Vortex electromagnetic wave radar multipath virtual image suppression method and system

Abstract

The invention provides a vortex electromagnetic wave radar multipath virtual image suppression method and system, and relates to the technical field of radar imaging virtual image suppression, and the method comprises the steps: adjusting the circular ring radiuses corresponding to different modes in a uniform concentric circular ring array according to the prior information of a target pitch angle, and obtaining the radar emission configuration of main lobe alignment; performing time domain sampling on the multi-path vortex radar echo signal in each mode to form a two-dimensional radar echo matrix; analyzing the obtained two-dimensional radar echo matrix and the MISO system echo after phase compensation by using an azimuth dimension point spread function to obtain dual-system imaging features; and performing modal domain FFT and time domain pulse compression processing on the multipath echo features under the MISO and MIMO systems by using fast Fourier transform and pulse compression, and finally outputting a virtual image suppressed synthetic radar image. The multi-path virtual image suppression method has the beneficial effects that the suppression of the multi-path virtual image is realized by utilizing the characteristic that the real image positions of the imaging results are completely the same and the virtual image positions are different under the multi-transmitting and single-receiving systems.

Description

Technical Field

[0001] The present invention relates to the technical field of radar imaging virtual image suppression, and more specifically, to a method and system for suppressing multipath virtual images of a vortex electromagnetic wave radar. Background Art

[0002] The precise detection and imaging technology of low-altitude targets (such as unmanned aerial vehicles, cruise missiles, etc.) is an important research direction in the current radar field and has an urgent need in military defense and civilian security. However, the multipath effect commonly existing in the complex low-altitude electromagnetic environment causes false target echoes from ground / seasurface reflections to be mixed in the radar received signal, seriously reducing the imaging resolution and target recognition reliability.

[0003] In traditional radar imaging technologies, such as synthetic aperture radar or inverse synthetic aperture radar, it is necessary to rely on the relative motion between the radar and the target to obtain the target Doppler information. However, the resolution is limited by the radar wavelength and the synthetic aperture length. Corresponding multipath suppression technologies, such as sub-aperture fusion, spatial diversity, and polarization filtering, are often limited in the high-precision imaging scenario of low-altitude targets. The vortex electromagnetic wave carrying orbital angular momentum (OAM) can achieve sub-wavelength resolution of the target without the relative motion between the radar and the target due to its unique helical phase wavefront and modal orthogonality. Therefore, the vortex electromagnetic wave radar shows extremely important value in the research of imaging low-altitude targets with multipath effects due to its excellent super-resolution imaging ability. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and system for suppressing multipath virtual images of a vortex electromagnetic wave radar to improve the above problems. To achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0005] In a first aspect, the present application provides a method for suppressing multipath virtual images of a vortex electromagnetic wave radar, including:

[0006] Obtaining the prior information of the target elevation angle and the parameter configuration of the uniform concentric ring array, and adjusting the ring radius corresponding to different modes in the uniform concentric ring array according to the prior information of the target elevation angle, so that the divergence angle of the OAM wave of each mode is aligned with the target elevation angle, thereby making the target fall into the main lobe of the uniform concentric ring array radar to obtain a radar transmission configuration with the main lobe aligned;

[0007] Based on the radar transmission configuration with the main lobe aligned and the target elevation angle information, through a preset two-line propagation model, an OAM echo signal model in a smooth sea surface scenario is established to obtain the multipath vortex electromagnetic wave radar echo signals in the MISO and MIMO systems;

[0008] Perform time-domain sampling on the multipath vortex radar echo signals in each mode to obtain row vectors, and arrange the row vectors obtained from time-domain sampling in different modes column by column to form a two-dimensional radar echo matrix. Among them, for the MISO system, it is necessary to perform phase compensation preprocessing on the Bessel envelope to achieve focusing of the target azimuth;

[0009] Use the azimuthal point spread function to analyze the obtained two-dimensional radar echo matrix and the echo of the MISO system after phase compensation, characterize the multipath echo characteristics under the MISO and MIMO systems, and analyze the imaging coordinate laws under the two systems to obtain the dual-system imaging characteristics with the same real image coordinates and different virtual image coordinates, where the defocusing degree of the virtual image of the MISO system is twice that of the MIMO system;

[0010] According to the dual-system imaging characteristics, use the fast Fourier transform and pulse compression to perform modal-domain FFT and time-domain pulse compression processing on the multipath echo characteristics under the MISO and MIMO systems respectively, generate the imaging results of the two systems, and perform Hadamard product imaging fusion on the imaging results of the two systems, and finally output a synthetic radar image with virtual image suppression.

[0011] Preferably, obtain the prior information of the target elevation angle and the parameter configuration of the uniform concentric ring array, and adjust the ring radii corresponding to different modes in the uniform concentric ring array according to the prior information of the target elevation angle, so that the divergence angles of the OAM waves of each mode are aligned with the target elevation angle, so that the target falls within the main lobe of the uniform concentric ring array radar, and obtain a radar transmission configuration with the main lobe aligned, including:

[0012] Obtain the elevation angle information of the target through an external sensor or preset conditions, and based on the elevation angle information of the target, calculate the ring radii corresponding to each mode, which satisfy a linear relationship, and its calculation formula is as follows:

[0013]

[0014] In the formula, k is the wave number, l is the mode number, and θ0 is the divergence angle of the multi-mode OAM wave of the uniform concentric ring array;

[0015] Adjust the ring radii of different modes in the uniform concentric circle array, so that the divergence angle of the OAM wave of each mode m satisfies that the main lobe directions of the beams of all modes are aligned with the actual elevation angle of the target;

[0016] Optimize the structure of the uniform concentric ring array based on the Bessel function modulation effect, determine the number of ring array elements, and thus complete the radar transmitter configuration.

[0017] Preferably, based on the radar transmission configuration aligned with the main lobe and the target elevation angle information, a smooth sea surface scenario OAM echo signal model is established through a preset two-line propagation model, and the multi-path vortex electromagnetic wave radar echo signals in MISO and MIMO systems are obtained, including:

[0018] According to the uniform concentric circular array parameters of the radar transmission configuration aligned with the main lobe, the field value expression of the direct path A - B is established in a three-dimensional rectangular coordinate system, where A is the radar and B is the target to be measured. The calculation formula is as follows;

[0019]

[0020] In the formula, k is the wave number, l is the mode number, r d is the distance from the UCCA to the target, a l is the circular ring radius corresponding to the OAM wave of the UCCA transmitting mode l, N is the number of circular ring array elements corresponding to the UCCA, θ is the elevation angle, J l (·) is the l-th order Bessel function of the first kind, S(·) is the linear frequency modulation signal envelope, τ d is the propagation delay;

[0021] In the mirror coordinate system, the field value expression of the mirror path A - C - B is derived, where C is the signal reflection point, and the mirror elevation angle is related through coordinate transformation. The calculation formula is as follows:

[0022]

[0023] In the formula, k is the wave number, l is the mode number, r d is the distance from the UCCA to the target, a l is the circular ring radius corresponding to the OAM wave of the UCCA transmitting mode l, N is the number of circular ring array elements corresponding to the UCCA, θ is the elevation angle, J l (·) is the l-th order Bessel function of the first kind, S(·) is the linear frequency modulation signal envelope, τ r is the propagation delay of the mirror field, Γ is the reflection coefficient of the smooth sea surface, Δr, Δθ and are the spherical coordinate offsets of the coordinate system O'-x'y'z' relative to the coordinate system O-xyz;

[0024] Combine the field values of the direct and mirror paths to establish the total echo signal of the four propagation paths in the MISO system;

[0025] In the MIMO system, the transmitting or receiving shares a uniform concentric circular array, and the total echo signal is the superposition of the contributions of each array element's transceiver. The vortex radar echo in the MIMO system under multiple paths is established.

[0026] Preferably, the multi-path vortex radar echo signals in each mode are sampled in the time domain to obtain row vectors, and the row vectors obtained by time-domain sampling in different modes are arranged in columns to form a two-dimensional radar echo matrix, which includes:

[0027] The multi-path vortex radar echo signals in each mode are discretely sampled in the time domain to obtain corresponding row vectors;

[0028] The row vectors obtained by time-domain sampling in different modes are arranged in columns to construct a two-dimensional radar echo matrix, where different rows and different columns of the two-dimensional radar echo matrix respectively contain echo information of different modes;

[0029] For the MISO system, preprocessing of phase compensation is performed on the Bessel envelope, and its calculation formula is as follows:

[0030]

[0031] In the formula, J lθ = J l (ka l sinθ), k is the wave number, l is the number of modes, a l is the ring radius corresponding to the OAM wave of the UCCA transmission mode l;

[0032] Preferably, the obtained two-dimensional radar echo matrix and the echo of the MISO system after phase compensation are analyzed using the azimuth dimension point spread function to characterize the multi-path echo characteristics in the MISO and MIMO systems, which includes:

[0033] The two-dimensional radar echo matrix is analyzed using the azimuth dimension point spread function to characterize the azimuth dimension characteristics of the imaging result.

[0034] Through PSF analysis, the multi-path echo characteristics in the MISO and MIMO systems are characterized, including the main lobe and sidelobe structures; for the MISO system, after preprocessing of phase compensation for the direct echo path A-B-A, the calculation formula of its multi-path azimuth dimension PSF is as follows:

[0035]

[0036] In the formula, J lθ = J l (ka l sinθ), a l is the ring radius corresponding to the OAM wave of the UCCA transmission mode l, θ is the pitch angle, Φ comp (l) is the phase compensation function, and l is the number of modes;

[0037] Among them, the calculation formula of the multi-path azimuth dimension PSF in the MIMO system is as follows:

[0038]

[0039] where J l θ = J l (ka l sinθ), a l is the radius of the ring corresponding to the OAM wave of the UCCA transmission mode l, θ is the elevation angle, l is the mode number, and Δθ is the spherical coordinate offset of the coordinate system O'-x'y'z' relative to the coordinate system O-xyz.

[0040] In a second aspect, the present application also provides a system for suppressing multipath virtual images of a vortex electromagnetic wave radar, including:

[0041] An acquisition module: used to acquire the prior information of the target elevation angle and the parameter configuration of the uniform concentric ring array, and adjust the ring radius corresponding to different modes in the uniform concentric ring array according to the prior information of the target elevation angle, so that the divergence angles of the OAM waves of each mode are aligned with the target elevation angle, so that the target falls within the main lobe of the uniform concentric ring array radar, and a radar transmission configuration with the main lobe aligned is obtained;

[0042] A building module: used to establish an OAM echo signal model in a smooth sea surface scenario based on the radar transmission configuration with the main lobe aligned and the target elevation angle information through a preset two-line propagation model, and obtain the multipath vortex electromagnetic wave radar echo signals in the MISO and MIMO systems;

[0043] An arrangement module: used to perform time-domain sampling on the multipath vortex radar echo signals in each mode to obtain row vectors, and arrange the row vectors obtained by time-domain sampling in different modes in columns to form a two-dimensional radar echo matrix. Among them, for the MISO system, phase compensation preprocessing is performed on the Bessel envelope to achieve focusing of the target azimuth;

[0044] An analysis module: used to analyze the obtained two-dimensional radar echo matrix and the echo of the MISO system after phase compensation by using the azimuth dimension point spread function, characterize the multipath echo characteristics in the MISO and MIMO systems, and analyze the imaging coordinate laws in the two systems to obtain the dual-system imaging characteristics with the same real image coordinates and different virtual image coordinates, where the defocus degree of the virtual image in the MISO system is twice that of the MIMO system;

[0045] A processing module: used to perform modal domain FFT and time-domain pulse compression processing on the multipath echo characteristics in the MISO and MIMO systems respectively according to the dual-system imaging characteristics by using fast Fourier transform and pulse compression, generate the imaging results of the two systems, and perform Hadamard product imaging fusion on the imaging results of the two systems, and finally output a synthetic radar image with virtual image suppression.

[0046] In a third aspect, the present application also provides a device for suppressing multipath virtual images of a vortex electromagnetic wave radar, including:

[0047] A memory for storing a computer program;

[0048] A processor for implementing the steps of the method for suppressing multipath virtual images of the vortex electromagnetic wave radar when executing the computer program.

[0049] In a fourth aspect, the present application also provides a readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the above-mentioned method for suppressing multipath virtual images based on a vortex electromagnetic wave radar are implemented.

[0050] The beneficial effects of the present invention are as follows:

[0051] The present invention sets the detection of low-altitude targets by an airborne radar as the scenario; based on the two-line propagation model, the echo signal models of the vortex electromagnetic wave radar in the MISO system and the MIMO system under a smooth sea surface are derived; through the azimuthal point spread function, the position offset law of multipath virtual images in the two systems is revealed, and the conclusion that the virtual image positions are different in the two systems is obtained; based on this, an imaging fusion algorithm based on the Hadamard product is proposed to achieve the suppression of multipath virtual images; through numerical simulation examples, the correctness of the virtual image distribution law and the effectiveness of the virtual image suppression method are verified. Using the position offset law of multipath virtual images in the two systems, an imaging fusion algorithm based on the Hadamard product is proposed to achieve the suppression of multipath virtual images, and it is applied to the field of suppressing virtual images in radar imaging. The designed method for suppressing virtual images in vortex electromagnetic wave radar imaging can effectively reconstruct the real image of low-altitude targets, providing a new idea for high-resolution imaging of low-altitude targets.

[0052] Other features and advantages of the present invention will be described in the subsequent specification, and part of them will become obvious from the specification, or be understood by implementing the embodiments of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures specifically pointed out in the written specification, claims, and drawings. Description of the Drawings

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0054] Figure 1 It is a schematic flow chart of the method for suppressing multipath virtual images of the vortex electromagnetic wave radar described in the embodiments of the present invention;

[0055] Figure 2 Schematic diagram of the UCCA imaging observation coordinate system described in the embodiments of the present invention;

[0056] Figure 3 Schematic diagram of the low-altitude target echo model in the airborne vortex electromagnetic wave radar scenario described in the embodiments of the present invention;

[0057] Figure 4 Schematic diagram of the radar echo matrix structure described in the embodiments of the present invention;

[0058] Figure 5 Schematic diagram of the imaging processing process described in the embodiments of the present invention;

[0059] Figure 6 Multi-path Bessel envelope and PSF curve - MISO result diagram described in the embodiments of the present invention, where Figure a is the schematic diagram of the A-B-A / A-B-C-A path, and Figure b is the schematic diagram of the A-C-B-A / A-C-B-C-A path;

[0060] Figure 7 Multi-path Bessel envelope and PSF curve - MIMO result diagram described in the embodiments of the present invention, where Figure a is the schematic diagram of the A-B-A path, Figure b is the schematic diagram of the A-C-B-A / A-B-C-A path, and Figure c is the schematic diagram of the A-C-B-C-A path;

[0061] Figure 8 Single-target point multi-path vortex two-dimensional normalized imaging result diagram described in the embodiments of the present invention, where Figure a is the schematic diagram of the A-B-A path, Figure b is the schematic diagram of the A-B-A path, Figure c is the schematic diagram of the A-B-C-A path, Figure d is the schematic diagram of the A-C-B-C-A path, and Figure e is the schematic diagram of the multi-path synthesis path;

[0062] Figure 9 Multi-path vortex imaging result diagram of the aircraft target described in the embodiments of the present invention, where Figure a is the example model, Figure b is the MISO imaging result, Figure c is the MIMO imaging result, and Figure d is the schematic diagram of the virtual image suppression result;

[0063] Figure 10 Schematic diagram of the structure of the vortex electromagnetic wave radar multi-path virtual image suppression device described in the embodiments of the present invention.

[0064] In the figure: 701, acquisition module; 702, establishment module; 703, arrangement module; 704, analysis module; 705, processing module; 800, vortex electromagnetic wave radar multi-path virtual image suppression device; 801, processor; 802, memory; 803, multimedia component; 804, I / O interface; 805, communication component. Detailed implementation manners

[0065] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. Components of the embodiments of the present invention described and illustrated herein generally may be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0066] It should be noted that like reference numerals and letters denote like items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of the present invention, terms such as "first", "second", etc. are only used for descriptive distinction and cannot be understood as indicating or implying relative importance.

[0067] Embodiment 1:

[0068] This embodiment provides a method for suppressing multipath virtual images of a vortex electromagnetic wave radar.

[0069] It should be noted that in this embodiment, UCCA is a uniform concentric circular array.

[0070] See Figure 1 , which shows that this method includes step S100, step S200, step S300, step S400, and step S500.

[0071] S100. Obtain the prior information of the target elevation angle and the parameter configuration of the uniform concentric circular array, and adjust the circular ring radius corresponding to different modes in the uniform concentric circular array according to the prior information of the target elevation angle, so that the divergence angles of the OAM waves of each mode are aligned with the target elevation angle, thereby making the target fall within the main lobe of the uniform concentric circular array radar. The UCCA structure is as Figure 2 shown, and a radar transmission configuration with the main lobe aligned is obtained.

[0072] It can be understood that in this step S100, it includes S101, S102, and S103, where:

[0073] S101. Obtain the elevation angle information of the target through an external sensor or preset conditions, and calculate the circular ring radius corresponding to each mode based on the elevation angle information of the target, which satisfies a linear relationship. The calculation formula is as follows:

[0074]

[0075] In the formula, k is the wave number, l is the mode number, and θ0 is the divergence angle of the multi-mode OAM wave of the uniform concentric ring array;

[0076] It should be noted that UCCA can weaken the influence of the Bessel function modulation effect on the imaging result, improve the signal-to-noise ratio of the echo energy, reduce the imaging sidelobe, and thus improve the imaging quality.

[0077] S102. Adjust the radii of the rings of different modes in the uniform concentric circle array, so as to make the divergence angle of the OAM wave of each mode m satisfy that the main lobe directions of the beams of all modes are aligned with the actual elevation angle of the target;

[0078] S103. Optimize the structure of the uniform concentric ring array based on the Bessel function modulation effect, and determine the number of ring array elements, so as to complete the configuration of the radar transmitting end.

[0079] S200. Based on the radar transmitting configuration with main lobe alignment and the target elevation angle information, establish an OAM echo signal model in a smooth sea surface scenario through a preset two-line propagation model, and obtain the multi-path vortex electromagnetic wave radar echo signals in the MISO and MIMO systems.

[0080] It should be noted that a radar echo model is constructed. The OAM wave is generated by the UCCA designed in step S1. Now, an OAM echo signal model in a smooth sea surface scenario is established based on the preset two-line propagation model. A radar echo model is constructed. The OAM wave is generated by the UCCA designed in step S1. Now, an OAM echo signal model in a smooth sea surface scenario is established based on the preset two-line propagation model. As Figure 3 shown, O-xyz is a three-dimensional rectangular coordinate system centered on the UCA, O'-x'y'z' is the sea surface mirror coordinate system, A is the radar radiation source, B is the target point to be measured, A' and B' are the mirror points corresponding to the radar and the target to be measured symmetric about the sea level, respectively, and C is the sea surface reflection point.

[0081] It can be understood that in this step S200, it includes S201, S202, S203 and S204, where:

[0082] S201. According to the parameters of the uniform concentric ring array of the radar transmitting configuration with main lobe alignment, establish an expression of the field value of the direct path A-B in the three-dimensional rectangular coordinate system, and its calculation formula is as follows;

[0083]

[0084] In the formula, k is the wave number, l is the mode number, r d is the distance from the UCCA to the target, a lis the radius of the ring corresponding to the OAM wave of mode l sent by UCCA, N is the number of ring array elements corresponding to UCCA, θ is the elevation angle, J l (·) is the Bessel function of the first kind of order l, S(·) is the envelope of the chirp signal, τ d is the propagation delay;

[0085] S202. Derive the expression of the field value of the mirror path A-C-B in the mirror coordinate system, and relate the mirror elevation angle through coordinate transformation. The calculation formula is as follows:

[0086]

[0087] In the formula, k is the wave number, l is the mode number, r d is the distance from UCCA to the target, a l is the radius of the ring corresponding to the OAM wave of mode l sent by UCCA, N is the number of ring array elements corresponding to UCCA, θ is the elevation angle, J l (·) is the Bessel function of the first kind of order l, S(·) is the envelope of the chirp signal, τ r is the propagation delay of the mirror field, Γ is the reflection coefficient of the smooth sea surface, Δr, Δθ and are the spherical coordinate offsets of the coordinate system O'-x'y'z' relative to the coordinate system O-xyz;

[0088] S203. Combine the field values of the direct and mirror paths to establish the total echo signal of the four propagation paths in the MISO system;

[0089] S204. In the MIMO system, the transmitting or receiving uses a common uniform concentric ring array. The total echo signal is the superposition of the contributions of each array element for transmission and reception. Establish the vortex radar echo in the MIMO system for each path. Assume that the backscattering coefficient of the target is σ, and denote J l (ka l sinθ) = J lθ , J l [ka l sin(θ + Δθ)] = J l(θ+Δθ) . In the MISO system, the receiving antenna is located at the center of the UCA. The vortex radar echoes E MISO(ABA) , E MISO(ACBA) , E MISO(ABCA) , E MISO(ACBCA) can be written as follows respectively:

[0090]

[0091] In the formula, l is the mode number, a l is the radius of the ring corresponding to the OAM wave of mode l sent by UCCA, N is the number of ring array elements corresponding to UCCA, Jl (ka l sinθ) = J lθ , J l [ka l sin(θ + Δθ)] = J l(θ+Δθ) , where J l (·) is the l-th order Bessel function of the first kind, where k is the wave number, r d is the distance from UCCA to the target, S(·) is the envelope of the chirp signal, τ r is the propagation delay of the mirror field, τ d is the propagation delay, Γ is the reflection coefficient of the smooth sea surface. Δr, Δθ and are the spherical coordinate offsets of the coordinate system O'-x'y'z' relative to the coordinate system O-xyz.

[0092] In the MIMO system, the transmitting antennas are simultaneously used as receiving antennas, and the receiving mode is the same as the transmitting mode. By summing up the received signals of each array element, the total echo signal can be obtained. Under the two-way action, the transmission and reception of the signal satisfy reciprocity. Therefore, the MIMO system vortex radar echoes under the four paths can be written as:

[0093]

[0094]

[0095] In the formula, l is the mode number, a l is the ring radius corresponding to the OAM wave of the l-th mode transmitted by UCCA, N is the number of ring array elements corresponding to UCCA, J l (ka l sinθ) = J lθ , J l [ka l sin(θ + Δθ)] = J l(θ+Δθ) , where J l (·) is the l-th order Bessel function of the first kind, where k is the wave number, r d is the distance from UCCA to the target, S(·) is the envelope of the chirp signal, τ r is the propagation delay of the mirror field, τ d is the propagation delay, Γ is the reflection coefficient of the smooth sea surface. Δr, Δθ and are the spherical coordinate offsets of the coordinate system O'-x'y'z' relative to the coordinate system O-xyz. So far, the multi-path vortex electromagnetic wave radar echo model of the MISO / MIMO system has been established in step S2.

[0096] S300. Perform time-domain sampling on the multipath vortex radar echo signals in each mode to obtain a row vector, and arrange the row vectors obtained by time-domain sampling in different modes in columns to form a two-dimensional radar echo matrix. For the MISO system, perform phase compensation preprocessing on the Bessel envelope to achieve focusing of the target azimuth.

[0097] It can be understood that in this step S300, it includes S301, S302, S303, and S304, where:

[0098] S301. Perform time-domain discrete sampling on the multipath vortex radar echo signals in each mode to obtain the corresponding row vector;

[0099] S302. Arrange the row vectors obtained by time-domain sampling in different modes in columns to construct a two-dimensional radar echo matrix, where different rows and different columns of the two-dimensional radar echo matrix respectively contain echo information of different modes;

[0100] S303. For the MISO system, perform phase compensation preprocessing on the Bessel envelope, and its calculation formula is as follows:

[0101]

[0102] In the formula, J lθ = J l (ka l sinθ), k is the wave number, l is the mode number, and a l is the ring radius corresponding to the OAM wave of the UCCA transmission mode l;

[0103] S304. Realize the decoupling of target azimuth and distance information through normalizing the Bessel function amplitude modulation.

[0104] It should be noted that based on the multipath vortex electromagnetic wave radar echo model derived from the above steps, UCCA receives the multimode vortex radar echoes from the target according to the MISO system and the MIMO system respectively. The specific sampling steps are: (1) Perform time-domain sampling on the multipath vortex radar echoes in each mode to obtain a row vector; (2) Arrange the row vectors obtained by time-domain sampling in different modes in columns to obtain a two-dimensional radar echo matrix. Different rows of this matrix contain echo information of different modes, which can be used for decoupling of target azimuth information, and different columns contain echo information of different times, which can be used for decoupling of target distance information. The structure of the radar echo matrix is as Figure 4 shown, where for the MISO system, it is necessary to perform phase compensation preprocessing on the Bessel envelope J lθ to achieve focusing on the target azimuth. By multiplying the MISO echo in mode l by the phase compensation function Φ comp(l) can achieve Bessel compensation in the MISO system, and then achieve focusing on the target azimuth. By comparing the multipath echo models under the two systems analyzed in the above steps, it can be found that the echo delay is only related to the echo path and has nothing to do with the radar system. However, there are significant differences between the azimuth-dimensional Fourier transform pairs and the Bessel envelope under the two systems.

[0105] S400. Analyze the obtained two-dimensional radar echo matrix and the echo of the MISO system after phase compensation using the azimuth-dimensional point spread function, and characterize the multipath echo characteristics under the MISO and MIMO systems. As the impulse response of the imaging system, the main lobe and sidelobe structures of the PSF can reflect the actual imaging results of the target. Analyze the imaging coordinate laws under the two systems, and obtain the dual-system imaging characteristics with the same real image coordinates and different virtual image coordinates. Among them, the defocus degree of the virtual image in the MISO system is twice that of the MIMO system.

[0106] It can be understood that in this step S400, it includes S401 and S402, where:

[0107] S401. Analyze the two-dimensional radar echo matrix using the azimuth-dimensional point spread function; S402. Through PSF analysis, characterize the multipath echo characteristics under the MISO and MIMO systems, including the main lobe and sidelobe structures. For the MISO system, after the phase compensation preprocessing for the direct echo path A - B - A, the calculation formula for the multipath azimuth-dimensional PSF is as follows:

[0108]

[0109] In the formula, J lθ = J l (ka l sinθ), a l is the ring radius corresponding to the OAM wave of the UCCA transmission mode l, θ is the elevation angle, Φ comp (l) is the phase compensation function, and l is the mode number;

[0110] Among them, the calculation formula for the multipath azimuth-dimensional PSF under the MIMO system is as follows:

[0111]

[0112] In the formula, J lθ = J l (ka l sinθ), a l is the ring radius corresponding to the OAM wave of the UCCA transmission mode l, θ is the elevation angle, l is the mode number, and Δθ is the spherical coordinate offset of the coordinate system O'-x'y'z' relative to the coordinate system O-xyz.

[0113] It should be noted that by analyzing the imaging coordinates under the two systems through PSF, the following rules are found:

[0114] (1) In the MISO system, the Bessel envelope Φ comp (l)J lθ under the A-B-A and A-B-C-A echo paths is always positive with the change of mode l, and its PSF has a spectral peak at 0°, which can achieve the focusing of the target azimuth; while the Bessel envelope Φ comp (l)J l(θ+Δθ) under the A-C-B-A and A-C-B-C-A echo paths alternates between positive and negative with the change of mode l, and its PSF has a spectral peak at which is , showing a defocusing phenomenon.

[0115] (2) In the MIMO system, the Bessel envelopes and under the A-B-A and A-C-B-C-A echo paths are always positive with the change of mode l, and its PSF has a spectral peak at 0°, which can achieve the focusing of the target azimuth; while the Bessel envelopes J lθ J l(θ+Δθ) under the A-C-B-A and A-B-C-A echo paths alternate between positive and negative with the change of mode l, and its PSF has a spectral peak at which is , showing a defocusing phenomenon, and the defocusing degree is exactly half of that in the MISO system. Furthermore, based on the fast Fourier transform and pulse compression for point target two-dimensional imaging, the imaging coordinates under the two systems are shown in Tables 1 and 2 as follows:

[0116] Table 1 Two-dimensional imaging coordinates - MISO result table

[0117]

[0118] Table 2 Two-dimensional imaging coordinates - MIMO result table

[0119]

[0120] S500. According to the imaging characteristics of the dual systems, the multi-path echo characteristics under the MISO and MIMO systems are respectively processed by modal domain FFT and time domain pulse compression using the fast Fourier transform and pulse compression, the imaging results of the two systems are generated, and the imaging results of the two systems are fused by Hadamard product imaging, and finally the synthetic radar image with virtual image suppression is output.

[0121] It can be understood that in this step, based on the conclusion that the real image coordinates are the same while the virtual image coordinates are different under the two imaging systems in step S400, the imaging results under the two systems can be obtained by processing the modal domain and time domain of the radar echo matrix using FFT and PC respectively. and The imaging processing process is as Figure 5 shown. And based on the imaging results obtained in the above steps and the imaging matrices under the two systems are subjected to Hadamard product imaging fusion according to the following formula to achieve virtual image suppression. The calculation formula is as follows:

[0122]

[0123] In this embodiment, the multi-path virtual image suppression of the vortex electromagnetic wave radar of the present invention is adopted, which specifically includes the following steps:

[0124] Step 1: Verify the correctness of the multi-path vortex radar echo model. The radar emits horizontally polarized waves, and the simulation parameters of the example are shown in Table 1.

[0125] Step 2: Construct the OAM echo signal model in the smooth sea surface scene of the two-line propagation model.

[0126] Step 3: The UCCA radar receives the multi-mode vortex radar echoes from the target according to the MISO system and the MLMO system respectively.

[0127] Step 4: The simulation results of the Bessel envelopes and PSF curves under the two systems are respectively as Figure 6 and Figure 7 shown.

[0128] It can be seen from Figure 6 that for the MISO system, under the echo paths A - B - A / A - B - C - A, its Bessel envelope is always positive, and the PSF shows a spectral peak at zero frequency, demonstrating the ability of focused imaging; under the echo paths A - C - B - A / A - C - B - C - A, its Bessel envelope oscillates around 0, and the PSF shows symmetric spectral peaks at ( is 72°), that is, the defocus phenomenon. Similarly, it can be seen from Figure 7 that for the MIMO system, under the echo paths A - B - A / A - C - B - C - A, its Bessel envelope is always positive and the PSF is focused at zero frequency; while under the echo paths A - C - B - A / A - B - C - A, its Bessel envelope also shows alternating positive and negative oscillations, and the PSF shows a defocus phenomenon at, and the defocus degree is exactly half of that of the MISO system, as shown in Table 3.

[0129] Table 3 Simulation parameter table of multi-path vortex two-dimensional imaging for a single target point

[0130]

[0131] Step 5. To more intuitively view the point target imaging results under each path, Figure 8 The multi-path imaging coordinates of Figure 8 and Table 4 show that under the two radar systems, the imaging coordinates of point targets on different paths fully conform to the conclusions in Table 1 and Table 2, verifying the correctness of the multi-path vortex electromagnetic wave radar echo model derived in this paper. From Figure 8 (e), it can be further seen that the real image positions of the imaging results under the two systems are exactly the same while the virtual image positions are different, verifying the feasibility of the multi-path virtual image suppression algorithm proposed in this paper;

[0132] Table 4 Results of multi-path vortex two-dimensional imaging coordinates of single target point

[0133]

[0134] Step 6. Use an aircraft model to simulate the imaging results under the two systems and the imaging results after multi-path virtual image suppression to verify the correctness of the multi-path virtual image suppression algorithm. The target is located within the main lobe of the radar and the radar emits horizontally polarized waves. Keep other simulation parameters unchanged except for the target parameters. The imaging results are as shown in Figure 9 . From Figure 9 (b) and Figure 9 (c), it can be seen that under the MISO and MIMO systems, the vortex imaging results contain a large number of virtual images generated by multi-path reflections, which is not conducive to target reconstruction. However, by comparing the imaging results under the two systems, it can be found that there are significant differences in the distribution of virtual images. Based on this, after performing dot product processing on the imaging results under the two systems, Figure 9 (d) has almost no virtual image interference, and the true image of the aircraft target is well reconstructed, verifying the effectiveness of the method proposed in this paper.

[0135] Embodiment 2:

[0136] This embodiment provides a multi-path virtual image suppression system for a vortex electromagnetic wave radar. The system includes:

[0137] An acquisition module 701: configured to acquire the prior information of the target elevation angle and the parameter configuration of the uniform concentric circular array, and adjust the circular ring radius corresponding to different modes in the uniform concentric circular array according to the prior information of the target elevation angle, so that the divergence angles of the OAM waves of each mode are aligned with the target elevation angle, thereby making the target fall within the main lobe of the uniform concentric circular array radar to obtain a radar transmission configuration with the main lobe aligned;

[0138] Establishment module 702: Based on the radar transmission configuration with main lobe alignment and the target elevation angle information, through a preset two-line propagation model, establish the OAM echo signal model in a smooth sea surface scenario, and obtain the multipath vortex electromagnetic wave radar echo signals in MISO and MIMO systems;

[0139] Arrangement module 703: Used to perform time-domain sampling on the multipath vortex radar echo signals in each mode to obtain row vectors, and arrange the row vectors obtained by time-domain sampling in different modes column by column to form a two-dimensional radar echo matrix. Among them, for the MISO system, perform phase compensation preprocessing on the Bessel envelope to achieve focusing in the target azimuth;

[0140] Analysis module 704: Used to analyze the obtained two-dimensional radar echo matrix and the MISO system echo after phase compensation by using the azimuth dimension point spread function, characterize the multipath echo characteristics in MISO and MIMO systems, and analyze the imaging coordinate rules in the two systems to obtain the dual-system imaging characteristics with the same real image coordinates and different virtual image coordinates, where the defocus degree of the virtual image in the MISO system is twice that of the MIMO system;

[0141] Processing module 705: Used to perform modal domain FFT and time-domain pulse compression processing on the multipath echo characteristics in MISO and MIMO systems respectively according to the dual-system imaging characteristics by using fast Fourier transform and pulse compression, generate the imaging results of the two systems, and perform Hadamard product imaging fusion on the imaging results of the two systems, and finally output the synthetic radar image with virtual image suppression.

[0142] Specifically, the acquisition module 701 includes:

[0143] Calculation unit: Used to obtain the target elevation angle information through an external sensor or preset conditions, and calculate the ring radius corresponding to each mode based on the target elevation angle information, which satisfies a linear relationship. The calculation formula is as follows:

[0144]

[0145] In the formula, k is the wave number, l is the mode number, and θ0 is the divergence angle of the multi-mode OAM wave of the uniform concentric ring array;

[0146] Adjustment unit: Used to adjust the ring radii of different modes in the uniform concentric circle array, so as to ensure that the divergence angle of the OAM wave of each mode m satisfies that the main lobe directions of the beams of all modes are aligned with the actual elevation angle of the target;

[0147] Determination unit: Used to optimize the structure of the uniform concentric ring array based on the Bessel function modulation effect, determine the number of ring array elements, and thus complete the configuration of the radar transmitting end.

[0148] Specifically, the establishing module 702 includes:

[0149] The first establishing unit: It is used to establish the field value expression of the direct path A - B in the three - dimensional rectangular coordinate system according to the uniform concentric circular array parameters of the radar emission configuration with the main lobe aligned, and its calculation formula is as follows;

[0150]

[0151] In the formula, k is the wave number, l is the mode number, r d is the distance from the UCCA to the target, a l is the circular ring radius corresponding to the OAM wave of the UCCA transmitting mode l, N is the number of circular ring array elements corresponding to the UCCA, θ is the elevation angle, J l (·) is the Bessel function of the first kind of order l, S(·) is the linear frequency - modulated signal envelope, τ d is the propagation delay;

[0152] The correlation unit: It is used to derive the field value expression of the mirror path A - C - B in the mirror coordinate system, and correlate the mirror elevation angle through coordinate transformation. Its calculation formula is as follows:

[0153]

[0154] In the formula, k is the wave number, l is the mode number, r d is the distance from the UCCA to the target, a l is the circular ring radius corresponding to the OAM wave of the UCCA transmitting mode l, N is the number of circular ring array elements corresponding to the UCCA, θ is the elevation angle, J l (·) is the Bessel function of the first kind of order l, S(·) is the linear frequency - modulated signal envelope, τ r is the propagation delay of the mirror field, Γ is the reflection coefficient of the smooth sea surface, Δr, Δθ and is the spherical coordinate offset of the coordinate system O'-x'y'z' relative to the coordinate system O-xyz;

[0155] The second establishing unit: It is used to combine the field values of the direct and mirror paths to establish the total echo signal of the four propagation paths in the MISO system;

[0156] The third establishing unit: It is used in the MIMO system to transmit or receive a common uniform concentric circular array, and the total echo signal is the superposition of the contributions of each array element's transceiver. It establishes the vortex radar echo of the MIMO system under the multi - path situation.

[0157] Specifically, the arranging module 703 includes:

[0158] The sampling unit: It is used to perform time - domain discretized sampling on the multi - path vortex radar echo signals in each mode to obtain the corresponding row vectors;

[0159] Building unit: used to arrange the row vectors obtained by time-domain sampling in different modes in columns to construct a two-dimensional radar echo matrix, where different rows and different columns of the two-dimensional radar echo matrix respectively contain echo information in different modes;

[0160] Preprocessing unit: for the MISO system, used to perform phase compensation preprocessing on the Bessel envelope, and its calculation formula is as follows:

[0161]

[0162] In the formula, J lθ = J l (ka l sinθ), k is the wave number, l is the number of modes, a l is the ring radius corresponding to the OAM wave of the UCCA transmission mode l;

[0163] Modulation unit: used to achieve decoupling of target azimuth and distance information by normalizing the Bessel function amplitude modulation.

[0164] Specifically, the analysis module 704 includes:

[0165] Analysis unit: used to analyze the two-dimensional radar echo matrix by using the azimuth dimension point spread function; through PSF analysis, characterize the multipath echo characteristics in MISO and MIMO systems, including the main lobe and sidelobe structures; for the MISO system, after performing phase compensation preprocessing on the direct echo path A-B-A, the calculation formula of its multipath azimuth dimension PSF is as follows:

[0166]

[0167] In the formula, J lθ = J l (ka l sinθ), a l is the ring radius corresponding to the OAM wave of the UCCA transmission mode l, θ is the pitch angle, Φ comp (l) is the phase compensation function, and l is the number of modes;

[0168] Among them, the calculation formula of the multipath azimuth dimension PSF in the MIMO system is as follows:

[0169]

[0170] In the formula J l θ = J l (ka l sinθ), a l$r_l$ is the radius of the ring corresponding to the OAM wave of mode $l$ sent by UCCA, $\theta$ is the elevation angle, $l$ is the mode number, and $\Delta\theta$ is the spherical coordinate offset of the coordinate system $O'-x'y'z'$ relative to the coordinate system $O-xyz$.

[0171] It should be noted that for the system in the above embodiments, the specific manners in which each module performs operations have been described in detail in the embodiments related to the method, and will not be elaborated here.

[0172] Embodiment 3:

[0173] Corresponding to the above method embodiment, in this embodiment, a device for suppressing multipath virtual images of a vortex electromagnetic wave radar is also provided. A device for suppressing multipath virtual images of a vortex electromagnetic wave radar described below can be correspondingly referred to the method for suppressing multipath virtual images of a vortex electromagnetic wave radar described above.

[0174] Figure 10 is a block diagram of a device 800 for suppressing multipath virtual images of a vortex electromagnetic wave radar shown according to an exemplary embodiment. As Figure 10 shown, the device 800 for suppressing multipath virtual images of a vortex electromagnetic wave radar includes: a processor 801 and a memory 802. The device 800 for suppressing multipath virtual images of a vortex electromagnetic wave radar further includes one or more of a multimedia component 803, an I / O interface 804, and a communication component 805.

[0175] Among them, the processor 801 is used to control the overall operation of the vortex electromagnetic wave radar multipath virtual image suppression device 800 to complete all or part of the steps in the above-mentioned vortex electromagnetic wave radar multipath virtual image suppression method. The memory 802 is used to store various types of data to support the operation of the vortex electromagnetic wave radar multipath virtual image suppression device 800. These data may include, for example, instructions for any application program or method operating on the vortex electromagnetic wave radar multipath virtual image suppression device 800, as well as application program-related data, such as contact data, sent and received messages, pictures, audio, video, and so on. The memory 802 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read-Only Memory (EPROM), Programmable Read-Only Memory (PROM), Read-Only Memory (ROM), magnetic memory, flash memory, magnetic disk or optical disk. The multimedia component 803 may include a screen and an audio component. Among them, the screen can be, for example, a touch screen, and the audio component is used to output and / or input audio signals. For example, the audio component may include a microphone for receiving external audio signals. The received audio signal can be further stored in the memory 802 or sent through the communication component 805. The audio component also includes at least one speaker for outputting audio signals. The I / O interface 804 provides an interface between the processor 801 and other interface modules, and the above-mentioned other interface modules can be a keyboard, a mouse or buttons, etc. These buttons can be virtual buttons or physical buttons. The communication component 805 is used for wired or wireless communication between the vortex electromagnetic wave radar multipath virtual image suppression device 800 and other devices. Wireless communication, such as Wi-Fi, Bluetooth, Near Field Communication (NFC), 2G, 3G or 4G, or a combination of one or more of them. Therefore, the corresponding communication component 805 may include: a Wi-Fi module, a Bluetooth module or an NFC module.

[0176] In an exemplary embodiment, the vortex electromagnetic wave radar multipath virtual image suppression device 800 may be implemented by one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), controllers, microcontrollers, microprocessors, or other electronic components, and is used to execute the above-mentioned vortex electromagnetic wave radar multipath virtual image suppression method.

[0177] In another exemplary embodiment, a computer-readable storage medium including program instructions is further provided. When the program instructions are executed by a processor, the steps of the above-mentioned vortex electromagnetic wave radar multipath virtual image suppression method are implemented. For example, the computer-readable storage medium may be the above-mentioned memory 802 including program instructions, and the above program instructions may be executed by the processor 801 of the vortex electromagnetic wave radar multipath virtual image suppression device 800 to complete the above-mentioned vortex electromagnetic wave radar multipath virtual image suppression method.

[0178] Embodiment 4:

[0179] Corresponding to the above method embodiment, in this embodiment, a readable storage medium is further provided. A readable storage medium described below and a vortex electromagnetic wave radar multipath virtual image suppression method described above can be mutually referred to.

[0180] A computer program is stored on the readable storage medium. When the computer program is executed by a processor, the steps of the vortex electromagnetic wave radar multipath virtual image suppression method in the above method embodiment are implemented.

[0181] The readable storage medium may specifically be a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disc, etc., which are various readable storage media that can store program codes.

[0182] In summary, the purpose of the present invention is to expand the existing radar multipath virtual image suppression method and provide an imaging fusion algorithm based on the Hadamard product to suppress the virtual image caused by the multipath effect. Different from other radar multipath virtual image suppression methods, which need to rely on the relative motion of the radar and the target to obtain the target Doppler information, the method of the present invention can achieve sub-wavelength level resolution of the target without the relative motion of the radar and the target, and provides a new solution for the effective detection of low-altitude targets. It cleverly utilizes the characteristics that the real image position of the imaging result is exactly the same but the virtual image position is different in the two systems of multiple transmission and single reception, and realizes the suppression of multipath virtual images.

[0183] The present invention analyzes the virtual image spatial domain offset characteristics and Bessel spectrum envelope differences under the direct echo path and the reflected echo path under the MISO / MIMO system, and performs Hadamard product fusion on the imaging results under the dual system to achieve the suppression of multipath virtual images. The simulation results show that compared with the OAM imaging results under a single system, the method proposed in this paper can effectively eliminate the interference of multipath virtual images on the imaging results and reconstruct the two-dimensional real image of the low-altitude target. In addition, compared with traditional synthetic aperture or inverse synthetic aperture radar, the advantage of this method is that it can achieve high-resolution imaging of the target without relying on the relative motion between the radar and the target, providing a new solution for the effective identification of low-altitude and low-speed targets.

[0184] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0185] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for suppressing multipath virtual images of a vortex electromagnetic wave radar, characterized in that, Including: Obtain the prior information of the target elevation angle and the parameter configuration of the uniform concentric circular array, and adjust the circular ring radius corresponding to different modes in the uniform concentric circular array according to the prior information of the target elevation angle, so that the divergence angles of the OAM waves of each mode are aligned with the target elevation angle, so that the target falls within the main lobe of the uniform concentric circular array radar, and obtain the radar transmission configuration with the main lobe aligned; Based on the radar transmission configuration with the main lobe aligned and the target elevation angle information, establish an OAM echo signal model in a smooth sea surface scenario through a preset two-line propagation model, and obtain the multi-path vortex electromagnetic wave radar echo signals in MISO and MIMO systems; Perform time-domain sampling on the multi-path vortex radar echo signals in each mode to obtain row vectors, and arrange the row vectors obtained by time-domain sampling in different modes in columns to form a two-dimensional radar echo matrix. Among them, for the MISO system, perform phase compensation preprocessing on the Bessel envelope to achieve focusing of the target azimuth; Use the azimuth dimension point spread function to analyze the obtained two-dimensional radar echo matrix and the echo of the MISO system after phase compensation, characterize the multi-path echo characteristics in MISO and MIMO systems, and analyze the imaging coordinate rules in the two systems to obtain the dual-system imaging characteristics with the same real image coordinates and different virtual image coordinates, where the defocus degree of the virtual image in the MISO system is twice that of the MIMO system; According to the dual-system imaging characteristics, use the fast Fourier transform and pulse compression to perform modal domain FFT and time-domain pulse compression processing on the multi-path echo characteristics in MISO and MIMO systems respectively, generate the imaging results of the two systems, and perform Hadamard product imaging fusion on the imaging results of the two systems, and finally output the synthetic radar image with virtual image suppression.

2. The method for suppressing multipath virtual images of a vortex electromagnetic wave radar according to claim 1, wherein, The obtaining of the prior information of the target elevation angle and the parameter configuration of the uniform concentric circular array, and adjusting the circular ring radius corresponding to different modes in the uniform concentric circular array according to the prior information of the target elevation angle, so that the divergence angles of the OAM waves of each mode are aligned with the target elevation angle, so that the target falls within the main lobe of the uniform concentric circular array radar, and obtain the radar transmission configuration with the main lobe aligned, which includes: Obtain the elevation angle information of the target through an external sensor or a preset condition, and calculate the circular ring radius corresponding to each mode based on the elevation angle information of the target, which satisfies a linear relationship. The calculation formula is as follows: In the formula, k is the wave number, l is the mode number, and θ0 is the divergence angle of the multi-mode OAM wave of the uniform concentric circular array; Adjust the circular ring radius of different modes in the uniform concentric circular array, so as to ensure that the divergence angle of the OAM wave of each mode m satisfies that the main lobe directions of all modes are aligned with the actual elevation angle of the target; Optimize the structure of the uniform concentric circular array based on the Bessel function modulation effect, determine the number of circular array elements, and thus complete the configuration of the radar transmitter.

3. The method for suppressing multipath virtual images of a vortex electromagnetic wave radar according to claim 1, characterized in that The establishing of the OAM echo signal model in a smooth sea surface scenario based on the radar transmission configuration with the main lobe aligned and the target elevation angle information through a preset two-line propagation model, and obtaining the multi-path vortex electromagnetic wave radar echo signals in MISO and MIMO systems, which includes: According to the parameters of the uniform concentric circular array for the radar transmission configuration with main lobe alignment, establish the field value expression of the direct path A - B in the three - dimensional rectangular coordinate system, and its calculation formula is as follows; where k is the wave number, l is the mode number, and r d is the distance from the UCCA to the target, a l is the radius of the ring corresponding to the OAM wave of mode l sent by the UCCA, N is the number of ring array elements corresponding to the UCCA, θ is the elevation angle, J l (·) is the Bessel function of the first kind of order l, S(·) is the envelope of the chirp signal, and τ d is the propagation delay; Derive the field value expression of the mirror path A - C - B in the mirror coordinate system, and relate the mirror elevation angle through coordinate transformation. Its calculation formula is as follows: where k is the wave number, l is the mode number, r d is the distance from the UCCA to the target, a l is the radius of the ring corresponding to the OAM wave of mode l transmitted by the UCCA, N is the number of ring array elements corresponding to the UCCA, θ is the elevation angle, J l (·) is the Bessel function of the first kind of order l, S(·) is the envelope of the chirp signal, τ r is the propagation time delay of the mirror image field, Γ is the reflection coefficient of the smooth sea surface, Δr, Δθ and are the spherical coordinate offsets of the coordinate system O'-x'y'z' relative to the coordinate system O-xyz; Combine the field values of the direct and mirror paths to establish the total echo signal of the four propagation paths in the MISO system; In the MIMO system, the transmitting or receiving shares the uniform concentric circular array. The total echo signal is the superposition of the contributions of each array element for transmission and reception, and establish the echo of the vortex radar in the MIMO system for each path.

4. The method for suppressing multipath virtual images of a vortex electromagnetic wave radar according to claim 1, characterized in that Perform time - domain sampling on the multi - path vortex radar echo signal for each mode to obtain a row vector, and arrange the row vectors obtained by time - domain sampling in different modes in columns to form a two - dimensional radar echo matrix, which includes: Perform time - domain discretized sampling on the multi - path vortex radar echo signal for each mode to obtain the corresponding row vector; Arrange the row vectors obtained by time - domain sampling in different modes in columns to construct a two - dimensional radar echo matrix, where different rows and different columns of the two - dimensional radar echo matrix contain echo information of different modes respectively; For the MISO system, perform phase compensation pre - processing on the Bessel envelope, and its calculation formula is as follows: where J lθ = J l (ka l sinθ), k is the wave number, l is the mode number, and a l is the radius of the ring corresponding to the OAM wave of the UCCA transmitting mode l; Realize the decoupling of target azimuth and range information by normalizing the amplitude modulation of the Bessel function.

5. The method for suppressing multipath virtual images of a vortex electromagnetic wave radar according to claim 1, wherein Use the azimuth - dimension point spread function to analyze the obtained two - dimensional radar echo matrix and the echo of the MISO system after phase compensation, and characterize the multi - path echo characteristics in the MISO and MIMO systems, which includes: Use the azimuth - dimension point spread function to analyze the two - dimensional radar echo matrix; through PSF analysis, characterize the multi - path echo characteristics in the MISO and MIMO systems, including the main lobe and sidelobe structures; for the MISO system, after performing phase compensation pre - processing on the direct echo path A - B - A, the calculation formula of its multi - path azimuth - dimension PSF is as follows: where J lθ = J l (ka l sinθ), a l is the radius of the ring corresponding to the OAM wave of the UCCA transmission mode l, θ is the elevation angle, Φ comp (l) is the phase compensation function, and l is the mode number; Among them, the calculation formula of the multi - path azimuth - dimension PSF in the MIMO system is as follows: where J l θ = J l (ka l sinθ), a l is the radius of the ring corresponding to the OAM wave of the UCCA transmission mode l, θ is the elevation angle, l is the mode number, and Δθ is the spherical coordinate offset of the coordinate system O'-x'y'z' relative to the coordinate system O-xyz.

6. A vortex electromagnetic wave radar multipath virtual image suppression system, based on the vortex electromagnetic wave radar multipath virtual image suppression method described in claim 1, characterized in that, Include: Acquisition module: used to acquire the prior information of the target elevation angle and the parameter configuration of the uniform concentric circular array, and adjust the circular ring radius corresponding to different modes in the uniform concentric circular array according to the prior information of the target elevation angle, so that the divergence angle of the OAM wave of each mode is aligned with the target elevation angle, so that the target falls within the main lobe of the uniform concentric circular array radar, and obtain the radar transmission configuration with main lobe alignment; Establishment module: used to establish the OAM echo signal model in the smooth sea surface scenario based on the radar transmission configuration with main lobe alignment and the target elevation angle information through a preset two - line propagation model, and obtain the multi - path vortex electromagnetic wave radar echo signals in the MISO and MIMO systems; Arrangement module: used to perform time - domain sampling on the multi - path vortex radar echo signal for each mode to obtain a row vector, and arrange the row vectors obtained by time - domain sampling in different modes in columns to form a two - dimensional radar echo matrix. For the MISO system, perform phase compensation pre - processing on the Bessel envelope to achieve the focusing of the target azimuth; Analysis module: It is used to analyze the obtained two-dimensional radar echo matrix and the echo of the MISO system after phase compensation by using the azimuth-dimensional point spread function, characterize the multipath echo characteristics under the MISO and MIMO systems, analyze the imaging coordinate rules under the two systems, and obtain the dual-system imaging characteristics with the same real image coordinates and different virtual image coordinates. Among them, the defocus degree of the virtual image of the MISO system is twice that of the MIMO system; Processing module: It is used to perform modal-domain FFT and time-domain pulse compression processing on the multipath echo characteristics under the MISO and MIMO systems respectively by using fast Fourier transform and pulse compression according to the dual-system imaging characteristics, generate the imaging results of the two systems, and perform Hadamard product imaging fusion on the imaging results of the two systems, and finally output the synthetic radar image with virtual image suppression.

7. The vortex electromagnetic wave radar multipath virtual image suppression system according to claim 6, characterized in that The acquisition module, which includes: Calculation unit: It is used to obtain the pitch angle information of the target through an external sensor or preset conditions, and calculate the ring radius corresponding to each mode based on the pitch angle information of the target, which satisfies a linear relationship. The calculation formula is as follows: In the formula, k is the wave number, l is the mode number, and θ0 is the divergence angle of the multimode OAM wave of the uniform concentric ring array; Adjustment unit: It is used to adjust the ring radius of different modes in the uniform concentric circle array, so as to ensure that the divergence angle of the OAM wave of each mode m satisfies that the main lobe directions of the beams of all modes are aligned with the actual pitch angle of the target; Determination unit: It is used to optimize the structure of the uniform concentric ring array based on the Bessel function modulation effect, determine the number of ring array elements, and thus complete the configuration of the radar transmitting end.

8. The vortex electromagnetic wave radar multipath virtual image suppression system according to claim 6, wherein, The establishment module, which includes: The first establishment unit: It is used to establish the field value expression of the direct path A-B in the three-dimensional rectangular coordinate system according to the parameters of the uniform concentric ring array with the main lobe aligned radar transmitting configuration. The calculation formula is as follows; where k is the wave number, l is the mode number, r d is the distance from the UCCA to the target, a l is the radius of the ring corresponding to the OAM wave of mode l sent by the UCCA, N is the number of ring array elements corresponding to the UCCA, θ is the elevation angle, J l (·) is the Bessel function of the first kind of order l, S(·) is the envelope of the chirp signal, τ d is the propagation delay; Correlation unit: It is used to deduce the field value expression of the mirror path A-C-B in the mirror coordinate system, and correlate the mirror pitch angle through coordinate transformation. The calculation formula is as follows: where k is the wave number, l is the mode number, and r d is the distance from the UCCA to the target, a l is the radius of the ring corresponding to the OAM wave of mode l transmitted by the UCCA, N is the number of ring array elements corresponding to the UCCA, θ is the elevation angle, J l (·) is the Bessel function of the first kind of order l, S(·) is the envelope of the chirp signal, τ r is the propagation delay of the mirror image field, Γ is the reflection coefficient of the smooth sea surface, Δr, Δθ, and are the spherical coordinate offsets of the coordinate system O'-x'y'z' relative to the coordinate system O-xyz; The second establishment unit: It is used to combine the field values of the direct and mirror paths to establish the total echo signal of the four propagation paths under the MISO system; The third establishment unit: It is used to transmit or receive a common uniform concentric ring array under the MIMO system. The total echo signal is the superposition of the contributions of each array element's transceiver, and establish the vortex radar echo of the MIMO system under the path.

9. The vortex electromagnetic wave radar multipath virtual image suppression system according to claim 6, characterized in that The arrangement module, which includes: Sampling unit: It is used to perform time-domain discretized sampling on the multipath vortex radar echo signal under each mode to obtain the corresponding row vector; Construction unit: It is used to arrange the row vectors obtained by time-domain sampling under different modes in columns to construct a two-dimensional radar echo matrix, where different rows and different columns of the two-dimensional radar echo matrix contain echo information of different modes; Preprocessing unit: For the MISO system, it is used to perform phase compensation preprocessing on the Bessel envelope. The calculation formula is as follows: where J lθ = J l (ka l sinθ), k is the wave number, l is the mode number, a l is the radius of the ring corresponding to the OAM wave of the UCCA sending mode l; Modulation unit: It is used to realize the decoupling of the target azimuth and range information by normalizing the Bessel function amplitude modulation.

10. The vortex electromagnetic wave radar multipath virtual image suppression system according to claim 6, characterized in that The analysis module, which includes: Analysis unit: used to analyze the two-dimensional radar echo matrix by using the azimuth dimension point spread function; through PSF analysis, characterize the multipath echo characteristics in MISO and MIMO systems, including the main lobe and sidelobe structures; for the MISO system, after performing phase compensation preprocessing on the direct echo path A-B-A, the calculation formula for its multipath azimuth dimension PSF is as follows: Where J lθ = J l (ka l sinθ), a l is the radius of the ring corresponding to the OAM wave of the UCCA transmission mode l, θ is the pitch angle, Φ comp (l) is the phase compensation function, and l is the mode number; Among them, the calculation formula for the multipath azimuth dimension PSF in the MIMO system is as follows: where J lθ = J l (ka l sinθ), a l is the radius of the ring corresponding to the OAM wave of the UCCA transmission mode l, θ is the elevation angle, l is the mode number, and Δθ is the spherical coordinate offset of the coordinate system O'-x'y'z' relative to the coordinate system O-xyz.

Images