Radar forward-looking imaging method and device based on orbital angular momentum interference

Abstract

The application relates to a radar forward-looking imaging method and device based on orbital angular momentum interference. The method comprises the following steps: generating a main OAM mode echo and a secondary OAM mode echo by using a target imaging echo equation; performing defocusing elimination processing and OAM domain phase interference processing on the main OAM mode echo and the secondary OAM mode echo respectively according to an imaging algorithm to obtain a wrapped orbital angular momentum interference phase result; performing defocusing elimination processing and OAM domain phase interference processing on a non-zero reference OAM mode echo and a zero mode echo respectively according to the imaging algorithm to obtain an all-around unwrapped interference phase result; and performing calculation on the wrapped interference phase result and the all-around unwrapped interference phase result, performing inversion calculation on the obtained phase-unwrapped interference phase result, and obtaining a radar forward-looking target imaging result. The method can reduce the complexity and cost of an electromagnetic vortex three-dimensional imaging radar system.

Description

Technical Field

[0001] This application relates to the field of radar imaging technology, and in particular to a radar forward-looking imaging method and apparatus based on orbital angular momentum interferometry. Background Technology

[0002] Traditional radar interferometric 3D imaging technology mainly relies on spatial baseline configuration to form multi-angle observations. It uses primary and secondary antennas at different locations to radiate conventional planar electromagnetic waves to illuminate the radar's forward-looking target. The echo signals are processed to obtain a two-dimensional high-resolution radar complex image. The target's third-dimensional information is reconstructed by utilizing the path difference and phase difference. Typically, higher reconstruction accuracy requires longer baselines, increasing system burden and cost, and is difficult to apply in many space-constrained platforms. Vortex electromagnetic waves are special electromagnetic waves carrying orbital angular momentum, with their phase wavefront exhibiting a twisted spiral distribution. Unlike the conventional planar electromagnetic wave excitation of traditional interferometric radar, under vortex electromagnetic wave illumination, there is a definite modulation relationship between the phase of the primary-secondary OAM mode echo interference, the target azimuth information, and the number of OAM modes. This characteristic can be used to achieve radar forward-looking target imaging. Vortex electromagnetic waves have received widespread attention and research in the fields of radar target rotating Doppler detection and super-resolution imaging, demonstrating their advantages and potential over traditional radar detection and imaging methods.

[0003] Currently, the main method for three-dimensional imaging with electromagnetic vortex radar is the forward-looking target imaging method based on traversing different OAM mode ranges. However, this method requires generating a large number of vortex electromagnetic waves carrying different OAM mode numbers, which greatly increases the complexity and cost of electromagnetic vortex three-dimensional imaging radar systems. Summary of the Invention

[0004] Therefore, it is necessary to provide a radar forward-looking imaging method and device based on orbital angular momentum interferometry that can reduce the complexity and cost of electromagnetic vortex three-dimensional imaging radar systems, in order to address the above-mentioned technical problems.

[0005] A forward-looking radar imaging method based on orbital angular momentum interferometry, the method comprising:

[0006] Using a radar platform to observe the moving scene in the forward-looking direction, the target in the forward-looking area is illuminated by a vortex electromagnetic wave with a fixed frequency bandwidth and carrying two different OAM modes generated by a circular array antenna, and the target's backscattering coefficient and position information are obtained.

[0007] The target imaging echo equation is constructed based on the modulation effect of the radar-target geometry, target backscattering coefficient, and position information on the transmitted signal.

[0008] The main OAM mode echo and the secondary OAM mode echo are generated using the target imaging echo equation. The main OAM mode echo and the secondary OAM mode echo are defocused and eliminated according to the imaging algorithm to obtain a range-elevation two-dimensional high-resolution radar complex image.

[0009] OAM domain phase interferometry processing was performed on the range-elevation two-dimensional high-resolution radar complex image to obtain the entangled orbital angular momentum interferometry phase results;

[0010] Based on the imaging algorithm, defocusing elimination processing and OAM domain phase interference processing are performed on the non-zero reference OAM mode and zero mode echoes respectively to obtain omnidirectional unentangled orbital angular momentum interference phase results;

[0011] The phase interference results of orbital angular momentum with entanglement and orbital angular momentum with no entanglement are used to calculate the phase interference results of orbital angular momentum with no phase entanglement.

[0012] The phase results of the orbital angular momentum interferometry without phase entanglement are inverted to obtain the radar forward-looking target imaging results.

[0013] In one embodiment, the target imaging echo equation is constructed based on the modulation effect of the radar-target geometry, target backscattering coefficient, and position information on the transmitted signal, including:

[0014] Based on the radar-target geometry and the modulation effect of the target backscattering coefficient and position information on the transmitted signal, the target imaging echo equation is constructed as follows:

[0015]

[0016] Where, f′∈[f c -B r / 2,f c +B r / 2] represents the frequency variable, l = l M Represents the main OAM mode echo, l = l S This represents the secondary OAM mode echo, where N is the number of antenna elements, n represents the serial number of the transmitting element, and m represents the serial number of the receiving element. This indicates that the vortex electromagnetic wave at the transmitting end is related to the coordinates. The goals mutually motivate each other, φ represents the result of the interaction between the conventional electromagnetic wave formed by the receiver beam and the target. n ψ represents the orientation and position of the array element. m The phase of the receiving array element excitation, k is the wavenumber vector, and r n r m This represents the distance vector from the transmitting element and the receiving element to the target. Let be the RCS coefficient of the q-th scattering center of the target, where Q represents the total number of scattering centers and q represents the index of the scattering center. Let z be the instantaneous slant range between the radar and the target, z∈[-L / 2,L / 2] be the position variable of the radar's forward-looking motion trajectory, c be the speed of electromagnetic waves in a vacuum, j represent the imaginary unit, π be pi, exp(·) represent an exponential function with the natural constant e as its base, and H be the instantaneous slant range between the radar and the target. l and K l These represent different echo coefficients.

[0017] In one embodiment, the main OAM mode echo and the secondary OAM mode echo are defocused and eliminated according to the imaging algorithm to obtain a range-elevation two-dimensional high-resolution radar complex image, including:

[0018] Defocusing removal processing is performed on the main OAM mode echo and the secondary OAM mode echo using either the BPA algorithm or the PFI imaging algorithm, resulting in a range-elevation two-dimensional high-resolution radar complex image.

[0019]

[0020] in, This represents the two-way transmission and reception pattern function of the primary OAM mode. For the two-way transmission and reception pattern function of the sub-OAM mode, This indicates the two-way integrated beam pointing, where R represents the range variable and θ represents the elevation angle variable. Indicates the pitch angle of the target scattering point. Indicates the azimuth angle of the target scattering point. This indicates the target distance focusing result. This indicates the target pitch and focus result.

[0021] In one embodiment, OAM domain phase interferometry is performed on the range-elevation two-dimensional high-resolution radar complex image to obtain the entangled orbital angular momentum interferometry phase result, including:

[0022] OAM domain phase interferometry was performed on the range-elevation two-dimensional high-resolution radar complex image to obtain the orbital angular momentum interferometry phase results;

[0023] The phase results of orbital angular momentum interference are calculated to obtain the phase results of entangled orbital angular momentum interference.

[0024] In one embodiment, OAM domain phase interferometry is performed on the range-elevation two-dimensional high-resolution radar complex image to obtain orbital angular momentum interferometry phase results, including:

[0025] OAM domain phase interferometry processing was performed on the range-elevation two-dimensional high-resolution radar complex image to obtain the orbital angular momentum interferometry phase result.

[0026]

[0027] Where Δl represents the OAM modal difference, σ α,β Represents the scattering coefficient of a pixel. This represents the pixel representation of the target distance focusing result, where α represents the distance pixel index and β represents the pitch pixel index. Represents the distance between pixels. Represents the pitch angle of a pixel. Represents the azimuth angle of a pixel. This represents the pixel-based result of the target pitch focusing.

[0028] In one embodiment, the orbital angular momentum interference phase result is calculated to obtain the entangled orbital angular momentum interference phase result, including:

[0029] The phase results of the orbital angular momentum interference were calculated, and the phase results of the entangled orbital angular momentum interference were obtained as follows:

[0030] φ VEiR-wrap (α,β;|Δl|=2l max )=φ VEiR-Ture (α,β;|Δl|=2l max -2π·ξ(α,β)

[0031] Among them, l M =-l S =l max ξ(α,β) represents the fuzzy number.

[0032] In one embodiment, defocusing and phase interferometry processing in the OAM domain are performed on the non-zero reference OAM mode and zero mode echoes respectively according to the imaging algorithm to obtain omnidirectional, untangled orbital angular momentum interferometry phase results, including:

[0033] Based on the BPA algorithm or PFI imaging algorithm, defocusing and phase interferometry processing are performed on the non-zero reference OAM mode and zero mode echoes, respectively, to obtain the omnidirectional, unentangled orbital angular momentum interferometry phase results.

[0034]

[0035] In one embodiment, the orbital angular momentum interference phase results are calculated using both the entangled orbital angular momentum interference phase results and the omnidirectional unentangled orbital angular momentum interference phase results, to obtain the unentangled orbital angular momentum interference phase results, including:

[0036] Dividing the phase result of the entangled orbital angular momentum interferometry by the phase result of the unentangled orbital angular momentum interferometry in all directions yields the ambiguity number.

[0037]

[0038] Substituting the fuzzy numbers into the phase result of the entangled orbital angular momentum interference, we obtain the phase result of the orbital angular momentum interference without phase entanglement.

[0039] In one embodiment, the phase result of the orbital angular momentum interferometry without phase winding is inverted to obtain the radar forward-looking target imaging result, including:

[0040] Inversion calculations were performed on the phase results of the orbital angular momentum interferometry without phase wrapping to obtain the radar forward-looking target imaging results.

[0041]

[0042] A forward-looking radar imaging device based on orbital angular momentum interferometry, the device comprising:

[0043] The target imaging echo module is used to observe the moving scene in the forward-looking area using the radar platform. It generates vortex electromagnetic waves with a fixed frequency bandwidth and two different OAM modes based on a circular array antenna to illuminate the target in the forward-looking area, thereby obtaining the target backscattering coefficient and position information. The target imaging echo equation is constructed based on the modulation effect of the radar-target geometry and the target backscattering coefficient and position information on the transmitted signal.

[0044] The module for calculating the entangled orbital angular momentum interferometry phase results is used to generate the main OAM mode echo and the secondary OAM mode echo using the target imaging echo equation. According to the imaging algorithm, the main OAM mode echo and the secondary OAM mode echo are defocused and eliminated to obtain a range-elevation two-dimensional high-resolution radar complex image. The OAM domain phase interferometry processing is performed on the range-elevation two-dimensional high-resolution radar complex image to obtain the entangled orbital angular momentum interferometry phase results.

[0045] The module for calculating the orbital angular momentum interferometry phase results without phase wrapping is used to perform defocusing and phase interferometry processing on the non-zero reference OAM mode and zero mode echoes respectively according to the imaging algorithm to obtain the orbital angular momentum interferometry phase results without phase wrapping in all directions; the orbital angular momentum interferometry phase results without phase wrapping are calculated using the orbital angular momentum interferometry phase results with wrapping and the orbital angular momentum interferometry phase results without phase wrapping in all directions.

[0046] The radar forward-looking target imaging module is used to invert the phase results of the orbital angular momentum interferometry without phase winding to obtain the radar forward-looking target imaging results.

[0047] The aforementioned radar forward-looking imaging method and apparatus based on orbital angular momentum interferometry utilizes a radar platform moving towards the forward-looking observation scene. A circular array antenna generates vortex electromagnetic waves with a fixed frequency bandwidth, carrying two different OAM modes, to illuminate the target in the forward-looking region, obtaining the target's backscattering coefficient and position information. Based on the radar-target geometric relationship and the modulation effect of the target's backscattering coefficient and position information on the transmitted signal, a target imaging echo equation is constructed. The intrinsic relationship between the target azimuth information and the number of OAM modes in the primary and secondary OAM mode echoes is analyzed. High-resolution imaging algorithms are used to process the primary and secondary OAM complex images. For different OAM interferometry strategies, a phase-unwound orbital angular momentum interferometry phase result is obtained. Finally, based on the orbital angular momentum interferometry phase result, high-precision reconstruction and imaging of the radar target azimuth information are achieved. This invention utilizes only the echo information of vortex electromagnetic waves carrying a very small number of OAM modes. Two or three non-zero OAM mode echoes can achieve high-precision reconstruction and imaging of the forward-looking target azimuth of the radar. On the one hand, it breaks through the limitation of the baseline length of traditional interferometric radar on the improvement of the accuracy of third-dimensional information reconstruction; on the other hand, it greatly reduces the complexity and cost of electromagnetic vortex three-dimensional imaging radar systems that need to traverse a large number of different OAM modes. Attached Figure Description

[0048] Figure 1 This is a flowchart illustrating a radar forward-looking imaging method based on orbital angular momentum interferometry in one embodiment.

[0049] Figure 2 This is a schematic diagram of a forward-looking target imaging scene model based on orbital angular momentum interferometry in one embodiment;

[0050] Figure 3 This is a schematic diagram of the process for forward-looking target imaging based on dual OAM mode orbital angular momentum interferometry in one embodiment;

[0051] Figure 4 This is a schematic diagram of the process for forward-looking target imaging based on three non-zero OAM mode orbital angular momentum interferometry in another embodiment;

[0052] Figure 5 The following are images of radar forward-looking targets in one embodiment: (a) is the orbital angular momentum interferometric radar echo map of the metal sphere under the main and secondary OAM modes obtained by electromagnetic calculation; (b) is the orbital angular momentum interferometric radar echo map of the complex aircraft target under the main and secondary OAM modes obtained by electromagnetic calculation; (c) is the imaging result of the metal sphere by conventional interferometric radar; (d) is the imaging result of the aircraft target; (e) is the imaging result of the forward-looking target by the orbital angular momentum interferometric radar of this application; and (f) is an enlarged view of the imaging result of the forward-looking target by the orbital angular momentum interferometric radar of this application.

[0053] Figure 6This is a structural block diagram of a radar forward-looking imaging device based on orbital angular momentum interferometry in one embodiment. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0055] In one embodiment, such as Figure 2 As shown, a radar forward-looking imaging method based on orbital angular momentum interferometry is provided, including the following steps:

[0056] Step 102: Using the radar platform to observe the moving scene in the forward-looking direction, the target in the forward-looking area is illuminated by a vortex electromagnetic wave with a fixed frequency bandwidth and carrying two different OAM modes generated by the circular array antenna, and the target backscattering coefficient and position information are obtained; the target imaging echo equation is constructed based on the modulation effect of the radar-target geometric relationship and the target backscattering coefficient and position information on the transmitted signal.

[0057] Using a radar platform moving at a speed v toward the forward-looking observation area Ω, such as Figure 2 As shown, the length of the track formed from point D to point E is L. The midpoint of the forward-looking motion track is defined as the origin O of the imaging coordinate system. Any two mutually perpendicular radial directions of the circular array antenna are defined as the X, Y, and Z axes, which are aligned with the velocity direction. During radar movement, the primary OAM mode is l. M The secondary OAM mode is l S The vortex electromagnetic wave illuminates the target in the forward-looking area. During reception, the echo is recorded using a conventional beam after beamforming, combined with a center frequency of f. c Bandwidth is B r The target imaging echo equations of the main and secondary OAM mode echoes are obtained by constructing the linear frequency modulated or step frequency transmitted signal waveforms, which are used to acquire the phase of the main and secondary OAM complex images and the unwound orbital angular momentum interference.

[0058] Step 104: Generate the main OAM mode echo and the secondary OAM mode echo using the target imaging echo equation. Perform defocusing removal processing on the main OAM mode echo and the secondary OAM mode echo according to the imaging algorithm to obtain a range-elevation two-dimensional high-resolution radar complex image. Perform OAM domain phase interferometry processing on the range-elevation two-dimensional high-resolution radar complex image to obtain the entangled orbital angular momentum interferometry phase result.

[0059] This application, through the observation of the target imaging echo equations of the main and secondary OAM mode echoes, reveals that the parameter H in both echoes... lThe expression contains the same four types of phase modulation functions. The first phase term is a Fourier transform pair consisting of the frequency variable and the target distance, used to achieve high-resolution range imaging. The second phase term is a Fourier transform pair consisting of the track position and the cosine of the target elevation angle, used to achieve high-resolution elevation imaging. The third phase term is a secondary interference term related to the target distance and elevation, causing defocusing in the imaging result, which needs to be compensated for. The fourth phase term is the phase constant term caused by the path difference. The main and secondary OAM mode echoes have the same form; however, in traditional interferometric radar, the different equivalent phase centers of the main and secondary antenna positions make the constant phase corresponding to this path difference different. In addition, the parameter K in both echoes... l These are modulation functions formed by multiplying their respective OAM mode numbers by the target azimuth angle. Clearly, this indicates that the target azimuth information is directly modulated into the OAM domain echo phase, providing theoretical support for obtaining the target's third-dimensional information. This application is based on... Figure 3 The processing flow of the dual OAM modal interferometric imaging algorithm shown is as follows: First, the primary and secondary OAM mode echoes are processed based on the BPA or PFI algorithm to obtain focused high-resolution radar composite images of the primary and secondary OAM modes (range-elevation). Then, OAM domain phase interferometry processing is performed to obtain the orbital angular momentum interferometric phase result. From the orbital angular momentum interferometric phase result, it can be seen that for each range-elevation imaging unit, the corresponding orbital angular momentum interferometric phase result is composed of the product of the primary and secondary OAM mode difference and the target azimuth angle. Combining the error transfer function, based on the relationship between the target azimuth angle, the primary-secondary OAM mode difference, and the orbital angular momentum interferometry term in the orbital angular momentum interferometric phase result, the azimuth reconstruction accuracy is derived as follows:

[0060]

[0061] in, This represents the mean square error of orientation reconstruction. The mean square error of the interferometric phase measurement. The measurement error of the main and secondary OAM modes.

[0062] As can be seen from the orientation reconstruction accuracy, as the absolute value of the difference between the primary and secondary OAM modes |Δl|=|l M -l S The larger the value of |, the higher the azimuth reconstruction accuracy. Clearly, higher azimuth reconstruction accuracy requires a larger difference between the primary and secondary OAM modes. A larger OAM mode difference corresponds to a smaller unambiguous range. Table 1 shows different dual OAM mode interference strategies.

[0063] Table 1

[0064]

[0065] The range of OAM modes that a circular array antenna can generate is [-l] max ,l max Both the primary and secondary OAM modes take values ​​within this range. Assume a certain intermediate OAM mode is l. mid Therefore, the combined azimuth reconstruction accuracy and the unambiguous range of azimuth imaging... It is easy to see that the azimuth reconstruction accuracy corresponding to different dual OAM modal interferometry strategies satisfies the following relationship:

[0066]

[0067] The relationship between the unambiguous azimuth imaging ranges corresponding to different dual OAM modal interferometry strategies is as follows:

[0068]

[0069] Clearly, when using only dual OAM modes for forward-looking target interferometric imaging, there is a trade-off between higher reconstruction accuracy and a larger unambiguous azimuth imaging range, requiring a compromise between the performance of the two to choose the OAM interferometric strategy.

[0070] Step 106: According to the imaging algorithm, defocus elimination processing and OAM domain phase interference processing are performed on the non-zero reference OAM mode and zero mode echoes respectively to obtain the omnidirectional unwound orbital angular momentum interference phase result; the wrapped orbital angular momentum interference phase result and the omnidirectional unwound orbital angular momentum interference phase result are used to calculate to obtain the phase-unwound orbital angular momentum interference phase result.

[0071] To simultaneously achieve higher reconstruction accuracy and a larger unambiguous imaging range, this application proposes a three-non-zero OAM modal interferometry strategy as shown in Table 2, where the main OAM mode, the secondary OAM mode, and the reference OAM mode are all non-zero.

[0072] Table 2

[0073] Modal Strategy 1 Strategy 2 Main OAM mode <![CDATA[+l max or -l max ]]> <![CDATA[+l max or -l max ]]> Sub-OAM mode <![CDATA[+l max or -l max ]]> <![CDATA[+l max or -l max ]]> Reference OAM mode +1 -1

[0074] In dual-OAM modal interferometry strategies and imaging methods, a large primary-secondary OAM modal difference |Δl| can achieve higher azimuth reconstruction accuracy. However, a large primary-secondary OAM modal difference causes the true interference phase to exceed [-π,π] or [0,2π], while the actual acquired interference phase can only take values ​​between [-π,π] or [0,2π]. Therefore, by solving for the ambiguity number ξ(α,β) in equation (1), the true interference phase can be recovered from the actual acquired interference phase, and then the true azimuth position of the target can be obtained by inversion, breaking through the limitation between higher reconstruction accuracy and a larger azimuth-unambiguous imaging range.

[0075] φ VEiR-Ture(α,β;|Δl|=2l)=φ VEiR-wrap (α,β; |Δl|=2l)+2π·ξ(α,β) (1)

[0076] Based on the unambiguous imaging range, it is easy to see that when |Δl|=1, an unambiguous imaging range of [-π,π] in all directions can be obtained. Therefore, as shown in Table 2, when the non-zero OAM reference mode is designed as l R =+1 or l R When the value is -1, phase interference with the zero OAM mode echo can produce an all-around unwrapped interference phase.

[0077] Specifically, such as Figure 4 The flowchart of the three non-zero OAM modal interferometric imaging method shown firstly focuses on the main OAM mode l. M Echo, sub-OAM mode S The echo, after range-elevation high-resolution imaging using BPA or PFI imaging algorithms, undergoes OAM domain phase interferometry processing to obtain the entangled interferometric phase result, which can be expressed as...

[0078] φ VEiR-wrap (α,β;|Δl|=2l max )=φ VEiR-Ture (α,β;|Δl|=2l max )-2π·ξ(α,β) (2)

[0079] Among them, l M =-l S =l max Theoretical true interferometric phase results

[0080] Secondly, regarding the reference non-zero OAM mode |l R |=1 echo, zero-mode echo, range-elevation high-resolution imaging using BPA or PFI imaging algorithms, and OAM domain phase interferometry processing are performed to obtain omnidirectional, untangled interferometric phase results, which can be expressed as

[0081]

[0082] Then, dividing the primary-secondary OAM modal interference phase result shown in equation (2) by the reference OAM modal interference phase result shown in equation (3), we obtain:

[0083]

[0084] Further simplification of this formula yields,

[0085]

[0086] Where φVEiR-wrap (α,β; |Δl|=2l)<2π, therefore, the fuzzy number obtained is,

[0087]

[0088] Substituting equation (6) into equation (2), we can obtain the interference phase result with large OAM mode difference and no phase entanglement.

[0089] Step 108: Invert the phase results of the orbital angular momentum interferometry without phase entanglement to obtain the radar forward-looking target imaging results.

[0090] In the aforementioned radar forward-looking imaging method based on orbital angular momentum interferometry, this application utilizes a radar platform moving towards the forward-looking observation scene. A circular array antenna generates vortex electromagnetic waves with a fixed frequency bandwidth, carrying two different OAM modes, to illuminate the target in the forward-looking region, obtaining the target's backscattering coefficient and position information. Based on the radar-target geometric relationship and the modulation effect of the target's backscattering coefficient and position information on the transmitted signal, a target imaging echo equation is constructed. The intrinsic relationship between the target azimuth information and the number of OAM modes in the primary and secondary OAM mode echoes is analyzed. High-resolution imaging algorithms are used to process the primary and secondary OAM complex images. For different OAM interferometry strategies, a phase-unwound orbital angular momentum interferometry phase result is obtained. Finally, based on the orbital angular momentum interferometry phase result, high-precision reconstruction and imaging of the radar target azimuth information are achieved. This invention utilizes only the echo information of vortex electromagnetic waves carrying a very small number of OAM modes. Two or three non-zero OAM mode echoes can achieve high-precision reconstruction and imaging of the forward-looking target azimuth of the radar. On the one hand, it breaks through the limitation of the baseline length of traditional interferometric radar on the improvement of the accuracy of third-dimensional information reconstruction; on the other hand, it greatly reduces the complexity and cost of electromagnetic vortex three-dimensional imaging radar systems that need to traverse a large number of different OAM modes.

[0091] In one embodiment, the target imaging echo equation is constructed based on the modulation effect of the radar-target geometry, target backscattering coefficient, and position information on the transmitted signal, including:

[0092] Based on the radar-target geometry and the modulation effect of the target backscattering coefficient and position information on the transmitted signal, the target imaging echo equation is constructed as follows:

[0093]

[0094] Where, f′∈[f c -B r / 2,f c +B r / 2] represents the frequency variable, l = l M Represents the main OAM mode echo, l = l SThis represents the secondary OAM mode echo, where N is the number of antenna elements, n represents the serial number of the transmitting element, and m represents the serial number of the receiving element. This indicates that the vortex electromagnetic wave at the transmitting end is related to the coordinates. The goals mutually motivate each other, φ represents the result of the interaction between the conventional electromagnetic wave formed by the receiver beam and the target. n ψ represents the orientation and position of the array element. m The phase of the receiving array element excitation, k is the wavenumber vector, and r n r m This represents the distance vector from the transmitting element and the receiving element to the target. Let be the RCS coefficient of the q-th scattering center of the target, where Q represents the total number of scattering centers and q represents the index of the scattering center. Let z be the instantaneous slant range between the radar and the target, z∈[-L / 2,L / 2] be the position variable of the radar's forward-looking motion trajectory, c be the speed of electromagnetic waves in a vacuum, j represent the imaginary unit, π be pi, exp(·) represent an exponential function with the natural constant e as its base, and H be the instantaneous slant range between the radar and the target. l and K l These represent different echo coefficients.

[0095] In a specific embodiment, the echo coefficient H l and K l The expression is,

[0096]

[0097]

[0098] In one embodiment, the main OAM mode echo and the secondary OAM mode echo are defocused and eliminated according to the imaging algorithm to obtain a range-elevation two-dimensional high-resolution radar complex image, including:

[0099] Defocusing removal processing is performed on the main OAM mode echo and the secondary OAM mode echo using either the BPA algorithm or the PFI imaging algorithm, resulting in a range-elevation two-dimensional high-resolution radar complex image.

[0100]

[0101] in, This represents the two-way transmission and reception pattern function of the primary OAM mode. For the two-way transmission and reception pattern function of the sub-OAM mode, This indicates the two-way integrated beam pointing, where R represents the range variable and θ represents the elevation angle variable. Indicates the pitch angle of the target scattering point. Indicates the azimuth angle of the target scattering point. This indicates the target distance focusing result. This indicates the target pitch and focus result.

[0102] In one embodiment, OAM domain phase interferometry is performed on the range-elevation two-dimensional high-resolution radar complex image to obtain the entangled orbital angular momentum interferometry phase result, including:

[0103] OAM domain phase interferometry was performed on the range-elevation two-dimensional high-resolution radar complex image to obtain the orbital angular momentum interferometry phase results;

[0104] The phase results of orbital angular momentum interference are calculated to obtain the phase results of entangled orbital angular momentum interference.

[0105] In one embodiment, OAM domain phase interferometry is performed on the range-elevation two-dimensional high-resolution radar complex image to obtain orbital angular momentum interferometry phase results, including:

[0106] OAM domain phase interferometry processing was performed on the range-elevation two-dimensional high-resolution radar complex image to obtain the orbital angular momentum interferometry phase result.

[0107]

[0108] Where Δl represents the OAM modal difference, σ α,β Represents the scattering coefficient of a pixel. This represents the pixel representation of the target distance focusing result, where α represents the distance pixel index and β represents the pitch pixel index. Represents the distance between pixels. Represents the pitch angle of a pixel. Represents the azimuth angle of a pixel. This represents the pixel-based result of the target pitch focusing.

[0109] In one embodiment, the orbital angular momentum interference phase result is calculated to obtain the entangled orbital angular momentum interference phase result, including:

[0110] The phase results of the orbital angular momentum interference were calculated, and the phase results of the entangled orbital angular momentum interference were obtained as follows:

[0111] φ VEiR-wrap (α,β;|Δl|=2l max )=φ VEiR-Ture (α,β;|Δl|=2l max -2π·ξ(α,β)

[0112] Among them, l M =-l S =l max ξ(α,β) represents the fuzzy number.

[0113] In one embodiment, defocusing and phase interferometry processing in the OAM domain are performed on the non-zero reference OAM mode and zero mode echoes respectively according to the imaging algorithm to obtain omnidirectional, untangled orbital angular momentum interferometry phase results, including:

[0114] Based on the BPA algorithm or PFI imaging algorithm, defocusing and phase interferometry processing are performed on the non-zero reference OAM mode and zero mode echoes, respectively, to obtain the omnidirectional, unentangled orbital angular momentum interferometry phase results.

[0115]

[0116] In one embodiment, the orbital angular momentum interference phase results are calculated using both the entangled orbital angular momentum interference phase results and the omnidirectional unentangled orbital angular momentum interference phase results, to obtain the unentangled orbital angular momentum interference phase results, including:

[0117] Dividing the phase result of the entangled orbital angular momentum interferometry by the phase result of the unentangled orbital angular momentum interferometry in all directions yields the ambiguity number.

[0118]

[0119] Substituting the fuzzy numbers into the phase result of the entangled orbital angular momentum interference, we obtain the phase result of the orbital angular momentum interference without phase entanglement.

[0120] In one embodiment, the phase result of the orbital angular momentum interferometry without phase winding is inverted to obtain the radar forward-looking target imaging result, including:

[0121] Inversion calculations were performed on the phase results of the orbital angular momentum interferometry without phase wrapping to obtain the radar forward-looking target imaging results.

[0122]

[0123] In one embodiment, assuming the radar flight speed is v = 200 m / s, the transmitted signal frequency is f0 = 10 GHz, and the frequency bandwidth is B r =600MHz, main OAM mode is l M =+1, secondary OAM mode is -1, respectively targeting Figure 5 (a) The metal sphere, Figure 5 Electromagnetic calculations were performed on the complex aircraft target shown in (b) to obtain the orbital angular momentum interferometric radar echoes in their respective primary and secondary OAM modes. Under the same system configuration, the imaging results of conventional interferometric radar on metal spheres and aircraft targets are as follows: Figure 5 (c) and Figure 5 As shown in (d). The forward-looking target imaging results based on the orbital angular momentum interferometric radar proposed in this application are as follows: Figure 5 (e) Figure 5 As shown in (f), under the same signal-to-noise ratio conditions, compared with the imaging results of traditional interferometric radar, the imaging results of this application are consistent with the theoretical position and have higher reconstruction accuracy, verifying the feasibility and effectiveness of this application.

[0124] It should be understood that, although Figure 1 The steps in the flowchart are shown sequentially as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order in which these steps are executed, and they can be performed in other orders. Figure 1 At least some of the steps in the process may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed 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 some of the sub-steps or stages of other steps.

[0125] In one embodiment, such as Figure 6 As shown, a forward-looking radar imaging device based on orbital angular momentum interferometry is provided, comprising: a target imaging echo module 602, a coiled orbital angular momentum interferometry phase result calculation module 604, a non-coiled orbital angular momentum interferometry phase result calculation module 606, and a forward-looking radar target imaging module 608, wherein:

[0126] The target imaging echo module 602 is used to observe the moving scene in the forward-looking direction using a radar platform. It generates vortex electromagnetic waves with a fixed frequency bandwidth and two different OAM modes based on a circular array antenna to illuminate the target in the forward-looking area, thereby obtaining the target backscattering coefficient and position information. The target imaging echo equation is constructed based on the modulation effect of the radar-target geometric relationship and the target backscattering coefficient and position information on the transmitted signal.

[0127] The winding orbital angular momentum interferometry phase result calculation module 604 is used to generate the main OAM mode echo and the secondary OAM mode echo using the target imaging echo equation. According to the imaging algorithm, the main OAM mode echo and the secondary OAM mode echo are defocused and eliminated respectively to obtain a range-elevation two-dimensional high-resolution radar complex image. The range-elevation two-dimensional high-resolution radar complex image is then subjected to OAM domain phase interferometry processing to obtain the winding orbital angular momentum interferometry phase result.

[0128] The orbital angular momentum interferometry phase result calculation module 606 without phase wrapping is used to perform defocusing elimination processing and OAM domain phase interferometry processing on the non-zero reference OAM mode and zero mode echoes respectively according to the imaging algorithm to obtain the orbital angular momentum interferometry phase result without phase wrapping in all directions; the orbital angular momentum interferometry phase result without phase wrapping is obtained by calculation using the orbital angular momentum interferometry phase result with wrapping and the orbital angular momentum interferometry phase result without phase wrapping in all directions.

[0129] The radar forward-looking target imaging module 608 is used to perform inversion calculations on the phase results of orbital angular momentum interferometry without phase winding to obtain the radar forward-looking target imaging results.

[0130] In one embodiment, the target imaging echo module 602 is further configured to construct a target imaging echo equation based on the modulation of the transmitted signal according to the radar-target geometry, the target backscattering coefficient, and position information, including:

[0131] Based on the radar-target geometry and the modulation effect of the target backscattering coefficient and position information on the transmitted signal, the target imaging echo equation is constructed as follows:

[0132]

[0133] Where, f′∈[f c -B r / 2,f c +B r / 2] represents the frequency variable, l = l M Represents the main OAM mode echo, l = l S This represents the secondary OAM mode echo, where N is the number of antenna elements, n represents the serial number of the transmitting element, and m represents the serial number of the receiving element. This indicates that the vortex electromagnetic wave at the transmitting end is related to the coordinates. The goals mutually motivate each other, φ represents the result of the interaction between the conventional electromagnetic wave formed by the receiver beam and the target. n ψ represents the orientation and position of the array element. m The phase of the receiving array element excitation, k is the wavenumber vector, and r n r m This represents the distance vector from the transmitting element and the receiving element to the target. Let be the RCS coefficient of the q-th scattering center of the target, where Q represents the total number of scattering centers and q represents the index of the scattering center. Let z be the instantaneous slant range between the radar and the target, z∈[-L / 2,L / 2] be the position variable of the radar's forward-looking motion trajectory, c be the speed of electromagnetic waves in a vacuum, j represent the imaginary unit, π be pi, exp(·) represent an exponential function with the natural constant e as its base, and H be the instantaneous slant range between the radar and the target. l and Kl These represent different echo coefficients.

[0134] In one embodiment, the winding orbital angular momentum interference phase result calculation module 604 is further configured to perform defocusing removal processing on the main OAM mode echo and the secondary OAM mode echo respectively according to the imaging algorithm, to obtain a range-elevation two-dimensional high-resolution radar complex image, including:

[0135] Defocusing removal processing is performed on the main OAM mode echo and the secondary OAM mode echo using either the BPA algorithm or the PFI imaging algorithm, resulting in a range-elevation two-dimensional high-resolution radar complex image.

[0136]

[0137] in, This represents the two-way transmission and reception pattern function of the primary OAM mode. For the two-way transmission and reception pattern function of the sub-OAM mode, This indicates the two-way integrated beam pointing, where R represents the range variable and θ represents the elevation angle variable. Indicates the pitch angle of the target scattering point. Indicates the azimuth angle of the target scattering point. This indicates the target distance focusing result. This indicates the target pitch and focus result.

[0138] In one embodiment, the winding orbital angular momentum interferometry phase result calculation module 604 is further used to perform OAM domain phase interferometry processing on the range-elevation two-dimensional high-resolution radar complex image to obtain the winding orbital angular momentum interferometry phase result, including:

[0139] OAM domain phase interferometry was performed on the range-elevation two-dimensional high-resolution radar complex image to obtain the orbital angular momentum interferometry phase results;

[0140] The phase results of orbital angular momentum interference are calculated to obtain the phase results of entangled orbital angular momentum interference.

[0141] In one embodiment, the wound orbital angular momentum interferometry phase result calculation module 604 is also used to perform OAM domain phase interferometry processing on the range-elevation two-dimensional high-resolution radar complex image to obtain orbital angular momentum interferometry phase results, including:

[0142] OAM domain phase interferometry processing was performed on the range-elevation two-dimensional high-resolution radar complex image to obtain the orbital angular momentum interferometry phase result.

[0143]

[0144] Where Δl represents the OAM modal difference, σα,β Represents the scattering coefficient of a pixel. This represents the pixel representation of the target distance focusing result, where α represents the distance pixel index and β represents the pitch pixel index. Represents the distance between pixels. Represents the pitch angle of a pixel. Represents the azimuth angle of a pixel. This represents the pixel-based result of the target pitch focusing.

[0145] In one embodiment, the winding orbital angular momentum interference phase result calculation module 604 is further used to calculate the winding orbital angular momentum interference phase result, including:

[0146] The phase results of the orbital angular momentum interference were calculated, and the phase results of the entangled orbital angular momentum interference were obtained as follows:

[0147] φ VEiR-wrap (α,β;|Δl|=2l max )=φ VEiR-Ture (α,β;|Δl|=2l max -2π·ξ(α,β)

[0148] Among them, l M =-l S =l max ξ(α,β) represents the fuzzy number.

[0149] In one embodiment, the orbital angular momentum interferometry (OAM) phase result calculation module 606, which calculates the phase result without phase entanglement, is further configured to perform defocusing removal processing and OAM domain phase interferometry processing on the non-zero reference OAM mode and zero mode echoes respectively according to the imaging algorithm, to obtain omnidirectional, unentangled orbital angular momentum interferometry phase results, including:

[0150] Based on the BPA algorithm or PFI imaging algorithm, defocusing and phase interferometry processing are performed on the non-zero reference OAM mode and zero mode echoes, respectively, to obtain the omnidirectional, unentangled orbital angular momentum interferometry phase results.

[0151]

[0152] In one embodiment, the orbital angular momentum interference phase result calculation module 606 without phase winding is further used to calculate, using the orbital angular momentum interference phase result with winding and the orbital angular momentum interference phase result without winding in all directions, to obtain the orbital angular momentum interference phase result without phase winding, including:

[0153] Dividing the phase result of the entangled orbital angular momentum interferometry by the phase result of the unentangled orbital angular momentum interferometry in all directions yields the ambiguity number.

[0154]

[0155] Substituting the fuzzy numbers into the phase result of the entangled orbital angular momentum interference, we obtain the phase result of the orbital angular momentum interference without phase entanglement.

[0156] In one embodiment, the radar forward-looking target imaging module 608 is further configured to perform inversion calculations on the phase results of the orbital angular momentum interferometry without phase winding, to obtain the radar forward-looking target imaging results, including:

[0157] Inversion calculations were performed on the phase results of the orbital angular momentum interferometry without phase wrapping to obtain the radar forward-looking target imaging results.

[0158]

[0159] Specific limitations regarding the radar forward-looking imaging device based on orbital angular momentum interferometry can be found in the limitations of the radar forward-looking imaging method based on orbital angular momentum interferometry mentioned above, and will not be repeated here. Each module in the aforementioned radar forward-looking imaging device based on orbital angular momentum interferometry can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in hardware or independently of the processor in a computer device, or stored in software in the memory of a computer device, so that the processor can call and execute the operations corresponding to each module.

[0160] 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.

[0161] 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.

Claims

1. A method for radar forward-looking imaging based on orbital angular momentum interference, characterized in that, The method includes: Using a radar platform to observe the moving scene in the forward-looking direction, the target in the forward-looking area is illuminated by a vortex electromagnetic wave with a fixed frequency bandwidth and carrying two different OAM modes generated by a circular array antenna, and the target's backscattering coefficient and position information are obtained. The target imaging echo equation is constructed based on the radar-target geometry and the modulation effect of the target backscattering coefficient and position information on the transmitted signal. The main OAM mode echo and the secondary OAM mode echo are generated using the target imaging echo equation. The main OAM mode echo and the secondary OAM mode echo are defocused and eliminated according to the imaging algorithm to obtain a range-elevation two-dimensional high-resolution radar complex image. OAM domain phase interferometry processing is performed on the range-elevation two-dimensional high-resolution radar complex image to obtain the entangled orbital angular momentum interferometry phase result; Based on the imaging algorithm, defocusing elimination processing and OAM domain phase interference processing are performed on the non-zero reference OAM mode and zero mode echoes respectively to obtain omnidirectional unentangled orbital angular momentum interference phase results; The orbital angular momentum interference phase results without phase winding are calculated using the results of the entangled orbital angular momentum interference phase and the results of the omnidirectional unentangled orbital angular momentum interference phase. The phase results of the orbital angular momentum interferometry without phase entanglement are inverted to obtain the radar forward-looking target imaging results.

2. The method of claim 1, wherein, The target imaging echo equation is constructed based on the radar-target geometry and the modulation effect of the target backscattering coefficient and position information on the transmitted signal, including: Based on the radar-target geometry and the modulation effect of the target backscattering coefficient and position information on the transmitted signal, the target imaging echo equation is constructed as follows: where f' ∈ [f c -B r / 2,f c +B r / 2] represents the frequency variable, l = l M represents the main OAM mode echo, l = l S represents the secondary OAM mode echo, N is the number of antenna elements, n represents the serial number of the transmitting element, m represents the serial number of the receiving element, represents the mutual excitation result of the transmitting end vortex electromagnetic wave and the target with coordinates , represents the mutual excitation result of the receiving end beamformed conventional electromagnetic wave and the target, φ n is the azimuth position of the element, ψ m is the excitation phase of the receiving element, k is the wave number vector, r n , r m are the distance vector of the transmitting element and the receiving element to the target, is the RCS coefficient of the q = 1, 2, 3,..., Q scattering centers of the target, Q represents the total number of scattering centers, q represents the serial number of the scattering center, is the instantaneous slant range between the radar and the target, z ∈ [-L / 2, L / 2] is the variable of the radar front-looking motion track position, c is the propagation speed of electromagnetic wave in vacuum, j represents the imaginary unit, π is the circular constant, exp(·) represents the exponential function with the natural constant e as the base, H l and K l represent different echo coefficients.

3. The method of claim 2, wherein, According to the imaging algorithm, the main OAM mode echo and the secondary OAM mode echo are defocused and eliminated respectively to obtain a range-elevation two-dimensional high-resolution radar complex image, including: The main OAM mode echo and the secondary OAM mode echo are defocused and eliminated according to the BPA algorithm or the PFI imaging algorithm, respectively, to obtain a range-elevation two-dimensional high-resolution radar complex image. wherein, represents the main OAM mode transmit-receive bi-directional pattern function, represents the secondary OAM mode transmit-receive bi-directional pattern function, represents the transmit-receive bi-directional composite beam pointing, R represents a distance variable, and θ represents an elevation angle variable, represents the target scattering point elevation angle, represents the target scattering point azimuth angle, represents the target distance focusing result, represents the target elevation focusing result.

4. The method of claim 3, wherein, OAM domain phase interferometry processing is performed on the range-elevation two-dimensional high-resolution radar complex image to obtain the entangled orbital angular momentum interferometry phase results, including: OAM domain phase interferometry processing is performed on the range-elevation two-dimensional high-resolution radar complex image to obtain the orbital angular momentum interferometry phase result; The orbital angular momentum interference phase results are calculated to obtain the entangled orbital angular momentum interference phase results.

5. The method of claim 4, wherein, OAM domain phase interferometry is performed on the range-elevation two-dimensional high-resolution radar complex image to obtain orbital angular momentum interferometry phase results, including: OAM domain phase interferometry processing was performed on the range-elevation two-dimensional high-resolution radar complex image to obtain the orbital angular momentum interferometry phase result. wherein Δl represents the OAM mode difference, σ α,β denotes the scattering coefficient of the pixel point, denotes the pixel point form of the target range focusing result, a denotes the range pixel point index, and β denotes the pitch pixel point index, denotes the range of the pixel point, denotes the pitch angle of the pixel point, denotes the azimuth angle of the pixel point, denotes the pixel point form of the target pitch focusing result.

6. The method of claim 5, wherein, The orbital angular momentum interference phase results are calculated to obtain the entangled orbital angular momentum interference phase results, including: The orbital angular momentum interference phase result is calculated to obtain the entangled orbital angular momentum interference phase result as follows: φ VEiR-wrap (α,β; |Δl| = 2l max ) = φ VEiR-Ture (α,β; |Δl| = 2l max ) - 2π · ξ(α,β) where l M = -l S = l max , ξ(α, β) denotes a fuzzy number.

7. The method of claim 6, wherein, According to the imaging algorithm, the non-zero reference OAM mode echo and the zero mode echo are respectively subjected to defocusing elimination processing and OAM domain phase interference processing, and omnidirectional unwound orbital angular momentum interference phase results are obtained, including: According to the BPA algorithm or the PFI imaging algorithm, the non-zero reference OAM mode echo and the zero mode echo are respectively subjected to defocusing elimination processing and OAM domain phase interference processing, and the omnidirectional unwound orbital angular momentum interference phase results are obtained.

8. The method of claim 7, wherein, The unwound orbital angular momentum interference phase results are calculated by using the wrapped orbital angular momentum interference phase results and the omnidirectional unwound orbital angular momentum interference phase results, and unwound orbital angular momentum interference phase results without phase winding are obtained, including: The wrapped orbital angular momentum interference phase results are divided by the omnidirectional unwound orbital angular momentum interference phase results, and the ambiguity number is obtained. The ambiguity number is substituted into the wrapped orbital angular momentum interference phase results, and the unwound orbital angular momentum interference phase results without phase winding are obtained.

9. The method of claim 8, wherein, The unwound orbital angular momentum interference phase results without phase winding are subjected to inversion calculation, and radar forward-looking target imaging results are obtained, including: The unwound orbital angular momentum interference phase results without phase winding are subjected to inversion calculation, and the radar forward-looking target imaging results are obtained.

10. A radar forward-looking imaging device based on orbital angular momentum interference, characterized in that, The device comprises: A target imaging echo module is configured to move a radar platform towards a forward-looking observation scene, irradiate a forward-looking area target with vortex electromagnetic waves of a fixed frequency bandwidth and carrying two different OAM modes generated by a circular array antenna, obtain target backscattering coefficients and position information, and construct a target imaging echo equation according to the modulation effect of the radar-target geometric relationship and the target backscattering coefficients and position information; A wrapped orbital angular momentum interference phase result calculation module is configured to generate main OAM mode echoes and auxiliary OAM mode echoes by using the target imaging echo equation, perform defocusing elimination processing on the main OAM mode echoes and the auxiliary OAM mode echoes according to an imaging algorithm, obtain a distance-elevation two-dimensional high-resolution radar complex image, and perform OAM domain phase interference processing on the distance-elevation two-dimensional high-resolution radar complex image to obtain wrapped orbital angular momentum interference phase results; An unwound orbital angular momentum interference phase result calculation module is configured to perform defocusing elimination processing and OAM domain phase interference processing on non-zero reference OAM mode echoes and zero mode echoes according to an imaging algorithm, obtain omnidirectional unwound orbital angular momentum interference phase results, and calculate unwound orbital angular momentum interference phase results without phase winding by using the wrapped orbital angular momentum interference phase results and the omnidirectional unwound orbital angular momentum interference phase results; A radar forward-looking target imaging module is configured to perform inversion calculation on the unwound orbital angular momentum interference phase results without phase winding to obtain radar forward-looking target imaging results.

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