Multi-bit coded polarization conversion metasurface for RCS reduction

Abstract

The invention provides a multi-bit coding polarization conversion metasurface for RCS (radar cross section) reduction, which is used for realizing broadband radar cross section RCS reduction in a frequency band of 8-26GHz, the metasurface is composed of a chessboard type multi-bit coding array composed of M * M super units, each super unit comprises 4 * 4 metasurface units, the metasurface unit is of a symmetrical sandwich structure composed of a bidirectional arrow and a defective rectangular ring and sequentially comprises a metal copper layer, a dielectric layer and a metal copper layer from the upper layer to the bottom layer. Wherein eight types of metasurface units are obtained by regulating and controlling the width l2 of the defect rectangle with the phase difference theta. According to the coding metasurface, a better RCS reduction effect is achieved, and an effective solution is provided for reducing electromagnetic wave scattering.

Description

Technical Field

[0001] The present invention relates to the field of communication technology, and in particular to a multi-bit coded polarization conversion metasurface for RCS reduction. Background Art

[0002] With the rapid development of radar detection technology, radar stealth technology has gradually become an important indicator for measuring the performance of flying targets. The most critical concept in radar stealth technology is the radar cross section (RCS), which is a physical quantity that characterizes the intensity of the echo generated by the target under the irradiation of radar waves. In practical applications, stealth technology is achieved by reducing the RCS of the detected target.

[0003] In the prior art, RCS reduction is achieved by setting up a checkerboard metasurface. However, the units of these metasurfaces have a specific period, which means that only the phase of the metasurface unit can be designed. In addition, the traditional checkerboard coding is used, which has a certain effect on RCS reduction within the working frequency band, but the 10dB RCS reduction bandwidth is discontinuous and has certain limitations. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings and defects in the prior art and provide a multi-bit coded polarization conversion metasurface for RCS reduction, which is used to achieve broadband radar cross section (RCS) reduction. The metasurface has a symmetrical structure, produces the same electromagnetic scattering for x-polarization and y-polarization, and is polarization insensitive.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A multi-bit coded polarization conversion metasurface for RCS reduction, wherein the metasurface is used to achieve broadband radar cross-section RCS reduction, wherein the metasurface is composed of a chessboard-type multi-bit coding array consisting of M×M super units, each of which includes 4×4 metasurface units, and the metasurface unit is a symmetrical sandwich structure consisting of a bidirectional arrow and a defective rectangular ring, and the metal copper layer, the dielectric layer, and the metal copper layer are arranged from the top to the bottom layer;

[0007] Among them, 8 categories of metasurface units are obtained by adjusting the width l2 of the defect rectangle of the phase difference θ.

[0008] According to the above technical means, in order to obtain multi-bit phase responses with different phase differences, the metasurface units are optimized and designed, including 8 categories of metasurface units.

[0009] Furthermore, the phase difference between adjacent metasurface units in the 8 categories of metasurface units is 45°.

[0010] According to the above technical means, in order to realize multi-bit coding, the metasurface unit of the present invention adopts three bit coding methods.

[0011] Furthermore, the multi-bit coding of the metasurface includes 1-bit coding, 2-bit coding and 3-bit coding, wherein the 1-bit coding is composed of two digital units of "0" and "1" arranged in an alternating manner, the 2-bit coding is composed of three digital units of "00", "01" and "11" arranged in an alternating manner, and the 3-bit coding is composed of eight digital units of "000", "001", "010", "011", "100", "101", "110" and "111" arranged in an alternating manner.

[0012] According to the above technical means, the metasurface structure designed by the present invention has a sandwich structure, which is divided into metal copper-medium-metal copper, and corresponding parameters are set according to the specific structure.

[0013] Furthermore, the period of the metasurface unit is 8.6 mm.

[0014] Furthermore, the thickness of the metal copper of the upper layer and the thickness of the metal copper of the bottom layer are both 0.018 mm.

[0015] Furthermore, the dielectric material of the middle layer is FR4, wherein the dielectric constant is 2.2, the loss tangent is 0.001, and the thickness is 2.7 mm.

[0016] Furthermore, the metasurface has broadband polarization conversion efficiency in the frequency band of 11.2 to 25.6 GHz, with a polarization conversion rate greater than 90%, and has four resonance points in total.

[0017] Beneficial effects of the present invention:

[0018] The metasurface unit of the present invention has a broadband polarization conversion efficiency in the frequency band of 11.2 to 25.6 GHz, a polarization conversion rate greater than 90%, and a total of four resonance points. By optimizing the design of the unit structure size, multi-bit phase responses with phase differences of 180°, 90° and 45° are obtained respectively. Genetic algorithms are used to optimize the coding design to obtain better RCS reduction effects. Compared with ideal metal conductors of the same size, multi-bit optimized coding achieves more than 10dB RCS reduction in the frequency band of 11 to 25 GHz. Compared with traditional chessboard-coded metasurfaces, multi-bit optimized coding metasurfaces can achieve a wider RCS reduction bandwidth. The simulation results verify the proposed metasurface's ability to regulate electromagnetic waves and reduce broadband RCS, providing an effective method for reducing electromagnetic wave scattering. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of a super surface unit of the present invention;

[0020] Figure 2 are the reflection coefficients Ryx, Rxx and PCR of the metasurface unit of the present invention when l2=4.4 mm and θ=45°;

[0021] Figure 3 A schematic diagram of a multi-bit encoding PCM unit of the present invention;

[0022] Figure 4 A schematic diagram of the reflection phase of a metasurface unit of the present invention;

[0023] Figure 5 A schematic diagram of the chessboard-coded metasurface and digital units "0" and "1" of the present invention;

[0024] Figure 6 It is the 3D / 2D scattering pattern of the chessboard-coded metasurface of the present invention;

[0025] Figure 7 It is the flow chart of the optimization of the super surface genetic algorithm of the present invention;

[0026] Figure 8 This is a schematic diagram of the optimized multi-bit coding metasurface in the present invention;

[0027] Fig. 9 The simulation results of the single-station RCS (a) and RCS reduction (b) of the multi-bit coding metasurface and the metal plate under x and y polarization of the present invention are shown;

[0028] Fig.10 This is the 3D far-field scattering diagram of the multi-bit coded metasurface of the present invention. DETAILED DESCRIPTION

[0029] The following will describe the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, not for limiting the scope of protection of the present invention.

[0030] In this embodiment, a multi-bit coded polarization conversion metasurface for RCS reduction is proposed to achieve broadband radar cross-section RCS reduction. The metasurface is composed of a chessboard-like multi-bit coded array consisting of M×M super units, each of which includes 4×4 metasurface units. The metasurface unit is a symmetrical structure consisting of a bidirectional arrow and a defective rectangular ring.

[0031] like Figure 1As shown, the metasurface unit of the present invention has a sandwich structure, the upper layer is a metal copper layer, the middle layer is a dielectric layer, and the bottom layer is a metal copper layer. Among them, the period p = 8.6mm. The thickness of the upper and bottom metal copper layers is t = 0.018mm, and the middle dielectric material is FR4 (dielectric constant ε r =2.2, loss tangent tanδ=0.001), thickness h=2.7 mm. Since the metasurface unit is a symmetrical structure, it produces the same electromagnetic scattering for x-polarization and y-polarization, so the designed metasurface is polarization insensitive.

[0032] like Figure 2 As shown, it is a schematic diagram of the reflection coefficients Ryx, Rxx and PCR of the metasurface unit of the present invention when l2=4.4mm and θ=45°.

[0033] In this embodiment, periodic boundary conditions are set in CST Microwave Studio software, the operating frequency is 8 to 26 GHz, and the frequency domain solver is used for electromagnetic simulation, and the polarization conversion ratio (PCR) is defined as:

[0034]

[0035] Where R xy and R yx represents the cross-polarization reflection coefficient, R yy and R xx The reflection coefficient of the designed metasurface unit under the conditions of l2 = 4.4 mm and θ = 45° and the PCR simulation results are shown in Figure 2 The main polarization reflection coefficient has an amplitude less than -10 dB in the 11.2-25.6 GHz frequency band, the corresponding PCR is greater than 90%, and there are four resonance points in the working frequency band.

[0036] In order to obtain multi-bit phase responses with different phase differences, the metasurface unit is optimized and designed, mainly by adjusting the two parameters l2 and phase difference θ. The schematic diagram of the optimized multi-bit metasurface unit structure is shown in Figure 3 As shown, the phase difference between adjacent metasurface units is 45°. Figure 4 The reflection coefficient phase of each metasurface unit is given. Next, the 8 design units are encoded, and the relative phase and encoding corresponding to each unit are shown in Table 1.

[0037] Table 1 Relative phase and coding of multi-bit metasurface units

[0038]

[0039] In this embodiment, Table 1 gives the relative phase and coding content of the multi-bit metasurface unit, including 1-bit coding, 2-bit coding and 3-bit coding, wherein the 1-bit coding is composed of two digital units of "0" and "1" arranged in an alternating manner, the 2-bit coding is composed of three digital units of "00", "01" and "11" arranged in an alternating manner, and the 3-bit coding is composed of eight digital units of "000", "001", "010", "011", "100", "101", "110" and "111" arranged in an alternating manner.

[0040] In this embodiment, in order to keep consistent with the boundary conditions of the periodic unit designed by the simulation software, the super unit constituting the array is composed of 4×4 designed minimum unit structures. Taking a 6×6 chessboard-type 1-bit coding metasurface as an example, the structural schematic diagram and its super unit are as follows: Figure 5 When a plane wave is incident vertically, the chessboard-like 1-bit coded metasurface will disperse the incident wave in four main directions, thereby reducing the backscattering in the mirror direction. The 3D / 2D scattering diagram is shown in Figure 6 shown.

[0041] In order to further achieve broadband RCS reduction, a random sequence can be used to disperse the incident electromagnetic wave in any direction, and a genetic algorithm can be used to achieve optimization. Figure 7 In the optimization process, the plane array theory is used as an auxiliary function. Assuming that the plane wave is incident vertically, the far-field function of the super surface scattering composed of N×N super units of size D can be expressed as:

[0042]

[0043] Among them, θ and are the elevation angle and azimuth angle in any direction respectively; is the relative phase of the super unit. Taking a 1-bit coding metasurface as an example, its values ​​are 0° and 180°; k is the vacuum wave number; is the super mode function. To simplify the calculation, The blur in the far field can be ignored, thus obtaining the directivity function of the metasurface of any coding sequence:

[0044]

[0045] According to formula (3), the fitness function of the optimization algorithm is defined as the maximum value of the directional function At this time, the smaller the fitness function value is, the smaller the corresponding scattering is.

[0046] Through multiple optimization iterations of genetic algorithm, we finally get Figure 8 Three multi-bit broadband low-scattering coding metasurfaces are shown.

[0047] like Fig. 9 As shown in the figure, the simulation results of the single-station RCS and RCS reduction of the multi-bit coding metasurface under the condition of normal incidence of plane wave in two polarizations are given, and compared with the metal plate of the same size. Fig. 9 (a) It can be seen that the optimized coded metasurface achieves broadband RCS reduction within the frequency band, and has almost the same RCS reduction effect under x-polarization and y-polarization. In order to observe its RCS reduction performance more intuitively, Fig. 9 (b) The RCS reduction values ​​of the multi-bit coded metasurface under two polarizations are given, and its RCS reduction performance is judged based on the 10dB RCS reduction. Fig. 9 (b) It can be seen that the traditional chessboard coding has a certain effect on RCS reduction within the working frequency band, but the 10dB RCS reduction bandwidth is discontinuous and has certain limitations. After using a random coding sequence and optimizing it with a genetic algorithm, the designed coding metasurface achieves a RCS reduction of more than 10dB in the 11-25GHz frequency band, with a relative bandwidth of about 77.7%. Fig.10 The 3D far-field scattering diagrams of some multi-bit coded metasurfaces are given. It should be pointed out that the phase of the super-units constituting the entire array will change with the frequency, such as Figure 4 As shown in , therefore, the 3D far-field diagrams of the same coding metasurface at different frequencies are also different. Fig.10 It can be seen that the designed coded metasurface scatters the incident electromagnetic waves in multiple directions, thereby significantly reducing the single-station RCS in the mirror direction.

[0048] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or change made by a person skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. Multi-bit coded polarization conversion metasurface for RCS reduction, characterized in that The metasurface is used to achieve broadband radar cross-section (RCS) reduction. The metasurface is composed of a chessboard-type multi-bit coding array consisting of M×M super units, each of which includes 4×4 metasurface units. The metasurface unit is a symmetrical sandwich structure consisting of a bidirectional arrow and a defective rectangular ring, and from the top layer to the bottom layer, there are a metal copper layer, a dielectric layer, and a metal copper layer. Among them, 8 categories of metasurface units are obtained by adjusting the phase difference θ between adjacent metasurface units and the width l2 of the defective rectangular ring.

2. The single-layer multi-bit coded polarization conversion metasurface according to claim 1, characterized in that: The phase difference between adjacent metasurface units in the 8 categories of metasurface units is 45°.

3. The single-layer multi-bit coded polarization conversion metasurface according to claim 1, characterized in that: The multi-bit coding of the metasurface includes 1-bit coding, 2-bit coding and 3-bit coding, wherein the 1-bit coding is composed of two digital units "0" and "1" arranged in an alternating manner, the 2-bit coding is composed of three digital units "00", "01" and "11" arranged in an alternating manner, and the 3-bit coding is composed of eight digital units "000", "001", "010", "011", "100", "101", "110" and "111" arranged in an alternating manner.

4. The single-layer multi-bit coded polarization conversion metasurface according to claim 1, characterized in that: The period of the metasurface unit is 8.6 mm.

5. The single-layer multi-bit coded polarization conversion metasurface according to claim 1, characterized in that: The thickness of the metal copper of the upper layer and the thickness of the metal copper of the bottom layer are both 0.018 mm.

6. The single-layer multi-bit coded polarization conversion metasurface according to claim 1, characterized in that: The dielectric material of the middle layer is FR4, wherein the dielectric constant is 2.2, the loss tangent is 0.001, and the thickness is 2.7 mm.

7. The single-layer multi-bit coded polarization conversion metasurface according to claim 1, characterized in that: The metasurface has broadband polarization conversion efficiency in the frequency band of 11.2 to 25.6 GHz, a polarization conversion rate greater than 90%, and a total of four resonance points.

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