P-K wave band ultra-wideband microwave absorber

Abstract

The invention belongs to the technical field of microwave absorbers, and particularly discloses a P-K wave band ultra-wideband microwave absorber which comprises a bottom plate, and a first frequency selection surface layer, a second frequency selection surface layer and an active frequency selection surface layer are sequentially arranged on the upper end face of the bottom plate in the first direction, a first spacing layer is arranged between the first frequency selection surface layer and the second frequency selection surface layer, a second spacing layer is arranged between the second frequency selection surface layer and the active frequency selection surface layer, and a third spacing layer is arranged between the active frequency selection surface layer and the bottom plate. Broadband high-efficiency absorption from a low-frequency P wave band to a high-frequency K wave band can be achieved, and good angle stability and polarization insensitivity are achieved.

Description

Technical Field

[0001] This application belongs to the field of microwave absorber technology, specifically relating to a P~K band ultra-wideband microwave absorber. Background Technology

[0002] Currently, research and design of broadband microwave absorbers mainly focus on higher frequency bands such as L, S, C, X, and Ku. However, when attempting to extend the high-efficiency absorption capability to lower frequency bands (such as the P-band), two key technical bottlenecks are encountered, as shown below: 1. The contradiction between narrow low-frequency absorption bandwidth and structural thickness: When existing technologies extend to low-frequency bands (especially the P-band), they generally suffer from a significant narrowing of the absorption bandwidth. More importantly, to achieve effective absorption in the low-frequency band, it is usually necessary to greatly increase the physical thickness (i.e., cross-sectional dimensions) of the absorber, which directly conflicts with the stringent requirements of modern electromagnetic compatibility, stealth platforms, and other applications for miniaturization, lightweighting, and thinning of devices.

[0003] 2. The engineering challenge of balancing ultra-wideband and thinness: Although researchers have made progress in improving absorption efficiency and expanding operating bandwidth through the design of artificial electromagnetic media (such as frequency-selective surfaces FSS and metamaterials), how to simultaneously achieve ultra-wideband and efficient microwave absorption covering the P-band (low frequency) to the K-band (high frequency) under the constraint of limited and thin profiles remains an extremely challenging engineering problem.

[0004] In summary, existing microwave absorber designs have not yet been able to systematically overcome the constraints between low-frequency absorption performance and overall structural thinning. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this application is to provide a P-K band ultrawideband microwave absorber. This application can achieve wideband high-efficiency absorption from the low-frequency P-band to the high-frequency K-band, while maintaining an extremely thin structure thickness and exhibiting good angular stability and polarization insensitivity.

[0006] To achieve the above objectives, this application provides the following technical solution: A P-K band ultra-wideband microwave absorber includes: a base plate, on the upper surface of which a first frequency selective surface layer, a second frequency selective surface layer, and an active frequency selective surface layer are sequentially disposed along a first direction. A first spacer layer is disposed between the first and second frequency selective surface layers, a second spacer layer is disposed between the second and active frequency selective surface layers, and a third spacer layer is disposed between the active frequency selective surface layer and the base plate. The first frequency selective surface layer is used to absorb high-frequency electromagnetic waves from the X-band to the K-band, the second frequency selective surface layer is used to absorb mid-frequency electromagnetic waves from the S-band to the C-band, and the active frequency selective surface layer is used to tunably absorb low-frequency electromagnetic waves from the P-band to the L-band, thereby achieving ultra-wideband microwave absorption from the P-band to the K-band.

[0007] Preferably, the side of the first frequency selective surface layer facing away from the second frequency selective surface layer is provided with an absorbing structure.

[0008] Preferably, the absorbing structure includes several cross-shaped structural units, wherein each structural unit is composed of two orthogonal rectangular resistive film strips overlapping each other, which are parallel and perpendicular to the incident electric field direction, respectively.

[0009] Preferably, the side of the second frequency selection surface layer facing the first spacer layer is provided with a bandwidth extension structure.

[0010] Preferably, the bandwidth expansion structure includes several double-ring structural units, wherein each double-ring structural unit is composed of an inner square resistive film ring and an outer square resistive film ring, and the inner square resistive film ring and the outer square resistive film ring are not directly connected to each other, nor are the outer square resistive film rings directly connected to adjacent structural units.

[0011] Preferably, the active frequency selective surface layer has periodically arranged metal patch units on the side facing the second spacer layer.

[0012] Preferably, each metal patch unit is loaded with a lumped resistor and a varactor diode.

[0013] Compared with the prior art, the beneficial effects of this application are as follows: This application successfully designed an ultra-wideband microwave absorber covering the 0.49–24.97 GHz (-10 dB absorption bandwidth) by cascading an active frequency selective surface (AFSS) absorber with tunable broadband absorption characteristics and a traditional passive frequency selective surface (FSS) absorber, through simulation analysis and performance optimization. The absorber achieves an absorptivity of over 90% under perpendicular incidence and maintains a stable absorptivity of around 80% within the 0–45° oblique incidence range. The introduction of the AFSS layer effectively reduces the overall structural profile thickness to only 0.0336λL (λL is the wavelength corresponding to the lowest operating frequency). Furthermore, thanks to the symmetrical design of the structure, the absorber exhibits excellent polarization insensitivity. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of a P~K band ultrawideband microwave absorber provided in one embodiment of this application; Figure 2 yes Figure 1 A schematic diagram of the equivalent circuit model of the FSSⅠ layer in the absorber is shown; Figure 3 yes Figure 1 A schematic diagram of the equivalent circuit model of the FSSⅡ layer in the absorber is shown; Figure 4 yes Figure 1 A schematic diagram of the equivalent circuit model of the AFSS layer in the absorber is shown. Figure 5 yes Figure 1 The absorber shown has different frequencies. C v Schematic diagram of transverse electric wave absorption characteristics at a certain value; Figure 6 yes Figure 1 The absorber shown has different frequencies. C v Schematic diagram of transverse magnetic wave absorption characteristics at a certain value; Figure 7 yes Figure 1 The absorber shown has different frequencies. C v A schematic diagram of the normalized impedance curve at a given value; Figure 8 yes Figure 1 The absorber shown has different frequencies. C v A schematic diagram of the absorption rate curve at a given value; Figure 9 yes Figure 1 The FSSⅠ layer in the absorber shown was obtained through equivalent circuit model and full-wave simulation. S 11 | A diagram showing the comparison of the curves; Figure 10 yes Figure 1 The FSSⅡ layer in the absorber shown was obtained through equivalent circuit model and full-wave simulation. S 11 | A diagram showing the comparison of the curves; Figure 11 yes Figure 1 The AFSS layer in the absorber shown was obtained through simulation using an equivalent circuit model. S 11 |A schematic diagram of the curve; Figure 12 yes Figure 1 The AFSS layer in the absorber shown was obtained through full-wave simulation. S 11 |A schematic diagram of the curve; Figure 13 yes Figure 1 A schematic diagram of the overall equivalent circuit model of the absorber shown. Figure 14 yes Figure 1 The absorber shown passes through Figure 13 The equivalent circuit model shown in the simulation results at different frequencies are different. C v Schematic diagram of absorption characteristics at a value; Figure 15 yes Figure 1 The absorber shown passes through Figure 13 The equivalent circuit model shown in the simulation results at different frequencies are different. C v A schematic diagram of the absorption rate curve at a given value; Figure 16 yes Figure 1 A schematic diagram of the surface current distribution of the FSSⅠ, FSSⅡ, and AFSS layers of the absorber at 18.7 GHz; Figure 17 yes Figure 1 A schematic diagram of the surface current distribution of the FSSⅠ, FSSⅡ, and AFSS layers of the absorber at 20.3 GHz; Figure 18 yes Figure 1 The diagram shows the surface current distribution of the FSSⅠ, FSSⅡ, and AFSS layers of the absorber at 23.3 GHz. Figure 19 yes Figure 1 The absorber shown is in C v A schematic diagram comparing the transverse electromagnetic wave absorption rate with different incident angles at a value of 0.75pF. Figure 20 yes Figure 1 The absorber shown is in Cv A schematic diagram of the transverse magnetic wave absorptivity curve at different incident angles when the absorptivity is 0.75pF. Figure 21 yes Figure 1 The absorber shown is in C v A schematic diagram comparing the single-station RCS performance of a 500×500mm absorber plate and a metal plane of the same size at a voltage of 0.75pF. Detailed Implementation

[0015] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0016] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0017] In this application, unless otherwise expressly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0018] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0019] Figure 1 This is a schematic diagram of the structure of a P-K band ultrawideband microwave absorber provided in an exemplary embodiment of this application, as shown below. Figure 1 As shown, the microwave absorber has a coordinate system, which is defined in this application as follows: the plane containing the XY axes is parallel to the horizontal plane, the Z-axis is perpendicular to the plane containing the XY axes, the X-axis points to the right, and the Y-axis points towards the observer's location. The direction of the Z-axis towards the plane containing the XY axes is denoted as the first direction (i.e.,...). Figure 1 The direction opposite to the Z-axis is designated as the first direction; the direction of the Y-axis is designated as the second direction; and the direction of the X-axis is designated as the third direction. It should be noted that this coordinate system is only used to define the relative positions and orientations of the components in space within this application. Specifically, the microwave absorber includes: a base plate, on the upper surface of which a first frequency selective surface layer (FSSI layer), a second frequency selective surface layer (FSSII layer), and an active frequency selective surface layer (AFSS layer) are sequentially disposed along the first direction. A first spacer layer (e.g., ...) is disposed between the first and second frequency selective surface layers. Figure 1 A second spacer layer (such as spacer layer I) is provided between the second frequency selective surface layer and the active frequency selective surface layer. Figure 1 A third spacer layer (such as spacer layer II) is provided between the active frequency selective surface layer and the base plate. Figure 1 (Separator layer III in the middle).

[0020] In this embodiment, the microwave absorber adopts a multi-layer composite structure design, with a first frequency selective surface layer, a second frequency selective surface layer, and an active frequency selective surface layer sequentially arranged along the first direction. Each functional layer is physically isolated and electromagnetically coupled between them through spacer layers, and a metal base plate is provided at the bottom as a reflective layer. Through this combination of multi-layer spacer and frequency selective surface structure, not only can ultra-wideband microwave absorption characteristics from low-frequency P-band to high-frequency K-band be achieved, but also good angular stability and polarization insensitivity characteristics can be obtained while maintaining an extremely thin structural thickness, thereby effectively solving the contradiction between low-frequency absorption bandwidth and structural thickness.

[0021] In another exemplary embodiment, such as Figure 1 As shown, the side of the first frequency selective surface layer facing away from the second frequency selective surface layer is provided with an absorbing structure.

[0022] In this embodiment, the absorbing structure includes several cross-shaped structural units. Each structural unit is composed of two orthogonal rectangular resistive film strips overlapping each other, which are parallel and perpendicular to the incident electric field direction, respectively.

[0023] The first frequency selective surface layer (FSSI layer) serves as the uppermost resistive frequency selective surface of the microwave absorber, and it has a thickness of 0.168 mm and a relative permittivity of ε. r =3.48, loss tangent is tanδ r A Rogers RO4350B dielectric substrate with a sheet resistance of 0.0037 is used as a carrier, on which a resistive film with a sheet resistance of 70 Ω / sq is printed to form a cross-shaped structural unit. For example, this structural unit is formed by two sets of orthogonal rectangular resistive strips with a length L = 7.6 mm and a width W = 1.2 mm, overlapping each other, with a gap W between the strips. g =0.4 mm, and arranged with a period of P=16 mm. Its structure is based on two mutually perpendicular resistive strips responding to incident electric fields with different polarization directions, which is equivalent to two series RLC circuits in parallel, thereby exciting two resonant absorption peaks at 9.7 GHz and 18.7 GHz, realizing the effective absorption of high-frequency electromagnetic waves in the X~K band.

[0024] It should be noted that the choice of a cross-shaped structure as the absorbing unit for the first frequency selection surface layer is primarily based on its excellent dual-polarization absorption capability and dual-resonance characteristics in the high-frequency band (X-band to K-band), which can provide high-frequency support for ultra-wideband absorption. The simple geometry and regular periodic arrangement of the cross-shaped structure not only facilitate electromagnetic coupling with the underlying FSSII and AFSS layers, but also make it easy to achieve high-precision printing on standard dielectric substrates, which is beneficial for the thinning of the overall structure. By optimizing the length, width, and gap parameters of the cross-shaped strips, two adjacent resonant absorption peaks can be excited in the target frequency band (such as 9.7 GHz and 18.7 GHz in this design), thereby effectively expanding the high-frequency absorption bandwidth. In contrast, traditional square patch structures can usually only generate a single resonance, which is difficult to meet the requirements of wideband absorption; while complex structures such as the Jerusalem cross have certain design flexibility, they have disadvantages such as structural complexity, high processing difficulty, and limited bandwidth expansion capability. Therefore, the cross-shaped structure shows a better balance between overall performance and engineering implementation.

[0025] Furthermore, the FSSI layer is configured with a first equivalent circuit model. The FSSI layer can be viewed as being formed by the overlapping of two grid cells in different directions, one parallel to the electric field direction and the other perpendicular to the electric field direction. For example... Figure 2 As shown, the first equivalent circuit model is represented by two series-connected RLC circuits connected in parallel, where C1 represents the gap capacitance at the tips of the two grid cells parallel to the electric field direction, and C2 represents the capacitance perpendicular to the electric field direction with a spacing of P / 2-W. gThe gap capacitance of the two grid cells, L1 and L2 represent the equivalent inductance of the two grid cells in different directions, R1 and R2 represent the equivalent resistance, the subscript "1" indicates parallel to the electric field direction, "2" indicates perpendicular to the electric field direction, and C1=0.055 pF, L1=3.04 nH, R1=R2=304 Ω, C2=0.0049 pF, L2=0.8nH.

[0026] In another exemplary embodiment, the side of the second frequency selection surface layer facing the first spacer layer is provided with a bandwidth extension structure.

[0027] In this embodiment, the bandwidth expansion structure includes several double-ring structural units. Each double-ring structural unit is composed of an inner square resistive film ring and an outer square resistive film ring. The inner square resistive film ring and the outer square resistive film ring are not directly connected, nor are the outer square resistive film rings directly connected to adjacent structural units.

[0028] In this embodiment, the FSSII layer serves as the resistive frequency selective surface of the absorber's intermediate layer. It utilizes the same Rogers RO4350B dielectric substrate as the FSSI layer, on which a resistive film with a sheet resistance of 70 Ω / sq is printed to form a double-ring structural unit. This structural unit consists of two independent square resistive rings, one inner and one outer. For example, the outer ring has an outer side length D1 = 15.8 mm and a linewidth W1 = 1.5 mm, while the inner ring has an outer side length D2 = 9.5 mm and a linewidth W2 = 2.25 mm. The rings are arranged with a period P = 16 mm and are not interconnected. Its operating principle is based on the coupling capacitance and equivalent inductance formed by the inner and outer square rings and adjacent units. The equivalent circuit can be characterized as a parallel combination of two series RLC circuits corresponding to the outer and inner rings, respectively, thereby exciting a resonant absorption peak at 5.28 GHz. This primarily enables effective absorption of S~C band electromagnetic waves and further extends the overall absorption bandwidth through coupling with the upper and lower layers.

[0029] It's important to note that the primary purpose of employing a double-loop structure for bandwidth extension is to introduce multiple resonant modes within a limited space, thereby effectively expanding the absorption bandwidth. Compared to a single-loop structure, the double-loop structure can form two adjacent resonant peaks through the coupling capacitance between the inner and outer loops and their respective equivalent inductances, achieving impedance matching over a wider frequency band. Furthermore, the double-loop structure exhibits good symmetry and polarization insensitivity, maintaining stable absorption performance over a wide angular range. Compared to cross-shaped or square patch structures, the double-loop structure demonstrates superior bandwidth extension capabilities in the low-frequency bands (such as the S and C bands) and is easier to electromagnetically couple with upper and lower layers, improving overall absorption efficiency. Comparative analyses have been verified during the design process using equivalent circuit models and full-wave simulations, showing that the double-loop structure outperforms single-loop or simple patch structures in both absorption bandwidth and absorption rate in the mid-frequency band.

[0030] It should also be noted that the inner square resistive film ring is not directly connected to the outer square resistive film ring, nor is the outer ring directly connected to adjacent units. This is to avoid forming continuous conductive paths, thereby preventing unnecessary low-frequency reflections or parasitic resonances. Direct connection would increase coupling between structural units, altering equivalent circuit parameters, causing a shift in the originally designed resonant frequency, disrupting the impedance matching characteristics of the absorber, and ultimately reducing absorption rate and bandwidth performance. Furthermore, maintaining inter-ring isolation helps preserve the symmetry and periodicity of the structure, ensuring stability under different polarizations and incident angles. This design approach has been reflected in the subsequent equivalent circuit model, and its necessity and superiority have been verified through simulation.

[0031] In addition, a second equivalent circuit model is set on the FSSII layer, such as Figure 3 As shown, the equivalent circuit model is represented by a series connection of R3, L3, C3 and a series connection of R4, L4, C4 connected in parallel. C3 represents the coupling capacitance between the two outer square rings, L3 and R3 represent the equivalent inductance and equivalent resistance of the outer square ring, respectively, C4 represents the coupling capacitance between the inner and outer square rings, L4 and R4 represent the equivalent inductance and equivalent resistance of the inner square ring, respectively, and Z2 represents the intrinsic impedance of spacer layer II. For example, C3 = 0.24 pF, L3 = 8.569 nH, R3 = 330 Ω, L4 = 0.936 nH, C4 = 0.087 pF, and R4 = 139 Ω.

[0032] In another exemplary embodiment, the active frequency selective surface layer is provided with periodically arranged metal patch units on the side facing the second spacer layer, and each metal patch unit is loaded with a lumped resistor and a varactor diode.

[0033] In this embodiment, the AFSS layer is composed of periodically arranged square metal patch units, with adjacent metal patch units connected by metal interconnects. Furthermore, each metal patch unit is loaded with a lumped resistor R. v and varactor diodes C v Among them, the lumped resistance R v With varactor diode C v The layers are connected in parallel and connected to the underlying metal substrate via metal vias to form a resonant circuit. This AFSS layer is printed on a 0.168 mm thick Rogers RO4350B dielectric substrate with a relative permittivity ε. r =3.48, loss tangent tanδ r =0.0037. The periodicity constant P of the AFSS layer is 16 mm, the side length A of the square patch is 6 mm, the gap G between adjacent patches is 0.5 mm, and the gap between the patches with the lumped resistor and varactor diode is... G v The value is 3mm. The capacitance of the varactor diode is adjusted. C v By varying the absorption rate from 0.75 pF to 9 pF, the broadband tunable absorption characteristics of the AFSS layer in the P~L band can be achieved.

[0034] In addition, a third equivalent circuit model is set on the AFSS layer, such as Figure 4 As shown, the equivalent circuit model is represented by circuit I and circuit II connected in parallel. Circuit I consists of a parallel Rv-C6 circuit, an inductor L6, and a parallel L8-C8 circuit connected in series; circuit II consists of a series C5-C... v The circuit consists of inductor L5 and a parallel circuit of L7-C7 connected in series. L5 and L6 are the equivalent inductances of the square patch panels, L7 and L8 are the equivalent inductances of the connecting lines between adjacent square patch panels, C5 and C6 are the coupling capacitances between the two square patch panels connecting the active device, C7 and C8 are the coupling capacitances between two adjacent square patch panels, and Z3 is the intrinsic impedance of spacer layer III. Since spacer layers I, II, and III are all PMI (Polymethacrylimide) foam, therefore, Z1 = Z2 = Z3 = Z0 / And L5=L6=0.135 nH, L7=L8=5.057 nH, C5=C6=0.1pF, C7=C8=0.126 pF, R v =400 Ω, C v =0.75 pF~9 pF.

[0035] Figure 5 yes Figure 1The absorber shown has different frequencies. C v Schematic diagram of transverse electric wave absorption characteristics at a certain value; Figure 6 yes Figure 1 The absorber shown has different frequencies. C v A schematic diagram of the transverse magnetic wave absorption characteristics at a given value. (See diagram for example.) Figure 5 and Figure 6 As shown, when the capacitance of the varactor diode... C v When varying from 9 pF to 0.75 pF, the absorber exhibits a bandwidth of S11 < -10 dB covering almost the entire P-K band in both polarization modes. This demonstrates that the absorber proposed in this application can achieve ultra-wideband and high-efficiency absorption performance in the P-K band, and is polarization insensitive.

[0036] Furthermore, according to the definition of absorber absorption rate, the absorption rate of the absorber proposed in this application is A(ω)=1-R(ω)=1-│S11│ 2 And R(ω) = (Zn-1) / (Zn+1), where Zn = Re(Zn) + Im(Zn) is the normalized impedance of the absorber. Therefore, the absorptivity and normalized impedance Z can be obtained as follows. n Relationship: A(ω)=2 / (Re(Zn)+Im(Zn)+1) From the above equation, we can see that if the absorption rate is to be close to 1, the real part Re(Zn) of the normalized impedance of the absorber needs to be close to 1, while the imaginary part Im(Zn) needs to be close to 0.

[0037] Figure 7 yes Figure 1 The absorber shown is at different frequencies and different C v A schematic diagram of the normalized impedance curve at a given value, from Figure 7 It can be seen that within the entire operating frequency band, when C v When varying from 0.75 to 9 pF, the real part of the normalized impedance changes from 0.49 GHz to 24.97 GHz, always fluctuating around 1, while the imaginary part remains stable around 0. This indicates that the input impedance of the absorber proposed in this application achieves good matching with the free-space impedance over a wide frequency range, thus verifying its broadband and efficient absorption characteristics.

[0038] Figure 8 yes Figure 1 The absorber shown has different frequencies. C v A schematic diagram of the absorption rate curve at a certain value, as shown below. Figure 8 As shown, when Cv When varying within the range of 0.75 to 9 pF, absorption of 90% or higher is achieved in the range of 0.49 to 24.97 GHz, indicating that the absorber can achieve ultra-wideband high-efficiency absorption in the P~K band.

[0039] Figure 9 yes Figure 1 The FSSⅠ layer in the absorber shown was obtained through equivalent circuit model and full-wave simulation. S 11 | A diagram showing the comparison of the curves; Figure 10 yes Figure 1 The FSSⅡ layer in the absorber shown was obtained through equivalent circuit model and full-wave simulation. S 11 | A diagram showing the comparison of the curves; Figure 11 yes Figure 1 The AFSS layer in the absorber shown was obtained through simulation using an equivalent circuit model. S 11 |A schematic diagram of the curve; Figure 12 yes Figure 1 The AFSS layer in the absorber shown was obtained through full-wave simulation. S 11 A schematic diagram of the curve. (For example...) Figures 9 to 12 As shown, the FSSⅠ layer has two resonant absorption peaks at 9.7 GHz and 18.7 GHz, mainly responsible for absorption in the X~K band. The FSSⅡ layer has one resonant absorption peak at 5.28 GHz, mainly responsible for absorption in the SC band; while the AFSS layer, when the varactor diode capacitance... C v Adjustable absorption in the PL band can be achieved by varying the voltage between 0.75pF and 9pF. Furthermore, the results obtained from the equivalent circuit model and full-wave simulation of the three-layer structure show high agreement, with the positions of each absorption peak remaining consistent. This explains the absorption mechanism of each FSS layer from the perspective of the equivalent circuit. Notably, the introduction of the AFSS layer brings in a large, voltage-adjustable capacitor, enabling the absorber to achieve absorption at lower frequencies while maintaining a constant structural profile thickness.

[0040] Furthermore, this application cascades the equivalent circuit models corresponding to the above-mentioned three-layer structure of FSSⅠ layer, FSSⅡ layer and AFSS layer, to obtain the following: Figure 13 The overall equivalent circuit model of the absorber is shown. Furthermore, by analyzing... Figure 13 Simulation of the equivalent circuit model shown yields the following results: Figure 14 The absorber shown is in C v Schematic diagram of absorption characteristics at values ​​and as shown Figure 15 The absorption rate curve shown is from... Figure 14 and Figure 15 It can be seen that the simulation results deviate slightly from the full-wave simulation results. This is mainly because the established equivalent circuit model does not take into account the coupling effect between structures.

[0041] Figure 16 , Figure 17 and Figure 18 These are schematic diagrams showing the surface current distribution of the FSSⅠ, FSSⅡ, and AFSS layers of the absorber at 18.7 GHz, 20.3 GHz, and 23.3 GHz, respectively. Figures 16 to 18 The surface current distribution shown indicates that at 18.7 GHz, the current is mainly concentrated in the outer rings of the FSSⅠ and FSSⅡ layers and the AFSS layer, suggesting that the resonance peak is primarily excited by the electromagnetic coupling effect between these three layers. At 20.3 GHz and 23.3 GHz, the current is mainly concentrated in the FSSⅠ and AFSS layers, indicating that the absorption performance is significantly affected by the coupling between these two layers. Although the absorption rate decreases slightly in this frequency band, it still remains around 90%. Overall, the results obtained from the two simulation methods show good consistency, verifying that the absorber possesses ultra-wideband and high-efficiency absorption performance in the P~K band range. Furthermore, the feasibility and effectiveness of the proposed structure are further confirmed from the perspective of the equivalent circuit model.

[0042] Figure 19 and Figure 20 The absorber was demonstrated in C v Comparison of transverse electric and transverse magnetic wave absorption rate curves at different incident angles when the flux density is 0.75 pF. Figure 19 and Figure 20 It can be seen that in transverse electromagnetic wave mode, as the incident angle increases from 0° to 45°, the absorptivity decreases with increasing incident angle, remaining stable within the 0-30° range, until the incident angle increases to 45°, at which point the absorptivity drops to approximately 80%. In transverse magnetic wave mode, as the incident angle gradually increases, the low-frequency absorption peak shifts slightly towards higher frequencies, but remains generally stable, with the absorptivity consistently around 90%. This demonstrates that the absorber proposed in this application can achieve good angular stability within the 0 to 45° range.

[0043] Figure 21 It is the absorber in C v The single-station RCS performance of the absorber plate (length × width = 500 × 500 mm) at a voltage of 0.75 pF was analyzed and compared with that of a metal plane of the same size. Figure 21As can be seen, the absorber proposed in this application can achieve high RCS reduction in the ultra-wideband P~K band. Furthermore, the absorber's polarization insensitivity and angular stability make it a promising candidate for military stealth applications.

[0044] Furthermore, this application compares the described microwave absorber with existing microwave absorbers, and the specific comparison results are shown in Table 1: Table 1 Comparison Results

[0045] Table 1 compares the absorber proposed in this application with some existing broadband microwave absorbers. As can be seen from Table 1, the absorption range of most existing broadband microwave absorbers is in the L-Ku band, and their absorption bandwidth is generally within 20 GHz, while their thickness is typically around 0.1λ. L Left and right (λ) L (This refers to the wavelength corresponding to the minimum operating frequency). The ultra-wideband microwave absorber proposed in this application has an absorption bandwidth of 24.48 GHz, covering multiple bands from P to K, exhibiting superior ultra-wideband microwave absorption characteristics compared to existing absorbers. Furthermore, the overall thickness of the absorber proposed in this application is only 0.0336λ. L This makes the designed ultrawideband microwave absorber have a wider range of applications.

[0046] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural changes made based on the content of this application's specification and drawings, or any direct or indirect application thereof, are prohibited.

Claims

1. A P-K band ultrawideband microwave absorber, characterized in that, The absorber includes: Base plate, The upper surface of the base plate is sequentially provided with a first frequency selective surface layer, a second frequency selective surface layer, and an active frequency selective surface layer along a first direction, wherein, A first spacer layer is disposed between the first frequency selection surface layer and the second frequency selection surface layer; a second spacer layer is disposed between the second frequency selection surface layer and the active frequency selection surface layer; and a third spacer layer is disposed between the active frequency selection surface layer and the base plate. The first frequency-selective surface layer is used to absorb high-frequency electromagnetic waves from the X-band to the K-band; The second frequency-selective surface layer is used to absorb intermediate frequency electromagnetic waves from the S-band to the C-band; The active frequency-selective surface layer is used to tunably absorb low-frequency electromagnetic waves from the P-band to the L-band, so as to achieve ultra-wideband microwave absorption from the P-band to the K-band.

2. The microwave absorber according to claim 1, characterized in that, The side of the first frequency selective surface layer facing away from the second frequency selective surface layer is provided with a wave-absorbing structure.

3. The microwave absorber according to claim 2, characterized in that, The absorbing structure includes: Several cross-shaped structural units, among which, Each structural unit consists of two orthogonal rectangular resistive film strips overlapping each other, parallel and perpendicular to the incident electric field direction, respectively.

4. The microwave absorber according to claim 1, characterized in that, The second frequency selection surface layer has a bandwidth extension structure on the side facing the first spacer layer.

5. The microwave absorber according to claim 4, characterized in that, The bandwidth expansion structure includes: Several two-sided ring structural units, among which, Each double-ring structural unit consists of an inner square resistive film ring and an outer square resistive film ring, and the inner square resistive film ring and the outer square resistive film ring are not directly connected to each other, nor are the outer square resistive film rings directly connected to adjacent structural units.

6. The microwave absorber according to claim 1, characterized in that, The active frequency selective surface layer has periodically arranged metal patch units on the side facing the second spacer layer.

7. The microwave absorber according to claim 6, characterized in that, Each metal patch unit is loaded with a lumped resistor and a varactor diode.

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