CN-116184347-B - Airborne radar folding clutter suppression method based on range gating and subspace projection

CN116184347BCN 116184347 BCN116184347 BCN 116184347BCN-116184347-B

Abstract

The invention discloses an airborne radar folding clutter suppression method based on distance gating and subspace projection, which relates to the technical field of airborne radar signal processing, and the method utilizes inter-pulse agile waveforms with distance gating characteristics to obtain the clutter reconstruction result of the distance section by carrying out subspace projection after the distance section is back-passed from a distance dimension, and loop iteration is carried out among the distance segments, so that the mutual influence among the clutter in each distance segment is eliminated, the reconstruction of the clutter in the different distance segments is realized, then the folding clutter suppression is realized on the clutter in the non-own distance segment from the received echo, the target detection is carried out, and the detection capability of the airborne radar on the long-distance low-speed weak target is effectively improved. The method has the advantages of simple implementation, low calculation complexity, good folding clutter suppression effect and the like.

Inventors

REN LIXIANG
LIU ZIHAO
FAN HUAYU
WANG HONGXIN
WANG CHAOXU
MAO ERKE

Assignees

北京理工大学

Dates

Publication Date: 20260508
Application Date: 20221229

Claims (9)

1. The airborne radar folding clutter suppression method based on the range gating and subspace projection is characterized by comprising the following steps of: Step 1, estimating a distance interval of clutter distribution according to a scene; step 2, determining clutter Doppler coverage according to radar parameters; step 3, vectorizing the total echo along a fast time dimension to obtain a vectorized total echo; Step 4, determining the maximum distance segment number of the clutter echo subsection according to the radar parameters And numbering each distance segment to be reconstructed as a variable , Take the value of Initializing ; Step 5, determining clutter subspace and constructing a first clutter scattering unit according to the geometric relation between the radar antenna and the clutter scattering unit A distance segment clutter projection matrix; step 6, setting the first A receiving filter bank corresponding to the distance segment; Step 7, reconstructing clutter of each distance segment by sub-space projection of the distance segment to obtain the first clutter Clutter reconstruction results of the distance segments; Step 8, order Self-increase 1, if After updating Then re-order Repeating the steps 5 to 7 to realize loop iteration among the distance segments until the iteration process converges; Step 9, subtracting the reconstructed non-local distance segment clutter from the vectorized total echo of each distance segment to obtain a clutter reconstruction result of each distance segment, and performing inverse quantization along a fast time dimension to complete accurate reconstruction of each distance segment clutter and effective suppression of folded clutter; And 10, detecting targets in the scene in the distance segments by subtracting the reconstructed distance segments from the total echo, constructing subspaces of the targets for the distance segments with the targets, updating the subspaces of the distance segments where the targets are located, updating the projection matrix of the distance segments where the targets are located, and repeating the steps 7-10 until the reconstruction result of subtracting the distance segments from the total echo is smaller than a set threshold value, thereby completing target detection.
2. The method for suppressing folded clutter of airborne radar based on range gating and subspace projection according to claim 1, wherein the step 1 is to estimate a distance interval of clutter distribution according to a scene, specifically: the maximum detection distance range of the airborne radar is The specific relation is as shown in formula (1): (1) Wherein the method comprises the steps of In order to be able to take the altitude of the flight, For the radar transmit power to be high, In order to transmit the antenna gain, For the effective receiving area of the antenna, Is the scattering cross-sectional area of the radar illuminated area, Minimum detectable signal for the receiver; I.e. the distance interval of clutter distribution.
3. The method for folding clutter suppression of airborne radar based on range gating and subspace projection according to claim 1 or 2, wherein the step 2 is to determine the clutter doppler coverage according to radar parameters, specifically: The flying speed of the airborne radar relative to the ground is Wavelength of Clutter Doppler coverage Calculated from formula (2): (2)。
4. the method for folding clutter suppression of airborne radar based on range gating and subspace projection according to claim 3, wherein the step 3 comprises vectorizing the total echo along the fast time dimension, specifically: Total echo is , Is a three-dimensional matrix with dimensions of Wherein Corresponding to the number of the pulses, Corresponding to the number of the array elements, Corresponding to the number of sampling points in one PRT, and comparing along the fast time dimension Vectorizing, converting the three-dimensional matrix into a two-dimensional matrix to obtain vectorized total echo ; Is of the dimension of 。
5. The method for folding clutter suppression of airborne radar based on range gating and subspace projection according to claim 4, wherein the step 4 is to determine the maximum distance segment number P of clutter echo subdivisions according to radar parameters; Distance interval according to clutter distribution in step 1 Distance range corresponding to a distance segment Calculating the number of distance segments to be reconstructed from the method (3) : (3), Wherein the method comprises the steps of Representing an upward rounding.
6. The method for folding clutter suppression of airborne radar based on range gating and subspace projection of claim 5, wherein said step 5 is to determine clutter subspaces and construct the th according to the geometric relationship between radar antennas and clutter scattering units The distance section clutter projection matrix specifically comprises: obtained by the geometrical relationship between the radar antenna and the clutter scattering unit, (4) Wherein the method comprises the steps of Representing the doppler frequency of the clutter scattering unit, For the angle between the clutter scattering unit and the radar antenna in the azimuth dimension, For the pitch angle of the clutter scattering unit, In order to be a yaw angle, Is cone angle and meets Defining the angle-Doppler plane as Wherein Representing the pulse repetition frequency PRF, equation (4) is further represented as, (5) The square and simplification of the two sides of the step (5) are carried out simultaneously, (6) As can be seen from (6), the clutter spectrum is a cluster of elliptical equations in the angle-Doppler plane, and the angular range is yaw angle according to the different array placement forms Taking different values, and distinguishing the distribution characteristics of clutter in an angle-Doppler plane; When the yaw angle is At this time, the equation (6) is degenerated to a straight line: (7) Wherein the method comprises the steps of Slope of corresponding clutter ridge in the angle-doppler plane; let the degree of freedom of the constructed clutter subspace be According to experience The result of the calculation of formula (8) Doppler coverage for clutter for interval The discretization is carried out so that the product, (8) Obtaining the discrete Doppler frequency of the constructed clutter subspace Wherein , , Represent the first The discretized Doppler frequency can calculate the angle corresponding to each discretized Doppler frequency according to the relation between the angle of the formula (7) and Doppler frequency As shown in formula (9): (9) The expression (9) can be used to obtain the product Corresponding angle Further, the first step can be obtained Distance segment clutter subspace Doppler vector steering Vector oriented with angle dimension , And (3) with The first of (3) Expression of each steering vector (10) Wherein the method comprises the steps of The distance between the array elements is the distance between the array elements, In (a) Corresponds to the first Each distance segment, then the estimated clutter subspace Expressed by formula (11): (11) Wherein the method comprises the steps of Represents the kronetime product; degrees of freedom of clutter under positive side view conditions according to the Brennan criterion Approximately satisfies (12), (12) While the constructed clutter subspace degree of freedom Greater than Thus, the subspace constructed Part of information irrelevant to clutter needs to be removed, and clutter subspace is provided Singular value decomposition is performed, as shown in formula (13), (13) Wherein the method comprises the steps of For diagonal matrix, the elements on the diagonal correspond to A large singular value greater than 0dB, 、 Respectively is Left singular vector and right singular vector corresponding to each large singular value in (a) and diagonal matrix Element correspondence on diagonal Small singular values of less than 0dB, 、 Respectively is Left singular vectors and right singular vectors corresponding to each small singular value in the (a); Removal by truncated singular value decomposition After the small singular values and the subspaces corresponding to the small singular values, The space formed by the expansion is the clutter subspace after the clutter irrelevant information is removed; Construction of the first through (14) Projection matrix corresponding to clutter in each distance segment : (14)。
7. The method for folding clutter suppression of airborne radar based on range gating and subspace projection according to any one of claims 1,2, 4, 5 and 6, wherein said step 6 is to set up the first The receiving filter group corresponding to the distance section specifically comprises: If the parameters in each pulse of the inter-pulse agile waveform are the same as the modulation form and only the initial phases among pulses are different, the receiving filter bank is designed through a matched filter bank with time delay agile phase change; If the modulation patterns within each pulse are different, the receive filter bank uses a joint mismatch filter to improve the range side lobe modulation RSM effect caused by the inter-pulse modulation pattern variation.
8. The method for suppressing folded clutter of airborne radar based on range gating and subspace projection as claimed in claim 6, wherein said step 7 is to reconstruct clutter of each range segment by sub-space projection of each range segment to obtain the first range segment Clutter reconstruction results of the distance segments are as follows: when to the first Dividing the clutter in the distance segment by the first Clutter reconstruction results of other distance segments outside the distance segment are obtained from total echo Is subtracted as the first Input to a distance segment receiving filter bank As shown in the formula (15), (15) Initial clutter reconstruction results for each range segment ; The reconstruction process comprises the following steps of setting the first Receive filter bank for individual distance segments, aligned in the fast time dimension Pulse compression gating Echo of each distance segment, the first obtained after gating Echo data of each distance segment is Using constructed projection matrix pairs Performing subspace projection to obtain the first Clutter projection results for distance segments As shown in formula (16); (16) Wherein the method comprises the steps of Is the first Projection matrixes corresponding to the clutter in each distance segment; For a pair of Pulse compression inverse processing is carried out along the fast time dimension to obtain the first Clutter reconstruction results for individual distance segments 。
9. The method for folding clutter suppression of airborne radar based on range gating and subspace projection according to claim 8, wherein in step 10, the subspace of the distance segment where the target is located is updated, and the projection matrix of the distance segment where the target is located is updated, specifically: Constructing subspaces of objects as ; Updating the subspace of the distance segment where the target is located according to (17), (17) And updating the projection matrix for the distance segment using equation (14).

Description

Airborne radar folding clutter suppression method based on range gating and subspace projection Technical Field The invention relates to the technical field of airborne radar signal processing, in particular to an airborne radar folding clutter suppression method based on range gating and subspace projection. Background The ground-based radar is affected by the curvature of the earth, the detection distance is limited, and in order to obtain a longer detection distance, the radar is erected on an airplane, and the airborne radar is born. However, in the down-looking search scene, the clutter spectrum Doppler spread is serious due to the platform motion, so that the clear region of the Doppler dimension after moving object detection (Moving Target Detection, MTD) and Pulse Doppler (PD) processing is greatly compressed. Therefore, most airborne radars work under medium and high repetition frequency conditions, but due to the fixed parameters of the transmitted waveforms, the medium and high repetition frequencies mean serious distance ambiguity, so that clutter echoes in each pulse repetition period (Pulse Repetition Time, PRT) are folded along a fast time dimension, and long-distance targets need to compete with short-distance strong clutter, which causes the detection capability of the airborne radars to long-distance low-speed weak targets to be reduced. To ameliorate this problem, the most widely used method at present is the Space-time adaptive signal Processing (STAP) technique. STAP is a space-time two-dimensional filtering technology, and an optimal space-time two-dimensional filter is constructed by calculating a covariance matrix of clutter and noise through independent co-distributed training samples without targets. However, according to RMB criteria, if a space-time filter with a performance loss of less than 3dB relative to the optimal filter is desired, an independent co-distributed training sample with 2 times of system freedom is required, but in a practical complex scene, non-ideal factors such as clutter non-uniformity, non-stationarity and system distortion cause difficulty in obtaining data samples meeting the requirements, and also cause a significant decrease in the performance of STAP in practice. Therefore, folding clutter caused by fixed waveform parameters is still a problem to be solved by the airborne radar remote detection. Disclosure of Invention In view of the above, the invention provides an airborne radar folding clutter suppression method based on range gating and subspace projection, which can suppress folding clutter caused by waveform parameter fixation, and has low computational complexity and good folding clutter suppression effect. In order to achieve the above purpose, the technical scheme of the invention is an airborne radar folding clutter suppression method based on range gating and subspace projection, which comprises the following steps: And step 1, estimating a distance interval of clutter distribution according to a scene. And 2, determining the clutter Doppler coverage range according to radar parameters. And 3, vectorizing the total echo along a fast time dimension to obtain the vectorized total echo. And 4, determining the maximum distance segment number P of clutter echo branches according to radar parameters, numbering each distance segment to be reconstructed as a variable P, wherein the P is 1,2, and initializing p=1. And 5, determining a clutter subspace and constructing a clutter projection matrix of the p-th distance segment according to the geometric relation between the radar antenna and the clutter scattering unit. And 6, setting a receiving filter bank corresponding to the p-th distance segment. And 7, reconstructing clutter of each distance segment by sub-space projection of the distance segment to obtain a clutter reconstruction result of the p-th distance segment. And 8, enabling P to be increased by 1, if P is updated and P is greater than P, enabling P to be 1 again, and repeating the steps 5 to 7 to realize loop iteration between distance segments until the iteration process converges. And 9, subtracting the reconstructed non-local distance segment clutter from the vectorized total echo of each distance segment to obtain a clutter reconstruction result of each distance segment, and performing inverse quantization along a fast time dimension to complete accurate reconstruction of each distance segment clutter and effective suppression of folded clutter. And 10, detecting targets in the scene in the distance segments by subtracting the reconstructed distance segments from the total echo, constructing subspaces of the targets for the distance segments with the targets, updating the subspaces of the distance segments where the targets are located, updating the projection matrix of the distance segments where the targets are located, and repeating the steps 7-10 until the reconstruction result of subtracting the distance segments from the total