High and Low Frequency Hybrid Electromagnetic Scattering Analysis Method Based on VSBR-MoM

Abstract

The present invention discloses a method for analyzing high-low frequency hybrid electromagnetic scattering based on VSBR-MoM. The specific steps are as follows: First, in the software ANSYS, the metal-dielectric hybrid model is meshed. For the dielectric part of the model, volume meshing is used, and for the surface of the metal part of the model, triangular facets are used for meshing; the electrically large-sized dielectric is divided into the high-frequency VSBR domain, and the electrically small-sized metal is divided into the low-frequency MoM region; by accumulating the scattered fields of the ray tubes in the high-frequency region and the surface currents in the low-frequency region, the contributions of the two high-low frequency regions are accumulated to obtain the total far field of the overall composite target, and the radar cross section is calculated. The present invention combines the advantages of the volume meshed shooting and bouncing ray method and the method of moments, and solves the problems that the VSBR method cannot accurately calculate electrically small-sized targets and the MoM method consumes a large amount of computing resources.

Description

Technical Field

[0001] The invention belongs to the technical field of numerical calculation of target electromagnetic scattering characteristics, and in particular relates to a high- and low-frequency mixed electromagnetic scattering analysis method based on VSBR-MoM. Background Art

[0002] In today's military or civilian engineering practice, studying the electromagnetic scattering characteristics of complex targets is of great significance to radar detection and identification.

[0003] When facing composite targets such as dielectric platforms and weapons on them or radomes and antennas, where there are electrically large dielectrics and electrically small metals, using the commonly used moment method to accurately calculate the whole often requires a huge amount of memory resources and time resources. If the volume segmentation bouncing ray method is used for calculation, this high-frequency method naturally cannot meet the calculation accuracy requirements when facing electrically small targets, and there are theoretical errors. Summary of the invention

[0004] The purpose of the present invention is to provide a high- and low-frequency mixed electromagnetic scattering analysis method based on VSBR-MoM, which combines the advantages of high efficiency of the VSBR method and high precision of the MoM method, and solves the problem of low efficiency and precision of electromagnetic scattering simulation of mixed targets of electrically large-sized dielectrics and electrically small-sized metals.

[0005] The technical solution to achieve the purpose of the present invention is as follows: In the first aspect, the present invention provides a high-low frequency mixed electromagnetic scattering analysis method based on VSBR-MoM, the steps are as follows:

[0006] Step 1, dividing the composite model of the electrically large-sized medium and the electrically small-sized metal into high-frequency and low-frequency regions, dividing the electrically large-sized medium into a high-frequency region, and dividing the electrically small-sized metal into a low-frequency region;

[0007] Step 2: The low-frequency region model is divided and fitted using a triangular mesh, and the side length of the triangular mesh is set to be between one-twelfth and one-eighth of a wavelength; for the target in the low-frequency region, the moment method is used for calculation;

[0008] Step 3: The high-frequency region model is divided and fitted using a tetrahedral unit grid, and the side length of the divided tetrahedral unit is set to be between one-sixth of a wavelength and one-quarter of a wavelength; for targets in the high-frequency region, the volume division bouncing ray method is used for calculation;

[0009] Step 4, under the irradiation of plane waves, the surface electromagnetic current of the composite target is calculated by considering the mutual coupling between the high-frequency and low-frequency regions, where the surface electromagnetic current of the medium in the high-frequency VSBR region is simulated by the output ray tube, and the surface current of the metal in the low-frequency MoM region is represented by the RWG basis function;

[0010] Step 5: Calculate the far-field scattering field of the composite model based on the current distributions of the ray tubes in the high-frequency region and the low-frequency region, and finally obtain the radar cross-section of the composite model.

[0011] In a second aspect, the present invention provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, the steps of the method described in the first aspect are implemented.

[0012] In a third aspect, the present invention provides a computer-readable storage medium, on which a computer program is stored. When the program is executed by a processor, the steps of the method described in the first aspect are implemented.

[0013] Compared with the prior art, the present invention has the following remarkable advantages: (1) For electrically large-sized dielectrics, the present invention adopts the volume-discretized shooting and bouncing ray method (VSBR). Compared with the accurate algorithm, the method of moments (MoM), the calculation efficiency is greatly improved, and the memory requirement is reduced. (2) At the same time, considering the problem that the high-frequency method is inaccurate for calculating electrically small-sized structures, the method of moments is used for electrically small-sized metals, taking into account the accuracy of the calculation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a diagram of the composite model.

[0015] Figure 2 It is a comparison diagram of the RCS calculation results between the present method and the method of moments.

[0016] Figure 3 It is a schematic flow chart of the coupling between the high-frequency and low-frequency regions of the present method. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] The present invention proposes a high-low frequency hybrid electromagnetic scattering analysis method based on the volume-discretized shooting and bouncing ray method (VSBR) and the method of moments (MoM). The present invention takes into account the advantages of both methods and solves the problems that the VSBR method cannot accurately calculate electrically small-sized targets and the MoM method consumes a large amount of computing resources. The coupling between the high-frequency and low-frequency regions is solved by an iterative method.

[0018] The following further describes the present invention in detail with reference to the drawings and specific embodiments. The specific steps are as follows:

[0019] Step 1: Divide the high-frequency and low-frequency regions of the mixed model of the dielectric cube and the metal sphere shown in Figure 1 Divide the dielectric cube into the high-frequency region and the metal sphere into the low-frequency region.

[0020] Step 2: The surface of the metal sphere is meshed and fitted using triangular surface elements, and the side length of the meshed grid is one-tenth of the wavelength. The moment method is used to calculate the metal sphere, and the surface current distribution is obtained according to the boundary conditions and the electric field integral equation.

[0021] Step 3: The dielectric cube part is imported into the software ANSYS and meshed and fitted using tetrahedral element meshes. The two different dielectric bodies are numbered, and the side length of the meshed grid is one-fifth of the wavelength. The volume dissection and bouncing ray method is used to calculate the dielectric cube, and then the surface elements of the target surface are regarded as a series of ray tubes to simulate the propagation process of electromagnetic waves in the dielectric body. The ray tubes propagate along a straight line in a homogeneous dielectric, and reflection and transmission occur at the interfaces between different dielectrics and between the dielectric and air until all the ray tubes exit the dielectric body.

[0022] Step 4: Under the illumination of a plane wave, considering the mutual coupling between the high-frequency and low-frequency regions, the surface electromagnetic current of the composite target is calculated. Among them, the surface electromagnetic current of the dielectric in the high-frequency VSBR region is simulated by the outgoing ray tubes, and the metal surface current in the low-frequency MoM region is represented by the RWG basis function.

[0023] For the coupling process between the high-frequency region and the low-frequency region, it is implemented in combination with Figure 3 the following process.

[0024] 1) Irradiate the composite model with a plane wave. First, assume that the induced current on the entire surface of the composite target is zero. The cube in the high-frequency region is only excited by the plane wave. The triangles on the dielectric surface in the high-frequency region are regarded as a series of ray tubes, and the rays enter the dielectric body when they shine on the dielectric surface and perform path and field strength tracking until they leave the dielectric body.

[0025] 2) Use the outgoing ray tubes from the high-frequency VSBR region as the excitation source to generate a scattered electric field in the low-frequency MoM region and excite the metal in the low-frequency region together with the plane wave. According to the boundary conditions, establish the electric field integral equation on the target surface to obtain the surface induced current of the metal target in the low-frequency region

[0026]

[0027] In Equation (1), ω is the angular frequency of the incident wave, μ is the magnetic permeability of free space, is the Laplace operator, represents the field point, represents the source point, and are the surface current and magnetic current of the ray tubes exiting the dielectric body. is the dyadic Green's function. After derivation, it can be expressed by the following formula:

[0028]

[0029] In Equation (2), where k is the wave number, is the scalar Green's function, x', y', z' are the coordinates of the source point in the rectangular coordinate system, and x, y, z are the coordinates of the field point in the rectangular coordinate system, is the absolute spatial distance between the source point and the field point.

[0030] 3) Use the induced current on the surface of the metal target in the low-frequency region to excite the scattered electric field and the scattered magnetic field to jointly excite the medium in the high-frequency region with the plane wave, reform the ray tube to perform path tracking and field strength tracking until the ray tube leaves the target.

[0031]

[0032] Among them, the expression of refers to Equation (2), and after derivation, it can be expressed in the following form:

[0033]

[0034] 4) Repeat the iterative process of 2) and 3) until where i is the number of iterations and ε is the error, representing that the entire target reaches stability after being irradiated by the plane wave, and the iterative process ends. In this embodiment, ε is taken as 0.001.

[0035] Step 5, calculate the far-field scattered field of the composite model according to the ray tube in the high-frequency region and the current distribution in the low-frequency region, and finally obtain the radar cross-section of the composite model.

[0036] The far field is obtained by accumulating the contributions of the fields generated by the equivalent electromagnetic currents in the high- and low-frequency regions:

[0037]

[0038] In the formula, and are the far-field scattered fields generated by the equivalent current and the equivalent magnetic current respectively, is the equivalent current density, is the equivalent magnetic current density, k is the wave number, η is the wave impedance in free space, is the far-field direction, The center point of the surface element where the ray tube exits the dielectric body, and r is the distance from the surface element to the far field. Among them, the equivalent surface electromagnetic current in the high-frequency VSBR dielectric region is obtained by ray tracing, accumulating the ray tubes of the emitted objects to obtain the total current and total magnetic current, and then calculating; the equivalent current in the low-frequency MoM metal region is obtained by solving the matrix equation to obtain the current coefficients of the basis functions.

[0039] In the high-frequency VSBR dielectric region, in the high-frequency VSBR dielectric region, the equivalent electromagnetic current density on the surface of the dielectric body is calculated by using field strength tracing to obtain the electric field and magnetic field:

[0040]

[0041] Among them, is the normal vector of the triangular surface element on the surface of the VSBR region, and are the total current and total magnetic current of the ray tubes of the dielectric body emitted from the object.

[0042] In the low-frequency MoM metal region, the equivalent current is represented by the obtained RWG basis function:

[0043]

[0044] In the formula, M is the total number of expansion terms, m represents the number of a certain term, is the RWG basis function, a m is the obtained expansion coefficient.

[0045] Finally, the radar cross section will be calculated through the formula according to the far-field scattering field.

[0046] Figure 2 This is the comparison diagram of the RCS calculation results between this method and the method of moments.

[0047] Embodiment

[0048] In this embodiment, the electromagnetic scattering calculation of a composite model of electrically large-sized dielectric and electrically small-sized metal is carried out. The dielectric cube is composed of 8 small cubes, each cube has a side length of 0.5 m and a height of 0.25 m, and the radius of the sphere is 0.25 m. Among them, the dielectric cube is the VSBR region, and the metal sphere is the MoM region. The dielectric constants of the two cubes are ε r1 = 2 - j1.0, ε r2 = 4.0 - j0.1, the magnetic permeability μ r = 1.0. The incident direction of the plane wave is θ = 45°, and the far-field observation point is -90° ≤ θ ≤ 90°, and the angular interval is 1°. The calculation frequency is 1 GHz, and the polarization mode is VV polarization.

[0049] Table 1 Comparison of Memory and Computational Time between the Present Method and the Method of Moments

[0050]

[0051] It can be seen from Table 1 that the present method has advantages over the method of moments in terms of both memory and computational time.

Claims

1. A high-low frequency hybrid electromagnetic scattering analysis method based on VSBR-MoM, characterized in that Here are the steps: Step 1, dividing the composite model of the electrically large-sized medium and the electrically small-sized metal into high-frequency and low-frequency regions, dividing the electrically large-sized medium into a high-frequency region, and dividing the electrically small-sized metal into a low-frequency region; Step 2: The low-frequency region model is divided and fitted using a triangular mesh, and the side length of the triangular mesh is set to be between one-twelfth and one-eighth of a wavelength; for the target in the low-frequency region, the moment method is used for calculation; Step 3: The high-frequency region model is divided and fitted using a tetrahedral unit grid, and the side length of the divided tetrahedral unit is set to be between one-sixth of a wavelength and one-quarter of a wavelength; for targets in the high-frequency region, the volume division bouncing ray method is used for calculation; Step 4, under the irradiation of plane waves, the surface electromagnetic current of the composite target is calculated by considering the mutual coupling between the high and low frequency regions, wherein the surface electromagnetic current of the medium in the high frequency VSBR region is simulated by the output ray tube, and the surface current of the metal in the low frequency MoM region is represented by the RWG basis function; the mutual coupling between the high and low frequency regions is considered by iteratively updating the current distribution by taking the two regions as excitation sources, and the specific method is as follows: 1) Using plane waves to illuminate the composite model, first assume that the induced current on the target surface is zero, and the high-frequency region is only excited by the plane wave. In the high-frequency region, the triangle on the surface of the medium is regarded as a series of ray tubes. The rays shine on the medium surface and enter the medium body to track the path and field intensity until they leave the medium body; 2) Use the radiation tube emitted in the high-frequency VSBR region as the excitation source to generate a scattered electric field in the low-frequency MoM region Together with the plane wave, excite the metal in the low-frequency region, establish the electric field integral equation of the target surface according to the boundary conditions, and obtain the surface induced current of the metal target in the low-frequency region 3) Using the induced current on the surface of a metallic target in the low-frequency region to excite the scattered electric field scattered magnetic field and the plane wave to excite the dielectric in the high-frequency region, reforming the ray tube for path tracing and field strength tracing until the ray tube leaves the target; 4) Repeat the iterative process in 2) and 3) until when it indicates that the entire target reaches stability after being irradiated by the plane wave, and the iterative process ends; where i is the number of iterations of the coupling process, and ε is the allowed error; Step 5, according to the current distribution of the high-frequency region ray tube and the low-frequency region, the far-field scattering field of the composite model is calculated, and finally the radar scattering cross section of the composite model is obtained.

2. The high-low frequency hybrid electromagnetic scattering analysis method based on VSBR-MoM according to claim 1, wherein The volume decomposition bouncing ray method described in step 3 performs ray tracing inside the target; the target is fitted with tetrahedral units whose interior is a uniform medium, and different tetrahedrons have different electromagnetic properties according to the specific medium distribution of the target; then the surface elements of the target are regarded as ray tubes to simulate the propagation process of electromagnetic waves in the middle of the dielectric body; the ray tubes propagate along a straight line in the uniform medium, and reflection and transmission occur at different dielectric interfaces until all ray tubes are emitted from the dielectric body.

3. The high-low frequency hybrid electromagnetic scattering analysis method based on VSBR-MoM according to claim 1, characterized in that The radiation tube emitted from the high-frequency VSBR region is used as an excitation source to generate a scattered electric field in the low-frequency MoM region Together with the plane wave, the metal in the low-frequency region is excited. According to the boundary conditions, an electric field integral equation of the target surface is established to obtain the surface induced current of the metal target in the low-frequency region where ω is the angular frequency of the incident wave, μ is the magnetic permeability of free space, is the Laplacian operator, represents the field point, represents the source point, and are the surface current and magnetic current of the ray tube exiting the dielectric body, is the dyadic Green's function.

4. The high-low frequency hybrid electromagnetic scattering analysis method based on VSBR-MoM according to claim 3, characterized in that It is represented by the following formula: In the formula, k is the wave number, is the scalar Green's function, x', y', z' are the coordinates of the source point in the rectangular coordinate system, and x, y, z are the coordinates of the field point in the rectangular coordinate system. is the absolute distance in space between the source point and the field point.

5. The high-low frequency hybrid electromagnetic scattering analysis method based on VSBR-MoM according to claim 1, wherein The induced surface current on the metal target in the low-frequency region excites the scattered electric field scattered magnetic field and the plane wave are used to excite the medium in the high-frequency region, and a new ray tube is reformed for path tracing and field strength tracing until the ray tube leaves the target:

6. The method for analyzing high-low frequency hybrid electromagnetic scattering based on VSBR-MoM according to claim 5, characterized in that Expressed in the following form:

7. The high-low frequency hybrid electromagnetic scattering analysis method based on VSBR-MoM according to claim 1, characterized in that To calculate the far-field scattering of the composite model described in step 5, it is necessary to accumulate the contributions of the two regions to the far field. The specific method is as follows: The far field is obtained by summing the contributions of the fields generated by the equivalent electromagnetic currents in the high and low frequency regions: In the formula, and are the far-field scattering fields generated by the equivalent current and equivalent magnetic current respectively, is the equivalent current density, is the equivalent magnetic current density, k is the wave number, η is the wave impedance in free space, is the far-field direction, is the center point of the surface element where the ray tube exits the dielectric body, r is the distance from the surface element to the far field; among them, the equivalent surface electromagnetic current in the high-frequency VSBR dielectric region is obtained by ray tracing and accumulating the ray tubes exiting the object to obtain the total current and total magnetic current, and then calculating; the equivalent current in the low-frequency MoM metal region is obtained by solving the matrix equation to obtain the current coefficients of the basis functions.

8. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the program, the steps of the method according to any one of claims 1 to 7 are implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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