Transmission / reflection mode reconfigurable frequency selection wave absorber applied to C / X wave band

Abstract

The invention provides a transmission / reflection mode reconfigurable frequency selection wave absorber applied to a C / X wave band, which is composed of units arranged periodically, and each unit comprises a loss type frequency selection surface layer, an air layer and a reconfigurable lossless frequency selection surface layer from top to bottom, the loss-type frequency selection surface layer is used for generating two broadband absorption bands in a C wave band and an X wave band, a narrow-band low-loss transmission window is formed between the two broadband absorption bands, a 2.5-dimensional integrated design that an upper layer metal pattern and a lower layer metal pattern are orthogonally arranged and share a central capacitor element is adopted, and the loss-type frequency selection surface layer is of an up-down symmetrical and left-right symmetrical structure; the reconfigurable lossless frequency selection surface layer is used for achieving electric control switching of working modes and comprises a second dielectric substrate, a third dielectric substrate, a top layer metal pattern, a middle layer metal pattern and a bottom layer metal pattern, and the bottom layer metal pattern is located on the lower surface of the third dielectric substrate and is a reconfigurable metal pattern loaded with a PIN diode.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic wave propagation and reception, and relates to a reconfigurable dual-mode frequency selective rasorber (FSR) structure design. The application is applied to a multi-station radar stealth antenna cover, operates in a C band and an X band, and has wide absorption bands, high absorption rates and reconfigurable transmission / reflection characteristics. BACKGROUND

[0002] With the rapid development of modern electronic warfare and radar detection technology, the battlefield electromagnetic environment is becoming increasingly complex, and the effectiveness of traditional radar countermeasures is severely challenged. High-value military platforms are facing the threat of coordinated detection from multi-station / distributed radar systems, and their survivability is severely restricted. Therefore, developing a new type of antenna cover structure that can have both low observability (stealth) and self-communication / detection functions is of great national defense significance for improving the all-around survivability and situational awareness of combat platforms.

[0003] As a kind of spatial electromagnetic filter, the frequency selective surface (FSS) can selectively transmit or reflect electromagnetic waves according to frequency. It was early applied to antenna covers to realize the functions of in-band wave transmission and out-band stealth. Its principle is to reduce the radar cross section (RCS) by reflecting the out-band electromagnetic waves to non-threatening directions. However, under the multi-station radar system, these directionally reflected electromagnetic waves are easily captured by other receiving stations in different directions, thereby exposing the target position and significantly reducing the stealth effectiveness. On the other hand, although the traditional electromagnetic absorber can achieve wideband absorption and RCS reduction by dissipating incident wave energy, it will seriously block the normal radiation and reception of the built-in antenna, making it difficult to meet the compatibility requirements of communication and detection.

[0004] To solve the above-mentioned contradiction, the frequency selective rasorber (FSR) emerges as the times require. The FSR is usually composed of a lossy frequency selective layer and a lossless frequency selective layer, and its core function is to realize low-loss transmission of electromagnetic waves in a specific passband, while realizing high-efficiency electromagnetic absorption in the stopband on both sides or a single side of the passband. According to the relative position of the passband and the absorption band in the frequency spectrum, the FSR can be mainly divided into three types: transmission-absorption (T-A) type, absorption-transmission (A-T) type and absorption-transmission-absorption (A-T-A) type. Among them, the A-T-A type FSR has an absorption band on both sides of the passband, which can more effectively suppress out-of-band scattering and realize a lower-loss in-band transmission window. At the same time, its structure is usually more conducive to realizing low-profile design and frequency tuning, so it has significant advantages and wider application prospects in the field of radar stealth antenna covers.

[0005] However, the existing A-T-A type FSR, especially the design for the key military frequency bands such as C-band and X-band, still faces several technical bottlenecks: first, most designs are passive fixed structures, and once the processing is completed, the electromagnetic properties (passband and absorption band) cannot be changed, lacking the flexibility of reconfiguration to deal with dynamic electromagnetic threats and complex task scenarios; second, in order to realize wide-frequency absorption and high-performance transmission, the size of the structural unit is usually large, which is not conducive to conformal and integrated applications; third, the existing reconfigurable FSR research mostly focuses on the switching between “transmission” and “absorption” states, lacking the ability to actively switch between “transmission” and “reflection” modes in the same core frequency band. The lack of this mode switching capability limits its application in advanced tactical scenarios that require active electromagnetic deception, cooperative communication or thermal management control. Therefore, developing a dual-mode reconfigurable FSR that works in C / X-band, has miniaturization characteristics, and can actively and flexibly reconfigure its transmission and reflection characteristics in the same frequency band has become a key direction that needs to be broken through in this technical field. SUMMARY

[0006] In order to overcome the defects of the existing frequency selective absorber (FSR) structure, such as fixed function, unable to dynamically respond to complex electromagnetic environment, and difficult to balance wide absorption, low loss transmission and miniaturization design in C and X bands, the present application aims to provide a reconfigurable dual-mode frequency selective absorber structure. The structure not only realizes wideband efficient absorption and low insertion loss transmission in C and X bands, but also can switch between A-T-A and A-R-A working modes in the same center frequency band through electrical control, thereby significantly improving the adaptability and survivability of radar stealth antenna cover in complex battlefield environment.

[0007] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is: A transmission / reflection mode reconfigurable frequency selective absorber applied to C / X band, composed of periodically arranged units, each unit including a lossy frequency selective surface layer, an air layer and a reconfigurable lossless frequency selective surface layer from top to bottom, characterized in that the lossy frequency selective surface layer is used to generate two wideband absorption bands in C and X bands, and form a narrowband low-loss transmission window between the two wideband absorption bands, adopting a 2.5-dimensional integrated design of orthogonal arrangement of upper and lower metal patterns and sharing a central capacitor element, with upper and lower symmetry and left and right symmetry structure; the air layer 7 is located between the lossy frequency selective surface layer and the reconfigurable lossless frequency selective surface layer; The reconfigurable lossless frequency selective surface layer is used to realize electrical control switching of working mode, including a second dielectric substrate 8, a third dielectric substrate 9, and a top layer metal pattern 3, a middle layer metal pattern 4 and a bottom layer metal pattern 5, the bottom layer metal pattern 5 is located below the third dielectric substrate 9, and is a reconfigurable metal pattern loaded with a PIN diode 26, the reconfigurable metal pattern includes a gear-shaped patch 25 in the middle and four arrow-shaped patches 24 at the four corners, and the gear-shaped patch 25 and each arrow-shaped patch 24 are connected through the PIN diode 26; the direct current biasing network of the reconfigurable lossless frequency selective surface layer includes a top layer biasing line 19 and a middle layer biasing line 22 arranged in the top layer metal pattern 3 and the middle layer metal pattern 4 respectively, a metal via hole 20 and a metal blind hole 21 located at the edge of the top layer metal pattern 3; the on-off state of the PIN diode is controlled by an external direct current power supply through the direct current biasing network.

[0008] Furthermore, when a reverse bias is applied to the PIN diode to put it in the OFF state, the reconfigurable lossless frequency selective surface layer exhibits high impedance near the transmission center frequency, which works in conjunction with the upper layer of the lossy frequency selective surface layer to form a low insertion loss transmission window. At this time, the frequency selective absorber operates in ATA mode. When a forward bias is applied to the PIN diode to put it in the ON state, the reconfigurable lossless frequency selective surface layer forms a high reflection window near the reflection center frequency. At this time, the frequency selective absorber operates in ARA mode.

[0009] Furthermore, the top metal pattern 3 of the reconfigurable lossless frequency selection surface layer is located on the upper surface of the second dielectric substrate 8 and is a wide cross-shaped metal ring 18; the middle metal pattern 4 is connected between the second dielectric substrate 8 and the third dielectric substrate 9 and is a grid-shaped metal patch 23.

[0010] Furthermore, the lossy frequency selective surface layer includes a first dielectric substrate 6 and an upper metal pattern 1 and a lower metal pattern 2 fabricated on its upper surface and lower surface, respectively. The upper metal pattern 1 includes a slot-shaped capacitor 12 located in the middle and two pairs of interconnected square metal patches 11 located on both sides of the slot-shaped capacitor 12. The two pairs of square metal patches 11 are connected to the same side plate of the slot-shaped capacitor 12. Two L-shaped meandering inductors 15 extend from the two pairs of square metal patches 11 to both sides. A lumped resistor 14 and an S-shaped meandering inductor 10 are provided on the L-shaped meandering inductor 15. Two parallel slot capacitors 13 perpendicular to the direction of their plates are respectively provided on both sides of the slot-shaped capacitor 12. The S-shaped meandering inductor 10 of the upper metal pattern is connected in parallel with the parallel slot capacitors 13 of the lower metal pattern 2 through capacitor metal vias 16 and inductor metal vias 17 penetrating the first dielectric substrate 6, thereby forming a parallel LC resonant circuit in three-dimensional space.

[0011] Furthermore, the lumped resistor 14 is positioned near the end, and the S-shaped meandering inductor 10 is positioned at the edge of the cell.

[0012] Furthermore, the thicknesses of the first dielectric substrate 6, the second dielectric substrate 8, and the third dielectric substrate 9 are adjusted between 0.4 mm and 3 mm depending on the materials used.

[0013] The features and beneficial effects of this invention are: 1. Compared with existing FSRs that have fixed functions or only switch in frequency domain separation mode (such as XU YX, WU WW, SHI QZ, et al. Design of miniaturized and highly selective frequency selective rasorber based on compact spiral resonator [J]. Electronics Letters, 2024, 60(21).), this invention breaks through the traditional design paradigm and realizes active electronic control switching between the two working modes of "ATA" and "ARA" in the same core frequency band (about 7.8GHz) of C-band and X-band.

[0014] 2. This invention, through an innovative orthogonal shared structure and 2.5D resonant design, excites multiple resonant points in the C-band and X-band, achieving broadband absorption superior to similar designs (such as WANG M, XIANG Z, LI Y, et al. Active Frequency-Selective Rasorber With Switchable Dual Operating Modes [J]. IEEE Antennasand Wireless Propagation Letters, 2024, 23(10): 3178-82.). Full-wave simulations show that in the 4.42-7.12 GHz and 8.56-10.7 GHz frequency bands, the absorption rate (A = 1 - |S 11 | 2 - |S 21 | 2 All are better than 90%.

[0015] 3. By employing a shared central capacitor across upper and lower layers and a 2.5-dimensional resonant structure, this invention achieves the aforementioned excellent broadband performance while compressing the unit cell period size to 8.5 mm. Calculated at the lowest absorption frequency of 4.42 GHz, its electrical size is only 0.12 mm. λ LIt is superior to existing miniaturized designs of the same type (such as BAKSHI SC, MITRA D, TEIXEIRA F L. Multifunctional Frequency Selective Rasorber With Dual Mode and Continuous Tunability [J]. IEEE Transactions on Antennas and Propagation, 2021, 69(9):5704-15.). Attached Figure Description

[0016] Figure 1 This is a three-dimensional exploded view of a unit of the present invention, showing the relative positional relationship of the lossy frequency selective surface layer, the air layer, and the reconfigurable lossless frequency selective surface layer.

[0017] Figure 2 This is a schematic diagram of the planar structure of the upper metal pattern 1 of the loss-type frequency selective surface layer of the present invention.

[0018] Figure 3 This is a front view of the top metal pattern 3 unit in the reconfigurable lossless frequency selective surface layer of the present invention.

[0019] Figure 4 This is a front view of the unit of the middle layer metal pattern 4 in the reconfigurable lossless frequency selection surface layer of the present invention.

[0020] Figure 5 This is a front view of the unit of the bottom metal pattern 5 in the reconfigurable lossless frequency selection surface layer of the present invention.

[0021] Figure 6 This is a schematic diagram showing the key dimensions of the upper metal pattern 1 of the loss-type frequency selective surface layer described in this invention.

[0022] Figure 7 This is a schematic diagram showing the unit structure dimensions of the top metal pattern 3 in the reconfigurable lossless frequency selection surface layer described in this invention.

[0023] Figure 8 This is a schematic diagram showing the unit structure dimensions of the intermediate metal pattern 4 in the reconfigurable lossless frequency selection surface layer described in this invention.

[0024] Figure 9 This is a schematic diagram showing the unit structure dimensions of the bottom metal pattern 5 in the reconfigurable lossless frequency selection surface layer described in this invention.

[0025] Figure 10 The return loss (|S) obtained by simulation of the FSR structure described in this invention in ATA mode.11 |) Frequency response curve.

[0026] Figure 11 The insertion loss (|S) obtained by simulation of the FSR structure described in this invention in ATA mode. 21 |) Frequency response curve.

[0027] Figure 12 The return loss (|S) obtained by simulation of the FSR structure described in this invention in ARA mode. 11 |) Frequency response curve.

[0028] Figure 13 The insertion loss (|S) obtained by simulation of the FSR structure described in this invention in ARA mode. 21 |) Frequency response curve.

[0029] Figure 14 This is the absorption rate curve obtained by simulating the FSR structure described in this invention in ATA mode.

[0030] Figure 15 This is the absorption rate curve obtained by simulating the FSR structure described in this invention in ARA mode.

[0031] Among them, 1. Upper metal pattern, 2. Lower metal pattern, 3. Top metal pattern, 4. Middle metal pattern, 5. Bottom metal pattern, 6. First dielectric substrate, 7. Air layer, 8. Second dielectric substrate, 9. Third dielectric substrate, 10. S-shaped meandering inductor, 11. Square metal patch, 12. Slot capacitor, 13. Parallel slot capacitor, 14. Lumped resistor, 15. L-shaped meandering inductor, 16. Capacitor metal via, 17. Inductor metal via, 18. Wide cross-shaped metal ring, 19. Top bias line, 20. Metal via, 21. Metal blind via, 22. Middle layer bias line, 23. Grid-shaped metal patch, 24. Arrow-shaped patch, 25. Gear-shaped patch, 26. PIN diode. Detailed Implementation

[0032] The purpose of this invention is to overcome the problems of existing frequency-selective absorber structures having fixed functions, being unable to respond in dynamic electromagnetic environments, and being difficult to simultaneously achieve broadband high absorption rate, low-loss transmission, and miniaturized design in the C-band and X-band. This invention provides a dual-mode frequency-selective absorber structure with reconfigurable characteristics. This invention proposes a novel frequency-selective absorber that operates in both the C-band and X-band, and can flexibly switch between two operating modes—"absorption-transmission-absorption" and "absorption-reflection-absorption"—within the same core frequency band via electronic control. While achieving high absorption rate, it can also provide good transmission or reflection effects as needed.

[0033] This frequency-selective absorber consists of periodically arranged units, each comprising a lossy frequency-selective surface (AFSS) layer, an air layer, and a reconfigurable lossless frequency-selective surface (FSS) layer. The AFSS layer's dielectric substrate features geometrically identical but spatially orthogonally arranged metal patterns on both sides. This design enhances the structure's dual-polarization response and facilitates miniaturization. Its central patch, meandering line structure, and lumped resistors together form a resonant and lossy circuit. A slot capacitor connected to the other side via metal vias constitutes a 2.5-dimensional resonant unit, crucial for achieving broadband absorption and generating a transmission window. The reconfigurable lossless frequency-selective surface layer consists of three metal layers and two dielectric substrate layers, with a PIN diode and corresponding DC bias network integrated at the bottom layer. By controlling the diode's on / off state, the equivalent impedance of this layer at the target point (approximately 7.8 GHz) can be altered, resulting in high impedance (open circuit) or low impedance (short circuit) characteristics, thus controlling the entire structure to behave as a transmission or reflection window at that frequency.

[0034] The loss-type frequency-selective surface layer is used to generate two broadband absorption bands in the C-band and X-band, and to form a narrow-band low-loss transmission window between these two absorption bands. This layer employs a 2.5D integrated design with two orthogonally arranged upper and lower metal patterns sharing a central capacitor element, effectively reducing the electrical size of the unit. Specifically, this layer consists of a first dielectric substrate 6 and upper and lower metal patterns 1 and 2 fabricated thereon. The first dielectric substrate 6 is made of Rogers RO4003 material, which has a relative permittivity of [missing information]. ε r1 It is 3.55, and the thickness is... h 1 is 0.8 mm. The upper metal pattern 1 includes four square metal patches 11, a slotted capacitor 12, an L-shaped meandering inductor 15 extending from two opposite sides of the patch, a lumped resistor 14 connected to the end of the meandering line, and an S-shaped meandering inductor 10 located at the edge of the unit. The planar geometry of the lower metal pattern 2 is exactly the same as that of the upper metal pattern 1, but it is rotated 90 degrees around the z-axis. The upper S-shaped meandering inductor 10 is connected in parallel with the parallel slotted capacitor 13 of the lower metal pattern 2 through the capacitor metal via 16 and the inductor metal via 17 penetrating the first dielectric substrate 6, thus forming a 2.5-dimensional parallel LC resonant circuit in three-dimensional space. The lumped resistor 14 has a resistance of 300 ohms, uses a 0402 standard package, and is a key component for realizing electromagnetic energy dissipation.

[0035] The air layer 7 is located between the lossy frequency selective surface layer and the reconfigurable lossless frequency selective surface layer, and its thickness is... tThe thickness is 5.0 mm. The introduction of this air layer is used to precisely adjust the electromagnetic coupling strength and phase relationship between the lossy frequency selective surface layer and the reconfigurable lossless frequency selective surface layer, and to optimize the impedance matching of the overall structure. It is one of the key design parameters for achieving broadband absorption and narrowband transmission / reflection performance.

[0036] The reconfigurable lossless frequency selective surface layer is the core module for realizing the electronically controlled switching of the operating mode. It consists of a second dielectric substrate 8, a third dielectric substrate 9, and a top metal pattern 3, a middle metal pattern 4, and a bottom metal pattern 5 fabricated thereon. Both the second dielectric substrate 8 and the third dielectric substrate 9 are made of F4B material, with a relative permittivity of [missing information]. ε r2 It is 2.65, and the thickness is... h Both are 1.0 mm. The top layer metal pattern 3 is fabricated on the upper surface of the second dielectric substrate 8 and is a wide cross-shaped metal ring 18. The middle layer metal pattern 4 is fabricated between the second dielectric substrate 8 and the third dielectric substrate 9 and is a grid-shaped metal patch 23. The bottom layer metal pattern 5 is fabricated on the lower surface of the third dielectric substrate 9 and is a reconfigurable metal pattern with a PIN diode 26 loaded on it. The arrow-shaped patch 24 and the gear-shaped patch 25 are connected by the PIN diode 26. In addition, this layer also integrates an independent DC bias network, which includes a top layer bias line 19, a middle layer bias line 22, a metal via 20, and a metal blind via 21 arranged on the top layer metal pattern 3 and the middle layer metal pattern 4.

[0037] The on / off state of the PIN diode is controlled by an external DC power supply through the bias network. When a reverse bias voltage is applied to the PIN diode to put it in the off state, the reconfigurable lossless frequency selective surface layer at the center frequency... f T The high impedance near 7.8 GHz, combined with the upper lossy frequency selective surface layer, forms a low insertion loss transmission window, at which point the entire frequency selective absorber operates in ATA mode. When a forward bias is applied to the PIN diode to turn it on, the reconfigurable lossless frequency selective surface layer at the center frequency... f R (Also around 7.8 GHz) it exhibits a low impedance close to a short circuit, equivalent to a metal ground plane, forming a high reflection window, at which point the entire structure operates in ARA mode.

[0038] The working principle of this invention is explained in detail based on transmission line theory and impedance matching principle. The characteristic impedance of free space is denoted as Z0, and the equivalent input impedance of the loss-type frequency selective surface (AFSS) layer at the air interface is denoted as Z. AThe equivalent input impedance of the reconfigurable lossless frequency selective surface (FSS) layer is denoted as Z. L The electric length of the air layer is denoted by θ, where θ = βt and β = 2π / λ is the phase constant. t Let Z be the air layer thickness. The entire FSR structure can be considered as a two-port network, and its ABCD matrix can be derived from Z. A Z L And θ is derived. Based on transmission line theory, the reflection coefficient |S 11 |and transmission coefficient|S 21 | can be represented as relating to Z0, Z A Z L The function of θ is determined by the transmission matrix of the cascaded network.

[0039] In the absorption band, to achieve efficient absorption, the transmission coefficient |S| is required to be high. 21 | Approaching 0, this is achieved through the design of a reconfigurable lossless frequency-selective surface layer equivalent impedance Z. L This is achieved by approaching 0 (i.e., the layer is equivalent to an ideal ground plane). Simultaneously, to achieve perfect absorption (i.e., the reflectance coefficient |S0)... 11 (approaching 0), the surface layer impedance Z needs to be selected for the lossy frequency. A Achieving conjugate matching with the input impedance of the air-ground plane composite structure viewed from this layer. In Z... L When = 0, the matching condition simplifies to: in j Imaginary unit. This condition indicates that by precisely designing the structure of the loss-mode frequency-selective surface layer and the thickness of the air layer, so that its equivalent impedance satisfies the above complex relationship at the absorption frequency, complete absorption of electromagnetic energy can be achieved.

[0040] Within the transmission band of the ATA mode, the reflection coefficient |S| is required to be... 11 |Approaching 0 and the transmission coefficient|S 21 | approaches 1 to achieve low-loss transmission of electromagnetic waves. This requires both the lossy frequency selective surface layer and the reconfigurable lossless frequency selective surface layer to exhibit extremely high impedance at that frequency, i.e., Z0. A Approaching infinity and Z L Approaching infinity (i.e., both layers of the structure are in a parallel resonant state, exhibiting open-circuit characteristics). At this point, electromagnetic waves can penetrate the entire structure with almost no reflection.

[0041] Within the reflection band of the ARA mode, the reflection coefficient |S| is required to be... 11 |Approaching 1 and the transmission coefficient|S 21 | Approaching 0, to achieve total reflection of electromagnetic waves. This is achieved by making the reconfigurable lossless frequency selectable surface layer equivalent impedance ZL Approaching 0 (i.e., the layer is in a short-circuit state), while simultaneously selecting the surface layer impedance Z for the loss-type frequency. A This is achieved by significantly deviating from the aforementioned conjugate matching condition. In this case, the structure is equivalent to a metallic ground plane at the target frequency, and the incident wave is mostly reflected.

[0042] The lossy frequency selection surface layer has a center transmission frequency. f T (Corresponding to ATA mode) or center reflection frequency f R (Corresponding to ARA mode) It mainly depends on its own resonant characteristics and the coupling of the air layer. By adjusting the geometric parameters of the 2.5D meandering line structure and the size of the center patch, its equivalent inductance and capacitance can be controlled, thereby satisfying Z at a specific frequency (approximately 7.8GHz). A The condition approaches infinity. Simultaneously, by controlling the on / off state of the PIN diode, the impedance state (Z0) of the reconfigurable lossless frequency selectable surface layer at the same frequency point can be switched. L Approaching infinity or Z L (Approaching 0), thereby enabling the overall structure to dynamically switch between ATA mode and ARA mode.

[0043] This invention integrates reconfigurable functionality into a reconfigurable lossless frequency selective surface layer based on the aforementioned impedance design principle. By utilizing the broadband absorption and frequency selectivity characteristics of the lossy frequency selective surface layer, a novel frequency selective absorber with broadband high absorption in both the C-band and X-band, and capable of flexibly and reliably switching between transmission and reflection modes within the same core frequency band, is finally realized.

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] This invention relates to a novel reconfigurable frequency-selective absorber structure for low-observable radomes in multi-station radars, as shown in the attached figure. Figure 1As shown, the overall structure comprises three parts: a lossy frequency selective surface layer, an air layer 7, and a reconfigurable lossless frequency selective surface layer. The lossy frequency selective surface layer consists of an upper metal pattern 1, a lower metal pattern 2, and a first dielectric substrate 6 sandwiched between them. The reconfigurable lossless frequency selective surface layer consists of a top metal pattern 3, a middle metal pattern 4, a bottom metal pattern 5, a second dielectric substrate 8, and a third dielectric substrate 9. Each metal layer is a copper-clad layer with a thickness of 1 ounce (1 oz refers to the weight of a uniform copper foil on a 1 square foot area of ​​28.35 g; the average thickness of the copper foil is expressed in terms of weight per unit area. This is well known in the art). The thicknesses of the first dielectric substrate 6, the second dielectric substrate 8, and the third dielectric substrate 9 can be adjusted between 0.4 mm and 3 mm depending on the selected materials; specific preferred values ​​are given in this embodiment.

[0046] In this invention, the first dielectric substrate 6 of the loss-type frequency selective surface layer preferably has a relative permittivity. ε r Rogers RO4003 material with a relative permittivity of 3.55. The second dielectric substrate 8 and the third dielectric substrate 9 of the reconfigurable lossless frequency-selective surface layer preferably have a relative permittivity of 3.55. ε r =2.65 F4B material. The entire FSR consists of multiple elements arranged periodically in a two-dimensional plane to form an infinitely large array. From Figure 1 As can be seen, the projection of a single unit onto the xoy plane is a square, with a period P of 8.5 mm. An air layer 7, with optimized thickness, exists between the lossy frequency selective surface layer and the reconfigurable lossless frequency selective surface layer.

[0047] The 3D coordinate settings are as follows: Figure 1 As shown, the input port uses a 50-ohm standard coaxial external antenna horn to excite a plane wave in the far field. Input port one is located at... xoy Plane perpendicular z On the positive axis direction, output port two is set at the same level as the axis. xoy Plane perpendicular z In the direction of the negative axis.

[0048] Example 1 A 30×30 array FSR structure with dimensions of 255mm×255mm×7.8mm was designed. The loss-selective frequency selective surface layer uses Rogers RO4003 dielectric material, which has a loss tangent of 0.0027 and a dielectric constant of 3.55. The lossless frequency selective surface layer uses F4B dielectric material, which has a dielectric constant of 2.65. The metal surface uses 0.035mm thick copper foil with a conductivity of 5.8E+0.07S / m. The coordinate axis settings are shown in the attached figure. Figure 1As shown, the origin of the coordinate system is located at the center of the lower metal pattern 2 of the lossy frequency selective surface layer. The first high-gain horn antenna (not shown in the figure) is used as input port one, and its position is set at... xoy Plane perpendicular z The plane position is 17.5m on the axis; the second high-gain horn antenna (not shown in the figure) is used as input port two, and its position is set at the same level as... xoy Plane perpendicular z The plane position with an axis coordinate of -17.5m.

[0049] In this embodiment, the two patch planes of the lossy frequency selective surface layer are both square in shape, and the two planes are adjacent to each other. z The axis rotates 90 degrees perpendicularly, and its material is copper, with dimensions of 255mm × 255mm × 1oz (0.035mm). It consists of 900 lossy frequency-selective surface-mount units. The two patch planar unit structures are as follows: Figure 2 and Figure 6 As shown. The loss-type frequency selective surface layer has a lumped resistor with a package size of 0402, which is 1 mm long and 0.5 mm wide, and each resistor has a resistance of 300 ohms.

[0050] In this embodiment, the top metal pattern 1, middle metal pattern 2, and bottom metal pattern 3 of the reconfigurable lossless frequency selective surface layer are all square in shape, made of copper, and have dimensions of 255mm × 255mm × 1oz (0.035mm). It consists of 900 reconfigurable lossless frequency selective surface layer units. The top metal pattern 1, middle metal pattern 2, and bottom metal pattern 3 are arranged from top to bottom as follows: Figure 3 , Figure 4 and Figure 5 As shown.

[0051] In this embodiment, the first dielectric substrate 6 has a square shape, is made of Rogers RO4003, has a dielectric constant of 3.55, and has dimensions of 255mm × 255mm × 0.8mm.

[0052] In this embodiment, both the second dielectric substrate 8 and the third dielectric substrate 9 are square in shape, made of F4B, with a dielectric constant of 2.65, and have dimensions of 255mm × 255mm × 1mm.

[0053] The specific dimensions of each part in the FSR unit are as follows: Figure 6 , Figure 7 , Figure 8 and Figure 9 As shown. Among them, P =8.5mm, C 1 = 3.4 mmC 2 = 3.8mm, C 3 = 5mm C 4 = 4mm w 1 = 0.2 mm w 2 = 1mm w 3 = 0.5mm l 1 = 1.1 mm l 2 = 2.4 mm l 3 = 0.9 mm l 4 = 0.8 mm l 5 = 1.5mm l 6 = 1.45mm l 7 = 3.2mm l 8 = 4.5mm l 9 = 1.05mm g 1 = 1.2 mm g 2 = 0.5mm, g 3 = 4.9mm g 4 = 1.25mm g 5 = 1.3mm g 6 = 2mm g 7 = 1.5mm s =2.2mm, h 1 = 0.8 mm h 2 = 1mm. Therefore, the dimensions of each FSR unit are 8.5mm × 8.5mm × 7.8mm. Each FSR unit has the same composition. The single-sided loss-selective frequency selective surface metal planar unit includes a central patch structure, two series-connected meandering lines, two lumped resistors, two parallel-connected meandering lines, two slotted capacitor structures, and eight metal vias. The lossless frequency selective surface metal unit includes a wide cross-shaped metal ring 18, a grid-shaped metal patch 23, an arrow-shaped patch 24, and a gear-shaped patch 25.

[0054] In lossy frequency selective surface layer, the upper metal pattern 1 and the lower metal pattern 2 have the same component layout, but the lower metal pattern 2 is along the upper metal pattern 1. z This is obtained by rotating the axis 90 degrees. Taking the upper metal pattern 1 as an example, as follows... Figure 2 As shown, the slot capacitor 12 and the square metal patch 11 are connected to the L-shaped meandering inductor 15 and the lumped resistor 14. The S-shaped meandering inductor 10 is connected in parallel with the slot capacitor 13 on the bottom plane through the capacitor metal via 16 and the inductor metal via 17.

[0055] The top layer of the reconfigurable lossless frequency selection surface layer is a wide cross-shaped metal ring 18 with a side length of [missing information]. l 8 and l 9. The ring width is w1; The middle layer consists of a grid-shaped metal patch 23, with a parallel line spacing of... g 4; The bottom layer consists of arrow-shaped patch 24 and gear-shaped patch 25.

[0056] In this embodiment, the upper metal pattern 1, lower metal pattern 2, top metal pattern 3, middle metal pattern 4, and bottom metal pattern 5 are all made of copper-clad laminate, which can be fabricated using printed circuit board technology and prepared on the first dielectric substrate 6, second dielectric substrate 8, and third dielectric substrate 9 using chemical etching or etching methods. Figure 2 , 3 The FSR structure is shown in Figures 4 and 5. The material of the copper-clad laminate can be selected appropriately according to the application environment. To protect the metal surface, gold plating can be applied to the metal pattern. Depending on the application environment, the fabricated frequency-selective absorber structure can be further protected against environmental degradation. For example, to prevent water damage and cope with adverse environments such as acid, alkali, and salt spray, a dielectric protective film can be grown on the frequency-selective absorber structure through chemical vapor deposition.

[0057] The ATA mode return loss of the FSR structure described in this invention is |S 11 |Insertion loss|S 21 The absorption rate curves are shown below. Figure 10 , Figure 11 and Figure 14 As shown; ARA mode return loss |S 11 |Insertion loss|S 21 The absorption rate curves are shown below. Figure 12 , Figure 13 and Figure 15 As shown. Return loss |S 11 | refers to the scattering parameters measured from the input of the excitation signal at port one and the output at port one. If the return loss is |S 11 If the signal strength is below -10dB, the signal transmitted back to port one via the FSR structure proposed in this invention is relatively low, indicating that the FSR structure proposed in this invention has excellent noise reflection suppression capabilities. Insertion loss |S 21 | refers to the scattering parameters measured at port 2 when the excitation signal is input at port 1. If the insertion loss |S 21 If the signal transmission through the FSR structure proposed in this invention reaches port two with almost no loss (above the industry limit of -3dB), it demonstrates that the FSR structure proposed in this invention has excellent in-band transmission capability. Figure 10 and Figure 11 As shown, in ATA mode, the return loss |S 11The curve consistently maintains a value no higher than -10dB within the 4.38GHz-10.86GHz frequency band, indicating that this invention can effectively suppress the reflected signal intensity in the C-band and X-band. Simultaneously, the insertion loss |S 21 The curve consistently maintains a value no lower than -1dB within the 7.56GHz-8.02GHz frequency band, indicating that the present invention can effectively guarantee signal transmission performance within the passband. For example... Figure 12 and Figure 13 As shown, in ARA mode, the insertion loss |S 21 The curve consistently maintains a value no higher than -10dB within the 4GHz-12GHz frequency band, indicating that this invention can effectively suppress the transmitted signal intensity in the C-band and X-band. Simultaneously, the return loss |S 11 The curve consistently maintains a value no lower than -3dB within the 7.5GHz-8.36GHz frequency band, indicating that the present invention can effectively guarantee the signal reflection effect within the passband.

[0058] The definition of absorption rate is: Absorption = 1 - |S 11 | 2 -|S 21 | 2 Absorption refers to the absorption rate, such as Figure 14 As shown, in ATA mode, the absorption rate curve is no lower than 0.8 in the 4-7.45GHz and 9.04-10.92GHz frequency bands, indicating that the present invention can effectively absorb noise signals in the C-band and X-band, reducing noise signal reflection and transmission. Meanwhile, the absorption rate curve is no higher than 0.2 in the 7.74GHz-8.3GHz frequency band, indicating that the present invention can effectively guarantee signal transmission performance within the passband. Figure 15 As shown, in ARA mode, the absorption rate curve is not lower than 0.8 in the frequency ranges of 4.42-7.12GHz and 8.56-10.7GHz, indicating that the present invention can effectively absorb noise signals in the C-band and X-band, reducing the reflection and transmission of noise signals. At the same time, the absorption rate curve is not higher than 0.2 in the frequency range of 7.79GHz-8.41GHz, indicating that the present invention can effectively ensure the signal reflection effect in the passband range.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, alterations, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A transmission / reflection mode reconfigurable frequency-selective absorber for C / X band, comprising periodically arranged units, each unit including, from top to bottom, a lossy frequency-selective surface layer, an air layer, and a reconfigurable lossless frequency-selective surface layer, characterized in that, The lossy frequency selective surface layer is used to generate two broadband absorption bands in the C-band and X-band, and to form a narrow-band low-loss transmission window between the two broadband absorption bands. It adopts a 2.5-dimensional integrated design with two layers of metal patterns arranged orthogonally and sharing a central capacitor element, and has a symmetrical structure both vertically and horizontally. The air layer (7) is located between the lossy frequency selective surface layer and the reconfigurable lossless frequency selective surface layer. The reconfigurable lossless frequency selective surface layer is used to realize the electronically controlled switching of the working mode. It includes a second dielectric substrate (8), a third dielectric substrate (9), a top metal pattern (3), a middle metal pattern (4), and a bottom metal pattern (5). The bottom metal pattern (5) is located on the lower surface of the third dielectric substrate (9) and is a reconfigurable metal pattern loaded with PIN diodes (26). The reconfigurable metal pattern includes a gear-shaped patch (25) located in the middle and four arrow-shaped patches (24) located at the four corners. The gear-shaped patch (25) and each arrow-shaped patch (24) are connected by PIN diodes (26). The DC bias network of the reconfigurable lossless frequency selective surface layer includes a top bias line (19) and a middle bias line (22) arranged on the top metal pattern (3) and the middle metal pattern (4), a metal via (20), and a metal blind via (21) located near the edge of the top metal pattern (3). The on / off state of the PIN diode is controlled by an external DC power supply through the DC bias network.

2. The transmission / reflection mode reconfigurable frequency-selective absorber according to claim 1, characterized in that, When a reverse bias is applied to the PIN diode to put it in the OFF state, the reconfigurable lossless frequency selective surface layer exhibits high impedance near the transmission center frequency. This, in conjunction with the upper layer of the lossy frequency selective surface layer, forms a low insertion loss transmission window. In this case, the frequency selective absorber operates in ATA mode. When a forward bias is applied to the PIN diode to put it in the ON state, the reconfigurable lossless frequency selective surface layer forms a high reflection window near the reflection center frequency. In this case, the frequency selective absorber operates in ARA mode.

3. The transmission / reflection mode reconfigurable frequency-selective absorber according to claim 2, characterized in that, The top metal pattern (3) of the reconfigurable lossless frequency selective surface layer is located on the upper surface of the second dielectric substrate (8) and is a wide cross-shaped metal ring (18); the middle metal pattern (4) is connected between the second dielectric substrate (8) and the third dielectric substrate (9) and is a grid-shaped metal patch (23).

4. The transmission / reflection mode reconfigurable frequency-selective absorber according to claim 1, characterized in that, The loss-type frequency selective surface layer includes a first dielectric substrate (6) and an upper metal pattern (1) formed on its upper surface and a lower metal pattern (2) formed on its lower surface; the upper metal pattern (1) includes a slot-shaped capacitor (12) located in the middle and two pairs of interconnected square metal patches (11) located on both sides of the slot-shaped capacitor (12), the two pairs of square metal patches (11) are respectively connected to the same side plate of the slot-shaped capacitor (12), and two L-shaped meandering line inductors (11) extend from the two pairs of square metal patches (11) to both sides. 5) A lumped resistor (14) and an S-shaped meandering inductor (10) are provided on the L-shaped meandering inductor (15); two parallel slot capacitors (13) perpendicular to the direction of their plates are respectively provided on both sides of the slot capacitor (12); the S-shaped meandering inductor (10) of the upper metal pattern is connected in parallel with the parallel slot capacitor (13) of the lower metal pattern (2) through the capacitor metal through-hole (16) and the inductor metal through-hole (17) penetrating the first dielectric substrate (6), thereby forming a parallel LC resonant circuit in three-dimensional space.

5. The transmission / reflection mode reconfigurable frequency-selective absorber according to claim 1, characterized in that, The lumped resistor (14) is located near the end, and the S-shaped meandering inductor (10) is located at the edge of the cell.

6. The transmission / reflection mode reconfigurable frequency-selective absorber according to claim 1, characterized in that, The thickness of the first dielectric substrate (6), the second dielectric substrate (8) and the third dielectric substrate (9) is adjusted between 0.4 mm and 3 mm depending on the material selected.

7. The transmission / reflection mode reconfigurable frequency-selective absorber according to claim 1, characterized in that, The thickness of the air layer is 5.0 mm.

8. The transmission / reflection mode reconfigurable frequency-selective absorber according to claim 1, characterized in that, The first dielectric substrate is made of Rogers RO4003 material, which has a relative permittivity of ε r1 The dielectric constant is 3.55, and the thickness is 0.8 mm; the lumped resistor has a resistance of 300 ohms and uses a 0402 standard package; both the second and third dielectric substrates are made of F4B material, and their relative permittivity is... ε r2 The thickness is 2.65 mm and the width is 1.0 mm.

9. The transmission / reflection mode reconfigurable frequency-selective absorber according to claim 1, characterized in that, The first dielectric substrate has dimensions of 255mm × 255mm × 0.8mm; the second and third dielectric substrates are made of F4B and both have dimensions of 255mm × 255mm × 1mm.

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