Single-pulse electromagnetic vortex imaging method, device and equipment based on frequency diversity

Abstract

The present invention relates to a single-pulse electromagnetic vortex imaging method, device, and apparatus based on frequency diversity. The method comprises: performing filtering matching and incoherent accumulation on the acquired first echo signal to obtain a one-dimensional range image; gridding the imaging range area to obtain a plurality of range units, and then generating a cancellation reference signal corresponding to each range unit; calculating a second echo signal based on the cancellation reference signal and the first echo signal; downsampling the second echo signal based on the orbital angular momentum modal interval, and then compensating the Bessel term and the residual phase term to obtain data for each range unit; performing azimuth imaging based on the data for each range unit to obtain a two-dimensional coarse image corresponding to the range unit; and performing power constraints on each range unit of the two-dimensional coarse image using the one-dimensional range image to obtain a two-dimensional image of the imaging area. The present invention can support rapid imaging under multi-modality.

Description

Technical Field

[0001] The present invention relates to the technical field of radar signal processing, and in particular to a single-pulse electromagnetic vortex imaging method, device and equipment based on frequency diversity. Background Art

[0002] Because the echo phase contains orbital angular momentum (OAM) modes and azimuthally coupled Fourier pairs, electromagnetic vortex waves (EMVs) carrying OAM introduce a new degree of freedom for radar detection. EMV-based radar imaging technology not only enables standalone forward-looking imaging but is also compatible with traditional radar imaging systems (such as inverse synthetic aperture radar (ISAR), synthetic aperture radar (SAR), and bistatic SAR), thereby improving the performance of traditional radar imaging methods. This technology can obtain two-dimensional or three-dimensional structural features and size information of targets in forward-looking scenes (such as ships and aircraft).

[0003] However, existing EMV generation methods have significant limitations. Typically, EMV generation relies on step-by-step phase modulation of the elements in a uniform circular array (UCA), but this method can only generate one specific OAM mode at a time. Radar imaging applications require OAM beams to transmit multiple OAM modes in a short period of time, requiring faster switching of OAM modes to avoid potential azimuth image migration. Traditional step-by-step phase modulation methods struggle to meet this requirement.

[0004] Current OAM mode switching methods primarily include positive and negative dual-mode coupled OAM beams and waveform diversity multiplexing of OAM modes. However, while positive and negative dual-mode coupled OAM beams can cut switching time in half, they still require significant transmission time when there are a large number of modes. Waveform diversity, on the other hand, requires finding multiple sets of orthogonal phase-coding sequences for each OAM mode to isolate high-purity OAM modes, which is extremely challenging in practice. Therefore, existing methods still face significant difficulties in efficiently transmitting multimodal vortex electromagnetic waves. Summary of the Invention

[0005] Based on this, it is necessary to provide a single-pulse electromagnetic vortex imaging method, device and equipment based on frequency diversity that can support rapid imaging in multi-modality to address the above technical problems.

[0006] A single-pulse electromagnetic vortex imaging method based on frequency diversity, the method comprising:

[0007] Generate electromagnetic vortex waves for transmission based on frequency diversity to obtain first echo signals of multiple targets located on a cone surface with the same pitch angle;

[0008] performing multi-matched filtering on the first echo signal to obtain a multi-matched filtering output signal; performing incoherent accumulation on the multi-matched filtering output signal to obtain a one-dimensional range image;

[0009] Determine an imaging distance area, divide the imaging distance area into a grid to obtain a plurality of distance units, and then generate a cancellation reference signal corresponding to each of the distance units;

[0010] Calculating based on the cancellation reference signal and the first echo signal to obtain a second echo signal corresponding to the distance unit;

[0011] setting an orbital angular momentum modal interval, downsampling the second echo signal according to the orbital angular momentum modal interval, calculating a compensation function, and performing Bessel term and residual phase term compensation on the orbital angular momentum mode using the compensation function to obtain data for each range unit;

[0012] Perform azimuth imaging based on the data of each range unit to obtain a two-dimensional coarse image corresponding to the range unit;

[0013] Power constraints are performed on each range unit of the two-dimensional coarse image using the one-dimensional range image to obtain a two-dimensional image of the imaging area.

[0014] A single-pulse electromagnetic vortex imaging device based on frequency diversity, comprising:

[0015] A first echo signal acquisition module is used to generate electromagnetic vortex waves for transmission based on frequency diversity, and acquire first echo signals of multiple targets located on a cone surface with the same pitch angle;

[0016] a one-dimensional range image acquisition module, configured to perform multi-matched filtering on the first echo signal to obtain a multi-matched filtering output signal; and perform incoherent accumulation on the multi-matched filtering output signal to obtain a one-dimensional range image;

[0017] a cancellation reference signal calculation module, configured to determine an imaging distance region, divide the imaging distance region into a grid to obtain a plurality of distance units, and then generate a cancellation reference signal corresponding to each of the distance units;

[0018] a second echo signal acquisition module, configured to perform calculations based on the cancellation reference signal and the first echo signal to obtain a second echo signal corresponding to the distance unit;

[0019] a two-dimensional matrix reconstruction module, configured to set an orbital angular momentum modal interval, downsample the second echo signal according to the orbital angular momentum modal interval, calculate a compensation function, and perform Bessel term and residual phase term compensation on the orbital angular momentum mode using the compensation function to obtain data for each range unit;

[0020] A two-dimensional coarse image construction module is used to perform azimuth imaging based on the data of each range unit to obtain a two-dimensional coarse image corresponding to the range unit;

[0021] The two-dimensional image construction module is used to perform power constraints on each distance unit of the two-dimensional coarse image through the one-dimensional range image to obtain a two-dimensional image of the imaging area.

[0022] A computer device comprises a memory and a processor, wherein the memory stores a computer program and the processor implements the steps of a single-pulse electromagnetic vortex imaging method based on frequency diversity when executing the computer program.

[0023] The above-mentioned single-pulse electromagnetic vortex imaging method, device and equipment based on frequency diversity. Generate electromagnetic vortex waves for transmission based on frequency diversity, obtain first echo signals of multiple targets located on a cone surface with the same pitch angle; perform multi-matched filtering on the first echo signals to obtain multi-matched filter output signals; perform incoherent accumulation on the multi-matched filter output signals to obtain a one-dimensional range image; determine the imaging range area, grid the imaging range area to obtain a number of range units, and then generate a cancellation reference signal corresponding to each range unit; calculate based on the cancellation reference signal and the first echo signal to obtain a second echo signal corresponding to the range unit; set the orbital angular momentum modal interval, downsample the second echo signal based on the orbital angular momentum modal interval, calculate the compensation function, and compensate the orbital angular momentum mode for Bessel terms and residual phase terms using the compensation function to obtain data for each range unit; perform azimuth imaging based on the data of each range unit to obtain a two-dimensional coarse image corresponding to the range unit; and perform power constraints on each range unit of the two-dimensional coarse image using the one-dimensional range image to obtain a two-dimensional image of the imaging area.

[0024] The present invention uses a frequency-diversified uniform circular array to generate an orbital angular momentum multiplexing beam, achieving traversal of all modes within a single pulse, capable of rapidly generating multimodal electromagnetic vortex waves. By emitting electromagnetic vortex waves, a first echo signal is obtained. The first echo signal is then processed in two parts: on the one hand, multiple matched filtering and incoherent accumulation are performed on the first echo signal to obtain a one-dimensional range image; on the other hand, the first echo signal is compensated using a reference signal for cancellation, and the second echo signal is compensated for Bessel terms and residual phase terms using a compensation function to obtain data for each range unit. Azimuth imaging is then performed using the data for each range unit to obtain a two-dimensional coarse image corresponding to the range unit; and then, combined with the one-dimensional range image, a two-dimensional image of the target is synthesized. Through such processing, the decoupled azimuth and range information in the echo signal can be obtained using only a single pulse echo data. By compensating and shifting the single pulse echo data, a two-dimensional electromagnetic vortex imaging result of the forward-looking scene is obtained, thereby improving orbital angular momentum multiplexing efficiency and imaging speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0026] Figure 1 1 is a flow chart of a single-pulse electromagnetic vortex imaging method based on frequency diversity in one embodiment;

[0027] Figure 2 Schematic diagram of an apparatus for generating an orbital angular momentum (OAM) modal multiplexing electromagnetic vortex wave (EMV) beam based on frequency in one embodiment;

[0028] Figure 3 Schematic diagram of imaging results of a single point target using electromagnetic vortex waves (EMV) generated by a conventional method in one embodiment;

[0029] Figure 4 Schematic diagram of imaging results of a single point target using electromagnetic vortex waves (EMV) generated by the method of the present invention in one embodiment;

[0030] Figure 5 A schematic diagram showing a comparison between the method of the present invention and a conventional method on an azimuthal image cross section in one embodiment;

[0031] Figure 6 A schematic diagram of imaging results of multiple point targets using a Fourier transform method using a conventional method to generate electromagnetic vortex waves (EMV) in one embodiment;

[0032] Figure 7 Schematic diagram of imaging results of multiple point targets using Fourier transform method using electromagnetic vortex waves (EMV) generated by the method of the present invention in one embodiment;

[0033] Figure 8 A schematic diagram of imaging results of multiple point targets using a sparse Bayesian imaging algorithm using a conventional method to generate electromagnetic vortex waves (EMV) in one embodiment;

[0034] Figure 9 A schematic diagram of imaging results of multiple point targets generated by the method of the present invention using a sparse Bayesian imaging algorithm in one embodiment;

[0035] Figure 10 1 is a structural block diagram of a single-pulse electromagnetic vortex imaging device based on frequency diversity in one embodiment;

[0036] Figure 11 FIG. 1 is a diagram showing the internal structure of a computer device in one embodiment.

[0037] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0039] It should be noted that the terms "first," "second," and so on, used in this disclosure are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features being referred to. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of this disclosure, "plurality" means at least two, such as two or three, unless otherwise specifically defined.

[0040] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0041] The following describes the embodiments of the present invention in detail with reference to the accompanying drawings.

[0042] Example 1

[0043] This embodiment discloses a single-pulse electromagnetic vortex imaging method based on frequency diversity. It uses a frequency-diversity uniform circular array to generate an orbital angular momentum multiplexing beam, achieves traversal of all modes within a single pulse, can quickly generate multi-modal electromagnetic vortex waves, and obtains a first echo signal by transmitting the electromagnetic vortex wave; then the first echo signal is processed in two parts: on the one hand, the first echo signal is subjected to multi-matched filtering and incoherent accumulation to obtain a one-dimensional range image; on the other hand, the first echo signal is compensated using a cancellation reference signal, and the second echo signal is compensated for Bessel terms and residual phase terms using a compensation function to obtain data for each range unit; then, azimuth imaging is performed using the data for each range unit to obtain a two-dimensional coarse image corresponding to the range unit; and then, a two-dimensional image of the target is synthesized by combining the one-dimensional range image. Through such processing, it is possible to obtain the decoupled azimuth and range information in the echo signal using only a single pulse echo data. By compensating and shifting the single pulse echo data, a two-dimensional electromagnetic vortex imaging result of the forward-looking scene is obtained, thereby improving the efficiency of orbital angular momentum multiplexing and imaging speed. The problem of how to achieve fast and high-purity mode switching and separation of multi-mode electromagnetic vortex waves while ensuring high transmission efficiency is solved.

[0044] like Figure 1 As shown, a single-pulse electromagnetic vortex imaging method based on frequency diversity is provided, comprising the following steps:

[0045] Step 201 : Generate electromagnetic vortex waves for transmission according to frequency diversity, and obtain first echo signals of multiple targets located on a cone surface with the same pitch angle.

[0046] As can be understood, using a frequency-diverse uniform circular array (UC-FDA) to generate electromagnetic vortex waves (EMVs) that reuse orbital angular momentum (OAM) enables traversal of all OAM modes within a single pulse, allowing each pulse to simultaneously carry information from multiple OAM modes, significantly improving data transmission efficiency and reducing data transmission time. Furthermore, traversal of all OAM modes within a single pulse eliminates the need to switch modes between multiple pulses, significantly reducing mode switching time.

[0047] When the radar antenna's beam is pointed at a specific elevation angle, multiple targets may be distributed within the equiangular cone formed by the radar beam at that angle. These targets may be within the same elevation range but at different azimuths or distances. Therefore, the first echo signal received by the radar may be a composite reflection signal from these targets, requiring processing of the first echo signal to effectively distinguish these targets.

[0048] Step 202: Perform multi-matched filtering on the first echo signal to obtain a multi-matched filtering output signal; perform incoherent accumulation on the multi-matched filtering output signal to obtain a one-dimensional range image.

[0049] As you can understand, multi-matched filtering involves applying multiple matched filters to an echo signal to improve the ability to detect echo signals with different characteristics. This allows the radar to extract target information from different angles or conditions, thereby better identifying and classifying targets. Incoherent accumulation accumulates the amplitudes of the output signals from multiple matched filters to increase the total signal energy and improve the detection signal-to-noise ratio. By applying multi-matched filtering and incoherent accumulation to the first echo signal, the resulting one-dimensional range profile clearly reflects the distribution of each target's echo intensity along the range direction.

[0050] Step 203 : determining an imaging distance region, dividing the imaging distance region into grids to obtain a number of distance units, and then generating a cancellation reference signal corresponding to each distance unit.

[0051] Step 204 : Calculate based on the cancellation reference signal and the first echo signal to obtain a second echo signal corresponding to the range unit.

[0052] It can be understood that determining the imaging range area is to lock onto the specific range where the target is located, thereby focusing on the critical area, avoiding data processing in irrelevant areas, and improving processing efficiency and imaging quality. Gridding the imaging range area can more accurately determine the specific location of the target and provide a precise location distribution of the target. Then, by generating a corresponding offset reference signal for each distance unit, possible interference in the first echo signal is eliminated, helping to correct errors that may occur during the imaging process and obtain a second echo signal. By offsetting the reference signal to eliminate background signals, the true target signal can be more clearly distinguished, improving the accuracy of target detection and identification; it can also make the final radar image have higher resolution and contrast.

[0053] Step 205 , setting the orbital angular momentum modal interval, down-sampling the second echo signal according to the orbital angular momentum modal interval, calculating a compensation function, and performing Bessel term and residual phase term compensation on the orbital angular momentum mode using the compensation function to obtain data for each range unit.

[0054] It's understood that in orbital angular momentum modes, electromagnetic vortex waves have spiral wavefronts. As propagation distance increases, these wavefronts may become distorted due to medium inhomogeneities or other factors. By setting the orbital angular momentum modal spacing, each OAM mode can maintain sufficient orthogonality during transmission or imaging, reducing interference between the modes and ensuring accurate signal demodulation and processing.

[0055] The second echo signal is downsampled according to the orbital angular momentum modal interval, and a compensation function is calculated. The Bessel term and the residual phase term of the orbital angular momentum mode are compensated by the compensation function, which can correct the wavefront distortion and the distortion of each mode during the propagation process, ensure that the orbital angular momentum mode in the second echo signal maintains its characteristics, avoid information loss or distortion, and eliminate modal mismatch and interference.

[0056] Step 206 : Perform azimuth imaging based on the data of each range unit to obtain a two-dimensional coarse image corresponding to the range unit.

[0057] It can be understood that the data of each distance unit is stretched into a two-dimensional matrix, and then a two-dimensional coarse image is obtained through azimuth image transformation. Azimuth imaging is a process used to process the echo signal of the target in the azimuth direction to generate an image of the target in that direction. By simultaneously processing the azimuth images of all distance units in the imaging distance area, a two-dimensional coarse image can be obtained. The obtained two-dimensional coarse image can quickly display the approximate position and distribution of the target, can quickly detect whether the target exists, and estimate the azimuth and distance of the target. Moreover, by first generating a two-dimensional coarse image, the area of ​​interest can be quickly screened and identified, reducing the computational burden of subsequent fine imaging. In addition, since noise and clutter usually behave inconsistently in different distance units, by comparing the echo data of different distance units, the two-dimensional coarse image can display a more consistent signal, thereby helping to identify and filter out some obvious noise and clutter signals.

[0058] Step 207 : Power constraint is performed on each range unit of the two-dimensional coarse image using the one-dimensional range image to obtain a two-dimensional image of the imaging area.

[0059] It can be understood that a one-dimensional range profile reflects the echo intensity distribution of each target in the range dimension. By applying power constraints to each range cell in the two-dimensional coarse image using the one-dimensional range profile, we can reduce target positioning errors caused by noise and scatterers, improving the accuracy of the target in the image. It can also effectively suppress irrelevant signals, improving imaging quality, and significantly improving radar imaging and target detection accuracy, especially in complex scenes and low signal-to-noise ratio environments.

[0060] In the specific implementation process of step 201, see Figure 2 , construct a uniform circular array based on the number of array elements N and radius a, and design the pulse width T based on the frequency offset Δf between array elements p So that Δf = 1 / T p . Emit electromagnetic vortex waves, and then use random phase encoding waveform The echo signal of the target P located at (r, θ, φ) can be obtained, and the expression is:

[0061]

[0062] Where l(t′) represents the orbital angular momentum mode, which is a function that evolves with time and is expressed as l(t′) = NΔf(t′), where t′ = t-2r / c represents the intra-pulse time, and k0 represents the wave number corresponding to the signal center frequency f0. Within a pulse width, the mode it transmits can just traverse

[0063] When the radar antenna beam points to a certain elevation angle, multiple targets may be distributed on the equiangular cone formed by the radar beam at that angle. For the first echo signal of the cone with multiple targets located at the same elevation angle θ0, the expression is:

[0064]

[0065] Where, (r q ,θ0,φ q ) represents the position of the qth target, σ q (r q ,θ0,φ q ) represents the scattering coefficient of the qth target; Q = 1, 2, 3…, q represents the target number; θ0 represents the pitch angle; represents the random phase-coded echo waveform obtained by delaying the distance unit where the qth target is located; N represents the number of array elements; l(t′ q ) represents the orbital angular momentum mode of the qth target; represents the additional phase term generated by the electromagnetic vortex; represents the Bessel amplitude term; k0 represents the wave number corresponding to the signal center frequency f0; a represents the radius of the uniform circular array.

[0066] In the specific implementation process of step 202, the first echo signal is subjected to multi-matched filtering processing, that is, a corresponding matched filter is designed for each frequency offset, and pulse compression is performed on the transmitted signal waveform to obtain corresponding matched filter output signals, respectively, which are expressed as follows:

[0067]

[0068] Where s rm (t) represents the first echo signal; e -j2πmΔft represents the multi-matched filter corresponding to each frequency offset design, where m = 0, 1, 2, ..., N-1; represents the conjugate of the transmitted waveform; Represents a convolution operation.

[0069] Then, the multi-matched filter output signals are non-coherently accumulated. In this embodiment, envelope addition is performed to obtain a one-dimensional range image, which is expressed as:

[0070]

[0071] Where y m (t) represents the multi-matched filter output signal.

[0072] In the specific implementation process of step 203, the imaging distance area [R min ,R max ], set the distance grid length Δr according to the requirements, and use the distance grid length Δr to analyze the imaging distance area [R min ,R max ] to divide the grid and get N r distance units Match it with the range resolution, and then generate the corresponding offset reference signal for each range unit. The expression is:

[0073]

[0074] Where, t b ′ represents the intra-pulse time of the corresponding b-th distance unit, which is expressed as t b ′=t-2r b / c, where t represents real time, r b represents the distance unit and c represents the speed of light; represents the conjugate of the transmitted waveform delayed by b range units.

[0075] In the specific implementation process of step 204, the corresponding distance unit r is obtained by calculating based on the offset reference signal and the first echo signal. b The second echo signal is expressed as:

[0076]

[0077] Due to the orthogonality of the phase coded signal, for the b The output will be 0, and only the echo information of this distance unit will be retained.

[0078] During the specific implementation of step 205, the orbital angular momentum modal interval Δl is set according to the intra-pulse time and the orbital angular momentum modal variation law, the second echo signal is downsampled according to the orbital angular momentum modal interval Δl, and a compensation function is calculated. The orbital angular momentum mode is compensated for Bessel terms and residual phase terms using the compensation function to obtain data for each range unit.

[0079] The expression of the compensation function is:

[0080]

[0081] Where, represents the phase term that needs to be compensated; Represents the Bessel magnitude term for the b-th distance unit.

[0082] In the specific implementation process of step 206, after compensation, the power spectrum estimation or sparse reconstruction method can be used to perform azimuth imaging to obtain a two-dimensional coarse image. The power spectrum estimation is specifically:

[0083] According to the data of each distance unit, the azimuth image corresponding to each distance unit is directly obtained by performing Fourier transform on the data of each distance unit. The expression is:

[0084]

[0085] The specific method of sparse reconstruction is as follows: according to the data of each range unit, the sparse reconstruction method is used to model the second echo signal based on the sparse recovery theory to obtain the corresponding azimuth image, whose matrix expression is:

[0086]

[0087] Where Q b Indicates the distance unit r b The target set of L max Indicates the maximum number of modes that the array can produce; L min Indicates the minimum number of modes that the array can produce; It represents the additional phase term generated by the processed electromagnetic vortex in the bth distance unit; Indicates the Nth l The corresponding mode is located at the distance unit r b Echo; N l Indicates the number of modal samples; M s Indicates the number of grids used to divide the azimuth image; l (·) and σ (·) They represent the orbital angular momentum mode and the elements in the one-dimensional azimuth image corresponding to the distance unit respectively; n (·) represents the noise of the corresponding sampling point; Φ (·) represents the elements in the observation matrix, where · represents the replaceable variables.

[0088] After the model is established, it can be solved directly by orthogonal matching pursuit, basis pursuit denoising, sparse Bayesian and other methods. The azimuth images of all distance units in the set imaging distance area are processed simultaneously to obtain the entire two-dimensional coarse image within the observation range.

[0089] In the specific implementation process of step 207, the obtained one-dimensional distance image y outTwo-dimensional coarse image of the set imaging area Multiply them together, perform energy constraint on the azimuth image of each distance unit, and obtain a two-dimensional imaging result.

[0090] Although this embodiment Figure 1 The steps in the diagram are shown in the order indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. In addition, Figure 1 At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0091] In one of the embodiments, the method proposed in the present invention is verified.

[0092] The results of imaging using the traditional method of generating electromagnetic vortex waves are as follows: Figure 3 and Figure 6 As shown, the single-point target is located at 1000m, with an azimuth angle of 0rad and a pitch angle of 0.15πrad; the pitch angles of the multi-point targets are all 0.15πrad, and the distance and azimuth are (990m, 0rad), (990m, 0.3πrad), (1000m, 0rad), and (1000m, 0.3πrad). The imaging area is set to 950m to 1050m, and the distance grid width is 1.5m. The radar parameters are set as follows: center frequency 10GHz, frequency deviation between elements 100kHz, circular array radius 15cm, phase encoding width 10ns, pulse width 10us, OAM mode number -15 to 15, modal sampling interval 1, and number of transmitted pulses 1. The parameter settings of the traditional electromagnetic vortex imaging method are the same except that the frequency deviation is not used. Figure 3 This is the imaging result of a single point target after the traditional method emits 31 pulses of different modes (-15 to 15 modes) and performs pulse compression, modal domain compensation and transformation. It can be seen that the traditional method can perform two-dimensional imaging well. Figure 4 and Figure 3 By comparison, it can be found that the imaging effect of the method proposed by the present invention is similar to that of the traditional method. Figure 5 Comparison of the azimuthal profiles of the two methods further illustrates that the two methods have similar performances, but the present invention only requires a single pulse for imaging. Figure 6 and Figure 7 The imaging results of multi-point targets are obtained by using the traditional method and the Fourier transform method of the present invention respectively. Figure 8 and Figure 9 These are the azimuth imaging results of the traditional method and the present invention based on the sparse Bayesian algorithm. By comparison, it can be found that by adopting the sparse Bayesian method, the present invention can still achieve super-resolution with a single pulse, and the super-resolution effect is comparable to that of the traditional method. Under this condition, the present invention effectively improves the efficiency of electromagnetic vortex wave (EMV) imaging.

[0093] Example 2

[0094] Based on the single-pulse electromagnetic vortex imaging method based on frequency diversity in Example 1, this embodiment discloses a single-pulse electromagnetic vortex imaging device based on frequency diversity, such as Figure 10 As shown, the device includes: a first echo signal acquisition module 401, a one-dimensional range image acquisition module 402, a cancellation reference signal calculation module 403, a second echo signal acquisition module 404, a two-dimensional matrix reconstruction module 405, a two-dimensional coarse image construction module 406 and a two-dimensional image construction module 407, wherein:

[0095] The first echo signal acquisition module 401 is used to generate electromagnetic vortex waves for transmission according to frequency diversity, and acquire first echo signals of multiple targets located on a cone surface with the same pitch angle.

[0096] The one-dimensional range image acquisition module 402 is configured to perform multi-matched filtering on the first echo signal to obtain a multi-matched filtering output signal; and perform incoherent accumulation on the multi-matched filtering output signal to obtain a one-dimensional range image.

[0097] The cancellation reference signal calculation module 403 is used to determine an imaging distance area, divide the imaging distance area into grids to obtain a number of distance units, and then generate a cancellation reference signal corresponding to each of the distance units.

[0098] The second echo signal acquisition module 404 is configured to perform calculations based on the cancellation reference signal and the first echo signal to obtain a second echo signal corresponding to the range unit.

[0099] The two-dimensional matrix reconstruction module 405 is used to set the orbital angular momentum modal interval, downsample the second echo signal according to the orbital angular momentum modal interval, calculate the compensation function, and compensate the orbital angular momentum mode for Bessel terms and residual phase terms using the compensation function to obtain data for each range unit.

[0100] The two-dimensional coarse image construction module 406 is used to perform azimuth imaging according to the data of each range unit to obtain a two-dimensional coarse image corresponding to the range unit.

[0101] The two-dimensional image construction module 407 is configured to perform power constraints on each range unit of the two-dimensional coarse image using the one-dimensional range image to obtain a two-dimensional image of the imaging area.

[0102] In this embodiment, the specific working processes and working principles of the first echo signal acquisition module 401, the one-dimensional range image acquisition module 402, the offset reference signal calculation module 403, the second echo signal acquisition module 404, the two-dimensional matrix reconstruction module 405, the two-dimensional coarse image construction module 406, and the two-dimensional image construction module 407 are the same as those in Example 1, and therefore are not further described in this embodiment. Each unit module can be implemented in whole or in part by software, hardware, or a combination thereof. Each unit module can be embedded in or independent of a processor in a computer device in the form of hardware, or can be stored in a memory in the computer device in the form of software, so that the processor can call and execute the operations corresponding to each of the above unit modules.

[0103] Example 3

[0104] like Figure 11 As shown, a computer device is provided, which may be a server, including a processor, a memory, a network interface, and a database. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of the operating system and computer program in the non-volatile storage medium. The database of the computer device is used to store the data in the above-mentioned embodiment 1. The network interface of the computer device is used to communicate with an external terminal via a network connection. When the computer program is executed by the processor, the method in the above-mentioned embodiment 1 is implemented.

[0105] It should be noted that the above memory can be independent or integrated with the processor. When the memory is independently provided, the terminal device further includes a bus for connecting the memory and the processor.

[0106] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0107] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0108] The above-described embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that a person skilled in the art would be able to make numerous modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A single-pulse electromagnetic vortex imaging method based on frequency diversity, characterized in that: The method comprises: Generate electromagnetic vortex waves for transmission based on frequency diversity to obtain first echo signals of multiple targets located on a cone surface with the same pitch angle; performing multi-matched filtering on the first echo signal to obtain a multi-matched filtering output signal; performing incoherent accumulation on the multi-matched filtering output signal to obtain a one-dimensional range image; Determine an imaging distance area, divide the imaging distance area into a grid to obtain a plurality of distance units, and then generate a cancellation reference signal corresponding to each of the distance units; Calculating based on the cancellation reference signal and the first echo signal to obtain a second echo signal corresponding to the distance unit; setting an orbital angular momentum modal interval, downsampling the second echo signal according to the orbital angular momentum modal interval, calculating a compensation function, and performing Bessel term and residual phase term compensation on the orbital angular momentum mode using the compensation function to obtain data for each range unit; Perform azimuth imaging based on the data of each range unit to obtain a two-dimensional coarse image corresponding to the range unit; Power constraints are performed on each range unit of the two-dimensional coarse image using the one-dimensional range image to obtain a two-dimensional image of the imaging area.

2. The single-pulse electromagnetic vortex imaging method based on frequency diversity according to claim 1, characterized in that: The first echo signal expression is: Where (rq, θ0, φq) represents the position of the qth target, σq(rq, θ0, φq) represents the scattering coefficient of the qth target; Q = 1, 2, 3, q ​​represents the target number; θ0 represents the pitch angle; represents the random phase-coded echo waveform obtained by delaying the distance unit where the qth target is located; N represents the number of array elements; l(t′ q ) represents the orbital angular momentum mode of the qth target; represents the additional phase term generated by the electromagnetic vortex; represents the Bessel amplitude term; k0 represents the wave number corresponding to the signal center frequency f0; a represents the radius of the uniform circular array.

3. The single-pulse electromagnetic vortex imaging method based on frequency diversity according to claim 2, characterized in that: Perform multi-matched filtering on the first echo signal to obtain a multi-matched filtering output signal, which is expressed as: Where s rm (t) represents the first echo signal; e -j2πmΔft represents the multi-matched filter corresponding to each frequency offset design, where m = 0, 1, 2, ..., N-1; represents the conjugate of the transmitted waveform; Represents a convolution operation.

4. The single-pulse electromagnetic vortex imaging method based on frequency diversity according to claim 3, characterized in that: The multi-matched filter output signals are incoherently accumulated to obtain a one-dimensional range image, which is expressed as: Where y m (t) represents the multi-matched filter output signal.

5. The single-pulse electromagnetic vortex imaging method based on frequency diversity according to any one of claims 1 to 4, characterized in that: Determining an imaging distance area, dividing the imaging distance area into a grid to obtain a plurality of distance units, and then generating a cancellation reference signal corresponding to each of the distance units, including: Determine the imaging distance area [R min ,R max ], set the distance grid length to Δr, and divide the imaging distance area into grids according to the distance grid length Δr, and get N r distance units For each distance unit, a corresponding cancellation reference signal is generated, and the cancellation reference signal expression is: Where, t b ′ represents the intra-pulse time of the corresponding b-th range unit; represents the conjugate of the transmitted waveform delayed by b range units.

6. The single-pulse electromagnetic vortex imaging method based on frequency diversity according to claim 5, characterized in that: Calculation is performed based on the cancellation reference signal and the first echo signal to obtain a second echo signal corresponding to the range unit, which is expressed as: Where (rq, θ0, φq) represents the position of the qth target, σq(rq, θ0, φq) represents the scattering coefficient of the qth target; Q = 1, 2, 3, q ​​represents the target number; θ0 represents the pitch angle; represents the random phase-coded echo waveform obtained by delaying the distance unit where the qth target is located; N represents the number of array elements; l(t′ q ) represents the orbital angular momentum mode of the qth target; represents the additional phase term generated by the electromagnetic vortex; represents the Bessel amplitude term of the qth target; k0 represents the wave number corresponding to the signal center frequency f0; a represents the radius of the uniform circular array.

7. The single-pulse electromagnetic vortex imaging method based on frequency diversity according to claim 6, characterized in that: The expression of the compensation function is: Where, represents the phase term that needs to be compensated; Represents the Bessel magnitude term for the b-th distance unit.

8. The single-pulse electromagnetic vortex imaging method based on frequency diversity according to claim 7, characterized in that: Azimuth imaging is performed based on the data of each range unit to obtain a two-dimensional coarse image corresponding to the range unit, including: According to the data of each range unit, a corresponding azimuth image corresponding to each range unit is directly obtained by performing Fourier transform on the data of each range unit; or according to the data of each range unit, a sparse reconstruction method is used to model the second echo signal based on the sparse recovery theory to obtain the corresponding azimuth image; By transforming the aspect image, a two-dimensional rough image is obtained.

9. A single-pulse electromagnetic vortex imaging device based on frequency diversity, characterized in that: The device comprises: A first echo signal acquisition module is used to generate electromagnetic vortex waves for transmission based on frequency diversity, and acquire first echo signals of multiple targets located on a cone surface with the same pitch angle; a one-dimensional range image acquisition module, configured to perform multi-matched filtering on the first echo signal to obtain a multi-matched filtering output signal; and perform incoherent accumulation on the multi-matched filtering output signal to obtain a one-dimensional range image; a cancellation reference signal calculation module, configured to determine an imaging distance region, divide the imaging distance region into a grid to obtain a plurality of distance units, and then generate a cancellation reference signal corresponding to each of the distance units; a second echo signal acquisition module, configured to perform calculations based on the cancellation reference signal and the first echo signal to obtain a second echo signal corresponding to the distance unit; a two-dimensional matrix reconstruction module, configured to set an orbital angular momentum modal interval, downsample the second echo signal according to the orbital angular momentum modal interval, calculate a compensation function, and perform Bessel term and residual phase term compensation on the orbital angular momentum mode using the compensation function to obtain data for each range unit; A two-dimensional coarse image construction module is used to perform azimuth imaging based on the data of each range unit to obtain a two-dimensional coarse image corresponding to the range unit; The two-dimensional image construction module is used to perform power constraints on each distance unit of the two-dimensional coarse image through the one-dimensional range image to obtain a two-dimensional image of the imaging area.

10. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the single-pulse electromagnetic vortex imaging method based on frequency diversity according to any one of claims 1 to 8 are implemented.

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