Method and device for generating electromagnetic vortex wave, and method and device for detecting vortex radar

Abstract

The application discloses a vortex electromagnetic wave generation method. A single-frequency optical carrier is modulated by a step frequency signal, and the generated modulated optical signal is divided into N paths. Different time delays are introduced into the N modulated optical signals respectively, the time delays introduced into the first path to the Nth path are in a step increase with a fixed increment At, then the N modulated optical signals after the time delay are photoelectrically converted to obtain radio frequency signals of N channels. The radio frequency signals of the first channel to the Nth channel are used to stimulate the first antenna array element to the Nth antenna array element respectively to generate vortex electromagnetic waves. The first antenna array element to the Nth antenna array element are arranged in an equal interval in a clockwise / inverse clockwise direction to form a uniform circular array with N antenna array elements. The application further discloses a vortex electromagnetic wave generation device and a vortex radar detection method and device. The application does not need additional hardware devices such as a phase shifter, and can quickly generate a vortex electromagnetic wave with multiple modes, a large bandwidth and reconfigurable parameters through a single sweep frequency cycle.

Description

Technical Field

[0001] This invention relates to a method for generating vortex electromagnetic waves, belonging to the technical field of vortex electromagnetic wave radar (hereinafter referred to as vortex radar). Background Technology

[0002] Radar imaging technology is not limited by natural conditions and has important applications in fields such as space target surveillance, remote sensing mapping, and ocean observation. Most existing high-resolution radars are based on the range-Doppler principle, achieving high range resolution by transmitting broadband signals and high azimuth resolution by utilizing the large virtual synthetic aperture formed by the relative motion between the radar and the target. However, they rely on the lateral relative motion between the radar and the target and lack forward-looking imaging capabilities, only able to detect and track targets using side-looking or oblique-looking methods. To address this, solutions such as monopulse imaging technology and array radar imaging technology have been proposed, which can improve the angular resolution of radar to some extent. However, the resolution is limited by the aperture size and cannot obtain detailed azimuth information of the target.

[0003] Orbital angular momentum (OAM) is a physical quantity related to the phase wavefront distribution of electromagnetic waves. When orbital angular momentum modulation is applied to conventional electromagnetic waves, vortex electromagnetic waves are formed, whose phase wavefronts exhibit a helical structure. This allows for the modulation of desired information, enhancing the information transmission and acquisition capabilities of electromagnetic waves. When using electromagnetic vortex waves with multi-mode orbital angular momentum for target detection, differentially distributed electromagnetic excitations will be generated at different scattering points of the target within the beam, resulting in more spatial information contained in the target's scattered echo. Utilizing vortex electromagnetic waves can overcome the resolution limitation caused by the real aperture beamwidth when using conventional planar electromagnetic waves, providing a feasible solution for high-resolution forward-looking radar imaging. However, existing vortex radar systems are limited by the operating bandwidth of electronic devices, making it difficult to generate broadband vortex electromagnetic waves, thus limiting the radar's range resolution. Furthermore, most traditional vortex radars use phased array antenna models to generate vortex electromagnetic waves, requiring multiple phase shifters to achieve phase shifting between array elements, leading to high hardware costs and complexity, which is detrimental to practical applications. Meanwhile, in traditional vortex electromagnetic wave generation systems, due to limitations of the generation model, only different modes of vortex electromagnetic waves can be generated in a time-sharing manner, which greatly wastes time resources, resulting in low radar imaging efficiency and the inability to detect fast-moving targets. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for generating vortex electromagnetic waves that does not require additional hardware devices such as phase shifters, and can quickly generate multi-mode, large-bandwidth and parameter-reconfigurable vortex electromagnetic waves for target detection with only a single frequency sweep cycle.

[0005] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems:

[0006] A method for generating vortex electromagnetic waves involves modulating a single-frequency optical carrier with a step-frequency signal and dividing the generated modulated optical signal into N channels, where N is an integer greater than 2. Different delays are introduced into each of these N modulated optical signals, with the delays introduced into the first to Nth channels increasing in a stepwise manner with a fixed increment Δt. The N modulated optical signals after the delays are then subjected to photoelectric conversion to obtain N channels of radio frequency (RF) signals. The RF signals from the first to Nth channels are used to excite the first to Nth antenna array elements to generate vortex electromagnetic waves. The first to Nth antenna array elements are arranged at equal intervals in a clockwise / counterclockwise direction to form a uniform circular array with N antenna array elements.

[0007] Preferably, the vortex electromagnetic wave parameters are set and adjusted according to the following formula:

[0008] N = L

[0009]

[0010]

[0011]

[0012] Where L is the total number of modes of vortex electromagnetic waves, and T f Δl is the mode conversion period of the vortex electromagnetic wave, f0 and Δf are the initial frequency and sweep frequency interval of the step frequency signal, respectively, K is a positive integer, and Z represents the positive integer field.

[0013] Based on the same inventive concept, the following technical solutions can also be obtained:

[0014] A vortex electromagnetic wave generating device, comprising:

[0015] The excitation signal generation unit is used to modulate a single-frequency optical carrier with a step frequency signal and divide the generated modulated optical signal into N paths, where N is an integer greater than 2; different delays are introduced for each of these N modulated optical signals, and the delays introduced for the first to Nth paths increase stepwise with a fixed increment Δt; then the N modulated optical signals after the delay are converted into photoelectric signals to obtain N channels of radio frequency signals.

[0016] The antenna array is a uniform circular array with N antenna elements. The first to Nth antenna elements are arranged at equal intervals in a clockwise / counterclockwise direction, and the radio frequency signals of the first to Nth channels are used as excitation signals to generate vortex electromagnetic waves.

[0017] Preferably, the vortex electromagnetic wave parameters are set and adjusted according to the following formula:

[0018] N = L

[0019]

[0020]

[0021]

[0022] Where L is the total number of modes of vortex electromagnetic waves, and T f Δl is the mode conversion period of the vortex electromagnetic wave, f0 and Δf are the initial frequency and sweep frequency interval of the step frequency signal, respectively, K is a positive integer, and Z represents the positive integer field.

[0023] A vortex radar detection method involves transmitting vortex electromagnetic waves towards a target and receiving the target's scattered echoes using a single antenna to achieve target imaging; the vortex electromagnetic waves are generated using the vortex electromagnetic wave generation method described in the previous technical solution.

[0024] Furthermore, the target imaging method is as follows: using the modulated optical signal without introduced delay as the reference optical signal, the received target reflected echo is subjected to microwave photonic mixing processing, and the obtained signal is subjected to photoelectric detection to obtain an intermediate frequency signal carrying target information; data sampling is performed on each frequency component contained in the intermediate frequency signal under each orbital angular momentum mode to obtain a frequency-topological charge two-dimensional data matrix with frequency and orbital angular momentum mode as the horizontal and vertical axes, respectively; firstly, a fast Fourier transform is performed on the data along the frequency axis to obtain a one-dimensional range image under different orbital angular momentum modes, and then a fast Fourier transform is performed along the topological charge domain to achieve azimuth focusing, thereby obtaining the final two-dimensional imaging result.

[0025] A vortex radar detection device includes a transmitting end for emitting vortex electromagnetic waves toward a target, and a receiving end for receiving the target's scattered echo with a single antenna to achieve target imaging; the transmitting end is a vortex electromagnetic wave generating device as described above.

[0026] Furthermore, the target imaging method is as follows: using the modulated optical signal without introduced delay as the reference optical signal, the received target reflected echo is subjected to microwave photonic mixing processing, and the obtained signal is subjected to photoelectric detection to obtain an intermediate frequency signal carrying target information; data sampling is performed on each frequency component contained in the intermediate frequency signal under each orbital angular momentum mode to obtain a frequency-topological charge two-dimensional data matrix with frequency and orbital angular momentum mode as the horizontal and vertical axes, respectively; firstly, a fast Fourier transform is performed on the data along the frequency axis to obtain a one-dimensional range image under different orbital angular momentum modes, and then a fast Fourier transform is performed along the topological charge domain to achieve azimuth focusing, thereby obtaining the final two-dimensional imaging result.

[0027] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0028] 1. The technical solution of this invention utilizes the advantages of microwave photonic radar technology, such as large bandwidth and low loss, and only requires a laser source to generate vortex electromagnetic waves with a large operating bandwidth, which greatly improves its range resolution capability.

[0029] 2. The technical solution of this invention achieves phase shift between multiple channels required to generate vortex electromagnetic waves by introducing time-delay optical fiber, eliminating the need for multiple sets of phase shifting devices, which greatly reduces the complexity of the system and the hardware cost.

[0030] 3. The technical solution of this invention can generate multi-mode, wide-bandwidth vortex electromagnetic waves by using a single-cycle frequency sweep process, avoiding the time-division working mode in traditional generation schemes, saving time resources, and greatly improving detection efficiency.

[0031] 4. The generated vortex electromagnetic waves have the characteristics of large bandwidth and multiple modes, which can achieve high-resolution detection in both range and azimuth directions.

[0032] 5. By adjusting the step frequency signal, delay fiber, and antenna array, the bandwidth, total number of modes, mode spacing, mode conversion period, and other parameters of the generated vortex electromagnetic wave can be flexibly reconstructed. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the vortex radar detection device of the present invention;

[0034] Figure 2 This is a schematic diagram illustrating the principle of the imaging algorithm.

[0035] Figure 3 The field strength distribution of the generated vortex electromagnetic waves at frequencies ranging from 18 GHz to 18.0034 GHz is shown.

[0036] Figure 4The phase distribution diagram of the generated vortex electromagnetic waves at frequencies from 18 GHz to 18.0034 GHz is shown.

[0037] Figure 5 The graph shows the relationship between the OAM mode and frequency of the generated vortex electromagnetic wave from 18 GHz to 18.14 GHz.

[0038] Figure 6 The image shows the results of the imaging simulation. Detailed Implementation

[0039] To address the shortcomings of existing technologies, this invention aims to improve the operating bandwidth of traditional vortex electromagnetic radar by utilizing the large bandwidth and low loss characteristics of microwave photonic signal generation and processing technology. It also introduces a multi-channel optical delay link to generate large-bandwidth, multi-mode, and parameter-reconfigurable vortex electromagnetic waves through single-cycle frequency sweeping, thereby reducing system complexity and significantly improving detection efficiency. Furthermore, based on the signal generation method, a corresponding imaging processing method is proposed, enabling two-dimensional high-resolution forward-looking radar imaging to be completed in a single transmission and reception process.

[0040] The vortex electromagnetic wave generation method of the present invention modulates a single-frequency optical carrier with a step-frequency signal and divides the generated modulated optical signal into N channels, where N is an integer greater than 2. Different delays are introduced into these N channels of modulated optical signals, with the delays introduced into the first to N channels increasing stepwise by a fixed increment Δt. Then, the N channels of modulated optical signals after the delay are photoelectrically converted to obtain N channels of radio frequency signals. The radio frequency signals of the first to N channels are used to excite the first to N antenna array elements to generate vortex electromagnetic waves. The first to N antenna array elements are arranged at equal intervals in a clockwise / counterclockwise direction to form a uniform circular array with N antenna array elements.

[0041] The vortex electromagnetic wave generating device of the present invention includes:

[0042] The excitation signal generation unit is used to modulate a single-frequency optical carrier with a step frequency signal and divide the generated modulated optical signal into N paths, where N is an integer greater than 2; different delays are introduced for each of these N modulated optical signals, and the delays introduced for the first to Nth paths increase stepwise with a fixed increment Δt; then the N modulated optical signals after the delay are converted into photoelectric signals to obtain N channels of radio frequency signals.

[0043] The antenna array is a uniform circular array with N antenna elements. The first to Nth antenna elements are arranged at equal intervals in a clockwise / counterclockwise direction, and the radio frequency signals of the first to Nth channels are used as excitation signals to generate vortex electromagnetic waves.

[0044] The vortex radar detection device of the present invention includes a transmitting end for transmitting vortex electromagnetic waves toward a target, and a receiving end for receiving the target's scattered echo with a single antenna to achieve target imaging; the transmitting end is the vortex electromagnetic wave generating device as described above.

[0045] Furthermore, the target imaging method is as follows: using the modulated optical signal without introduced delay as the reference optical signal, the received target reflected echo is subjected to microwave photonic mixing processing, and the obtained signal is subjected to photoelectric detection to achieve photoelectric conversion, thereby obtaining an intermediate frequency signal carrying target information; data sampling is performed on each frequency component contained in the intermediate frequency signal under each orbital angular momentum mode to obtain a frequency-topological charge two-dimensional data matrix with frequency and orbital angular momentum mode as the horizontal and vertical axes, respectively; firstly, a fast Fourier transform is performed on the data along the frequency axis to obtain a one-dimensional range image under different orbital angular momentum modes, and then a fast Fourier transform is performed along the topological charge domain to achieve azimuth focusing, thereby obtaining the final two-dimensional imaging result.

[0046] To facilitate public understanding, the technical solution of the present invention will be described in detail below through a specific embodiment and in conjunction with the accompanying drawings:

[0047] The vortex radar detection device constructed in this embodiment is as follows: Figure 1 As shown, it includes a transmitter and a receiver.

[0048] At the transmitting end, the laser generates a single-frequency optical carrier wave, which is then fed into a Mach-Zehnder modulator. A step-frequency signal generated by an arbitrary waveform generator is used as the driving signal to modulate the optical carrier wave entering the Mach-Zehnder modulator. The step-frequency signal can be expressed as:

[0049] S t (m,t)=rect(t / T pm )exp[j2πf c (m)t]

[0050] Where m = 1, 2, ..., M represents the pulse number, M is the total number of pulses in the step frequency signal, t is the signal time, and rect(t / T) pm ) represents a rectangular window, T pm f is the duration of a single pulse signal. c (m) is the center frequency of the m-th pulse.

[0051] The modulated optical signal output from the Mach-Zehnder modulator is divided into N channels, where N is an integer greater than 2. Different delay fibers of varying lengths are added to each channel to introduce different delays. The delays introduced in the first to Nth channels increase in a stepwise manner with a fixed increment Δt. Then, the N delayed modulated optical signals are photoelectrically converted to obtain N channels of radio frequency (RF) signals. These N channels of RF signals are then transmitted to an antenna array for transmission to the target. Figure 1 As shown, the transmitting antenna array is a uniform circular array placed in the xoz plane with a radius of a. N antenna elements are uniformly distributed on the ring. The first to Nth antenna elements are arranged at equal intervals in a clockwise / counterclockwise direction, and the radio frequency signals of the first to Nth channels are used as excitation signals to generate vortex electromagnetic waves.

[0052] Based on the required range resolution ρ for radar application scenarios r azimuth resolution ρ a Maximum detection range R max The bandwidth B, the total number of modes L, and the mode transition period T required to generate vortex electromagnetic waves are determined according to the following formulas. f Based on this, the stepped frequency signal and antenna array were designed:

[0053]

[0054]

[0055]

[0056] Where c is the speed of light.

[0057] The bandwidth of the step frequency signal is the bandwidth B of the vortex electromagnetic wave.

[0058] Based on the formula N = L, set the number of transmitter channels and the number of antenna array elements N.

[0059] According to the formula:

[0060]

[0061]

[0062] Set the initial frequency f0 of the step frequency signal and the frequency sweep interval Δf; where Δl is the vortex electromagnetic wave mode conversion interval, and K is any positive integer that takes a value in the positive integer field Z.

[0063] According to the formula: The delay difference Δt is obtained, and the length of the delay fiber in each channel is adjusted so that the modulated optical signals of any two adjacent channels have the same delay difference Δt. This ultimately creates a stepped delay with a fixed increment of Δt between each channel. Therefore, the delay corresponding to the nth element is: t n = t + n·Δt.

[0064] For any point P(r,θ,φ) in the far field, when the frequency of the step-frequency signal is f, the field strength formed by the signal emitted by the uniform circular array can be expressed as:

[0065]

[0066] in and r n Let |rr| be the position vectors of point P and the nth antenna element, respectively. Using the infinitesimal dipole approximation, |rr| is used. n |≈r can be used to represent the amplitude, and |rr can be used instead. n |≈r-asinθcos(φ-φ n Make a phase approximation, where φ n Let be the azimuth angle of the nth antenna element.

[0067] The electric field strength can then be approximated as:

[0068]

[0069] Where Δψ(f) = 2πfΔt. If we let:

[0070]

[0071] The field strength can then be rewritten as:

[0072]

[0073] From the phase term Therefore, the beam generated by the uniform circular array is a vortex electromagnetic beam carrying OAM, and its OAM mode l(f) varies with frequency, i.e., it is frequency-dependent. Simultaneously, due to the discrete sampling of the spatial phase of the transmitting antenna array around the circle, according to the Nyquist sampling theorem, the frequency variation of the broadband stepped-frequency signal will cause the OAM mode of the vortex electromagnetic beam to change with frequency T. f The frequency changes rapidly. By adjusting the step frequency signal, delay fiber, and antenna array, the bandwidth, total number of modes, mode spacing, and mode transition period of the generated vortex electromagnetic wave can be flexibly reconstructed.

[0074] The system detects forward-looking targets using vortex electromagnetic waves with a large bandwidth and rapidly changing periodic OAM mode, and receives the target's scattered echo using a single antenna. For example... Figure 1As shown, at the receiving end, using the modulated optical signal without introduced delay as the reference optical signal, microwave photonic mixing processing is performed on the received target reflected echo, and photoelectric detection is performed on the obtained signal to obtain an intermediate frequency signal carrying target information; then, as... Figure 2 As shown, the acquired intermediate frequency signal contains Each frequency component corresponds to an OAM mode from l1 to l L It exhibits a periodic, continuous change. To decouple the two-dimensional information of frequency and topological charge domain, and to reconstruct the range and azimuth information of the target respectively, this invention samples data from each frequency component contained in the intermediate frequency signal under each orbital angular momentum mode. Taking OAM mode equal to l1 as an example, the specific sampling process is as follows: taking the first frequency component f1 of OAM mode equal to l1 as the starting point, sampling the acquired intermediate frequency signal samples at intervals of L frequency components, finally obtaining a set of elements with a number of... The data. Furthermore, according to OAM mode l1 to l L The intermediate frequency signal was sampled L times, and the resulting L sets of data were arranged in a frequency-topological charge two-dimensional data matrix with frequency and orbital angular momentum mode as the horizontal and vertical axes, respectively. First, a fast Fourier transform was performed on the data along the frequency axis to obtain a one-dimensional range image under different orbital angular momentum modes. Then, a fast Fourier transform was performed along the topological charge domain to achieve azimuth focusing, thus obtaining the final two-dimensional imaging result.

[0075] To verify the technical effect of this invention, simulation experiments were conducted. In the experiment, a waveform generator produced a stepped-frequency signal with a bandwidth of 8 GHz (18-26 GHz) and a sweep interval of 225 kHz as the driving signal for the electro-optic modulator. The total number of OAM modes to be generated was set to 16, and the maximum detectable range of the radar was 41.6 m. Based on this, the OAM mode conversion period was calculated to be 3.6 MHz, the number of antenna elements to be 16, and the inter-channel delay difference Δt to be 0.2778 μs. An observation window parallel to the antenna array plane was set to observe the generated vortex electromagnetic waves. The distance between the observation window and the antenna array was 20 m, and the width was 1 m in both the horizontal and vertical directions. The field strength, phase, and OAM mode characteristics observed when the signal frequency was from 18 GHz to 18.0034 GHz are as follows: Figure 3 , Figure 4 and Figure 5As shown in the figure. The observation results show that the technical solution of this invention can effectively generate frequency-dependent broadband vortex electromagnetic waves. The OAM mode changes rapidly and periodically with frequency. Furthermore, under the simulation parameters of this embodiment, the OAM mode changes continuously from -7 to 8 with a mode interval of 1, and the period of change is equal to the set 3.6MHz. Further, in the simulation experimental scenario, four ideal scattering points with positions (19.95, 0.175, 0), (20, 0.175, 0.25), (20, 0.175, -0.25), and (20.05, 0.175, 0) are set as the detected targets. The generated frequency-dependent vortex electromagnetic waves are used to detect them, and the received echoes are reconstructed using the imaging processing scheme proposed in this invention. The resulting imaging results are shown in the figure. Figure 6 As shown in the figure, the imaging results demonstrate that the detection and imaging method proposed in this invention can reconstruct the two-dimensional information of forward-looking targets. The targets are well separated, and the reconstructed position information is accurate, with good focusing performance and a resolution close to the theoretical resolution. Simulation results show that, compared to traditional vortex electromagnetic radar imaging methods, the frequency-dependent microwave photonic vortex electromagnetic radar rapid imaging method proposed in this invention utilizes the advantages of microwave photonic radar technology, such as large bandwidth and low loss, to generate vortex electromagnetic waves with a large operating bandwidth, greatly improving the radar's range resolution. Simultaneously, by introducing a time-delay fiber to achieve the phase shift between multiple channels required for generating vortex electromagnetic waves, multiple phase-shifting devices are eliminated, significantly reducing system complexity and hardware costs. Furthermore, multi-mode, large-bandwidth vortex electromagnetic waves can be generated using a single frequency sweep cycle, avoiding the time-division multiplexing mode in traditional generation schemes. Combined with the imaging processing method proposed in this invention, rapid and high-resolution radar detection can be achieved in both range and azimuth directions. Moreover, by adjusting the sweep frequency signal, the delay fiber, and the antenna array, the bandwidth, total number of modes, mode spacing, and mode conversion period of the generated vortex electromagnetic wave can be flexibly reconstructed.

Claims

1. A method for generating vortex electromagnetic waves, characterized in that, A single-frequency optical carrier is modulated using a step-frequency signal, and the generated modulated optical signal is divided into... N road, N It is an integer greater than 2; it is this N Different delays are introduced into the modulated optical signals of each path, from the 1st to the 2nd. N The delay introduced by the path is a fixed increment. The increments are stepped, and then a delay is introduced. N The modulated optical signals are respectively converted into photoelectric signals to obtain N Radio frequency signals of each channel; From the 1st to the 1st N The radio frequency signals of each channel respectively affect the first to the second channels. N Each antenna element is excited to generate a vortex electromagnetic wave, wherein the first to the second... N The antenna elements are arranged at equal intervals in a clockwise / counterclockwise direction to form a [structure / structure]. N A uniform circular array of antenna elements; Set and adjust the vortex electromagnetic wave parameters according to the following formula: ； in, L This represents the total number of modes of vortex electromagnetic waves. T f The mode transition period of the vortex electromagnetic wave. The interval for vortex electromagnetic wave mode conversion. These are the initial frequency and sweep interval of the step frequency signal, respectively. K Z represents a positive integer, where Z is a positive integer field.

2. A vortex electromagnetic wave generating device, characterized in that, include: The excitation signal generation unit is used to modulate a single-frequency optical carrier with a step frequency signal and divide the generated modulated optical signal into... N road, N It is an integer greater than 2; it is this N Different delays are introduced into the modulated optical signals of each path, from the 1st to the 2nd. N The delay introduced by the path is a fixed increment. The increments are stepped, and then a delay is introduced. N The modulated optical signals are respectively converted into photoelectric signals to obtain N Radio frequency signals of each channel; Antenna array, which has N A uniform circular array of antenna elements, arranged at equal intervals in a clockwise / counterclockwise direction, from the 1st to the 2nd. N Each antenna element is represented by the first to the second... N The radio frequency signals of each channel are used as excitation signals to generate vortex electromagnetic waves; Set and adjust the vortex electromagnetic wave parameters according to the following formula: ； in, L This represents the total number of modes of vortex electromagnetic waves. T f The mode transition period of the vortex electromagnetic wave. The interval for vortex electromagnetic wave mode conversion. These are the initial frequency and sweep interval of the step frequency signal, respectively. K Z represents a positive integer, where Z is a positive integer field.

3. A vortex radar detection method, comprising transmitting vortex electromagnetic waves toward a target and receiving the target's scattered echo using a single antenna to achieve target imaging; characterized in that, The vortex electromagnetic wave is generated using the vortex electromagnetic wave generation method as described in claim 1.

4. The vortex radar detection method as described in claim 3, characterized in that, The target imaging method is as follows: using the modulated optical signal without introduced delay as the reference optical signal, the received target reflected echo is subjected to microwave photonic mixing processing, and the obtained signal is subjected to photoelectric detection to obtain an intermediate frequency signal carrying target information; data sampling is performed on each frequency component contained in the intermediate frequency signal under each orbital angular momentum mode to obtain a frequency-topological charge two-dimensional data matrix with frequency and orbital angular momentum mode as the horizontal and vertical axes, respectively; firstly, a fast Fourier transform is performed on the data along the frequency axis to obtain a one-dimensional range image under different orbital angular momentum modes, and then a fast Fourier transform is performed along the topological charge domain to achieve azimuth focusing, thereby obtaining the final two-dimensional imaging result.

5. A vortex radar detection device, comprising a transmitting end for emitting vortex electromagnetic waves toward a target, and a receiving end for receiving the target's scattered echo using a single antenna to achieve target imaging; characterized in that, The transmitting end is the vortex electromagnetic wave generating device as described in claim 2.

6. The vortex radar detection device as described in claim 5, characterized in that, The target imaging method is as follows: using the modulated optical signal without introduced delay as the reference optical signal, the received target reflected echo is subjected to microwave photonic mixing processing, and the obtained signal is subjected to photoelectric detection to obtain an intermediate frequency signal carrying target information; data sampling is performed on each frequency component contained in the intermediate frequency signal under each orbital angular momentum mode to obtain a frequency-topological charge two-dimensional data matrix with frequency and orbital angular momentum mode as the horizontal and vertical axes, respectively; firstly, a fast Fourier transform is performed on the data along the frequency axis to obtain a one-dimensional range image under different orbital angular momentum modes, and then a fast Fourier transform is performed along the topological charge domain to achieve azimuth focusing, thereby obtaining the final two-dimensional imaging result.

Images