A method for suppressing side lobes of arc-shaped synthetic aperture radar

Abstract

The embodiment of the present invention provides a method for suppressing the side lobes of an arc-shaped synthetic aperture radar, comprising the following steps: obtaining the echo signal of the arc-shaped synthetic aperture radar; performing imaging processing on the echo signal using a wave number domain algorithm to obtain a point target impulse response; analyzing the imaging results with continuous point targets, analyzing the overlapping properties of false signals generated by impulse responses of two continuous point targets that are smaller than the distance resolution. By gradually and iteratively identifying point target information, separating the real point target signals that are smaller than the distance resolution according to the overlapping properties of the continuous point targets, and extracting the main lobe of the real target signal during the processing, the influence of the side lobe alignment reduction on the amplitude size of the reconstruction of the surrounding targets and the false target peak formed by the overlapping accumulation of multiple side lobes can be effectively avoided, thereby realizing the side lobe suppression of arc-shaped synthetic aperture radar imaging with continuous point targets.

Description

Technical Field

[0001] The invention belongs to the technical field of arc-shaped synthetic aperture two-dimensional imaging, and in particular relates to an arc-shaped synthetic aperture radar sidelobe suppression method. Background Art

[0002] The arc synthetic aperture working mechanism not only has the advantages of all-weather and all-day monitoring of traditional radars, but also has the characteristics of 360° all-round observation and high resolution, playing an increasingly important role in target monitoring, target elevation detection, radar target imaging diagnosis and other fields. The arc synthetic aperture radar system is a linear system, so impulse response is usually used to describe its performance indicators. The image formed by the echo signal of a point target after focusing is a sinc function. Because the sidelobe value of the sinc function is high, the sidelobe of a strong target may drown out a nearby weak target, resulting in blurred imaging.

[0003] The traditional method to suppress signal sidelobes is to window the received signal to reduce the sidelobes to an acceptable level for target detection. Commonly used window functions include Hanning window, Hamming window, Blackman window, Kaiser window, etc. However, windowing will cause the main lobe to widen, the signal-to-noise ratio to be lost, and the signal's distance resolution and target detection performance to deteriorate.

[0004] The CLEAN algorithm was originally developed by radio astronomers Proposed in 1974, it is a process of searching and iterating one-dimensional data based on the idea of ​​recursion, which is used to alleviate the sidelobe effect caused by limited observation data, thereby improving the quality of synthetic aperture imaging in radio astronomy. In view of the imaging characteristics of arc synthetic aperture radar point targets, the CLEAN algorithm can also be used to eliminate the sidelobes in arc synthetic aperture radar signal detection. The traditional CLEAN algorithm identifies the main lobe through step-by-step iteration, eliminates the sidelobes, and reconstructs the position and amplitude information of the real target. When the sidelobes are aligned, it may interfere with other point target signals, so it is only suitable for processing radar echoes of discrete point targets; in addition, for radar signals with continuous point targets, the sidelobes of strong targets will compete with the mainlobes of adjacent weak targets, thereby interfering with the weak targets, and even strong targets and weak targets accumulate to form false targets. At this time, the position of the signal peak is no longer the mainlobe peak of the strongest target, so the traditional CLEAN algorithm is no longer applicable to eliminate radar signals with continuous point targets.

[0005] In summary, for the sidelobe suppression of arc synthetic aperture radar imaging, improvements are made on the basis that the traditional CLEAN algorithm is only applicable to processing discrete point targets. Summary of the invention

[0006] In view of the above problems in the prior art, an object of an embodiment of the present invention is to provide a method for suppressing side lobes of an arc-shaped synthetic aperture radar.

[0007] The technical solution adopted in the embodiment of the present invention is a method for suppressing side lobes of an arc-shaped synthetic aperture radar, comprising the following steps:

[0008] Acquire the echo signal of arc synthetic aperture radar;

[0009] The wave number domain algorithm is used to process the echo signal and obtain the impulse response of the point target.

[0010] For echo signals with continuous point targets, the overlapping properties of false signals generated by impulse responses of two continuous point targets smaller than the range resolution are analyzed;

[0011] By gradually iteratively identifying point target information, the real point target signals smaller than the range resolution are separated according to the overlapping properties of the false signals generated by the impulse responses of continuous point targets, and the main lobe of the real target signal is extracted during the processing to obtain the real target signal. This can effectively avoid the influence of sidelobe alignment attenuation on the amplitude of the reconstruction of the surrounding targets and the false target peak formed by the overlapping accumulation of multiple side lobes, thereby achieving sidelobe suppression for arc synthetic aperture radar imaging with continuous point targets.

[0012] Furthermore, in the step of acquiring the echo signal of the arc synthetic aperture radar, the echo signal is subjected to frequency demodulation and RVP compensation.

[0013] Furthermore, the imaging process of the echo signal using the wave number domain algorithm to obtain the impulse response of the point target specifically includes:

[0014] Perform two-dimensional fast Fourier transform on the echo signal to the wave number domain;

[0015] The stationary phase is obtained by numerical solution in the wave number domain, and the range accumulation is performed after the phase is compensated in the range direction to complete the focusing in the range direction;

[0016] Performing an inverse fast Fourier transform in azimuth on the accumulated result to complete focusing in azimuth;

[0017] The two-dimensional imaging of the point target is completed, and the system response of the point target is the point target impulse response.

[0018] Furthermore, the analysis of the echo signal with continuous point targets and the analysis of the overlapping properties of false signals generated by impulse responses of two continuous point targets smaller than the range resolution specifically include:

[0019] Analyze the overlapping characteristics of impulse responses of continuous point targets. When two adjacent target signals overlap, a false signal with a widened main lobe will be generated.

[0020] The overlapping nature of the false signal is obtained based on the characteristic analysis of the two overlapping impulse responses;

[0021] Furthermore, the point target information is identified by step-by-step iteration, and the real point target signal smaller than the distance resolution is separated according to the overlapping properties of the continuous point targets, and the main lobe of the real target signal is extracted during the processing to obtain the real target signal, which can effectively avoid the influence of the sidelobe alignment reduction on the amplitude of the reconstruction of the surrounding targets and the false target peak formed by the overlapping accumulation of multiple side lobes, and realize the sidelobe suppression of the radar imaging with continuous point targets, which specifically includes:

[0022] By gradually iteratively identifying the real point target information, the real point target signals smaller than the distance resolution are separated according to the overlapping properties of continuous point targets, and the main lobe of the point target impulse response is extracted during the processing to obtain the real target signal. This can effectively avoid the influence of sidelobe alignment attenuation on the reconstructed amplitude of the surrounding targets and the false target peaks formed by the overlapping accumulation of multiple side lobes.

[0023] Compared with the existing technology, this method separates weak targets masked by strong targets by analyzing the impulse response properties of overlapping signals formed by continuous point targets. In addition, it fully considers the impact of sidelobe reduction on surrounding point targets and effectively avoids the amplitude influence of other real targets during sidelobe suppression by gradually iteratively extracting the main lobe of the point target, thus ensuring good sidelobe suppression effect on the basis of restoring the real target signal.

[0024] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention.

[0025] This summary of various implementations or examples of the technology described in this disclosure is not a comprehensive disclosure of the entire scope or all features of the disclosed technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In the drawings, which are not necessarily drawn to scale, the same reference numerals may describe similar parts in different views. The same reference numerals with letter suffixes or different letter suffixes may represent different instances of similar parts. The accompanying drawings generally illustrate various embodiments by way of example and not limitation, and together with the specification and claims, are used to illustrate the embodiments of the invention. When appropriate, the same reference numerals are used throughout the drawings to refer to the same or similar parts. Such embodiments are illustrative and are not intended to be exhaustive or exclusive embodiments of the present apparatus or method.

[0027] Figure 1 Schematic diagram of false signals generated by the overlap of two targets.

[0028] Figure 2 This is a two-dimensional imaging diagram of continuous point targets according to an embodiment of the present invention.

[0029] Figure 3 It is a distance profile diagram of continuous point targets according to an embodiment of the present invention.

[0030] Figure 4 Graph showing sidelobe suppression results according to an embodiment of the present invention.

[0031] Figure 5 Schematic diagram of the process flow of an embodiment of the present invention.

[0032] Figure 6 FIG. 4 is a schematic diagram of a process of separating two overlapping signals according to an embodiment of the present invention.

[0033] Figure 7 The figure is a flow chart of an algorithm according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0036] In order to keep the following description of the embodiments of the present invention clear and concise, detailed descriptions of well-known functions and well-known components are omitted.

[0037] See also Figure 5 , Figure 6 and Figure 7 The embodiment of the present invention provides a method for suppressing side lobes of an arc-shaped synthetic aperture radar, comprising the following steps:

[0038] Step S1: Acquire the echo signal of the arc synthetic aperture radar.

[0039] In some embodiments, a transmission signal model and an echo signal model of an arc synthetic aperture radar are established. The arc synthetic aperture radar system uses a linear frequency modulated continuous wave (FMCW) signal. FMCW obtains the precise position and scattering information of the target by analyzing the phase information of the echo signal, thereby achieving rapid imaging of the target.

[0040] Step S11: The FMCW transmission signal is:

[0041]

[0042] in is a rectangular window function of T, t is the slow time, T is the pulse duration of the transmitted signal, and f c is the center frequency, K is the modulation slope of the FMCW transmission signal, the signal bandwidth is B = KT, and the time delay from the transmitting antenna to the receiving antenna is

[0043] Step S12: The echo signal received by the arc synthetic aperture antenna is:

[0044]

[0045] Where σ is the scattering coefficient of the point target, c is the propagation speed of the electromagnetic wave, R n is the distance from the radar antenna to the point target.

[0046] Step S13: To facilitate subsequent imaging processing, the echo signal obtained in step S12 is demodulated and RVP compensated. At this time, the echo signal is:

[0047]

[0048] Where θ is the azimuth angle of the antenna in the horizontal plane at time n, ρ r is the point spread function in the distance direction, w α is the antenna beam pattern, θ a is the antenna azimuth beamwidth, θ m is the azimuth angle of the point target, and f is the frequency domain variable of the wave propagation time t in the range direction.

[0049] Step S2: Using a wave number domain algorithm to perform imaging processing on the echo signal to obtain a point target impulse response.

[0050] In some embodiments, a wave number domain algorithm is used to perform imaging processing on the echo signal to obtain a high-resolution point target focused image.

[0051] Step S21: Perform a range-to-Fourier transform on the echo signal of step S13

[0052]

[0053] Where (x n ,y n ) is the coordinate position of the arc synthetic aperture antenna in the rectangular coordinate system, and (x, y) is the coordinate position of the point target in the rectangular coordinate system.

[0054] Step S22: Perform azimuth Fourier transform on the signal of step S21. The signal after 2D-FFT is a two-dimensional frequency domain signal:

[0055]

[0056] where k r is the wave number in the distance direction, k θ is the spatial angular frequency in azimuth, R arc is the radius of the arc-shaped synthetic aperture, and R0 is the distance from the point target to the observation center of the arc-shaped synthetic aperture.

[0057] Step S23: Then, a fixed phase is obtained by numerical solution in the wave number domain, and after compensating the phase in the range direction, range accumulation is performed to complete focusing in the range direction;

[0058]

[0059] where k c is the center wave number.

[0060] Step S24: Perform azimuth inverse fast Fourier transform to complete azimuth focusing:

[0061]

[0062] Step S3: Analyze the echo signals with continuous point targets, and analyze the overlapping properties of false signals generated by impulse responses of two continuous point targets smaller than the range resolution.

[0063] In some embodiments, the overlapping properties of false signals generated by impulse responses of two consecutive point targets smaller than the range resolution are analyzed. Compared with discrete point targets, in radar signals with continuous point targets, two point targets smaller than the range resolution will cause serious sidelobe interference, and the main lobe peak of the point target overlaps with the main lobe and side lobe of the surrounding point targets, resulting in an increase in the target peak and a widening of the main lobe. At this time, the peaks accumulate and form new false target peaks.

[0064] Step S31: Analyze the overlapping characteristics of continuous point target signals. When two adjacent target signals overlap, a false signal with a widened main lobe will be generated, such as Figure 1 As shown, assuming O c1 The scattering coefficient is greater than O c2The scattering coefficient of c1 On the left side.

[0065] O sum The main lobe of the signal is widened, and P1 and P5 are false signals O sum The edge position of the main lobe, and P1 corresponds to O c1 The left edge of the main lobe, P5 corresponds to O c2 The right edge of the main lobe, P2 corresponds to O c2 The left edge position of the signal main lobe and its value is M2, P3 is the peak position of the false target and its value is M3, P4 corresponds to O c1 The right edge position of the main lobe of the signal and its value is M4.

[0066] Step S32: False Signal O sum The peak value of is increased after the superposition of two real signals. According to the characteristics of two overlapping impulse responses, the following formula can be obtained:

[0067]

[0068] in O c1 The main lobe peak and its position are O c2 The main lobe peak and its position are

[0069] Step S33: When the point target with a larger scattering coefficient is on the left, the value of M4 is 0. c1 The value corresponding to the right edge of the signal main lobe; when the point target with a larger scattering coefficient is on the right, the value of M4 is 0 c1 The value corresponding to the left edge of the signal main lobe.

[0070] Step S4: By gradually iteratively identifying point target information, the real point target signals smaller than the distance resolution are separated according to the overlapping properties of the impulse responses of continuous point targets, and the main lobe of the real target signal is extracted during the processing, which can effectively avoid the influence of sidelobe alignment reduction on the amplitude of the reconstruction of the surrounding targets, and realize the sidelobe suppression of arc synthetic aperture radar imaging with continuous point targets.

[0071] In some embodiments, an improved CLEAN algorithm is used to perform sidelobe suppression on the range profile signal of a focused image with continuous point targets.

[0072] The traditional CLEAN algorithm identifies the main lobe through step-by-step iteration and eliminates the side lobes of point targets. This may interfere with other point target signals when the side lobes are aligned. On this basis, the improved CLEAN algorithm extracts the main lobe of the real target signal in the step-by-step iteration process, which can effectively avoid the influence of sidelobe alignment and elimination on the reconstruction amplitude of surrounding targets.

[0073] The real point target information is identified step by step and iteratively, and the real point target signal is separated according to the overlapping nature of continuous point targets. Finally, the main lobe of the point target impulse response is extracted. The improved CLEAN algorithm can be used to achieve sidelobe suppression of radar signals with continuous point targets. The specific steps are as follows:

[0074] Step S41: Initial iteration index r=0, initial signal is S r , and let Q r =S r , the initial target signal is T r =0.

[0075] Step S42: Find S r The maximum value M r and its position P r , that is, M r =max(|S r |),P r = arg{max(|S r |)}.

[0076] Step S43: P r If the main lobe is not widened, step S46 is executed. Widening indicates that the target signal overlaps. The false signal of the main lobe widening is 0. sum , at this time O sum =O c1 +O c2 .

[0077] Step S44: According to the characteristics of the false signal, the two real signals O c1 and O c2 Separation. sum The signal with M4 as the peak is subtracted from the The impulse response of e ,Right now:

[0078]

[0079] There are two cases to discuss. When the point target with a larger scattering coefficient is on the left, if It means that the value of M4 is small, let M4 = M4 + a, otherwise let M4 = M4 - a; when the point target with a larger scattering coefficient is on the right, if This indicates that M4 is smaller, so let M4=M4+a, otherwise let M4=M4-a.

[0080] The simulation results show that 0.05 is the most appropriate value. Repeat this step and adjust the value of M4 until the original signal O e The peak position is at That satisfies the following formula:

[0081]

[0082] At this time, M4 is the real signal O c2 The main lobe peak SignalO e is the recovered signal O c1 , O c1 The main lobe peak is Right now O c1 , O c2 The main lobe peak and main lobe position have been determined, which can achieve the separation of two real target signals.

[0083] Step S45: The signal S r The main lobe at the maximum value of the overlapping signal is subtracted to facilitate judgment in the subsequent iterative process.

[0084]

[0085] At this time, the real target signal T r for:

[0086]

[0087] At this point, the two real target signals have been restored, and then step S49 is executed.

[0088] Step S46: In Q r Subtract P r The impulse response at , let:

[0089]

[0090] Step S47: Q r The standard deviation of r If the signal is at the maximum value, then the target is the real target, and then step S48 is executed. Otherwise, the value at the maximum value in the signal is set to 0, that is, M r =0, and go to step S42.

[0091] Step S48: The signal S r The main lobe at the current maximum value in minus:

[0092]

[0093] At this time, the real target signal T r for:

[0094]

[0095] Step S49: Calculate the current S r If the standard deviation is less than the noise level, step S410 is executed. If not, the value at the maximum value of the signal at this time is set to 0, that is, M r =0, and go to step S42.

[0096] Step S410: T r It is the real target extracted from the range profile signal.

[0097] The effect of the present invention can be verified by the following simulation experiments:

[0098] 1) Simulation conditions

[0099] The arc synthetic aperture radar uses a frequency modulated continuous wave signal with a center frequency of 17.25GHz and a bandwidth of 0.5GHz. The radius of the arc synthetic aperture radar is 0.6m, the antenna beam width is 60°, the scanning angle range of the synthetic aperture antenna is -60°-60°, and the number of azimuth sampling is 301. Five discrete target points at the same azimuth (θ=0) are set in the observation area. Their distances to the radar and scattering coefficients are different. The distances from the point target position to the center of the arc synthetic aperture reference circle are 480m, 490m, 490.2m, 515m, and 520m, respectively, and the scattering coefficients are 1, 0.2, 0.3, 0.25, and 0.1, respectively. The scattering coefficients of the five point targets are quite different, and the distance between the second point target and the third point target is less than the distance resolution ρ under this simulation parameter. r .

[0100] 2) Simulation content

[0101] Under the above simulation parameters, the arc synthetic aperture radar sidelobe suppression method based on the improved CLEAN algorithm of the present invention is used to suppress the sidelobe of the range profile of the point target imaging of the arc synthetic aperture radar. Figure 2 is the imaging result of the point target with arc-shaped synthetic aperture. Figure 2 It can be seen that the second point target and the third point target overlap in the imaging results to form a false target. Figure 3 is the distance profile of continuous point targets, from Figure 3 It can be seen that the main lobe of the false signal formed by the second point target and the third point target is widened, and the amplitude increases to 0.42 due to superposition, generating a false target with a scattering coefficient of 0.42. Figure 4 is the result after the side lobe suppression of the present invention, from Figure 4It can be seen that five real point targets are recovered and the side lobes are suppressed. It can be seen that the present invention can effectively suppress the side lobe suppression of point target imaging of the arc synthetic aperture radar.

[0102] The above description is intended to be illustrative rather than restrictive, and those skilled in the art may make changes, modifications, substitutions and variations to the above embodiments within the scope of the present disclosure. Moreover, the above examples (or one or more of them) may be used in combination with each other, and it is contemplated that these embodiments may be combined with each other in various combinations or permutations.

Claims

1. A method for suppressing side lobes of an arc-shaped synthetic aperture radar, characterized in that: The steps include: Acquire the echo signal of arc synthetic aperture radar; The wave number domain algorithm is used to process the echo signal and obtain the impulse response of the point target. For echo signals with continuous point targets, the overlapping properties of false signals generated by impulse responses of two continuous point targets smaller than the range resolution are analyzed; The specific ones include: Step S31: Analyze the overlapping characteristics of consecutive point target signals. When two adjacent target signals overlap, a false signal with a widened main lobe will be generated. c1 The scattering coefficient is greater than O c2 The scattering coefficient of c1 On the left side; P1 and P5 are false signals O sum The edge position of the main lobe, and P1 corresponds to O c1 The left edge of the main lobe, P5 corresponds to O c2 The right edge of the main lobe, P2 corresponds to O c2 The left edge position of the signal main lobe and its value is M2, P3 is the peak position of the false target and its value is M3, P4 corresponds to O c1 The right edge position of the main lobe of the signal and its value is M4; Step S32: False Signal O sum The peak value of is increased after the superposition of two real signals. According to the characteristics of two overlapping impulse responses, the following formula can be obtained: in O c1 The main lobe peak and its position are O c2 The main lobe peak and its position are Step S33: When the point target with a larger scattering coefficient is on the left, the value of M4 is 0. c1 The value corresponding to the right edge of the signal main lobe; when the point target with a larger scattering coefficient is on the right, the value of M4 is 0 c1 The value corresponding to the left edge of the signal main lobe; By gradually iterating and identifying point target information, the real point target signal smaller than the range resolution is separated according to the overlapping properties of the false signals generated by the impulse responses of continuous point targets, and the main lobe of the real target signal is extracted during the processing to obtain the real target signal, thereby realizing the sidelobe suppression of arc synthetic aperture radar imaging with continuous point targets. The specific ones include: Step S41: Initial iteration index r=0, initial signal is S r , and let Q r =S r , the initial target signal is T r =0; Step S42: Find S r The maximum value M r and its position P r , that is, M r =max(|S r |),P r = arg{max(|S r |)}; Step S43: P r If the main lobe is not widened, step S46 is executed. Widening indicates that the target signal overlaps. The false signal of the main lobe widening is 0. sum , at this time O sum =O c1 +O c2 ; Step S44: According to the characteristics of the false signal, the two real signals O c1 and O c2 Separation; at this time in O sum The signal with M4 as the peak is subtracted from the The impulse response of e ,Right now: When the point target with a larger scattering coefficient is on the left, It means that the value of M4 is small, let M4 = M4 + a, otherwise let M4 = M4 - a; when the point target with a larger scattering coefficient is on the right, if It means that M4 is small, so let M4=M4+a, otherwise let M4=M4-a; Repeat this step and adjust the value of M4 until the original signal is O e The peak position is at That satisfies the following formula: At this time, M4 is the real signal O c2 The main lobe peak SignalO e is the recovered signal O c1 , O c1 The main lobe peak is Right now O c1 , O c2 The main lobe peak and main lobe position have been determined, which can achieve the separation of two real target signals; Step S45: The signal S r The main lobe at the maximum value of the overlapping signal is subtracted; At this time, the real target signal T r for: At this point, the two real target signals have been restored, and then step S49 is executed. Step S46: In Q r Subtract P r The impulse response at , let: Step S47: Q r The standard deviation of r If the signal is at the maximum value, then the step S48 is executed; otherwise, the value at the maximum value in the signal is set to 0, that is, M r =0, and go to step S42; Step S48: The signal S r The main lobe at the current maximum value in minus: At this time, the real target signal T r for: Step S49: Calculate the current S r If the standard deviation of M is less than the noise level, step S410 is executed; if it is not satisfied, the value at the maximum value of the signal at this time is set to 0, that is, M r =0, and go to step S42; Step S410: T r It is the real target extracted from the range profile signal.

2. The arc-shaped synthetic aperture radar sidelobe suppression method according to claim 1, characterized in that: In the acquisition of the echo signal of the arc synthetic aperture radar, the echo signal is subjected to frequency demodulation and residual video phase compensation.

3. The arc-shaped synthetic aperture radar sidelobe suppression method according to claim 1, characterized in that: The imaging process of the echo signal using the wave number domain algorithm to obtain the impulse response of the point target specifically includes: Perform two-dimensional fast Fourier transform on the echo signal to the wave number domain; A fixed phase is obtained by numerical solution in the wave number domain, and range accumulation is performed after the phase is compensated in the range direction to complete the focusing in the range direction; Performing an inverse fast Fourier transform in azimuth on the accumulated result to complete focusing in azimuth; The two-dimensional imaging of the point target is completed, and the system response of the point target is the point target impulse response.

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