Missile-borne radar terahertz fast imaging method based on high-frequency electromagnetic scattering algorithm

Abstract

The application discloses a missile-borne radar terahertz fast imaging method based on a high-frequency electromagnetic scattering algorithm, and comprises the following steps: dividing a real imaging scene containing a background and a target into a plurality of grid surface units; determining the grid surface units in the irradiation range of a transmitting antenna beam from the plurality of grid surface units; determining the grid surface units that can be irradiated by the transmitting antenna beam from the grid surface units in the irradiation range of the transmitting antenna beam; calculating the radar image intensity of each irradiated grid surface unit and the coordinates of the corresponding points of each irradiated grid surface unit in a two-dimensional image of the real imaging scene; and obtaining the two-dimensional image of the real imaging scene according to the radar image intensity of the irradiated grid surface units and the coordinates of the corresponding points in the two-dimensional image of the real imaging scene. The application can greatly improve the simulation speed while ensuring the image precision.

Description

Technical Field

[0001] This invention belongs to the field of terahertz imaging technology, specifically relating to a rapid terahertz imaging method for missile-borne radar based on a high-frequency electromagnetic scattering algorithm. Background Technology

[0002] In recent years, terahertz imaging has been widely applied in various fields such as medicine, communications, passenger security checks, agricultural product inspection, and national defense due to its significant and unique properties, such as strong penetration, strong anti-interference capability, narrow beamwidth, and high carrier frequency. Notably, its combination with SAR imaging has overcome many limitations and bottlenecks, offering greater research value and broader application prospects. Compared to traditional microwave imaging, one advantage of terahertz imaging is its ability to obtain high-resolution radar images. However, higher frequencies and resolutions pose greater challenges to electromagnetic scattering simulation techniques. For imaging simulations of real-world ultra-large scenes, the traditional method of generating scattered echoes and imaging using simulated SAR detection processes to obtain the two-dimensional scattered echo matrix is ​​extremely time-consuming, especially in the terahertz band. Higher resolution further increases the computational load, making it difficult to meet the data production requirements for large samples.

[0003] Currently, two-dimensional synthetic aperture radar (SAR) image simulation based on high-frequency scattering algorithms is mainly used to simulate the real SAR detection process. Following the SAR "walk-stop" mode, the high-frequency scattering algorithm is used to simulate the scattered echoes at each receiving position in the flight trajectory, forming an azimuth-range echo matrix. The final SAR image is then obtained using SAR imaging processing algorithms.

[0004] However, current SAR imaging simulations typically employ a technique that simulates the SAR detection process, first simulating the scattered echo and then imaging it. For imaging simulations of real-world, ultra-large scenes, obtaining the two-dimensional scattered echo matrix is ​​extremely time-consuming, especially in the terahertz band. Higher resolution further increases the computational load, making it difficult to meet the data production requirements for large samples. In other words, current SAR imaging simulation methods suffer from high complexity and slow efficiency in modeling missile-borne radar imaging simulations in high-resolution, large-scene environments, failing to meet the requirements for rapid data production with large sample sizes. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a rapid terahertz imaging method for missile-borne radar based on a high-frequency electromagnetic scattering algorithm.

[0006] The technical problem to be solved by this invention is achieved through the following technical solution:

[0007] This invention provides a rapid terahertz imaging method for missile-borne radar based on a high-frequency electromagnetic scattering algorithm, comprising:

[0008] The real imaging scene, including the background and the target, is divided into multiple mesh elements;

[0009] From the plurality of grid elements, determine the grid elements that are within the illumination range of the transmitting antenna beam;

[0010] From the grid elements within the illumination range of the transmitting antenna beam, determine the grid elements that can be illuminated by the transmitting antenna beam;

[0011] Calculate the radar image intensity of each illuminated grid cell, and the coordinates of the corresponding point of each illuminated grid cell in the two-dimensional image of the real imaging scene;

[0012] The two-dimensional image of the real imaging scene is obtained based on the radar image intensity of the illuminated grid elements and the coordinates of the corresponding points in the two-dimensional image of the real imaging scene.

[0013] In some embodiments, determining the grid cells within the illumination range of the transmitting antenna beam from the plurality of grid cells includes:

[0014] For each of the plurality of grid elements, the line connecting the center of the grid element and the position of the transmitting antenna is taken as the initial incident ray of the grid element;

[0015] Calculate the angle between the initial incident ray of the grid element and the beam direction of the transmitting antenna;

[0016] When the included angle is less than half the beamwidth, it indicates that the grid element is within the illumination range of the transmitting antenna beam; otherwise, it indicates that the grid element is not within the illumination range of the transmitting antenna beam.

[0017] In some implementations, each grid cell corresponds to an initial incident ray, which is a line connecting the center of the grid cell to the position of the transmitting antenna; determining the grid cells that can be illuminated by the transmitting antenna beam from the grid cells within the illumination range of the transmitting antenna beam includes:

[0018] From the grid elements within the illumination range of the transmitting antenna beam, determine the grid elements whose initial incident rays are not blocked by the target or background in the real imaging scene, and obtain the grid elements directly illuminated by the transmitting antenna beam.

[0019] From the grid elements within the illumination range of the transmitting antenna beam, determine the grid element to which the initial incident ray corresponding to at least one grid element directly illuminated by the transmitting antenna beam bounces and then strikes, thus obtaining the grid element illuminated by the reflected transmitting antenna beam.

[0020] Both the grid elements directly illuminated by the transmitting antenna beam and the grid elements illuminated by the reflected transmitting antenna beam are considered as the grid elements illuminated by the transmitting antenna beam.

[0021] In some implementations, the step of calculating the radar image intensity of each illuminated grid cell includes:

[0022] For each illuminated grid cell, determine the scattering field of that illuminated grid cell;

[0023] Based on the scattered field of the illuminated grid element, the distance from the center of the illuminated grid element to the receiving antenna, and the wave number of the electromagnetic wave, the radar image intensity of the illuminated grid element is determined by two-dimensional inverse Fourier transform.

[0024] In some implementations, the expression for the radar image intensity of each illuminated grid cell is as follows:

[0025]

[0026] Where ω = 2πf, f is the frequency of the incident wave, and k is the wave number of the electromagnetic wave. Let r be the incident direction, r be the distance from the center of the illuminated grid element to the receiving antenna, and e be the incident direction. i and h i R represents the amplitude vectors of the electric and magnetic fields, respectively. TE and R TM These are the reflection coefficients of the target for TE and TM waves, respectively. and ε and μ are the direction vectors of the TE and TM waves, respectively, and k0 is the wave number corresponding to the radar center frequency. ω is the incident direction corresponding to the center angle during radar sweep. A Let ω be the angular velocity, η be the angular scan time, j be the imaginary unit, and m represent the number of bounces of the initial incident ray incident on the illuminated grid cell. Specifically, m is 1 when the illuminated grid cell is directly illuminated by the transmitting antenna beam, and m is greater than or equal to 2 when the illuminated grid cell is illuminated by the reflected transmitting antenna beam. Let j' be the bounce direction of the initial incident ray. Let r be the normal vector of the j'-th mesh element on the bounce path of the initial incident ray. nLet be the center coordinates of the illuminated mesh element, ΔS be the area of ​​the illuminated mesh element, x be the x-coordinate of the point corresponding to the illuminated mesh element in the 2D image of the real imaging scene, and y be the y-coordinate of the point corresponding to the illuminated mesh element in the 2D image of the real imaging scene. Let z be the z-axis direction in the Cartesian coordinate system. Let be the normal vector of the illuminated mesh element. k is the width of the radar scan angle. max The maximum value of k is k. min The minimum value of k. This refers to the scattering direction corresponding to the center of each scanning angle of the radar.

[0027] In some implementations, when the wave emitted by the transmitting antenna is a terahertz wave, R TE R TM The expressions are as follows:

[0028] R TE =R 0TE exp(-(4πσ / λ) 2 cos 2 θ);

[0029] R TM =R 0TM exp(-(4πσ / λ) 2 cos 2 θ);

[0030] Where θ is the angle between the incident wave and the incident surface, and R 0TE R is the reflection coefficient of a smooth plane to TE waves. 0TM σ is the reflection coefficient of the smooth plane to the TM wave, λ is the wavelength of the incident wave, and σ is the roughness of the incident surface.

[0031] In some implementations...

[0032]

[0033] Where, Δk=k max -k min d m The total bounce path of the initial incident ray that bounces m times after hitting the illuminated grid element.

[0034] In some implementations, the expressions for the x-coordinate and the y-coordinate are as follows:

[0035]

[0036] Where, d mThe total bounce path of the initial incident ray that bounces m times after hitting the illuminated grid element.

[0037] In some embodiments, determining, from the grid elements within the illumination range of the transmitting antenna beam, the grid element to which the initial incident ray corresponding to at least one grid element directly illuminated by the transmitting antenna beam bounces after incident, and obtaining the grid element illuminated by the reflected transmitting antenna beam, includes:

[0038] Using a ray tracing method, the initial incident ray corresponding to each grid cell directly illuminated by the transmitting antenna beam is sequentially subjected to a ray tracing intersection test with the real imaging scene. Based on the ray tracing intersection test results, from the grid cells within the illumination range of the transmitting antenna beam, the grid cells to which the initial incident ray corresponding to at least one grid cell directly illuminated by the transmitting antenna beam bounces are selected.

[0039] The selected grid elements are used as the grid elements illuminated by the reflected transmitting antenna beam.

[0040] In some embodiments, when obtaining the two-dimensional image of the real imaging scene based on the radar image intensity of the illuminated grid elements and the coordinates of the corresponding points in the two-dimensional image of the real imaging scene, the method further includes:

[0041] When two or more illuminated grid elements have the same coordinates as the corresponding points in the two-dimensional image of the real imaging scene, the radar image intensities of the two or more illuminated grid elements are accumulated, and the accumulated radar image intensity is taken as the radar image intensity of that point.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] This invention proposes a fast radar imaging technology based on a high-frequency electromagnetic scattering algorithm. Two-dimensional radar images can be obtained by performing ray tracing at a single incident angle of the transmitting antenna beam. This technology effectively combines electromagnetic scattering theory with radar imaging theory, which can greatly improve simulation speed while ensuring image accuracy. It effectively solves the problems of high complexity and slow efficiency in simulation modeling of missile-borne radar imaging in high-resolution large scenes, and can meet the requirements of rapid data production under large sample sizes.

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0045] Figure 1This is a flowchart illustrating a rapid terahertz imaging method for missile-borne radar based on a high-frequency electromagnetic scattering algorithm, provided in an embodiment of the present invention.

[0046] Figure 2 This is a flowchart illustrating the process of determining a grid element illuminated by a transmitting antenna beam, as provided in an embodiment of the present invention.

[0047] Figure 3 This is a schematic diagram of an exemplary composite scene including ships and the sea surface provided by an embodiment of the present invention;

[0048] Figure 4 The method of the present invention provided in the embodiments of the present invention is used to... Figure 3 A schematic diagram of a two-dimensional radar image obtained when performing two-dimensional imaging on a composite scene. Detailed Implementation

[0049] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0050] Figure 1 This is a flowchart illustrating a rapid terahertz imaging method for missile-borne radar based on a high-frequency electromagnetic scattering algorithm, as provided in an embodiment of the present invention. Figure 1 As shown, the method includes:

[0051] S101. Divide the real imaging scene containing the background and the target into multiple mesh elements.

[0052] Here, existing surface segmentation methods can be used to divide the real imaging scene containing the background and the target into a mesh model of the real imaging scene. Based on this mesh model, all the mesh elements of the real imaging scene can be obtained.

[0053] For example, each mesh element can be a triangular element, and the coordinates of the three vertices of the triangular element represent the position information of the triangular element in the real imaging scene.

[0054] S102. From multiple grid elements, determine the grid elements that are within the illumination range of the transmitting antenna beam.

[0055] S103. From the grid elements within the illumination range of the transmitting antenna beam, determine the grid elements that can be illuminated by the transmitting antenna beam.

[0056] S104. Calculate the radar image intensity of each illuminated grid element, and the coordinates of the corresponding point in the two-dimensional image of the real imaging scene for each illuminated grid element.

[0057] S105. Based on the radar image intensity of the illuminated grid elements and the coordinates of the corresponding points in the two-dimensional image of the real imaging scene, obtain the two-dimensional image of the real imaging scene.

[0058] In this invention, S102 can be implemented through the following steps:

[0059] S1021. For each of the multiple grid elements, the line connecting the center of the grid element and the position of the transmitting antenna is taken as the initial incident ray of the grid element.

[0060] Here, the initial incident ray of a grid cell is a ray that is directed from the position of the transmitting antenna to the center of the grid cell.

[0061] S1022. Calculate the angle between the initial incident ray of the grid element and the direction of the transmitting antenna beam.

[0062] S1023. When the included angle is less than half of the beamwidth, it indicates that the grid element is within the illumination range of the transmitting antenna beam; otherwise, it indicates that the grid element is not within the illumination range of the transmitting antenna beam.

[0063] Here, if the included angle is greater than or equal to half the beamwidth, it indicates that the grid element is not within the illumination range of the transmitting antenna beam.

[0064] In this invention, S103 can be achieved through the following steps:

[0065] S1031. From the grid elements within the illumination range of the transmitting antenna beam, determine the grid elements whose initial incident rays are not blocked by the target or background in the real imaging scene, and obtain the grid elements directly illuminated by the transmitting antenna beam.

[0066] S1032. From the grid elements within the illumination range of the transmitting antenna beam, determine the grid element to which the initial incident ray corresponding to at least one grid element directly illuminated by the transmitting antenna beam bounces and then strikes, thus obtaining the grid element illuminated by the reflected transmitting antenna beam.

[0067] Here, a ray tracing method can be used to sequentially perform ray tracing intersection tests between the initial incident ray corresponding to each grid cell directly illuminated by the transmitting antenna beam and the actual imaging scene. Then, based on the ray tracing intersection test results, from the grid cells within the illumination range of the transmitting antenna beam, the grid cells that are illuminated by the initial incident ray corresponding to at least one grid cell directly illuminated by the transmitting antenna beam after bouncing are selected. Finally, the selected grid cells are taken as the grid cells illuminated by the reflected transmitting antenna beam.

[0068] S1033. Both the grid elements directly illuminated by the transmitting antenna beam and the grid elements illuminated by the reflected transmitting antenna beam are considered as grid elements illuminated by the transmitting antenna beam.

[0069] For example, Figure 2 This is a flowchart illustrating the process of determining the grid elements illuminated by the transmitting antenna beam. For example... Figure 2 As shown, after obtaining the mesh model of the real imaging scene, all mesh elements (i.e., mesh cells) obtained by reading the mesh model of the real imaging scene can be stored in a memory container to construct the initial incident ray of each mesh element. Then, the initial incident rays that are not blocked by the target or background are identified and stored. Finally, the mesh elements illuminated by the transmitting antenna beam are determined based on the initial incident rays that are not blocked by the target or background.

[0070] In the terahertz band, the beam of missile-borne radar antenna is usually narrow. In response to the illumination of narrow beam antennas, this invention proposes the ray tracing technology under antenna beam illumination as described in S102 to S103 above. This technology can determine the grid elements in the target and background that are illuminated by the beam.

[0071] In this invention, S104 can be implemented through the following steps:

[0072] S1041. For each illuminated grid element, determine the scattered field E of that illuminated grid element. s (ω,r).

[0073] S1042, Based on the scattered field E of the illuminated grid element s The radar image intensity of the illuminated grid element is determined by using (ω,r), the distance r from the center of the illuminated grid element to the receiving antenna, and the wave number k of the electromagnetic wave through a two-dimensional inverse Fourier transform.

[0074] Specifically, the expression for the radar image intensity of each illuminated grid cell is as follows:

[0075]

[0076] Where ω = 2πf, f is the frequency of the incident wave, and k is the wave number of the electromagnetic wave. Let r be the incident direction, r be the distance from the center of the illuminated grid element to the receiving antenna, and e be the incident direction. i and h i R represents the amplitude vectors of the electric and magnetic fields, respectively. TE and R TM These are the reflection coefficients of the target to TE and TM waves, respectively. and ε and μ are the direction vectors of the TE and TM waves, respectively, and k0 is the wave number corresponding to the radar center frequency. ω is the incident direction corresponding to the center angle during radar sweep. A Let ω be the angular velocity, η be the angular scanning time, j be the imaginary unit, and m represent the number of bounces of the initial incident ray incident on the illuminated grid cell. m is 1 when the illuminated grid cell is directly illuminated by the transmitting antenna beam, and greater than or equal to 2 when the illuminated grid cell is illuminated by a reflected transmitting antenna beam. Let j' be the bounce direction of the initial incident ray. Let r be the normal vector of the j'-th mesh element on the bounce path of the initial incident ray. n Let be the center coordinates of the illuminated mesh element, ΔS be the area of ​​the illuminated mesh element, x be the x-coordinate of the point corresponding to the illuminated mesh element in the 2D image of the real imaging scene, and y be the y-coordinate of the point corresponding to the illuminated mesh element in the 2D image of the real imaging scene. Let z be the z-axis direction in the Cartesian coordinate system. Let be the normal vector of the illuminated mesh element. k is the width of the radar scan angle. max The maximum value of k is k. min The minimum value of k. This refers to the scattering direction corresponding to the center of each scanning angle of the radar.

[0077] The expression for the radar image intensity of each illuminated grid cell is obtained through the following formula derivation:

[0078] According to the theory of physical optics scattering, the scattering electric field E of each grid element... s (ω,r) can be written as the following formula (1):

[0079]

[0080] in, The scattering direction corresponding to each scanning angle of the radar. Let be the normal vector of this mesh element. Let r be the direction vector from the transmitting antenna to the origin, r′ be the distance from the center of the grid cell to the receiving antenna, and E(ω,r′) and H(ω,r′) be the electric and magnetic fields, respectively. Considering the propagation path of multiple bounces, E... s (ω,r) can be rewritten as the following formula (2):

[0081]

[0082] make Let m be the direction of the m-th ray bounce. Let be the normal vector of the j'th mesh element on the bounce path of the ray, then the following formula (3) holds:

[0083]

[0084] Based on the theory of inverse synthetic aperture radar imaging under small bandwidth and small angle, this invention develops a fast radar imaging technology. Under the small bandwidth and small angle approximation, the following formulas (4) and (5) can be obtained:

[0085]

[0086]

[0087] When the mesh element is small enough, the integral in the above formula (2) can be written as the following formula (6):

[0088]

[0089] At this time, the scattering field E of the grid element s (ω,r) can be simplified to the following formula (7):

[0090]

[0091] Therefore, the contribution of this grid element to the radar image intensity can be obtained through a two-dimensional inverse Fourier transform, that is, the contribution of this grid element to the radar image intensity is as described above.

[0092]

[0093] In this invention, the solutions to the two integrals in the formula for calculating the radar image intensity of each illuminated grid element are as follows:

[0094]

[0095] Where, Δk=k max -k min d m The total bounce path of the initial incident ray that bounces m times after hitting the illuminated grid element.

[0096] Furthermore, based on the solutions to these two integrals, the expressions for the x and y coordinates of the point corresponding to the illuminated mesh element in the two-dimensional image of the real imaging scene are as follows:

[0097]

[0098] That is, the contribution of the illuminated grid element to the radar image intensity of the two-dimensional image of the real imaging scene is located in the range direction. and orientation ) place.

[0099] In this invention, when the electromagnetic wave frequency increases to the terahertz band, the wavelength of the terahertz wave is comparable to that of a rough surface microstructure. The rough surface will significantly influence the propagation mechanism of the terahertz wave, with scattering playing a crucial role in propagation. In the low-frequency terahertz band, a metallic target can be considered an ideal conductor with a micro-rough surface. When the incident wave is incident at a certain angle θ with the surface, the oblique incident reflectivity of the rough surface can be expressed as: R s =R0 exp(-(4πσ / λ) 2 cos 2 θ), where R0 is the reflection coefficient of the smooth surface. For scattering field calculations in the terahertz frequency band, this invention uses this formula to calculate the equivalent reflection coefficient of the rough surface, and then applies the calculated equivalent reflection coefficient to the scattering calculation. Therefore, in this invention, when the wave emitted by the transmitting antenna is a terahertz wave, the aforementioned J... a and M a R in TE R TM The expressions are as follows:

[0100] R TE =R 0TE exp(-(4πσ / λ) 2 cos 2 θ);

[0101] R TM =R 0TM exp(-(4πσ / λ) 2 cos 2 θ);

[0102] Where θ is the angle between the incident wave and the incident surface, and R 0TE R is the reflection coefficient of a smooth plane to TE waves. 0TM σ is the reflection coefficient of the smooth plane to the TM wave, λ is the wavelength of the incident wave, and σ is the roughness of the incident surface.

[0103] In this invention, regarding S105 above, after obtaining the radar image intensity of all illuminated grid elements and the coordinates of the corresponding points in the two-dimensional image of the real imaging scene, if the coordinates of the points corresponding to two or more illuminated grid elements in the two-dimensional image of the real imaging scene are the same, the radar image intensities of the two or more illuminated grid elements are accumulated, and the accumulated radar image intensity is taken as the radar image intensity of that point; then, given the coordinates of different points and the radar image intensity of each point, the two-dimensional image of the real imaging scene can be obtained.

[0104] This invention proposes a fast radar imaging technology based on a high-frequency electromagnetic scattering algorithm. Two-dimensional radar images can be obtained by performing ray tracing at a single incident angle of the transmitting antenna beam. This technology effectively combines electromagnetic scattering theory with radar imaging theory, which can greatly improve simulation speed while ensuring image accuracy. It effectively solves the problems of high complexity and slow efficiency in simulation modeling of missile-borne radar imaging in high-resolution large scenes, and can meet the requirements of rapid data production under large sample sizes.

[0105] The technical effects of the present invention will be further illustrated below through specific simulation experiments.

[0106] Figure 3 This is a composite scene (i.e., the aforementioned real imaging scene) requiring two-dimensional imaging, including ships and the sea surface. The ships are the targets, and the sea surface is the background, with dimensions of 600m × 600m. When the aforementioned rapid terahertz imaging method for missile-borne radar based on a high-frequency electromagnetic scattering algorithm is used to image this composite scene, the terahertz frequency is 220GHz, the incident angle is 35°, the azimuth angle is 12°, the missile-target distance is 15km, the beamwidth is 2°, the imaging area is 500m × 500m, and the resolution is 0.15m. The resulting two-dimensional radar image of this composite scene is as follows: Figure 4 As shown, the simulation time consumed was 12 seconds. Clearly, this invention can significantly improve simulation speed while maintaining image accuracy.

[0107] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0108] In this specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude multiple instances. While different embodiments may describe certain measures, this does not mean that these measures cannot be combined to produce a good effect.

[0109] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A rapid terahertz imaging method for missile-borne radar based on a high-frequency electromagnetic scattering algorithm, characterized in that, include: The real imaging scene, including the background and the target, is divided into multiple mesh elements; From the plurality of grid elements, determine the grid elements that are within the illumination range of the transmitting antenna beam; From the grid elements within the illumination range of the transmitting antenna beam, determine the grid elements that can be illuminated by the transmitting antenna beam; Calculate the radar image intensity of each illuminated grid cell, and the coordinates of the corresponding point of each illuminated grid cell in the two-dimensional image of the real imaging scene; The two-dimensional image of the real imaging scene is obtained based on the radar image intensity of the illuminated grid element and the coordinates of the corresponding point in the two-dimensional image of the real imaging scene. The expression for the radar image intensity of each illuminated grid element is as follows: ； ； ； ； in, , Let the frequency be the incident wave. The wave number of electromagnetic waves. The incident direction, Let be the distance from the center of the illuminated grid element to the receiving antenna. and These are the amplitude vectors of the electric field and the magnetic field, respectively. and These are the reflection coefficients of the target for TE and TM waves, respectively. and These are the direction vectors of the TE wave and the TM wave, respectively. and These are the dielectric constant and magnetic permeability, respectively. The wave number corresponding to the radar center frequency. The incident direction corresponding to the center angle during radar scanning. Angular velocity, For angle scan time, The imaginary unit, This represents the number of bounces of the initial incident ray incident on the illuminated grid cell, where the illuminated grid cell is the grid cell directly illuminated by the transmitting antenna beam. The value is 1 when the illuminated grid element is the same grid element illuminated by the reflected transmitting antenna beam. Greater than or equal to 2, For the initial incident ray The direction of the next bounce. The first incident ray bounce path on the first The normal vector of each mesh element. Let these be the center coordinates of the illuminated mesh element. Let be the area of ​​the illuminated mesh element. The point corresponding to the illuminated mesh element in the two-dimensional image of the real imaging scene. coordinate, The point corresponding to the illuminated mesh element in the two-dimensional image of the real imaging scene. coordinate, For Cartesian coordinate system Axial direction, Let be the normal vector of the illuminated mesh element. The width of the radar scan angle. for The maximum value, for The minimum value, The scattering direction corresponding to the center of each scanning angle of the radar. The initial incident ray incident on the illuminated grid cell passes through The total bounce path after each bounce.

2. The terahertz fast imaging method for missile-borne radar based on high-frequency electromagnetic scattering algorithm according to claim 1, characterized in that, Determining the grid elements within the illumination range of the transmitting antenna beam from the plurality of grid elements includes: For each of the plurality of grid elements, the line connecting the center of the grid element and the position of the transmitting antenna is taken as the initial incident ray of the grid element; Calculate the angle between the initial incident ray of the grid element and the beam direction of the transmitting antenna; When the included angle is less than half the beamwidth, it indicates that the grid element is within the illumination range of the transmitting antenna beam; otherwise, it indicates that the grid element is not within the illumination range of the transmitting antenna beam.

3. The terahertz fast imaging method for missile-borne radar based on high-frequency electromagnetic scattering algorithm according to claim 1, characterized in that, Each grid cell corresponds to an initial incident ray, which is the line connecting the center of the grid cell to the position of the transmitting antenna; Determining the grid elements that can be illuminated by the transmitting antenna beam from the grid elements within the illumination range of the transmitting antenna beam includes: From the grid elements within the illumination range of the transmitting antenna beam, determine the grid elements whose initial incident rays are not blocked by the target or background in the real imaging scene, and obtain the grid elements directly illuminated by the transmitting antenna beam. From the grid elements within the illumination range of the transmitting antenna beam, determine the grid element to which the initial incident ray corresponding to at least one grid element directly illuminated by the transmitting antenna beam bounces and then strikes, thus obtaining the grid element illuminated by the reflected transmitting antenna beam. Both the grid elements directly illuminated by the transmitting antenna beam and the grid elements illuminated by the reflected transmitting antenna beam are considered as the grid elements illuminated by the transmitting antenna beam.

4. The terahertz fast imaging method for missile-borne radar based on high-frequency electromagnetic scattering algorithm according to claim 3, characterized in that, The steps for calculating the radar image intensity of each illuminated grid cell include: For each illuminated grid cell, determine the scattering field of that illuminated grid cell; Based on the scattered field of the illuminated grid element, the distance from the center of the illuminated grid element to the receiving antenna, and the wave number of the electromagnetic wave, the radar image intensity of the illuminated grid element is determined by two-dimensional inverse Fourier transform.

5. The terahertz fast imaging method for missile-borne radar based on high-frequency electromagnetic scattering algorithm according to claim 4, characterized in that, When the wave emitted by the transmitting antenna is a terahertz wave, , The expressions are as follows: ； ； in, The angle between the incident wave and the incident surface. The reflection coefficient of a smooth plane to TE waves, The reflection coefficient of a smooth plane to a TM wave. The wavelength of the incident wave is... The roughness of the incident surface.

6. The terahertz fast imaging method for missile-borne radar based on high-frequency electromagnetic scattering algorithm according to claim 4, characterized in that, ； ； in, = , The initial incident ray incident on the illuminated grid cell passes through The total bounce path after each bounce.

7. The terahertz fast imaging method for missile-borne radar based on high-frequency electromagnetic scattering algorithm according to claim 4 or 6, characterized in that, The Coordinates and the stated The expressions for the coordinates are as follows: ； 。 8. The terahertz fast imaging method for missile-borne radar based on high-frequency electromagnetic scattering algorithm according to claim 3, characterized in that, The step of determining, from the grid elements within the illumination range of the transmitting antenna beam, the grid element to which the initial incident ray corresponding to at least one grid element directly illuminated by the transmitting antenna beam bounces after bouncing, and obtaining the grid element illuminated by the reflected transmitting antenna beam, includes: Using a ray tracing method, the initial incident ray corresponding to each grid cell directly illuminated by the transmitting antenna beam is sequentially subjected to a ray tracing intersection test with the real imaging scene. Based on the ray tracing intersection test results, from the grid cells within the illumination range of the transmitting antenna beam, the grid cells to which the initial incident ray corresponding to at least one grid cell directly illuminated by the transmitting antenna beam bounces are selected. The selected grid elements are used as the grid elements illuminated by the reflected transmitting antenna beam.

9. The terahertz fast imaging method for missile-borne radar based on high-frequency electromagnetic scattering algorithm according to claim 1, characterized in that, When obtaining the two-dimensional image of the real imaging scene based on the radar image intensity of the illuminated grid elements and the coordinates of the corresponding points in the two-dimensional image of the real imaging scene, the method further includes: When two or more illuminated grid elements have the same coordinates as the corresponding points in the two-dimensional image of the real imaging scene, the radar image intensities of the two or more illuminated grid elements are accumulated, and the accumulated radar image intensity is taken as the radar image intensity of that point.

Images