Cascade type frequency selective surface with steep transition zone and wide passband

Abstract

The invention discloses a cascade frequency selective surface with a steep transition band and a wide passband. The cascade frequency selective surface sequentially comprises a frequency selective surface with a steep sideband, a honeycomb core layer and a frequency selective surface with a wide passband from top to bottom along a Z-axis direction, the frequency selective surface with the steep sideband is used for providing a frequency response characteristic of rapid roll-off at the edge of a passband to form a steep transition band; the frequency selective surface with the wide passband is used for providing a broadband wave-transparent characteristic and a broadband stop-band suppression characteristic; the honeycomb core layer is used for cascading a frequency selective surface with a steep sideband and a frequency selective surface with a wide passband; and electromagnetic coupling between the upper and lower layers of frequency selection surfaces is reduced, so that the frequency selection surface with a steep sideband and the frequency selection surface with a wide passband maintain relatively independent resonance characteristics. According to the invention, the square annular patch with central symmetry is used, and the four branches are added, so that the symmetry enables the angle to be stable, and the processing complexity is simplified.

Description

Technical Field

[0001] This invention belongs to the field of frequency selective surface design, specifically relating to a steep transition band and wide passband cascaded frequency selective surface. Background Technology

[0002] Currently, with the development of wireless communication technology, frequency selective surfaces (FSS) have been widely used in various fields such as antenna systems, electromagnetic stealth, and wireless communication systems due to their unique spatial filtering characteristics. In antenna systems, they often function in a cascaded "antenna-FSS-antenna" architecture. The FSS can transmit through specific frequency bands while effectively filtering out frequencies outside those bands, solving signal crosstalk problems in complex electromagnetic environments. In stealth aircraft radomes, they can significantly reduce the radar cross-section (RCS), greatly improving penetration and stealth capabilities. In the field of electromagnetic shielding, as a broadband absorber structure, they achieve energy absorption, suppress out-of-band radiation interference, and achieve electromagnetic compatibility.

[0003] Frequency selective surfaces (FSTs) are typically composed of repeating unit structures, each consisting of a metal patch and a dielectric substrate. The shape and size of the metal patch, the dielectric constant of the dielectric substrate, and other parameters determine the FST's frequency characteristics. When electromagnetic waves propagate onto the FST, they are reflected, transmitted, or absorbed by the metal patch. By adjusting the shape and size of the metal patch, the reflection and transmission of electromagnetic waves can be controlled, thereby achieving filtering functionality for specific frequency bands.

[0004] Frequency selective surfaces come in many types, the most common being single-layer and multi-layer surfaces. Typically, single-layer surface selective surfaces are implemented using a single dielectric substrate and a layer of metal pattern, often in simple shapes such as rings, square slots, or Y-shaped patches. Because single-layer surface selective surfaces operate based on the resonant modes of an electric field, their bandwidth and roll-off factor are not ideal. While some studies have proposed miniaturization methods or employed multi-mode resonance techniques to improve performance, they still lag significantly behind multi-layer surface selective surfaces in their ability to perform different functions across different frequency bands.

[0005] A multi-layer frequency selective surface (M-FSS) is a structure composed of multiple cascaded frequency selective surfaces. It can provide more complex frequency selectivity characteristics, such as multiple transmission or reflection bands, as well as a wider operating bandwidth and better angular stability. Compared with traditional single-layer frequency selective surfaces, multi-layer frequency selective surfaces can be designed with finer frequency response characteristics to meet more complex application requirements.

[0006] In 2024, Santhya Premdharshini Premkumar et al. from the Indian National Institute of Technology proposed a single-layer frequency selective surface based on an improved compass crosshair structure, achieving X-band bandstop and Ku-band transmission performance, while also possessing angular stability and polarization insensitivity. However, this element generates only one transmission zero, resulting in a narrow stopband bandwidth, poor suppression, and gradual sideband attenuation.

[0007] In summary, existing single-layer frequency selective surfaces have limited functionality, narrow bandwidth, low roll-off factor, and poor incident angle stability. Existing multi-layer frequency selective surfaces with wide passbands generally have wide transition bands, resulting in poor suppression of the transition band. Narrow transition band frequency selective surfaces with steep sideband characteristics generally have narrow stopbands, making it difficult to meet the suppression requirements in the low-frequency band and the wide passband requirements in the high-frequency band. Summary of the Invention

[0008] In order to overcome the shortcomings of the existing technology, the present invention aims to provide a steep transition band and wide passband cascaded frequency selective surface. The surface structure has the characteristics of excellent incident angle stability. The frequency selective surface uses a square annular patch with central symmetry and adds four branches. Its symmetry can stabilize the angle and simplify the processing complexity.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A cascaded frequency selective surface with steep transition bands and wide passbands, consisting of a frequency selective surface with steep sidebands, a honeycomb core layer, and a frequency selective surface with wide passbands, arranged sequentially from top to bottom along the Z-axis. The frequency selective surface with steep sidebands is used to provide a fast roll-off frequency response at the passband edge, forming a steep transition band; thereby significantly improving the ability to suppress adjacent interference frequency bands. The frequency selective surface with a wide passband is used to provide wideband transmission characteristics and wideband stopband suppression characteristics, ensuring that the overall structure after cascading has excellent out-of-band shielding effect while meeting the requirements of wideband transmission.

[0010] The honeycomb core layer is used to cascade a frequency selective surface with steep sidebands and a frequency selective surface with wide passbands; at the same time, its low dielectric constant characteristic is used to reduce the electromagnetic coupling between the upper and lower frequency selective surfaces, so that the two can maintain relatively independent resonance characteristics.

[0011] The geometric center of the unit with the frequency selective surface with steep sidebands and the geometric center of the unit with the frequency selective surface with wide passbands are kept coincident along the Z-axis in a direction perpendicular to the dielectric substrate. The dielectric substrate is a plane composed of the X-axis and Y-axis, which ensures that the cascaded unit structure has geometric central symmetry and ensures the consistency of electromagnetic response in both TE (transverse electric) and TM (transverse magnetic) polarization modes.

[0012] The thickness of the honeycomb core layer needs to be optimized according to the operating wavelength, typically a quarter wavelength of the center frequency or an odd multiple thereof, to act as an impedance matching layer, eliminate interlayer reflections, and ensure good impedance matching and high transmittance of the cascaded system within the passband. Since frequency selective surfaces with steep sidebands and wide passband frequency selective surfaces introduce additional reflection phase at resonance, the actual honeycomb core layer thickness needs to be phase-compensated and optimized from the theoretical value. Through full-wave electromagnetic simulation optimization, this embodiment sets the honeycomb core layer thickness to 3.95 mm.

[0013] The frequency selection surface of the steep transition zone includes a square annular metal patch layer, a dielectric substrate, a rectangular metal patch layer, and an adhesive layer arranged sequentially from top to bottom along the Z-axis direction; A square annular metal patch layer is printed on the upper surface of dielectric substrate one, and a rectangular metal patch layer is printed on the lower surface of dielectric substrate one. The square annular metal patch layer includes a square annular metal patch and four arms, and the square annular metal patch and the four arms form the same plane on the X-axis and Y-axis. The four arms are respectively perpendicularly arranged on the four sides of the square annular metal patch. The rectangular metal patch layer consists of four symmetrical rectangular patches. One end is located at the edge of the adhesive layer, and the other end is located at the bottom of the metal via. Due to the addition of these four branches, the Ku-band transmission coefficient is improved, and the passband transmittance is increased.

[0014] Four metal vias penetrate the dielectric substrate. The upper end of the metal via is located on the annular edge of the square annular metal patch layer on the upper surface, and the lower end is located on the upper surface of the end of the rectangular metal patch layer. The metal vias, the square annular metal patch layer, and the rectangular metal patch layer form a resonant structure. An adhesive layer is located between the rectangular metal patch layer and the underlying honeycomb core layer, and is used to bond and fix the frequency selective surface layer to the honeycomb core layer.

[0015] A square ring-shaped metal patch and a metal via form a resonant structure and generate a stopband. The position and suppression of the stopband can be changed by adjusting the size of the upper ring of the square ring-shaped metal patch. As the linewidth of the square ring increases, the stopband gradually moves to higher frequencies, and as the side length of the square ring increases, the stopband gradually moves to lower frequencies.

[0016] The inner wall length of the square ring-shaped metal patch is p1, and the outer wall length is p2; the length of the four arms is p3, and the width is p4; the length of the rectangular metal patch layer is p5, and the width is p6. Where p1=2.2-2.3mm, p2=4.15-4.35mm, p3=0.95-1.05mm, p4=0.12-0.3mm, p5=0.75-0.8mm, and p6=1.95-2.05mm.

[0017] The wide passband frequency selective surface includes, from top to bottom along the Z-axis, an adhesive layer two, an annular metal patch layer one, a dielectric substrate two, and an annular metal patch layer two. The second adhesive layer is located between the lower surface of the honeycomb core layer and the first annular metal patch layer; the first annular metal patch layer is printed on the upper surface of the second dielectric substrate, and the second annular metal patch layer is printed on the lower surface of the second dielectric substrate.

[0018] The first annular metal patch layer and the second annular metal patch layer are concentrically arranged, and the first annular metal patch layer and the second annular metal patch layer respectively include an outer ring and an inner ring that are concentrically arranged. The outer ring radius of the second annular metal patch layer is greater than the outer ring radius of the first annular metal patch layer, and the inner ring radius of the first annular metal patch layer is greater than the inner ring radius of the second annular metal patch layer.

[0019] The first and second annular metal patch layers provide transmission zeros. The annular layer one controls the zero near 8 GHz, and the annular layer two controls the zero near 10 GHz. Through this differentiated size design, the two independent transmission zeros are spaced appropriately apart, thus forming a continuous high-suppression stopband together in the 8-10 GHz wide frequency range.

[0020] By adjusting the radius of the upper and lower rings respectively, the positions of the two transmission zeros can be independently controlled, thereby flexibly adjusting the stopband bandwidth and out-of-band suppression of the frequency selection surface to meet the needs of different application scenarios.

[0021] The values ​​of each parameter were obtained through optimization: inner ring radius r1 = 1.25-1.35mm, outer ring radius r2 = 3.35-3.45mm for the first annular metal patch layer, and inner ring radius r3 = 1.05-1.15mm, outer ring radius r4 = 3.4-3.55mm for the second annular metal patch layer.

[0022] The beneficial effects of this invention are: This invention cascades a low-frequency wide-stopband and high-frequency wide-passband frequency-selective unit with a frequency-selective unit having a steep transition sideband. Combining the structural resonance characteristics of both, three key transmission zeros are generated in the X-band: the upper frequency-selective unit with the steep sideband utilizes a square ring, metal vias, and rectangular stubs to form an LC series resonant circuit, generating a high-Q transmission zero near 10.7 GHz, adjacent to the passband; the lower wide-passband frequency-selective unit utilizes a double-layer circular ring structure to generate two transmission zeros near 8.2 GHz and 9.8 GHz. The superposition of these three zeros enables the cascaded structure to achieve a high suppression ratio of greater than 30 dB in the X-band and a wide-passband performance of 33.3% in the Ku-band, while maintaining the steep transition band characteristics. Furthermore, the passband drift rate is only 6.8% at 40° oblique incidence under TE polarization, achieving excellent angular stability.

[0023] In this invention, the steep sideband characteristics (i.e., the rapid roll-off characteristic caused by the transmission zero being close to the passband edge) of a frequency-selective surface with steep sidebands are mainly excited by an LC series resonant structure composed of an upper square annular metal patch, a lower metal structure, and metal vias connecting the upper and lower layers. This invention employs a multi-stub design for the lower metal structure, specifically by setting four centrally symmetrical rectangular patches. This multi-stub design, without compromising the steep sideband characteristics, effectively improves impedance matching by introducing additional coupling capacitors, thereby increasing the transmission coefficient and improving passband flatness.

[0024] This invention employs a nested ring and double-layer metal patch structure on a wide passband frequency selection surface. By adjusting the diameters of the upper and lower metal rings, with the upper ring controlling the zero point near 8 GHz and the lower ring controlling the zero point near 10 GHz, multiple spaced transmission zero points are generated within the target frequency band, achieving a wide stopband and high suppression that cannot be achieved by traditional single-zero structures.

[0025] This invention employs a cascaded frequency selective surface and uses a low dielectric constant intermediate dielectric layer to reduce the coupling between the two units, allowing the two units to be designed and optimized independently, greatly simplifying the design process, and ensuring that the performance of the cascaded unit is compatible with the radiation characteristics of the two units before cascading. Attached Figure Description

[0026] Figure 1 is a three-dimensional structural schematic diagram of a frequency selective surface with steep sidebands provided in an embodiment of the present invention.

[0027] In the figure: (a) is a structural diagram of a frequency selective surface unit with steep sidebands; (b) is a schematic diagram of the upper metal patch layer of the frequency selective surface; (c) is a schematic diagram of the lower metal patch layer of the frequency selective surface.

[0028] Figure 2This is a schematic diagram of the simulation results of a frequency-selective surface with steep sidebands provided in an embodiment of the present invention.

[0029] Figure 3 is a three-dimensional structural schematic diagram of the wide passband frequency selective surface provided in an embodiment of the present invention.

[0030] In the figure: (a) is a structural diagram of the wide passband frequency selective surface unit; (b) is a schematic diagram of the upper ring patch of the wide passband frequency selective surface; (c) is a schematic diagram of the lower ring patch of the wide passband frequency selective surface.

[0031] Figure 4 This is a schematic diagram of the simulation results of the wide passband frequency selective surface provided in the embodiment of the present invention.

[0032] Figure 5 is a three-dimensional structural schematic diagram of the cascaded frequency selective surface unit structure provided in an embodiment of the present invention.

[0033] In the figure: (a) is a structural diagram of the frequency selective surface unit; (b) is a side view of the frequency selective surface unit.

[0034] Figure 6 is a schematic diagram of the simulation results of the frequency-selective surface provided in the embodiment of the present invention; Figure: (a) Simulation results of transmission coefficient under TE polarization with oblique incidence at 0-40°; (b) Simulation results of transmission coefficient under TM polarization with oblique incidence at 0-30°. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings.

[0036] As shown in Figure 1, the frequency-selective surface with steep sidebands provided in this embodiment of the invention includes: a square annular metal patch layer 1, a dielectric substrate 2, metal vias 3 penetrating the dielectric substrate, a rectangular metal patch layer 4, and an adhesive layer 5. The metal patches and metal vias form a resonant structure and generate a stopband, arranged with central symmetry to ensure the stability of the incident wave. When an electromagnetic wave is incident on the upper surface, the square annular metal patch layer 1 induces a surface current. This current flows through the four metal vias 3 penetrating the dielectric substrate 2 and couples to the four rectangular metal patch layers 4 on the lower surface. This three-dimensional structure introduces a vertical inductive component and an additional interlayer capacitance component, thereby forming a high-quality LC series resonant circuit. At 10.7 GHz, this circuit resonates strongly, exhibiting extremely low impedance, totally reflecting the incident electromagnetic wave, thus forming a deep transmission zero. The transmission coefficient curve drops rapidly at this point, achieving steep transition band characteristics.

[0037] The size of the metal patch affects the position of the zero point and the degree of suppression at the zero point. Through optimization, the size of the square ring metal patch is obtained. The inner wall length of the square ring metal patch is p1, the outer wall length is p2, the length of the four arms is p3, and the width is p4; the length of the rectangular metal patch layer 4 is p5, and the width is p6. Where p1=2.25mm, p2=4.25mm, p3=1mm, p4=0.12mm, p5=0.78mm, and p6=2mm.

[0038] like Figure 2 As shown, under TE polarization, the transmission zero point is located at 10.7 GHz with normal incidence and the suppression reaches 36 dB. Under TM polarization, the transmission zero point is located at 10.7 GHz with normal incidence and the suppression reaches 37 dB. The two curves almost overlap.

[0039] As shown in Figure 3, the wide passband frequency selective surface provided in this embodiment of the invention includes: an adhesive layer 6, an annular metal patch layer 7, a dielectric substrate 8, and an annular metal patch layer 9. The upper and lower annular layers can provide transmission zeros, and the circumference of the annulus determines the resonant frequency; as the circumference of the annulus increases, the resonant point shifts to lower frequencies. The larger radius annulus in this invention generates a resonant zero in the lower frequency band (approximately 8 GHz), while the slightly smaller radius annulus generates a resonant zero in the higher frequency band (approximately 10 GHz). The superposition of these two discrete zeros forms a wide stopband with high suppression in the 8-10 GHz range. Simultaneously, utilizing the broadband electromagnetic coupling effect between the upper and lower annulus layers, a flat and wide passband transmission characteristic is formed in the 13-18 GHz range. The values ​​of each parameter were obtained through optimization. (b) The inner ring radius r1 of the circular metal patch layer 7 is 1.3 mm and the outer ring radius r2 is 3.4 mm. (c) The inner ring radius r3 of the circular metal patch layer 9 is 1.1 mm and the outer ring radius r4 is 3.55 mm.

[0040] like Figure 4 As shown, under TE polarization, the two zeros are 8.2GHz and 9.8GHz, respectively, the 8-10GHz stopband suppression is greater than 29.79dB, and the -3dB bandwidth is 13.27-18GHz; under TM polarization, the positions of the two zeros remain unchanged, the 8-10GHz stopband suppression is greater than 30.45dB, and the -3dB bandwidth is 13.31-18GHz; the transmission coefficient curves of the two polarization modes almost overlap.

[0041] As shown in Figure 5, the steep transition band and wide passband cascaded frequency selective surface provided in this embodiment of the invention includes a frequency selective surface with steep sidebands, a honeycomb core layer 10, and a wide passband frequency selective surface. The two frequency selective surfaces are cascaded together through the honeycomb core layer to optimize the thickness of the honeycomb core layer, ensuring that the cascaded system is compatible with the radiation characteristics of both while maintaining the independent radiation characteristics of the two frequency selective surfaces.

[0042] As shown in Figure 6(a), under TE polarization, with normal incidence, the suppression at 12 GHz is 17.98 dB, the passband is 12.86–18 GHz, and the stopband suppression at 8–10 GHz is greater than 36 dB. When the incident angle increases to 40°, the passband is 13.21–18 GHz, the stopband suppression at 8–10 GHz is 28 dB, and the suppression at 12 GHz increases to 22.39 dB, with a passband variation rate of 6.80%. When the incident angle varies within the range of 10°–40°, the passband decreases with increasing incident angle, the overall transmission coefficient curve changes little, and the performance is almost unaffected. Therefore, it exhibits good angular stability in TE mode.

[0043] As shown in Figure 6(b), under TM polarization, at normal incidence, the suppression is 18.74 dB at 12 GHz, the passband is 12.88-18 GHz, and the stopband suppression is greater than 25 dB at 8-10 GHz. When the incident angle varies in the range of 10°-30°, the passband decreases with the increase of the incident angle, and the overall transmission coefficient curves almost overlap, thus exhibiting good stability in TM mode.

[0044] The materials and thicknesses of the steep transition band and wide passband cascaded frequency selection surface in this embodiment, from top to bottom, are shown in the table below: Material Thickness (mm) copper layer 0.018 Dielectric layer 2.50 copper layer 0.018 Adhesive film 0.24 honeycomb core 3.95 Adhesive film 0.24 copper layer 0.018 Dielectric layer 3.52 In the wide passband frequency selective surface of this invention, the metal pattern employs nested circular rings. To achieve multiple transmission zeros within the wide stopband, other resonant structures can also be used, such as square rings, open rings, or other combinations of patches. By rationally designing these patches on the upper and lower metal layers to generate transmission zeros at different frequencies, the invention's objective of widening the stopband and improving suppression can also be achieved.

[0045] The cascaded dielectric layer of this invention uses a honeycomb core material with a dielectric constant of 1.05. To achieve low-coupling cascading of two FSS units, it is not limited to using a honeycomb core; other materials with low dielectric constants can also be used, such as specific foam materials or other low-loss support structures. By selecting such materials of appropriate thickness, the inventive objectives of reducing inter-unit coupling and simplifying independent optimization can also be achieved.

Claims

1. A cascaded frequency selective surface with a steep transition band and wide passband, characterized in that, Along the Z-axis, from top to bottom, are a frequency selective surface with steep sidebands, a honeycomb core layer (10), and a frequency selective surface with wide passbands; The frequency selective surface with steep sidebands is used to provide a rapid roll-off frequency response at the passband edge, forming a steep transition band; The frequency selective surface with a wide passband is used to provide wideband transmittance characteristics and wideband stopband suppression characteristics; The honeycomb core layer (10) is used to cascade a frequency selective surface with steep sidebands and a frequency selective surface with wide passbands; reduce the electromagnetic coupling between the upper and lower frequency selective surfaces, and make the frequency selective surface with steep sidebands and the frequency selective surface with wide passbands maintain relatively independent resonant characteristics.

2. The steep transition band, wide passband cascaded frequency selective surface according to claim 1, characterized in that, The geometric center of the unit with the frequency selective surface with steep sidebands and the geometric center of the unit with the frequency selective surface with wide passbands are kept coincident along the Z-axis in a direction perpendicular to the dielectric substrate. The dielectric substrate is a plane composed of the X-axis and Y-axis, which ensures that the cascaded unit structure has geometric central symmetry and ensures the consistency of electromagnetic response in both TE transverse electric and TM transverse magnetic polarization modes.

3. The steep transition band, wide passband cascaded frequency selective surface according to claim 2, characterized in that, The thickness of the honeycomb core layer (10) is one-quarter of the wavelength corresponding to the center frequency or an odd multiple thereof.

4. The steep transition band, wide passband cascaded frequency selective surface according to claim 3, characterized in that, The frequency selection surface of the steep transition zone includes a square annular metal patch layer (1), a dielectric substrate (2), a rectangular metal patch layer (4), and an adhesive layer (5) arranged sequentially from top to bottom along the Z-axis. A square annular metal patch layer (1) is printed on the upper surface of dielectric substrate one (2), and a rectangular metal patch layer (4) is printed on the lower surface of dielectric substrate one (2). The rectangular metal patch layer (4) consists of four symmetrical rectangular patches, one end of which is located at the edge of adhesive layer one (5), and the other end is located at the bottom of metal through hole (3). The metal through hole (3) penetrates dielectric substrate one (2). There are four metal through holes (3), with the upper end located at the annular edge of the square annular metal patch layer (1) on the upper surface and the lower end located at the upper surface of the end of the rectangular metal patch layer (4). The metal through hole (3), the square annular metal patch layer (1), and the rectangular metal patch layer (4) form a resonant structure. The adhesive layer one (5) is located between the rectangular metal patch layer (4) and the honeycomb core layer (10) below, and is used to bond and fix the frequency selective surface layer to the honeycomb core layer (10).

5. The steep transition band, wide passband cascaded frequency selective surface according to claim 4, characterized in that, The metal patch layer (1) includes a square ring-shaped metal patch and four arms, and the square ring-shaped metal patch and the four arms form the same plane on the X-axis and Y-axis; wherein, the four arms are respectively arranged perpendicularly on the four sides of the square ring-shaped metal patch; The square ring-shaped metal patch and the metal through hole (3) form a resonant structure and generate a stopband. The position and suppression of the stopband can be changed by adjusting the size of the upper ring of the square ring-shaped metal patch. As the linewidth of the square ring increases, the stopband gradually moves to the higher frequency, and as the side length of the square ring increases, the stopband gradually moves to the lower frequency.

6. The steep transition band, wide passband cascaded frequency selective surface according to claim 5, characterized in that, The inner wall length of the square ring-shaped metal patch is p1, and the outer wall length is p2; the length of the four arms is p3, and the width is p4; the length of the rectangular metal patch layer (4) is p5, and the width is p6; Where p1 is 2.2-2.3mm, p2 is 4.15-4.35mm, p3 is 0.95-1.05mm, p4 is 0.12-0.3mm, p5 is 0.75-0.8mm, and p6 is 1.95-2.05mm.

7. A steep transition band, wide passband cascaded frequency selective surface according to claim 6, characterized in that, The wide passband frequency selective surface includes, from top to bottom along the Z-axis, an adhesive layer two (6), an annular metal patch layer one (7), a dielectric substrate two (8), and an annular metal patch layer two (9). The second adhesive layer (6) is located between the lower surface of the honeycomb core layer (10) and the first annular metal patch layer (7); the first annular metal patch layer (7) is printed on the upper surface of the second dielectric substrate (8), and the second annular metal patch layer (9) is printed on the lower surface of the second dielectric substrate (8).

8. The steep transition band, wide passband cascaded frequency selective surface according to claim 7, characterized in that, The first annular metal patch layer (7) and the second annular metal patch layer (9) are arranged concentrically, and the first annular metal patch layer (7) and the second annular metal patch layer (9) respectively include an outer ring and an inner ring arranged concentrically; The outer ring radius of the second annular metal patch layer (9) is greater than the outer ring radius of the first annular metal patch layer (7), and the inner ring radius of the first annular metal patch layer (7) is greater than the inner ring radius of the second annular metal patch layer (9). The first annular metal patch layer (7) and the second annular metal patch layer (9) provide transmission zeros. The annular ring of the first annular metal patch layer (7) is used to control the zero near 8 GHz, and the annular ring of the second annular metal patch layer (9) is used to control the zero near 10 GHz. Together, they form a continuous high-suppression stopband in the wide frequency range of 8-10 GHz.

9. A steep transition band, wide passband cascaded frequency selective surface according to claim 8, characterized in that, The inner ring radius of the metal patch layer (7) is r1=1.25-1.35mm and the outer ring radius is r2=3.35-3.45mm. The inner ring radius of the metal patch layer (9) is r3=1.05-1.15mm and the outer ring radius is r4=3.4-3.55mm.

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