High efficiency transmissive reflective polarization conversion metasurface

Abstract

This invention discloses a high-efficiency transmission-reflection polarization conversion metasurface, belonging to the technical field of electromagnetic wave manipulation. A plurality of transmission polarization conversion metal structure layers arranged in an array are disposed between a first dielectric substrate and a second dielectric substrate, and a plurality of reflection polarization conversion metal structure layers arranged in an array are correspondingly disposed on the top of a third dielectric substrate. An air layer is disposed between the second and third dielectric substrates. Metal grids are respectively disposed on the bottom of the first dielectric substrate and the top of the second dielectric substrate, and Fabry cavities are formed between adjacent metal grids. The metasurface of this invention possesses both transmission and reflection polarization conversion functions. The high-efficiency transmission polarization conversion ensures normal in-band communication, while the high-efficiency reflection polarization conversion can change the polarization of radar detection waves. This invention can be used in embedded antenna cavities and radomes.

Description

Technical Field

[0001] This invention belongs to the technical field of electromagnetic wave manipulation, specifically relating to a high-efficiency transmission-reflection polarization conversion metasurface. Background Technology

[0002] Metasurfaces, as a novel type of artificial electromagnetic metamaterial, possess the ability to control the phase, amplitude, and polarization of electromagnetic waves, and offer advantages such as low profile, easy integration, and ease of fabrication. Among them, transmission-reflection metasurfaces can control waves arriving from both sides of the surface, greatly improving space utilization and enhancing environmental adaptability; polarization-conversion metasurfaces can control the polarization state of electromagnetic waves, which can be used to improve antenna gain and reduce radar cross section (RCS). Therefore, transmission-reflection metasurfaces with polarization conversion capabilities have attracted much attention.

[0003] Currently, to further reduce the RCS of carrier platforms, the design and installation of antennas in embedded or common forms is an unstoppable trend. For embedded antennas, the presence of a cavity is unavoidable, and the scattering of the cavity is more complex than that of a regular metal plate, worsening the stealth performance of the carrier platform. At this point, the importance of a low-scattering radome is self-evident. It must not only efficiently transmit radiated electromagnetic waves to maintain normal communication, but also achieve low scattering characteristics under radar detection. Transmissive-reflective polarization-conversion metasurfaces can effectively achieve this function—the high-efficiency transmission band ensures good external radiation from the cavity antenna while simultaneously achieving polarization conversion; the polarization-conversion reflection band, on the one hand, can convert the polarization state of the detection wave, preventing enemy radar from receiving the reflected wave and reducing the possibility of platform exposure; on the other hand, rotating the reflection polarization-conversion structure 90 degrees can achieve a 180-degree phase difference in the reflected wave, and by arranging the rotating elements in a checkerboard pattern, the reflected waves can be canceled out, achieving the effect of reducing the RCS.

[0004] In existing technologies, most polarization conversion metasurfaces are either purely transmissive or purely reflective. For radome requirements, a single transmissive polarization conversion surface can maintain normal in-band communication, but its ability to control out-of-band probe waves is weak. In-band probe waves are more likely to pass through the polarization conversion metasurface and enter the cavity, resulting in strong scattering. A single reflective polarization conversion metasurface cannot meet the requirement of maintaining normal communication. There are also polarization conversion metasurfaces that combine both transmissive and reflective operating modes, but most cannot achieve polarization conversion functionality in both modes. For example, Chinese patent CN115566435B discloses a transmissive-reflective reconfigurable polarization conversion metasurface based on a PIN diode. Its transmissive and reflective operating modes are controlled by the PIN diode. In transmissive mode, it can achieve cross-polarization transmission of incident ray-polarized waves, and in reflective mode, it can achieve co-polarization reflection of incident ray-polarized waves. It cannot achieve polarization conversion functionality in reflective mode, making it unsuitable for use as a low-scattering radome.

[0005] Currently, in the terahertz field, some scholars have proposed ultrawideband transmission-reflection polarization conversion metasurfaces, using photosensitive materials such as Si and Ge to achieve switching between transmission and reflection polarization conversion. However, this requires additional pump light illumination, and radar and terrestrial communications are mainly concentrated in the radio frequency X-band (8-12 GHz). In the radio frequency range, a few scholars have also proposed metasurfaces that combine transmission and reflection polarization conversion functions, but these are mostly achieved by utilizing the polarization selectivity of gratings or by loading pins with defects. The results are mostly that the transmission and reflection polarization conversion operating frequency bands are far apart, or the transmission and reflection operate at a single or multiple frequency point, with low transmission or reflection amplitudes. For multi-band common-aperture radomes, this is not conducive to normal communication in the broadband range. In addition, narrowband or single-frequency reflection polarization conversion cannot well meet the broadband low-scattering requirements of radomes.

[0006] In summary, there is currently little research on multifunctional metasurfaces that combine transmission and reflection polarization conversion. The few existing metasurfaces that combine transmission and reflection polarization conversion have significantly different operating bandwidths, making it impossible to achieve wide-band functional coverage, or their single-frequency or multi-frequency operation cannot meet practical needs. Summary of the Invention

[0007] The purpose of this invention is to provide a high-efficiency transmission-reflection polarization conversion metasurface, which aims to solve the above-mentioned problems.

[0008] This invention is mainly achieved through the following technical solutions:

[0009] A high-efficiency transmission-reflection polarization conversion metasurface includes a first dielectric substrate, a second dielectric substrate, and a third dielectric substrate arranged sequentially from bottom to top. A plurality of transmission-reflection polarization conversion metal structure layers are arranged in an array between the first and second dielectric substrates, and a plurality of reflection-reflection polarization conversion metal structure layers are arranged in an array on the top of the third dielectric substrate. An air layer is provided between the second and third dielectric substrates. Metal grids are respectively provided at the bottom of the first dielectric substrate and at the top of the second dielectric substrate, and Fabry cavities are formed between adjacent metal grids.

[0010] To better realize the present invention, the adjacent metal grids are arranged perpendicularly, the metal grids include a number of metal grid strips distributed in a matrix, and the width of the metal grid strips is 0.4 mm, and the spacing between adjacent metal grid strips is 0.4 mm.

[0011] To better realize the present invention, the transmission polarization conversion metal structure layer is further described as a double-slit ring with an inner circle and an outer square, obtained by cutting a square metal patch with a hollow circle at the center along the first L-shaped through groove. The transmission polarization conversion metal structure layer is symmetrical about the Y-axis by rotating it 45 degrees. The vertical turning point of the first L-shaped through groove is connected to the hollow circle.

[0012] To better realize the present invention, the transmission polarization conversion metal structure layer further includes an L-shaped first metal patch and a square second metal patch; the first metal patch and the second metal patch form a first L-shaped through groove, and the centers of the first metal patch and the second metal patch form a hollow circle.

[0013] To better realize the present invention, the width of the first L-shaped through groove is g2, the diameter of the hollow circle is d, and the side length of the square metal patch is l3; wherein, g2 = 0.8mm, d = 2.8mm, and l3 = 14.2mm.

[0014] To better realize the present invention, the reflective polarization conversion metal structure layer is further provided as an open ring obtained by cutting a quarter of the L-shaped structure from a square annular metal patch along the second L-shaped through groove, and the reflective polarization conversion metal structure layer is symmetrical about the Y-axis by rotating it 45 degrees.

[0015] To better realize the present invention, the square annular metal patch is further provided with a hollow square at its center, and the side length of the hollow square is l2; the side length of the square annular metal patch is l1, and the width of the second L-shaped through groove is g1; wherein, l1 = 6.3mm, l2 = 2.5mm, and g1 = 0.4mm.

[0016] To better realize the present invention, the thicknesses of the first dielectric substrate, the second dielectric substrate and the third dielectric substrate are h1, h2 and h3 respectively, and the thickness of the air layer is air_h; wherein, h1 = 4.4mm, h2 = 2.8mm, h3 = 2.2mm and air_h = 1.5mm.

[0017] A high-efficiency transmission-reflection polarization conversion metasurface includes several arrayed units. Each unit comprises a first dielectric substrate, a second dielectric substrate, and a third dielectric substrate arranged sequentially from bottom to top. A transmission polarization conversion metal structure layer is disposed between the first and second dielectric substrates, and a reflection polarization conversion metal structure layer is disposed on the top of the third dielectric substrate. An air layer is disposed between the second and third dielectric substrates. Metal grids are respectively disposed on the bottom of the first dielectric substrate and the top of the second dielectric substrate, and Fabry cavities are formed between adjacent metal grids.

[0018] To better realize the present invention, the transmission polarization conversion metal structure layer is further described as a double-slit ring with an inner circle and an outer square, obtained by cutting a square metal patch with a hollow circle at the center along the first L-shaped through groove. The transmission polarization conversion metal structure layer is symmetrical about the Y-axis by rotating it 45 degrees. The vertical turning point of the first L-shaped through groove is connected to the hollow circle.

[0019] To better realize the present invention, the reflective polarization conversion metal structure layer is further provided as an open ring obtained by cutting a quarter of the L-shaped structure from a square annular metal patch along the second L-shaped through groove, and the reflective polarization conversion metal structure layer is symmetrical about the Y-axis by rotating it 45 degrees.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) The metasurface of this invention has both transmission polarization conversion and reflection polarization conversion functions. The high-efficiency transmission polarization conversion of this invention can ensure normal communication within the band, and the high-efficiency reflection polarization conversion can change the polarization of radar detection waves. Secondly, this invention can achieve the dispersion of reflected waves through a checkerboard arrangement, further reducing the RCS. This invention can be used in embedded antenna cavity radomes, and compared with traditional polarization conversion surfaces, the space utilization is effectively improved and the functions are expanded. Specifically, under X-polarized wave incident: this invention achieves transmission polarization conversion in the 7-8.4 GHz frequency band (relative bandwidth 18.2%); and achieves reflection polarization conversion in the 8.8-10.1 GHz frequency band (relative bandwidth 13.8%), while the polarization conversion rate is higher than 90% in the 7-10 GHz frequency band (relative bandwidth 35.3%).

[0022] (2) Based on the traditional single-sided polarization conversion metasurface, this invention enhances the metasurface's ability to control the polarization of incident waves on both sides, improving and broadening the working performance and application range of such metasurfaces, and meeting the application requirements of cavity radomes for embedded antennas on aircraft platforms. Specifically, this invention utilizes the high frequency selectivity of the Fabry cavity to treat it as an equivalent reflective ground plane of a high-frequency reflective polarization conversion structure layer, thereby achieving the integration of transmission and reflection functions. The metasurface of this invention has a wide and tightly connected transmission and reflection polarization conversion operating frequency band. The connection and non-interference between the transmission and reflection operating bands are mainly attributed to the good steep drop characteristics of the inner circular and outer square polarization conversion layer, as well as the air layer between the reflective and transmission layers, which effectively weakens the coupling between the transmission and reflection layers. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the perspective structure of the high-efficiency transmission-reflection polarization conversion metasurface of the present invention;

[0024] Figure 2 for Figure 1 Top view;

[0025] Figure 3 This is an exploded view of the transmission-reflection polarization conversion unit.

[0026] Figure 4 This is a schematic diagram of the transmission polarization conversion metal structure layer.

[0027] Figure 5 This is a schematic diagram of the reflective polarization conversion metal structure layer;

[0028] Figure 6 This is a schematic diagram of the metal grid structure;

[0029] Figure 7 The unit scattering coefficient under x-polarized wave incident in Example 1;

[0030] Figure 8 The scattering coefficient of the unit under incident y-polarized wave in Example 1;

[0031] Figure 9 The polarization azimuth rotation angle and ellipticity are given in Example 1.

[0032] Figure 10 The polarization conversion rate of transmission and reflection in Example 1 is denoted as .

[0033] Wherein: 1-first dielectric substrate, 2-second dielectric substrate, 3-third dielectric substrate, 4-transmission polarization conversion metal structure layer, 5-reflection polarization conversion metal structure layer. Detailed Implementation

[0034] Example 1:

[0035] A high-efficiency transmission-reflection polarization conversion metasurface, such as Figure 1 (The upper and lower metal grids are hidden) and Figure 2 As shown, the present invention has a three-layer structure from bottom to top: a first dielectric substrate, a second dielectric substrate, and a third dielectric substrate. The bottom of the first dielectric substrate and the top of the second dielectric substrate are printed with metal grids of the same size, placed perpendicularly to each other. Between the first and second dielectric substrates are several transmission polarization conversion metal structure layers arranged in an array. Correspondingly, the top of the third dielectric substrate has several reflection polarization conversion metal structure layers arranged in an array. An air layer exists between the third and second dielectric substrates. Preferably, the transmission polarization conversion metal structure layers and the reflection polarization conversion metal structure layers are arranged in a 10×10 array.

[0036] Preferably, the first dielectric substrate is made of F4B with a dielectric constant of 2.65, a tangent loss angle of 0.0009, and a thickness of h1; the second dielectric substrate is also made of F4B with a thickness of h2; and the third dielectric substrate is made of F4B with a thickness of h3. Figure 6 As shown, the metal grid comprises a plurality of metal strips arranged in a matrix, with each strip having a width of 0.4 mm and a spacing of 0.4 mm between adjacent strips. The thickness of the air layer is air_h.

[0037] A Fabry cavity is formed between the metal grids printed on the first and second dielectric substrates, significantly improving the transmission polarization conversion efficiency. The transmission polarization conversion metal structure layer between the first and second dielectric substrates is a double-slit ring with an inner circle and an outer square, such as... Figure 4 As shown, the overall structure is symmetrical along the straight line y = -x. When linearly polarized light is incident, it excites a current component whose direction is perpendicular to the polarization of the incident wave, thereby realizing the polarization conversion function. The principle of achieving high-efficiency transmission polarization conversion by combining the first and second dielectric substrates with the transmission polarization conversion metal structure layer is the same as that of the existing Chinese patent CN115566435B. However, the difference is that the double-slit ring with an inner circle and an outer square used in this invention has a better steep drop in transmission amplitude compared to the double-slit circular ring used previously, which lays the groundwork for subsequent high-efficiency reflection polarization conversion.

[0038] The reflective polarization conversion metal structure layer at the top of the third dielectric substrate is a double-slit square ring minus a quarter structure (the dashed line in the figure), such as... Figure 5 As shown, similarly symmetrical along the line y = -x, when linearly polarized light is incident, it excites a current component whose direction is perpendicular to the polarization of the incident wave. An air layer exists between the reflective layer and the second dielectric substrate, its function being to extend the reflective operating bandwidth.

[0039] The working principle of the transmission-reflection polarization conversion metasurface unit of the present invention is as follows:

[0040] When a low-frequency x-polarized wave is incident, the reflective polarization conversion metal structure layer is relatively small compared to the wavelength of the low-frequency electromagnetic wave, resulting in a small induced current, essentially equivalent to "air." The low-frequency linearly polarized wave smoothly enters the Fabry cavity between the second and first dielectric substrates, achieving cross-polarization transmission through the transmission polarization conversion metal structure layer. When a high-frequency linearly polarized wave is incident, the transmission polarization conversion metal structure layer no longer generates a strong current component perpendicular to the polarization of the incident wave, losing its polarization conversion function. At this point, the bottom metal grid acts as a complete metal ground plane for the electromagnetic wave within the cavity, preventing the incident x-polarized wave from passing through it. In this case, the first and second dielectric substrates and the transmission polarization conversion metal structure layer are considered as a whole, existing as the reflective metal ground plane of the top reflective polarization conversion layer, thus achieving the reflective polarization conversion function. After completing the initial design, simulation analysis was performed using CST Microwave Studio software. After optimizing the unit structure dimensions, the transmission and reflection operating bands can be closely adjacent, achieving functional coverage across a wide frequency band.

[0041] Preferably, the specific dimensions are as follows:

[0042] g1=0.4mm, g2=0.8mm, d=2.8mm, l1=6.3mm, l2=2.5mm, l3=14.2mm, h1=4.4mm,

[0043] h2=2.8mm, h3=2.2mm, air_h=1.5mm.

[0044] like Figure 7 As shown, under the illumination of a small-polarization incident wave, the transmission and reflection coefficients of the unit cells of the transmission-reflection polarization conversion metasurface are analyzed, where t yx r represents the x-polarized incident y-polarized transmission coefficient. yx t represents the x-polarized incident y-polarized reflection coefficient. xx r represents the x-polarized incident x-polarized transmission coefficient. xx This represents the x-polarized incident x-polarized reflection coefficient. From Figure 7 It can be clearly seen that the unit of the present invention achieves the transmission polarization conversion function in the range of 7 to 8.4 GHz and the reflection polarization conversion function in the range of 8.8 to 10.1 GHz. The transmission and reflection amplitudes are both higher than -1 dB, the polarization conversion function covers 40% of the bandwidth, and the single-sided suppression rate of the transmission band reaches -29 dB.

[0045] like Figure 8As shown, the transmission and reflection coefficients of the metasurface unit under y-polarized incident wave irradiation are analyzed. This unit achieves co-polarized reflection function in the range of 7 to 8.4 GHz and cross-polarized transmission function in the range of 8.8 to 10.1 GHz, with both transmission and reflection amplitudes higher than -1 dB.

[0046] like Figure 9 As shown, (a) represents the polarization azimuth rotation angle and ellipticity of the element in transmission mode under x-polarized incident light; (b) represents the polarization azimuth rotation angle and ellipticity of the element in reflection mode under x-polarized incident light. In the 7–8.5 GHz band, the ellipticity is between ±1 degree, indicating high polarization purity of the transmitted wave. Simultaneously, the polarization azimuth rotation angle is +90° or -90°, indicating that the polarization direction of the transmitted wave is rotated by 90° relative to the incident wave, i.e., x-polarized incident light is converted to y-polarized transmission. In the 8.8–10.1 GHz band, the ellipticity is approximately between ±10 degrees, indicating lower circular polarization purity. Simultaneously, the polarization azimuth rotation angle is approximately -90°, indicating that the polarization direction of the reflected wave is rotated by approximately 90° relative to the incident wave, i.e., x-polarized incident light is converted to y-polarized reflection. Furthermore, as... Figure 10 As shown, the polarization conversion rate of the unit under x-polarized incident radiation in two operating modes can be analyzed. It can be found that the polarization conversion rate in the 7-10 GHz band is higher than 90%.

[0047] In summary, this invention provides a construction approach for a transmission-reflection unit. Its innovation lies in improving the space utilization of the single-sided polarization conversion unit, realizing a metasurface unit with both high-efficiency transmission and reflection polarization conversion functions, and exhibiting wide bandwidth and good steep-dip characteristics. It expands the functionality of the single-sided polarization conversion unit, providing a feasible, low-cost solution for cavity radomes of embedded antennas on aircraft platforms.

[0048] Example 2:

[0049] A high-efficiency transmission-reflection polarization conversion metasurface is proposed, consisting of 10×10 units arranged in an array. For example... Figure 3 As shown, the unit includes a first dielectric substrate, a second dielectric substrate, and a third dielectric substrate arranged sequentially from bottom to top. A transmission polarization conversion metal structure layer is disposed between the first and second dielectric substrates, and a reflection polarization conversion metal structure layer is correspondingly disposed on the top of the third dielectric substrate; an air layer is disposed between the second and third dielectric substrates; as shown... Figure 6 As shown, metal grids are respectively provided at the bottom of the first dielectric substrate and at the top of the second dielectric substrate, and Fabry cavities are formed between adjacent metal grids.

[0050] A fabric cavity is formed between the metal grids printed on the first and second dielectric substrates, which greatly improves the transmission polarization conversion efficiency. For example... Figure 4 As shown, the transmission polarization conversion metal structure layer between the first and second dielectric substrates is a double-slit ring with an inner circle and an outer square. The overall structure is symmetrically rotated 45 degrees along the Y-axis. When linearly polarized light is incident, it excites a current component whose direction is perpendicular to the polarization of the incident wave, thereby realizing the polarization conversion function. The principle of achieving high-efficiency transmission polarization conversion by combining the first and second dielectric substrates with the transmission polarization conversion metal structure layer is the same as that of the existing Chinese patent CN115566435B. However, the difference is that the double-slit ring with an inner circle and an outer square used in this invention has a better steep drop in transmission amplitude compared to the double-slit circular ring used previously, which lays the groundwork for subsequent high-efficiency reflection polarization conversion.

[0051] like Figure 5 As shown, the reflective polarization conversion metal structure layer on top of the third dielectric substrate is a double-slit square ring minus a quarter structure (the dashed part in the figure), which is also symmetrically rotated 45 degrees along the Y-axis. When linearly polarized light is incident, it will excite a current component whose direction is perpendicular to the polarization of the incident wave. There is an air layer between the reflective layer and the second dielectric substrate, which serves to extend the reflective working bandwidth.

[0052] Preferably, such as Figure 4 As shown, the transmission polarization conversion metal structure layer includes an L-shaped first metal patch and a square second metal patch; the first metal patch and the second metal patch form a first L-shaped through groove, and the centers of the first metal patch and the second metal patch form a hollow circle. The width of the first L-shaped through groove is g2, the diameter of the hollow circle is d, and the side length of the square metal patch is l3.

[0053] Preferably, such as Figure 5 As shown, the reflective polarization conversion metal structure layer is an open ring obtained by cutting a quarter of the L-shaped structure away from a square annular metal patch along the second L-shaped through groove. The reflective polarization conversion metal structure layer is symmetrical about the Y-axis by rotating it 45 degrees. The square annular metal patch has a hollow square at its center, and the side length of the hollow square is l2; the side length of the square annular metal patch is l1, and the width of the second L-shaped through groove is g1.

[0054] The thicknesses of the first dielectric substrate, the second dielectric substrate, and the third dielectric substrate are h1, h2, and h3, respectively, and the thickness of the air layer is air_h.

[0055] Preferably, the dimensional parameters are as follows:

[0056] g1=0.4mm, g2=0.8mm, d=2.8mm, l1=6.3mm, l2=2.5mm, l3=14.2mm, h1=4.4mm,

[0057] h2=2.8mm, h3=2.2mm, air_h=1.5mm.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A high-efficiency transmission-reflection polarization conversion metasurface unit, characterized in that, It includes a first dielectric substrate, a second dielectric substrate, and a third dielectric substrate arranged sequentially from bottom to top; a plurality of transmission polarization conversion metal structure layers arranged in an array are disposed between the first dielectric substrate and the second dielectric substrate, and a plurality of reflection polarization conversion metal structure layers arranged in an array are disposed on the top of the third dielectric substrate; an air layer is disposed between the second dielectric substrate and the third dielectric substrate. Metal grids are respectively provided at the bottom of the first dielectric substrate and at the top of the second dielectric substrate, and a Fabry cavity is formed between adjacent metal grids. The transmission polarization conversion metal structure layer is a double-slit ring with an inner circle and an outer square, obtained by cutting a square metal patch with a hollow circle in the center along the first L-shaped through groove. The transmission polarization conversion metal structure layer is symmetrical about the Y-axis by rotating it 45 degrees. The vertical turning point of the first L-shaped through groove is connected to the hollow circle. The reflective polarization conversion metal structure layer is an open ring obtained by cutting a quarter of the L-shaped structure away from a square annular metal patch along the second L-shaped through groove. The reflective polarization conversion metal structure layer is symmetrical about the Y-axis by rotating it 45 degrees.

2. The high-efficiency transmission-reflection polarization conversion metasurface unit according to claim 1, characterized in that, The width of the first L-shaped through groove is g2, the diameter of the hollow circle is d, and the side length of the square metal patch is g2. l 3; in, g 2 = 0.8 mm d =2.8mm, l 3 = 14.2 mm.

3. The high-efficiency transmission-reflection polarization conversion metasurface unit according to claim 1, characterized in that, The square annular metal patch has a hollowed-out square at its center, and the side length of the hollowed-out square is [missing information]. l 2; The side length of the square annular metal patch is l 1. The width of the second L-shaped through groove is g 1; in, l 1 = 6.3 mm l 2 = 2.5mm, g 1 = 0.4 mm.

4. A high-efficiency transmission-reflection polarization conversion metasurface unit according to any one of claims 1-3, characterized in that, The thicknesses of the first dielectric substrate layer, the second dielectric substrate layer, and the third dielectric substrate layer are respectively... h 1. h 2 and h 3. The thickness of the air layer is air_h ;in, h 1 = 4.4 mm h 2 = 2.8mm, h 3 = 2.2mm air_h =1.5mm.

5. A high-efficiency transmission-reflection polarization conversion metasurface, characterized in that, The device comprises several units arranged in an array. Each unit includes a first dielectric substrate, a second dielectric substrate, and a third dielectric substrate arranged sequentially from bottom to top. A transmission polarization conversion metal structure layer is disposed between the first and second dielectric substrates, and a reflection polarization conversion metal structure layer is disposed on the top of the third dielectric substrate. An air layer is disposed between the second and third dielectric substrates. Metal grids are disposed on the bottom of the first dielectric substrate and the top of the second dielectric substrate, and Fabry cavities are formed between adjacent metal grids. The transmission polarization conversion metal structure layer is a double-slit ring with an inner circle and an outer square, obtained by cutting a square metal patch with a hollow circle in the center along the first L-shaped through groove. The transmission polarization conversion metal structure layer is symmetrical about the Y-axis by rotating it 45 degrees. The vertical turning point of the first L-shaped through groove is connected to the hollow circle. The reflective polarization conversion metal structure layer is an open ring obtained by cutting a quarter of the L-shaped structure away from a square annular metal patch along the second L-shaped through groove. The reflective polarization conversion metal structure layer is symmetrical about the Y-axis by rotating it 45 degrees.

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