Radar space-time space angle measurement method based on three channels

Abstract

The invention discloses a radar space-time space angle measurement method based on three channels, and belongs to the field of radar signal processing. The input of the radar space-time space angle measurement method is a target echo radio frequency signal, and the output is a target point containing angle information. The radar space-time space angle measurement method mainly comprises the steps of antenna front-end processing, signal preprocessing, airspace sub-beam synthesis, time-domain signal processing, airspace sum-difference beam synthesis, constant false alarm detection, sum-difference amplitude comparison angle measurement, target information output and the like, and finally the azimuth angle and the pitch angle of a target in a radar coordinate system in the airspace are measured and calculated. The angle measurement method is suitable for a two-dimensional phased array system radar, the problem that a traditional phase angle measurement method is sensitive to noise is solved, and the usage amount of hardware computing resources can be kept small.

Description

Technical Field

[0001] The invention relates to the field of radar detection systems and radar signal processing, and in particular to a three-channel based radar space-time angle measurement method. Background Art

[0002] Phased array radar is an array radar that achieves electronic scanning through phase control. Traditional mechanical scanning radar has many disadvantages, such as slow scanning speed and inability to track multiple targets simultaneously. Phased array radar radiates energy through a large number of independent antenna units and performs power synthesis in space to form the required beam direction, which can achieve fast scanning without inertia, flexible pointing and high data rate.

[0003] The general phased array radar signal processing usually includes the following steps: the receiver divides the antenna array into four sub-arrays and receives the RF signals of four channels, followed by down-conversion and orthogonal demodulation. The signals of the four channels form three channel signals of sum, azimuth difference and elevation difference in the airspace, and then perform subsequent time domain processing. The detection of moving target points can be completed through matching filtering, moving target detection and constant false alarm detection. After the moving target point is detected, in order to calculate the azimuth and elevation angles of the target in the radar coordinate system in the airspace, the sum-difference ratio angle measurement method is usually used. First, determine whether the phase difference between the difference signal and the sum signal is greater than 0, so as to determine the offset direction relative to the beam center; then use the difference channel signal modulus ratio and the signal modulus value, and find the angle corresponding to the difference and ratio by looking up the table, and then calculate the offset angle. At this time, combined with the angle of the beam center, the azimuth and elevation angle of the target in the radar coordinate system in the airspace can be calculated.

[0004] The above-mentioned method of using spatial domain beamforming and then performing sum-difference ratio angle measurement requires comparing the phases of the sum channel signal and the difference channel signal, and the phase of the signal is easily affected by interference such as noise. In the actual test process, if the phase difference between the sum channel and the difference channel is large, it is easy to exceed the range of -180° to 180° under interference, resulting in phase inversion, and ultimately leading to large errors in angle measurement. Summary of the invention

[0005] The present invention proposes a radar space-time and difference ratio angle measurement method. Compared with the prior art, the significant advantage of the present invention is that the angle offset is judged by replacing the phase with the amplitude, thus avoiding the phase judgment inversion phenomenon caused by the phase error; at the same time, the space-time three-channel processing step is adopted to reduce the number of signal channels that need to be processed in the time domain processing process, saving circuit resources and improving the efficiency of signal processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 The present invention is a flow chart of a three-channel radar space-time angle measurement method.

[0007] Figure 2 This is the distribution diagram of quadrants A, B, C, and D on the front side of the phased array antenna array. DETAILED DESCRIPTION

[0008] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The present invention can be implemented in different forms and is not limited to the embodiments described herein. On the contrary, the embodiments are provided to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0009] In this example, the drone is released as a target and the two-dimensional phased array pulse radar system is started. In the radar coordinate system, the radar is used as the origin, and the beam transmits and receives radio frequency signals with a certain direction as the beam center. The beam center direction contains azimuth and pitch angle information. Once the drone enters the radar beam detection range, detection can be performed. The transmission signal selected in this example is a linear frequency modulation signal with an intermediate frequency of 125MHz, a bandwidth of 18MHz, and a pulse width of 20μs. The number of coherent accumulation pulses N in the same beam direction is 256.

[0010] Step 1: The phased array radar antenna array transmits a radio frequency pulse signal, and the radio frequency signal reflected by the target is then received by the antenna array. The digital antenna array is divided into four quadrants, A, B, C, and D, according to the position distribution, and receives the radio frequency echo signals of the four channels A, B, C, and D respectively. The antenna array quadrant distribution is as follows: Figure 2 The receiver down-converts the RF signal to an intermediate frequency and obtains four-quadrant analog intermediate frequency signals A, B, C, and D.

[0011] Step 2: The four-quadrant analog intermediate frequency signal is converted into a digital signal through a DAC, and the number of sampled digital sequence points M is 2048. It is divided into I and Q paths through orthogonal demodulation. The method of orthogonal demodulation is to respectively convert the echo signal sampling sequence into two orthogonal local oscillator signals 2cos(ω o n) and -2sin(ω o n) are multiplied and then passed through a low-pass filter to obtain four baseband signals A, B, C, and D. Each signal contains I and Q components.

[0012] The channel processing of the four channels is exactly the same, but due to the influence of hardware assembly process and noise, the signals of the four channels may have amplitude and phase distortion, resulting in poor amplitude and phase consistency, affecting the subsequent detection performance. At this time, the I and Q signals of the four quadrants should be compensated for amplitude and phase through measurement calibration. After calibration, the four-quadrant digital baseband signals of A, B, C, and D can be obtained, in which each channel contains I and Q components and enters the subsequent beamforming module.

[0013] Step 3: Beamforming can be achieved by using an adder. The three signals Sum_dis, Left_dis and Up_dis are formed in sequence. The specific calculation formula is as follows.

[0014] Sum_dis=A+B+C+D

[0015] Left_dis=A+C

[0016] Up_dis=A+B

[0017] The formed Sum_dis, Lef_dis and Up_dis are the sub-beam three-channel range-dimensional signals, and each channel contains I and Q components.

[0018] Step 4: First, pulse compression is completed in the time domain using the matched filtering method. The specific method of matched filtering is to convolve the matched filter coefficient with the signal. The time domain signal expression is:

[0019]

[0020] Where s(t) is a component of the three-channel range-dimensional signal of the sub-beam described in step 2, and h(t) is the matched filter coefficient. The frequency response H(f) of h(t) is conjugate with the frequency response S(f) of the input signal, that is,

[0021] Y(f)=S(f)H(f)=S(f)S * (f)

[0022] The above formula also shows that time domain convolution corresponds to frequency domain multiplication. In this example, since convolution is difficult to implement for digital circuits, the frequency domain multiplication algorithm is also used. The three signals of Sum_dis, Left_dis and Up_dis are first transformed by M=2048 points of FFT, multiplied by the frequency response of the matched filter coefficient, and then transformed by IFFT to obtain the signal after pulse compression.

[0023] Secondly, the pulse pressure results of the range dimension signal of each channel are rearranged. In this example, for the direction of the beam, N = 256 pulses are continuously transmitted for coherent accumulation, and the number of echo sampling points of each pulse is M = 2048 points. The data of the signal with 256 pulse repetition periods is rearranged to form an M*N data matrix. The horizontal axis of this matrix corresponds to the range gate of the radar data.

[0024] Again: the data matrix is ​​subjected to DC removal by column to reduce the influence of fixed target echo on subsequent target detection. Specifically, for each column in the data matrix, the average value is calculated, and all the data in the column are subtracted from the average value to eliminate the influence of fixed echo sampled in each pulse repetition period. The signal after DC removal is then subjected to a 20dB Taylor window by column to suppress the spectrum leakage of the signal.

[0025] Finally, the M*N data matrix is ​​subjected to N-point FFT by column to extract the speed information of the moving target. After the FFT is completed, the data matrix is ​​converted into a range-Doppler spectrum. The data in the range-Doppler spectrum is taken out by column to obtain the sum channel speed dimension signal Sum, the left channel speed dimension signal Left and the upper channel speed dimension signal Up, that is, the sub-beam three-channel speed dimension signal.

[0026] Step 5: First, form the sum and difference beam signals. Beam forming can be achieved by using an adder. The specific calculation formula of the sum channel velocity dimension signal is as follows.

[0027] Diff_a = 2 × Left - Sum

[0028] Diff_e=2×Up-Sum

[0029] Secondly, the azimuth offset direction d_a and the elevation offset direction d_e are determined from the sub-beam three-channel velocity-dimensional signal. The algorithm for the offset direction is as follows.

[0030]

[0031] In this example, a is the direction of the beam center that is biased to the left, and e is the direction of the beam center that is biased to the top.

[0032] Finally, the azimuth difference channel velocity dimension signal Diff_a, the pitch difference channel velocity dimension signal Diff_e and the sum channel velocity dimension signal Sum, that is, the sum and difference three-channel velocity dimension signal, are sent in parallel to the subsequent constant false alarm detection step and the sum-difference ratio angle measurement step, and the offset direction is sent to the sum-difference ratio angle measurement step at the same time.

[0033] Step 6: In this example, the constant false alarm detection algorithm is divided into the speed dimension constant false alarm detection algorithm and the distance dimension constant false alarm detection algorithm; the detection work of the constant false alarm algorithm mainly processes the Sum channel. After the Sum finds the target, the corresponding target points of the remaining channels are directly sent out for subsequent processing.

[0034] First, the I and Q signal components of the Sum channel are modulo processed to facilitate subsequent signal energy calculation.

[0035] Secondly, perform speed dimension constant false alarm detection. Find the point with the largest amplitude, i.e., energy, in each column, and treat the remaining points as noise. Compare the energy of the point with the noise. If it meets the threshold requirement, package the energy, speed gate and other information of the point for subsequent operations.

[0036] Finally, perform speed dimension constant false alarm detection. For each column of the maximum energy point found, rearrange it into a row of speed dimension energy. For this row of speed dimension energy, use the sliding window method to compare the energy with the surrounding noise in turn. If it meets the threshold requirements, the energy, speed gate, distance gate and other information of the point are packaged as the target point trace information for output.

[0037] Step 7: According to the moving target point information output by the constant false alarm, calculate the ratios k_a and k_e of the target corresponding point difference channel velocity dimension signal and the sum channel velocity dimension signal. The calculation method is as follows.

[0038]

[0039] By combining the ratio with the azimuth offset direction d_a and the elevation offset direction d_e in step 5, the azimuth offset offset_a and the elevation offset offset_e of the target relative to the beam center can be determined by looking up the V-curve table.

[0040] Step 8: Combining the beam center angle described in step 1 and the target offset described in step 7, the azimuth and elevation angles of the target in the spatial coordinate system with the radar as the origin can be calculated. The beam center angle is the azimuth angle c_a and the elevation angle c_e, so the calculation method for the azimuth angle and elevation angle of the target is

[0041] a_a=c_a+offset_a

[0042] a_e=c_e+offset_e

[0043] After the above steps, it can be proved that the radar system of this example can correctly output the azimuth and pitch angle information of the target after adopting the improved space-time sum-difference ratio angle measurement method. Since the traditional phase comparison method is not used for the determination of the offset direction in step 7, the angle measurement process avoids the phase judgment inversion caused by system noise, which greatly improves the accuracy of angle detection. In addition, the sum-difference ratio angle measurement described in this example requires five signals of Sum, azimuth difference Diff_a, pitch difference Diff_e, left Left and up Up to complete, but through the three-channel radar space-time angle measurement method of the present invention, in the process of time domain processing, only three data need to be processed, which saves hardware resources and improves the efficiency of signal processing.

[0044] In the above examples, all functions can be realized, or part of the functions can be realized as needed.

[0045] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

Claims

1. A three-channel radar space-time angle measurement method, characterized in that: The following steps are involved: Step S100: Antenna front-end processing. The antenna array receives the target echo RF signal. The antenna subarray synthesizes the A, B, C, and D four-quadrant RF signals, and then down-converts them to the intermediate frequency. Output the A, B, C, and D four-quadrant analog intermediate frequency signals to step S200; output the beam center angle in the radar coordinate system in the airspace to step S800. Step S200: Signal preprocessing: Perform analog-to-digital conversion on the four-quadrant analog intermediate frequency signals A, B, C, and D, and preprocess them into four-quadrant digital baseband signals A, B, C, and D through operations such as digital mixing. Step S300: Spatial sub-beam synthesis: The four-quadrant digital baseband signals A, B, C, and D are synthesized in the spatial domain into a sum beam channel distance dimension signal Sum_dis, a left beam channel distance dimension signal Left_dis, and an upper beam channel distance dimension signal Up_dis, that is, a sub-beam three-channel distance dimension signal. Step S400: Time domain signal processing. Pulse compression, range gate rearrangement, moving target detection and other operations are performed on the sub-beam three-channel range dimension signal, and the sum beam channel velocity dimension signal Sum_spd, the left beam channel velocity dimension signal Left_spd and the upper beam channel velocity dimension signal Up_spd, i.e., the sub-beam three-channel velocity dimension signal, are output. Step S500: Spatial domain sum and difference beam synthesis. The sub-beam three-channel velocity dimension signal is synthesized in the spatial domain into the sum beam channel velocity dimension signal Sum_spd, the azimuth difference channel velocity dimension signal Diff_a_spd and the pitch difference channel velocity dimension signal Diff_e_spd, that is, the sum and difference three-channel velocity dimension signal. During the sum and difference beam synthesis process, the azimuth offset direction d_a and the pitch offset direction d_e are calculated at the same time. The sum and difference three-channel velocity dimension signal and the azimuth offset direction d_a and the pitch offset direction d_e are output to step S700; the sum channel velocity dimension signal Sum is output to step S600. Step S600: CFAR detection. A CFAR detection algorithm is used for the velocity dimension signal Sum_spd of the sum beam channel, and the moving target point trace information is output to steps S700 and S800. The moving target point trace information includes the target range gate number m, velocity gate number n, energy e, etc. Step S700: Sum-difference ratio angle measurement. In combination with the moving target point information, the azimuth offset offset_a and the pitch offset offset_e are calculated according to the sum-difference three-channel velocity dimensional signal, the azimuth offset direction d_a and the pitch offset direction d_e. Step S800: Output target information. According to the azimuth offset offset_a and elevation offset offset_e and the beam center angle, the azimuth angle a_a and elevation angle a_e of the target in the radar coordinate system in the airspace are calculated. Combined with the moving target point information, a target point containing angle information is obtained.

2. The three-channel radar space-time angle measurement method according to claim 1, characterized in that: The specific process of step S100 includes: Step S101: The antenna array transmits a radio frequency signal in a certain direction. After being reflected by a moving target, the antenna array receives the echo radio frequency signal. Step S102: evenly divide the antenna array into four antenna sub-arrays A, B, C, and D. Each antenna sub-array is combined into a quadrant to form A, B, C, and D four-quadrant radio frequency signals. Step S103: using a mixer to down-convert the four-quadrant RF signals A, B, C, D into four-quadrant analog intermediate frequency signals A, B, C, D. Step S104: outputting the four-quadrant analog intermediate frequency signals A, B, C, and D and the beam center angle to steps S200 and S800 for subsequent processing.

3. The three-channel radar space-time angle measurement method according to claim 1, characterized in that: The specific process of step S200 includes: Step S201: using ADC to sample the four-quadrant analog intermediate frequency signals A, B, C, and D, and convert them into four-quadrant digital intermediate frequency signals A, B, C, and D. Step S202: performing digital mixing quadrature demodulation and low-pass filtering on the four-quadrant digital intermediate frequency signals A, B, C, and D to generate four-quadrant digital baseband signals A, B, C, and D.

4. The three-channel radar space-time angle measurement method according to claim 1, characterized in that: The specific process of step S300 includes: According to the four-quadrant digital baseband signals A, B, C, and D, the sum beam channel distance dimension signal Sum_dis, the left beam channel distance dimension signal Left_dis, and the upper beam channel distance dimension signal Up_dis are generated, and the calculation formula is as follows. Sum_dis=A+B+C+D Left_dis=A+C Up_dis=A+B 5. The three-channel radar space-time angle measurement method according to claim 1, characterized in that: The specific process of step S400 includes: Step S401: Generate a matched filter according to the transmission waveform. The frequency response H(f) of the matched filter and the frequency response S(f) of the input signal satisfy the following relationship. Y(f)=S(f)H(f)=S(f)S * (f) Step S402: Use the matched filter to perform matched filtering on the sub-beam three-channel range-dimensional signal to obtain the sub-beam three-channel range-dimensional signal pulse pressure result. Step S403: Perform range gate rearrangement on the sub-beam three-channel range-dimension signal pulse compression results respectively. Rearrange the N sub-beam three-channel range-dimension signal pulse compression results coherently accumulated at the same beam center into an N×M radar data matrix, where M is the number of points in each sub-beam three-channel range-dimension signal pulse compression result sequence. Step S404: Use a moving target detection algorithm to process the radar data matrix to obtain an N×M range-Doppler spectrum. Take out the data in the range-Doppler spectrum by column to obtain the sum beam channel velocity dimension signal Sum_spd, the left beam channel velocity dimension signal Left_spd and the upper beam channel velocity dimension signal Up_spd, that is, the sub-beam three-channel velocity dimension signal.

6. The three-channel radar space-time angle measurement method according to claim 1, characterized in that: The specific process of step S500 includes: Step S501: Generate an azimuth difference channel velocity-dimensional signal Diff_a_spd and an elevation difference channel velocity-dimensional signal Diff_e_spd from the sub-beam three-channel velocity-dimensional signal, and the calculation method is as follows. Diff_a = 2 × Left - Sum Diff_e=2×Up-Sum Step S502: Parallel to step S501, the azimuth offset direction d_a and the elevation offset direction d_e are determined from the sub-beam three-channel velocity dimension signal. The algorithm for the offset direction is as follows. Step S503: The azimuth difference channel velocity dimension signal Diff_a_spd, the pitch difference channel velocity dimension signal Diff_e_spd and the sum beam channel velocity dimension signal Sum_spd described in step S501 are the sum difference three-channel velocity dimension signal. The sum difference three-channel velocity dimension signal is simultaneously output to step S700; the sum beam channel velocity dimension signal Sum and the offset direction are output to step S700.

7. The three-channel radar space-time angle measurement method according to claim 1, characterized in that: The specific process of step S600 includes: A constant false alarm detection algorithm is used for the sum beam three-channel velocity dimension signal to find the moving target point, and the target velocity gate number m, distance gate number n, energy e and other information are packaged into moving target point information and output to step S700 and step S800.

8. The three-channel radar space-time angle measurement method according to claim 1, characterized in that: The specific process of step S700 includes: Step S701: According to the moving target point information, extract the data points Sum(n,m), Diff_a(n,m) and Diff_e(n,m) corresponding to the target from the sum and difference three-channel velocity-dimensional signals. Step S702: Calculate the ratios k_a and k_e of the target corresponding difference channel velocity dimension signal and the sum beam channel velocity dimension signal data points. The calculation method is as follows. Step S703: Based on the V-curve characteristics of the beam and the sum-difference ratios k_a and k_e, combined with the azimuth offset direction d_a and the elevation offset direction d_e, a table is looked up to obtain the azimuth offset offset_a and the elevation offset offset_e of the target.

9. The three-channel radar space-time angle measurement method according to claim 1, characterized in that: The specific process of step S800 includes: Step S801: Calculate the azimuth angle a_a and elevation angle a_e of the target in the radar coordinate system in the airspace according to the beam center angle and the target offset. The beam center angle includes the azimuth angle c_a and the elevation angle c_e. The target azimuth and elevation angle calculation formulas are as follows. a_a=c_a+offset_a a_e=c_e+offset_e Step S802: Combine the azimuth angle and pitch angle of the target with the moving target point information in step S600, and output the target point containing the angle information.

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