Multimodal High-Time-Efficiency Electromagnetic Vortex Imaging Method and Device Based on Orthogonal Polyphase Code

Abstract

This invention proposes a multi-modal, high-time-efficiency electromagnetic vortex imaging method and apparatus based on orthogonal polyphase codes. By utilizing orthogonal polyphase coding modulation, a uniform circular array simultaneously transmits vortex electromagnetic waves of multiple modes to illuminate the target, ensuring the consistency of target observation information. By performing matched filtering on the target echo received by a single antenna and the orthogonal coded signals corresponding to different modes, individual mode information is demodulated, obtaining target echoes in different modes. The demodulated echo signals are further processed using imaging techniques to obtain a high-resolution two-dimensional image of the target. Compared to imaging by traversing vortex electromagnetic waves carrying the orbital angular momentum of a single mode, this invention uses phase-coded modulation to allow vortex electromagnetic waves of different modes to simultaneously illuminate the target, and demodulates all modes in a single reception at the receiving end, making it suitable for scenarios with high imaging timeliness requirements.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic vortex imaging technology, and in particular to a multimodal high-time-efficiency electromagnetic vortex imaging method and device based on orthogonal multiphase codes. Background Technology

[0002] Radar imaging technology can acquire the structural features and size information of targets within the observation area by emitting specific microwave electromagnetic signals and processing the echo signals. It is an all-weather, all-day target perception method with wide applications in public and national defense security fields. It is an important technical means to achieve environmental surveying, target surveillance, and precision strikes.

[0003] Improving radar imaging resolution facilitates the refined extraction of target features. Theoretically, the azimuth resolution of a radar depends on the aperture size of the transmitting antenna; the larger the aperture, the higher the azimuth resolution. To improve azimuth resolution, existing radar systems typically employ synthetic aperture imaging (SAR) technology to create a virtual aperture, or use distributed antenna arrays to create an equivalent large aperture. However, under forward-looking observation conditions, the radar illumination angle is essentially aligned with the target's direction of motion, making it difficult to generate significant relative azimuth motion. The resulting virtual aperture is relatively small, hindering high-resolution imaging. Furthermore, distributed antenna arrays require significant space resources, making them difficult to mount on mobile platforms and limiting their application scenarios.

[0004] In recent years, electromagnetic vortex imaging technology, which utilizes the unique phase distribution structure of vortex electromagnetic waves to achieve beam-in-beam target resolution, has attracted widespread attention. Electromagnetic vortex imaging technology leverages the Fourier transform duality between the number of orbital angular momentum modes and the target azimuth angle. By traversing different orbital angular momentum modes, it acquires target azimuth information, overcoming the limitations of actual antenna aperture and achieving high azimuth resolution without relying on the relative motion between the radar and the target. Currently, electromagnetic vortex imaging mainly utilizes vortex electromagnetic waves carrying single orbital angular momentum to sequentially illuminate the target, followed by joint processing of target echoes from different modes. This imaging method requires traversing different modes to acquire observation information. However, for moving targets in forward-looking scenarios, the positions of the radar and the target change over time, affecting the performance of traditional electromagnetic vortex imaging based on orbital angular momentum traversal, thus limiting the application scenarios of electromagnetic vortex imaging. Summary of the Invention

[0005] To address the technical problems existing in the prior art, this invention proposes a multimodal, high-time-efficiency electromagnetic vortex imaging method and apparatus based on orthogonal polyphase codes. This invention can improve the illumination efficiency of vortex electromagnetic waves and enhance the imaging capability of this technology for targets with high imaging timeliness requirements.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] On one hand, the present invention provides a multimodal high-time-efficiency electromagnetic vortex imaging method based on orthogonal polyphase codes, comprising:

[0008] Construct a uniform circular array to simultaneously emit vortex electromagnetic waves of the same frequency but different modes, with each mode of vortex electromagnetic wave modulated by an orthogonal polyphase coded signal.

[0009] By changing the excitation signal frequency of the uniform circular array, it generates and emits vortex electromagnetic waves of different frequencies and multiplexed modes to irradiate the target.

[0010] A single receiving antenna is used to receive vortex electromagnetic wave target echoes of different frequencies and multiplexed modes, and down-conversion processing is performed to obtain a one-dimensional baseband echo signal carrying all mode information.

[0011] Reference signals for orthogonal polyphase encoded signals corresponding to different modes are constructed and matched with baseband signals to obtain frequency-single-mode two-dimensional echo data.

[0012] Based on the parameters of the uniform circular array and the prior information of the target, the common phase term and Bessel function term of the frequency-single-mode two-dimensional echo data are compensated.

[0013] A two-dimensional Fourier transform is performed on the compensated frequency-single-mode two-dimensional echo data to obtain a range-azimuth two-dimensional image of the target.

[0014] Furthermore, the uniform circular array is composed of N identical antennas arranged at equal intervals of 2π / N on a circle.

[0015] Furthermore, the vortex electromagnetic waves emitted by the uniform circular array are vortex electromagnetic waves with multiplexed frequencies f and M modes, which are generated by the following method:

[0016] Let M be the topology payload used for multimodal multiplexing, and let L be the code length generated for each mode. c The period is T c Orthogonal polyphase coding c m (μ)∈{0,π / 2,π,3π / 2}, μ represents the μ-th code element, t∈[0,T] c ], τ c T represents the duration of a symbol. c =L c τ c , This represents the orthogonal waveform encoded signal of the m-th mode;

[0017] The excitation signal with frequency f is modulated by the incremental phase of a uniform circular array and M orthogonal waveform encoding signals to generate a vortex electromagnetic wave with frequency f and M modes multiplexed. Each mode of the vortex electromagnetic wave is modulated by an orthogonal polyphase encoding signal.

[0018] Furthermore, methods for acquiring frequency-single-mode two-dimensional echo data include:

[0019] For the echo signal corresponding to the q-th mode, the q-th mode corresponds to the q-th orthogonal waveform coded signal w among the M orthogonal waveform coded signals. q (t), using the conjugate of the q-th orthogonal waveform coded signal from M orthogonal waveform coded signals. As a reference signal, the baseband echo signal is matched and filtered to obtain the demodulated q-th mode one-dimensional echo signal.

[0020] Different modes were demodulated sequentially to obtain frequency-single-mode two-dimensional echo data.

[0021] On the other hand, the present invention provides a multimodal high-time-efficiency electromagnetic vortex imaging device based on orthogonal polyphase codes, comprising:

[0022] A uniform circular array is used to simultaneously emit vortex electromagnetic waves of the same frequency but different modes, with each mode of vortex electromagnetic wave modulated by an orthogonal polyphase coded signal.

[0023] The uniform circular array control module is used to change the excitation signal frequency of the uniform circular array, so that it generates and emits vortex electromagnetic waves of different frequencies and multiplexed modes to irradiate the target.

[0024] The receiving module uses a single receiving antenna to receive vortex electromagnetic wave target echoes of different frequencies and multiplexed modes, and performs down-conversion processing to obtain a one-dimensional baseband echo signal carrying all mode information.

[0025] The imaging module includes a first module, a second module, and a third module. The first module is used to construct reference signals for orthogonal polyphase encoded signals corresponding to different modes, and perform matched filtering with the baseband signal to obtain frequency-single-mode two-dimensional echo data. The second module is used to compensate for the common phase term and Bessel function term of the frequency-single-mode two-dimensional echo data according to the parameters of the uniform circular array and the prior information of the target. The third module is used to perform a two-dimensional Fourier transform on the compensated frequency-single-mode two-dimensional echo data to obtain a range-azimuth two-dimensional image of the target.

[0026] This invention utilizes vortex electromagnetic waves with multi-mode orbital angular momentum multiplexing for two-dimensional imaging of targets. Compared to imaging by traversing vortex electromagnetic waves carrying a single mode of orbital angular momentum, phase coding modulation allows vortex electromagnetic waves of different modes to simultaneously illuminate the target, ensuring the consistency of target observation information. This invention is suitable for scenarios with high requirements for imaging timeliness. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0028] Figure 1 This is a flowchart illustrating one embodiment;

[0029] Figure 2 This is a schematic diagram of the imaging module in one embodiment;

[0030] Figure 3 This is a schematic diagram comparing the imaging results of a point target using the method of the present invention with the ideal azimuth dimension imaging results in one embodiment.

[0031] Figure 4 This is a schematic diagram of the scattering model of an aircraft target used in one embodiment;

[0032] Figure 5 In one embodiment, the method of the present invention is used to... Figure 4 The diagram shows the imaging results of the aircraft target. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Reference Figure 1 One embodiment provides a multimodal high-time-efficiency electromagnetic vortex imaging method based on orthogonal polyphase codes, comprising:

[0035] Construct a uniform circular array to simultaneously emit vortex electromagnetic waves of the same frequency but different modes, with each mode of vortex electromagnetic wave modulated by an orthogonal polyphase coded signal.

[0036] By changing the excitation signal frequency of the uniform circular array, it generates and emits vortex electromagnetic waves of different frequencies and multiplexed modes to irradiate the target.

[0037] A single receiving antenna is used to receive vortex electromagnetic wave target echoes of different frequencies and multiplexed modes, and down-conversion processing is performed to obtain a one-dimensional baseband echo signal carrying all mode information.

[0038] Reference signals for orthogonal polyphase encoded signals corresponding to different modes are constructed and matched with baseband signals to obtain frequency-single-mode two-dimensional echo data.

[0039] Based on the parameters of the uniform circular array and the prior information of the target, the common phase term and Bessel function term of the frequency-single-mode two-dimensional echo data are compensated.

[0040] A two-dimensional Fourier transform is performed on the compensated frequency-single-mode two-dimensional echo data to obtain a range-azimuth two-dimensional image of the target.

[0041] This invention ensures the consistency of target observation information by simultaneously emitting vortex electromagnetic waves of multiple modes to illuminate the target; by performing matched filtering on the target echo received by a single antenna and the orthogonal coded signals corresponding to different modes, the individual mode information is demodulated to obtain the target echo under different modes; the demodulated echo signal is further processed by imaging to obtain a high-resolution two-dimensional image of the target.

[0042] In one embodiment, the uniform circular array is composed of N identical antennas arranged at equal intervals of 2π / N on a circle.

[0043] In one embodiment, the vortex electromagnetic wave emitted by the uniform ring array is a vortex electromagnetic wave with multiplexed frequencies f and M modes, which is generated by the following method:

[0044] Let M be the topology payload used for multimodal multiplexing, and let L be the code length generated for each mode. c The period is T c Orthogonal polyphase coding c m (μ)∈{0,π / 2,π,3π / 2}, μ represents the μ-th symbol, t is time, indicating that it is a function that changes with time, t∈[0,T] c ], τ c T represents the duration of a symbol. c =L c τ c , This represents the orthogonal waveform encoded signal of the m-th mode;

[0045] The excitation signal with frequency f is modulated by the incremental phase of a uniform circular array and M orthogonal waveform encoding signals to generate a vortex electromagnetic wave with frequency f and M modes multiplexed. Each mode of the vortex electromagnetic wave is modulated by an orthogonal polyphase encoding signal.

[0046] In one embodiment, a method for acquiring frequency-single-mode two-dimensional echo data includes:

[0047] For the echo signal corresponding to the q-th mode, the q-th mode corresponds to the q-th orthogonal waveform coded signal w among the M orthogonal waveform coded signals. q (t), using the conjugate of the q-th orthogonal waveform coded signal from M orthogonal waveform coded signals. As a reference signal, the baseband echo signal is matched and filtered to obtain the demodulated q-th mode one-dimensional echo signal.

[0048] Different modes were demodulated sequentially to obtain frequency-single-mode two-dimensional echo data.

[0049] In one specific embodiment, a multimodal high-time-efficiency electromagnetic vortex imaging method based on orthogonal polyphase codes is provided, comprising:

[0050] (1) Construct a uniform circular array so that it can simultaneously emit vortex electromagnetic waves of the same frequency but different modes. Each mode of vortex electromagnetic wave is modulated by an orthogonal polyphase coded signal.

[0051] N identical transmitting antennas are arranged at equal intervals of 2π / N on a circle of radius a to form a uniform circular array.

[0052] Selecting a transmitting antenna element with zero azimuth in a uniform circular array as the initial transmitting element, and sequentially numbering each transmitting element from 1 to N along the circumference counterclockwise, the azimuth of the nth transmitting antenna element is: This uniform circular array is used to generate vortex electromagnetic waves carrying multimode multiplexing.

[0053] When the number of transmitting antenna elements in a uniform circular ring array is N, the number of orbital angular momentum modes that can be generated satisfies the condition -N / 2 < l < N / 2. The number of topological charges used for multimode multiplexing is set to M, denoted as l1, l2, ..., l M , where l m Let m be a value of l, where m = 1, 2, ..., M.

[0054] Generate a code length of L for each mode. c The period is T c Orthogonal polyphase coding c m (μ)∈{0,π / 2,π,3π / 2}, μ represents the μ-th code element, τc T represents the duration of a symbol. c =L c τ c Then the orthogonal polyphase coded signal matrix is ​​represented as:

[0055] W(t) = [w1(t) w2(t)...w M (t)]

[0056] in, This represents the orthogonal waveform coded signal of the m-th mode, where m = 1, 2, ..., M, and t ∈ [0, T]. c ].

[0057] The correlation functions of orthogonal polyphase coded signals of different modes satisfy the following conditions:

[0058]

[0059] Wherein, let w be the orthogonal waveform coded signal among the M orthogonal waveform coded signals corresponding to the x-th mode. x (t), the y-th mode corresponds to the orthogonal waveform coded signal w in the M orthogonal waveform coded signals. y (t), x, y = 1, 2, ..., M, Indicates w x (t) and w y The correlation function of (t), where τ represents w x (t) and w y The time delay between (t) Indicates w y The conjugate of (t).

[0060] By using the incremental phase of a traditional uniform circular array and M orthogonal polyphase coded signals to modulate an excitation signal with frequency f, a vortex electromagnetic wave with frequency f and M modes multiplexed is generated, and each mode of the vortex electromagnetic wave is modulated by an orthogonal polyphase coded signal.

[0061] Among them, the transmitted signal s of the nth transmitting antenna element of the uniform circular array. n (t) is represented as:

[0062]

[0063] Where i represents the imaginary unit, Let l be the azimuth angle of the nth transmitting antenna element in a uniform circular array. m Let m be the number of topological loads generated, where m = 1, 2, ..., M.

[0064] (2) Change the excitation signal frequency of the uniform circular array to generate and emit vortex electromagnetic waves of different frequencies and multiplexed modes to irradiate the target.

[0065] Target The signal at that location can be represented as:

[0066]

[0067] Where r is the target distance and θ is the target pitch angle. Let τ be the target azimuth angle. n Let be the time delay from the uniform circular array to the target, and be the vector pointing from the origin to the target. Let be the vector pointing from the origin to the nth transmitting antenna.

[0068] (3) A single receiving antenna is used to receive the target echo of vortex electromagnetic waves of different frequencies and multiplexed modes, and down-conversion processing is performed to obtain a one-dimensional baseband echo signal carrying all mode information, as shown below:

[0069]

[0070] Where, τ r The time delay from the target to the receiving array element antenna.

[0071] (4) Construct reference signals for orthogonal polyphase encoded signals corresponding to different modes, and perform matched filtering with baseband signals to obtain frequency-single-mode two-dimensional echo data.

[0072] For the one-dimensional baseband echo signal corresponding to the q-th mode, the q-th orthogonal waveform coded signal w is one of the M orthogonal waveform coded signals corresponding to the q-th mode. q (t), the conjugate w of the q-th orthogonal waveform encoded from M orthogonal waveform encoded signals. q * Using (t) as a reference signal, matched filtering is performed on the one-dimensional baseband echo signal corresponding to the q-th mode to obtain the demodulated echo signal of the q-th mode. Let t n =τ n +τ r Then we have:

[0073]

[0074] Let q = 1, 2, ..., M, as follows Figure 2 As shown, different modes were demodulated sequentially to obtain frequency-single-mode two-dimensional echo data, as follows:

[0075]

[0076] Where i l For the common phase term e ilπ / 2 J l(kasinθ) represents the first kind of Bessel function term. From the above equation, it can be seen that the demodulated frequency-single-mode two-dimensional echo signal recovers the wavenumber k and target distance r, orbital angular momentum l and azimuth angle. The duality relationship.

[0077] (5) Based on the parameters of the uniform circular array and the prior information of the target, the common phase term and Bessel function term of the frequency-single-mode two-dimensional echo data are compensated.

[0078] The common phase e is compensated based on the orbital angular momentum mode number of the echo. ilπ / 2 The echo signal is then further processed using the following formula:

[0079] s(r)=s demo ·e iφ

[0080] Where φ represents the phase that needs to be compensated, when J l When (kasinθ) < 0, φ = π; otherwise, φ = 0.

[0081] (6) Perform a two-dimensional Fourier transform on the compensated frequency-single-mode two-dimensional echo data to obtain a range-azimuth two-dimensional image of the target.

[0082] The effectiveness of the above embodiments is further demonstrated by the following simulation experiments:

[0083] A program was written using MATLAB software, and the simulation parameters were set as follows: in the above embodiment, the excitation signal frequency f = 9.8~10GHz, the number of transmitting antenna elements of the uniform circular array N = 26, and the number of symbols L. c =256, element radius a=0.15, multiplexed mode number M=25, and phase can be {0,π / 2,π,3π / 2}. Using steps (1) and (2) in the above embodiment, a uniform circular array sequentially generates and transmits vortex electromagnetic waves of different frequencies, carrying M orbital angular momentum modes, to illuminate the target. A single receiving element antenna receives the target echo of vortex electromagnetic waves of different frequencies, and processes the target echo sequentially using steps (4), (5), and (6) in the above embodiment. The simulation results obtained in this embodiment are as follows: Figure 3 A schematic diagram comparing the imaging results of point targets using the method of the present invention with the ideal azimuth imaging results is provided. It can be seen that the method proposed in this invention is roughly the same as the ideal imaging results, which proves the effectiveness and reliability of the present invention. Figure 4 This is a schematic diagram of the scattering model of the aircraft target used in this embodiment; Figure 5 In this embodiment, the method of the present invention is used to... Figure 4The schematic diagram of the imaging results of the aircraft target shown demonstrates that multi-mode multiplexed electromagnetic vortex imaging still has excellent resolution performance in moving scenes.

[0084] In one embodiment, a multimodal high-time-efficiency electromagnetic vortex imaging device based on orthogonal polyphase codes is provided, comprising:

[0085] A uniform circular array is used to simultaneously emit vortex electromagnetic waves of the same frequency but different modes, with each mode of vortex electromagnetic wave modulated by an orthogonal polyphase coded signal.

[0086] The uniform circular array control module is used to change the excitation signal frequency of the uniform circular array, so that it generates and emits vortex electromagnetic waves of different frequencies and multiplexed modes to irradiate the target.

[0087] The receiving module uses a single receiving antenna to receive vortex electromagnetic wave target echoes of different frequencies and multiplexed modes, and performs down-conversion processing to obtain a one-dimensional baseband echo signal carrying all mode information.

[0088] The imaging module includes a first module, a second module, and a third module. The first module is used to construct reference signals for orthogonal polyphase encoded signals corresponding to different modes, and perform matched filtering with the baseband signal to obtain frequency-single-mode two-dimensional echo data. The second module is used to compensate for the common phase term and Bessel function term of the frequency-single-mode two-dimensional echo data according to the parameters of the uniform circular array and the prior information of the target. The third module is used to perform a two-dimensional Fourier transform on the compensated frequency-single-mode two-dimensional echo data to obtain a range-azimuth two-dimensional image of the target.

[0089] The implementation method of the above-mentioned uniform circular array, the generation method of vortex electromagnetic waves carrying multimode multiplexing, and the implementation method of each module can all adopt the technical solutions described in any of the foregoing embodiments, and will not be repeated here.

[0090] Matters not covered in this invention are common knowledge.

[0091] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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.

[0092] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

[0093] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multimodal, high-time-efficiency electromagnetic vortex imaging method based on orthogonal polyphase codes, characterized in that, include: Construct a uniform circular array to simultaneously emit vortex electromagnetic waves of the same frequency but different modes, with each mode of vortex electromagnetic wave modulated by an orthogonal polyphase coded signal. By changing the excitation signal frequency of the uniform circular array, it generates and emits vortex electromagnetic waves of different frequencies and multiplexed modes to irradiate the target. A single receiving antenna is used to receive vortex electromagnetic wave target echoes of different frequencies and multiplexed modes, and down-conversion processing is performed to obtain a one-dimensional baseband echo signal carrying all mode information. Reference signals for orthogonal polyphase encoded signals corresponding to different modes are constructed and matched with baseband signals to obtain frequency-single-mode two-dimensional echo data. Based on the parameters of the uniform circular array and the prior information of the target, the common phase term and Bessel function term of the frequency-single-mode two-dimensional echo data are compensated. A two-dimensional Fourier transform is performed on the compensated frequency-single-mode two-dimensional echo data to obtain a range-azimuth two-dimensional image of the target. The vortex electromagnetic waves emitted by the uniform circular array have a frequency of , Mode-multiplexed vortex electromagnetic waves are generated through the following method: Set the topology load for multimodal multiplexing to be Generate a set of code lengths for each mode. The period is Orthogonal polyphase coding , , Indicates the first Each code element Indicates the duration of a symbol. t It is time. , , Indicates the first Orthogonal waveform encoded signal of each mode, Represents the imaginary unit; Using the incremental phase of a uniform circular array A pair of orthogonal waveform encoded signals with frequency of The excitation signal is modulated to generate a frequency of , The vortex electromagnetic wave is a mode-multiplexed wave, and each mode of the vortex electromagnetic wave is modulated by an orthogonal polyphase coded signal. Methods for acquiring frequency-single-mode two-dimensional echo data include: For the The echo signal corresponding to the i-th mode, the i-th Each mode corresponds to The first orthogonal waveform coded signal Orthogonal waveform encoded signal ,use The first orthogonal waveform coded signal Conjugate of orthogonal waveform coded signals Using the baseband echo signal as a reference signal, matched filtering is performed on the demodulated signal to obtain the [missing signal]. One-dimensional echo signal in each mode; Different modes were demodulated sequentially to obtain frequency-single-mode two-dimensional echo data.

2. The multimodal high-time-efficiency electromagnetic vortex imaging method based on orthogonal polyphase codes according to claim 1, characterized in that, The uniform circular array is composed of The same antenna according to It is formed by arranging them at equal intervals on the circumference.

3. The multimodal high-time-efficiency electromagnetic vortex imaging method based on orthogonal polyphase codes according to claim 1, characterized in that, The correlation functions of orthogonal polyphase coded signals of different modes satisfy the following conditions: Among them, the number is recorded as follows Each mode corresponds to Orthogonal waveform encoded signals in a set of orthogonal waveform encoded signals , No. Each mode corresponds to Orthogonal waveform encoded signals in a set of orthogonal waveform encoded signals , , express and Related functions, express and The time delay between express . conjugate.

4. A multimodal, high-time-efficiency electromagnetic vortex imaging device based on orthogonal polyphase codes, characterized in that, include: A uniform circular array is used to simultaneously emit vortex electromagnetic waves of the same frequency but different modes, with each mode of vortex electromagnetic wave modulated by an orthogonal polyphase coded signal. The uniform circular array control module is used to change the excitation signal frequency of the uniform circular array, so that it generates and emits vortex electromagnetic waves of different frequencies and multiplexed modes to irradiate the target. The receiving module uses a single receiving antenna to receive vortex electromagnetic wave target echoes of different frequencies and multiplexed modes, and performs down-conversion processing to obtain a one-dimensional baseband echo signal carrying all mode information. The imaging module includes a first module, a second module, and a third module. The first module is used to construct reference signals for orthogonal polyphase encoded signals corresponding to different modes, and to perform matched filtering with the baseband signal to obtain frequency-single-mode two-dimensional echo data. The second module is used to compensate the common phase term and Bessel function term of the frequency-single-mode two-dimensional echo data based on the parameters of the uniform circular array and the prior information of the target; the third module is used to perform a two-dimensional Fourier transform on the compensated frequency-single-mode two-dimensional echo data to obtain the range-azimuth two-dimensional image of the target. The vortex electromagnetic waves emitted by the uniform circular array have a frequency of , Mode-multiplexed vortex electromagnetic waves are generated through the following method: Set the topology load for multimodal multiplexing to be Generate a set of code lengths for each mode. The period is Orthogonal polyphase coding , , Indicates the first Each code element Indicates the duration of a symbol. t It is time. , , Indicates the first Orthogonal waveform encoded signal of each mode, Represents the imaginary unit; Using the incremental phase of a uniform circular array A pair of orthogonal waveform encoded signals with frequency of The excitation signal is modulated to generate a frequency of , The vortex electromagnetic wave is a mode-multiplexed wave, and each mode of the vortex electromagnetic wave is modulated by an orthogonal polyphase coded signal. The method for acquiring frequency-single-mode two-dimensional echo data in the first module includes: For the The echo signal corresponding to the i-th mode, the i-th Each mode corresponds to The first orthogonal waveform coded signal Orthogonal waveform encoded signal ,use The first orthogonal waveform coded signal Conjugate of orthogonal waveform coded signals Using the baseband echo signal as a reference signal, matched filtering is performed on the demodulated signal to obtain the [missing signal]. One-dimensional echo signal in each mode; Different modes were demodulated sequentially to obtain frequency-single-mode two-dimensional echo data.

5. The multimodal high-time-efficiency electromagnetic vortex imaging device based on orthogonal polyphase codes according to claim 4, characterized in that, The uniform circular array is composed of The same antenna according to It is formed by arranging them at equal intervals on the circumference.

6. The multimodal high-time-efficiency electromagnetic vortex imaging device based on orthogonal polyphase codes according to claim 4, characterized in that, The correlation functions of orthogonal polyphase coded signals of different modes satisfy the following conditions: Among them, the number is recorded as follows Each mode corresponds to Orthogonal waveform encoded signals in a set of orthogonal waveform encoded signals , No. Each mode corresponds to Orthogonal waveform encoded signals in a set of orthogonal waveform encoded signals , , express and Related functions, express and The time delay between express . conjugate.

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