A method for estimating radar cross section of dielectric-coated targets

Abstract

The present invention discloses a method for estimating the radar cross section of a dielectric coated target, which relates to the field of radar application and is applicable to dielectric coated targets of electrically large size, and improves the calculation efficiency of the radar cross section while ensuring the calculation accuracy. The present invention is based on the characteristics of the target coating medium, and adopts a stepping method to calculate the reflection coefficient of the target surface; then the induced electromagnetic currents of different facets after the target is segmented are calculated respectively; based on the induced electromagnetic currents of different facets, the scattered electric field of each facet of the target is calculated respectively, and the scattered electric fields of the visible facets are summed to obtain the total scattered electric field of the target, and the radar cross section RCS is calculated accordingly. The present invention can be applied to the electromagnetic characteristic analysis of dielectric coated targets of electrically large size, and improves the calculation accuracy while ensuring the calculation efficiency.

Description

Technical Field

[0001] The invention relates to the field of radar application, in particular to a method for estimating radar cross section (RCS) of a coated medium target. Background Art

[0002] Stealth technology and anti-stealth technology occupy an important position in the field of electromagnetic scattering research. Effective means to reduce the target radar cross section include: 1. Absorbing incident electromagnetic waves by coating absorbing materials, such as ferrite, carbon fiber composite materials, etc.; 2. Optimizing the shape of the target to reduce the direct reflection of electromagnetic waves, such as the diamond design used by stealth aircraft; 3. Using plasma stealth technology to generate a plasma layer around the target to achieve the purpose of absorbing radar waves. Regardless of the method used, it is necessary to calculate and verify the designed radar cross section.

[0003] Regarding the coating medium method, a Chinese patent document with publication number CN116755054A proposes a method for obtaining the broadband RCS of the coating target based on the rational interpolation method, which uses the triangulation method to divide the external medium surface and the internal metal surface of the coating target (that is, divide it into facets), and define the RWG basis function; the frequency band of the broadband uniform plane wave irradiating the coated target is sampled at equal intervals; an EFIE-PMCHW equation group is established on the target surface at each sampling frequency point, and the EFIE-PMCHW equation group is solved using the moment method; the rational function interpolation method is used to obtain the induced electromagnetic current coefficient at each scanning point; and the broadband RCS of the coating target is obtained through the electromagnetic current coefficient at each scanning point.

[0004] For another example, a Chinese patent document with publication number CN108614251A proposes a radar cross-section visualization calculation method for a multi-coated target, which includes: step 1, using 3ds Max software to establish a multi-coated target model; step 2, meshing the multi-coated target model; step 3, exporting the model in 3DS file format; step 4, reading the multi-coated target model; step 5, calculating the radar cross-section of the multi-coated target model and visually displaying it.

[0005] The above existing technologies can only be applied to targets of a certain size, and have certain limitations for electrically large targets such as offshore coated ships. Since it is necessary to calculate the electromagnetic flow coefficient of each frequency point to obtain the target scattered electric field, the required memory space is large and the calculation efficiency is low; and the calculation of the coating medium segmentation is ignored, the calculation accuracy is limited, and it cannot meet the actual simulation requirements. Summary of the invention

[0006] The object of the present invention is to provide a method for estimating the radar cross section of a coated dielectric target in order to address all or part of the above-mentioned problems, which is suitable for analyzing the electromagnetic scattering characteristics of electrically large-sized coated targets, and improves the calculation accuracy of the radar cross section while ensuring the calculation efficiency.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A method for estimating radar cross section of a dielectric coating target, comprising:

[0009] Based on the target coating medium characteristics, the reflection coefficient of the target surface is calculated by using a step method;

[0010] Based on the reflection coefficient, respectively calculating the induced electromagnetic currents of different facets of the target segmentation;

[0011] Based on the induced electromagnetic currents of different surface elements, the scattered electric field of each surface element of the target is calculated respectively, and the scattered electric fields of the visible surface elements are summed to obtain the total scattered electric field of the target;

[0012] The radar cross section RCS is calculated based on the total scattered electric field of the target.

[0013] Furthermore, the reflection coefficient includes a vertical polarization reflection coefficient and a horizontal polarization reflection coefficient.

[0014] Furthermore, the calculation method of the horizontal polarization reflection coefficient is:

[0015]

[0016] Where A(n) = Z(n-1)R y (n)-Z(n)R y (n-1),B(n)=Z(n-1)R y (n)+Z(n)R y (n-1),

[0017]

[0018] is the incident wave number; ε r (n), μ r (n), D(n) and Z(n) are the relative permittivity, relative permeability, thickness and wave impedance of the nth layer of coating medium respectively; θ i represents the incident angle of the incident wave;

[0019] The calculation method of the vertical polarization reflection coefficient is:

[0020]

[0021] n≥2, n represents the layer of the coating medium, coating N L When the medium is n=N L +1, R v (n) and R h (n) represent the total vertical polarization reflection coefficient and horizontal polarization reflection coefficient of the surface of the coating medium ending at the nth layer, respectively.

[0022] Furthermore, the method for determining the visibility of the target segmented facets includes determining whether the facet is blocked by itself and determining whether the facet is blocked by other facets.

[0023] Furthermore, the method for determining whether a face element is blocked by itself includes:

[0024] Determine the incident wave vector The normal vector to the surface element m Is it satisfied? If so, the panel is not occluded by itself.

[0025] Furthermore, the method for determining whether a plane element is blocked by other plane elements includes:

[0026] By performing reverse ray tracing on the face element, it is determined whether the face element is blocked by other face elements.

[0027] Furthermore, the induced electromagnetic current includes an induced current and an induced magnetic current;

[0028] The calculation method of the induced magnetic current is:

[0029]

[0030] In the formula, represents the normal vector of the surface element, represents the incident wave vector, represents the unit vector of the horizontal polarization of the incident wave, represents the vertical polarization unit vector of the incident wave, represents the unit polarization vector of the incident wave, E0 represents the amplitude of the electric field, R v and R h They represent the vertical polarization reflection coefficient and horizontal polarization reflection coefficient of the surface element respectively;

[0031] The calculation method of the induced current is:

[0032]

[0033] Where η represents the wave impedance.

[0034] Furthermore, the scattered electric field of each facet of the target includes a primary scattered field and a secondary scattered field.

[0035] Furthermore, the calculation method of the scattered electric field of the target once scattered is:

[0036]

[0037] in, N is the number of facets of the target segmentation, I vis,m is the visibility factor of the face element m, which takes the value 1 for visible face elements and 0 otherwise;

[0038] In the formula, represents the scattered wave vector, represents the unit polarization vector of the scattered wave, M 0,m and J 0,m They represent the induced magnetic flux and induced current excited by the incident wave on the surface element m, I m is the first phase integral term, and r represents the distance from the observation point to the target.

[0039] Furthermore, the calculation method of the scattered electric field of the target in the secondary scattered field is:

[0040]

[0041] Where M 1,nm and J 1,nm They represent the induced magnetic flux and induced current of surface element n excited by the reflected wave of surface element m, I n is the second phase integral term, I vis,nm is the visibility factor of facet n, which takes the value of 1 if facet m is visible, and 0 otherwise.

[0042] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0043] The present invention proposes a hybrid electromagnetic model of geometric optics-physical optics (GO-PO / MM) based on the step method. The model can quickly obtain the reflection coefficient of the surface of the coated medium under different polarization conditions from the characteristic parameters of the coated medium. Compared with the traditional electromagnetic model, the radar cross section (RCS) of the target surface of the coated medium is affected by the segmentation size and takes a long time to calculate. The method of the present invention has high universality and fewer restrictions. For the radar cross section estimation of the coated medium target, while ensuring high calculation efficiency, it can well simulate the influence of different radar absorbing material parameters (such as dielectric constant, thickness, magnetic permeability, etc.) on the scattering characteristics of targets such as ships. And for the influence of different radar absorbing material parameters, the incident angle of the incident electromagnetic wave, etc. on the RCS of the target surface, the present invention provides a more accurate stealth performance evaluation with higher calculation accuracy. The present invention can be applied to the analysis of the coating electromagnetic characteristics of electrically large-sized targets in marine environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0045] Figure 1 The figure is a flow chart of a method for estimating radar cross section of a dielectric-coated target in one embodiment.

[0046] Figure 2 This is a reflection model diagram of a multi-layer coated medium.

[0047] Figure 3 It is a schematic diagram of surface element occlusion judgment.

[0048] Figure 4 This is a comparison chart of simulation results of different radar cross-section calculation models. DETAILED DESCRIPTION

[0049] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0050] Any feature disclosed in this specification (including any additional claims and abstract), unless otherwise stated, may be replaced by other equivalent or alternative features having similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0051] like Figure 1 As shown, an embodiment of the present application provides a method for estimating radar cross section of a coated medium target, comprising the following process:

[0052] S1. Based on the characteristics of the target coating medium, the reflection coefficient of the target surface is calculated using the step method.

[0053] The coating medium on the target surface can be multi-layered, and the material, thickness, etc. of each layer of the coating medium can be different. For this type of stealth means, the embodiment of the present application analyzes the influence of the coating medium characteristics on the target radar scattering cross section.

[0054] The coating medium characteristics include the relative dielectric constant and relative magnetic permeability of the coating layer determined by the material, as well as the thickness of the coating layer determined by the process, and the wave impedance, etc.

[0055] Usually, the target radar cross section is analyzed from two directions: horizontal polarization and vertical polarization. Correspondingly, the reflection coefficient of the target surface includes the vertical polarization reflection coefficient and the horizontal polarization reflection coefficient, which are expressed as R h R represents the horizontal polarization reflection coefficient of the target surface. v Represents the vertically polarized reflection coefficient of the target surface.

[0056] like Figure 2The figure shows the reflection model of a multi-layer coating medium, which shows the propagation path of the electromagnetic wave after it hits the target surface. The relative dielectric constant of the nth layer of coating medium is defined as ε r (n), relative magnetic permeability is μ r (n), thickness D(n), wave impedance Z(n), for N L The target layer is coated with a dielectric layer, and the reflection coefficient of the target surface is R h (N L +1) and R v (N L +1) can be calculated by the following formula:

[0057]

[0058] Where A(n) = Z(n-1)R y (n)-Z(n)R y (n-1),B(n)=Z(n-1)R y (n)+Z(n)R y (n-1),

[0059] θ i represents the angle of incidence of the incident wave.

[0060] Specifically, for the horizontal polarization reflection coefficient, the calculation method is:

[0061]

[0062] For the vertical polarization reflection coefficient of water, the calculation method is:

[0063]

[0064] In the above embodiment, n represents the layer of the coating medium. L When the medium is coated, n = N L +1, so n ≥ 2. And R h (n) and R v (n) respectively represent the total horizontal polarization reflection coefficient and vertical polarization reflection coefficient of the surface of the n-th coating medium, that is, for N L Layer coating medium, the reflection coefficient of the target surface R h =R h (N L +1), R v =R v (N L +1).

[0065] S2. Based on the reflection coefficient of the target surface, the induced electromagnetic currents of different facets of the target segmentation are calculated respectively.

[0066] When the incident electromagnetic wave (i.e., incident wave) hits the target surface, the electromagnetic energy will scatter in all directions, generating a primary scattering field. When the primary reflected wave of the target hits the target again, a secondary scattering field is generated. The radar cross section can be represented by the incident and scattered electromagnetic fields. The physical optics method is a high-frequency approximation method based on the surface current integral equation. It is widely used to calculate the radar cross section of the target. Its basic steps include: dividing the target model to obtain discrete triangular surface elements; performing occlusion judgment on the obtained discrete triangular surface elements to obtain the triangular surface elements of the required illuminated area, that is, judging which are visible surface elements; performing Gordon integration on the triangular surface elements in the illuminated area (i.e., visible) to obtain the scattered field electric field, thereby obtaining the RCS of the target.

[0067] According to the principle of physical optics, it can be assumed that the target only has induced current in the illuminated area and no induced current in the shadow area. Therefore, before calculating the radar cross section of the target, it is necessary to perform occlusion judgment on the discrete surface elements of the target.

[0068] In some embodiments, the visibility judgment method of the target segmented surface element includes judging whether the surface element is blocked by itself, that is, judging whether the incident wave is incident on the surface element directly; if the surface element is not blocked by itself, it is necessary to judge whether the surface element is blocked by other surface elements.

[0069] Specifically, assuming the incident wave vector is The normal vector of surface element m is Then the surface element m needs to meet two conditions to be visible to the incident wave and the first reflected wave:

[0070] 1) Incident wave vector The normal vector to the surface element m satisfy: If it satisfies this condition, then the surface element m is not occluded by itself.

[0071] 2) The incident wave and the first reflected wave are not blocked by other surface elements during the process of irradiating the surface element m. Figure 3 The figure shows a schematic diagram of facet occlusion judgment. Whether facet m is occluded by other facets can be judged by performing reverse ray tracing on facet m to traverse the facets.

[0072] The purpose of judging the visibility of a facet is to determine the visibility factor of each facet when performing facet integration.

[0073] S3. Based on the induced electromagnetic currents of different surface elements, the scattered electric field of each surface element of the target is calculated respectively, and the scattered electric fields of the visible surface elements are summed to obtain the total scattered electric field of the target.

[0074] The geometric optics-physical optics method is a high-frequency approximation method with high calculation accuracy, which is suitable for electromagnetic calculations of complex targets. The total tangential electromagnetic field can be obtained by summing the horizontally polarized and vertically polarized electromagnetic tangential fields. The induced electromagnetic flow includes the induced current and the induced magnetic flow. Through the tangential electromagnetic field, the induced current and the induced magnetic flow can be obtained accordingly.

[0075] In some embodiments, the calculation method of the induced magnetic current is:

[0076]

[0077] The calculation method of the induced current is:

[0078]

[0079] In the above formula, represents the normal vector of the surface element, represents the incident wave vector, represents the unit vector of the horizontal polarization of the incident wave, represents the vertical polarization unit vector of the incident wave, represents the unit polarization vector of the incident wave, E0 represents the amplitude of the electric field, R v and R h They represent the vertical polarization reflection coefficient and horizontal polarization reflection coefficient of the surface element respectively; η represents the wave impedance, and for an ideal conductor, its value is 1.

[0080] The total scattered electric field of the target includes the primary scattered field and the secondary scattered field, which mainly includes the primary scattered field excited by the incident wave and the secondary scattered field excited by the electromagnetic wave reflected by the target itself. The total scattered electric field of the target is integrated by the scattered electric field of the subdivided surface element. Therefore, the scattered electric field of each surface element of the target includes the primary scattered field and the secondary scattered field.

[0081] For the scattered electric field of the target once scattered, according to the Stratton-Chu integral equation, the far-zone scattered electric field of the surface element m can be expressed as:

[0082]

[0083] In the formula, represents the scattered wave vector, represents the unit polarization vector of the scattered wave, M 0,m and J 0,m They represent the induced magnetic flux and induced current excited by the incident wave on the surface element m, I m is the first phase integral term, r represents the distance from the observation point to the target, which is described by the Gordon integral method. r represents the distance from the observation point to the target.

[0084] Based on this, the calculation method of the scattered electric field of the target once scattered is:

[0085]

[0086] Where N is the number of facets of the target segmentation, I vis,m is the visibility factor of face m, which is 1 for visible face m and 0 otherwise.

[0087] For the surface element m that generates the primary scattering field, after reflecting the electromagnetic wave, it irradiates other surface elements to cause secondary scattering. In this embodiment, the surface element n is used to represent the surface element that causes secondary scattering.

[0088] The secondary scattered field generated by the surface element n can be induced by the induced current J on it by the primary scattered field of any surface element m. 1,nm and the induced magnetic current M 1,nm The calculation method of the scattered electric field of the target secondary scattering is:

[0089]

[0090] Where M 1,nm and J 1,nm They represent the induced magnetic flux and induced current of surface element n induced by the primary scattering field of surface element m, respectively. n is the second phase integral term, I vis,nm is the visibility factor of facet n, which takes the value of 1 if facet m is visible, and 0 otherwise.

[0091] In the embodiment of the present application, the total scattered electric field of the target is obtained by summing the scattered electric fields in the primary scattered field and the secondary scattered field.

[0092] Due to the coating medium, the total scattered electric field of the target is weighted by the total surface reflection coefficient R based on the sum of the scattered electric fields of the primary scattering and the secondary scattering.

[0093]

[0094] in,

[0095] In the formula, z c (k) is the characteristic impedance of the k-th layer of coating medium, γ(k) is the transmission constant of the k-th layer of coating medium, z0 is the wave impedance of free space, k represents the level of coating medium, c is the speed of light, and ω is the angular frequency.

[0096] Finally, the total scattered electric field of the target with the coating medium is:

[0097] S4. Calculate the radar cross section (RCS) based on the total scattered electric field of the target.

[0098] The target surface radar cross section is calculated based on the target total scattered electric field. This can be obtained according to the prior art and will not be described in detail in the embodiments of the present application.

[0099] According to the embodiments of the present application, for the conductive target coated with a medium, the reflection coefficient of the surface under different polarization conditions (vertical polarization or horizontal polarization) is calculated using the step method, which is independent of the size of the panel subdivision and is not limited by the panel subdivision size or the target size. It has high calculation efficiency and good universality. In order to verify the effectiveness of the geometric optics-physical optics (GO-PO / MM) hybrid electromagnetic model based on the step method proposed in the embodiments of the present application, a performance comparison is also carried out with a variety of radar scattering cross section calculation models in the embodiments of the present application. Figure 4 Shown are the RCS results of pure conductor dihedral corner reflectors calculated using the multi-layer fast multipole algorithm (MLFMM), GO-PO and PO algorithms, as well as the RCS results of coated dihedral corner reflectors calculated using MLFMM and GO-PO / MM.

[0100] Depend on Figure 4 It can be seen that for conductor targets, the calculation results of the GO-PO algorithm and MLFMM have small errors, which shows the correctness of multiple scattering. For coated targets, GO-PO / MM takes into account the influence of absorbing materials on the scattering field, effectively reduces the RCS of the target, and is basically consistent with the results obtained after MLFMM coating, which verifies the effectiveness of GO-PO / MM. The method of this application better reflects the influence of different radar absorbing materials on the RCS of targets such as ships while ensuring the calculation efficiency, and is suitable for the analysis of the coating electromagnetic characteristics of electrically large-sized targets in the marine environment and the study of stealth performance.

[0101] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A method for estimating radar cross section of a coated medium target, characterized in that: include: Based on the target coating medium characteristics, the reflection coefficient of the target surface is calculated by using a step method; Based on the reflection coefficient, respectively calculating the induced electromagnetic currents of different facets of the target segmentation; Based on the induced electromagnetic currents of different surface elements, the scattered electric field of each surface element of the target is calculated respectively, and the scattered electric fields of the visible surface elements are summed to obtain the total scattered electric field of the target; The radar cross section RCS is calculated based on the total scattered electric field of the target.

2. The method for estimating radar cross section of a coated medium target according to claim 1, characterized in that: The reflection coefficient includes a vertical polarization reflection coefficient and a horizontal polarization reflection coefficient.

3. The method for estimating radar cross section of a coating medium target according to claim 2, characterized in that: The calculation method of the horizontal polarization reflection coefficient is: where A(n) = Z(n - 1)R y (n) - Z(n)R y (n - 1), B(n) = Z(n - 1)R y (n) + Z(n)R y (n - 1), is the incident wave number; ε r (n), μ r (n), D(n) and Z(n) are the relative permittivity, relative permeability, thickness and wave impedance of the nth layer of coating medium respectively; θ i represents the incident angle of the incident wave; The calculation method of the vertical polarization reflection coefficient is: n≥2, n represents the layer of the coating medium, coating N L When the medium is n=N L +1, R v (n) and R h (n) represent the total vertical polarization reflection coefficient and horizontal polarization reflection coefficient of the surface of the coating medium ending at the nth layer, respectively.

4. The method for estimating radar cross section of a coating medium target according to claim 1, characterized in that: The method for determining the visibility of the target segmented facets includes determining whether the facet is blocked by itself and determining whether the facet is blocked by other facets.

5. The method for estimating radar cross section of a coating medium target according to claim 4, characterized in that: Methods for determining whether a face element is occluded by itself include: Determine the incident wave vector The normal vector to the surface element m Is it satisfied? If so, the panel is not occluded by itself.

6. The method for estimating radar cross section of a coating medium target according to claim 4, characterized in that: Methods for determining whether a surface element is blocked by other surfaces include: By performing reverse ray tracing on the face element, it is determined whether the face element is blocked by other face elements.

7. The method for estimating radar cross section of a coating medium target according to claim 1, characterized in that: The induced electromagnetic current includes an induced current and an induced magnetic current; The calculation method of the induced magnetic current is: In the formula, represents the normal vector of the surface element, represents the incident wave vector, represents the unit vector of the horizontal polarization of the incident wave, represents the vertical polarization unit vector of the incident wave, represents the unit polarization vector of the incident wave, E0 represents the amplitude of the electric field, R v and R h They represent the vertical polarization reflection coefficient and horizontal polarization reflection coefficient of the surface element respectively; The calculation method of the induced current is: Where η represents the wave impedance.

8. The method for estimating radar cross section of a coating medium target according to claim 7, characterized in that: The scattered electric field of each surface element of the target includes the primary scattered field and the secondary scattered field.

9. The method for estimating radar cross section of a coating medium target according to claim 8, characterized in that: The calculation method of the scattered electric field of the target once scattered is: in, N is the number of facets of the target segmentation, I vis,m is the visibility factor of the face element m, which takes the value 1 for visible face elements and 0 otherwise; In the formula, represents the scattered wave vector, represents the unit polarization vector of the scattered wave, M 0,m and J 0,m They represent the induced magnetic flux and induced current excited by the incident wave on the surface element m, I m is the first phase integral term, and r represents the distance from the observation point to the target.

10. The method for estimating radar cross section of a coating medium target according to claim 9, characterized in that: The calculation method of the scattered electric field of the target secondary scattered field is: Where M 1,nm and J 1,nm They represent the induced magnetic flux and induced current of surface element n excited by the reflected wave of surface element m, I n is the second phase integral term, I vis,nm is the visibility factor of facet n, which takes the value of 1 if facet m is visible, and 0 otherwise.

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