Frequency selection wave absorber structure applied to C wave band and X wave band

Abstract

The invention belongs to the technical field of electromagnetic wave propagation and reception, and provides a novel high-absorptivity and good-transmission-effect miniaturized frequency selection wave absorber structure working in a C wave band and an X wave band, and the frequency selection wave absorber structure applied to the C wave band and the X wave band comprises a plurality of units, each unit is composed of a loss layer loaded with lumped resistance and a lossless frequency selective surface (FSS) layer, the loss layer, the lossless layer first layer and the lossless layer second layer are sequentially arranged from top to bottom, and air is arranged between the loss layer and the lossless layer first layer; two surfaces of a dielectric of the loss layer are of the same coupling structure which is perpendicular to each other, the center of one surface of the dielectric is provided with two rectangular chip capacitors, a winding line structure extends along the direction of a rectangular chip, and the slot type capacitor is positioned on the other plane relative to the plane of the current loss layer and is connected with part of the winding line structure through a metal via hole to form a parallel loop. The method is mainly applied to frequency selection wave absorber structure design and manufacturing occasions.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic wave propagation and reception, and relates to a frequency selective absorber (FSR) structure design with a wide absorption band, high absorptivity and a wide wave transmission band, which is applied to a multi-station radar low-detectable radome and works in the C-band and X-band. Specifically, it relates to a frequency selective absorber structure applied to the C-band and X-band. Background Art

[0002] With the rapid development of radar detection technology and the increasing complexity of the electromagnetic environment, traditional radar systems are no longer applicable, which poses a serious threat to high-value targets. It is very meaningful to design a radar antenna cover that can enhance anti-detection capabilities and low detectability as well as the stability of the communication system.

[0003] Frequency Selective Surface (FSS) can transmit or reflect incident electromagnetic waves in space and can be regarded as a spatial filter. It has excellent filtering characteristics and is widely used in many fields such as communications, optics and low detectability technology. In the early single-base station detection, FSS reduces the radar cross section (RCS) by reflecting electromagnetic waves in other directions, thereby achieving low detectability. However, the traditional FSS can only reduce the RCS of a single-station radar system. In the case of a multi-station radar system, the out-of-band electromagnetic waves reflected by the FSS are easily captured by multi-station radar detection, thereby exposing the location of the protected device. The electromagnetic absorber structure can absorb electromagnetic waves within a specific frequency range and reduce the RCS, thereby achieving low detectability. However, while the traditional electromagnetic absorber achieves low detectability in a specific band, it also affects the radiation performance of the antenna in the band. In this context, FSR is proposed as an enhanced structure based on the traditional FSS technology. Compared with traditional FSS, FSR processes electromagnetic waves in non-working frequency bands by absorption and dissipation instead of outward reflection, which solves the detection challenges brought by multi-station radars in multi-domain environments, minimizes the RCS of the antenna in all directions outside its passband, and enhances its low detectability capability.

[0004] The FSR structure usually consists of a lossy layer and a lossless FSS layer, which exhibits a nearly complete transmission characteristic for electromagnetic waves within the passband and a high absorption efficiency outside the band. According to the relative position of the passband and the absorption band, the existing FSR can be divided into three categories: transmission-absorption (TA), absorption-transmission (AT) and absorption-transmission-absorption (ATA). Compared with TA and AT FSRs, ATA FSRs have many advantages, which are mainly reflected in the following points: First, ATA FSRs have a lower profile at a lower absorption bandwidth while maintaining good transmission characteristics; second, ATA FSRs have higher selectivity and easier adjustment of the operating frequency, and a simpler structure; third, ATA FSRs are more operable and are more convenient to achieve mode switching and frequency tunability. Therefore, these advantages make the application range of ATA FSRs wider.

[0005] There are various existing ATA-type FSR structures, but there are still few FSRs working in low frequency bands, and the challenge in designing C-band and L-band FSRs is to achieve miniaturization while maintaining an effective absorption state. Summary of the invention

[0006] In order to overcome the shortcomings of the prior art and solve the problems of low absorption efficiency, poor transmission effect and insufficient miniaturization of the existing FSR structure working in the C-band and X-band, the present invention aims to propose a new miniaturized frequency selective absorber structure with high absorption rate and good transmission effect working in the C-band and X-band. To this end, the technical solution adopted by the present invention is a frequency selective absorber structure applied to C-band and X-band, including several units, each of which is composed of a lossy layer loaded with a lumped resistor and a lossless frequency selective surface FSS layer, which are composed of a total of two parts, namely a lossy layer, a first lossless layer and a second lossless layer, from top to bottom, respectively, and air is between the lossy layer and the first lossless layer; the two sides of the dielectric of the lossy layer are mutually perpendicular identical coupling structures, and the center of one side of the dielectric is two rectangular patch capacitors to increase the equivalent capacitance value of the loop, and a meandering line structure is extended along the direction of the rectangular patch to provide series inductance and parallel inductance in the loop, and the gap-type capacitor is located on another plane relative to the current lossy layer plane, and is connected to part of the meandering line structure through metal vias to form a parallel loop, and the gap direction of the gap-type capacitor is perpendicular to the gap direction between the two rectangular patch capacitors; the lossless layer is composed of two layers of dielectrics of the first lossless layer and the second lossless layer that are tightly attached, and their corresponding three-sided metal structure planes to achieve in-band transmission, and the out-of-band is equivalent to a ground plane.

[0007] The lossless frequency selective surface (FSS) layer consists of two closely attached dielectric layers and metal plane structures on three planes. It exhibits a transmission effect at the resonant frequency and a reflection effect outside the band. When the electromagnetic wave signal reaches the frequency selective absorber (FSR), a part of the out-of-band signal is absorbed and dissipated by the lossy layer, and the remaining out-band signal reaches the lossless frequency selective surface (FSS) layer, is reflected and absorbed again by the lossy layer, and then transmits through the frequency selective absorber (FSR) structure, thereby achieving frequency selective absorption and transmission.

[0008] The meandering line structure forms an inductor, the central patch forms a capacitor, and the inductor and capacitor are connected in series to resonate to form an absorption band. The absorption band exists near the frequency f1, which is given by:

[0009]

[0010] It can be seen that relatively large effective inductance and capacitance values ​​can make the LC circuit have a lower absorption band frequency range when resonance occurs, which is conducive to the miniaturization of the FSR structure. Where f1 is the center frequency of the absorption band, C1 is the total capacitance of the series loop in the lossy layer, L1 is the total inductance of the series loop in the lossy layer, and C P is the total capacitance of the parallel loop in the lossy layer, L P is the total inductance of the parallel loop in the loss layer, and a is a calculation factor.

[0011] The lossless layer is composed of a top metal structure 3, a middle metal structure 4, a bottom metal structure 5, a first lossless layer medium 8 and a second lossless layer medium 9, wherein each metal layer is a copper-clad layer with a thickness of 1 ounce; the thickness of the medium, i.e., the dielectric substrate layers 6, 8, and 9, is 0.4mm-3mm depending on the material; Rogers RO4003 dielectric material with ε=3.55 is used as the substrate; the dielectric substrate layer unit is a square dielectric surface tightly attached to the metal structure of the frequency selective absorber surface; the input port uses a 50-ohm standard coaxial cable external antenna horn far-field excitation plane wave, the input port 1 is set in the positive axis direction of the z-axis perpendicular to the xoy plane, and the output port 2 is set in the negative axis direction of the z-axis perpendicular to the xoy plane.

[0012] The top metal plane of the lossy layer has the same layout as the bottom metal plane, but the bottom plane is obtained by rotating the top plane 90 degrees along the z-axis. The center patch 11 is connected to the series loop meandering line structure 14 and connected to the lumped resistor 13. The parallel loop meandering line structure 10 is connected in parallel with the gap-type capacitor of the bottom plane through a via structure such as metal vias 15 and 16.

[0013] The top metal structure 3 is a square copper ring 17 with a side length of l5 and a ring width of w2; the middle metal structure 4 is a square empty slot patch 18 with a side length of g1; and the bottom metal structure 5 is a cross empty slot patch 19.

[0014] The characteristics and beneficial effects of the present invention are:

[0015] 1. In the present invention, the middle structure of each FSR unit adopts two mutually perpendicular patch structures, which are the common parts in the dual polarization direction, improving the dual polarization effect of the FSR structure while promoting the miniaturization of the structure. Taking the lowest absorption frequency as the standard, the electrical size of the present invention is 0.12λ L However, in the latest literature on the same type of FSR, the miniaturization of the FSR unit structure is generally insufficient (such as S.N.Shi, Z.Z.Chai, S.Zhang, Y.P.Shi, and Y.F.Zhang, "A Switchable Frequency Selective Rasorber with a Broad Transmission Window at the X-Band," Electronics, vol.12, no.18, Sep 2023, Art no.3941.).

[0016] 2. The present invention can achieve an absorption rate of more than 80% in both the C-band and the X-band and form a transmission band in the absorption band. In the 4.32GHz-7.45GHz and 9.04-12.92GHz frequency bands, the absorption rate is not less than 80%. At the same time, in the 7.7GHz-8.8GHz frequency band, the insertion loss S21 can be maintained at no less than -3dB, and in the 4.78GHz-12.2GHz frequency band, the return loss S11 is maintained at no more than -10dB. However, in the same type of FSR in the latest literature, there is no frequency selective absorber that can achieve absorption in both C-band and X-band (such as YLDai et al., "Miniaturized frequency selective rasorber with absorption in SC band and transmission in X band," Physica Scripta, vol. 98, no. 2, Feb 2023, Art no. 025506. and SN Shi, ZZ Chai, S. Zhang, YP Shi, and YF Zhang, "A Tunable Frequency Selective Rasorber with Broad Passband and Low Transmission Loss at X-Band," Materials, vol. 16, no. 17, Sep 2023, Art no. 5787.). Therefore, the present invention can form a high-efficiency absorption band in both C-band and X-band and realize a transmission passband in the band, thereby improving and enhancing the anti-interference performance of the antenna in C-band and X-band. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a side schematic diagram of the three-dimensional arrangement of the present invention.

[0018] Figure 2 It is a front schematic diagram of a unit structure on one side of the vertical double-sided structure of the lossy layer of the present invention.

[0019] Figure 3 It is a front schematic diagram of the unit structure of the top plane metal of the first layer of the medium of the lossless FSS layer of the present invention.

[0020] Figure 4 It is a front schematic diagram of a unit structure of a plane metal tightly attached between the first dielectric layer and the second dielectric layer of the lossless FSS layer of the present invention.

[0021] Figure 5 It is a front schematic diagram of the unit structure of the bottom plane metal of the second layer medium of the lossless FSS layer of the present invention.

[0022] Figure 6 It is a schematic diagram of the unit structure dimensions of one side of the vertical double-sided structure of the lossy layer of the present invention.

[0023] Figure 7 It is a schematic diagram of the unit structure size of the top plane metal of the first layer of the medium of the lossless FSS layer of the present invention.

[0024] Figure 8 It is a schematic diagram of the unit structure size of the plane metal tightly attached between the first layer of medium and the second layer of medium of the lossless FSS layer of the present invention.

[0025] Fig. 9 It is a schematic diagram of the unit structure size of the bottom plane metal of the second layer of the medium of the lossless FSS layer of the present invention.

[0026] Fig.10 It is the return loss S11 band-stop characteristic curve of the FSR structure described in the present invention.

[0027] Fig.11 It is the insertion loss S21 bandpass characteristic curve of the FSR structure described in the present invention.

[0028] Fig.12 It is the absorption rate curve of the FSR structure described in the present invention.

[0029] Among them, 1. The top metal structure of the lossy layer, 2. The bottom metal structure of the lossy layer, 3. The top metal structure of the first dielectric layer of the lossless layer, 4. The plane metal structure tightly attached between the first dielectric layer and the second dielectric layer of the lossless layer, 5. The bottom metal structure of the second dielectric layer of the lossless layer, 6. The dielectric substrate of the lossy layer, 7. The air between the lossy layer and the lossless layer, 8. The first dielectric substrate of the lossless layer, 9. The second dielectric substrate of the lossless layer, 10. The parallel loop meandering line structure, 11. The central metal patch structure, 12. The gap-type capacitor structure, 13. The lumped resistor, 14. The series loop meandering line structure, 15. The metal via, 16. The metal via. DETAILED DESCRIPTION

[0030] The purpose of the present invention is to overcome the problems of low absorption efficiency, poor transmission effect and insufficient miniaturization of the existing FSR structure working in the C band and X band, and to provide a new type of miniaturized frequency selective absorber structure with high absorption rate and good transmission effect working in the C band and X band, and to propose a new type of miniaturized frequency selective absorber FSR working in the C band and X band, which can achieve high absorption rate and maintain good transmission effect. Each unit of the frequency selective absorber is composed of a loss layer loaded with lumped resistance and a lossless frequency selective surface FSS layer. The two sides of the dielectric of the loss layer are mutually perpendicular to the same coupling structure to promote the realization of structural miniaturization. The center is a rectangular patch capacitor to increase the equivalent capacitance value of the loop. A meander line structure is extended along the direction of the rectangular patch to provide series inductance and parallel inductance in the loop. The gap capacitor is located on another plane relative to the current loss layer plane, and is connected to part of the meander line structure through a metal via to form a parallel loop. The lossless layer is composed of two closely attached dielectric layers and three corresponding metal structure planes to achieve in-band transmission, and the out-of-band is equivalent to a ground plane. In the C-band and X-band, the present invention can achieve a wider absorption band with a standard absorption rate of 80%, and can obtain a good transmission band with a standard passband depth of -3dB.

[0031] A new type of miniaturized frequency selective absorber structure that can be applied to the radar antenna cover of the anti-multi-station radar detection system is proposed. When the electromagnetic wave signal reaches the FSR structure, it will first be absorbed by the loss layer to dissipate part of the energy. The lumped resistance of the loss layer can enhance the loss effect. The meander line structure has a large inductance, and the central patch can provide a large capacitance, which can be connected in series to form an absorption band. The gap-type capacitor and the meander line structure form a parallel loop, which "short-circuit" the absorption effect at the passband frequency and achieve transmission. According to the absorption band determination formula, assuming that the absorption band exists near the frequency f1, it is:

[0032]

[0033] It can be seen that relatively large effective inductance and capacitance values ​​can make the LC circuit have a lower absorption band frequency range when resonance occurs, which is conducive to the miniaturization of the FSR structure. Where f1 is the center frequency of the absorption band, C1 is the total capacitance of the series loop in the lossy layer, L1 is the total inductance of the series loop in the lossy layer, and C P is the total capacitance of the parallel loop in the lossy layer, L P is the total inductance of the parallel loop in the loss layer, and a is a calculation factor.

[0034] The lossless FSS layer is composed of two layers of dielectrics that are close together and metal plane structures on three planes. It shows a transmission effect at the resonant frequency and a reflection effect outside the band. Its out-of-band effect is similar to that of a metal ground plane. When the electromagnetic wave signal reaches the FSR, a portion of the out-of-band signal is absorbed and dissipated by the lossy layer, and the remaining out-of-band signal reaches the lossless FSS layer, is reflected and then absorbed again by the lossy layer, and a high absorption rate is achieved through a series of absorption-reflection processes. The signal within the passband is almost unaffected and is transmitted through the FSR structure, thereby achieving frequency selective wave absorption and transmission.

[0035] The present invention is further described in detail below with reference to the accompanying drawings and specific examples.

[0036] The present invention is a novel frequency selective absorber structure design for multi-station radar low-detectable radome, as shown in the attached Figure 1 . It includes three parts: a lossy layer, an air layer 7 and a lossless layer. The lossy layer is composed of a lossy layer top metal structure 1, a lossy layer bottom metal structure 2 and a lossy layer dielectric substrate 6. The lossless layer is composed of a top metal structure 3, a middle metal structure 4, a bottom metal structure 5, a first lossless layer dielectric 8 and a second lossless layer dielectric 9. Each metal layer is a copper-clad layer with a thickness of 1 ounce. (1 oz means that the uniform copper foil weight on an area of ​​1 square foot is 28.35 g, and the weight per unit area is used to express the average thickness of the copper foil. This is well known in the art.) The thickness of the dielectric substrate layers 6, 8, and 9 varies depending on the material, generally ranging from 0.4mm to 3mm.

[0037] The present invention uses Rogers RO4003 dielectric material with ε=3.55 as the substrate; the proposed frequency selective absorber model designs a novel planar antenna cover structure based on a series of unit periodic array arrangements. Figure 1 It can be seen that the dielectric substrate unit is square (8.5mm×8.5mm), the metal structure of the frequency selective absorber surface is closely attached to the dielectric surface, and there is free space between the lossy layer and the lossless layer.

[0038] The three-dimensional coordinate settings are as follows Figure 1 As shown in the figure, the input port uses a 50-ohm standard coaxial cable external antenna horn far-field excitation plane wave, input port 1 is set in the positive direction of the z-axis perpendicular to the xoy plane, and output port 2 is set in the negative direction of the z-axis perpendicular to the xoy plane.

[0039] Example 1

[0040] A 30×30 array FSR structure with a size of 255mm×255mm×7.5mm was designed. Both the lossy layer and the lossless layer dielectrics are made of Rogers RO4003 dielectric material, which has a loss tangent of 0.0027 and a dielectric constant of 3.55. The metal surface is made of copper foil with a thickness of 0.035mm and a conductivity of 5.8E+0.07S / m. The coordinate axis settings are as shown in the attached figure. Figure 1 As shown, the coordinate origin is assumed to be located at the center of the bottom layer of the lossy layer, input port 1 is set at a plane position with a z-axis coordinate of 30.5 mm perpendicular to the xoy plane, and input port 2 is set at a plane position with a z-axis coordinate of -35 mm perpendicular to the xoy plane.

[0041] In this embodiment, the two patch planes of the lossy layer are both square in shape, and the two planes are perpendicular to each other by 90 degrees along the z-axis. The material is copper, and the size is 255mm×255mm×1oz (0.35mm). It consists of 900 lossy layers. The unit structure direction of the two patch planes is as follows: Figure 2 and Figure 6 The lossy layer is loaded with a lumped resistor with a package size of 0402 and a length of 1 mm and a width of 0.5 mm, and a single resistance of 300 ohms.

[0042] The three patch planes of the lossless layer in this embodiment are all square in shape, made of copper, and have a size of 255mm×255mm×1oz (0.35mm). It consists of 900 lossless layers. The three lossless metal planes are as follows from top to bottom: Figure 3 , Figure 4 and Figure 5 shown.

[0043] In this embodiment, the dielectric substrate 6 is in a square shape, and its material is Rogers RO4003, whose dielectric constant is 3.55, and the size of the dielectric substrate is 255 mm×255 mm×0.5 mm.

[0044] In this embodiment, the dielectric substrate 8 and the dielectric substrate 9 are both square in shape, made of Rogers RO4003, with a dielectric constant of 3.55, and the dimensions of the dielectric substrates are both 255 mm×255 mm×1 mm.

[0045] The specific dimensions of each part in the FSR unit are as follows: Figure 6 , Figure 7 , Figure 8 and Fig. 9As shown. Among them, P = 8.5mm, c1 = 3.4mm, w1 = 0.2mm, w2 = 0.4mm, r = 0.4mm, d1 = 0.15mm, l1 = 2.3mm, l2 = 1.2mm, l3 = 0.7mm, l4 = 2.8mm, l5 = 6mm, g1 = 4.5mm, g2 = 1.2mm. Therefore, the size of each FSR unit is 8.5mm × 8.5mm. The basic composition of each FSR structural unit is the same. The single-sided lossy layer metal plane unit includes an intermediate patch structure, two series loop meandering line structures, two lumped resistors, two parallel loop meandering line structures, two gap-type capacitor structures and eight metal vias. The lossless layer unit includes a copper square ring 17, a square slot patch 18 and a cross slot patch 19.

[0046] The top metal plane of the lossy layer has the same layout as the bottom metal plane, but the bottom plane is obtained by rotating the top plane 90 degrees along the z-axis. Figure 2 As shown, the central patch 11 is connected to the series loop meandering line structure 14 and to the lumped resistor 13, and the parallel loop meandering line structure 10 is connected in parallel with the gap type capacitor (same as the gap type capacitor 12) of the bottom plane through the via structure such as metal vias 15 and 16.

[0047] The top layer of the lossless layer is a square copper ring 17 with a side length of l5 and a ring width of w2; the middle layer is a square empty slot patch 18 with a side length of g1; the bottom layer is a cross empty slot patch 19 with a cross slot width of g2.

[0048] The metal layers 1, 2, 3, 4, and 5 in this embodiment are all made of copper-clad boards, which can be prepared by a printed circuit board process, and a chemical corrosion method or an etching method is used to prepare copper-clad boards on dielectric substrates 6, 8, and 9. Figure 2 , 3 , 4, and 5. The material of the copper clad laminate can be reasonably selected according to the application environment. To protect the metal surface, the metal pattern can be protected by gold plating. According to the needs of the application environment, the prepared frequency selective absorber structure can be further protected by environmental adaptability. For example, in order to waterproof, cope with adverse environments such as acid, alkali, and salt spray, the frequency selective absorber structure is chemically vapor deposited to grow a dielectric protective film layer.

[0049] The return loss S11, insertion loss S21 and absorption rate curves of the FSR structure of the present invention are as follows: Fig.10 , Fig.11 and Fig.12As shown. The return loss S11 means the signal size measured when the excitation signal is input from port 1 and output from port 1. If the return loss S11 is lower than the industry limit of -10dB, the signal transmitted back to port 1 through the FSR structure proposed in the present invention is small, indicating that the FSR structure proposed in the present invention has a good function of suppressing noise reflection. The insertion loss S21 means the signal size measured when the excitation signal is input from port 1 and output from port 2. If the insertion loss S21 is higher than the industry limit of -3dB, the signal transmitted through the FSR structure proposed in the present invention to port 2 has almost no loss, indicating that the FSR structure proposed in the present invention has a good in-band transmission function. As shown Fig.10 and Fig.11 As shown, the return loss S11 curve is always maintained at a limit value of no higher than -10dB in the frequency band range of 4.78GHz-12.2GHz, indicating that the present invention can effectively suppress the reflected signal intensity of the C-band and X-band. At the same time, the insertion loss S21 curve is always maintained at a limit value of no lower than -3dB in the frequency band range of 7.7GHz-8.8GHz, indicating that the present invention can effectively guarantee the signal transmission effect within the passband range.

[0050] The definition of absorptivity is:

[0051] Absorption=1-|S11| 2 -|S21| 2

[0052] Absorption refers to the absorption rate, such as Fig.12 As shown, the absorption rate curve is not less than 0.8 in the frequency bands of 4.32-7.45 GHz and 9.04-12.92 GHz, indicating that the present invention can effectively absorb noise signals in the C band and X band and reduce the reflection and transmission of noise signals. At the same time, the absorption rate curve is not higher than 0.2 in the frequency band of 7.9 GHz-8.5 GHz, indicating that the present invention can effectively ensure the transmission effect of signals within the passband range.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any deformation, modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A frequency selective absorber structure for use in C-band and X-band, characterized in that: The invention comprises several units, each of which is composed of a lossy layer loaded with a lumped resistor and a lossless frequency selective surface (FSS) layer. From top to bottom, they are the lossy layer, the first lossless layer and the second lossless layer, and there is air between the lossy layer and the first lossless layer. The two sides of the dielectric of the lossy layer are mutually perpendicular identical coupling structures, and the center of one side of the dielectric is two rectangular patch capacitors to increase the equivalent capacitance value of the loop, and a meandering line structure is extended along the direction of the rectangular patch to provide series inductance and parallel inductance in the loop. The gap-type capacitor is located on another plane relative to the current lossy layer plane, and is connected to part of the meandering line structure through metal vias to form a parallel loop. The gap direction of the gap-type capacitor is perpendicular to the gap direction between the two rectangular patch capacitors. The lossless layer is composed of two layers of dielectrics, the first lossless layer and the second lossless layer, which are tightly attached, and their corresponding three-sided metal structure planes to achieve in-band transmission, and the out-of-band is equivalent to a ground plane.

2. The frequency selective absorber structure for use in C-band and X-band according to claim 1, characterized in that: The lossless frequency selective surface (FSS) layer consists of two closely attached dielectric layers and metal plane structures on three planes. It exhibits a transmission effect at the resonant frequency and a reflection effect outside the band. When the electromagnetic wave signal reaches the frequency selective absorber (FSR), a part of the out-of-band signal is absorbed and dissipated by the lossy layer, and the remaining out-band signal reaches the lossless frequency selective surface (FSS) layer, is reflected and absorbed again by the lossy layer, and then transmits through the frequency selective absorber (FSR) structure, thereby achieving frequency selective absorption and transmission.

3. The frequency selective absorber structure for use in C-band and X-band according to claim 1, characterized in that: The meander line structure forms an inductor, and the central patch forms a capacitor. The inductor and capacitor resonate in series to form an absorption band. The absorption band exists near the frequency f1, and is given by: It can be seen that relatively large effective inductance and capacitance values ​​can make the LC circuit have a lower absorption band frequency range when resonance occurs, which is conducive to the miniaturization of the FSR structure. Where f1 is the center frequency of the absorption band, C1 is the total capacitance of the series loop in the lossy layer, L1 is the total inductance of the series loop in the lossy layer, and C P is the total capacitance of the parallel loop in the lossy layer, L P is the total inductance of the parallel loop in the loss layer, and a is a calculation factor.

4. The frequency selective absorber structure for use in C-band and X-band according to claim 1, characterized in that: The lossless layer is composed of a top metal structure (3), a middle metal structure (4), a bottom metal structure (5), a first lossless layer medium (8) and a second lossless layer medium (9), wherein each metal layer is a copper-clad layer with a thickness of 1 ounce; the thickness of the medium, i.e., the medium substrate layer (6), (8), (9) is 0.4 mm-3 mm depending on the material; a Rogers RO4003 medium material with ε=3.55 is used as the substrate; the medium substrate layer unit is a square medium surface tightly attached to the metal structure of the frequency selective absorber surface; the input port adopts a 50 ohm standard coaxial line external antenna horn far-field excitation plane wave, the input port (1) is arranged in the positive axis direction of the z-axis perpendicular to the xoy plane, and the output port (2) is arranged in the negative axis direction of the z-axis perpendicular to the xoy plane.

5. The frequency selective absorber structure for use in C-band and X-band according to claim 1, characterized in that: The layout of components of the top metal plane of the lossy layer is the same as that of the bottom metal plane, but the bottom plane is obtained by rotating the top plane by 90 degrees along the z-axis, the center patch (11) is connected to the series loop meandering line structure (14) and connected to the lumped resistor (13), and the parallel loop meandering line structure (10) is connected in parallel with the gap-type capacitor of the bottom plane through a via structure such as metal vias (15) and (16); The top metal structure (3) is a square copper ring (17) with a side length of l5 and a ring width of w2; the middle metal structure (4) is a square empty slot patch (18) with a side length of g1; and the bottom metal structure (5) is a cross empty slot patch (19).

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