A wave absorber for ultra-wideband radar cross section reduction

Abstract

The application discloses a wave absorber for reducing the radar cross section of an ultra-wideband radar, comprising a plurality of unit structures arranged into an uneven super surface composed of M*N lattices, each lattice being composed of a plurality of unit structures arranged periodically, and each unit structure comprising a first dielectric substrate, a second dielectric substrate and a metal ground plate connected in sequence, a first loss layer being arranged on the first dielectric substrate, a second loss layer being arranged on the second dielectric substrate, a second air layer being arranged between the metal ground plate and the second dielectric substrate, and a first air layer being arranged between the first dielectric substrate and the second dielectric substrate. The technical scheme has the characteristics of simple structure and polarization insensitivity, and simultaneously has the stability in a wide angle and the performance of reducing the radar cross section of an ultra-wideband radar.

Description

Technical Field

[0001] This invention belongs to the field of radar detection technology, and particularly relates to an absorber for reducing the cross-section of ultra-wideband radar. Background Technology

[0002] Radar detection technology plays a crucial role in modern military warfare. The accompanying development of radar cross section (RCS) reduction technology is indispensable for stealth applications. Metamaterials and metasurfaces, with their flexible electromagnetic control capabilities, are effective ways to achieve RCS reduction.

[0003] RCS reduction methods include active cancellation, shaping, electromagnetic absorption, and passive cancellation. Electromagnetic absorption methods include converting the incident electromagnetic wave into a surface wave and using resistors for absorption. Structures that convert the incident electromagnetic wave into a surface wave are generally three-dimensional and complex. Traditional electromagnetic absorption methods have relatively narrow RCS reduction bandwidths, complex structures, and limited angular stability. Passive cancellation methods mainly include coded metasurfaces, phase gradient metasurfaces, checkerboard metasurfaces, and dartboard metasurfaces. Among these, coded metasurfaces and phase gradient metasurfaces have limited RCS reduction bandwidths. Phase cancellation and polarization conversion are the main RCS reduction mechanisms of checkerboard metasurfaces. The former achieves backward RCS reduction by using a 180°±37° phase difference between different scattered waves. The latter converts the energy of the incident wave into cross-polarization components, achieving co-polarized RCS reduction. However, many existing passive cancellation methods cannot simultaneously achieve ultra-wideband RCS reduction and wide-angle stability.

[0004] Overall, it is quite difficult to achieve stealth technology that simultaneously possesses ultra-wideband RCS reduction, polarization insensitivity, simple structure, and wide angular stability characteristics. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide an absorber for reducing the radar cross section (RCS) of an ultra-wideband radar. The absorber achieves RCS reduction based on a hybrid mechanism. In the low-frequency band, it relies on the absorption effect of a double-layer loss layer. In the mid-frequency band, it relies on the combined effect of absorption and phase cancellation due to the different lattice height differences of the absorber. In the high-frequency band, it achieves RCS reduction through phase cancellation. The absorber has the characteristics of simple structure, polarization insensitivity, and simultaneously has wide-angle stability and ultra-wideband radar cross section reduction performance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An absorber for reducing the cross-section of ultra-wideband radar includes: multiple unit structures arranged in an M×N lattice-based non-planar metasurface, each lattice consisting of multiple unit structures arranged periodically, each unit structure including: a first dielectric substrate, a second dielectric substrate, and a metal ground plane connected in sequence; a first loss layer on the first dielectric substrate, a second loss layer on the second dielectric substrate, a second air layer between the metal ground plane and the second dielectric substrate, and a first air layer between the first and second dielectric substrates; both the first and second loss layers are combinations of metal and resistors, the metal shape of the first loss layer being a metal square ring and a metal cross, and the metal shape of the second loss layer being a deformed Jerusalem cross with gaps; the resistors on the first and second loss layers are symmetrically distributed.

[0008] Preferably, nylon pillars are used for support between the first dielectric substrate and the second dielectric substrate, and between the metal floor and the second dielectric substrate.

[0009] Preferably, the overall dimensions of the absorber in the horizontal direction are 300×300mm. 2 .

[0010] Preferably, the first and second dielectric substrates are made of F4B material with a relative permittivity of ε. r =2.65, and the loss tangent is tanδ = 0.001.

[0011] Preferably, the unit period p of the absorber is 20mm, the overall thickness of the absorber is 12.006mm, the thickness of the first air layer and the second air layer are both 5mm, and the thickness of the first dielectric substrate and the second dielectric substrate are both 1mm.

[0012] Preferably, the metal material of the first and second loss layers is copper, and the thickness is 0.018 mm.

[0013] Preferably, the surface mount resistors on the first and second loss layers are packaged in a 0402 package, with a length of 1 mm and a width of 0.5 mm; wherein, in the first loss layer, the surface mount resistor R is shaped like a metal square ring. a A surface mount resistor R with a resistance of 590Ω and a shape resembling a metal cross. b The resistance is 140Ω; in the second loss layer, the chip resistor R is shaped like a deformed Jerusalem cross with gaps, located around the inner perimeter. c The resistance is 120Ω, and the surface mount resistors R are located around the outer perimeter. d The resistance is 430Ω.

[0014] Preferably, under vertical electromagnetic wave incidence, the absorber achieves a single-station RCS reduction of more than 10 dB in the ultra-wideband frequency band from 3.03 GHz to 56.58 GHz; at the same time, under oblique electromagnetic wave incidence, the absorber has wide-angle stability.

[0015] The present invention has the following beneficial effects:

[0016] 1. It can simultaneously achieve RCS reduction for ultra-wideband and large-angle oblique incidence performance;

[0017] 2. It features simple structure, insensitivity to polarization, and low cost;

[0018] 3. The combined effect of the two dielectric substrates and two air layers in the absorber unit structure can extend the absorption bandwidth of the flat absorber array;

[0019] 4. By adopting a combination of absorbing unit structure and uneven metal ground plane array arrangement, the RCS reduction bandwidth of the uneven absorber is greatly expanded. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the unit structure of the absorber for reducing the cross-section of ultra-wideband radar according to the present invention;

[0022] Figure 2 The diagram shows the equivalent circuit model of the unit structure of the present invention and the comparison of the amplitude of the reflection coefficient calculated by CST simulation and ECM; where (a) is the ECM of the unit structure when the electromagnetic wave is incident perpendicularly, and (b) is the comparison of the amplitude of the reflection coefficient calculated by simulation and ECM.

[0023] Figure 3 This refers to the reflection coefficient of the unit structure of the present invention when different loss layers are involved;

[0024] Figure 4 This is a schematic diagram of the layout of the uneven floor of the present invention (M=N=5,dx=dy=60mm);

[0025] Figure 5 The reflection phase of metal floors of different heights under vertical incidence is simulated in this invention.

[0026] Figure 6The RCS reduction results of different height combinations of metal flooring arrangements simulated in this invention;

[0027] Figure 7 This is a schematic diagram of the non-flat absorber array arrangement of the present invention;

[0028] Figure 8 This is a comparison diagram showing the RCS reduction of the flat absorber and the non-flat absorber under vertical incidence according to the present invention.

[0029] Figure 9 This invention provides a reduction in the RCS of the x-polarization and y-polarization of a non-flat absorber under vertical incidence.

[0030] Figure 10 The present invention simulates the RCS reduction of the non-flat absorber in the mirror direction of TE polarization and TM polarization under oblique incidence; where (a) is the simulation result under TE polarization and (b) is the simulation result under TM polarization.

[0031] Figure 11 This invention presents a comparison of three-dimensional bistatic scattering patterns of a flat metal floor and a non-flat absorber of the same size at 4 GHz, 15 GHz, 24 GHz, and 52 GHz under vertical y-polarized incident light. Among them, (a) is the comparison result at 4 GHz, (b) is the comparison result at 15 GHz, (c) is the comparison result at 24 GHz, and (d) is the comparison result at 52 GHz. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] Example 1:

[0035] like Figure 1As shown, this embodiment of the invention provides an absorber for reducing the cross-section of ultra-wideband radar, comprising: multiple unit structures arranged in an M×N lattice-based non-flat metasurface, each lattice consisting of multiple unit structures arranged periodically, each unit structure comprising: a first dielectric substrate, a second dielectric substrate, and a metal ground plane connected in sequence, with nylon pillars supporting the first and second dielectric substrates and the metal ground plane and the second dielectric substrate; a first loss layer is provided on the first dielectric substrate, a second loss layer is provided on the second dielectric substrate, a second air layer is provided between the metal ground plane and the second dielectric substrate, and a first air layer is provided between the first and second dielectric substrates; both the first and second loss layers are in the form of a combination of metal and resistors, the metal shape of the first loss layer being a metal square ring and a metal cross, and the metal shape of the second loss layer being a deformed Jerusalem cross with gaps; the metal material of the first and second loss layers is copper, with a thickness of 0.018 mm; the resistors on the first and second loss layers are symmetrically distributed for absorbing the energy of lower frequency electromagnetic waves. Uneven metasurfaces can expand the radar cross-section of the absorber array and reduce the bandwidth; the absorption bandwidth of the absorber at low frequencies can be expanded through the first air layer, the second air layer, the first loss layer, and the second loss layer; the combined effect of the first loss layer and the second loss layer can absorb electromagnetic wave energy at low frequencies, thereby reducing the radar cross-section at lower frequencies.

[0036] The surface mount resistors on the first and second loss layers are packaged in a 0402 package, with a length of 1mm and a width of 0.5mm. Specifically, in the first loss layer, the surface mount resistor R is shaped like a metal square ring. a A surface mount resistor R with a resistance of 590Ω and a shape resembling a metal cross. b The resistance is 140Ω; in the second loss layer, the chip resistor R is shaped like a deformed Jerusalem cross with gaps, located around the inner perimeter. c The resistance is 120Ω, and the surface mount resistors R are located around the outer perimeter. d The resistance is 430Ω.

[0037] The overall dimensions of the absorber in the horizontal direction are 300×300mm. 2 The absorber has a unit period p of 20 mm and an overall thickness of 12.006 mm. The thicknesses of the first and second air layers are both 5 mm, and the thicknesses of the first and second dielectric substrates are both 1 mm. Under perpendicular electromagnetic wave incidence, the absorber achieves a single-station RCS reduction of over 10 dB in the ultra-wideband frequency band from 3.03 GHz to 56.58 GHz; simultaneously, under oblique electromagnetic wave incidence, the absorber exhibits wide-angle stability.

[0038] The relative permittivity and thickness of the dielectric substrate, as well as the thickness of the air layer and the specific dimensions of the metal layer, are determined based on the operating frequency and bandwidth. In this embodiment of the invention, the dielectric substrate material used is F4B, with a relative permittivity of ε. r =2.65, loss tangent is tanδ=0.001, other structural dimensions are as follows: Figure 1 As shown, the unit structure period is p = 20 mm, the dielectric substrate thickness is t = 1 mm, the thickness of the first and second air layers is h = 5 mm, the length of the metal square ring in the first loss layer is l1 = 19.5 mm, the length of the metal cross in the first loss layer is l2 = 10.5 mm, the length of the inner metal of the deformed Jerusalem cross with gaps in the second loss layer is l3 = 14 mm, the length of the outer metal branch of the deformed Jerusalem cross with gaps in the second loss layer is l4 = 18 mm, the length of the inner center metal of the metal cross in the first loss layer is l5 = 2 mm, the metal width of the metal square ring in the first loss layer is w1 = 0.4 mm, and the length of the metal cross in the first loss layer is... The width of the metal is w2 = 2.5 mm. The width of the metal inside the deformed Jerusalem cross with gaps in the second loss layer is w3 = 3.5 mm. The width of the metal branch outside the deformed Jerusalem cross with gaps in the second loss layer is w4 = 0.5 mm. The width of the metal center inside the metal cross in the first loss layer is w5 = 1 mm. The width of the gaps in the metal cross in the first loss layer at 45° and -45° is w6 = 1 mm. The width of the gaps in the deformed Jerusalem cross with gaps in the second loss layer at 45° and -45° is w7 = 2 mm. The width of the metal gaps at all resistor locations in the first and second loss layers is w8 = 0.5 mm.

[0039] In one embodiment of the present invention, such as Figure 2 The figure shows the equivalent circuit model (ECM) of the unit, and the reflection coefficient of the unit structure is fitted using the equivalent circuit model. Figure 2 (a) is the ECM of the unit cell structure when electromagnetic waves are incident perpendicularly. The parameter values ​​of the lumped elements are as follows: R1 = 265Ω, L1 = 8.0nH, C1 = 0.260pF, R2 = 465Ω, L2 = 46.0nH, C2 = 0.004pF, R3 = 220Ω, L3 = 3.9nH, C3 = 0.048pF, R4 = 560Ω, L4 = 30.0nH, C4 = 0.032pF. In the equivalent circuit, the dielectric substrate and air layer are equivalent to transmission lines of different lengths, and the two loss layers are equivalent to four RLC circuits connected in parallel. Figure 2(b) compares the reflection coefficient amplitudes obtained through simulation and ECM calculation. It can be visually observed that the two curves show very similar trends. In the low-frequency range below 10.74 GHz, the two curves almost overlap. At the resonant frequencies of 3.2, 6.64, 10.74, 14.66, and 17.14 GHz, the reflection coefficient amplitudes calculated by ECM are almost equal to the simulated values. The absorption bandwidth of the simulated element ranges from 2.54 GHz to 17.52 GHz, with a relative bandwidth of 149.35%.

[0040] In one embodiment of the present invention, in order to observe the influence of different loss layers on the absorption performance, the reflection coefficients of the first loss layer, the second loss layer, and the two loss layers working together are simulated as follows: Figure 3 As shown, with only the first loss layer, the cell's operating bandwidth is from 2.86 GHz to 7.36 GHz. With only the second loss layer, the cell's operating bandwidth is from 5.90 GHz to 11.31 GHz. When both loss layers are involved, the cell's operating bandwidth is broadened, achieving absorption from 2.54 GHz to 17.52 GHz. A comparison clearly shows that the first loss layer primarily determines the absorption in the lower operating frequency band, while the second loss layer mainly affects the absorption in the middle operating frequency band. The absorption band from 11.31 GHz to 17.52 GHz is the result of the combined effect of the first and second loss layers. Therefore, the combined participation of different loss layers achieves a wide absorption band for the cell.

[0041] Furthermore, to further extend the RCS reduction bandwidth of the absorber, the unit structure of the absorber needs to be arranged into a non-planar metasurface composed of M×N lattices. Each lattice consists of several unit structures arranged periodically, and the height difference between each lattice is determined by the wavelength of the specific operating frequency. The size of the metasurface facet and the number of units in the lattice are periodically arranged and filled according to the size requirements of the application. In this embodiment of the invention, the number of lattices in the x and y directions is the same (M=N), the number of lattices at different heights is also the same, and the height difference between lattices is always an integer multiple of Δh (Δh=2.5mm).

[0042] In one embodiment of the present invention, such as Figure 4 The diagram shown is a schematic representation of the layout of the uneven floor of the present invention. Figure 4 The five different lattice heights shown are z = 0, Δh, 2Δh, 3Δh, and 4Δh. The height difference between adjacent lattices is 2.5 mm. Looking along the x and y directions, the lattice heights increase sequentially.

[0043] In one embodiment of the present invention, Figure 5The figure shows the simulated reflection phase of metal floors with different heights under vertical incidence. It can be seen that changing the floor height effectively alters the reflected wave phase, especially at frequency f = 30 GHz, where a 180° phase difference can be achieved. When multiple metal floors of different heights are randomly combined and arranged, wideband RCS reduction can be achieved.

[0044] In one embodiment of the present invention, Figure 6 The results shown are the simulated RCS reduction results for a metal floor. D represents the number of metal floor height types. When D=1, the metal floor is flat, and the RCS reduction is 0. As the number of metal floor height types increases, the 10dB RCS reduction bandwidth widens. When D=5, the RCS reduction bandwidth extends to 9.36-51GHz.

[0045] In one embodiment of the present invention, Figure 7 The diagram shows a schematic of the array arrangement of an uneven absorber. In this embodiment of the invention, the absorber array consists of 5×5 (300×300mm) 2 It consists of 3×3 (60×60mm) crystal lattices, each containing 3×3 (60×60mm) 2 () Unit structure.

[0046] In one embodiment of the present invention, Figure 8 The diagram shows a comparison of RCS reduction between flat and non-flat absorbing devices under vertical incidence. It should be noted that the RCS reduction is a comparison between an absorber of equal size and a flat metal ground plane. When D=1, the absorber is flat, achieving a 10dB RCS reduction from 2.7GHz to 17.1GHz, with a relative bandwidth of 145.45%. D=5 represents a non-flat absorbing device, achieving a 10dB RCS reduction from 3.03GHz to 56.58GHz, with a relative bandwidth of 179.67%. Therefore, non-flat absorbing devices can broaden the RCS reduction bandwidth of flat absorbing devices.

[0047] In one embodiment of the present invention, Figure 9 The figure shows the simulated RCS reduction of the non-flat absorber under vertical incidence, with x-polarization and y-polarization. It can be seen that the simulated RCS reduction curves for x-polarization and y-polarization almost overlap. An RCS reduction of 179.67% (3.03-56.58 GHz) in relative bandwidth can be achieved under both x- and y-polarization.

[0048] In one embodiment of the present invention, Figure 10 The figure shows the RCS reduction of the simulated non-flat absorber in the mirror directions of TE polarization and TM polarization under oblique incidence. Figure 10 (a) shows the simulation results under TE polarization. Figure 10(b) shows the simulation results under TM polarization. Under oblique incidence, the xoz surface is selected as the incident surface (azimuth angle φ). i =0), and the elevation angles with different incident angles are θ. i =0°, 15°, 30°, 45°, 60°. Under TE and TM polarization, the non-flat absorber can achieve ultra-wideband RCS reduction at different incident angles and has 60° angular stability.

[0049] In one embodiment of the present invention, Figure 11 The diagram shows a comparison of three-dimensional bistatic scattering patterns of a flat metal floor and a non-flat absorber of the same size under vertical y-polarized incidence at 4 GHz, 15 GHz, 24 GHz, and 52 GHz. Figure 11 (a) shows the comparison results at 4 GHz. Figure 11 (b) shows the comparison results at 15 GHz. Figure 11 (c) shows the comparison results at 24 GHz. Figure 11 (d) shows the comparison results at 52 GHz. As can be seen, the non-flat absorber can disperse energy in any direction at different frequencies, greatly reducing the RCS of the metal ground plane.

[0050] The ultra-wideband RCS reduction absorber is a novel artificial electromagnetic structure. This structure is characterized by its simplicity, low cost, indistinct polarization, ultra-wideband RCS reduction, and wide-angle stability, making it a potential candidate for future stealth applications.

[0051] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A wave absorber for ultra-wideband radar cross section reduction, characterized in that The application relates to a wave absorber. The wave absorber comprises a plurality of unit structures arranged into uneven super-surfaces with M*N lattices, each lattice is composed of a plurality of unit structures arranged periodically, and each unit structure comprises a first dielectric substrate, a second dielectric substrate and a metal ground plate connected in sequence, a first loss layer is arranged on the first dielectric substrate, a second loss layer is arranged on the second dielectric substrate, a second air layer is arranged between the metal ground plate and the second dielectric substrate, and a first air layer is arranged between the first dielectric substrate and the second dielectric substrate; the first loss layer and the second loss layer are both in the form of a combination of metal and resistance, the metal shape of the first loss layer is a metal square ring and a metal cross, the metal shape of the second loss layer is a deformed Jerusalem cross with a gap, and the resistances on the first loss layer and the second loss layer are symmetrically distributed; The first dielectric substrate and the second dielectric substrate and the metal ground plate and the second dielectric substrate are supported by nylon columns; The overall size of the wave absorber in the lateral direction is 300 x 300 mm 2 ; The first and second dielectric substrate materials are F4B, with a relative dielectric constant of ε r = 2.65, and a loss tangent of tan δ = 0.

001. The unit period p of the wave absorber is 20 mm, the overall thickness of the wave absorber is 12.006 mm, the thicknesses of the first air layer and the second air layer are both 5 mm, and the thicknesses of the first dielectric substrate and the second dielectric substrate are both 1 mm; The metal material of the first loss layer and the second loss layer is copper, and the thickness is 0.018 mm; The package model of the patch resistor on the first loss layer and the second loss layer is 0402, the resistance length is 1mm, and the width is 0.5mm; wherein, in the first loss layer, the shape is a metal square ring, and the patch resistor R a The resistance value is 590Ω, and the shape is a metal cross, and the patch resistor R b The resistance value is 140Ω; in the second loss layer, the shape is a deformed Jerusalem cross with a gap, and the patch resistor R c The resistance value is 120Ω, and the shape is a metal cross, and the patch resistor R d The resistance value is 430Ω; Under the vertical incidence of electromagnetic waves, the wave absorber realizes RCS single-station reduction of more than 10 dB in the super-wideband frequency range of 3.03 GHz to 56.58 GHz; meanwhile, under the oblique incidence of electromagnetic waves, the wave absorber has wide-angle stability.

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