Vortex electromagnetic wave target scattering modeling method based on physical optical method

Abstract

The invention discloses a vortex electromagnetic wave target scattering modeling method based on a physical optical method. The method comprises the following specific steps: determining whether an array element type is an ideal point source or an ideal electric dipole; when the array element type is an ideal electric dipole, determining a modal number range; otherwise, ending the operation; selecting an array element in the uniform circular array, and determining parameters of the array element; selecting a target, and calculating a scattering result generated by the target in the space; traversing all array elements in the uniform circular array to obtain a scattering result of the uniform circular array under the current modal number; and traversing the modal number to obtain a scattering result database of the uniform circular array. According to the method, model construction is simplified, model construction efficiency is improved, and the method can adapt to simulation application scenes changing in real time.

Description

Technical Field

[0001] The invention relates to the technical field of radar target scattering characteristics, and in particular to a vortex electromagnetic wave target scattering modeling method based on a physical optics method. Background Art

[0002] Vortex electromagnetic waves are a special form of electromagnetic waves whose modes are characterized by orbital angular momentum (OAM). As OAM changes, vortex waves theoretically have infinite states in the modal dimension.

[0003] As a method for calculating high-frequency electromagnetic scattering, the physical optics method can efficiently and accurately calculate the electromagnetic scattering characteristics of complex targets by improving and combining graphic computational electromagnetics, especially when considering edge diffraction. This method corrects the surface normal vector and then the surface current, thereby considering the diffraction at the edge and improving the efficiency of the algorithm.

[0004] Most of the current target detection and imaging systems use plane electromagnetic waves as radiation sources to illuminate the target, and obtain various types of target information by acquiring scattered echoes, so as to extract target feature information and present it in multi-dimensional visualization using different detection imaging methods. However, these imaging detection systems still have several problems that need to be solved. In terms of the construction of geometric scene models, most imaging methods need to establish a complex echo acquisition system when acquiring target information feature data. Therefore, it is necessary to provide a modeling method that is simpler, more efficient, easier to implement, and more adaptable to real-time changing simulation application scenarios. Summary of the invention

[0005] The purpose of the present invention is to provide a vortex electromagnetic wave target scattering modeling method based on physical optics method, establish a database that can reflect the mapping relationship between the modal number and the scattering result, simplify the construction of the model, and improve the adaptability of the model.

[0006] In order to achieve the above object, the present invention provides a vortex electromagnetic wave target scattering modeling method based on physical optics method, and the specific steps include:

[0007] Step 1, determine whether the array element type is an ideal point source or an ideal electric dipole;

[0008] Step 2: When the array element type is an ideal electric dipole, determine the range of the mode number; otherwise, terminate the operation;

[0009] Step 3, selecting an array element in the uniform circular array and determining the parameters of the array element;

[0010] Step 4, select a target and calculate the scattering result generated by the target in space;

[0011] Step 5, traverse all array elements in the uniform circular array to obtain the scattering result of the uniform circular array under the current mode number;

[0012] Step 6, traverse the mode number to obtain the scattering result database of the uniform circular array.

[0013] Optionally, the method for determining the maximum modal number range includes:

[0014]

[0015] In the formula, |l max | is the maximum mode number, and N is the number of array elements of the uniform circular array.

[0016] Optionally, the modal number range can be set as needed, and the set modal number range is a subset of the maximum modal number range.

[0017] Optionally, the parameters of the array elements include: geometric parameters and electromagnetic parameters; the geometric parameters include: array configuration, number of array elements, and spatial position of array elements; the electromagnetic parameters include: excitation phase, excitation amplitude, and directionality of each array element.

[0018] Optionally, step 4 further includes: importing a geometric model of the target, wherein the geometric model includes: facet index, facet vertex coordinates, and vertex index.

[0019] Optionally, the geometric model of the target is a PEC sphere, and the face element index, face element vertex coordinates, and vertex index are the index information of each triangular face element after the PEC sphere is divided into triangular face elements, as well as the position information in space after scene modeling; wherein, the position information includes the vertices of the triangular face elements.

[0020] Optionally, step 4 further includes:

[0021] The physical optics scattering result of an ideal electric dipole at a point in space is determined as follows:

[0022]

[0023] In the formula, E s (r) is the scattered field value at a certain point in the coordinate origin space, r is the spatial position of the ideal electric dipole, is the unit vector of the incident direction, is the unit vector of the scattering direction, is the unit normal vector of the outer surface of the scatterer target, η is the wave impedance of free space, E0 is the electric field intensity at the triangular surface element, H0 is the magnetic field intensity at the triangular surface element, k is the wave number, j represents the imaginary unit, and r′ is any position in space;

[0024] in, The integral part of the triangular surface element can be transformed by summing the integral part of the triangular surface element using the Gordon integral formula;

[0025]

[0026] Where w is the normal vector of the triangle, r′0 is the center point of the triangle, T n This is the summation calculation part when converting the integral into a summation formula of Gordon integral formula.

[0027] Optionally, the uniform circular array is re-divided, the number of array elements is reset, the modal number range is changed, and a target scattering result database within the modal number range is obtained.

[0028] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0029] (1) The present invention obtains a scattering result database of the uniform circular array by traversing all array elements in the uniform circular array and traversing all modal numbers, and establishes a mapping relationship between the modal number and the scattering result, so that the model can quickly change its scattering result when the modal number changes, and can adapt to the simulation application scenarios that change in real time, thereby improving the adaptability of the model.

[0030] (2) The present invention uses the PEC sphere as the target to perform triangular facet segmentation, and uses the facet file as the parameter for calculating the scattering result, which is convenient for parameter acquisition, and uses the Gordon integral formula to convert the scattering result into a simple summation formula, which is convenient for system operation calculation, simplifies the model construction, and improves the efficiency of model construction.

[0031] (3) The present invention uses the principle of vortex electromagnetic waves to obtain the relationship between the number of array elements and the range of mode numbers, ensuring that all possible scattering results can be covered in the process of traversing the mode numbers. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention is a flow chart of the method for modeling vortex electromagnetic wave target scattering based on physical optics method.

[0033] Figure 2 This is the distribution result of the scattered field amplitude when the mode number is 1 in Example 1.

[0034] Figure 3 This is the distribution result of the scattered field amplitude when the mode number is 3 in Example 1.

[0035] Figure 4 This is the distribution result of the scattered field phase when the mode number is 1 in Example 1.

[0036] Figure 5 This is the distribution result of the scattered field phase when the mode number is 3 in Example 1. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] In the description of the present invention, it should be noted that the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0039] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0040] like Figure 1 As shown, the specific steps of the present invention using a simulation method to implement the vortex electromagnetic wave target scattering modeling method based on the physical optics method include:

[0041] Step 1: According to the basic principle of uniform circular array generating vortex electromagnetic waves, determine whether the array element type is an ideal point source or an ideal electric dipole.

[0042] For an N-element uniform circular array in a two-dimensional plane, the array radius is a, all array elements in the array are arranged at equal intervals and have the same operating frequency, and the azimuth angles of each array element are Where n is the arrangement sequence number of the array element, and the sequence number of the base array element in the uniform circular array is marked as n=0, and N is the number of the array elements.

[0043] When a vortex electromagnetic wave with mode number l is generated, it is necessary to apply a phase shift of increasing magnitude to each level of the array element. in, is the excitation phase, that is, the phase difference between adjacent array elements.

[0044] Two types of radiation fields in the physical optics method can be selected as array elements in the uniform circular array, including:

[0045] When an ideal electric dipole is used as the array element of a uniform circular array, it can be known from the radiation principle of an ideal electric dipole that the i The radiated electric field E generated by an electric dipole with a dipole moment α at any position r′ in space i for:

[0046]

[0047] Where η is the wave impedance, which is generally 120π in free space; G(r i , r′) is the Green function; k is the wave number; ρ is r′-r i The module length, Then it is r′-r i is the unit vector of ; j represents the imaginary unit.

[0048] When an ideal point source is used as the array element of a uniform circular array, then the point source at the spatial position r i The radiated electric field E of an ideal point source at any position r′ in space i for:

[0049]

[0050] In the formula, represents the polarization unit vector.

[0051] During the simulation process, the setting parameters for establishing the uniform circular array model are substituted into Formula 1 or Formula 2. When the model setting parameters satisfy Formula 1, the array element type is determined to be an ideal electric dipole; when the model setting parameters satisfy Formula 2, the array element type is determined to be an ideal point source.

[0052] Step 2: When the array element type is an ideal electric dipole, calculate the range of the mode number; when the array element type is a point source, end the calculation.

[0053] Further deducing Equation 1, we can obtain the vector potential A(r) of the ideal electric dipole uniform circular array at any point in space, as shown in Equation 3.

[0054]

[0055] Where ω is the angular frequency of the excitation signal of the ideal electric dipole, μ0 is the magnetic permeability in vacuum, J is the electric dipole current density, N is the number of array elements, and J is l (kasinθ) is the Bessel function, θ is the pitch angle position information of a point in space in the spherical coordinate system, is the array element azimuth.

[0056] in, is the spherical phase factor, which mainly affects the spherical phase of the vortex electromagnetic wave in the radiation field. As the propagation distance of the radiation field increases, the energy of its beam gradually decreases; The rotation phase factor mainly affects the phase of the vortex electromagnetic wave in the azimuth, making the phase of the vortex electromagnetic wave change periodically at 2π in the azimuth. The spherical phase factor and the rotation phase factor interact with each other, making the phase of the vortex electromagnetic wave distributed in a spiral shape in space.

[0057] According to the principle of vortex electromagnetic waves, to generate a vortex electromagnetic wave with a mode number of l, it is necessary to apply The excitation phase of the uniform circular array is increased in an arithmetic progression. Since the number of array elements in the uniform circular array is limited and the phase change of the rotation phase factor is periodic, the relationship between the number of array elements and the range of the mode number is shown in Equation 4.

[0058]

[0059] In the formula, |l max | is the maximum number of modes.

[0060] In practical applications, the modal number range can be set as needed, but the set modal number range still needs to satisfy Formula 4, that is, the set modal number range is a subset of the maximum modal number range obtained by Formula 4.

[0061] Step 3: Select an array element in the uniform circular array and determine the parameters of the array element.

[0062] According to the radius and number of array elements of a two-dimensional uniform circular array, a uniform circular array is divided into equal parts and the position of each array element is calculated using the physical optics method in the simulation to obtain the geometric parameters of the uniform circular array; according to the parameter setting of the radiation source (i.e., the ideal electric dipole) during the simulation, the electromagnetic parameters of the ideal electric dipole array element are obtained; and combined with the actual application scenarios of the uniform circular array, the physical optics geometric coordinate system is introduced to determine the coordinates of the center position of the uniform circular array in the coordinate system and the direction of the array element's array normal.

[0063] The geometric parameters include: array configuration, number of array elements, and spatial position of array elements; the electromagnetic parameters include: excitation phase, excitation amplitude, and the direction of each array element.

[0064] Step 4: Select a target and calculate the scattering result generated by the target in space.

[0065] Import the geometric model of the target (i.e., a certain array element), the geometric model includes: facet index, facet vertex coordinates, and vertex index. In a preferred embodiment, the geometric model of the selected target is a PEC (Perfect Electric Conductor) sphere, the facet index, facet vertex coordinates, and vertex index are the index information of each triangular facet after the PEC sphere is meshed by triangular facets, and the position information in space after scene modeling; wherein, the position information includes the vertices of the triangular facets.

[0066] When the radiation field of an ideal electric dipole illuminates the target, the physical optics scattering result of the ideal electric dipole at a certain point in space is determined as shown in the following formula:

[0067]

[0068] In the formula, E s (r) is the scattered field value at a certain point in the coordinate origin space, r is the spatial position of the ideal electric dipole, is the unit vector of the incident direction, is the unit vector of the scattering direction, is the unit normal vector of the outer surface of the scatterer target, η is the free space wave impedance, E0 is the electric field intensity at the triangular surface element, and H0 is the magnetic field intensity at the triangular surface element.

[0069] in, is the triangular surface element integral part, and the triangular surface element integral part can be summed and transformed using the Gordon integral formula, as shown in Formula 6.

[0070]

[0071] Where w is the normal vector of the triangle, r′0 is the center point of the triangle, T n This is the summation calculation part when converting the integral into a summation formula of Gordon integral formula.

[0072] Substituting equation 6 into equation 5, we can obtain:

[0073]

[0074] Among them, w can be expressed as:

[0075]

[0076] T n It can be expressed as:

[0077]

[0078] Step 5, traverse all array elements in the uniform circular array to obtain the scattering result of the uniform circular array under the current mode number.

[0079] Determine whether the currently calculated electric dipole scattering result is the last electric dipole element in the uniform circular array.

[0080] If the currently calculated scattering result does not belong to the last array element, return to step 3.

[0081] If the currently calculated scattering result belongs to the last array element, the scattering results of all array elements are output and superimposed together as the scattering result of the uniform circular array under the mode number.

[0082] Step 6, traverse the mode number to obtain the scattering result database of the uniform circular array.

[0083] According to Formula 4, determine whether the current mode number exceeds the mode number range.

[0084] If the current mode number does not exceed the mode number range set in step 2, all target scattering results calculated for the current mode number are stored, and the process returns to step 3 to calculate the excitation phase under the next mode number and the target scattering results of the uniform circular array.

[0085] If the current mode number exceeds the mode number range set in step 2, the calculation of the scattering result is terminated, and all the mode numbers that have been calculated and their corresponding scattering results are output and used as the scattering result database of the uniform circular array.

[0086] In a preferred embodiment, the uniform circular array may be re-divided, the number of array elements may be reset, the modal number range may be changed, and a target scattering result database within the modal number range may be obtained.

[0087] Embodiment 1

[0088] Step 1: According to the basic principle of uniform circular array generating vortex electromagnetic waves, determine whether the array element type is an ideal point source or an ideal electric dipole.

[0089] In this embodiment, a uniform circular array with a radius of 10λ is set and divided into 16 array elements, that is, the uniform circular array is a 16-element uniform circular array; and the operating frequency is set to 3 GHz, and the radiation field satisfies equation 1, so that the array elements satisfy ideal electric dipoles.

[0090] Step 2: When the array element type is an ideal electric dipole, calculate the range of the modal number; when the array element type is a point source, end the calculation.

[0091] According to Formula 4, the mode number range of the 16-element uniform circular array is -8<1<8.

[0092] According to the excitation phase The excitation phase of the uniform circular array of this embodiment is obtained as follows: The corresponding excitation phase is applied to each array element in a cyclic order, so that the phases required to be applied to the array elements are in an arithmetic progression. When the modal number is 1, the phase of the base array element (n=0) is 0, the phase applied to the second array element (n=1) is π / 8, the phase required to be applied to the third array element (n=2) is π / 4, and so on, with an increase of π / 8 between each array element; when the modal number is 3, the phase of the base array element (n=0) is 0, the phase applied to the second array element (n=1) is 3π / 8, the phase required to be applied to the third array element (n=2) is 6π / 8, and the phase between each array element is 3π / 8.

[0093] Step 3: select an array element in the uniform circular array, and determine the parameters of the array element according to the relationship between the number of array elements in the uniform circular array and the range of the mode number.

[0094] A coordinate system is established on the 16-element uniform circular array so that all array elements are oriented toward the x-axis, and the spatial coordinates of each array element are marked as (x n ,y n , z n )(n≤15). After applying the corresponding excitation phase to each array element, the scattering result is calculated.

[0095] Step 4: Select the target and calculate the target scattering result generated by the array element in space.

[0096] The target is a PEC sphere with a radius of 2λ as the target for triangular surface segmentation, and the surface element file of the triangular surface element is imported. The physical optics scattering result at a certain point in the triangular surface element is calculated using Equation 7.

[0097] Step 5, traverse all array elements in the uniform circular array to obtain the scattering result of the uniform circular array under the current mode number.

[0098] Determine whether the array element number of the currently calculated scattering result is greater than or equal to 15. If the current array element number is 15, output the scattering results of all array elements and superimpose them together as the scattering result of the uniform circular array under the modal number; if the current array element number is less than 15, return to step 3 to calculate the scattering result of the next array element.

[0099] Step 6, traverse the mode number to obtain the scattering result database of the uniform circular array.

[0100] Determine whether the current mode number is within the range of -8<1<8. If so, store all target scattering results calculated under the current mode number and return to step 3 to calculate the target scattering result under the next mode. If it exceeds this range, terminate all calculation processes, output all calculated mode numbers and their corresponding target scattering results, and use them as the scattering result database of the uniform circular array.

[0101] In actual use, the modal number can be set and the target scattering result corresponding to the modal number can be searched in the database of the uniform circular array of this embodiment. When the input modal number is 1, the scattering field amplitude is as follows: Figure 2 As shown, the scattered field phase is Figure 4 As shown; when the input mode number is 3, the scattering field amplitude is as follows Figure 3 As shown, the scattered field phase is Figure 5 shown.

[0102] In summary, the present invention traverses all array elements in a uniform circular array and traverses all modal numbers to obtain a scattering result database of the uniform circular array, and establishes a mapping relationship between the modal number and the scattering result, so that the model can quickly change its scattering result when the modal number changes, thereby improving the adaptability of the model; by converting the scattering result into a simple summation formula, it is convenient for the system to run the calculation and simplifies the construction of the model.

[0103] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A vortex electromagnetic wave target scattering modeling method based on physical optics method, It is characterized in that The specific steps include: Step 1, determine whether the array element type is an ideal point source or an ideal electric dipole; Step 2: When the array element type is an ideal electric dipole, determine the range of the mode number; otherwise, terminate the operation; Step 3, selecting an array element in the uniform circular array and determining the parameters of the array element; Step 4, select a target and calculate the scattering result generated by the target in space; Step 5, traverse all array elements in the uniform circular array to obtain the scattering result of the uniform circular array under the current mode number; Step 6, traverse the mode number to obtain the scattering result database of the uniform circular array.

2. The vortex electromagnetic wave target scattering modeling method based on the physical optics method according to claim 1, It is characterized in that Methods for determining the maximum mode number range include: In the formula, |l max | is the maximum mode number, and N is the number of array elements of the uniform circular array.

3. The vortex electromagnetic wave target scattering modeling method based on the physical optics method according to claim 2, It is characterized in that The modal number range can be set as required, and the set modal number range is a subset of the maximum modal number range.

4. The vortex electromagnetic wave target scattering modeling method based on physical optics method according to claim 1, It is characterized in that The parameters of the array elements include: geometric parameters and electromagnetic parameters; the geometric parameters include: array configuration, number of array elements, and spatial position of array elements; the electromagnetic parameters include: excitation phase, excitation amplitude, and the direction of each array element.

5. The vortex electromagnetic wave target scattering modeling method based on physical optics method according to claim 1, It is characterized in that The step 4 also includes: importing a geometric model of the target, wherein the geometric model includes: facet index, facet vertex coordinates, and vertex index.

6. The vortex electromagnetic wave target scattering modeling method based on physical optics method according to claim 5, It is characterized in that The geometric model of the target is a PEC sphere, and the face element index, face element vertex coordinates, and vertex index are the index information of each triangular face element after the PEC sphere is divided into triangular face elements, as well as the position information in space after scene modeling; wherein, the position information includes the vertices of the triangular face elements.

7. The vortex electromagnetic wave target scattering modeling method based on physical optics method according to claim 1, It is characterized in that The step 4 also includes: The physical optics scattering result of an ideal electric dipole at a point in space is determined as follows: In the formula, E s (r) is the scattered field value at a certain point in the coordinate origin space, r is the spatial position of the ideal electric dipole, is the unit vector of the incident direction, is the unit vector of the scattering direction, is the unit normal vector of the outer surface of the scatterer target, η is the free space wave impedance, E 0 is the electric field strength at the triangular surface element, H 0 is the magnetic field intensity at the triangular surface element, k is the wave number, j represents the imaginary unit, and r′ is any position in space; in, The integral part of the triangular surface element can be transformed by summing the integral part of the triangular surface element using the Gordon integral formula; Where w is the normal vector of the triangle surface element, r′ 0 is the center point of the triangle surface element, T n This is the summation calculation part when converting the integral into a summation formula of Gordon integral formula.

8. The vortex electromagnetic wave target scattering modeling method based on physical optics method according to claim 1, It is characterized in that The uniform circular array is re-divided, the number of array elements is reset, the range of the modal number is changed, and a database of target scattering results within the range of the modal number is obtained.

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