achieve broadband, and is usually combined with other structures to optimize performance. For example, in the document “MA Sofi, K. Saurav, and SK Koul, “A linear to circular polarization reconfigurable converter based on frequency selective surface,” Microwave and Optical Technology Letters, vol. 63, no. 5, pp. 1425–1433, 2021.”, Sofi et al. improved the bandwidth and performance of the polarization conversion band by combining PCM with a frequency selective surface (FSS). Although the characteristics of FSS can effectively improve the bandwidth and in-band performance, the frequency selectivity (FS) performance at the edge of the conversion band was not greatly improved; therefore, the document “Y. Ren, H. Lin, R. Tang, Y. Wu, R. Zhou, and J. Xiong, “A multifunctional frequency selective polarization converter based on substrate integrated waveguide cavities,” Journal of Physics D:AppliedPhysics,vol.55,no.29,p.295101,2022.” Ren et al. introduced guided modes in PCM to achieve polarization conversion and frequency selection in the same frequency band; and in the literature “Y.Li,H.Li,Y.Wang,Y.Wang,and Q.Cao,“Anovelswitchable absorber / linear converter based on active metasurface and itsapplication,”IEEE Trans.Antennas Propag.,vol.68,no.11,pp.7688–7693,2020.”, Li et al. achieved a wider bandwidth.

[0003] However, there is almost no frequency selectivity at the edge of the conversion band. In order to achieve high FS at the edge of the conversion band, polarization conversion zeros (PC Zeros) are introduced in the design. For example, in the literature “Y.-T.Zhao, J.-J.Zhang, and B.Wu, “Lowprofile reflective polarization conversion metasurface with high frequency selectivity,” IEEE Trans.Antennas Propag., vol.70, no.11, pp.10 614–10 622, 2022.”, Zhao et al. introduced a single PC zero on one side of the conversion band, which effectively improved FS at high frequencies, but the operating bandwidth was narrow. In the literature “L.-L.Qiu,S.Fang,L.Zhu,L.Deng,S.Huang,Y.Wu,X.Gao,and X.Zhang,“Widebandhigh-selective linear polarization converter and its application inbifunctional metasurface for reduced isolation band,”IEEE Trans.AntennasPropag.,vol.71,no.3,pp.2735–2744,2023.” Qiu et al. proposed a polarization converter with a controllable zero on each side of the conversion band, achieving a conversion bandwidth of 46%, but the decline rate on both sides of the conversion band is not enough to achieve high FS, which belongs to a single polarization conversion response. In order to achieve high selectivity on one side, Wang et al. introduced two PC zeros at the same edge of the conversion band in the literature "J. Wang, H. Shi, X. Chen, J. Yi, J. Chen, A. Zhang, and H. Liu, "A second-order cross-polarization conversion metasurface with high frequency selectivity," IEEE Antennas Wireless Propag. Lett., 2023.", but these zeros are uncontrollable and have a narrow bandwidth. However, none of the above PCMs achieve broadband conversion with high FS at both ends of the conversion band, and their angular stability does not exceed 30 degrees; therefore, how to achieve a wide polarization conversion band and high frequency selectivity at both ends is a challenge facing polarization conversion metasurfaces.

[0004] In summary, the polarization conversion metasurface with high frequency selection characteristics has broad application prospects; therefore, the design and realization of a reflective polarization conversion metasurface with high frequency selectivity becomes the research focus of the present invention. Summary of the invention

[0005] The purpose of the present invention is to provide a high-frequency selective reflective polarization conversion metasurface with a fourth-order response, which is used to realize a polarization converter with a high polarization conversion rate. The present invention is composed of a frequency selective surface (FSS) and a coupling layer, and a coupled half-wavelength microstrip resonator is formed through the L-shaped microstrip line and the through hole of the bottom metal layer, which extends the response to a high order, improves the polarization conversion rate and widens the bandwidth; at the same time, the middle metal layer introduces a polarization conversion zero point to improve the frequency selection characteristics on both sides of the transmission band; and the structure of the polarization metasurface is rotationally symmetric, has dual polarization conversion characteristics, and has high application value in electromagnetic wave polarization conversion.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A high-frequency selective reflective polarization conversion metasurface with a fourth-order response is composed of M×N polarization conversion units arranged in an array, wherein the polarization conversion unit includes, from top to bottom, a first metal patch layer 1, a first dielectric layer 2, a first adhesive layer 3, a second dielectric layer 4, a second adhesive layer 5, a second metal patch layer 6, a third dielectric layer 7 and a third metal patch layer 8; characterized in that the first metal patch layer covers the upper surface of the first dielectric layer, and the two together constitute a frequency selective surface (FSS) unit structure; the second metal patch layer covers the upper surface of the third dielectric layer, the third metal patch layer is arranged on the lower surface of the third dielectric layer, and the three together constitute a coupling layer structure.

[0008] Furthermore, the first metal patch layer 1 is provided with a first combined groove structure, which is a 90° rotationally symmetrical structure along the center point of the first metal patch layer 1 and an axially symmetrical structure about the midline and diagonal of the first metal patch layer 1. It is specifically composed of a large square groove and four small square grooves, the large square groove is located at the center position, and the diagonal overlaps with the diagonal of the first metal patch layer, and the small square grooves are respectively located at the four corners of the large square groove, and the diagonal overlaps with the diagonal of the first metal patch layer in the same direction.

[0009] Furthermore, the second metal patch layer 6 is provided with a second combined groove structure and four straight grooves. The second combined groove structure is a 90° rotationally symmetrical structure along the center point of the second metal patch layer 6, and is axially symmetrical about the midline and diagonal of the second metal patch layer 6. It is specifically composed of four arc grooves, and the four arc grooves are located at the four corners of the second metal patch layer 6 and intersect each other end to end; the four straight grooves are respectively opened along the edges of the second metal patch layer 6, and the straight grooves are located in the middle of the corresponding edges.

[0010] Furthermore, the third metal patch layer 8 is composed of an L-shaped microstrip line and two rectangular microstrip lines, and the L-shaped microstrip line and the two rectangular microstrip lines are arranged to form a quasi-cross structure, and the quasi-cross structure is located on the midline of the lower surface of the third dielectric layer 7; the two rectangular microstrip lines are respectively provided with metal through holes 9 at the ends, and are connected to the second metal patch layer 6 through the metal through holes.

[0011] Furthermore, the frequency selective surface (FSS) unit structure is stacked on the upper surface of the second dielectric layer 4 through the first adhesive layer 3, and the coupling layer structure is stacked on the lower surface of the second dielectric layer 4 through the second adhesive layer 5, together constituting a reflective polarization conversion metasurface.

[0012] Furthermore, in the polarization conversion metasurface, the values ​​of M and N are both not less than 5.

[0013] In terms of working principle:

[0014] The present invention provides a high-frequency selective reflective polarization conversion metasurface with a fourth-order response, wherein the polarization conversion unit comprises, from top to bottom, a first metal patch layer 1, a first dielectric layer 2, a first adhesive layer 3, a second dielectric layer 4, a second adhesive layer 5, a second metal patch layer 6, a third dielectric layer 7 and a third metal patch layer 8; the first metal patch layer (top metal layer)

[0015] A metal patch with a square groove having a rotationally symmetrical structure is used to form the frequency selective surface part of the overall structure together with the first dielectric layer; the second metal patch layer (middle metal layer) introduces polarization conversion zero points by using circular arc grooves and straight line grooves having a rotationally symmetrical structure, the circular arc groove structure introduces polarization conversion zero points at high frequencies, and the straight line groove structure introduces polarization conversion zero points at low frequencies, thereby improving the frequency selectivity of the overall structure; at the same time, the middle metal layer is connected to the microstrip line of the third metal patch layer (bottom metal layer) through two metallized holes, the impedance in two vertical directions is adjusted, the linearly polarized electromagnetic incident wave is reflected and converted into a cross-polarized wave, and a reflective polarization conversion function is realized; and the L-shaped microstrip line and through hole of the bottom metal layer form a coupled half-wavelength microstrip resonator, which extends the response to high orders, expands the bandwidth, and improves the polarization conversion rate.

[0016] In summary, the beneficial effect of the present invention is to provide a high-frequency selective reflective polarization conversion metasurface with a fourth-order response, which has the following advantages:

[0017] 1. The present invention is composed of a frequency selective surface and a coupling layer. In the coupling layer, two polarization conversion (PC) zeros are introduced on both sides of the cross-polarization frequency band using a groove structure, thereby improving the frequency selectivity on both sides of the frequency band and achieving high frequency selectivity with transmission zeros and high polarization conversion rate (PCR) under low profile conditions;

[0018] 2. The high-order resonant response design of the present invention improves the polarization conversion efficiency and widens the bandwidth. The frequency selectivity of the transmission passband at the lower and upper band edges is 245dB / GHz and 305dB / GHz respectively. In the range of 6.17GHz to 7.25GHz (relative bandwidth 16.1%), the PCR is greater than 90%;

[0019] 3. The present invention has a wider bandwidth and higher frequency selectivity on both sides of the cross-polarization band while ensuring high PCR and dual-polarization characteristics;

[0020] 4. The present invention has the characteristics of small electrical size. The L-shaped microstrip line and the through hole of the bottom metal layer form a coupled half-wavelength microstrip resonator to extend the response to a high order, so that it has the characteristics of a fourth-order resonance response;

[0021] 5. The present invention adopts a rotationally symmetric structure, has dual polarization conversion characteristics, can work under x and y polarization incidence, has unchanged relative bandwidth and frequency selectivity, and has generally flat insertion loss within the passband. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a side view schematic diagram of a high-frequency selective reflective polarization conversion metasurface unit with fourth-order response in the present invention.

[0023] Figure 2 for Figure 1 Schematic diagram of the structure of the frequency selective surface unit in the polarization conversion metasurface unit shown.

[0024] Figure 3 for Figure 1 Schematic diagram of the structure of the second metal patch unit of the coupling structure in the polarization conversion metasurface unit shown.

[0025] Figure 4 for Figure 1 Schematic diagram of the structure of the third metal patch unit of the coupling structure in the polarization conversion metasurface unit shown.

[0026] Figure 5The test result diagram (Mea) and electromagnetic simulation result diagram (Sim) of the high-frequency selective reflection-type polarization conversion metasurface with fourth-order response in an embodiment of the present invention are shown, wherein (a) is the reflection coefficient, (b) is the transmission coefficient, and (c) is the polarization conversion rate. DETAILED DESCRIPTION

[0027] 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.

[0028] This embodiment provides a high-frequency selective reflective polarization conversion metasurface with a fourth-order response, which is composed of M×N polarization conversion units arranged in an array and adjacent to each other. The structure of the polarization conversion unit is as follows: Figure 1 As shown, from top to bottom, it includes: a first metal patch layer 1, a first dielectric layer 2, a first adhesive layer 3, a second dielectric layer 4, a second adhesive layer 5, a second metal patch layer 6, a third dielectric layer 7 and a third metal patch layer 8; wherein:

[0029] The first metal patch layer 1 covers the upper surface of the first dielectric layer 2, and the two together constitute a frequency selective surface (FSS) unit structure; Figure 2 As shown, the first metal patch layer 1 is provided with a first combined slot structure, which is a 90° rotationally symmetrical structure along the center point of the first metal patch layer 1 and an axially symmetrical structure about the midline and diagonal of the first metal patch layer 1, and is specifically composed of a large square slot and four small square slots, wherein the large square slot is located at the center, and the diagonal overlaps with the diagonal of the first metal patch layer, and the small square slots are respectively located at the four corners of the large square slot, and the diagonal overlaps with the diagonal of the first metal patch layer in the same direction;

[0030] The second metal patch layer 6 covers the upper surface of the third dielectric layer 7, and the third metal patch layer 8 is arranged on the lower surface of the third dielectric layer 7, and the three together constitute a coupling layer structure; Figure 3 As shown, the second metal patch layer 6 is provided with a second combined groove structure and four straight grooves, the second combined groove structure is a 90° rotationally symmetrical structure along the center point of the second metal patch layer 6, and is an axially symmetrical structure about the midline and diagonal line of the second metal patch layer 6, and is specifically composed of four arc grooves, which are located at the four corners of the second metal patch layer 6 and intersect each other end to end; the four straight grooves are respectively opened along the edges of the second metal patch layer 6, and the straight grooves are located in the middle of the corresponding edges; as shown Figure 4As shown, the third metal patch layer 8 is composed of an L-shaped microstrip line and two rectangular microstrip lines, and the L-shaped microstrip line and the two rectangular microstrip lines are arranged to form a cross-like structure, and the cross-like structure is located on the midline of the lower surface of the third dielectric layer 7; the L-shaped microstrip line is provided with a chamfer so that the three microstrip lines are separated from each other at the center of the cross-like structure; the two rectangular microstrip lines are respectively provided with metal through holes 9 at the ends, and are connected to the second metal patch layer 6 through the metal through holes 9; it is also explained that the microstrip lines at corresponding positions of adjacent polarization conversion units are connected after being adjacent, for example, Figure 4 The upper end of the L-shaped microstrip line in the coupling layer structure of the polarization conversion unit is connected to the rectangular microstrip line at the corresponding position in the coupling layer structure of the polarization conversion unit above it. Similarly, Figure 4 The left end of the L-shaped microstrip line in the coupling layer structure of the polarization conversion unit in the middle is connected to the rectangular microstrip line at the corresponding position in the coupling layer structure of the polarization conversion unit on its left side, thereby forming a longer L-shaped microstrip line;

[0031] The frequency selective surface (FSS) unit structure is stacked on the upper surface of the second dielectric layer 4 through the first glue layer 3, and the coupling layer structure is stacked on the lower surface of the second dielectric layer 4 through the second glue layer 5, together forming a reflective polarization conversion metasurface.

[0032] Specifically, in the frequency selective surface (FSS) unit structure of this embodiment, the width of the square slot structure is 0.4mm, the side length of the large square slot is 5.6mm, and the side length of the small square slot is 3.5mm. In the coupling layer structure, the width of the arc slot is 0.2mm, the radius is 4mm, the corresponding central angle is 228°, the width of the straight slot is 0.1mm, and the length is 12.7mm; the width of the L-shaped microstrip line and the rectangular microstrip line are both 0.8mm, the length of the two straight segments of the L-shaped microstrip line is 5.8mm, the length of the two rectangular microstrip lines is 6.9mm, and the diameter of the metal through hole is 0.6mm. The model of the first dielectric layer and the third dielectric layer is WL-CT350, with a thickness of 0.762 mm, a relative dielectric constant of 3.48, and a loss tangent of tanδ=0.004; the material model of the first adhesive layer and the second adhesive layer is WL-F4PP250, with a thickness of 0.05, a relative dielectric constant of 2.5, and a loss tangent of tanδ=0.004; the model of the second dielectric layer is F4B, with a thickness of 3 mm, a relative dielectric constant of 3, and a loss tangent of tanδ=0.0013.

[0033] The reflective polarization conversion metasurface in this embodiment is simulated and tested, and the test results (Mea) and the electromagnetic simulation results (Sim) are shown in Figure 5As shown, (a) is the reflection coefficient, (b) is the transmission coefficient, and (c) is the polarization conversion rate. It can be seen from the figure that the present invention can reflect the incident line polarization wave to the orthogonal direction in the 6.17-7.25GHz frequency band, with a relative bandwidth of 16.1%, and an in-band polarization conversion rate (Polarization conversion, PCR) greater than 0.9, achieving good broadband dual-polarization deflection performance; two controllable polarization conversion zero points (PC) introduced on both sides of the conversion band improve the frequency selectivity on both sides of the conversion band; 4 resonance points appear in the working band, and the high-order resonant response design enables the present invention to greatly improve the in-band polarization conversion rate while widening the bandwidth; the relative bandwidth and frequency selectivity under the x and y polarization incidence conditions remain unchanged, and the frequency response is basically the same, reflecting the dual polarization conversion characteristics of the present invention, and the insertion loss in the passband is generally flat.

[0034] 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 high-frequency selective reflective polarization conversion metasurface with a fourth-order response, which is composed of M×N polarization conversion units arranged in an array and adjacent to each other, wherein the polarization conversion units include, from top to bottom: A first metal patch layer (1), a first dielectric layer (2), a first adhesive layer (3), a second dielectric layer (4), a second adhesive layer (5), a second metal patch layer (6), a third dielectric layer (7) and a third metal patch layer (8); characterized in that the first metal patch layer covers the upper surface of the first dielectric layer, and the two together constitute a frequency selective surface (FSS) unit structure; the second metal patch layer covers the upper surface of the third dielectric layer, and the third metal patch layer is arranged on the lower surface of the third dielectric layer, and the three together constitute a coupling layer structure.

2. The high frequency selective reflective polarization conversion metasurface with fourth-order response according to claim 1, characterized in that: The first metal patch layer (1) is provided with a first combined groove structure, which is a 90° rotationally symmetrical structure along the center point of the first metal patch layer and an axially symmetrical structure about the center line and diagonal of the first metal patch layer. Specifically, the first combined groove structure is composed of a large square groove and four small square grooves, wherein the large square groove is located at the center, and the diagonal thereof overlaps with the diagonal of the first metal patch layer, and the small square grooves are respectively located at the four corners of the large square groove, and the diagonal thereof overlaps with the diagonal of the first metal patch layer in the same direction.

3. The high frequency selective reflective polarization conversion metasurface with fourth-order response according to claim 1, characterized in that: The second metal patch layer (6) is provided with a second combined groove structure and four straight grooves. The second combined groove structure is a 90° rotationally symmetrical structure along the center point of the second metal patch layer, and is an axially symmetrical structure about the midline and diagonal of the second metal patch layer. Specifically, it is composed of four arc grooves, which are located at the four corners of the second metal patch layer and intersect each other end to end. The four straight grooves are respectively opened along the edges of the second metal patch layer 6, and the straight grooves are located in the middle of the corresponding edges.

4. The high frequency selective reflective polarization conversion metasurface with fourth-order response according to claim 1, characterized in that: The third metal patch layer (8) is composed of an L-shaped microstrip line and two rectangular microstrip lines, the L-shaped microstrip line and the two rectangular microstrip lines are arranged to form a quasi-cross structure, and the quasi-cross structure is located on the midline of the lower surface of the third dielectric layer (7); the two rectangular microstrip lines are respectively provided with metal through holes (9) at their ends, and are connected to the second metal patch layer 6 through the metal through holes.

5. The high frequency selective reflective polarization conversion metasurface with fourth-order response according to claim 1, characterized in that: The frequency selective surface (FSS) unit structure is stacked on the upper surface of the second dielectric layer through a first glue layer, and the coupling layer structure is stacked on the lower surface of the second dielectric layer through a second glue layer, together forming a reflective polarization conversion metasurface.

6. The high frequency selective reflective polarization conversion metasurface with fourth-order response according to claim 1, characterized in that: In the polarization conversion metasurface, the values ​​of M and N are both not less than 5.

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