A large-period frequency selective surface window wave absorber device with gate lobe suppression capability

Abstract

This invention belongs to the field of absorber design technology and discloses a large-period frequency-selective surface window absorber device with grating lobe suppression capability. From top to bottom, it comprises: a loss layer, a dielectric substrate layer corresponding to the loss layer, an isolation layer, a lossless layer, and another dielectric substrate layer corresponding to the lossless layer; preferably, both the loss layer and the lossless layer adopt a double-layer design. This invention achieves grating lobe suppression characteristics by using a fractal square ring resistive film on the unit pattern topology of the loss layer; it achieves broadband impedance matching and absorption bandwidth expansion in the low-frequency absorption state by using a large unit period and cascading double loss layers; the transmission window is implemented by introducing a metal blocking gate on the loss layer unit, thus the overall structure has integrated absorption and transmission functions. This invention provides a large-period unit structure that can effectively expand the low-frequency absorption bandwidth while avoiding the grating lobe problem caused by large periods.

Description

Technical Field

[0001] This invention belongs to the field of absorber design technology, and more specifically, relates to a large-period frequency-selective surface window absorber device with grating lobe suppression capability. Background Technology

[0002] With the rapid development of radar detection technology, improving the stealth capabilities of military facilities and equipment has become an urgent priority. Radar Cross Section (RCS) is a crucial parameter for evaluating a target's stealth performance; reducing the RCS ensures low detectability. Conventional methods of reducing RCS, such as shape design stealth and applying stealth materials, can affect antenna radiation performance. Generally, adding a radome to the antenna ensures a transmission window within the antenna band while reducing the out-of-band RCS.

[0003] A frequency selective surface (FSS) is a periodic structure that exhibits absorption, reflection, and transmission properties to incident waves. By introducing a blocking gate structure into the FSS, a transparent window can be inserted, realizing a frequency selective surface window absorber that integrates absorption and transmission. One of the key performance requirements for window absorbers is broadband frequency response. To expand its potential applications in a wide range of electromagnetic shielding scenarios, the expansion of absorption bandwidth can be considered a never-ending pursuit. The widest possible absorption band is also crucial for improving the survivability of stealth platforms in complex detection environments. With the increasing application of low-frequency radar in stealth platform detection, developing window absorbers with low-frequency stealth capabilities has become extremely important. Furthermore, even a small extension of the absorption band to lower frequencies results in a significant increase in the percentage bandwidth, which is more challenging than extending the absorption bandwidth at higher frequencies.

[0004] Currently, the most common method for resistive sieve stencils (FSS) is to use small-period units to avoid grating lobes. By reducing the period, the frequency of grating lobes appears higher, thus shifting them out of the operating frequency band. However, for resistive sieve stencils, their equivalent impedance depends only on the topology and surface sheet resistance. In low-frequency absorption, to achieve broadband impedance matching, larger inductance and capacitance values ​​are required in the equivalent circuit. This inevitably necessitates the use of large-period units. Therefore, it is of great significance to address the grating lobe problem caused by using large-period units and to achieve the expansion of low-frequency absorption bandwidth and broadband absorption. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a large-period frequency selective surface window absorber device with grating lobe suppression capability. Its purpose is to solve the grating lobe problem caused by using large-period units and to broaden the absorption bandwidth.

[0006] To achieve the above objectives, the present invention provides a large-period frequency selective surface window absorber device with grating lobe suppression capability, comprising, from top to bottom: a loss layer, a dielectric substrate layer corresponding to the loss layer, an isolation layer, a lossless layer, and a dielectric substrate layer corresponding to the lossless layer; the loss layer adopts an absorption-type large-period frequency selective surface, and the lossless layer adopts a small-period frequency selective surface with reflection and transmission properties. The unit of the large-cycle frequency selective surface includes: a fractal square ring resistive film and a metal blocking gate; the fractal square ring resistive film is formed by bending a square ring resistive film inward in the central region of each of its four sides, and the four sides of the square ring resistive film include opposing first and second sides, opposing third and fourth sides, and the line connecting the geometric centers of the fractal square ring resistive film about the first and second sides. O symmetry; The first to fourth sides are all bent inward in the central region to form their respective protrusions. Two metal blocking gates are loaded on the first and second sides respectively. The two metal blocking gates are symmetrical about the protrusions of the corresponding sides. Metal blocking gates are symmetrically loaded on the two arms of the protrusion on the third side and the two arms of the protrusion on the fourth side. Among them, loading metal blocking gates on the resistive film means replacing the resistive film at the corresponding position with metal blocking gates.

[0007] Furthermore, the lengths of the two protruding arms on the third and fourth sides are greater than the lengths of the two protruding arms on the first and second sides.

[0008] Furthermore, the loss layer includes a first loss layer and a second loss layer, the dielectric substrate layer corresponding to the loss layer includes a first dielectric substrate layer and a second dielectric substrate layer, the isolation layer includes a first isolation layer, a second isolation layer and a third isolation layer, the lossless layer includes a first lossless layer and a second lossless layer, and the dielectric substrate layer corresponding to the lossless layer includes a third dielectric substrate layer and a fourth dielectric substrate layer. The layers are arranged from top to bottom as follows: first loss layer, first dielectric substrate layer, first isolation layer, second loss layer, second dielectric substrate layer, second isolation layer, first non-loss layer, third dielectric substrate layer, third isolation layer, second non-loss layer, and fourth dielectric substrate layer.

[0009] Furthermore, the ring width of the square ring resistive film is 1 to 3 mm, and the surface sheet resistance is 10 to 500 Ohm / sq; the length of the two protruding arms is 2 to 10 mm, and the distance between the two protruding arms is 0.5 to 1 mm.

[0010] Furthermore, the unit of the small-period frequency selection surface is a square ring structure loaded with a square plate structure forming a square ring gap.

[0011] Furthermore, the ring width of the square ring structure is 0.1–0.5 mm, and the line width of the square plate structure is 5–10 mm; The metal blocking door has a line width of 0.1–0.5 mm, a length of 1–5 mm, and a width of 1–2 mm.

[0012] Furthermore, the period of the frequency selection surface unit of the loss layer is 20–40 mm, and the gap between the units is 0.5–2 mm.

[0013] Furthermore, the period of the lossless layer frequency selective surface unit is half the period of the lossy layer frequency selective surface unit.

[0014] Furthermore, the isolation layer material is aramid paper honeycomb material or foam composite material; the dielectric substrate material is glass fiber reinforced epoxy resin or polyimide film.

[0015] Furthermore, the metal blocking door is a U-shaped metal blocking door; the U-shaped metal blocking door is formed by one or more U-shaped metal blocking doors stacked together.

[0016] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: (1) Unlike existing loss layer designs that use miniaturized unit periods to move grating lobes out of the operating frequency band, this invention uses a large-period resistive film frequency selective surface in the loss layer. By designing the frequency selective surface unit of the loss layer, the four sides of the large-period square ring resistive film are bent inward along the central region to form a fractal square ring resistive film, thereby dividing the square ring structure into four quasi-square ring structures. This simulates the characteristics of a small-period square ring array, making the large-period frequency selective surface used in the loss layer have phase continuity similar to that of a small-period array, realizing grating lobe suppression characteristics and removing the unit period limitation in the design. A metal blocking gate is introduced on the fractal square ring resistive film to insert a transmission window, giving the overall structure the function of both absorption and transmission. Using a large-period FSS unit can increase the series capacitance between units and reduce the series selectivity to achieve broadband impedance matching and broaden the absorption bandwidth.

[0017] (2) Preferably, the length of the two protruding arms on the third and fourth sides is greater than the length of the two protruding arms on the first and second sides. Simulation results show that it can have a better wave absorption effect.

[0018] (3) As a preferred option, the use of cascaded double loss layers (first loss layer and second loss layer) can further broaden the low-frequency absorption bandwidth and high-frequency transmission bandwidth; the design of double lossless layers can reduce the transition band from absorption to transmission.

[0019] (4) Preferably, the design of the loss layer resistive film parameters (surface sheet resistance, ring width, length of the two raised arms, distance between the two raised arms, etc.) makes the absorption frequency band of the loss layer target the L and S bands and below the L band. The longer the length of the inward bend of the four sides of the square ring resistive film (the longer the length of the two raised arms), the more similar the quasi-square ring and the small square ring are, and the closer the whole is to the small square ring array, and the better the grating lobe suppression effect is. The design of the metal blocking gate parameters (line width, length, width) and the lossless layer parameters (ring width of the square ring structure, line width of the square plate structure) makes the communication transmission frequency band target the X band. The design mode is simple, the functional layer structure is unified, easy to assemble, low cost, and low absorption frequency band.

[0020] (5) Preferably, the material of the dielectric substrate layer is glass fiber epoxy resin or polytetrafluoroethylene, and the material of the dielectric isolation layer is aramid paper honeycomb or low-density foam board, which has the characteristics of low weight and high flexibility. Therefore, compared with traditional dielectric absorbing materials, the present invention is a lightweight frequency selective surface window absorbing device, which is suitable for carriers that require low added weight.

[0021] In summary, this invention achieves the design of a large-period frequency selective surface window (FSS) absorber with grating lobe suppression capability. It improves the design of the loss layer of the window absorber by using a fractal square ring resistive film in the loss layer. The grating lobe suppression function is achieved by utilizing the characteristics of the small-period array structure simulated by the fractal square ring resistive film, thereby amplifying the period restriction. A parallel resonant structure (metal blocking gate) is then introduced to achieve integrated absorption and transmission. The unit structure is simple and easy to design. Regarding the number of loss layers, a double-loss layer cascade is used, combined with a large-period FSS unit to achieve broadband impedance matching and absorption bandwidth extension in the low-frequency absorption state. This invention uses a large-period unit structure and can effectively extend the absorption band to lower frequencies while avoiding the grating lobe problem caused by large periods. The two loss layers of this invention have broadband frequency response characteristics for both absorption and transmission. The bandpass filter combining two lossless layers achieves frequency response characteristics for both reflection and transmission, fulfilling flexible and broadband absorption and transmission band requirements as well as low-frequency absorption requirements, ensuring stable performance response of the radar antenna system. Attached Figure Description

[0022] Figure 1 This is a vertical cross-sectional schematic diagram of a large-period frequency-selective surface window absorber device with grating lobe suppression capability provided in an embodiment of the present invention.

[0023] Figure 2 This is a 3D structural schematic diagram of a unit pattern in a large-period frequency-selective surface window absorber device with grating lobe suppression capability provided in an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of the square ring resistive film structure in an embodiment of the present invention.

[0025] Figure 4 This is a schematic diagram of a fractal square ring resistive film formed by bending the four sides of the square ring resistive film inward in an embodiment of the present invention.

[0026] Figure 5 This is a schematic diagram of the loss layer FSS pattern topology provided in one embodiment of the present invention, with a cell period of 23 mm.

[0027] Figure 6 This is a schematic diagram of the lossless layer FSS pattern topology provided in one embodiment of the present invention, with a cell period of 11.5 mm.

[0028] Figure 7 This is a schematic diagram of the S-parameter characteristic curve of a large-period frequency-selective surface window absorber device with grating lobe suppression capability provided in one embodiment of the present invention.

[0029] Figure 8 This is a schematic diagram of the oblique incidence absorption rate curve of a large-period frequency-selective surface window absorber device with grating lobe suppression capability provided in one embodiment of the present invention.

[0030] Figure 9 This is a schematic diagram of the oblique incidence transmission characteristic curve of a large-period frequency-selective surface window absorber device with grating lobe suppression capability provided in one embodiment of the present invention.

[0031] Figure 10 This is a schematic diagram of the S-parameter characteristic curves of a large-period frequency-selective surface window absorber device with grating lobe suppression capability provided in another embodiment of the present invention.

[0032] Figure 11 This is a schematic diagram of the oblique incidence absorption rate curve of a large-period frequency-selective surface window absorber device with grating lobe suppression capability provided in another embodiment of the present invention.

[0033] Figure 12 This is a schematic diagram of the oblique incidence transmission characteristic curve of a large-period frequency-selective surface window absorber device with grating lobe suppression capability provided in another embodiment of the present invention.

[0034] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-First loss layer, 2-First dielectric substrate layer, 3-First isolation layer, 4-Second loss layer, 5-Second dielectric substrate layer, 6-Second isolation layer, 7-First non-loss layer, 8-Third dielectric substrate layer, 9-Third isolation layer, 10-Second non-loss layer, 11-Fourth dielectric substrate layer, 12-First side, 13-Second side, 14-Third side, 15-Fourth side, 16-Protrusion, 17-Metal blocking gate, 18-First arm of the protrusion, 19-Second arm of the protrusion. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0036] In this invention, the terms "first," "second," etc., used in the invention and accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0037] This invention provides a large-period frequency-selective surface window absorber device with grating lobe suppression capability, such as... Figure 1 and Figure 2 As shown, from top to bottom, it includes a first loss layer 1, a first dielectric substrate layer 2, a first isolation layer 3, a second loss layer 4, a second dielectric substrate layer 5, a second isolation layer 6, a first non-loss layer 7, a third dielectric substrate layer 8, a third isolation layer 9, a second non-loss layer 10, and a fourth dielectric substrate layer 11. The first loss layer 1 and the second loss layer 4 employ an absorption-type frequency selective surface, which is a large-period resistive film frequency selective surface with a blocking gate, used for low-frequency absorption and high-frequency transmission. It includes multiple FSS units arranged in a row-column periodic pattern. Specifically, the difference in sheet resistance and height between the two loss layers means that at low frequencies in the absorption band, the second loss layer 4 is mainly used for absorption, while at high frequencies in the absorption band, the first loss layer 1 is mainly used for absorption. The materials used for the two loss layers are resistive film and metal. To further broaden the absorption and transmission bandwidth while avoiding excessive loss layers that would degrade transmission performance, two loss layers are used. The first non-destructive layer 7 and the second non-destructive layer 10 employ metallic frequency selective surfaces with reflective and transparent properties to achieve reflective performance in the absorption band and transmittance at high frequencies. They include multiple FSS units arranged in a row and column periodic manner. The material used is metal, and the non-destructive layers are two-layered, which can broaden the reflection and transmission bandwidth and reduce the transition band from absorption to transmission.

[0038] The first isolation layer 3 is used to isolate the first loss layer 1 and the second loss layer 4, the second isolation layer 6 is used to isolate the second loss layer 4 and the first non-loss layer 7, and the third isolation layer 9 is used to isolate the first non-loss layer 7 and the second non-loss layer 10.

[0039] At low frequencies, when electromagnetic waves are incident on the wave-absorbing device in this embodiment of the invention, part of them are absorbed by the loss layer, and the remaining part is reflected by the lossless layer back to the loss layer for absorption again; at high frequencies, wave transmission is achieved.

[0040] In this embodiment of the invention, the lossy layers (first lossy layer 1 and second lossy layer 4) and the lossless layers (first lossless layer 7 and second lossless layer 10) have different FSS units and patterns. The first lossy layer 1 and the second lossy layer 4 use large-period FSS units to increase the series capacitance between units, thereby reducing series selectivity. This embodiment of the invention uses two cascaded lossy layers, which can shift the absorption band of the absorber to a lower frequency and achieve wider absorption. However, large-period FSS units cause the grating lobes to appear earlier in the operating frequency band. This embodiment of the invention specifically designs the material and pattern of the lossy layers to solve this technical problem. Specifically, as... Figures 3 to 5 As shown, the FSS unit of the loss layer includes a fractal square ring resistive film and a U-shaped metal blocking gate. The fractal square ring resistive film is formed by bending the square ring resistive film inward in the central region of each of its four sides. The four sides of the square ring resistive film include opposing first sides 12 and 13, and opposing third sides 14 and 15. The length of the first side 12 bent inward along its central region is equal to the length of the second side 13 bent inward along its central region, and the length of the third side 14 bent inward along its central region is equal to the length of the fourth side 15 bent inward along its central region. Preferably, the length of the first side 12 and the second side 13 bent inward is less than the length of the third side 14 and the fourth side 15 bent inward, so that the fractal square ring resistive film is formed by connecting the geometric centers of the first side 12 and the second side 13. O A symmetrical pattern. From the first to the fourth side, each side bends inward in the central region to form a protrusion 16. Two metal blocking gates 17 are loaded on both the first and second sides. In this embodiment, the metal blocking gates 17 are U-shaped metal blocking gates. The two U-shaped metal blocking gates on the first side are symmetrical about the protrusion on the first side, and the two U-shaped metal blocking gates on the second side are symmetrical about the protrusion on the second side. A metal blocking gate is loaded on the first arm 18 and the second arm 19 of the protrusion on the third side, and the metal blocking gates loaded on the two arms are symmetrical. Similarly, a metal blocking gate is symmetrically loaded on the first arm 18 and the second arm 19 of the protrusion on the fourth side. The location where the U-shaped metal blocking gates are set does not have a resistive film; that is, the resistive film at that location is replaced by a U-shaped metal blocking gate.

[0041] By designing the FSS (Fractal Separator) cells in the loss layer, the four sides of a large-period square ring are bent inwards at the center region to form a fractal square ring, dividing the square ring into four quasi-square rings. This simulates a small-period square ring array, giving the large-period FSS cells phase continuity similar to that of a small-period array, preventing the grating lobe from appearing and thus providing grating lobe suppression. Furthermore, a U-shaped metal blocking gate is introduced onto the fractal square ring to insert a transmission window, achieving integrated absorption and transmission performance of the loss layer.

[0042] In one optional implementation, the U-shaped metal blocking gate is formed by stacking multiple U-shaped metal blocking gates, selected according to the actual required wave transmission performance. In this embodiment of the invention, three U-shaped metal blocking gates are selected and stacked in reverse to form the required U-shaped metal blocking gate.

[0043] In this embodiment of the invention, the first non-damaging layer 7 and the second non-damaging layer 10 employ small-period FSS cells to avoid gate lobes; in some optional embodiments, each loss layer and non-damaging layer is fabricated as a whole with the corresponding dielectric substrate layer.

[0044] In one optional implementation, the period of the FSS unit of the first loss layer and the second loss layer is 20-40 mm. Using large-period FSS units can achieve a lower absorption frequency band. The period of the FSS unit of the first lossless layer and the second lossless layer is half the period of the loss layer unit.

[0045] In one optional implementation, the FSS unit ring width of the first and second loss layers is 1–3 mm, the length of the two protruding arms formed by bending inward in the central region of each side is 2–10 mm, the gap between the two protruding arms is 0.5–1 mm, the linewidth of the blocking gate structure is 0.1–0.5 mm, the length is 1–5 mm, the width is 1–2 mm, the gap between FSS units is 0.5–2 mm, and the sheet resistance of the resistive film surface is 10–500 Ohm / sq. The longer the inward bending length of the four sides (the longer the length of the two protruding arms), the more similar the quasi-square ring is to the small square ring, and the closer the whole is to the small square ring array, resulting in a better gate lobe suppression effect.

[0046] In one alternative implementation, such as Figure 6 As shown, the FSS units of the first and second lossless layers are square ring gaps composed of square ring structures loaded with square sheet structures.

[0047] In one optional implementation, the FSS unit ring width of the first and second non-destructive layers is 0.1 to 0.5 mm, and the line width of the square structure is 5 to 10 mm.

[0048] In one alternative embodiment, the dielectric substrate material is a glass fiber reinforced epoxy resin or a polyimide film with a thickness of 0.025~0.8 mm.

[0049] In one alternative embodiment, the aforementioned insulating layer material is an aramid paper honeycomb material or a foam composite material, with a relative permittivity ranging from 1.07 to 1.15, a loss tangent ranging from 0.0017 to 0.0039, and a thickness ranging from 1 to 30 mm.

[0050] To further illustrate the performance of the large-period frequency-selective surface window absorber device with grating lobe suppression capability provided by the present invention, the following detailed description is provided in conjunction with embodiments.

[0051] In one example, the frequency-selective surface window absorber device has dimensions of 300 mm × 300 mm and contains 12 × 12 periodic elements; wherein the FSS elements in the first loss layer 1 and the second loss layer 4 are both 23 mm × 23 mm in size. Figure 5 As shown, the FSS cell topologies of the first and second loss layers are identical, both using a fractal square ring resistive film as the main body. Two U-shaped metal blocking gates are loaded on the first and second sides of the square ring resistive film to replace the corresponding resistive film positions. The two U-shaped metal blocking gates are symmetrical about the protrusions on the corresponding sides. A U-shaped metal blocking gate is symmetrically loaded on the two arms of the protrusion on the third and fourth sides to replace the corresponding positions. The surface sheet resistance of the fractal square ring resistive film in the first loss layer is 250 Ohm / sq, and the surface sheet resistance of the fractal square ring resistive film in the second loss layer is 22 Ohm / sq. The gap between FSS cells is 0.5 mm, the ring width is 2 mm, the length of the two arms protruding on the third and fourth sides is 8 mm, and the length of the two arms protruding on the first and second sides is 2 mm. The gap between the four protruding arms is 0.5 mm, the blocking gate width is 1.4 mm, the length is 4 mm, and the line width is 0.1 mm.

[0052] Because fractals limit the design space of the U-shaped blocking gate size, in this embodiment of the invention, the loaded blocking gates form a symmetrical structure, not a centrally symmetrical one. Therefore, the window absorber device in this embodiment is unipolar.

[0053] The dimensions of the first and second lossless layers FSS units are both 11.5 mm × 11.5 mm, such as... Figure 6 As shown, the two lossless FSS units have the same topology, both consisting of a square ring structure with a square plate structure forming a square ring gap. The width of the square ring is 0.25 mm and the width of the square plate is 7 mm.

[0054] In this embodiment, both the first and second dielectric substrates are made of polytetrafluoroethylene (PTFE), with a relative permittivity of 2.2, a loss tangent of 0.002, and a thickness of 0.25 mm. The third and fourth dielectric substrates are made of glass fiber reinforced epoxy resin, with a relative permittivity of 4.4, a loss tangent of 0.025, and a thickness of 0.25 mm.

[0055] The isolation layer is made of foam composite material, with a size of 300 mm * 300 mm. The first isolation layer has a thickness of 15 mm, the second isolation layer has a thickness of 30 mm, and the third isolation layer has a thickness of 4 mm.

[0056] The window absorber model was modeled and simulated in the electromagnetic simulation software HFSS, and the simulation performance was as follows: Figure 7 As shown in the figure, the window absorber device proposed in this embodiment of the invention achieves an internal reflection coefficient S of 0.60~5.32 GHz (159.5% percentage bandwidth). 11 <-10 dB, transmission coefficient S 21 The absorption effect is <-10 dB, and the high-frequency transmission bandwidth is 7.72~10.10 GHz (26.7% percentage bandwidth). 21 >-1 dB, -3 dB transmission bandwidth is 7.31~12.42 GHz (S 21 Above -3 dB (51.8% of bandwidth), Figure 6 The S-parameters in the equation represent the reflection coefficient or transmission coefficient; oblique incidence performance is as follows: Figure 8 and Figure 9 As shown, the window absorber device proposed in this embodiment of the invention ensures performance stability under 45° oblique incidence. In addition, the unit period of the proposed window absorber device is 23 mm. At 60° oblique incidence, grating lobes should begin to appear at 7 GHz. However, as can be seen from the figure, the curve remains smooth within 14 GHz, and no obvious grating lobe stripes appear. This indicates that the window absorber device proposed in this embodiment of the invention has grating lobe suppression capability and delays the appearance of grating lobes.

[0057] In another example, the unit period of the first and second loss layers becomes 21 mm, the ring width of the fractal square ring resistive film becomes 1.5 mm, the sheet resistance of the first loss layer resistive film becomes 500 Ohm / sq, the sheet resistance of the second loss layer resistive film becomes 90 Ohm / sq, the unit period of the first and second lossless layers becomes 10.5 mm, the thickness of the first isolation layer becomes 12 mm, and the thickness of the second isolation layer becomes 20 mm.

[0058] The frequency-selective surface window absorber device measures 300 mm × 300 mm and contains 13 × 13 periodic units.

[0059] The window absorber model was modeled and simulated in the electromagnetic simulation software HFSS, and the simulation performance was as follows: Figure 10 As shown in the figure, the window absorber device proposed in this embodiment of the invention achieves a low reflection frequency band of 1.07~13.5 GHz (S 11 <-10 dB), the -10 dB absorption bandwidth covers 1.07~6.37 GHz (142.5% bandwidth), and the high-frequency transmission bandwidth is 8.21~10.40 GHz (23.5% bandwidth), its S 21 >-1 dB, -3 dB transmission bandwidth is 7.56~12.70 GHz (50.7% percentage bandwidth); oblique incidence performance is as follows Figure 11 and Figure 12 As shown in the figure, the window absorber device proposed in this embodiment of the invention ensures performance stability under 45° oblique incidence. In addition, the unit period of the proposed window absorber device is 21mm. When the oblique incidence is 60°, the grating lobes should start to appear at 7.7 GHz. However, as can be seen from the figure, the curve remains smooth within 14 GHz, and no obvious grating lobe stripes appear. This shows that the window absorber device proposed in this embodiment of the invention has grating lobe suppression capability and delays the appearance of grating lobes.

[0060] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A large-period frequency-selective surface window absorber device with grating lobe suppression capability, characterized in that, From top to bottom, it includes: a loss layer, a dielectric substrate layer corresponding to the loss layer, an isolation layer, a lossless layer, and a dielectric substrate layer corresponding to the lossless layer; the loss layer adopts an absorption-type large-period frequency selective surface, and the lossless layer adopts a small-period frequency selective surface with reflection and transmission properties. The unit of the large-cycle frequency selective surface includes: a fractal square ring resistive film and a metal blocking gate (17); the fractal square ring resistive film is formed by bending the square ring resistive film inward in the central region of all four sides, the four sides of the square ring resistive film include a first side (12) and a second side (13), a third side (14) and a fourth side (15), and the geometric center line of the fractal square ring resistive film about the first side (12) and the second side (13) is... O symmetry; The first side (12) to the fourth side (15) are all bent inward in the central region to form their respective protrusions (16). Two metal blocking gates (17) are loaded on the first side (12) and the second side (13). The two metal blocking gates (17) are symmetrical about the protrusions (16) of the corresponding side. Metal blocking gates (17) are symmetrically loaded on the two arms of the protrusion of the third side (14) and the two arms of the protrusion of the fourth side (15). Among them, loading metal blocking gates on the resistive film means replacing the resistive film at the corresponding position with metal blocking gates.

2. The large-period frequency selective surface window absorber device according to claim 1, characterized in that, The length of the two protruding arms on the third side (14) and the fourth side (15) is greater than the length of the two protruding arms on the first side (12) and the second side (13).

3. The large-period frequency-selective surface window absorber device according to claim 1 or 2, characterized in that, The loss layer includes a first loss layer (1) and a second loss layer (4), the dielectric substrate layer corresponding to the loss layer includes a first dielectric substrate layer (2) and a second dielectric substrate layer (5), the isolation layer includes a first isolation layer (3), a second isolation layer (6) and a third isolation layer (9), the lossless layer includes a first lossless layer (7) and a second lossless layer (10), the dielectric substrate layer corresponding to the lossless layer includes a third dielectric substrate layer (8) and a fourth dielectric substrate layer (11); The layers are arranged from top to bottom as follows: first loss layer (1), first dielectric substrate layer (2), first isolation layer (3), second loss layer (4), second dielectric substrate layer (5), second isolation layer (6), first non-loss layer (7), third dielectric substrate layer (8), third isolation layer (9), second non-loss layer (10), and fourth dielectric substrate layer (11).

4. The large-period frequency selective surface window absorber device according to claim 3, characterized in that, The square ring resistive film has a ring width of 1–3 mm and a surface sheet resistance of 10–500 Ohm / sq; the length of the two protruding arms is 2–10 mm, and the distance between the two protruding arms is 0.5–1 mm.

5. The large-period frequency selective surface window absorber device according to claim 3, characterized in that, The unit of the small-period frequency selection surface is a square ring structure with a square plate structure forming a square ring gap.

6. The large-period frequency selective surface window absorber device according to claim 5, characterized in that, The ring width of the square ring structure is 0.1 to 0.5 mm, and the line width of the square plate structure is 5 to 10 mm; The metal blocking door has a line width of 0.1–0.5 mm, a length of 1–5 mm, and a width of 1–2 mm.

7. The large-period frequency selective surface window absorber device according to claim 3, characterized in that, The period of the frequency-selective surface unit of the loss layer is 20–40 mm, and the gap between the units is 0.5–2 mm.

8. The large-period frequency selective surface window absorber device according to claim 7, characterized in that, The period of the lossless layer frequency selective surface unit is half the period of the lossy layer frequency selective surface unit.

9. The large-period frequency selective surface window absorber device according to claim 1, characterized in that, The isolation layer material is aramid paper honeycomb material or foam composite material; the dielectric substrate material is glass fiber reinforced epoxy resin or polyimide film.

10. The large-period frequency-selective surface window absorber device according to claim 1, characterized in that, The metal blocking door (17) is a U-shaped metal blocking door; the U-shaped metal blocking door is formed by one or more U-shaped metal blocking doors stacked together.

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