A Radar Target Characteristic Planning Method Based on a Forward Scattering Center Model

Abstract

This invention proposes a radar target characteristic planning method based on a forward scattering center model. This method plans the desired target characteristics according to actual design needs, selects an impedance surface to simulate the thin-coated PEC target surface, references the forward modeling process of the scattering center of an ideal conductive target, and employs a high-frequency calculation method for electromagnetic scattering of impedance targets to construct a scattering center model for electrically large targets with dielectric coating or local coating. By adjusting the coating dielectric parameters and coating area, the contribution and variation law of the target scattering center to the overall scattering, the formation process of scattering from the target's local structure, and the control of target characteristic signals are obtained. Through multiple iterative optimizations, the model reconstructs the target characteristics to meet the expected characteristics, thus achieving target characteristic planning. This invention can effectively meet the design requirements of sample target characteristic planning and shows significant advantages in the design and optimization of characteristic signal control.

Description

Technical Field

[0001] The present invention belongs to the field of radar target characteristic modeling and analysis, and particularly relates to a radar target characteristic planning method based on a forward model of scattering centers. Background Art

[0002] The characteristic data provided by traditional electromagnetic simulation is the result of the superposition of the scattering of each part (such as components) on the target, which is the overall scattering field or the total scattering field of the target. However, in the fields of radar target characteristic analysis and optimal design, target recognition and interpretation, etc., there is also an urgent need for the partial field scattering characteristics and scattering mechanisms of each structure on the target before synthesis in practical applications. Unfortunately,

[0003] Traditional electromagnetic simulation only provides the total field information of the entire target and is difficult to directly output the partial field information of each component or structure of the decomposed target. There is a lack of mapping relationship between the partial field characteristics of each component or structure of the target and its scattering structure, which has become an important obstacle restricting the development of radar target characteristic signal optimal design technology. In the high-frequency region of the electromagnetic field, the total scattering of a radar target can be expressed as the coherent superposition of the contributions of several local scattering sources, and these local scattering sources are usually called scattering centers. The scattering center concisely describes the electromagnetic scattering characteristics of the target in the high-frequency region, and the modeling and analysis of the scattering center play a key technical support role in target characteristic analysis and optimal design, target recognition and interpretation. The scattering center modeling approach is mainly divided into forward and reverse. The reverse approach starts from the measured or simulated radar echo data and obtains the parameters of each scattering center through parameter estimation and inversion optimization methods. The reverse approach essentially belongs to parameter estimation, and due to its inherent uncertainty, the obtained model lacks a clear physical meaning and the target characteristic information is severely lost. In recent years, some scholars have proposed a parametric forward modeling approach and method for the scattering centers of complex target components based on a geometric model. This approach is modeled based on high-frequency electromagnetic theory and the target geometry, thus ensuring that the modeling process is completely deterministic. This method uses a high-frequency modeling method to separate the scattering centers forward and quantitatively calculate the scattering contributions,推算模型参数,所建的参数化模型及其参数与部件、目标局部结构之间呈良好对应关系。该方法可同时提供目标整体散射数据、目标上各部分散射数据以及它们背后所“隐藏”的目标各部件与结构信息,散射中心的参数取值即是这些信息在电磁散射层面的表征。正向模型物理意义清晰,在样本目标各部件或结构与散射中心之间建立起清晰的映射关系,这些映射关系正是提升目标特性优化设计能力的重要基础。

[0004] It should be noted that there seems to be some garbled text in the original Chinese for the part about "推算模型参数,所建的参数化模型及其参数与部件、目标局部结构之间呈良好对应关系。该方法可同时提供目标整体散射数据、目标上各部分散射数据以及它们背后所“隐藏”的目标各部件与结构信息,散射中心的参数取值即是这些信息在电磁散射层面的表征。正向模型物理意义清晰,在样本目标各部件或结构与散射中心之间建立起清晰的映射关系,这些映射关系正是提升目标特性优化设计能力的重要基础。", which may affect the accuracy of the translation. I have tried my best to translate it based on the overall context. You may need to check and correct it according to the accurate original content.However, current forward models focus on PEC targets and cannot effectively simulate the electromagnetic scattering of targets in complex real-world environments. Considering that in real-world environments, field equipment targets are not composed of ideal PEC, but rather have thin dielectric layers coated on their highly conductive alloy surfaces—such as anti-corrosion paint or even locally coated with absorbing materials—to achieve a "surface" attenuation effect, it is necessary to extend the scope of forward models to non-PEC targets to meet the needs of radar target characteristic planning and characteristic signal control and optimization design. Summary of the Invention

[0005] This invention addresses the shortcomings of existing forward scattering center modeling methods by providing a radar target characteristic planning and feature signal control and optimization design method based on a forward scattering center model. The forward scattering center model of the coated target established in this invention has a clear physical mechanism, establishing a mapping relationship between each component or structure of the sample target and the scattering center, allowing for optimization design operations. It reveals the contribution and variation law of the target's scattering center to the overall scattering, as well as the formation process of scattering from local target structures, demonstrating significant advantages in the design and optimization of feature signal control.

[0006] The technical solution of this invention is a radar target characteristic planning method based on a forward scattering center model, characterized by comprising the following steps:

[0007] Step 1: Based on actual design needs, conduct radar target characteristic planning and design for the sample target under ideal conductivity conditions;

[0008] Step 2: Establish a scattering center model of the target under ideal conductivity to obtain target scattering source information, perform scattering source analysis on sample targets, and construct the correspondence between the strong scattering source of the target and the local structure of the target. The scattering characteristics of the target are mainly determined by the strong scattering source of the target. Therefore, in order to meet the actual design needs, it is usually selected to coat the strong scattering structure of the target with a material medium. The specific medium coating parameters and coating area need to be selected according to the radar target characteristic planning requirements in Step 1 and the absorption characteristics of the medium coating itself.

[0009] Step 3: The impedance surface is used to simulate the thin-coated PEC target surface. The absorption effect of the target surface on the incident electromagnetic wave is expressed by the impedance parameter. Referring to the forward modeling process of the PEC target scattering center, and using the high-frequency calculation method of impedance target electromagnetic scattering, the scattering center model of the dielectric-coated or locally coated electrically large target is constructed.

[0010] Step 4: Utilize the coated target scattering center model obtained in Step 3 to reconstruct the radar target characteristics and compare them with the expected characteristics. Examine and analyze the distribution of strong scattering sources in the coating model, the relative magnitudes of the scattering center amplitudes, and the consistency between the reconstructed RCS curve and SAR image and the expected results. Based on the error analysis results, adjust the material medium parameters and the coating area, select a dielectric coating with stronger or weaker wave absorption ability or choose to expand the material medium coating range. Through this process, the contribution of the target scattering center to the overall scattering and its variation law, the formation process of the local structure scattering of the target, and the control of the target characteristic signal can be obtained. After multiple iterations and optimizations until the model-reconstructed target characteristics meet the expected characteristics, the radar target characteristic planning is achieved.

[0011] Furthermore, the impedance surface is obtained by equivalent the thin dielectric coated on the ideal conductive target surface to an impedance surface without thickness, and the coating medium parameters are characterized by the surface impedance dyadic.

[0012] Furthermore, the scattering center model is an attribute scattering center model, and its expression is as follows:

[0013]

[0014] In the formula, is the amplitude parameter of the i-th scattering center, is the length parameter of the scattering center, is the frequency-dependent factor, is the three-dimensional position vector of the scattering center, is the azimuth angle of the incident wave, is the azimuth angle of the distributed scattering center. If the scattering center is local, then otherwise where j is the imaginary unit, f is the incident wave frequency, is the scattering center frequency, c is the speed of light, has no specific physical meaning.

[0015] Furthermore, the specific steps for the forward calculation of the model attribute parameters are as follows:

[0016] Determine the amplitude parameter based on the geometric physical optics mixed with the impedance boundary condition, i.e., the GO-PO high-frequency algorithm. The field amplitude on the primary action ray is directly calculated using the physical optics, i.e., the PO algorithm. For the field amplitude on the secondary and higher-order coupled action rays, the mixed geometric physical optics, i.e., the GO-PO method, is used to determine.

[0017] ]>Furthermore, the length parameter The method for obtaining the length parameter of the scattering center is as follows: Find the two equivalent endpoints of the "bright line" in the ray set of the distributed scattering center. Then, by projecting the two endpoints and subtracting the results, the length parameter of the scattering center can be obtained.

[0018]

[0019] In the formula: and These are the coordinates of the two endpoints on the x-axis and y-axis, respectively. These are the elevation and azimuth angles of the radar incident wave, respectively.

[0020] Furthermore, frequency-dependent factors The method to obtain it is as follows:

[0021] The frequency dependence factor is determined by reading the geometric information of the target and judging the scattering mechanism contained in each scattering center. .

[0022] Furthermore, the frequency dependence factors of dihedral and trihedral scattering structures The value is 1, representing the frequency dependence factor of the cylindrical surface and the top cap scattering structure. The value is 1 / 2, representing the frequency dependence factor of the diffraction scattering structure of the sphere and the straight edge. A value of 0 indicates the frequency dependence factor of the angular diffraction-scattering structure. The value is -1.

[0023] Furthermore, the three-dimensional position of the scattering center The reflection points of all rays in the corresponding subset are weighted to determine the reflection point. For a single-reflection ray, the geometric center of the illuminated surface is taken as the reflection point, i.e., the scattering center. For multiple-reflection rays, the reflection point is obtained by using the principle of equivalent calculation of phase difference based on optical path difference. The weight value is determined by the magnitude of the induced current on the target.

[0024] Furthermore, the specific formula for calculating the weight value is as follows:

[0025]

[0026] In the formula Let be the magnitude of the induced current in the surface element. For the first n The equivalent reflection point of the root ray. The coordinates are the center coordinates of the surface element.

[0027] Furthermore, the total scattered field of the target is the sum of the contributions from N scattering centers, that is:

[0028]

[0029] Forward modeling of scattering centers only requires calculating the set of scattering center parameters of the target in one observation attitude, and then giving... Substituting the range of small angle variations, step size, frequency range, and step size into the above formula, the SAR image of the target can be reconstructed.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] 1. The physical mechanism of the method of the present invention in establishing the forward model of the scattering center of the coated target is clear. It establishes a mapping relationship between each component or structure of the sample target and the scattering center, which can be used for optimization design operations. These mapping relationships are an important foundation for improving the optimization design capability of target characteristics.

[0032] 2. The method of the present invention performs target feature signal control and iterative optimization design. By analyzing the strong scattering source distribution of the coating model, the relative magnitude of the scattering center amplitude, and the consistency between the reconstructed RCS curve and SAR image and the expected results, appropriate coating medium parameters and coating area are selected. In this way, the contribution and variation law of the target scattering center to the overall scattering, as well as the formation process of the target local structure scattering, are known. The process is direct and simple, and the target feature signal control effect is obvious.

[0033] 3. Compared with existing technologies, the method of this invention enriches the content of forward modeling methods for scattering centers, and provides a low-cost technical means for the characteristic planning and rapid prediction of target radar characteristics in complex environments, and even supports many downstream practical application fields, including target detection and identification, target remote sensing, etc. Attached Figure Description

[0034] Figure 1 This is the overall framework diagram of the radar target characteristic planning method based on the forward scattering center model of this invention;

[0035] Figure 2 These are actual photographs of embodiments of the present invention;

[0036] Figure 3 : This is a schematic diagram of a model according to an embodiment of the present invention;

[0037] Figure 4 This is an exploded view of the model components in an embodiment of the present invention;

[0038] Figure 5 This is a comparison between the SAR image (right, PEC) reconstructed by the parametric model of the scattering center in this invention and the measured image (left), with the attitude angle being... θ =73°, φ =60°, similarity is 75.87%;

[0039] Figure 6: This is a schematic diagram of a partial coating situation according to an embodiment of the present invention;

[0040] Figure 7 This is a comparison between the reconstructed target SAR image and the measured image obtained by coating a local area of ​​the surface with isotropic impedance and establishing a scattering center model in the forward direction according to an embodiment of the present invention.

[0041] Figure 8 This is a comparison between the reconstructed target SAR image and the measured image obtained by positively establishing a scattering center model after coating anisotropic impedance on a local area of ​​the surface in an embodiment of the present invention; Detailed Implementation

[0042] To facilitate understanding and implementation of the present invention by those skilled in the art, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0043] A radar target characteristic planning method based on a forward scattering center model, such as... Figure 1 As shown, the specific steps include:

[0044] Step 1: Based on actual design needs, conduct radar target characteristic planning and design for the sample target under ideal conductivity conditions;

[0045] Step 2: Establish a scattering center model of the target under ideal conductivity to obtain target scattering source information, perform scattering source analysis on sample targets, and construct the correspondence between the strong scattering source of the target and the local structure of the target. The scattering characteristics of the target are mainly determined by the strong scattering source of the target. Therefore, in order to meet the actual design needs, it is usually selected to coat the strong scattering structure of the target with a material medium. The specific medium coating parameters and coating area need to be selected according to the radar target characteristic planning requirements in Step 1 and the absorption characteristics of the medium coating itself.

[0046] Step 3: The impedance surface is used to simulate the thin-coated PEC target surface. The absorption effect of the target surface on the incident electromagnetic wave is expressed by the impedance parameter. Referring to the forward modeling process of the PEC target scattering center, and using the high-frequency calculation method of impedance target electromagnetic scattering, the scattering center model of the dielectric-coated or locally coated electrically large target is constructed.

[0047] Step 4: Reconstruct the radar target characteristics using the coated target scattering center model obtained in Step 3 and compare it with the expected characteristics. Examine and analyze the distribution of strong scattering sources, the relative magnitude of scattering center amplitude, and the consistency between the reconstructed RCS curve and SAR image and the expected results. Based on the error analysis results, adjust the material medium parameters and coating area, select a medium coating with stronger or weaker absorption capacity, or expand the material medium coating range. This process can reveal the contribution and variation law of the target scattering center to the overall scattering, the formation process of the target's local structure scattering, and achieve target characteristic signal control. After multiple iterations of optimization, the model reconstructs the target characteristics until they meet the expected characteristics, thus realizing radar target characteristic planning.

[0048] In step 3, the impedance surface is equivalent to a thin dielectric coating on an ideal conductive target surface as an impedance surface with no thickness, and the coating dielectric parameters are characterized by the surface impedance dyadic.

[0049] In the high-frequency region of the electromagnetic field, the total scattering of a radar target can be represented as a coherent superposition of contributions from several local scattering sources, which are usually called scattering centers. Scattering centers concisely describe the electromagnetic scattering characteristics of a target in the high-frequency region. Modeling and analyzing scattering centers play a crucial technical support role in radar target identification and interpretation, and even become a key step in the identification and interpretation process. The main models describing scattering centers include: the ideal point scattering model, the attenuation exponent model, and the attribute scattering center model based on geometric diffraction theory (GTD). Among them, the attribute scattering center model characterizes the frequency characteristics of the target's scattering center, the geometric features of its corresponding structure, and its relationship with azimuth, revealing the true scattering mechanism of the target more accurately. The specific expression of the attribute scattering center model is as follows:

[0050] In the formula, Let be the amplitude parameter of the i-th scattering center. The length parameter of the scattering center. It is a frequency-dependent factor. It is the three-dimensional position vector of the scattering center. The incident wave azimuth angle, It is the azimuth angle of the distributed scattering center. If the scattering center is localized, then... ,otherwise ,in j For virtual part units, f The incident wave frequency, The scattering center frequency, c It's the speed of light. It has no specific physical meaning.

[0051] The specific steps for forward inference of model attribute parameters are as follows:

[0052] Amplitude parameters are determined using the Geometric Physical Optics (GO-PO) algorithm based on impedance boundary condition hybridity. The field amplitude on the primary coupling ray is directly calculated using the physical optics (PO) algorithm. For the field amplitude on secondary and higher coupling rays, the hybrid geometric physical optics (GO-PO) method is used. The length parameter of the scattering center... The method for obtaining the length parameter of the scattering center is as follows: Find the two equivalent endpoints of the "bright line" in the ray set of the distributed scattering center. Then, by projecting the two endpoints and subtracting the results, the length parameter of the scattering center can be obtained.

[0053]

[0054] In the formula: and These are the coordinates of the two endpoints on the x-axis and y-axis, respectively. These are the elevation and azimuth angles of the radar incident wave, respectively.

[0055] The frequency dependence factor α is obtained as follows: It is determined by reading the geometric information of the target and judging the scattering mechanism contained in each scattering center. Table 1 shows several typical scattering structures. α and L Values.

[0056] Table 1 Several typical scattering structures α and L Value

[0057]

[0058] Furthermore, the three-dimensional position of the scattering center The reflection points of all rays in the corresponding subset are weighted to determine the scattering center. For a single-reflection ray, the geometric center of the illuminated surface is taken as the reflection point. For multiple-reflection rays, the reflection point is obtained by calculating the phase difference using the optical path difference. The weight value is determined by the magnitude of the induced current on the target. The specific calculation formula is as follows:

[0059]

[0060] In the formula Let be the magnitude of the induced current in the surface element. For the first n The equivalent reflection point of the root ray. The coordinates are the center coordinates of the surface element.

[0061] The total scattered field of the target is the sum of the contributions from N scattering centers, that is:

[0062]

[0063] Forward modeling of scattering centers only requires calculating the set of scattering center parameters of the target in one observation attitude, and then giving... Substituting the range of small angle variations, step size, frequency range, and step size into the above formula, the SAR image of the target can be reconstructed.

[0064] The following example uses the T-72 main battle tank as the subject of study:

[0065] Step 1: Conduct radar target characteristic planning and design for the sample targets based on actual design needs. Previous studies have verified the effectiveness of the attribute scattering center parameterized forward modeling method in reproducing the electromagnetic scattering characteristics of complex targets such as the T-72 tank. Considering that the test objects in the MSTAR program are real targets, and the materials of field equipment targets are usually not composed of ideal PEC, non-metallic dielectric materials such as absorbing coatings or anti-rust paints are often applied to the surface of the target's high-conductivity alloys, or even locally coated with absorbing materials to achieve the effect of "surface" loss, it is necessary to discuss the "real" scattering characteristics of the T-72 with its non-ideal PEC material. A real-world image of the T-72 main battle tank is shown below. Figure 2 As shown.

[0066] Step 2: Establish a scattering center model of the T72 tank target under ideal conductivity conditions to obtain target scattering source information. The scattering center is extracted at a frequency of 9.6 GHz, with an incident plane wave zenith angle of 73° and an azimuth angle of 60°. A schematic diagram of the T72 tank model is shown below. Figure 3 As shown, the T72 main battle tank measures 7.54m × 2.52m × 1.91m. Considering the complexity of the target structure, and to ensure the accuracy of the scattering center model, the target CAD model was decomposed into 147 surface regions, approximately 530,000 facets. A schematic diagram of the target model's partitioning is shown below. Figure 4 As shown in Table 3, the calculation results of the scattering center parameters of the T72 tank under ideal conductivity conditions are shown in Table 3.

[0067] Table 2

[0068]

[0069] Table 2 lists the top 8 strong scattering centers of the target in this observation attitude, sorted by amplitude. Region index 87 is the region number of the target's left wheel arch, 147 is the turret, and 116-140 are the outer surfaces of the left wheels. Scattering center 1 originates from the reflection between the turret and the left wheel arch; scattering center 2 originates from the primary scattering of the turret; scattering centers 3-8 originate from the double scattering of the hubs and rims of multiple support wheels on the left side of the tank. The SAR image of the target in this attitude is reconstructed, and the scattering sources corresponding to the scattering centers are marked on the image. The images are then compared with measured images from the MSTAR dataset. The results are as follows: Figure 5As shown, the left image is a measured image of the T72 main station tank in the MSTAR dataset, and the right image is a reconstructed SAR image of the scattering center model of the T72 tank model under ideal conductivity conditions. The similarity between the two images is 75.87%.

[0070] The turret and revolver shroud, as strong scattering sources of PEC targets, exhibit significantly higher brightness in reconstructed SAR images compared to other scattering sources. However, measured values ​​at these locations are significantly lower than the reconstructed characteristic data of the PEC targets. Whether this is related to reduced conductivity after the target surface is "painted" should be considered first. Therefore, a target scattering center model should be established by coating the surfaces of strong scattering structures such as the turret and revolver shroud with an absorbing material to reconstruct target characteristic data. This model should then be compared and analyzed with the measured characteristic data to examine its effectiveness and rationality.

[0071] Step 3: The thin-coated PEC target surface is simulated using impedance surface modeling. The absorption effect of the target surface on the incident electromagnetic wave is expressed by the impedance parameter. Referring to the forward modeling process of the PEC target scattering center, and using the high-frequency calculation method of impedance target electromagnetic scattering, the model of the scattering center of the locally coated target is constructed.

[0072] Step 4: Using the target scattering center model obtained in Step 3, the radar target characteristics are reconstructed and compared with the expected characteristics. The coating medium parameters and coating area are adjusted to understand the contribution and variation of the target scattering center to the overall scattering, as well as the formation process of scattering from the target's local structure, thus achieving target characteristic signal control. This process is repeated iteratively until the model reconstructs the target characteristics to meet the expected characteristics, thus realizing the radar target characteristic planning.

[0073] Considering that the selection of impedance plane parameters mainly depends on the application purpose, the aim of this radar target characteristic planning is to select appropriate medium coating parameters and coating range through scattering source analysis, establish a scattering center model of the coated target, and make the model reconstruct the target characteristics close to the real radar target characteristics. The selection of medium coating parameters and coating range requires multiple iterative optimizations to obtain the optimal results. Due to space limitations, the following presents the target characteristic planning results of the T72 target's strong scattering structure under both isotropic and anisotropic medium coating conditions during the iterative optimization process.

[0074] In the high-frequency region of the electromagnetic field, the total scattering of a radar target can be represented as a coherent superposition of contributions from several local scattering sources, which are usually called scattering centers. Scattering centers concisely describe the electromagnetic scattering characteristics of a target in the high-frequency region. Modeling and analyzing scattering centers play a crucial technical support role in radar target identification and interpretation, and even become a key step in the identification and interpretation process. The main models describing scattering centers include: the ideal point scattering model, the attenuation exponent model, and the attribute scattering center model based on geometric diffraction theory (GTD). Among them, the attribute scattering center model characterizes the frequency characteristics of the target's scattering center, the geometric features of its corresponding structure, and its relationship with azimuth, revealing the true scattering mechanism of the target more accurately. The specific expression of the attribute scattering center model is as follows:

[0075] Table 3 shows the results of two strong scattering sources, the turret and the revolver cover, in an isotropic impedance medium. and anisotropic impedance media , , Variations in the amplitude parameters of the scattering center under two different coating conditions. Figure 6 A schematic diagram of the partial coating of a T72 tank target is provided, with the coated areas highlighted in color. Figure 7 and Figure 8 The results of reconstructing SAR images from scattering center models of targets coated with two different materials are presented, along with the results of MSTAR measured images.

[0076] Table 3

[0077]

[0078] Table 3 shows that the coating operation significantly attenuated the scattering amplitude of the coated scattering source, with the scattering intensity at scattering center 1 decreasing from 8.55 dB to -3.73 dB and even -12.47 dB. This is also evident in the reconstructed SAR images, where the brightness of the target's strong scattering center before coating is significantly reduced, and the weaker scattering sources before coating begin to dominate. The distribution of the target's strong scattering sources changes. The similarity between the reconstructed SAR images of the target under the two local coating conditions and the MSTAR dataset is 77.1% and 77.9%, respectively, both higher than that of the PEC target.

[0079] Subsequent iterative optimization of the dielectric coating parameters and coating range is expected to further improve the similarity between the model-reconstructed target characteristics and the measured data. This completes the entire process of radar target characteristic planning based on the forward scattering center model.

[0080] It should be understood that the above description of the preferred embodiments is quite detailed, but it should not be considered as a limitation on the scope of protection of this invention. Those skilled in the art, under the guidance of this invention, can make substitutions or modifications without departing from the scope of protection of the claims of this invention, and all such substitutions or modifications fall within the scope of protection of this invention. The scope of protection of this invention should be determined by the appended claims.

Claims

1. A radar target characteristic planning method based on a forward scattering center model, characterized in that, Includes the following steps: Step 1: Based on actual design needs, conduct radar target characteristic planning and design for the sample target under ideal conductivity conditions; Step 2: Establish a scattering center model of the target under ideal conductivity to obtain target scattering source information, perform scattering source analysis on sample targets, and construct the correspondence between the strong scattering source of the target and the local structure of the target. The scattering characteristics of the target are mainly determined by the strong scattering source of the target. Therefore, in order to meet the actual design needs, it is usually selected to coat the strong scattering structure of the target with a material medium. The specific medium coating parameters and coating area need to be selected according to the radar target characteristic planning requirements in Step 1 and the absorption characteristics of the medium coating itself. Step 3: The impedance surface is used to simulate the thin-coated PEC target surface. The absorption effect of the target surface on the incident electromagnetic wave is expressed by the impedance parameter. Referring to the forward modeling process of the PEC target scattering center, and using the high-frequency calculation method of impedance target electromagnetic scattering, the scattering center model of the dielectric-coated or locally coated electrically large target is constructed. Step 4: Reconstruct the radar target characteristics using the coated target scattering center model obtained in Step 3 and compare it with the expected characteristics. Examine and analyze the distribution of strong scattering sources, the relative magnitude of scattering center amplitude, and the consistency between the reconstructed RCS curve and SAR image and the expected results. Based on the error analysis results, adjust the material medium parameters and coating area, select a medium coating with stronger or weaker absorption capacity, or expand the material medium coating range. This process can reveal the contribution and variation law of the target scattering center to the overall scattering, the formation process of the target's local structure scattering, and achieve target characteristic signal control. After multiple iterations of optimization, the model reconstructs the target characteristics until they meet the expected characteristics, thus realizing radar target characteristic planning.

2. The radar target characteristic planning method based on the forward scattering center model according to claim 1, characterized in that, The impedance surface is equivalent to a thin dielectric coating on an ideal conductive target surface as an impedance surface with no thickness, and the coating dielectric parameters are characterized by surface impedance dyadic.

3. The radar target characteristic planning method based on the forward scattering center model according to claim 1, characterized in that, The scattering center model is a property scattering center model, and its expression is as follows: In the formula, A i Let L be the amplitude parameter of the i-th scattering center. i Let α be the length parameter of the scattering center. i As a frequency-dependent factor, z i =[x i ,y i ,z i ] is the three-dimensional position vector of the scattering center. The incident wave azimuth angle, L is the azimuth angle of the distributed scattering center. If the scattering center is localized, then L i =0, otherwise γ i =0, where j is the imaginary unit, f is the incident wave frequency, and f c γ is the scattering center frequency, c is the speed of light, and γ is the scattering center frequency. i It has no specific physical meaning.

4. The radar target characteristic planning method based on the forward scattering center model according to claim 3, characterized in that, The specific steps for the forward inference of the model attribute parameters are as follows: The amplitude parameter A is determined using the Geometric Physical Optics (GO-PO) high-frequency algorithm based on impedance boundary condition hybridity. i The field amplitude on the primary coupling ray is directly calculated using the physical optics (PO) algorithm. For the field amplitude on the secondary and higher coupling rays, the hybrid geometric physical optics (GO-PO) method is used to determine the field amplitude.

5. The radar target characteristic planning method based on the forward scattering center model according to claim 3, characterized in that, The length parameter L of the scattering center i The method for obtaining the value is as follows: Find the two equivalent endpoints of the "bright line" in the ray set of distributed scattering centers. Then, by projecting the values ​​of these two endpoints and subtracting them, the length parameter of the scattering center can be obtained. In the formula: x m ,y m and x n ,y n Let θ represent the coordinates of the two endpoints on the x-axis and y-axis, respectively; These are the elevation and azimuth angles of the radar incident wave, respectively.

6. The radar target characteristic planning method based on the forward scattering center model according to claim 3, characterized in that, Frequency-dependent factor α i The method to obtain it is as follows: The frequency dependence factor α is determined by reading the geometric information of the target and judging the scattering mechanism contained in each scattering center. i .

7. The radar target characteristic planning method based on the forward scattering center model according to claim 6, characterized in that, Frequency dependence factor α of dihedral and trihedral scattering structures i The frequency dependence factor α of the cylindrical surface and the top cap scattering structure is set to 1. i The frequency dependence factor α for spheres and straight-edge diffraction scattering structures is set to 1 / 2. i The frequency dependence factor α of the angular diffraction-scattering structure is set to 0. i The value is -1.

8. The radar target characteristic planning method based on the forward scattering center model according to claim 3, characterized in that, The three-dimensional position z of the scattering center i =[x i ,y i ,z i The reflection points of all rays in the corresponding subset are weighted to determine the reflection point. For a single-reflection ray, the geometric center of the illuminated surface is taken as the reflection point, i.e., the scattering center. For multiple-reflection rays, the reflection point is obtained by using the principle of equivalent phase difference calculation based on optical path difference. The weight value is determined by the magnitude of the induced current on the target.

9. The radar target characteristic planning method based on the forward scattering center model according to claim 8, characterized in that, The specific formula for calculating the weight value is as follows: In the formula w n =|J s (Q n )| represents the magnitude of the induced current in the surface element, Q n (x n ,y n (x) is the equivalent reflection point of the nth ray. n ,y n ,z n ) represents the coordinates of the center of the surface element.

10. The radar target characteristic planning method based on the forward scattering center model according to claim 1, characterized in that, The total scattered field of the target is the sum of the contributions from N scattering centers, that is: Forward modeling of scattering centers only requires calculating the set of scattering center parameters of the target in one observation attitude, and then giving... Substituting the range of small angle variations, step size, frequency range, and step size into the above formula, the SAR image of the target can be reconstructed.

Images