RCS characterization method for heterogeneous target passive scattering

Abstract

The invention relates to a heterogeneous target passive scattering RCS characterization method, and belongs to the technical field of radar and communication. The method comprises the following steps: firstly, judging a target surface roughness type based on a Rayleigh criterion, revealing a radio wave propagation mechanism of interaction between electromagnetic waves and a target, and constructing an RCS model in combination with target scattering characteristics; and then, in combination with target passive scattering characteristics and a bistatic radar equation, representing an RCS radiation direction mode caused by target passive scattering. Then, reconstructing a three-dimensional structure model by using the target electromagnetic parameters, and obtaining RCS data under different frequency bands and incident angles through full-wave simulation and microwave anechoic chamber measurement; and finally, fitting a normalized radiation direction mode by using simulation data and actually measured data, determining RCS model parameters, and verifying the accuracy and effectiveness of the model. According to the method, theoretical analysis and simulation technologies are effectively combined, passive scattering characteristics of heterogeneous targets can be accurately and efficiently represented, and powerful support is provided for development of radar detection and stealth technologies.

Description

Technical Field

[0001] The invention belongs to the field of radar and communication technology and relates to an RCS characterization method for passive scattering of heterogeneous targets Background Art

[0002] In the field of radar and communication technology, the passive scattering characteristics of a target are one of the important indicators for evaluating its detection performance and stealth capability. In particular, for heterogeneous targets (such as targets with plate-type layered structures), the accurate characterization of their passive scattering radar cross section (RCS) is particularly critical. 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 an ideal uniform target model, which approximates the target through simple geometric shapes and uniform electromagnetic parameters, which greatly limits the accuracy and applicability of the model when facing actual heterogeneous targets. For plate-type layered heterogeneous targets, due to their complex structure, diverse materials, and electromagnetic parameters that vary with frequency and position, accurate modeling and simulation of their passive scattering characteristics become particularly difficult.

[0004] To overcome these difficulties, researchers have been exploring more accurate and efficient methods for characterizing RCS of passive scattering from 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 to study the passive scattering characteristics of heterogeneous targets. Full-wave simulation methods can accurately simulate the propagation and scattering process of electromagnetic waves on complex targets, thereby obtaining accurate RCS data.

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

[0007] Therefore, how to combine theoretical analysis and simulation technology to establish an accurate and efficient method for characterizing the RCS of passive scattering of heterogeneous targets has become an important issue that needs to be urgently solved in the current field of radar and communication technology. Summary of the invention

[0008] In view of this, the purpose of the present invention is to provide an RCS characterization method for passive scattering of heterogeneous targets. The method includes the propagation mechanism of radio waves of heterogeneous targets, RCS characterization of passive scattering, full-wave simulation and measurement, and RCS parameter fitting and verification. First, based on the Rayleigh criterion, the propagation mechanism of radio waves of the interaction between electromagnetic waves and plate-type layered heterogeneous targets is revealed, and the RCS model of passive scattering of heterogeneous targets is constructed in combination with the target scattering characteristics; secondly, the radiation direction pattern of RCS caused by target passive scattering is characterized by combining the target passive scattering characteristics and the dual-base radar equation; then, the three-dimensional plate-type layered target structure model is reconstructed using the target electromagnetic parameters, and the RCS under different frequency bands and different incident angles is obtained through full-wave simulation, and the RCS distribution of target passive scattering is obtained by measuring in a microwave darkroom; finally, the normalized radiation direction pattern is fitted using simulation data and measured data, the RCS model parameters are determined, and the model accuracy and effectiveness are verified. This method provides a theoretical basis for passive scattering of space cooperative and non-cooperative targets.

[0009] In order to achieve the above object, the present invention provides the following technical solutions:

[0010] See also Figure 1 and Figure 2 , is a RCS characterization method for passive scattering of heterogeneous targets, including the following steps:

[0011] Step 1: Determine the surface roughness type of the plate-type layered heterogeneous target based on the Rayleigh criterion, and construct the RCS model of passive scattering of the heterogeneous target;

[0012] Step 2: Combining the passive scattering characteristics of the target with the bistatic radar equation, characterize the radiation direction pattern of the RCS caused by the passive scattering of the target;

[0013] Step 3: Reconstruct the three-dimensional plate-type hierarchical target structure model using electromagnetic parameters, obtain RCS simulation data at different frequency bands and different incident angles through full-wave simulation, and obtain the RCS distribution of target passive scattering by measuring in a microwave darkroom;

[0014] Step 4: Use simulation data and measured data to fit the normalized radiation direction pattern, determine the RCS model parameters, and verify the accuracy and effectiveness of the model.

[0015] Further, the step 1 is specifically as follows:

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

[0017]

[0018] Among them, σ h is the material roughness, λ is the wavelength of the incident wave, θ i is the angle of incidence;

[0019] Step 1-2: Determine the roughness type of the plate type layered heterogeneous target based on the roughness parameter g. The definitions of different roughness types are as follows:

[0020]

[0021] Steps 1-3: Based on the determined roughness type, construct the RCS model of passive scattering of heterogeneous targets. The RCS model is expressed as:

[0022]

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

[0024] 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 It is expressed as:

[0025]

[0026] The RCS model is expressed as:

[0027] σ=4πR 2 |R single 2 (5).

[0028] Further, the step 2 is specifically as follows:

[0029] Step 2-1: The transmitter has a normalized power radiation pattern and antenna gain G t The antenna transmits power P to the heterogeneous target t The power of the incident signal is expressed as:

[0030]

[0031] Among them, 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 expressed as:

[0033]

[0034] Where 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, and we get:

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

[0037] Among them, P scatter The total scattered power in the beam cross section, the scattering coefficient R single It is expressed as:

[0038] R single =Ae jφ (9)

[0039] Among them, 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 expressed as:

[0041]

[0042] Where G represents the beam cross-sectional gain, is the normalized radiation pattern of the receiving antenna, A r The aperture of the receiving antenna;

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

[0044]

[0045] in,

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

[0047]

[0048] Among them, the aperture of the receiving antenna is expressed as:

[0049]

[0050] Substituting formula (11) and formula (13) into formula (12), we get:

[0051]

[0052] The peak radiation directions of the transmitting antenna and the receiving antenna are both directed toward the center of the passive scattering target. The received power in the far field is rewritten as:

[0053]

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

[0055]

[0056] Combining formula (15) and formula (16), we get:

[0057]

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

[0059]

[0060] Based on the radiation characteristic theory, the directional pattern function in a specific scene It is defined as the superposition of the main lobe and the side lobe. The main lobe is composed of The side lobe part is represented by express, It 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] Sidelobe based on harmonic interference and scattering theory It is expressed as:

[0066]

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

[0068] The complete pattern model formula is express:

[0069]

[0070] Further, the step three is specifically as follows:

[0071] Step 3-1: First, study the propagation characteristics of single-layer materials, clarify the reflection and transmission capabilities of single-layer materials, and combine the measured electromagnetic parameters of the materials to invert; then, use the electromagnetic parameters of single-layer materials to reconstruct the heterogeneous structure model through full-wave simulation, and at the same time build a multi-layer iterative propagation model based on Fresnel theory;

[0072] Step 3-2: For the plate-type layered target structure model, obtain the RCS values ​​at different frequency bands and with different incident angles through full-wave simulation and calculate the RCS distribution of the target

[0073] Step 3-3: In a microwave darkroom, conduct frequency domain material electromagnetic propagation characteristic measurement based on a vector network analyzer to obtain the RCS value at each scattering angle. The measurement results are expressed as σ mea express;

[0074] Step 3-4: S 21 Defined as the ratio of the electric field intensity of the reflected signal to the incident signal, the scattering coefficient is given by S at each scattering angle. 21_mut With ideal smooth surface S 21_ideal The scattering coefficient R single It is expressed as:

[0075]

[0076] Steps 3-5: Based on formula (5), σ mea It is expressed as:

[0077]

[0078] Further, the step 4 is specifically as follows:

[0079] Step 4-1: The theoretical and measured values ​​of the reflection coefficient are jointly estimated under horizontal and vertical polarizations by the least squares fitting method; the fitting error is defined as the cumulative value of the mean square error between the theoretical and measured RCS values ​​under the two polarizations, that is:

[0080]

[0081] Among them, N j is the number of measured scattering angles, i is the order of the measured scattering angle, σ mea represents the RCS measurement value, σ single represents the theoretical value of RCS. 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 optimal model parameters;

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

[0083] Step 4-3: Verify the accuracy and validity of the antenna radiation pattern model: Compare the theoretical value of the antenna radiation pattern model with the measured value 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 the present invention are:

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

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

[0087] (3) The present 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 radiation pattern, the present 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 present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0091] Figure 1 Schematic diagram of passive scattering of heterogeneous targets;

[0092] Figure 2 This is a comparison chart of the antenna pattern theoretical value, full-wave simulation value and measured value. Figure 2 (a)~ Figure 2 (d) The incident angles are 30°, 40°, 50° and 60° respectively. DETAILED DESCRIPTION

[0093] The following describes the embodiments of the present invention by specific examples, and 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 noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0094] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0095] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0096] Embodiment 1, this embodiment firstly reveals the propagation mechanism of electromagnetic waves interacting with plate-type layered heterogeneous targets based on the Rayleigh criterion, and constructs the RCS model of passive scattering of heterogeneous targets in combination with the target scattering characteristics; secondly, the radiation direction pattern of RCS caused by passive scattering of the target is characterized in combination with the passive scattering characteristics of the target and the dual-base radar equation; then, the three-dimensional plate-type layered target structure model is reconstructed using the target electromagnetic parameters, and the RCS under different frequency bands and different incident angles is obtained through full-wave simulation, and the RCS distribution of target passive scattering is obtained by measuring in a microwave darkroom; finally, the normalized radiation direction pattern is fitted using simulation data and measured data, the RCS model parameters are determined, and the model accuracy and effectiveness are verified. This method provides a theoretical basis for passive scattering of cooperative and non-cooperative targets in space.

[0097] A method for characterizing RCS of passive scattering of heterogeneous targets comprises the following steps:

[0098] Step 1: Determine the surface roughness type of the plate-type stratified heterogeneous target based on the Rayleigh criterion, reveal the propagation mechanism of electromagnetic waves interacting with the plate-type stratified heterogeneous target, and construct the RCS model of passive scattering of heterogeneous targets in combination with the target scattering characteristics.

[0099] Step 2: Combining the passive scattering characteristics of the target with the bistatic radar equation, characterize the radiation direction pattern of the RCS caused by the passive scattering of the target.

[0100] Step 3: Use electromagnetic parameters to reconstruct the three-dimensional plate-type layered target structure model, obtain RCS simulation data at different frequency bands and different incident angles through full-wave simulation, and obtain the RCS distribution of target passive scattering in a microwave darkroom.

[0101] Step 4: Use simulation data and measured data to fit the normalized radiation direction pattern, determine the RCS model parameters, and verify the accuracy and effectiveness of the model.

[0102] Step 1 is as follows:

[0103] Step 1-1: Define g as the roughness parameter of the target surface of the plate type layered heterogeneous surface, g can be expressed as:

[0104]

[0105] Among them, σ h is the material roughness, λ is the wavelength of the incident wave, θ i is the angle of incidence.

[0106] Step 1-2: Determine the roughness type of the plate type layered heterogeneous target based on the roughness parameter g. The definitions of different roughness types are as follows:

[0107]

[0108] Steps 1-3: Based on the determined roughness type, construct the RCS model of passive scattering of heterogeneous targets. The RCS model can be expressed as:

[0109]

[0110] Where R represents the distance between the target and the radar antenna, E s represents the scattered electric field intensity, E i Represents the incident electric field strength.

[0111] 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 It can be expressed as:

[0112]

[0113] Therefore, the RCS model can also be expressed as:

[0114] σ=4πR 2 |R single 2 (5)

[0115] Step 2 is as follows:

[0116] Step 2-1: The transmitter has a normalized power radiation pattern and antenna gain G t The antenna transmits power P to the heterogeneous target t The power of the incident signal can be expressed as:

[0117]

[0118] Among them, R t represents the distance between the transmitter and the target, and S represents the cross-sectional area of ​​the beam.

[0119] For the beam cross section, the electric field of the incident signal can be expressed as:

[0120]

[0121] Where Z0 is the characteristic impedance of air and λ is the wavelength.

[0122] 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, and we can get:

[0123] P in |R single | 2 =P scatter (8)

[0124] Among them, P scatter The total scattered power in the beam cross section, the scattering coefficient R single It can be expressed as:

[0125] R single =Ae jφ (9)

[0126] Among them, A and e jφ represent the controllable amplitude and phase shift of the target respectively.

[0127] The power of the scattered signal received by the receiver from the passive scattering target is expressed as:

[0128]

[0129] Where G represents the beam cross-sectional gain, is the normalized radiation pattern of the receiving antenna, A r The aperture of the receiving antenna.

[0130] Combining formulas (7), (8), and (10), the electric field of the scattered signal received by the receiver from the beam cross section can be expressed as:

[0131]

[0132] in,

[0133] The signal power received by the receiver can be expressed as:

[0134]

[0135] Among them, the aperture of the receiving antenna can be expressed as:

[0136]

[0137] Substituting formula (11) and (13) into formula (12), we can obtain:

[0138]

[0139] The peak radiation directions of the transmitting antenna and the receiving antenna are both directed toward the center of the passive scattering target. The received power in the far field can be rewritten as:

[0140]

[0141] Based on the bistatic radar equation, the received power can be expressed as:

[0142]

[0143] Combining formula (15) and (16), we can get:

[0144]

[0145] Therefore, a normalized antenna pattern function model can be constructed to characterize the radiation direction pattern of RCS caused by target passive scattering. The model expression is:

[0146]

[0147] Based on the radiation characteristic theory, the directional pattern function in a specific scene It is defined as the superposition of the main lobe and the side lobe. The main lobe is composed of The side lobe part is represented by express, It can be expressed as:

[0148]

[0149] Based on the antenna pattern theory, the main lobe part f(θ) can be expressed as:

[0150]

[0151] 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 center direction of the main lobe.

[0152] Sidelobe based on harmonic interference and scattering theory It can be expressed as:

[0153]

[0154] Among them, B represents the amplitude of the side lobe, and k represents the speed of the side lobe oscillation.

[0155] Therefore, the complete pattern model formula is express:

[0156]

[0157] Step three is as follows:

[0158] Step 3-1: First, study the propagation characteristics of single-layer materials, clarify 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 heterogeneous structure model through full-wave simulation, and at the same time build a multi-layer iterative propagation model based on Fresnel theory.

[0159] Step 3-2: For the plate-type layered target structure model, obtain the RCS values ​​at different frequency bands and with different incident angles through full-wave simulation and calculate the RCS distribution of the target

[0160] Step 3-3: In a microwave darkroom, conduct frequency domain material electromagnetic propagation characteristic measurement based on a vector network analyzer to obtain the RCS value at each scattering angle. The measurement results are expressed as σ mea express.

[0161] Step 3-4: S 21 Defined as the ratio of the electric field intensity of the reflected signal to the incident signal, the scattering coefficient is given by S at each scattering angle. 21_mut With ideal smooth surface S 21_ideal The scattering coefficient R single It is expressed as:

[0162]

[0163] Steps 3-5: Based on formula (5), σ mea It is expressed as:

[0164]

[0165] Step 4 is as follows:

[0166] Step 4-1: The theoretical and measured values ​​of the reflection coefficient are jointly estimated under horizontal and vertical polarizations by the least squares fitting method; the fitting error is defined as the cumulative value of the mean square error between the theoretical and measured RCS values ​​under the two polarizations, that is:

[0167]

[0168] Among them, N j is the number of measured scattering angles, i is the order of the measured scattering angle, σ mea represents the RCS measurement value, σ single represents the theoretical value of RCS. The parameters G0, n, B and k in (22) are adjusted by the least squares method, and the parameters corresponding to the minimum RMSE are regarded as the optimal model parameters.

[0169] Step 4-2: Verify the accuracy and effectiveness of the structural model: Compare and analyze the full-wave simulation value of the plate-type layered target structure model with the actual measured value in the microwave darkroom to verify the rationality and applicability of the passive scatterer model.

[0170] Step 4-3: Verify the accuracy and validity of the antenna radiation pattern model: Compare the theoretical value of the antenna radiation pattern model with the measured value in the microwave anechoic chamber, and evaluate the accuracy and reliability of the model based on the root mean square error.

[0171] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for characterizing RCS of passive scattering of heterogeneous targets, characterized by: The following steps are involved: Step 1: Determine the surface roughness type of the plate-type layered heterogeneous target based on the Rayleigh criterion, and construct the RCS model of passive scattering of the heterogeneous target; Step 2: Combining the passive scattering characteristics of the target with the bistatic radar equation, characterize the radiation direction pattern of the RCS caused by the passive scattering of the target; Step 3: Reconstruct the three-dimensional plate-type hierarchical target structure model using electromagnetic parameters, obtain RCS simulation data at different frequency bands and different incident angles through full-wave simulation, and obtain the RCS distribution of target passive scattering by measuring in a microwave darkroom; Step 4: Use simulation data and measured data to fit the normalized radiation direction pattern, determine the RCS model parameters, and verify the accuracy and effectiveness of the model.

2. The RCS characterization method of heterogeneous target passive scattering according to claim 1 is characterized in that: The step 1 is specifically as follows: Step 1-1: Define g as the roughness parameter of the target surface of the plate type layered heterogeneous surface, g is expressed as: Among them, σ h is the material roughness, λ is the wavelength of the incident wave, θ i is the angle of incidence; Step 1-2: Determine the roughness type of the plate type layered heterogeneous target based on the roughness parameter g. The definitions of different roughness types are as follows: Steps 1-3: Based on the determined roughness type, construct the RCS model of passive scattering of heterogeneous targets. The RCS model is expressed as: Where R represents the distance between the 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 It is expressed as: The RCS model is expressed as: σ=4πR 2 |R single | 2 (5)。 3. The RCS characterization method of heterogeneous target passive scattering according to claim 1 is characterized by: The step 2 is specifically as follows: Step 2-1: The transmitter has a normalized power radiation pattern and antenna gain G t The antenna transmits power P to the heterogeneous target t The power of the incident signal is expressed as: in, 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 expressed as: Where 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 equals the total power of the scattered signal, and we get: P in |R single | 2 =P scatter (8) Among them, P scatter The total scattered power in the beam cross section, the scattering coefficient R single It is expressed as: R single =Ae jφ (9) Among them, A and e jφ represent the controllable amplitude and phase shift of the target respectively; The power of the scattered signal received by the receiver from the passive scattering target is expressed as: Where G represents the beam cross-sectional gain, is the normalized radiation pattern of the receiving antenna, A r The aperture of the receiving antenna; Combining equations (7), (8) and (10), the electric field of the scattered signal received by the receiver from the beam cross section is expressed as: in, The signal power received by the receiver is expressed as: Among them, the aperture of the receiving antenna is expressed as: Substituting formula (11) and formula (13) into formula (12), we get: The peak radiation directions of the transmitting antenna and the receiving antenna are both directed toward the center of the passive scattering target. The received power in the far field is rewritten as: Based on the bistatic radar equation, the received power is expressed as: Combining formula (15) and formula (16), we get: A normalized antenna pattern function model is constructed to characterize the radiation direction pattern of RCS caused by target passive scattering. The model expression is: Based on the radiation characteristic theory, the directional pattern function in a specific scene It is defined as the superposition of the main lobe and the side lobe. The main lobe is composed of The side lobe part is represented by express, It is expressed as: Based on the antenna pattern theory, the main lobe part f(θ) is expressed as: 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; Sidelobe based on harmonic interference and scattering theory It is expressed as: Where B represents the amplitude of the side lobe, and k represents the speed of the side lobe oscillation; The complete pattern model formula is express:

4. The RCS characterization method of heterogeneous target passive scattering according to claim 1 is characterized in that: The step three is specifically as follows: Step 3-1: First, study the propagation characteristics of single-layer materials, clarify the reflection and transmission capabilities of single-layer materials, and combine the measured electromagnetic parameters of the materials to invert; then, use the electromagnetic parameters of single-layer materials to reconstruct the heterogeneous structure model through full-wave simulation, and at the same time build a multi-layer iterative propagation model based on Fresnel theory; Step 3-2: For the plate-type layered target structure model, obtain the RCS values ​​at different frequency bands and with different incident angles through full-wave simulation and calculate the RCS distribution of the target Step 3-3: In a microwave darkroom, conduct frequency domain material electromagnetic propagation characteristic measurement based on a vector network analyzer to obtain the RCS value at each scattering angle. The measurement results are expressed as σ mea express; Step 3-4: S 21 Defined as the ratio of the electric field intensity of the reflected signal to the incident signal, the scattering coefficient is given by S at each scattering angle. 21_mut With ideal smooth surface S 21_ideal The scattering coefficient R single It is expressed as: Steps 3-5: Based on formula (5), σ mea It is expressed as:

5. The RCS characterization method of heterogeneous target passive scattering according to claim 1 is characterized in that: The step 4 is specifically as follows: Step 4-1: The theoretical and measured values ​​of the reflection coefficient are jointly estimated under horizontal and vertical polarizations by the least squares fitting method; the fitting error is defined as the cumulative value of the mean square error between the theoretical and measured RCS values ​​under the two polarizations, that is: Among them, N j is the number of measured scattering angles, i is the order of the measured scattering angle, σ mea represents the RCS measurement value, σ single represents the theoretical value of RCS. 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 optimal model parameters; Step 4-2: Verify the accuracy and effectiveness of the structural model: Compare and analyze the full-wave simulation value of the plate-type layered target structure model with the actual measured value in the microwave darkroom to verify the rationality and applicability of the passive scatterer model; Step 4-3: Verify the accuracy and validity of the antenna radiation pattern model: Compare the theoretical value of the antenna radiation pattern model with the measured value in the microwave anechoic chamber, and evaluate the accuracy and reliability of the model based on the root mean square error.

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