Rcs characterization method for heterogeneous target passive scattering

Abstract

The application relates to a method for characterizing the RCS of a heterogeneous target passive scattering, belonging to the technical field of radar and communication. Firstly, the method judges the target surface roughness type based on the Rayleigh criterion, reveals the electric wave propagation mechanism of electromagnetic wave interaction with the target, and constructs an RCS model in combination with the target scattering characteristics. Then, in combination with the target passive scattering characteristics and the bistatic radar equation, the RCS radiation direction mode caused by the target passive scattering is characterized. Then, the three-dimensional structure model is reconstructed by using the target electromagnetic parameters, and the RCS data under different frequency bands and incident angles are obtained through full-wave simulation and microwave darkroom measurement. Finally, the simulation data and the measured data are used to fit the normalized radiation direction mode, the RCS model parameters are determined, and the accuracy and effectiveness of the model are verified. The method effectively combines theoretical analysis and simulation technology, can accurately and efficiently characterize the passive scattering characteristics of a heterogeneous target, and provides strong support for the development of radar detection and stealth technology.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of radar and communication, and relates to a RCS characterization method for passive scattering of heterogeneous targets BACKGROUND

[0002] In the field of radar and communication, the passive scattering characteristics of targets are one of the important indicators for evaluating their detection performance and stealth capabilities. In particular, for heterogeneous targets (such as targets with layered plate structures), accurate characterization of the radar cross section (RCS) of their passive scattering is particularly crucial. However, due to the complexity and diversity of heterogeneous targets, the analysis and modeling of their passive scattering characteristics face many challenges.

[0003] Traditional RCS characterization methods are often based on ideal homogeneous target models, which approximate targets through simple geometric shapes and uniform electromagnetic parameters. This results in significant limitations in the accuracy and applicability of the model when faced with actual heterogeneous targets. For layered heterogeneous targets with plate structures, due to their complex structure, diverse materials, and electromagnetic parameters varying with frequency and position, accurate modeling and simulation of their passive scattering characteristics become particularly difficult.

[0004] In order to overcome these difficulties, researchers have been exploring more accurate and efficient RCS characterization methods for passive scattering of heterogeneous targets.

[0005] In recent years, with the rapid development of computational electromagnetics and simulation technology, full-wave simulation methods have gradually become an important means for studying the passive scattering characteristics of heterogeneous targets. Full-wave simulation methods can accurately simulate the propagation and scattering of electromagnetic waves on complex targets, thereby obtaining accurate RCS data.

[0006] However, full-wave simulation methods also have the disadvantages of large computational load and long simulation time. In practical applications, the accuracy and reliability of simulation data are often affected by factors such as model simplification, mesh division, and calculation precision.

[0007] Therefore, how to combine theoretical analysis and simulation technology to establish an accurate and efficient RCS characterization method for passive scattering of heterogeneous targets has become an important problem to be solved in the current field of radar and communication technology. SUMMARY

[0008] Therefore, the present application aims to provide a heterogeneous target passive scattering RCS characterization method. The method includes heterogeneous target electromagnetic wave propagation mechanism, passive scattering RCS characterization, full-wave simulation and measurement, RCS parameter fitting and verification. First, based on the Rayleigh criterion, the electromagnetic wave propagation mechanism of electromagnetic wave interaction with the layered heterogeneous target of plate type is revealed, and the RCS model of the passive scattering of the heterogeneous target is constructed combined with the target scattering characteristics. Second, combined with the target passive scattering characteristics and the bistatic radar equation, the radiation direction mode of the RCS caused by the target passive scattering is characterized. Third, the three-dimensional plate type layered target structure model is reconstructed using the target electromagnetic parameters, the RCS at different frequency bands and different incident angles is obtained through full-wave simulation, and the RCS distribution of the target passive scattering is obtained through microwave anechoic chamber measurement. Finally, the normalized radiation direction mode is fitted using the simulation data and the measured data, the RCS model parameters are determined, and the accuracy and effectiveness of the model are verified. The method provides a theoretical basis for the passive scattering of spatial cooperative and non-cooperative targets.

[0009] To achieve the above purpose, the present application provides the following technical solutions:

[0010] Please refer to Figure 1 and Figure 2 , a heterogeneous target passive scattering RCS characterization method, comprising the following steps:

[0011] Step 1: Based on the Rayleigh criterion, the surface roughness type of the layered heterogeneous target of plate type is judged, and the RCS model of the passive scattering of the heterogeneous target is constructed.

[0012] Step 2: Combined with the target passive scattering characteristics and the bistatic radar equation, the radiation direction mode of the RCS caused by the target passive scattering is characterized.

[0013] Step 3: The three-dimensional plate type layered target structure model is reconstructed using the electromagnetic parameters, the RCS simulation data at different frequency bands and different incident angles are obtained through full-wave simulation, and the RCS distribution of the target passive scattering is obtained through microwave anechoic chamber measurement.

[0014] Step 4: The normalized radiation direction mode is fitted using the simulation data and the measured data, the RCS model parameters are determined, and the accuracy and effectiveness of the model are verified.

[0015] Further, the step 1 is specifically:

[0016] Step 1-1: Define g as the roughness parameter of the surface of the layered heterogeneous target of plate type, g is represented as:

[0017]

[0018] Where, σ h is the material roughness, λ is the incident wave wavelength, θ i is the incident angle.

[0019] Step one-two: determine the roughness type of the plate type layered heterogeneous target based on the roughness parameter g, and the definition of different roughness types is as follows:

[0020]

[0021] Step one-three: based on the determined roughness type, construct the RCS model of the passive scattering of the heterogeneous target, and the RCS model is represented as:

[0022]

[0023] Wherein, R represents the distance between the measured target and the radar antenna, E s represents the scattering electric field intensity, E i represents the incident electric field intensity;

[0024] The normalized scattering coefficient R single is defined as the ratio of the scattering electric field intensity to the incident electric field intensity, and the scattering coefficient R single is represented as:

[0025]

[0026] The RCS model is represented as:

[0027] σ=4πR 2 |R single | 2 (5).

[0028] Further, the step two is specifically:

[0029] Step two-one: the transmitter transmits a signal with a power of P t to the heterogeneous target through an antenna with a normalized power radiation pattern and an antenna gain G t , and the power of the incident signal is represented as:

[0030]

[0031] Wherein, R t represents the distance between the transmitter and the target, and S represents the cross-sectional area of the beam;

[0032] For the beam cross section, the electric field of the incident signal is represented as:

[0033]

[0034] Wherein, Z0 is the characteristic impedance of air, and λ represents the wavelength;

[0035] According to the law of conservation of energy, the power of the incident signal multiplied by the square of the scattering coefficient modulus equals the total power of the scattered signal, which is:

[0036] P in |R single | 2 = P scatter (8)

[0037] where P scatter is the total scattered power of the beam cross section, and R single is the scattering coefficient.

[0038] R single = Ae jφ (9)

[0039] where A and e jφ represent the controllable amplitude and phase shift of the target, respectively.

[0040] The power of the scattered signal received by the receiver from the passive scattering target is represented as:

[0041]

[0042] where G represents the beam cross section gain, is the normalized radiation pattern of the receiving antenna, and A r is the aperture of the receiving antenna.

[0043] Combining equation (7), equation (8), and equation (10), the electric field of the scattered signal received by the receiver from the beam cross section is represented as:

[0044]

[0045] where

[0046] The signal power received by the receiver is represented as:

[0047]

[0048] where the aperture of the receiving antenna is represented as:

[0049]

[0050] Substituting equation (11) and equation (13) into equation (12) gives:

[0051]

[0052] The peak radiation direction of both the transmitting antenna and the receiving antenna points to the center of the passive scattering target, and the received power in the far field case is rewritten as:

[0053]

[0054] Based on the bistatic radar equation, the received power is expressed as:

[0055]

[0056] Combining equation (15) and equation (16) gives:

[0057]

[0058] A normalized antenna pattern function model is constructed to represent the radiation direction pattern of the target passive scattering caused by RCS, and the model expression is:

[0059]

[0060] Based on the radiation characteristic theory, the directional pattern function in a specific scene is: Defined as the superposition of the main lobe and the side lobe, the main lobe part is represented by , and the side lobe part is represented by , is expressed as:

[0061]

[0062] Based on the antenna pattern theory, the main lobe part f(θ) is expressed as:

[0063]

[0064] Where G0 represents the maximum gain of the main lobe, θ represents the scattering angle, n represents the main lobe shape parameter, and θ0 represents the center direction of the main lobe.

[0065] Based on the harmonic interference and scattering theory, the side lobe part is expressed as:

[0066]

[0067] Where B represents the amplitude of the side lobe, and k represents the oscillation speed of the side lobe.

[0068] The complete directional pattern model formula is represented by :

[0069]

[0070] Further, the third step is specifically:

[0071] Step three-one: Firstly, the single-layer material propagation characteristics are studied to determine the reflection and transmission ability of the single-layer material, and the measured electromagnetic parameters are inverted; then, the electromagnetic parameters of the single-layer material are used to reconstruct the special heterostructure model through full-wave simulation, and a multi-layer iterative propagation model based on Fresnel theory is constructed;

[0072] Step three-two: For the layered target structure model, the RCS values at different frequencies and with different incident angles are obtained through full-wave simulation, and the RCS distribution of the target is counted

[0073] Step three-three: In the microwave anechoic chamber, the frequency domain material electromagnetic propagation characteristics are measured based on the vector network analyzer, and the RCS value at each scattering angle is obtained. The measurement result is represented by σ mea ;

[0074] Step three-four: S 21 is defined as the ratio of the electric field intensity of the reflected signal to the incident signal, and the scattering coefficient is represented by the ratio of S 21_mut at each scattering angle to the ideal smooth surface S 21_ideal , and then the scattering coefficient R single is represented as:

[0075]

[0076] Step three-five: Based on formula (5), σ mea is represented as:

[0077]

[0078] Further, the step four is specifically:

[0079] Step four-one: Through the least square fitting method, the theoretical and measured values of the reflection coefficient are jointly estimated under horizontal polarization and vertical polarization; the fitting error is defined as the cumulative value of the mean square error between the theoretical and measured values of the RCS under the two polarizations, that is:

[0080]

[0081] Where, N j is the number of measured scattering angles, i is the measured scattering angle number, σ mea represents the RCS measured value, and σ single represents the RCS theoretical value. The parameters G0, n, B and k in formula (22) are adjusted by the least square method, and the parameters corresponding to the minimum RMSE are regarded as the best model parameters;

[0082] Step 4-2: Verify the accuracy and effectiveness of the structural model: Compare and analyze the full-wave simulation values ​​of the plate-type layered target structure model with the measured values ​​in the microwave anechoic chamber to verify the rationality and applicability of the passive scatterer model;

[0083] Step 4-3: Verify the accuracy and effectiveness of the antenna radiation pattern model: Compare the theoretical values ​​of the antenna radiation pattern model with the measured values ​​in the microwave anechoic chamber, and evaluate the accuracy and reliability of the model based on the root mean square error.

[0084] The beneficial effects of this invention are as follows:

[0085] (1) By combining theoretical analysis and simulation techniques, and considering the influence of target surface roughness and electromagnetic parameters, this invention can more accurately characterize the RCS characteristics of heterogeneous targets and is applicable to the RCS analysis of complex heterogeneous targets.

[0086] (2) Compared with the traditional full-wave simulation method, the present invention can effectively reduce the amount of simulation calculation and improve the simulation efficiency by constructing the RCS model and the normalized radiation direction mode.

[0087] (3) This invention can provide a theoretical basis for the passive scattering characteristics of cooperative and non-cooperative targets in space, and provide strong support for the further development of radar detection and stealth technology.

[0088] (4) By introducing the antenna pattern, this invention effectively correlates the results of simulation and measured data, improves the practicality and prediction accuracy of the model, and lays a theoretical foundation for signal propagation analysis, scattering modeling and system performance optimization in complex communication environments.

[0089] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0090] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0091] Figure 1 This is a schematic diagram of passive scattering from a heterogeneous target.

[0092] Figure 2 This is a comparison chart of theoretical, full-wave simulated, and measured values ​​of the antenna radiation pattern. Figure 2 (a)~ Figure 2 (d) represent incident angles of 30°, 40°, 50°, and 60°, respectively. Detailed Implementation

[0093] The present application is herein described, by way of example only, with reference to the accompanying drawings, with the following being a brief description of its salient features. The advantages and features of the present application will become apparent to those skilled in the art from the following description of the current best modes 2 of practicing the application. As will be realized, the application is capable of other different obvious aspects and embodiments, all without departing from the application. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not restrictive.

[0094] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:

[0095] The same or similar components in the drawings of the embodiments of the present application correspond to the same or similar components; in the description of the present application, it should be understood that if the terms "upper", "lower", "left", "right", "front", "back" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only for illustrative purposes, and cannot be understood as a limitation of the present application, for those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0096] Figure 2 is a comparison chart of the theoretical value, full-wave simulation value and measured value of the antenna pattern, Figure 2 (a)~(d) are respectively the incident angles of 30°, 40°, 50° and 60°. Figure 2

[0097] ​Embodiment 1, the embodiment first, based on the Rayleigh criterion reveals the electromagnetic wave and the layered heterogeneous target interaction of the plate type electromagnetic wave propagation mechanism, combined with the target scattering characteristics, the RCS model of the passive scattering of the heterogeneous target is constructed; second, combined with the target passive scattering characteristics and the bistatic radar equation, the radiation direction mode of the RCS caused by the target passive scattering is represented; then, the three-dimensional plate type layered target structure model is reconstructed by using the target electromagnetic parameters, the RCS under different frequency bands and different incident angles is obtained by full wave simulation, and the RCS distribution of the target passive scattering is obtained by measuring in the microwave darkroom; finally, the simulation data, the measured data are fitted to determine the RCS model parameters, and the accuracy and effectiveness of the model are verified. The method provides a theoretical basis for the passive scattering of the space cooperative and non-cooperative target.

[0098] A RCS characterization method of passive scattering of a heterogeneous target, comprising the following steps:

[0099] Step one: based on the Rayleigh criterion, the surface roughness type of the plate type layered heterogeneous target is determined, the electromagnetic wave propagation mechanism of the electromagnetic wave and the layered heterogeneous target interaction of the plate type is revealed, combined with the target scattering characteristics, the RCS model of the passive scattering of the heterogeneous target is constructed.

[0100] Step two: combined with the target passive scattering characteristics and the bistatic radar equation, the radiation direction mode of the RCS caused by the target passive scattering is represented.

[0101] Step three: the three-dimensional plate type layered target structure model is reconstructed by using the electromagnetic parameters, the RCS simulation data under different frequency bands and different incident angles are obtained by full wave simulation, and the RCS distribution of the target passive scattering is obtained by measuring in the microwave darkroom.

[0102] Step four: the simulation data, the measured data are fitted to determine the RCS model parameters, and the accuracy and effectiveness of the model are verified.

[0103] Step one is specifically:

[0104] Step one-one: define g as the roughness parameter of the plate type layered heterogeneous target surface, g can be expressed as:

[0105]

[0106] Where, σ h is the material roughness, λ is the incident wave wavelength, θ i is the incident angle.

[0107] Step one-two: determine the roughness type of the plate type layered heterogeneous target based on the roughness parameter g, the definition of different roughness types is as follows:

[0108]

[0109] Step one-three: Based on the determined roughness type, the RCS model of heterogeneous target passive scattering is constructed, which can be expressed as:

[0110]

[0111] Wherein, R represents the distance between the measured target and the radar antenna, E s represents the scattered electric field intensity, E i represents the incident electric field intensity.

[0112] The normalized scattering coefficient R single is defined as the ratio of the scattered electric field intensity to the incident electric field intensity, and the scattering coefficient R single can be expressed as:

[0113]

[0114] Therefore, the RCS model can also be expressed as:

[0115] σ=4πR 2 |R single | 2 (5)

[0116] Step two is specifically:

[0117] Step two-one: the transmitter transmits a signal with power P t to the heterogeneous target through an antenna with normalized power radiation pattern t and antenna gain G The power of the incident signal can be expressed as:

[0118]

[0119] Wherein, R t represents the distance between the transmitter and the target, and S represents the cross-sectional area of the beam.

[0120] For the beam cross section, the electric field of the incident signal can be expressed as:

[0121]

[0122] Wherein, Z0 is the characteristic impedance of air, and λ represents the wavelength.

[0123] According to the law of conservation of energy, the power of the incident signal multiplied by the square of the scattering coefficient modulus is equal to the total power of the scattered signal, which can be obtained:

[0124] P in |R single | 2 =P scatter (8)

[0125] where P scatter The total scattering power of the beam cross section, scattering coefficient R single can be expressed as:

[0126] R single = Ae jφ (9)

[0127] where A and e jφ represent the controllable amplitude and phase shift of the target, respectively.

[0128] The power of the scattering signal received by the receiver from the passive scattering target can be expressed as:

[0129]

[0130] where G represents the beam cross section gain, is the normalized radiation pattern of the receiving antenna, A r is the aperture of the receiving antenna.

[0131] Combining equations (7), (8), (10), the electric field of the scattering signal received by the receiver from the beam cross section can be expressed as:

[0132]

[0133] where,

[0134] The signal power received by the receiver can be expressed as:

[0135]

[0136] where the aperture of the receiving antenna can be expressed as:

[0137]

[0138] Substituting equations (11), (13) into equation (12) gives:

[0139]

[0140] The peak radiation direction of the transmitting antenna and the receiving antenna is directed to the center of the passive scattering target, and the received power in the far field case can be rewritten as:

[0141]

[0142] Based on the bistatic radar equation, the received power can be expressed as:

[0143]

[0144] Combining equations (15), (16) gives:

[0145]

[0146] Therefore, a normalized antenna pattern function model can be constructed to represent the radiation direction mode of the target passive scattering caused by RCS, and the model expression is:

[0147]

[0148] Based on the radiation characteristic theory, the directional pattern function in a specific scene is defined as the superposition of the main lobe and the side lobe, the main lobe is represented by , and the side lobe is represented by , which can be represented as:

[0149]

[0150] Based on the antenna pattern theory, the main lobe part f(θ) can be represented as:

[0151]

[0152] where G0 represents the maximum gain of the main lobe, θ represents the scattering angle, n represents the main lobe shape parameter, and θ0 represents the center direction of the main lobe.

[0153] Based on the harmonic interference and scattering theory, the side lobe part can be represented as:

[0154]

[0155] where B represents the amplitude of the side lobe, and k represents the oscillation speed of the side lobe.

[0156] Therefore, the complete directional pattern model formula is represented by :

[0157]

[0158] Step three is specifically:

[0159] Step three-1: First, study the propagation characteristics of single-layer materials, determine the reflection and transmission capabilities of single-layer materials, and combine the measured inversion material electromagnetic parameters; then, use the electromagnetic parameters of single-layer materials to reconstruct the special-shaped heterogeneous structure model through full-wave simulation, and construct a multi-layer iterative propagation model based on Fresnel theory.

[0160] Step three-2: For the plate-type layered target structure model, obtain the RCS values at different frequencies and different incident angles through full-wave simulation, and count the RCS distribution of the target

[0161] Step three-iii: In the microwave anechoic chamber, the frequency domain material electromagnetic propagation characteristics measurement based on the vector network analyzer is carried out, the RCS value under each scattering angle is obtained, and the measurement result is expressed as σ mea .

[0162] Step three-iv: S 21 is defined as the ratio of the electric field intensity of the reflected signal to the incident signal, and the scattering coefficient is expressed by the ratio of S 21_mut under each scattering angle to the ideal smooth surface S 21_ideal , and then the scattering coefficient R single is expressed as:

[0163]

[0164] Step three-v: Based on formula (5), σ mea is expressed as:

[0165]

[0166] Step four is specifically:

[0167] Step four-i: Through the least square fitting method, the theoretical value and the measured value of the reflection coefficient under horizontal polarization and vertical polarization are jointly estimated; the fitting error is defined as the cumulative value of the mean square error between the theoretical value and the measured value of the RCS under the two polarizations, that is:

[0168]

[0169] Where, N j is the number of measured scattering angles, i is the measured scattering angle serial number, σ mea represents the RCS measured value, and σ single represents the RCS theoretical value. The parameters G0, n, B and k in (22) are adjusted by the least square method, and the parameters corresponding to the minimum RMSE are regarded as the best model parameters.

[0170] Step four-ii: Verify the accuracy and effectiveness of the structure model: compare and analyze the full-wave simulation value of the layered target structure model with the microwave anechoic chamber measured value, and test the rationality and applicability of the passive scatterer model.

[0171] Step four-iii: Verify the accuracy and effectiveness of the antenna radiation pattern model: compare the theoretical value of the antenna radiation pattern model with the microwave anechoic chamber measured value, and evaluate the accuracy and reliability of the model based on the root mean square error.

[0172] Finally, it is to be explained that the above embodiments are only used to illustrate the technical solutions of the present application but not to limit the present application. Although the present application is described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions, and all should be covered in the scope of the claims of the present application.

Claims

1. A method of RCS characterization of a heterogeneous target passive scattering, characterized in that: The method comprises the following steps: Step one: judging the roughness type of the plate-type layered heterogeneous target surface based on the Rayleigh criterion, and constructing an RCS model of passive scattering of the heterogeneous target; Step two: combining the passive scattering characteristics of the target and the bistatic radar equation to represent the radiation direction mode of the RCS caused by the passive scattering of the target; the step two is specifically: Step two-one: the transmitter transmits a signal with power P to a heterogeneous target through an antenna with normalized power radiation pattern t and antenna gain G t The power of the incident signal is represented as: where R t represents the distance between the transmitter and the target, and S represents the cross-sectional area of the beam; For the beam cross section, the electric field of the incident signal is represented as: Wherein, Z0 is the characteristic impedance of air, and λ represents the wavelength; According to the law of conservation of energy, the power of the incident signal multiplied by the square of the scattering coefficient modulus is equal to the total power of the scattered signal, and the following formula is obtained: P in |R single | 2 = P scatter (8) where P scatter The total scattering power of the beam cross section, the scattering coefficient R single is expressed as: R single = Ae jφ (9) where A and e jφ respectively denote the controllable amplitude and phase shift of the target; The power of the scattered signal received by the receiver from the passive scattering target is represented as: where G represents a beam section gain, A is a normalized radiation pattern of the receiving antenna, r an aperture of the receiving antenna; Combining formula (7), formula (8) and formula (10), the electric field of the scattered signal received by the receiver from the beam cross section is represented as: wherein The signal power received by the receiver is represented as: Wherein, the aperture of the receiving antenna is represented as: Substituting formula (11) and formula (13) into formula (12) to obtain: The peak radiation directions of the transmitting antenna and the receiving antenna are both directed to the center of the passive scattering target, and the received power in the far field case is rewritten as: Based on the bistatic radar equation, the received power is represented as: Combining formula (15) and formula (16) to obtain: A normalized antenna pattern function model is constructed to represent the radiation direction mode of the RCS caused by the passive scattering of the target, and the model expression is: Based on the theory of radiation characteristics, the directional diagram function in a specific scenario is defined as the superposition of two parts, the main lobe part and the side lobe part The main lobe part is represented by The side lobe part is represented by is represented as:​ Based on the antenna pattern theory, the main lobe part f(θ) is represented as: Wherein, G0 represents the maximum gain of the main lobe, θ represents the scattering angle, n represents the main lobe shape parameter, and θ0 represents the main lobe center direction; Harmonic interference and scattering theory sidelobe portion is represented as: Wherein, B represents the amplitude of the side lobe, and k represents the oscillation speed of the side lobe; The complete pattern model formula is expressed by : Step three: reconstructing a three-dimensional plate-type layered target structure model by using electromagnetic parameters, obtaining RCS simulation data under different frequency bands and different incident angles through full-wave simulation, and obtaining the RCS distribution of the passive scattering of the target through microwave darkroom measurement; Step four: fitting the normalized radiation direction mode by using the simulation data and the measured data, determining the RCS model parameters, and verifying the accuracy and effectiveness of the model.

2. The method of claim 1, wherein: The step one is specifically: Step one-one: defining g as the roughness parameter of the plate-type layered heterogeneous target surface, and g is represented as: where σ h is the material roughness, λ is the incident wave length, θ i is the incident angle; Step one-two: determining the roughness type of the plate-type layered heterogeneous target based on the roughness parameter g, and the definitions of different roughness types are as follows: Step one-three: constructing an RCS model of passive scattering of the heterogeneous target based on the determined roughness type, and the RCS model is represented as: where R represents the distance between the measurement target and the radar antenna, E s represents the scattered electric field intensity, E i represents the incident electric field intensity; The normalized scattering coefficient R single defined as the ratio of the scattered electric field intensity to the incident electric field intensity, the scattering coefficient R single is expressed as: The RCS model is represented as: σ = 4πR 2 |R single | 2 (5).

3. The method of claim 2, wherein: The step three is specifically: Step three-one: firstly, studying the propagation characteristics of single-layer materials, determining the reflection and transmission capabilities of single-layer materials, and inversely calculating the electromagnetic parameters of the materials combined with the measurement; then, reconstructing the heterogeneous structure model by using the electromagnetic parameters of single-layer materials through full-wave simulation, and constructing a multi-layer iterative propagation model based on the Fresnel theory; Step three-two: for the plate-type layered target structure model, obtaining the RCS values under different frequency bands and different incident angles through full-wave simulation, and counting the RCS distribution of the target Step three-III: In the microwave darkroom, the frequency domain material electromagnetic propagation characteristics measurement based on the vector network analyzer is carried out, and the RCS value under each scattering angle is obtained, and the measurement result is expressed as σ mea . Step three-four: S 21 defined as the ratio of the reflected signal to the electric field strength of the incident signal, the scattering coefficient is represented by S 21_mut the ratio of the reflected signal to the electric field strength of the incident signal, the scattering coefficient is represented by S 21_ideal the ratio of the reflected signal to the electric field strength of the incident signal, the scattering coefficient is represented by S single is represented as: Step three - five: Based on equation (5), σ mea is represented as:

4. The method of claim 1, wherein: The step four is specifically: Step four-1: Joint estimation of the theoretical and measured values of the reflection coefficient under horizontal and vertical polarization by the least square fitting method; the fitting error is defined as the cumulative value of the mean square error between the theoretical and measured values of the RCS under the two polarizations, that is, where N j is the number of measured scattering angles, i is the serial number of measured scattering angle, σ mea represents the RCS measured value, σ single represents the RCS theoretical value, the parameters G0, n, B and k in formula (22) are adjusted by the least square method, and the parameters corresponding to the minimum RMSE are regarded as the best model parameters; Step four-2: Verify the accuracy and effectiveness of the structure model: compare the full-wave simulation values of the layered target structure model with the measured values in the microwave anechoic chamber to test the rationality and applicability of the passive scatterer model; Step four-3: Verify the accuracy and effectiveness of the antenna radiation pattern model: compare the theoretical values of the antenna radiation pattern model with the measured values in the microwave anechoic chamber to evaluate the accuracy and reliability of the model based on the root mean square error.

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