Dual-polarization frequency selective surface with high angle stability characteristic

Abstract

The invention belongs to the field of frequency selective surface (FSS) design, and particularly provides a dual-polarization frequency selective surface with a high angle stability characteristic, which is formed by periodically arranging M * N unit structures, each unit structure comprises a first metal patch layer T1, a first foam structure layer P1, a second metal patch layer T2, a first dielectric structure layer J1, a third metal patch layer T3, a second dielectric structure layer J2, a fourth metal patch layer T4, a second foam structure layer P2 and a fifth metal patch layer T5 which are sequentially stacked from top to bottom. Wherein T1 and T5 are completely identical, T2 and T4 are completely identical, P1 and P2 are completely identical, and J1 and J2 are completely identical; through the creative design of the unit structure, the frequency selective surface has a wide passband and low insertion loss wave transmission when electromagnetic waves are incident at a large angle, and the working frequency and bandwidth of TE and TM polarized electromagnetic waves can be independently regulated and controlled.

Description

A dual-polarization frequency-selective surface with high angular stability Technical Field

[0001] This invention belongs to the field of frequency selective surface (FSS) design, and specifically provides a dual-polarization frequency selective surface with high angular stability. Background Technology

[0002] With the development of communication technology, existing electromagnetic spectrum resources are becoming increasingly scarce, and electromagnetic interference is becoming more and more serious. Utilizing the selective transmission function of frequency-selective surfaces (FSS) allows electromagnetic waves within the desired frequency band to pass through almost without loss, while reflecting almost all electromagnetic waves in other frequency bands, thus solving the electromagnetic interference problem. Specifically, a frequency-selective surface is an artificial electromagnetic material formed by periodically extending identical metal patch units or aperture units on a metal screen along a one-dimensional or two-dimensional direction on a dielectric substrate. Based on the principle of electromagnetic resonance, FSS can selectively filter electromagnetic waves propagating in space, achieving ultra-low loss or even lossless transmission of incident electromagnetic waves in a specific frequency band, while reflecting almost all incident electromagnetic waves outside that band. The performance of an FSS is closely related to its unit structure, the incident angle of the electromagnetic wave, and its polarization. By carefully designing its unit shape, period, and substrate, its operating frequency and bandwidth can be precisely controlled. As an important electromagnetic functional material, FSS has extremely wide applications in radar radomes, antenna systems, polarization converters, satellite communications, and terahertz fields.

[0003] In real life, electromagnetic waves do not only come from a single direction, but can also be incident from all directions in space. Therefore, frequency selective surfaces must have high angular stability to meet the needs of practical applications. In recent years, a large number of studies have been carried out at home and abroad to improve the angular stability of frequency selective surfaces. As described in the 2018 paper "Single-Layer Frequency Selective Surface With Angular Stability Property", Tao Hong et al. designed a single-layer composite bent FSS unit consisting of a "well"-shaped annular patch and a "swastika"-shaped annular patch. This FSS unit is insensitive to polarization and has excellent angular stability. When the incident angle range is 0° to 85°, the maximum resonant frequency deviation is only 0.08 GHz. Similarly, in the 2022 paper "Second-Order, Single-Band and Dual-Band Bandstop Frequency Selective Surfaces at Millimeter Wave Regime", Soumik Dey et al. proposed a miniature low-profile second-order FSS suitable for single-band and dual-band resonance. Its filtering response has polarization insensitivity and remains highly stable within a 60° incident angle range. Finally, in the 2024 paper "A Conformal Miniaturized Bandpass Frequency-Selective Surface With Stable Frequency Response for Radome",... As described in the "Applications" section, Xianjun Sheng et al. proposed a composite patch-type FSS consisting of a central connecting structure and a ring structure. This FSS has good conformal stability and angular stability up to 75°.

[0004] However, most existing two-dimensional frequency selective surfaces (FSS) achieve large-angle stability by designing complex graphic structures or using specific materials. This not only increases design and manufacturing costs but also generally only ensures that the designed frequency does not shift significantly when electromagnetic waves are incident at angles greater than 60°, making it difficult to maintain highly stable transmission characteristics over a wide frequency range. Furthermore, existing FSSs generally employ rotationally symmetric structures to achieve dual polarization, resulting in consistent response curves for TE and TM polarized electromagnetic waves. Changing the FSS structure alters the transmission characteristics for both TE and TM polarized electromagnetic waves, making it impossible to achieve individual control over the operating frequency and bandwidth. Therefore, this invention provides a novel dual-polarized frequency selective surface with high angular stability. Summary of the Invention

[0005] The purpose of this invention is to provide a dual-polarization frequency selective surface with high angular stability, which has a wide passband and low insertion loss when electromagnetic waves are incident at large angles, and can independently control the operating frequency and bandwidth of TE and TM polarized electromagnetic waves.

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

[0007] A dual-polarization frequency-selective surface with high angular stability is composed of M×N periodically arranged unit structures. The unit structure comprises, from top to bottom, a first metal patch layer T1, a first foam structure layer P1, a second metal patch layer T2, a first dielectric structure layer J1, a third metal patch layer T3, a second dielectric structure layer J2, a fourth metal patch layer T4, a second foam structure layer P2, and a fifth metal patch layer T5, stacked sequentially. Specifically, the first metal patch layer T1 and the fifth metal patch layer T5 are identical, the second metal patch layer T2 and the fourth metal patch layer T4 are identical, the first foam structure layer P1 and the second foam structure layer P2 are identical, and the first dielectric structure layer J1 and the second dielectric structure layer J2 are identical.

[0008] Furthermore, the unit structure adopts a rectangular structure, defining its long side as the y-direction and its wide side as the x-direction; the first metal patch layer T1 adopts a first rectangular metal patch, which is set along the center, with its long side located in the y-direction and its wide side located in the x-direction, and the first metal patch layers of adjacent unit structures in the y-direction combine to form a capacitive structure.

[0009] Furthermore, the first metal patch layer T1 and the fifth metal patch layer T5 are respectively loaded onto a dielectric substrate of the same thickness, with the first metal patch layer T1 disposed on the upper surface of the dielectric substrate and the fifth metal patch layer T5 disposed on the lower surface of the dielectric substrate.

[0010] Furthermore, the unit structure adopts a rectangular structure, defining its long side as the y-direction and its wide side as the x-direction; the second metal patch layer T2 adopts a second rectangular metal patch, which is set along the center, with its long side located in the x-direction and its wide side located in the y-direction, and the second metal patch layers of adjacent unit structures in the x-direction combine to form a capacitive structure.

[0011] Furthermore, the unit structure adopts a rectangular structure, with its long side defined as the y-direction and its wide side as the x-direction; the third metal patch layer T3 adopts a rectangular metal sheet of the same size as the unit structure, and the rectangular metal sheet has a bent slit with a width of s1 etched along the midline of the x-direction and a bent slit with a width of s2 etched along the midline of the y-direction, and both bent slits are 180° rotationally symmetrical about the geometric center of the rectangular metal sheet.

[0012] Furthermore, both M and N are integers greater than or equal to 2.

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

[0014] This invention provides a dual-polarization frequency selective surface with high angular stability. An equivalent circuit with third-order resonance is constructed using equivalent circuit theory. A structural design with capacitive metal patch layers and irregular shapes in the x and y directions of the central metal patch layer is adopted. This enables the frequency selective surface to have good selectivity for TE and TM polarized electromagnetic waves incident from 0° to 70°. Ultimately, this invention has the advantages of high angular stability and dual polarization, and can independently control the operating frequency and bandwidth of TE and TM polarized electromagnetic waves.

[0015] Simulation results show that: 1. The frequency-selective surface in this invention exhibits good transmission characteristics for both TE and TM polarized electromagnetic waves in the range of 4.42-6.35 GHz (relative bandwidth 35.84%), forming a passband with an insertion loss as low as 0.47 dB, and demonstrating good reflection characteristics for electromagnetic waves outside the passband; 2. The frequency-selective surface in this invention exhibits excellent angular stability under both TE and TM polarization when electromagnetic waves are incident. For incident frequencies of 0°-70°, the transmission band with a TE polarization transmission coefficient above -3 dB is 4... 4.47-6.32GHz (relative bandwidth 34.29%), the transmission band with a TM polarization transmission coefficient above -3dB is 4.67-6.45GHz (relative bandwidth 32.01%); 3. Without changing the unit structure, by simply changing the size parameters of the surface metal patch layer and the thickness of the foam structure layer and dielectric structure layer, the transmission zeros of the TE and TM polarizations can be controlled separately, thereby adjusting their passband positions, achieving flexible design of the transmission frequency band and reducing design costs. Attached Figure Description

[0016] Figure 1 is a schematic diagram of the unit structure of the dual-polarization frequency selective surface with high angular stability in this invention.

[0017] Figure 2 is a schematic diagram of the structure of the first metal patch layer T1 in this invention.

[0018] Figure 3 is a schematic diagram of the structure of the second metal patch layer T2 in this invention.

[0019] Figure 4 is a schematic diagram of the structure of the third metal patch layer T3 in this invention.

[0020] Figure 5 is an equivalent circuit diagram of the unit structure of the dual-polarization frequency selective surface in this invention.

[0021] Figure 6 is a simplified equivalent circuit diagram of the unit structure of the dual-polarized frequency selective surface in this invention for TE-polarized incident electromagnetic waves.

[0022] Figure 7 shows the S-parameter simulation results of the simplified equivalent circuit of the dual-polarized frequency selective surface unit structure for TE-polarized incident electromagnetic waves in this invention.

[0023] Figure 8 is a simplified equivalent circuit diagram of the unit structure of the dual-polarized frequency selective surface in this invention for TM-polarized incident electromagnetic waves.

[0024] Figure 9 shows the S-parameter simulation results of the simplified equivalent circuit of the dual-polarized frequency selective surface unit structure for TM-polarized incident electromagnetic waves in this invention.

[0025] Figure 10 shows the S-parameter simulation results of the dual-polarization frequency-selective surface with high angular stability in Embodiment 1 of the present invention. In Figure 10(a), the S-parameter simulation results of TE polarization are shown, and in Figure 10(b), the S-parameter simulation results of TM polarization are shown.

[0026] Figure 11 shows the S-parameter simulation results of the dual-polarization frequency-selective surface with high angular stability in Embodiment 2 of the present invention. In Figure 11(a), the S-parameter simulation results of TE polarization are shown, and in Figure 11(b), the S-parameter simulation results of TM polarization are shown. Detailed Implementation

[0027] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0028] This embodiment provides a dual-polarization frequency selective surface with high angular stability. The frequency selective surface is composed of M×N identical unit structures arranged periodically (M and N are both integers greater than or equal to 2). The unit structure is shown in Figure 1, and from top to bottom includes: a first metal patch layer T1, a first foam structure layer P1, a second metal patch layer T2, a first dielectric structure layer J1, a third metal patch layer T3, a second dielectric structure layer J2, a fourth metal patch layer T4, a second foam structure layer P2, and a fifth metal patch layer T5. Among them, T1 and T5 are identical, and T2 and T4 are identical. P1 is located between T1 and T2, and P2 is located between T4 and T5. P1 and P2 are identical, and both have a thickness of h1. J1 is located between T2 and T3, and J2 is located between T3 and T4. J1 and J2 are identical, and both have a thickness of h2. All metal patch layers are tightly bonded to the foam structure layer and the dielectric structure layer, and the dimensions of all foam structure layers and dielectric structure layers are consistent with the dimensions of the entire unit structure.

[0029] Figure 2 shows a top view of the first metal patch layer T1 (the fifth metal patch layer T5). The metal patch is a rectangle with a length of l1 and a width of w1, located at the center of a unit structure with a length of dy and a width of dx. The first metal patch layer T1 (the fifth metal patch layer T5) in adjacent unit structures in the y direction are combined to form a capacitive structure. T1 is attached to the upper surface of a dielectric substrate with a minimum thickness of h0, and T5 is attached to the lower surface of the dielectric substrate with a minimum thickness of h0. The relative permittivity of the dielectric substrate material is 3.2, and the loss tangent is 0.008.

[0030] Figure 3 shows a top view of the second metal patch layer T2 (fourth metal patch layer T4). The metal patch is a rectangle with a length of l2 and a width of w2, and is also located at the center of the unit structure. The first metal patch layer T2 (fifth metal patch layer T4) in the adjacent unit structure in the x direction are combined to form a capacitive structure. T2 is attached to the upper surface of the first dielectric structure layer J1, and T4 is attached to the lower surface of the second dielectric structure layer J2. T1 and T2, and T4 and T5 are separated by a foam structure with a thickness of h1. The relative permittivity of the foam material used in the foam structure layer is 1.08, and the loss tangent is 0.008. Using foam material can minimize the weight and cost of the frequency selection surface.

[0031] Figure 4 shows a top view of the third metal patch layer T3. This metal patch is formed by etching a bent slit of width s1 along the x-direction and a bent slit of width s2 along the y-direction of a rectangular metal sheet of the same size as the unit cell. Both bent slits are 180° rotationally symmetrical about the geometric center of the rectangular metal sheet. The equivalent circuit of this patch can be simplified to a parallel LC circuit, which forms a passband in the resonant frequency band when electromagnetic waves are incident. T3 is separated from T2 and T4 by a dielectric structure layer with a thickness of h2. The dielectric material used has a relative permittivity of 3.2 and a loss tangent of 0.008. It should be noted that the specific dimensional parameters of the two bent slits can be optimized by simulation according to the actual application requirements.

[0032] In terms of working principle:

[0033] According to the equivalent circuit theory, the metal patches in the first metal patch layer T1 (the fifth metal patch layer T5) can be equivalent to an inductor L1, and the gap between adjacent metal patches can be equivalent to a capacitor C1. Therefore, the first metal patch layer T1 (the fifth metal patch layer T5) can be equivalent to a series LC circuit. Similarly, the metal patches in the second metal patch layer T2 (the fourth metal patch layer T4) can be equivalent to an inductor L2, and the gap between adjacent metal patches can be equivalent to a capacitor C2. Therefore, the second metal patch layer T2 (the fourth metal patch layer T4) can also be equivalent to a series LC circuit. The bending gap in the third metal patch layer T3 can be equivalent to a capacitor C3, and the remaining metal structure can be equivalent to an inductor L3. Therefore, the third metal patch layer T3 can be equivalent to a parallel LC circuit. In summary, the equivalent circuit of the entire unit structure is shown in Figure 5.

[0034] For TE-polarized incident electromagnetic waves, viewed from the y-direction, the metal patches in the first metal patch layer T1 (the fifth metal patch layer T5) have a relatively large width, and their equivalent inductance L1 is negligible. The metal patches in the second metal patch layer T2 (the fourth metal patch layer T4) also have a relatively large width, and their equivalent inductance L2 is negligible. The gap between adjacent unit metal patches is also relatively large, and their equivalent capacitance C2 is negligible. The equivalent capacitance C3 of the third metal patch layer T3 is mainly determined by the size of the bending gap in the x-direction. At this time, the equivalent circuit of the unit structure can be simplified as shown in Figure 6. The equivalent circuit is simulated using ADS simulation software. C1=0.102pF, h1=2mm, h2=2mm, L3=1.908nH, and C3=0.647pF are adjusted. The simulation results are shown in Figure 7. The results show that a third-order resonance with a wide passband and a good steep drop coefficient can be formed.

[0035] For TM-polarized incident electromagnetic waves, viewed from the x-direction, the metal patches in the first metal patch layer T1 (the fifth metal patch layer T5) have a relatively large width, and their equivalent inductance L1 is negligible. The gap between adjacent unit metal patches is also relatively large, and their equivalent capacitance C1 is also negligible. The metal patches in the second metal patch layer T2 (the fourth metal patch layer T4) have a relatively large width, and their equivalent inductance L2 is negligible. The equivalent capacitance C3 of the third metal patch layer T3 is mainly determined by the size of the bending gap in the y-direction. At this time, the equivalent circuit of the unit structure can be simplified as shown in Figure 8. The equivalent circuit is simulated using ADS simulation software. C2=0.194pF8, h2=2mm, L3=0.699nH, and C3=1.641pF are adjusted. The simulation results are shown in Figure 5. The results show that a third-order resonance with a wide passband and a good steep drop coefficient is also formed.

[0036] Therefore, this invention can achieve a wider passband and lower insertion loss transmission of electromagnetic waves when incident at a large angle on a frequency-selective surface, and can individually control the operating frequency and bandwidth of TE and TM polarized electromagnetic waves.

[0037] Furthermore, regarding high angular stability: as the incident angle of electromagnetic waves increases, the transmission performance of frequency selective surfaces for both TE-polarized and TM-polarized electromagnetic waves changes, but the trends of change for the two polarizations are different. Existing frequency selective surfaces generally design the unit structure as a square and use a rotationally symmetric structure to achieve dual polarization. Under TE and TM polarization, their equivalent circuits are exactly the same. This means that when the design parameters are optimized to make the electromagnetic waves of one polarization have high angular stability, the angular stability of the other polarization will deteriorate, making it difficult to achieve high angular stability under dual polarization. In this invention, by designing the unit structure as a rectangle (top view along the Z direction) and adopting different structural designs in the x and y directions, it presents different equivalent circuits under TE and TM polarization. By first adjusting parameters such as dx, h1, w2, l2, s2, w6 to optimize TM polarization, and then adjusting parameters such as dy, h2, w1, l1, s1, l3 to optimize TE polarization, it can achieve high angular stability under dual polarization. At the same time, the transmission zeros of the two polarizations, TE and TM, can be controlled separately to adjust the position of their passbands, thereby realizing flexible design of transmission frequency bands.

[0038] The beneficial effects of the present invention will be explained in detail below with reference to simulation tests.

[0039] Based on the inventive design of the unit structure in this invention, the transmission zeros of the two polarizations, TE and TM, can be controlled separately by changing the size parameters without changing the overall shape of the unit structure, thereby adjusting the position of the passband. Therefore, this invention provides two exemplary embodiments with completely identical overall shapes of the unit structure, differing only in the specific geometric size parameters, as shown in Table 1.

[0040] Table 1 Geometric Dimension Parameters

[0041]

[0042] Figure 10 shows the S-parameter simulation results of Example 1 when electromagnetic waves are incident at different angles. In Figure 10(a), the S-parameter simulation results are for TE polarization, and in Figure 10(b), the S-parameter simulation results are for TM polarization. S11-0° represents the reflection coefficient of port 1 when the incident angle is perpendicular; S11-35° represents the reflection coefficient of port 1 when the incident angle is 35°; S11-70° represents the reflection coefficient of port 1 when the incident angle is 70°; S21-0° represents the transmission coefficient from port 1 to port 2 when the incident angle is perpendicular; S21-35° represents the transmission coefficient from port 1 to port 2 when the incident angle is 35°; S21-70° represents the transmission coefficient from port 1 to port 2 when the incident angle is 70°. It can be seen that when electromagnetic waves are incident perpendicularly, the transmission band with a transmission coefficient of -3dB or higher for TE polarization is 4.38-6.35 GHz, with a minimum insertion loss of 0.51dB at 5.9 GHz; the transmission band with a transmission coefficient of -3dB or higher for TM polarization is 4.42-6.45 GHz, with a minimum insertion loss of 0.47dB at 5.36 GHz; when incident at 0°-70°, the transmission band with a transmission coefficient of -3dB or higher for TE polarization is 4.47-6.32 GHz, and the transmission band with a transmission coefficient of -3dB or higher for TM polarization is 4.67-6.45 GHz. Comparing Figure 10(a) and Figure 10(b), it can be seen that both TE and TM polarization have good angular stability and good reflection characteristics for electromagnetic waves outside the passband. Three resonant points appear within the operating frequency band. The design of the high-order resonant response allows this invention to broaden the operating bandwidth while greatly improving the steep descent coefficient.

[0043] Figure 11 shows the S-parameter simulation results of Example 2 when electromagnetic waves are incident at different angles. Figure 11(a) shows the S-parameter simulation results for TE polarization, and Figure 11(b) shows the S-parameter simulation results for TM polarization. It can be seen that when the electromagnetic wave is incident perpendicularly, the transmission band with a transmission coefficient of -3dB or higher for TE polarization is 4.20-6.34GHz, and it has the lowest insertion loss of 0.42dB at 5.88GHz; the transmission band with a transmission coefficient of -3dB or higher for TM polarization is 5.59-8.07GHz, and it has the lowest insertion loss of 0.48dB at 6.34GHz; when incident at 0°-70°, the transmission band with a transmission coefficient of -3dB or higher for TE polarization is 4.34-6.34GHz, and the transmission band with a transmission coefficient of -3dB or higher for TM polarization is 5.93-8.07GHz. Comparing Figure 11(a) and Figure 11(b), it can be seen that TE polarization and TM polarization are in different transmission frequency bands, and both have good angular stability and good reflection characteristics for electromagnetic waves outside the passband.

[0044] In summary, as can be seen from Figures 10 and 11, without changing the overall structure of the unit, by simply changing the size parameters of the metal patch layer and the thickness of the foam structure layer and the dielectric structure layer, the transmission zeros of the TE and TM polarizations can be controlled separately, thereby adjusting the position of their passbands. This allows for flexible design of the transmission frequency band and reduces design costs.

[0045] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A dual-polarization frequency-selective surface with high angular stability, composed of M×N periodically arranged unit structures; characterized in that, The unit structure includes, from top to bottom, a first metal patch layer T1, a first foam structure layer P1, a second metal patch layer T2, a first dielectric structure layer J1, a third metal patch layer T3, a second dielectric structure layer J2, a fourth metal patch layer T4, a second foam structure layer P2, and a fifth metal patch layer T5; wherein, the first metal patch layer T1 and the fifth metal patch layer T5 are completely identical, the second metal patch layer T2 and the fourth metal patch layer T4 are completely identical, the first foam structure layer P1 and the second foam structure layer P2 are completely identical, and the first dielectric structure layer J1 and the second dielectric structure layer J2 are completely identical.

2. The dual-polarization frequency selective surface with high angular stability as described in claim 1, characterized in that, The unit structure adopts a rectangular structure, with its long side defined as the y-direction and its wide side as the x-direction; the first metal patch layer T1 adopts a first rectangular metal patch, which is set along the center, with its long side located in the y-direction and its wide side located in the x-direction, and the first metal patch layers of adjacent unit structures in the y-direction combine to form a capacitive structure.

3. The dual-polarization frequency selective surface with high angular stability as described in claim 2, characterized in that, The first metal patch layer T1 and the fifth metal patch layer T5 are respectively loaded on a dielectric substrate of the same thickness. The first metal patch layer T1 is disposed on the upper surface of the dielectric substrate, and the fifth metal patch layer T5 is disposed on the lower surface of the dielectric substrate.

4. The dual-polarization frequency selective surface with high angular stability as described in claim 1, characterized in that, The unit structure adopts a rectangular structure, with its long side defined as the y-direction and its wide side as the x-direction; the second metal patch layer T2 adopts a second rectangular metal patch, which is set along the center, with its long side located in the x-direction and its wide side located in the y-direction, and the second metal patch layers of adjacent unit structures in the x-direction combine to form a capacitive structure.

5. The dual-polarization frequency selective surface with high angular stability as described in claim 1, characterized in that, The unit structure adopts a rectangular structure, with its long side defined as the y-direction and its wide side as the x-direction; the third metal patch layer T3 adopts a rectangular metal sheet of the same size as the unit structure, and the rectangular metal sheet has a bent slit with a width of s1 etched along the midline of the x-direction and a bent slit with a width of s2 etched along the midline of the y-direction. Both bent slits are 180° rotationally symmetrical about the geometric center of the rectangular metal sheet.

6. The dual-polarization frequency selective surface with high angular stability as described in claim 1, characterized in that, Both M and N are integers greater than or equal to 2.

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