A local search angle measurement method based on dual steering vectors to resist multipath

Abstract

The invention relates to a method for local search and angle measurement based on dual-steering vectors to resist multipath, and belongs to the field of radar signal processing technology, and in particular to solving the problem of accurate angle measurement under the condition of multipath reflection in the environment when the target is at low elevation angle, and has the advantages of fast convergence speed and high accuracy. Firstly, the radar related processing parameters are initialized, and then the radar echo dual-steering vector matrix is ​​constructed according to the terrain matching information; then the pulse compression alignment related channel data matrix is ​​performed; then the fixed-point spectrum peak search is performed to find the local maximum value, and the spectrum peak fine output result is optimized based on the local maximum value, and finally the angle information of the low-elevation angle target is estimated quickly and accurately, and the low-elevation angle measurement accuracy of the radar under multipath conditions is effectively improved, which is conducive to the radar to capture and track the target stably and with high precision.

Description

Technical Field

[0001] The invention belongs to the technical field of radar signal processing. Background Art

[0002] Radar target angle measurement is a key link in the field of radar signal processing. In complex environments, especially under multipath conditions, the intermediate frequency echo information of radar targets is affected by reflected waves, which causes great interference to the estimation of target angle information. Sea clutter with complex statistical characteristics normally exists in the sea / low-altitude channel detected by radar, and the signal-to-noise ratio of target echo fluctuates strongly, which seriously affects the radar's angle measurement performance for low-altitude high-threat targets under multipath conditions. All of the above needs urgently require an engineering application method for anti-multipath angle measurement, which can be matched according to the radar detection background to solve the problem of poor angle detection accuracy of low-elevation angle targets, and ultimately achieve the purpose of improving the probability of target detection.

[0003] The paper "MLS anti-multipath angle measurement algorithm based on homomorphic filtering" (Journal of Chongqing University of Posts and Telecommunications, 2015, Vol.27No.4pp:535-541) proposed the use of "homomorphic filtering anti-multipath angle measurement algorithm, established a signal model based on double symmetry characteristics, then converted the convolution feature system into a linear system, and finally extracted the signal from the mixed signal to achieve accurate measurement of pulse time difference and other problems". The above article mainly solves the problem of angle measurement accuracy under multipath conditions, but the algorithm has a large coupling with the sampling rate and amplitude attenuation, and there are problems with stability.

[0004] Reference: C 2 In the "Research on Algorithms to Resist Multipath Interference" (Computer Measurement and Control, 2016, Vol. 14, No. 12pp: 1654-1656), it is proposed to use "traditional multi-target resolution algorithms to track and measure target elevation angles in low-angle multipath environments, which can improve the angle measurement accuracy under specific environments". These all use traditional single-pulse angle measurement technology to measure angles and track targets, and require a large number of snapshots and a high signal-to-noise ratio to accurately measure angles. In addition, in the process of radar automatic tracking and angle measurement, problems such as the inability to meet real-time requirements and low signal-to-noise ratio have not been further confirmed. In short, the above methods have high requirements on the signal-to-noise ratio of the target and have certain limitations in their application in actual engineering environments. Summary of the invention

[0005] In view of the complex and changeable environment and the drastic fluctuation of echoes when the radar measures angles at low elevation angles, the present invention proposes an anti-multipath local search angle measurement method based on dual steering vectors. The method makes full use of the mathematical model and physical process when the multipath effect occurs, combines the relevant characteristics of the direct wave and the reflected wave, matches the terrain composite coefficient according to the geographical environment information, and integrates these parameters into the construction of the dual steering vector. Finally, the method of local peak search is introduced on the basis of spectral peak search, which solves the problems of large engineering calculation amount and slow real-time performance.

[0006] The construction of dual guidance vectors is based on the composite parameters of the ground or sea surface and the spatial physical relationship between the target and the radar. After constructing the spectrum peak function, the local search range is set, and then the peak points of the local search are interpolated to obtain a refined output estimated angle.

[0007] The specific technical solution of the present invention is:

[0008] 1) First, the radar angle measurement related parameters radar height information H R , the number of radar array elements is M rows and N columns, and the radar carrier frequency information is F Z , radar environment matching coefficient σ R +jσ I 、The 3dB beamwidth θ of the radar receiving beam in azimuth and elevation A and θ E Initialize and construct a dual steering vector matrix based on the environment information.

[0009] 2) Perform digital pulse compression based on the radar intermediate frequency data and perform distance dimension alignment processing based on the reference array element.

[0010] 3) Check whether the matching reflection coefficient needs to be updated. If yes, update the environment matching reflection coefficient according to the specific distance unit, otherwise keep the default value. After the matching is completed, construct the signal spectrum peak function and search for the local value extreme value of the spectrum peak function.

[0011] 4) Perform interpolation operations based on the local values ​​in the above steps, and after a refined search, output the angle estimation value corresponding to the maximum value of the spectrum peak.

[0012] A further improvement of the present invention is that the mathematical model of the dual steering vectors in step 1) is:

[0013] A double =A(θ d )+(σ R +jσ I )exp(-j2π△R / λ)A(θ s )

[0014] The direct wave steering vector matrix A(θ d) is an M×N dimensional matrix. The wavelength corresponding to the radar carrier frequency is λ, and the path difference between the direct wave and the reflected wave is defined as △R. The reflected steering vector matrix A(θ s ) is also a matrix of M×N dimensions.

[0015] A further improvement of the present invention is that the distance dimension alignment in step 2) adopts the correlation function alignment method, and the pulse compression output obtained by the matrix reference array element is then subjected to correlation function calculation at the relevant distance unit, and finally the adjacent maximum value is found for distance alignment output.

[0016] A further improvement of the present invention is that the environmental matching reflection coefficient in step 3) is stored according to environmental information and indexed according to distance units, and the environmental matching parameter is updated after the detection control information needs to update the environmental matching parameter. The spectrum peak search function is constructed as:

[0017]

[0018] According to the current beam center pointing angle θ α The direction of [θ α -2θ 3dB ,θ α +2θ 3dB ] is the search boundary, and the angle step is θ 3dB / 10 to search the local range and determine the local extreme point P of the spectrum function MAX (θ) to find the corresponding angle θ α .

[0019] A further improvement of the present invention is that in step 4), based on the local extreme value, the target signal-to-noise ratio exceeds 12 dB, and θ 3dB After linear interpolation at intervals of / 100, continue to search for the maximum value of the target spectrum function P MAX_LAST (θ), thus obtaining the final angle θ LAST α .

[0020] The following is combined with Figure 1 The present invention is described in further detail. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a processing flow chart of the present invention.

[0022] Figure 2 It is a spatial layout diagram of a practical embodiment of the present invention.

[0023] Figure 3 It is a comparison diagram of the angle measurement results of the present invention.

[0024] Figure 4It is a comparison diagram between the present invention and the traditional spectrum peak search. DETAILED DESCRIPTION

[0025] In view of the problems related to the need for high signal-to-noise ratio and ambiguity in angle measurement under multipath conditions in traditional radar target angle measurement, the anti-multipath local search angle measurement method based on dual steering vectors proposed in the present invention can improve the angle measurement accuracy under multipath conditions, and can still obtain relatively ideal angle measurement accuracy under conditions of low signal-to-noise ratio, which has important engineering application value. Figure 1 The specific process is described as follows:

[0026] Step 1: First, the radar angle measurement related parameters radar height information H R , the number of radar array elements is M rows and N columns, and the radar carrier frequency information is F Z , radar environment matching coefficient σ R +jσ I 、The 3dB beamwidth θ of the radar receiving beam in azimuth and elevation A and θ E Initialize and construct a dual-steering vector matrix based on environmental information;

[0027] Step 2: The CPU, as the main control device, performs digital pulse compression according to the radar intermediate frequency data and performs distance dimension alignment processing according to the reference array element;

[0028] Step 3: Check whether the matching reflection coefficient needs to be updated. If yes, update the environment matching reflection coefficient according to the specific distance unit, otherwise keep the default value. After the matching is completed, construct the signal spectrum peak function and search for the local value extreme value of the spectrum peak function;

[0029] Step 4: Perform interpolation operations based on the local values ​​in the above steps, and after a refined search, output the angle estimation value corresponding to the maximum value of the spectrum peak.

[0030] The feasibility of the method of the present invention is further verified by examples below.

[0031] Specific as Figure 2 The figure shows the spatial position diagram of the typical multipath effect encountered by the radar when estimating the target angle at a low elevation angle. The radar is mounted at a height of , and the actual target height is . The intermediate frequency echo received by the radar contains the influence of the direct wave and the reflected wave, which causes the radar intermediate frequency echo phase to be

[0032] Figure 3Shown is a comparison diagram of the root mean square error of the angle measurement results after the design of the anti-multipath local search angle measurement method based on dual steering vectors of the present invention and the angle measurement results obtained by the MUSIC and DBF methods. It can be seen from the figure that the radar intermediate frequency echo can be correctly processed on this hardware architecture platform, which also fully verifies the effectiveness and feasibility of the method of the present invention.

[0033] Figure 4 Shown is a comparison chart of the software running time after the design of the dual-steering vector-based anti-multipath local search angle measurement method of the present invention, local search extreme value and then interpolation optimization, and the time using the conventional spectrum peak search algorithm without optimization by the design means of the present invention.

Claims

1. A dual-steering vector-based anti-multipath local search angle measurement method, characterized in that: The following steps are involved: 1) Initialize radar angle measurement related functions and functions, extract environmental variables according to different environmental parameters, including sea clutter reflection coefficient; construct dual steering vector matrix; 2) Perform pulse compression processing on the radar intermediate frequency data for each digital array channel, and align and calibrate multiple channel data according to the calibration channel data; 3) Detect the matching reflection coefficient, and if the environment variable information is used, update the corresponding spectrum peak search corresponding dual-guide vector, otherwise initialize the dual-guide vector matrix function according to the default environment information, and then search and confirm the local spectrum peak maximum value; 4) If the signal-to-noise ratio of the target exceeds 12dB, interpolation is performed within the set range based on the local maximum value, and a refined search is performed to finally obtain the relevant angle information; The mathematical model of the dual-steering vector in step 1) is: A double =A(θ d )+(σ R +jσ I )exp(-j2πΔR / λ)A(θ s ) Among them A double is a dual-steering vector mathematical model, the direct wave steering vector matrix A(θ d ) is a matrix of M×N dimensions. The wavelength corresponding to the radar carrier frequency is λ, and the path difference between the direct wave and the reflected wave is defined as ΔR; the reflected guidance vector matrix A(θ s ) is also a matrix of M×N dimensions; The environment matching reflection coefficient in step 3) is stored according to the environment information and indexed according to the distance unit. After the detection control information needs to update the environment matching parameter, the environment matching parameter is updated. The spectrum peak search function is constructed as follows: According to the current beam center pointing angle θ α The direction of [θ α -2θ 3dB ,θ α +2θ 3dB ] is the search boundary, and the angle step is θ 3dB / 10 to search the local range and determine the local extreme point P of the spectrum function MAX (θ) to find the corresponding angle θ α .

2. The method for anti-multipath local search angle measurement based on dual steering vectors according to claim 1 is characterized in that: The distance dimension alignment in step 2) adopts the correlation function alignment method. After the pulse compression output obtained by the matrix reference array element, the correlation function calculation is performed according to the relevant distance unit, and finally the adjacent maximum value is found for distance alignment output.

3. The method for anti-multipath local search angle measurement based on dual steering vectors according to claim 1, characterized in that: In step 4), based on the local extreme value, the target signal-to-noise ratio exceeds 12 dB. 3dB After linear interpolation at intervals of / 100, continue to search for the maximum value of the target spectrum function P MAX_LAST (θ), thus obtaining the final angle θ LAST α .

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