Frequency Stepped Signal Radar Imaging Method Based on Phase Cancellation

Abstract

The present invention discloses a frequency stepped signal radar imaging method based on phase cancellation to improve the high-resolution imaging effect of high-speed moving targets. The frequency stepped signal radar imaging method of the present invention includes the following steps: (10) Transmitting frequency stepped signals: Alternately transmitting two sets of frequency stepped signals, where the pulse repetition period of one set of frequency stepped signals is twice that of the other frequency stepped signal; (20) Obtaining echo signals: Obtaining echo data reflected by target scattering points; (30) Range image motion compensation: Using an improved phase cancellation algorithm to perform range image velocity phase compensation on the echo data; (40) Frequency stepped signal range imaging: Performing an inverse Fourier transform on the echo sampling sequence and then performing oversampling stitching to obtain a high-resolution stationary range image of the moving target.

Description

Technical Field

[0001] The present invention belongs to the technical field of radar imaging, and specifically relates to a frequency stepped signal radar imaging method based on phase cancellation. Background Art

[0002] Using radar to achieve one-dimensional high-resolution imaging of targets not only has the advantages of all-weather, all-time, and active detection of radar, but also can obtain detailed information in the range direction of the target, thereby improving the ability to detect, locate, and identify targets. Since the frequency stepped signal was proposed in the late 1970s, due to its advantages such as small instantaneous receiving bandwidth, large bandwidth synthesis, and low hardware requirements, it has been widely used in military, medical, exploration, autonomous driving and other fields.

[0003] During the frequency stepped radar imaging process, the high-resolution range image of the target will be affected by the moving speed, resulting in range migration of the imaging points and waveform divergence. Range migration will lead to inaccurate ranging, and waveform divergence will cause the range image to be distorted, which will seriously affect the subsequent target recognition and ultimately reduce the target imaging quality. It is necessary to eliminate the influence of the target speed on target imaging before imaging.

[0004] Currently, the frequency stepped signal radar imaging method, as described in the Chinese invention patent "A Method for Estimating Target Motion Parameters of a Frequency Stepped Radar" (Application No.: CN110441749A, Publication Date: July 19, 2019), includes the following steps: obtaining the echo signal of the target; removing the carrier and the quadratic phase term from the echo signal; obtaining the range-velocity two-dimensional parameter spectrum based on the echo signal after removing the carrier and the quadratic phase term; and denoising the range-velocity two-dimensional parameter spectrum to obtain the parameters of target motion.

[0005] In the above frequency stepped radar imaging process, the target speed is estimated first, then motion compensation is performed, and finally target imaging is achieved. The calculation time is too long, so the real-time performance is not high and it is not suitable for fast imaging of high-speed targets.

[0006] In addition to the traditional speed compensation method, the waveform can also be designed to cancel the influence of speed on the imaging of the target point through the phase cancellation algorithm. Two stepped-frequency signals are designed to be emitted sequentially as described in the paper "A New Approach for Synthesizing the Range Profile of Moving Targets via Stepped-Frequency Waveforms" published by Chen H Y, Liu Y X, Jiang W, etc. (IEEE Geoscience & Remote Sensing Letters, 2006, 3(3): 406-409). The pulse repetition period of one signal is twice that of the other. Combining with the later algorithm to cancel the target speed, false targets will appear in the low signal-to-noise ratio environment for this waveform design, which is not conducive to distinguishing the imaging position of the actual target.

[0007] In summary, the problem of the existing technology is that the resolution effect of stepped-frequency signal radar imaging on moving targets is poor in the low signal-to-noise ratio environment. Summary of the Invention

[0008] The purpose of the present invention is to provide a stepped-frequency signal radar imaging method based on phase cancellation to improve the high-resolution imaging effect of high-speed moving targets.

[0009] The technical solution to achieve the purpose of the present invention is as follows:

[0010] A stepped-frequency signal radar imaging method based on phase cancellation includes the following steps:

[0011] (10) Stepped-frequency signal transmission: Alternately transmit two groups of stepped-frequency signals, where the pulse repetition period of one group of stepped-frequency signals is twice that of the other stepped-frequency signal;

[0012] (20) Echo signal acquisition: Acquire the echo data reflected by the target scatterer;

[0013] (30) Range image motion compensation: Adopt an improved phase cancellation algorithm to perform range image speed phase compensation on the echo data;

[0014] (40) Stepped-frequency signal range imaging: Perform an inverse Fourier transform on the echo sampling sequence, and then perform oversampling splicing to obtain a high-resolution stationary range image of the moving target.

[0015] Compared with the existing technology, the present invention has the following significant advantages:

[0016] 1. Small computational amount: According to the dual-pulse composition imaging of the phase cancellation algorithm, the speed estimation step is omitted, and the algorithm flow is relatively simple. While ensuring the target imaging quality, the processing time is short.

[0017] 2. Good imaging resolution effect: The present invention improves the two groups of frequency stepped signals transmitted sequentially into improved cross transmission, and improves the phase cancellation algorithm to achieve high-resolution imaging of high-speed moving targets. The imaging effect of high-speed moving targets under small signal-to-noise ratio is better than that of existing algorithms.

[0018] The following further describes the present invention in detail with reference to the drawings and specific embodiments. Description of the Drawings

[0019] Figure 1 It is the main flow chart of the frequency stepped signal radar imaging method based on phase cancellation of the present invention.

[0020] Figure 2 It is the cross waveform of the dual pulse group frequency stepped signal transmitted.

[0021] Figure 3 is Figure 1 The flow chart of the step of obtaining the echo signal in

[0022] Figure 4 is Figure 1 The flow chart of the range image motion compensation step in

[0023] Figure 5 is Figure 1 The flow chart of the high-resolution range imaging step of the frequency stepped signal in

[0024] Figure 6 It is the high-resolution range imaging graph of the dual pulse group when SNR = 15dB. Specific Embodiments

[0025] As Figure 1 shown, the frequency stepped radar imaging method based on phase cancellation of the present invention includes the following steps:

[0026] (10) Transmission of frequency stepped signals: Alternately transmit two groups of frequency stepped signals, where the pulse repetition period of one group of frequency stepped signals is 2 times that of the other frequency stepped signal;

[0027] The two groups of alternately transmitted frequency stepped signals are dual pulse group transmission waveforms that are relatively insensitive to the target speed. The cross waveform of the dual pulse group frequency stepped signal transmitted is as Figure 2 shown.

[0028] (20) Acquisition of echo signals: Acquire the echo data reflected by the target scatterers;

[0029] As Figure 3 shown, the step (20) of acquiring echo signals includes:

[0030] (21) Signal collection: Collect the echo signals of the dual-pulse-group frequency-stepped signals;

[0031] (22) Coherent demodulation: Perform coherent demodulation processing on the echo signals to obtain the mixed signals r1(t) and r2(t).

[0032] (30) Range profile motion compensation: Use an improved phase cancellation algorithm to perform range profile velocity phase compensation on the echo data;

[0033] Improve on the existing phase cancellation algorithm, and perform range profile velocity phase compensation on the echo data through the new algorithm, thereby canceling the influence of velocity on imaging.

[0034] As Figure 4 shown, the (30) range profile motion compensation step includes:

[0035] (31) Signal sampling: Perform co-range sampling on the mixed signals r1(t) and r2(t) to obtain the echo sampling sequences r1(m, n) and r2(m, n) of two pulse groups, where the co-range sampling points are t1 = nT r + mT s , t2 = NT r + n2T r + mT s ,

[0036] where m is the sampling unit sequence, n is the stepping length, T r is the pulse period, f s is the sampling rate of the received signal, T s is the reciprocal of the sampling rate, i.e., the sampling time;

[0037] (32) Velocity phase compensation: According to the following improved phase cancellation algorithm formula, perform phase cancellation on the nth echo sampling sequence of each pulse group to obtain the echo after range profile motion compensation:

[0038]

[0039] (40) Frequency-stepped signal range imaging: Perform inverse Fourier transform on the echo sampling sequence, and then perform oversampling stitching to obtain the high-resolution stationary range profile of the moving target;

[0040] As Figure 5 shown, the (40) frequency-stepped signal high-resolution range imaging includes the following steps:

[0041] (41) Inverse Fourier transform: Perform inverse Fourier transform on the echo r(m, n) after range profile velocity compensation column by column and perform normalization to obtain the normalized high-resolution range profile;

[0042] (42) Oversampling stitching: Set the imaging distance range to the length of a range gate. When synthesizing the power spectrum of sampling points, splice adjacent range images, and then through the method of selecting the maximum value at the same range, compare the maximum data and splice it into a range image to obtain a high-resolution static range image of the moving target.

[0043] There is a certain redundancy in the normalized high-resolution range image, and then oversampling stitching is performed to remove the redundancy. Set the imaging distance range to the length of a range gate. When synthesizing the power spectrum of sampling points, splice adjacent range images, and then through the method of selecting the maximum value at the same range, compare the maximum data and splice it into a range image, as Figure 6 shown.

[0044] Using the solution of the present invention, it is used to realize the imaging of moving targets in a low signal-to-noise ratio environment, provides an idea for imaging high-speed moving targets, solves the problem of difficult experimental implementation, and effectively improves the experimental efficiency.

Claims

1. A frequency stepped signal radar imaging method based on phase cancellation, characterized in that It includes the following steps: (10) Frequency stepped signal emission: Alternately emit two groups of frequency stepped signals, where the pulse repetition period of one group of frequency stepped signals is twice that of the other frequency stepped signal; (20) Echo signal acquisition: Acquire the echo data reflected by the target scatterer; (30) Range image motion compensation: Use an improved phase cancellation algorithm to perform range image velocity phase compensation on the echo data; (31)Signal sampling: For the signal after mixing perform sampling at the same distance to obtain the echo sampling sequences of two pulse groups , where the sampling points at the same distance are respectively , , Wherein, is the sampling unit sequence, is the step length, is the pulse period, is the sampling rate of the received signal, is the reciprocal of the sampling rate, i.e., the sampling time; (32)Velocity phase compensation: According to the following improved phase cancellation algorithm formula, perform phase cancellation on the th echo sampling sequence of each pulse group to obtain the echo after range image motion compensation: ； (40) Frequency stepped signal range imaging: Perform an inverse Fourier transform on the echo sampling sequence, and then perform oversampling stitching to obtain a high-resolution stationary range image of the moving target.

2. The frequency stepped signal radar imaging method based on phase cancellation according to claim 1, wherein The step (20) of echo signal acquisition includes: (21) Signal collection: Collect the echo signals of the dual-pulse group frequency stepped signals; (22) Coherent demodulation: The echo signal is subjected to coherent demodulation processing to obtain the mixed signal. .

3. The frequency stepped signal radar imaging method based on phase cancellation according to claim 1, wherein The step (40) of frequency stepped signal range imaging includes: (41) Inverse Fourier transform: For the echo after velocity compensation of the range image Perform the inverse Fourier transform column by column and normalize it to obtain the normalized high-resolution range image; (42) Oversampling stitching: Set the imaging range to the length of one range gate. When synthesizing the power spectrum of the sampling points, splice adjacent range images, and then compare the maximum data through the method of selecting the maximum value at the same range and splice it into a range image to obtain a high-resolution stationary range image of the moving target.

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