Concentric circular array design-based vortex electromagnetic wave radar forward-looking imaging method and system, storage medium and electronic device

Abstract

The application discloses a vortex electromagnetic wave radar forward-looking imaging method and system based on a concentric circular array design, a storage medium and an electronic device, and specifically comprises the following steps: establishing a new system radar imaging model according to a radar working mode; designing a concentric circular array and a vortex mode transmitting function; deriving a return model; obtaining distance direction high-resolution information of a target; performing distance correction, phase decoupling and Bessel amplitude compensation on the azimuth direction of the return, and coherently superimposing the compensated return to reestablish a dual relationship between a mode and an azimuth angle; and finally, realizing vortex electromagnetic wave radar forward-looking two-dimensional imaging through fast Fourier transform on the azimuth direction. The forward-looking imaging can increase the observation time of a region of interest, keep the region of interest in a main lobe range, enhance the strength of a return, increase return information, and effectively improve the azimuth direction resolution.

Description

Technical Field

[0001] This application relates to the field of signal processing technology, and in particular to a forward-looking imaging method, system, digitally readable storage medium, and electronic device for vortex electromagnetic wave radar based on a concentric ring array design. Background Technology

[0002] Microwave imaging is characterized by its ability to operate in all weather conditions and around the clock, making it widely used in geological exploration, damage assessment, forest remote sensing, and reconnaissance and surveillance. Radar imaging technology, exemplified by synthetic aperture radar (SAR), utilizes its large transmit bandwidth and synthetic aperture processing techniques to achieve high resolution in both range and azimuth dimensions. However, when radar is required to operate in forward-looking mode, the Doppler bandwidth drops sharply, making it impossible to utilize Doppler information for azimuth processing to obtain high azimuth resolution. This hinders forward-looking target imaging and results in inherent blind spots.

[0003] In recent years, orbital angular momentum has provided a new degree of freedom for information transmission, attracting considerable attention in the field of radar imaging. Electromagnetic waves carrying orbital angular momentum are called vortex electromagnetic waves, which have helical phase characteristics. Their wavefronts propagate helically along the beam axis in space, and the difference in echo phase is crucial for radar imaging. Therefore, this characteristic offers a new possibility for its application in forward-looking imaging.

[0004] Previous vortex electromagnetic wave radars mostly used uniform circular arrays to generate vortex electromagnetic waves. As the transmission mode changes, the main lobe of the electromagnetic wave also changes accordingly, which cannot guarantee that the main lobe will always illuminate the region of interest. This paper adopts a concentric ring array to transmit multimode vortex electromagnetic waves independently in a time-division manner, so that electromagnetic waves of different modes always illuminate the same area, realizing a spotting mode similar to that in synthetic aperture radar. Starting from the imaging scene of forward-looking radar and the geometric configuration of the concentric ring array, an echo signal model was constructed. Based on the original range Doppler algorithm, phase and amplitude compensation were added. Coherent superposition was used to make the mode and azimuth angle satisfy the duality relationship in the Fourier transform again, so as to obtain the target azimuth information and make up for the inherent blind zone of radar imaging. Summary of the Invention

[0005] The purpose of this application is to provide a forward-looking imaging method, system, storage medium, and electronic device for vortex electromagnetic wave radar based on a concentric ring array design, so as to solve or alleviate the problems existing in the prior art.

[0006] To achieve the above objectives, this application provides the following technical solution:

[0007] This application provides a forward-looking imaging method for vortex electromagnetic wave radar based on a concentric ring array design. The method includes: Step S101, establishing a new radar imaging model according to the radar's operating mode; Step S102, designing the transmission functions for the concentric ring array and vortex mode; Step S103, deriving the echo model based on the relative motion between the radar and the target; Step S104, transmitting a large-bandwidth linear frequency modulated signal in the range direction to obtain high-resolution range information of the target; Step S105, performing range correction on the echo obtained after pulse compression; Step S106, performing azimuth modulation phase decoupling and Bessel amplitude compensation on the range-corrected echo, and coherently superimposing the compensated echo to reconstruct the duality between the mode and the azimuth angle; Step S107, performing a fast Fourier transform on the azimuth direction to reconstruct a two-dimensional image.

[0008] Preferably, in step S101, the geometric configuration of radar imaging is established according to the forward-looking operating mode of the radar, and the elevation angle θ between the radar and the target is defined as the angle between the target and the radar flight direction; the azimuth angle is defined as... The angle between the distance between the radar and the target projected onto the plane of the circular array and the height axis.

[0009] Preferably, in step S102, a vortex emission mode that varies linearly with slow time is designed:

[0010]

[0011] Where η represents slow time, i.e., radar flight time; K l Indicates the mode switching rate; l ini This represents the mode of radar transmission at the initial moment.

[0012] Furthermore, the radius of the concentric ring array is calculated and designed based on the azimuth relationship between the radar and the target:

[0013]

[0014] Where x(η) represents a set of values ​​for the main lobe pointing angle of the Bessel function in the current transmission mode, a(η) represents the radius of the designed concentric rings, k represents the wavenumber of the signal, a represents the initial ring radius, and J l (x) represents the l-th order Bessel function of the first kind.

[0015] Preferably, in step S103, the echo signal model is derived based on the relative motion between the radar and the target:

[0016]

[0017] Where θ(η) is the elevation angle at each moment, and r(η) is the instantaneous slant range between the radar and the target. The azimuth angle of the target is represented by f0, the carrier frequency of the signal is represented by K. r Let θ(η) be the frequency modulation slope of the linear frequency modulated signal, and c represent the speed of light. θ(η) can be expressed as:

[0018]

[0019] Where r0 represents the initial distance between the radar and the target, θ0 represents the initial elevation angle between the radar and the target, and v represents the speed of the radar carrier.

[0020] Preferably, in step S104, a wide-bandwidth linear frequency modulated signal is transmitted in the range direction, and high-resolution target range information is obtained through pulse compression. The signal after down-conversion and pulse compression can be expressed as:

[0021]

[0022] Where w r [·] indicates the distance to the envelope, B w f represents the range pulse bandwidth. c denoted by carrier frequency, k by wavenumber, and a by the radius of the ring.

[0023] By utilizing the relative motion between the carrier aircraft and the target, it can be deduced that:

[0024]

[0025] Performing a Taylor expansion on the obtained instantaneous slant range yields the following results:

[0026]

[0027] Preferably, in step S105, the echo obtained in step S104 after range pulse compression is transformed into the range Doppler domain, and the range is corrected using the range Doppler algorithm. The resulting signal can be expressed as:

[0028]

[0029] Preferably, in step S106, a phase compensation factor and a Bessel amplitude compensation factor are designed to compensate for the echo, wherein the phase compensation factor h liner (η) can be expressed as:

[0030]

[0031] The Bessel amplitude compensation factor, based on the designed vortex launch mode and the target revisit angle, can be expressed as:

[0032]

[0033] The compensated echo can be represented as:

[0034]

[0035] Then, the echoes are coherently superimposed in the slow time domain to transform them into the modal domain:

[0036]

[0037] After the above compensation and coherent superposition, the modes and azimuth angles in the echo signal regain the duality relationship.

[0038] Preferably, in step S107, the signal obtained in step S106 is subjected to a fast Fourier transform in the modal domain to obtain the azimuth information of the target and obtain a focused two-dimensional target image.

[0039]

[0040] Where w a [·] indicates the azimuth envelope, B l This represents the total number of modes in the modal domain.

[0041] This application also provides a forward-looking imaging system for vortex electromagnetic wave radar based on a concentric ring array design, comprising: a data acquisition unit configured to receive echo signals from the illuminated imaging area; a pulse compression unit configured to perform pulse compression on the range-direction echo, thereby obtaining high-resolution range-direction information of the target; a range correction unit configured to perform range correction in the azimuth direction; a compensation unit configured to compensate for the azimuth modulation phase and Bessel amplitude of the echo; a coherent superposition unit configured to perform azimuth superposition on the compensated echo in a certain manner to reconstruct the duality between the mode and the azimuth angle; and an azimuth focusing unit configured to perform a fast Fourier transform on the modal domain of the superimposed signal, thereby reconstructing a two-dimensional image.

[0042] Beneficial effects:

[0043] The forward-looking imaging method for vortex electromagnetic wave radar based on concentric ring array design provided in this application first establishes a new radar imaging model according to the radar's operating mode. Then, the concentric ring array and vortex mode transmission function are designed. Based on the radar imaging model, the concentric ring array, and the vortex mode transmission function, the echo model is derived according to the relative motion between the radar and the target. Based on a wide-bandwidth linear frequency modulated signal, high-resolution range information of the target is obtained through pulse compression. The pulse-compressed signal is transformed to the range-Doppler domain, and range correction is performed using the range-Doppler algorithm. Phase and amplitude compensation are performed based on the azimuth modulation phase and Bessel amplitude modulation generated during radar motion. For the compensated signal, coherent superposition in the slow-time direction is performed according to the designed vortex mode transmission function, reconstructing the duality between the vortex mode and the azimuth angle. Based on the duality between the vortex mode and the azimuth angle, a fast Fourier transform is performed on the modal domain of the coherently superimposed signal to reconstruct a two-dimensional image. Attached Figure Description

[0044] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. Wherein:

[0045] Figure 1 This is a schematic diagram of the process of the present invention;

[0046] Figure 2 Simulation diagrams and azimuth slices of single-point and multi-point targets provided for some embodiments of the present invention;

[0047] Figure 3 The simulation image and orientation slice image of the point target obtained by traditional methods;

[0048] Figure 4 Geometric configuration diagrams provided for some embodiments of the present invention;

[0049] Figure 5 This is a unit configuration diagram of the present invention. Detailed Implementation

[0050] The present application will now be described in detail with reference to the accompanying drawings and embodiments. Various examples are provided by way of explanation and not by way of limitation. In fact, those skilled in the art will recognize that modifications and variations can be made to the present application without departing from the scope or spirit thereof. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the present application encompass such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0051] Exemplary methods

[0052] like Figure 1 As shown, the forward-looking imaging method of vortex electromagnetic wave radar based on concentric ring array design includes:

[0053] In step S101, the geometric configuration of radar imaging is established according to the forward-looking operating mode of the radar, and the elevation angle θ between the radar and the target is defined as the angle between the target and the radar flight direction; the azimuth angle is defined as... The angle between the distance between the radar and the target projected onto the plane of the circular array and the height axis.

[0054] In step S102, a vortex emission mode that varies linearly with slow time is designed:

[0055]

[0056] Where η represents slow time, i.e., radar flight time; K l Indicates the mode switching rate; l ini This represents the mode of radar transmission at the initial moment.

[0057] Furthermore, the radius of the concentric ring array is calculated and designed based on the azimuth relationship between the radar and the target:

[0058]

[0059] Where x(η) represents a set of values ​​for the main lobe pointing angle of the Bessel function in the current emission mode, and a(η) represents the radius of the designed concentric rings.

[0060] In step S103, the echo signal model is derived based on the relative motion between the radar and the target:

[0061]

[0062] Where θ(η) is the elevation angle at each moment, and r(η) is the instantaneous slant range between the radar and the target, θ(η) can be expressed as:

[0063]

[0064] Where r0 represents the initial distance between the radar and the target, θ0 represents the initial elevation angle between the radar and the target, and v represents the speed of the radar carrier.

[0065] In step S104, a wide-bandwidth linear frequency modulated signal is transmitted in the range direction. High-resolution range information of the target is obtained through pulse compression. The signal after down-conversion and pulse compression can be expressed as:

[0066]

[0067] Where w r [·] indicates the distance to the envelope, B w f represents the range pulse bandwidth. c denoted by carrier frequency, k by wavenumber, and a by the radius of the ring.

[0068] By utilizing the relative motion between the carrier aircraft and the target, it can be deduced that:

[0069]

[0070] Performing a Taylor expansion on the obtained instantaneous slant range yields the following results:

[0071]

[0072] In step S105, the echo obtained in step S104 after range pulse compression is transformed into the range Doppler domain, and the range is corrected using the range Doppler algorithm. The resulting signal can be expressed as:

[0073]

[0074] In step S106, a phase compensation factor and a Bessel amplitude compensation factor are designed to compensate for the echo, wherein the phase compensation factor h liner (η) can be expressed as:

[0075]

[0076] The Bell amplitude compensation factor, based on the designed vortex launch mode and the target revisit angle, can be expressed as:

[0077]

[0078] The compensated echo can be represented as:

[0079]

[0080] Then, the echoes are coherently superimposed in the slow time domain to transform them into the modal domain:

[0081]

[0082] After the above compensation and coherent superposition, the modes and azimuth angles in the echo signal regain the duality relationship.

[0083] In step S107, the signal obtained in step S106 is subjected to fast Fourier transform in the modal domain to obtain the azimuth information of the target and obtain a focused two-dimensional target image.

[0084]

[0085] Where w a [·] indicates the azimuth envelope, B l This represents the total number of modes in the modal domain.

[0086] This method increases the observation time of the region of interest and ensures that the region of interest remains within the main lobe, enhancing the echo amplitude and increasing its information content. This method improves the range-Doppler algorithm, enabling rapid decoupling of azimuth and slow-time information and performing echo amplitude compensation. Based on... Figure 2 single point target and Figure 3 As can be seen from the azimuth slice image, simulation experiments show that the azimuth-focused image obtained by this method is at least 2.4 times better than that of the traditional method.

[0087] Exemplary System

[0088] This application also provides a forward-looking imaging system for vortex electromagnetic wave radar based on a concentric ring array design, such as... Figure 5 As shown, it includes: a data acquisition unit configured to receive echo signals from the illuminated imaging area; a pulse compression unit configured to perform pulse compression on the range echo, thereby obtaining high-resolution range information of the target; a range correction unit configured to perform range correction in the azimuth direction; a compensation unit configured to compensate for the azimuth modulation phase and Bessel amplitude of the echo; a coherent superposition unit configured to perform azimuth superposition on the compensated echo in a certain manner to reconstruct the duality between mode and azimuth angle; and an azimuth focusing unit configured to perform a fast Fourier transform on the modal domain of the superimposed signal, thereby reconstructing a two-dimensional image.

[0089] The forward-looking imaging method of vortex electromagnetic wave radar based on concentric ring array design provided in this application can achieve target imaging at any forward-looking angle, which will not be described in detail here.

[0090] Exemplary device

[0091] This application provides an electronic device, including a storage medium, an antenna, and a processor; the processor is suitable for executing various programs; the antenna is used for receiving and transmitting signals; the memory is used for storing multiple programs; characterized in that, when the memory executes the programs on the processor, it implements the aforementioned vortex electromagnetic wave radar forward-looking imaging method based on concentric ring array design.

[0092] Since the forward-looking imaging of vortex electromagnetic wave radar based on concentric ring array design has been described in detail in the specific implementation method examples, it will not be repeated here.

[0093] The antenna, including monopulse antennas and array antennas, is one of the most critical components in the radar system. The memory includes digital radio frequency memory. The processor includes a central processing unit (CPU), a network processor (NP), etc., and can also be a digital signal processor, application-specific integrated circuit (ASIC), off-the-shelf programmable gate array (FPGA), control circuit, or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components. It can implement or execute the methods, steps, and logic block diagrams disclosed in the embodiments of this application. The general-purpose processor can be a microprocessor or any conventional processor.

[0094] The antenna can be specifically configured to transmit linear frequency modulated signals carrying different modes and receive the echoes.

[0095] Specifically, the processor can be configured to: perform pulse compression on the range echo to obtain high-resolution range information of the target; perform range correction on the azimuth direction; perform azimuth modulation phase and Bessel amplitude compensation on the range-corrected signal; perform azimuth coherent superposition on the compensated signal in a certain way to reconstruct the duality between mode and azimuth angle; and perform fast Fourier transform on the modal domain of the superimposed signal to reconstruct a two-dimensional image.

[0096] It should be noted that, depending on the implementation needs, the various components / steps described in the embodiments of this application can be broken down into more components / steps, or two or more components / steps or parts of the operation of components / steps can be combined into new components / steps to achieve the purpose of the embodiments of this application.

[0097] The methods described above according to the embodiments of this application can be implemented in hardware, software, or a combination of hardware and software. The hardware portion can be implemented using dedicated logic; the software portion can be stored in memory (such as a CD-ROM, RAM, hard disk, or magnetic disk), or implemented as a raw storage medium downloaded over a network, located on a remote recording medium or a non-transitory machine storage medium, and has appropriate instructions directed to the system and methods for execution. Furthermore, when a general-purpose computer accesses the code used to implement the methods shown herein, the execution of the code transforms the general-purpose computer into a dedicated computer for executing the methods shown herein.

[0098] Those skilled in the art will understand that the above-described devices and methods can be implemented using computer-executable instructions or included in processor control code. Whether these functions are implemented in hardware / software or a combination of both depends on the specific application and constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of the embodiments of this application.

[0099] It should be noted that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for the device and system embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the method embodiments.

[0100] The device and system embodiments described above are merely illustrative. The units referred to as separate entities may or may not be physically separate. The entities mentioned as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0101] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A forward-looking imaging method for vortex electromagnetic wave radar based on concentric ring array design, characterized in that, include: Step S101: Establish a new radar imaging model based on the radar's operating mode, defining the elevation angle θ between the radar and the target as the angle between the target and the radar's flight direction; define the azimuth angle... The angle between the projection of the distance between the radar and the target onto the plane of the circular array and the height axis; Step S102: Design the emission function for the concentric ring array and vortex mode; Step S103: Derive the echo model based on the relative motion between the radar and the target; Step S104: Transmit a wide-bandwidth linear frequency modulated signal in the range direction, and obtain high-resolution range information of the target through pulse compression; Step S105: Perform distance correction on the signal obtained from the distance-to-pulse compression in step S104; Step S106: Decouple and perform Bessel amplitude compensation on the azimuth phase modulation term of the range-corrected echo obtained in step S105, and coherently superimpose it in the slow time domain to reconstruct the duality between the mode and the azimuth angle; in step S106, design a phase compensation factor and a Bessel amplitude compensation factor to compensate for the echo, wherein the phase compensation factor h liner (η) is represented as: Where f0 is the carrier frequency of the signal, v is the speed of the radar carrier, θ0 is the initial elevation angle between the radar and the target, c is the speed of light, η is the slow time, k is the wave number of the signal, and j is the imaginary unit. The Bessel amplitude compensation factor, based on the designed vortex launch mode and the target revisit angle, is expressed as follows: Where a is the radius of the ring used at the initial moment, l(η) is the vortex transmission mode that varies linearly with slow time, r0 represents the initial distance between the radar and the target, θ0 represents the initial elevation angle between the radar and the target, and v represents the speed of the radar carrier. The compensated echo is represented as follows: Where t is the fast time. B is the azimuth of the target. w For the range-direction pulse bandwidth, w r [·] indicates the distance to the envelope; Then, the echoes are coherently superimposed in the slow time domain to transform them into the modal domain: Where K l Mode switching rate; After the above compensation and coherent superposition, the modes and azimuth angles in the echo signal re-satisfy the duality relationship. Step S107: Perform a fast Fourier transform on the signal obtained in step S106 that is decoupled from the slow time in the azimuth direction to obtain a forward-looking two-dimensional focused image of the vortex electromagnetic wave radar.

2. The forward-looking imaging method for vortex electromagnetic wave radar based on concentric ring array design according to claim 1, characterized in that, The vortex mode emission function mentioned in step S102 is a vortex emission mode that varies linearly with slow time: Where η represents slow time, i.e., radar flight time; K l Indicates the mode switching rate; l ini The mode of radar transmission at the initial moment. This represents the floor function; Furthermore, the radius of the concentric ring array is calculated and designed based on the azimuth relationship between the radar and the target: Where x(η) represents a set of values ​​for the main lobe pointing angle of the Bessel function in the current transmission mode, a(η) represents the radius of the designed concentric rings, k represents the wavenumber of the signal, a represents the initial ring radius, and J l (x) represents the l-th order Bessel function of the first kind.

3. The forward-looking imaging method for vortex electromagnetic wave radar based on concentric ring array design according to claim 2, characterized in that, The echo signal model in step S103 is as follows: Where θ(η) is the elevation angle at each moment, and r(η) is the instantaneous slant range between the radar and the target. The azimuth angle of the target is represented by f0, the carrier frequency of the signal is represented by K. r Let θ(η) be the frequency modulation slope of the linear frequency modulated signal, and c represent the speed of light; where θ(η) is expressed as: Where r0 represents the initial distance between the radar and the target, θ0 represents the initial elevation angle between the radar and the target, v represents the speed of the radar carrier, k represents the wave number, and a represents the radius of the circle.

4. The forward-looking imaging method for vortex electromagnetic wave radar based on concentric ring array design according to claim 3, characterized in that, Step S104 specifically includes the following steps: transmitting a wide-bandwidth linear frequency modulated signal in the range direction, obtaining high-resolution target range direction information through pulse compression, and the signal after down-conversion and pulse compression is represented as: Where w r [·] indicates the distance to the envelope, B w f represents the range pulse bandwidth. c denoted by carrier frequency, k by wavenumber, and a by the radius of the ring. Using the relative motion between the carrier aircraft and the target, the following can be derived: Performing a Taylor expansion on the obtained instantaneous slant range, we get:

5. The forward-looking imaging method for vortex electromagnetic wave radar based on concentric ring array design according to claim 4, characterized in that, In step S105, the echo obtained in step S104 after range pulse compression is transformed into the range Doppler domain, and the range is corrected using the range Doppler algorithm. The resulting signal is represented as follows:

6. The forward-looking imaging method for vortex electromagnetic wave radar based on concentric ring array design according to claim 5, characterized in that, In step S107, the signal obtained in step S106 is subjected to a fast Fourier transform in the modal domain to obtain the azimuth information of the target, thus obtaining a focused two-dimensional target image. Where w a [·] indicates the azimuth envelope, B l This represents the total number of modes in the modal domain.

7. A system for a forward-looking imaging method of vortex electromagnetic wave radar based on the concentric ring array design of claim 1, characterized in that, include: The data acquisition unit is configured to receive the echo signal of the irradiated imaging area; A pulse compression unit is configured to perform pulse compression on the range echo; Based on this, high-resolution range information of the target is obtained; The range correction unit is configured to perform range correction in the azimuth direction. The compensation unit is configured to compensate for the azimuth modulation phase and Bessel amplitude of the echo. The coherent stacking unit is configured to perform azimuth stacking on the compensated echoes in a certain manner to reconstruct the dual relationship between the mode and the azimuth. The azimuth focusing unit is configured to perform a fast Fourier transform on the modal domain of the superimposed signal, and then reconstruct a two-dimensional image based on this.

8. A storage medium storing a plurality of programs, characterized in that, The program application is loaded and executed by a processor to implement the forward-looking imaging method of vortex electromagnetic wave radar based on concentric ring array design as described in any one of claims 1-6.

9. An electronic device, comprising a storage medium and a processor; the processor being adapted to execute various programs; and a memory for storing multiple programs; characterized in that, When the memory executes the program on the processor, it implements the forward-looking imaging method of vortex electromagnetic wave radar based on concentric ring array design as described in any one of claims 1-6.

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