A polarization conversion metasurface design method for broadband radar cross section reduction

Abstract

A polarization conversion metasurface design method is used to realize wideband radar scattering cross section reduction. The feature is to design a polarization conversion metasurface unit first, each polarization conversion metasurface unit includes a bottom metal unit, an upper layer metal etching microstructure unit and a dielectric substrate unit; the configuration of different polarization conversion units is described by the difference of metal etching microstructure and the change of dielectric substrate thickness; the single polarization conversion metasurface unit is modeled, the scattering characteristics are calculated, the configuration optimization and parameter optimization of the metal etching microstructure and the dielectric substrate unit of the polarization conversion unit are carried out based on the genetic algorithm, and the optimal polarization conversion unit structure is obtained; the polarization conversion metasurface with periodic metal etching microstructure array is constructed, the polarization conversion metasurface capable of reducing scattering is designed, and the scattering characteristics are calculated. The mirror polarization conversion metasurface is used as the implementation form to realize the scattering reduction of the incident electromagnetic wave, which is conducive to the automatic design of the polarization conversion metasurface with special working frequency requirements.

Description

Technical Field

[0001] This invention belongs to the field of microwave technology and relates to a polarization conversion metasurface design method for achieving broadband radar cross-section reduction. Background Technology

[0002] In modern warfare, the rapid development of battlefield environmental detection technology has posed a serious threat to various military equipment. Therefore, research into electromagnetic stealth technology for military equipment is urgently needed. Radar, as one of the most commonly used detection devices in modern warfare, primarily tracks targets by acquiring the electromagnetic scattering of radar waves emitted by a target object. The stronger the electromagnetic scattering, the greater the likelihood of the target object being detected by radar. The radar cross section (RCS) is the effective scattering area of ​​a target to incident radar waves, a parameter that quantitatively characterizes the scattering characteristics of a target object. Traditional approaches to RCS reduction typically fall into two categories: one is to change the shape design to reduce scattering or change the direction of electromagnetic scattering to deviate from a dangerous direction. Shape design and the addition of enclosures are methods to reduce or deviate from reflected electromagnetic waves by changing the shape, but this can easily affect the functionality of the electromagnetic equipment itself. Alternatively, some materials can absorb the energy of incident electromagnetic waves and convert it into heat energy for dissipation. For example, radar absorbing materials, frequently used in electromagnetic equipment, reduce RCS by consuming the energy of incident electromagnetic waves and converting it into other forms of energy. While traditional radar-absorbing materials can absorb electromagnetic waves to a large extent, their operating bandwidth is very narrow, and their nature of converting energy dissipation into heat makes targets easily detectable by infrared detection systems. In recent years, with the continuous development of microwave technology, more and more novel artificial electromagnetic metamaterials and artificial electromagnetic metasurfaces have come into the researchers' view, providing more new ideas for electromagnetic stealth design.

[0003] The primary function of polarization-conversion metasurfaces is to modulate the polarization state of electromagnetic waves, i.e., to change the direction of the electric field. Polarization conversion means that the incident and reflected electromagnetic waves will have a 180° phase difference in their electric field directions. This polarization conversion characteristic of the unit can be used to reduce the scattering cross-section (RCS). When polarization-conversion units are arranged in a predetermined mirror configuration, the reflected waves generated by the unit and its mirror unit are 180° out of phase, causing destructive interference between the electromagnetic waves. A metasurface composed of such units is called a mirror polarization-conversion metasurface. The scattering reduction capability of a mirror polarization-conversion metasurface can be more clearly represented by the polarization conversion rate (PCR) of the polarization-conversion units. The higher the PCR, the more cross-polarized electromagnetic waves there are, and the greater the RCS reduction. Therefore, increasing the PCR of the unit in the required frequency band can better reduce the scattering level of the antenna. However, designing units for the required scattering reduction frequency band often requires designers to have extensive design knowledge and experience, and also consumes a significant amount of the designer's time and effort. Therefore, in order to provide ideas for the design of polarization conversion metasurfaces and to provide a reference for designers, this invention proposes an automated design method for polarization conversion surfaces with scattering reduction. Summary of the Invention

[0004] This invention provides a polarization conversion metasurface design method to achieve radar cross section reduction within the target frequency band.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for designing polarization-conversion metasurfaces for reducing the cross-section of broadband radar includes:

[0007] A polarization conversion metasurface unit is designed, each polarization conversion metasurface unit including a bottom metal unit, an upper metal etched microstructure unit and a dielectric substrate unit; the range of the upper metal microstructure unit attached to each polarization conversion surface unit and the thickness of the dielectric substrate unit are used as the design domain;

[0008] The attachment range of the metal etched microstructure unit is divided into four grid arrays with equal area along the diagonal. The attachment and absence of the metal layer in one grid array (the metal structure of the other three grid arrays is directly or indirectly generated by its mirror symmetry) and the dielectric substrate thickness parameters are controlled and adjusted by a one-dimensional array. The configuration of different polarization conversion units is described by the difference of the metal etched microstructure and the change of the dielectric substrate thickness.

[0009] A single polarization conversion metasurface unit is modeled, and its scattering characteristics are calculated. The design objective is to maximize the average polarization conversion rate of the polarization conversion metasurface unit for the swept incident wave in the target frequency band. Based on a genetic algorithm, the configuration and parameters of the metal-etched microstructure and dielectric substrate unit of the polarization conversion unit are optimized to obtain the optimal polarization conversion unit structure. A polarization conversion metasurface with a periodic array of metal-etched microstructures is constructed. The metasurface includes several square polarization conversion metasurface units arranged in a mirror manner. Based on the obtained optimal polarization conversion metasurface unit configuration, the units are arranged using destructive interference technology to construct a polarization conversion metasurface that can reduce scattering, and its scattering characteristics are calculated.

[0010] The scattering characteristics of a single polarization conversion metasurface unit are modeled, with the design objective being to maximize the average polarization conversion rate of the unit for a swept frequency incident wave within a certain frequency band. Based on a genetic algorithm, the configuration of the upper surface metal microstructure within the unit and the thickness parameters of the dielectric substrate unit are optimized to obtain the optimal polarization conversion unit structure. This includes constructing the following optimization model:

[0011]

[0012] Where χ represents the one-dimensional matrix of design variables for the metal microstructure, n represents the number of rectangular grids in the design domain, and each element in the array x i (i∈[1,n],i∈Z) represents the attachment and absence of the metal layer, 0≤x i <0.5 indicates that metallic material is missing within the mesh, and 0.5≤x i ≤1 indicates that there is metallic material attached to the grid, h represents the thickness of the dielectric substrate, PCR represents the polarization conversion rate of the incident wave, which is obtained by electromagnetic simulation analysis software, and N represents the number of selected frequency sampling points.

[0013] The method of optimizing the configuration and parameters of the polarization conversion unit's metallic microstructure and dielectric substrate unit based on a genetic algorithm to obtain the optimal scattering reduction structure includes: defining the population size, i.e., the number of individuals in the population is p, each individual is represented by a gene sequence G, G is a one-dimensional array with n+1 gene positions, and the relationship between each element of the array design variable and each gene position of each individual is: x i =g i h=x n+1 ; Generate p random arrays as the initial population, with each random number serving as the gene sequence of each individual. Establish polarization conversion units corresponding to the gene arrays of each individual in this generation. Evaluate the design target values ​​of each polarization conversion unit established in this generation using numerical calculation methods, and then proceed to the optimization process; During the optimization process, select the optimal variable χ from the previous generation population. optAs the parent of the next generation population, the next generation population is generated through crossover mutation. The configuration of the metal microstructure in the corresponding polarization conversion unit and the thickness parameter of the dielectric substrate are established based on the gene sequence of each individual in the population. The design goal corresponding to each unit of the newly generated population is evaluated, and the polarization conversion unit with the optimal design goal in this generation is found.

[0014] The polarization conversion metasurface for reducing the cross section of broadband radar is constructed using destructive interference technology based on the designed unit configuration. The metasurface consists of 2×2 grids, each grid consists of 2×2 polarization conversion units, and each grid is mirror-symmetric to the others.

[0015] This invention uses a mirror polarization conversion metasurface to reduce the scattering of incident electromagnetic waves. By using the upper metal microstructure and the thickness of the dielectric substrate as the design domain, the radar cross section in the target frequency band is reduced through the reasonable automated design of the configuration of the polarization conversion unit. This is beneficial for the automated design of polarization conversion metasurfaces with special operating frequency band requirements. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the design process for obtaining the optimal scattering-reducing metasurface for this invention.

[0017] Figure 2 This is a diagram of the metal microstructure configuration of the unit designed in this invention;

[0018] Figure 3 This is a top view of the design domain and the designed unit of the present invention;

[0019] In the picture: Attach metal materials; Missing metallic material;

[0020] Figure 4 This is a side view of the unit designed in this invention;

[0021] Figure 5 The polarization conversion rate curve of the unit designed in this invention;

[0022] Figure 6 This is a schematic diagram of the unit cell arrangement used in a 2×2 mirror polarization conversion metasurface.

[0023] Figure 7 This is a comparison of the single-station RCS of a 2×2 mirror polarization conversion metasurface and a metal plate of the same area. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0025] Figure 1 The flowchart for obtaining the optimal scattering reduction metasurface structure of the present invention includes the design of unit cells and the design of unit cell arrangement, wherein the unit cell configuration design includes the following steps:

[0026] a) The present invention constructs a reflective polarization conversion metasurface with a periodic metal etching microstructure array. The metasurface includes 16 square polarization conversion metasurface units arranged in a mirror manner. Each unit includes a bottom metal plate unit, an upper metal microstructure unit, and a dielectric substrate unit disposed between the bottom metal plate unit and the upper metal microstructure unit.

[0027] b) The range of the upper metal microstructure unit attached to each polarization conversion unit and the thickness of the dielectric substrate unit are used as the design domain. The attachment range of the metal microstructure unit is divided into a rectangular grid array. The attachment and absence of the rectangular metal layer and the dielectric substrate thickness parameters in each grid array are controlled and adjusted by a one-dimensional array. The configuration of different polarization conversion units is described by the differences in the metal microstructure in the grid array and the changes in the dielectric substrate thickness.

[0028] c) Model a single polarization conversion metasurface unit, calculate its scattering characteristics, and take the maximum average polarization conversion rate of the polarization conversion metasurface unit for a certain frequency sweeping incident wave as the design objective. Based on the genetic algorithm, optimize the configuration and parameters of the polarization conversion unit to obtain the optimal scattering reduction structure.

[0029] d) Model a single polarization-conversion metasurface unit and calculate its scattering characteristics. With the design objective of maximizing the average polarization conversion rate of the unit cells for a swept-frequency incident wave as the target, optimize the configuration and parameters of the polarization-conversion unit using a genetic algorithm to obtain the optimal scattering reduction structure.

[0030] e) The scattering characteristics of the polarization conversion unit are modeled, with the average value of the polarization conversion rate of the unit for a swept incident wave of a certain frequency band as the design objective. Based on the genetic algorithm, the configuration optimization of the upper surface metal microstructure in the unit and the parameter optimization of the unit thickness parameters of the dielectric substrate are performed to obtain the optimal polarization conversion unit structure, including constructing the following optimization formula:

[0031]

[0032] Where χ represents a one-dimensional array of design variables for the metal microstructure, n represents the number of meshes within the design domain, and each element x in the array represents a different value. i (i∈[1,n],i∈Z) represents the attachment and absence of the metal layer, 0≤x i <0.5 indicates that metallic material is missing within the mesh, and 0.5≤x i≤1 indicates that the grid contains metallic material, h represents the thickness of the dielectric substrate, PCR represents the polarization conversion efficiency of the incident wave, obtained from electromagnetic simulation analysis software, and N represents the number of selected frequency sampling points; the optimization of the configuration of the metallic microstructure of the polarization conversion unit and the thickness of the dielectric substrate based on the genetic algorithm to obtain the optimal scattering reduction structure includes: defining the population size, i.e., the number of individuals in the population is p, each individual is represented by a gene sequence G, G is a one-dimensional array with n+1 gene positions, and the relationship between each element of the array design variable and each gene position of each individual is: x i =g i h=x i+1 ; Generate p random arrays as the initial population, with each random number serving as the gene sequence of each individual. Establish polarization conversion units (PCUs) based on the gene arrays of each individual in this generation. Evaluate the design target value of the established PCUs in this generation using numerical calculation methods, and then proceed to the optimization process. During the optimization process, select the optimal variable χ from the previous generation population. opt As the parent of the next generation population, the next generation population is generated through crossover mutation. The configuration of the metal microstructure in the corresponding polarization conversion unit and the thickness parameter of the dielectric substrate are established based on the gene sequence of each individual in the population. The design goal corresponding to each unit of the newly generated population is evaluated, and the polarization conversion unit with the optimal design goal in this generation is found.

[0033] Figure 2 This represents the optimal metal microstructure configuration of the unit obtained after optimization.

[0034] Figure 3 This is a top view of the polarization conversion unit proposed in this invention, wherein the width of the dielectric substrate is a = 13 mm; the side length of the metal material attachment area is d = 11 mm, and the area marked by the dashed line is the metal material attachment area, which is divided into four regions of equal area along the diagonal of the cross section, namely 2-1, 2-2, 2-3 and 2-4. In this embodiment, 2-1 is the selected grid array design domain, and 2-2 is generated by mirror symmetry. 2-3 and 2-4 are generated by mirror symmetry of 2-1 and 2-2. The remaining material attachment areas are generated by mirror symmetry. The design and inner grid are square with a side length of w = 0.5 mm. Figure 4 The image shows a side view of the designed unit. The dielectric substrate thickness is h = 3.46 mm. In this embodiment, the polarization conversion metasurface is covered with a metal layer, with the lower side fully covered by a metal layer and the upper side covered with a metal microstructure. The material is PEC, and the dielectric substrate material is F4B with a relative permittivity of 2.65.

[0035] In an embodiment of the present invention, the unit and metasurface are simulated using the full-wave simulation software HFSS, with the simulation frequency band set to 6-14 GHz, and the incident wave being a TE wave incident along the negative Z-axis. When the incident wave is perpendicular, the polarization conversion unit can achieve a polarization conversion rate of over 0.9 in a wide frequency range of 6.14 GHz to 13.79 GHz.

[0036] Figure 7 This is a comparison diagram of the monostatic RCS of an embodiment of the present invention and a metal plate of the same area. In the embodiment of the present invention, in order to observe the scattering reduction effect of the designed 2×2 mirror polarization conversion metasurface, its effect is compared with that of a metal plate of the same area. The normal monostatic RCS achieves a significant reduction across the entire frequency band.

Claims

1. A method for designing polarization-conversion metasurfaces for reducing the cross-section of broadband radar, characterized in that, include: Design a polarization conversion metasurface unit, each polarization conversion metasurface unit includes a bottom metal unit, an upper metal etched microstructure unit and a dielectric substrate unit, and the range of the upper metal microstructure unit attached to each polarization conversion surface unit and the thickness of the dielectric substrate unit are used as the design domain. The attachment range of the metal etched microstructure unit is divided into four grid arrays with equal area along the diagonal. The attachment and absence of the metal layer and the thickness of the dielectric substrate within one grid array are controlled and adjusted by a one-dimensional array. The metal structures of the other three grid arrays are generated directly or indirectly by their mirror symmetry. The configuration of different polarization conversion units is described by the differences in the metal etched microstructure and the change in the thickness of the dielectric substrate. A single polarization conversion metasurface unit is modeled, and its scattering characteristics are calculated. The design objective is to maximize the average polarization conversion rate of the polarization conversion metasurface unit for the swept incident wave of the target frequency band. Based on a genetic algorithm, the configuration and parameters of the metal etched microstructure and dielectric substrate unit of the polarization conversion unit are optimized to obtain the optimal polarization conversion unit structure. A polarization conversion metasurface with a periodic metal etched microstructure array is constructed. The metasurface includes several square polarization conversion metasurface units arranged in a mirror manner. Based on the obtained optimal polarization conversion metasurface unit configuration, the units are arranged according to the destructive interference technique to design a polarization conversion metasurface that can reduce scattering, and its scattering characteristics are calculated. The modeling of a single polarization-conversion metasurface unit includes: With the goal of maximizing the polarization conversion rate of the unit cell for a swept frequency incident wave in a certain frequency band, the optimal polarization conversion unit structure is obtained by optimizing the configuration of the upper surface metal microstructure within the unit cell and optimizing the thickness parameters of the dielectric substrate unit cell based on a genetic algorithm. This includes constructing the following optimization model: in: A one-dimensional array representing the design variables of the metal microstructure, where n represents the number of meshes in the design domain, and each element in the array... ( The ) indicates the attachment and absence of the corresponding metal layer within the grid. This indicates that metallic material is missing within the grid. This indicates that the mesh contains metallic material. The thickness of the substrate is represented by PCR, which represents the polarization conversion rate of the incident wave, obtained from electromagnetic simulation analysis software, and N represents the number of selected frequency sampling points.

2. The polarization conversion metasurface design method for radar cross-section reduction according to claim 1, characterized in that, The method of optimizing the configuration and parameters of the metal etched microstructure and dielectric substrate unit of the polarization conversion unit based on the genetic algorithm to obtain the optimal scattering reduction structure includes: Define the population size as p, i.e., the number of individuals in the population. Each individual is represented by a gene sequence G, which is a one-dimensional array with n+1 digits in the gene sequence. The relationship between each element of the array variable and each digit of the gene sequence in each individual is as follows: = h= Generate p random arrays as the initial population, with each random number representing the gene sequence of each individual. Establish polarization conversion units (PCUs) based on the gene arrays of each individual in this generation. Evaluate the design target values ​​of each PCU established in this generation using numerical calculation methods, and then proceed to the optimization process. During the optimization process, select the optimal variables from the previous generation population. As the parent of the next generation population, the next generation population is generated through crossover mutation. The configuration of the metal microstructure in the corresponding polarization conversion unit and the thickness parameter of the dielectric substrate are established based on the gene sequence of each individual in the population. The design goal corresponding to each unit of the newly generated population is evaluated, and the polarization conversion unit with the optimal design goal in this generation is found.

3. The polarization conversion metasurface design method for reducing the cross-section of broadband radar according to claim 1, characterized in that, Based on the designed unit configuration, a polarization conversion metasurface is constructed using destructive interference technology. The metasurface consists of 2×2 grids, each grid consisting of 2×2 polarization conversion units, and each grid is mirror-symmetric to the others.

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