Band-pass type active frequency selective surface based on double-element composite loading

Abstract

The invention discloses a band-pass type active frequency selective surface based on double-element composite loading. The band-pass type active frequency selective surface comprises at least one resonance unit which is periodically arranged, the resonance unit sequentially comprises a top metal frequency selection surface layer, a first dielectric structure layer, a middle metal feed layer, a second dielectric structure layer and a bottom metal frequency selection surface layer from top to bottom; the top metal layer and the bottom metal layer are composed of square ring aperture grooves subjected to deformation processing, and the middle feed layer is of a cross zigzag metal structure, plays a role in coupling an electromagnetic field and serves as a bias network of the AFSS. And the metal through holes penetrate through the resonance units in the vertical direction, so that the middle layer feeder line can respectively provide reverse bias voltage for independently regulating and controlling the resonance frequency for the PINs and the variable capacitance diodes on the top layer and the bottom layer. According to the invention, the functions of band switching and wide-range frequency tuning can be met, so that the problem of insertion loss increase caused by limited design frequency regulation and control range and element loading of the AFSS in the prior art can be solved.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic field and microwave technology, in particular to a bandpass active frequency selective surface structure based on dual-element composite loading. Background Art

[0002] A frequency selective surface (FSS) is a two-dimensional periodic artificial electromagnetic structure with spatial filtering properties. Composed of subwavelength metal patches or aperture units arranged at a specific spatial period, it can exhibit either band-rejection or band-pass characteristics for spatial electromagnetic waves, tailored to different needs. Band-pass FSSs, as spatial filtering structures, can achieve both in-band transmission and steep out-of-band cutoff. In the military, one of its key applications is as radar radomes, reducing radar cross section (RCS) and protecting the system's signal reception from external interference.

[0003] Traditional bandpass types are mostly fixed-frequency designs, which are difficult to adapt to dynamic needs in complex electromagnetic environments. Active Frequency Selective Surface (AFSS) adds electronic control devices to the traditional structure, which can achieve reconfigurable characteristics by dynamically adjusting external excitations to control electromagnetic performance. It can actively adjust its own filtering characteristics according to changes in external working conditions to cope with electromagnetic compatibility issues in multiple tasks and scenarios. The combination of bandpass frequency selective surfaces and active reconfigurable technology represents a leap forward in the development of electromagnetic functional materials from "passive fixed" to "active intelligent". Active tuning technology enables FSS to respond to changes in the electromagnetic environment in real time, providing key technical reserves for cutting-edge fields such as terahertz communications and radar anti-interference.

[0004] Considering that radar operates over a wide frequency range, the frequency regulation of a typical active structure, when loaded with a single electronically controlled element, is limited to a single frequency point. Furthermore, with the rapid development of communications technology, the X- and Ku-bands have been designated as crucial for military and space communications. Given their importance, flexible control over the operating frequency tuning within these bands is crucial.

[0005] Therefore, how to provide a high-performance active frequency selective surface that can be applied to the X-Ku band, meet the requirements of frequency tuning in a wide range and have low insertion loss is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0006] In response to the above research status, the present invention provides a bandpass active frequency selective surface based on dual-element composite loading, which can meet the band switching and wide-range frequency tuning functions, so as to solve the problems of limited frequency control range of AFSS design and increased insertion loss caused by component loading in the existing technology.

[0007] The present invention provides a bandpass active frequency selective surface based on dual-element composite loading, comprising at least one periodically arranged resonant unit; the resonant unit comprises, from top to bottom, a top metal frequency selective surface layer, a first dielectric structure layer, an intermediate metal feed layer, a second dielectric structure layer, and a bottom metal frequency selective surface layer; further comprising: a metal via structure, a top PIN diode, and a bottom varactor diode, wherein:

[0008] The top metal frequency selective surface layer is a centrosymmetrical structure, comprising an etched bent square ring aperture groove, wherein the inner portion of the area enclosed by the bent square ring aperture groove is an inner square metal patch with outwardly bent branches, and the outer portion of the area enclosed by the bent square ring aperture groove is an outer square metal patch with inwardly bent depressions on all sides, and the inner square metal patch and the outer square metal patch are insulated from each other; a top PIN diode is embedded in the top metal frequency selective surface layer, and the feeding end of the top PIN diode is connected to the outer square metal patch, and the other end is connected to the inner square metal patch;

[0009] The middle metal feed layer is a cross-shaped zigzag metal patch symmetrically distributed relative to the center of the structure;

[0010] The first dielectric structure layer is arranged between the top metal frequency selective surface layer and the middle metal feed layer; the second dielectric structure layer is arranged between the middle metal feed layer and the bottom metal frequency selective surface layer;

[0011] The bottom metal frequency selective surface layer has the same structure as the top metal frequency selective surface layer and is positioned correspondingly; the bottom metal frequency selective surface layer is embedded with a bottom varactor diode, a feeding end of the bottom varactor diode is connected to the outer square metal patch thereof, and the other end is connected to the inner square metal patch thereof;

[0012] The metal via structure passes through the resonant unit and sequentially connects the inner square metal patch of the top metal frequency selective surface layer, the cross-zigzag metal patch and the inner square metal patch of the bottom metal frequency selective surface layer for cooperating with the bias voltage feeding.

[0013] Preferably, the top metal frequency selective surface layer and the bottom metal frequency selective surface layer are symmetrical about their respective centers, and the top metal frequency selective surface layer, the bottom metal frequency selective surface layer and the middle metal feed layer are rotationally symmetrical about the metal via structure in the vertical incident direction.

[0014] Preferably, the bent square ring aperture grooves of the top metal frequency selective surface layer and the bottom metal frequency selective surface layer are arranged along orthogonal directions; the cross-zigzag metal patch is arranged at a 45° rotation relative to the bent square ring aperture groove; and the metal via structure passes through the center intersection of the cross-zigzag metal patch.

[0015] Preferably, the resonant unit is square, and after multiple resonant units are closely arranged in a matrix to form an m×m matrix, m≥3; the metal patches between the top metal frequency selective surface layers of adjacent array resonant units and the bottom metal frequency selective surface layers of adjacent array resonant units are connected, and the middle metal feed layers of adjacent array resonant units form a connected feeding grid.

[0016] Preferably, the bent square ring aperture groove is obtained by bending the four groove edges of the square ring aperture groove structure, including: bending outward perpendicular to the extension direction of the groove edge to form a similar Type bending groove.

[0017] Preferably, the class The two slot arms of the bending slot perpendicular to the slot edge of the square ring aperture slot structure have different lengths.

[0018] Preferably, the cross-shaped metal patch includes a cross-shaped metal patch, and the four branches of the cross-shaped metal patch are subjected to multiple bending processes, including: bending along a direction perpendicular to the extension direction of the branch and alternately bending to both sides of the branch in sequence to form multiple Type bending part.

[0019] Preferably, the top PIN diode is provided with two, which are respectively embedded in the top metal frequency selective surface layer and arranged oppositely. The metal patch is located at the bending groove position, and the two ends are respectively located at the inner square metal patch area position and the outer square metal patch area position.

[0020] Preferably, the bottom layer varactor diodes are provided with two, which are respectively embedded in the bottom metal frequency selective surface layer and arranged oppositely. The metal patch is located at the bending groove position, and the two ends are respectively located at the inner square metal patch area position and the outer square metal patch area position.

[0021] Preferably, the top metal frequency selective surface layer and the bottom metal frequency selective surface layer are both made of copper material with a thickness of 17-35 μm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention integrates the bias network and the unit structure into a reasonable structural integration design. The bias network can not only feed the diode but also reduce the influence on the transmission response of the unit structure.

[0024] By controlling the PIN diodes and varactor diodes embedded in the top and bottom layers, it is possible to switch between the two operating bands and continuously tune the operating frequency within the two bands. The frequency tuning range is wide, which makes up for the reconfigurable defects of loading varactor diodes and PIN diodes separately.

[0025] The present invention adopts a symmetrical structure and a miniaturized bending structure design, so that the model has good angle stability and polarization stability on the basis of meeting the frequency tuning requirements.

[0026] The present invention offers flexible frequency tuning over a wide range of 10.2-15.2 GHz, low insertion loss, and insensitivity to wide angles of oblique incidence and polarization, making it suitable for complex electromagnetic environments. Furthermore, it can be implemented using high-frequency printed circuit board technology, resulting in low cost and simple processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only embodiments of the present invention. Those skilled in the art can also derive other drawings based on the provided drawings without inventive effort.

[0028] Figure 1 A schematic diagram of the overall structure of an active frequency selective surface model provided by an embodiment of the present invention;

[0029] Figure 2 A schematic diagram of the structure of a top metal frequency selective surface layer and a bottom metal frequency selective surface layer provided by an embodiment of the present invention;

[0030] Figure 3 A schematic diagram of the structure of the intermediate feed layer provided in an embodiment of the present invention;

[0031] Figure 4 A cross-sectional view of the active frequency selective surface model structure provided by an embodiment of the present invention;

[0032] Figure 5 Frequency response curve of the active frequency selective surface provided by an embodiment of the present invention in TE polarization mode without loading a diode;

[0033] Figure 6 The frequency response characteristics of the PIN diode loaded on the top metal layer when switching on / off in the TE polarization mode provided by the embodiment of the present invention;

[0034] Figure 7 Frequency response curves of the embodiment of the present invention provided in the TE polarization mode when the top and bottom metal layers are loaded with PIN and varactor diodes respectively;

[0035] Figure 8 The reflection coefficient curve of the loaded dual-element structure under TE polarization mode at 0-60° oblique incidence frequency response curve provided by the embodiment of the present invention;

[0036] Figure 9 The transmission coefficient curve of the dual-element structure loaded in the TE polarization mode at 0-60° oblique incidence frequency response curve provided by the embodiment of the present invention;

[0037] Figure 10 A detailed diagram of the bending structure of a cross-zigzag metal patch provided in an embodiment of the present invention;

[0038] Figure 11 A diagram illustrating the three-fold bending processing state of a cross-zigzag metal patch provided in an embodiment of the present invention.

[0039] In the figure, 1-top metal frequency selective surface layer; 2-first dielectric structure layer; 3-middle metal feed layer; 4-second dielectric structure layer; 5-bottom metal frequency selective surface layer; 6-metal via structure; 7-top PIN diode; 8-bottom varactor diode; 11, 51-bent square ring aperture groove; 12, 52-inner square metal patch; 13, 53-outer square metal patch; 31-cross zigzag metal patch; 32- Type bending part; 110, 510-type Type bending groove; 111, 511-slot arm. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] The present invention discloses a bandpass active frequency selective surface based on dual-element composite loading, such as Figure 1-4 As shown, it includes at least one periodically arranged resonant unit; the resonant unit includes, from top to bottom, a top metal frequency selective surface layer 1, a first dielectric structure layer 2, an intermediate metal feed layer 3, a second dielectric structure layer 4, and a bottom metal frequency selective surface layer 5; it also includes: a metal via structure 6, a top PIN diode 7, and a bottom varactor diode 8, wherein:

[0042] The top metal frequency selective surface layer 1 is a centrosymmetrical structure, comprising an etched bent square ring aperture groove 11. The inner portion of the area enclosed by the bent square ring aperture groove 11 is an inner square metal patch 12 with outwardly bent branches, and the outer portion of the area enclosed by the bent square ring aperture groove 11 is an outer square metal patch 13 with inwardly bent depressions on all sides. The inner square metal patch 12 and the outer square metal patch 13 are two nested parts, insulated from each other. The top metal frequency selective surface layer 1 has a top PIN diode 7 embedded therein, and the feeding end of the top PIN diode 7 is connected to the outer square metal patch 13, and the other end is connected to the inner square metal patch 12.

[0043] The middle metal feed layer 3 is a cross-shaped zigzag metal patch 31 symmetrically distributed relative to the center of the structure;

[0044] The first dielectric structure layer 2 is provided between the top metal frequency selective surface layer 1 and the middle metal feed layer 3; the second dielectric structure layer 4 is provided between the middle metal feed layer 3 and the bottom metal frequency selective surface layer 5;

[0045] The bottom metal frequency selective surface layer 5 has the same structure as the top metal frequency selective surface layer 1 and is positioned correspondingly; the bottom metal frequency selective surface layer 5 has a bottom varactor diode 8 embedded therein, the feeding end of the bottom varactor diode 8 being connected to the outer square metal patch 53 thereof, and the other end being connected to the inner square metal patch 52 thereof;

[0046] A metal via structure 6 runs through the resonant unit, sequentially connecting the inner square metal patch 12 of the top metal FSS layer 1, the cross-shaped zigzag metal patch 31, and the inner square metal patch 52 of the bottom metal FSS layer 5, providing bias voltage feed. The cross-shaped zigzag metal patch structure 31, combined with the metal via structure 6, forms the bias network for the active FSS.

[0047] In this embodiment of the present invention, the cross-zigzag patch in the middle layer not only couples the electromagnetic field but also serves as the bias network for the AFSS. The entire structure is symmetrical with respect to the middle layer, with the middle layer's intersection aligned with the centers of the upper and lower layers. The entire unit structure model is vertically connected by metal vias, enabling the middle layer feed lines to provide reverse bias voltages for independently regulating the resonant frequencies of the PIN diodes and varactor diodes on the top and bottom layers, respectively. This enables DC power feeding and frequency tuning of the active devices.

[0048] In one embodiment, the top metal frequency selective surface layer 1 and the bottom metal frequency selective surface layer 5 are symmetrical about their respective centers, and the top metal frequency selective surface layer 1, the bottom metal frequency selective surface layer 5 and the middle metal feed layer 3 are rotationally symmetrical about the metal via structure 6 in the vertical incident direction.

[0049] In one embodiment, the bent square ring aperture grooves of the top metal frequency selective surface layer 1 and the bottom metal frequency selective surface layer 5 are arranged along orthogonal directions; the cross-zigzag metal patch 31 is arranged at a 45° rotation relative to the bent square ring aperture groove; and the metal via structure 6 passes through the center intersection of the cross-zigzag metal patch 31.

[0050] In one embodiment, the resonant units of a unit cycle are square, and multiple resonant units are closely arranged in a matrix to form an m×m matrix, where m ≥ 3. Then, the positive and negative feed lines are connected. The metal patches between the top metal frequency selective surface layers 1 of adjacent array resonant units and between the bottom metal frequency selective surface layers 5 of adjacent array resonant units are connected, and the middle metal feed layers 3 of adjacent array resonant units form a connected feed grid.

[0051] In this embodiment, the length of the square side of the resonant unit of one unit period is 10+0.5 mm.

[0052] In one embodiment, Figure 2 As shown, the bent square ring aperture groove 11 is obtained by bending the four groove edges of the square ring aperture groove structure, including: bending outward perpendicular to the extension direction of the groove edge to form a similar Similarly, the bent square ring aperture groove 11 is obtained by bending the four groove edges of the square ring aperture groove structure, including: bending outward perpendicular to the extension direction of the groove edge to form a similar Type bending groove 510.

[0053] In this embodiment, the class The two groove arms 111 of the bending groove 110 perpendicular to the groove edge of the square ring aperture groove structure have different lengths. The two groove arms 511 of the bending groove 510 perpendicular to the groove edge of the square ring aperture groove structure are of different lengths.

[0054] In practice, the square ring aperture slot structure undergoes two deformation and bending processes. The first bend extends 1.04mm parallel to the edge of the square ring aperture slot structure and 1.3mm vertically. The second bend extends 1.56mm parallel to the edge of the square ring aperture slot structure and 1.04mm vertically. The bent square ring aperture slot is 1.1mm away from the edge of the metal frequency selective surface layer and has an aperture width of 0.52mm. The aperture slot is etched away from the top and bottom metal layers.

[0055] In one embodiment, the inner width of the bent square ring aperture groove 11 after bending and deformation is 0.5-0.6 mm.

[0056] In one embodiment, Figure 3As shown, the cross-shaped metal patch 31 includes a cross-shaped metal patch, and the four branches of the cross-shaped metal patch are bent multiple times, including: bending along the direction perpendicular to the branch extension and alternately bending to both sides of the branch to form multiple Shaped bending portion 32.

[0057] In this embodiment, Figure 10 As shown, the cross metal patch is processed by bending the branches three times, and the width of the branches in the cross zigzag metal patch 31 is 0.2-0.3mm. The inner width a of the bending portion 32 is 0.4 mm, the outer width b is 0.8 mm, the length c of the bending section after the second bending is 1.7 mm, and the total length d of each branch after the third bending is 6.97 mm. The third bending is to better increase the angular stability of the overall model. Figure 11 As shown, it is a schematic diagram of the state of three complete straight jumps. Figure 11 (a) is a non-bending branch structure, which is the basic cross patch. Figure 11 (b) is a secondary bending branch structure, forming a Type bending portion 32, Figure 11 (c) is a three-bend branch structure, where the width and length of each bend are the same. The cross patch is rotated 45° to enhance the coupling effect, and finally evolves into Figure 3 form.

[0058] In this embodiment, the cross-shaped zigzag metal patch 31 acts as a parallel inductor, coupling with the top metal frequency selective surface layer 1 and the bottom metal frequency selective surface layer 5 .

[0059] In one embodiment, there are two top-layer PIN diodes 7, which are respectively embedded in the top-layer metal frequency selective surface layer 1 and arranged in opposite directions. The two ends are located at the inner square metal patch 12 area and the outer square metal patch 13 area. Figure 1 As shown, two top-layer PIN diodes 7 are loaded in the etched aperture of the top-layer square ring bent aperture structure in a direction parallel to the y-axis. Figure 1 As shown, two PIN diodes are loaded at the top layer A and B, and two varactor diodes are loaded at the bottom layer C and D.

[0060] In one embodiment, there are two bottom varactor diodes 8, which are respectively embedded in the bottom metal frequency selective surface layer 5 and arranged opposite to each other. The two ends are located at the inner square metal patch 52 area and the outer square metal patch 53 area. Figure 1As shown, two bottom-layer varactor diodes 8 are loaded in the gaps of the bottom-layer square ring bent aperture structure along the direction parallel to the y-axis.

[0061] In this embodiment, the top-layer PIN diode 7 and the bottom-layer varactor diode 8 are loaded using a reflow soldering technique, and the power supply components are soldered onto the processed plate.

[0062] In one embodiment, the top metal frequency selective surface layer 1 and the bottom metal frequency selective surface layer 5 are both made of copper material with a thickness of 17-35 μm, and are prepared on the first dielectric structure layer 2 and the second dielectric structure layer 4 by printing, electrochemical corrosion or magnetron sputtering. The metal layers are both treated with surface gold deposition process for anti-oxidation.

[0063] In one embodiment, the metal via structure 6 is made of copper, and the via length is the entire model cross-section length.

[0064] In one embodiment, the first dielectric structure layer 2 and the second dielectric structure layer 4 are made of Rogers RT5880 plate with stable performance, and the relative dielectric constant ε r =2.2+0.02, loss tangent value tanδ=0.0009 / 0.0004.

[0065] In one embodiment, the thickness of the first dielectric structure layer 2 and the second dielectric structure layer 4 are both 0.1-0.2 mm.

[0066] In one embodiment, the total thickness of the overall structure model is 2h+3d, where h=0.1mm represents the thickness of the dielectric layer and d=0.035mm represents the thickness of the metal patch layer. In this embodiment, the total thickness of the cross section of the overall structure model is 0.305mm. The dielectric material is Rogers 5880 (relative dielectric constant ε r =2.2, loss tangent tanδ = 0.001). Metal vias run through the entire structure and connect the top and bottom metal layers for easy power feeding. The via radius r is 0.1 mm.

[0067] like Figure 5 As shown in the figure, the numerical simulation results of the present invention example under TE polarization mode and normal incidence of electromagnetic wave are given. At this time, the bandpass resonance point of the S parameter curve is 12.2GHz, and the -3dB working bandwidth is

[0068] 1.8GHz (11.37-13.17GHz), indicating that the model has excellent frequency response characteristics of low loss and high transmission within the working frequency band, the reflection coefficient curve is flat in the stopband region, and the out-of-band suppression characteristics are good.

[0069] like Figure 6As shown, first, a top-layer PIN diode is loaded in the AFSS model. When the top-layer PIN diode is turned on or off, the resonant frequency is switched between the X-band and the Ku-band by switching the on-off state of the switch.

[0070] like Figure 6 As shown, in the embodiment of the present invention, two top-level PIN diodes are symmetrically placed at A and B in the y-axis direction of the top-level annular slot unit, and the AFSS operating frequency is switched between different bands by controlling the different bias states of the top-level PIN diodes.

[0071] like Figure 6 As shown, in the example of the present invention, the top PIN diode is regarded as an ideal switch, and the resistance is set to a small resistance of 1.5Ω when it is turned on, and is set to a capacitance of 0.3pF or a large resistance of 10kΩ when it is turned off to be equivalent to an open circuit. The internal resistance of the top PIN diode is ignored in the example of the present invention.

[0072] like Figure 6 The figure shows the reflection coefficient curves of the AFSS in the TE polarization mode, when loaded with only the top PIN diode in the ON / OFF state. When the top PIN diode is in the off state, the resonant point within the passband is located in the X band, with a resonant frequency of 12.2 GHz. The transmission performance within the passband is excellent, with a -3dB relative bandwidth of 14.8%. When the top PIN diode is in the on state, the new resonant frequency appears at 14.1 GHz (Ku band), and the insertion loss increases, exhibiting stopband characteristics within the original passband.

[0073] like Figure 7 As shown in the figure, based on the above AFSS model, a bottom varactor diode is added. This example shows the case where two top PIN diodes and two bottom varactor diodes are loaded simultaneously. By applying different reverse bias voltages to the bottom varactor diodes, the lumped capacitance is continuously changed, thereby obtaining a tunable passband response.

[0074] like Figure 7 As shown, in the example of the present invention, only the variation range of the equivalent capacitance value of the bottom varactor diode is given, and the equivalent resistance value of the bottom varactor diode is set to 1.5Ω, and the equivalent inductance value is 0.7nH.

[0075] like Figure 7The figure shows the reflection coefficient curve of the AFSS structure loaded with both a top PIN diode and a bottom varactor diode under TE polarization. Under normal electromagnetic wave incidence, in the PIN-OFF state, with an equivalent capacitance of 0pF, the center frequency of the AFSS response is 12.3GHz. When the bottom varactor diode is loaded with small capacitors of equivalent capacitance C = 0.02pF / 0.04pF / 0.08pF, the passband frequency gradually shifts to lower frequencies, ranging from 10.2-12.3GHz.

[0076] like Figure 7 As shown, in the example of the present invention, when PIN-ON is turned on without loading the underlying varactor diode, the new operating frequency appears at 14.1 GHz. When a small capacitor with an equivalent capacitance of C = 0.02 pF / 0.03 pF is loaded on the underlying varactor diode, the resonant frequency shifts to a high frequency range of 12.3-14.1 GHz.

[0077] like Figure 7 As shown, in the embodiment of the present invention, when the PIN-ON is forward-conducted and loaded with a larger capacitance, such as C = 0.5pF and 0.85pF, the operating frequency moves to a high frequency range of 14.1-15.2GHz.

[0078] like Figure 7 As shown, the model described in the example of the present invention is flexibly tuned in each frequency range and the spectrum is superimposed on each other, and finally continuous frequency tuning with an insertion loss below -1dB is achieved in the entire frequency coverage range of 10.2-15.2GHz.

[0079] like Figure 8 As shown in the figure, the reflection coefficient curve of AFSS in the oblique incidence range of 0°-60° of electromagnetic waves is given when an equivalent capacitance of 0.02pF is loaded in the PIN-OFF state in an example of the present invention. The passband shows a stable transmission response, and the resonant center frequency only shifts by 0.1GHz.

[0080] like Figure 9 As shown, the transmission coefficient curve of AFSS in the oblique incidence range of 0°-60° is given when an equivalent capacitance of 0.02pF is loaded in the PIN-OFF state in an example of the present invention. The -3dB passband bandwidth does not decrease in several steps, showing a stable passband response.

[0081] like Figure 9 As shown in the figure, when the electromagnetic wave has an oblique incident angle of 60°, the high-order harmonics appear at high frequencies, and the AFSS has weak resonance in the out-of-band response. However, the parasitic resonance in the stopband does not affect its bandpass characteristics, and the -3dB wave transmission band can still be maintained in the main passband (10.9-12.8GHz). The results show that the AFSS model has good angular stability within a large oblique incidence range.

[0082] In summary, the present invention discloses a bandpass active frequency selective surface model based on dual-element composite loading. This model can achieve passband frequency tuning with sub-1dB insertion loss within the 10.2-15.2 GHz range using dual-element switching control and capacitance adjustment. This design offers the advantages of low insertion loss and a wide frequency tuning range, overcoming the reconfigurable limitations of single-element loading with varactor or PIN diodes. It also exhibits excellent angular and polarization stability, making it more suitable for complex electromagnetic environments.

[0083] The above is a detailed introduction to a bandpass active frequency selective surface based on dual-element composite loading provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the ideas of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

[0084] In this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

Claims

1. A bandpass active frequency selective surface based on dual-element composite loading, characterized in that: comprising at least one periodically arranged resonant unit; The resonant unit comprises, from top to bottom, a top metal frequency selective surface layer (1), a first dielectric structure layer (2), an intermediate metal feed layer (3), a second dielectric structure layer (4), and a bottom metal frequency selective surface layer (5); and further comprises: a metal via structure (6), a top PIN diode (7), and a bottom varactor diode (8), wherein: The top metal frequency selective surface layer (1) is a centrally symmetrical structure, comprising an etched bent square ring aperture groove, wherein the inner portion of the bent square ring aperture groove encloses an inner square metal patch (12) with outwardly bent branches, and the outer portion of the bent square ring aperture groove encloses an outer square metal patch (13) with inwardly bent recesses on all sides, and the inner square metal patch (12) and the outer square metal patch (13) are insulated; the top metal frequency selective surface layer (1) is embedded with a top PIN diode (7), and the feeding end of the top PIN diode (7) is connected to the outer square metal patch (13), and the other end is connected to the inner square metal patch (12); The intermediate metal feed layer (3) is a cross-shaped zigzag metal patch (31) symmetrically distributed relative to the center of the structure; The first dielectric structure layer (2) is arranged between the top metal frequency selection surface layer (1) and the middle metal feed layer (3); the second dielectric structure layer (4) is arranged between the middle metal feed layer (3) and the bottom metal frequency selection surface layer (5); The bottom metal frequency selective surface layer (5) has the same structure as the top metal frequency selective surface layer (1), and the positions are correspondingly arranged; the bottom metal frequency selective surface layer (5) is embedded with a bottom varactor diode (8), and the feeding end of the bottom varactor diode (8) is connected to the outer square metal patch (53) thereof, and the other end is connected to the inner square metal patch (52) thereof; The metal via structure (6) passes through the resonant unit and sequentially connects the inner square metal patch (12) of the top metal frequency selective surface layer (1), the cross-shaped zigzag metal patch (31) and the inner square metal patch (52) of the bottom metal frequency selective surface layer (5) for cooperating with bias voltage feeding.

2. A bandpass active frequency selective surface based on dual-element composite loading according to claim 1, characterized in that: The top metal frequency selective surface layer (1) and the bottom metal frequency selective surface layer (5) are both symmetrical about their respective centers, and the top metal frequency selective surface layer (1), the bottom metal frequency selective surface layer (5) and the intermediate metal feed layer (3) are rotationally symmetrical about the metal via structure (6) in the vertical incident direction.

3. The bandpass active frequency selective surface based on dual-element composite loading according to claim 1, characterized in that: The bent square ring aperture grooves of the top metal frequency selective surface layer (1) and the bottom metal frequency selective surface layer (5) are arranged along orthogonal directions; the cross-shaped zigzag metal patch (31) is arranged with a 45° rotation relative to the bent square ring aperture groove; and the metal via structure (6) passes through the central intersection of the cross-shaped zigzag metal patch (31).

4. The bandpass active frequency selective surface based on dual-element composite loading according to claim 1, characterized in that: The resonant unit is square, and after a plurality of the resonant units are closely arranged in a matrix manner to form an m×m matrix, m≥3; the metal patches between the top metal frequency selection surface layers (1) of adjacent array resonant units and between the bottom metal frequency selection surface layers (5) of adjacent array resonant units are connected, and the middle metal feeding layers (3) of adjacent array resonant units form a connected feeding grid.

5. The bandpass active frequency selective surface based on dual-element composite loading according to claim 1, characterized in that: The bent square ring aperture groove is obtained by bending the four groove edges of the square ring aperture groove structure, including: bending outward perpendicular to the extending direction of the groove edge to form a similar Type bending groove.

6. The bandpass active frequency selective surface based on dual-element composite loading according to claim 5, characterized in that: The class The two slot arms of the bending slot perpendicular to the slot edge of the square ring aperture slot structure have different lengths.

7. The bandpass active frequency selective surface based on dual-element composite loading according to claim 1, characterized in that: The cross-shaped metal patch (31) comprises a cross-shaped metal patch, and the four branches of the cross-shaped metal patch are subjected to multiple bending processes, including: bending along a direction perpendicular to the extension direction of the branch and alternately bending toward both sides of the branch in sequence to form multiple Shaped bending portion (32).

8. The bandpass active frequency selective surface based on dual-element composite loading according to claim 1, characterized in that: The top PIN diode (7) is provided with two, which are respectively embedded in the top metal frequency selective surface layer (1) and arranged in a manner similar to The two ends are located at the inner square metal patch (12) area and the outer square metal patch (13) area respectively.

9. The bandpass active frequency selective surface based on dual-element composite loading according to claim 1, characterized in that: The bottom layer varactor diodes (8) are provided with two, which are respectively embedded in the bottom layer metal frequency selective surface layer (5) and arranged in a relatively similar manner. The two ends are located at the inner square metal patch (52) area and the outer square metal patch (53) area respectively.

10. The bandpass active frequency selective surface based on dual-element composite loading according to claim 1, characterized in that: The top metal frequency selective surface layer (1) and the bottom metal frequency selective surface layer (5) are both made of copper material with a thickness of 17-35 μm.

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