A Sawtooth Wave Radar Speed Measurement Extension Method Based on Amplitude Comparison Angle Measurement Mode

Abstract

The present invention discloses a sawtooth wave radar speed measurement expansion method based on an amplitude comparison angle measurement mode, belonging to the technical field of radar speed measurement, and comprising the following steps: S1: The transmitting antennas of a radar transmitter alternately transmit linear frequency modulation continuous wave signals with the same sweep period T at scanning position one and scanning position two; S2: For a target located at a distance R and with a speed v in the direction of the radar, first collect data one at M scanning position ones and data two at M scanning position twos; S3: Eliminate the constant phase difference caused by the change in the antenna direction pointing in the phases of data one and data two; S4: Perform coherent processing through two-dimensional FFT so that after data one and data two are combined, the signal is fully utilized to improve the signal-to-noise ratio; S5: Perform CFAR detection on the target; S6: Perform speed ambiguity resolution according to the phase difference on the distance-speed frequency spectra after the two-dimensional FFT of data one and data two respectively.

Description

Technical Field

[0001] The present invention belongs to the technical field of radar speed measurement, and particularly relates to a sawtooth wave radar speed measurement extension method based on an amplitude comparison angle measurement mode. Background Art

[0002] Existing sawtooth wave radars generally perform range-velocity decoupling through two-dimensional FFT. According to the Nyquist sampling theorem, when the sampling rate in the slow-time dimension is less than the Doppler frequency shift generated by the target movement, velocity ambiguity will occur. To resolve velocity ambiguity, radars usually adopt a multiple-frequency operation mode. The selected multiple frequencies are relatively prime with a certain frequency unit, and the frequency is regularized. The unambiguous Doppler frequency range is their least common multiple. However, the current multiple-frequency operation mode has problems such as low time utilization rate, high hardware / computation complexity, and poor robustness.

[0003] Considering that there is a target with a speed of v in front of the radar, the Doppler frequency shift is f v = 2v / λ, and the radar sweep repetition frequency is f T . When the Doppler frequency shift is greater than the radar sweep repetition frequency, according to the sampling theorem, there will be ambiguity in the Doppler frequency measurement, which can be expressed as follows: In the formula is the apparent Doppler frequency shift under the sampling frequency f T , and m is an integer. According to the formula v = fλ / 2, the corresponding velocity ambiguity can be expressed as: where v T = f T λ / 2 is the maximum unambiguous speed measurement range under the sampling frequency 1 / T, is the ambiguous speed under the sampling frequency 1 / T.

[0004] To resolve velocity ambiguity, radars usually adopt multiple frequencies operation mode. The selected multiple frequencies are relatively prime with a certain frequency unit, and the frequency is regularized. The unambiguous Doppler frequency range is their least common multiple: where lcm(·) is the least common multiple. For a target with an actual Doppler frequency shift of f v , the apparent Doppler frequencies corresponding to different PRFs are: Then there should be: According to the velocity-Doppler frequency shift formula, the velocity expression can be changed to: Searching within a certain range to find those that satisfy the formula, the unambiguous Doppler velocity of the target can be obtained. According to the principle of resolving velocity ambiguity with multiple PRFs, a sawtooth wave radar can send two sawtooth wave signals with different sweep periods. The time-domain diagram of the transmitted signal is as shown in Figure 1As shown, the transmitting antenna first transmits N1 chirp continuous waves with a sweep period of T1, and then transmits N2 chirp continuous waves with a sweep period of T2. Assuming that the target speed remains unchanged, the ambiguous Doppler frequencies at the sampling rates of 1 / T1 and 1 / T2 are estimated based on Data 1 and Data 2 respectively, and the target ambiguous speed is calculated. Finally, velocity unambiguous is performed using the formula. The algorithm flow chart is as Figure 2 shown.

[0005] The traditional multiple PRF velocity unambiguous algorithm has the following disadvantages: low time utilization rate. In traditional processing, the same number of chirp continuous waves are transmitted, that is, N1 = N2, so that Data 1 and Data 2 obtain the same signal processing gain through two-dimensional FFT, while losing part of the utilization of system time. High computational complexity. The same level of complexity of signal processing is performed on Data 2 and Data 1, and the computational amounts of two-dimensional FFT and CFAR detection are relatively large, wasting hardware resources. Poor robustness. The traditional multiple PRF velocity unambiguous algorithm needs to detect the target in both CFAR detections, otherwise velocity unambiguous cannot be performed. The CFAR detection threshold is related to multiple factors, and it cannot ensure accurate target detection under low signal-to-noise ratio conditions. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a signal processing method for velocity expansion in the case of amplitude comparison angle measurement.

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] A sawtooth wave radar velocity measurement expansion method based on the amplitude comparison angle measurement mode, comprising the following steps:

[0009] S1: The transmitting antenna of the radar transmitter alternately transmits chirp continuous wave signals with the same sweep period of T at scan position 1 and scan position 2;

[0010] S2: For a target located at the direction, at a distance of R and with a speed of v, first collect M pieces of Data 1 at scan position 1, and M pieces of Data 2 at scan position 2;

[0011] S3: Eliminate the constant phase difference caused by the change of the antenna direction pointing in the phase of Data 1 and Data 2 for each received echo signal;

[0012] S4: Perform coherent accumulation processing through two-dimensional FFT, so that after Data 1 and Data 2 are combined, the signal is fully utilized to improve the signal-to-noise ratio.

[0013] S5: Perform CFAR detection on the target;

[0014] S6: Velocity ambiguity resolution is performed based on the phase difference on the range-velocity spectra after the two-dimensional FFT of Data 1 and Data 2 respectively.

[0015] Further, for a target located in the direction of the radar, at a range of R and a velocity of v, the far-field envelope signal received by the radar at time t from Scan Position 1 is expressed as:

[0016]

[0017] where, x k (t) is the input envelope signal of antenna element k, is the pattern of antenna element k, is the time delay of antenna element k in the direction ; N is the number of antenna arrays;

[0018] The far-field envelope signal received by the radar at time t + T, after one sweep period, from Scan Position 2 is expressed as:

[0019]

[0020] Further, the constant phase difference Δ1 caused by the change in the antenna direction pointing in the phases of Data 1 and Data 2 in step S3 is:

[0021]

[0022] where, Δ(k) is the phase of the k-th element signal. After eliminating the constant phase difference Δ1, the phase difference between Scan Position 1 and Scan Position 2 only contains velocity spread.

[0023] Further, the maximum unambiguous velocity is λ / 2T.

[0024] Further, step S4 specifically includes the following steps: First, perform two-windowed Fourier transforms on the received multiple echo signals respectively to obtain the two-dimensional images of range-Doppler of Data 1 and Data 2. Then, merge the range-Doppler of Data 1 and the range-Doppler of Data 2. Since the constant phase difference has been eliminated in step S3, all the phases of Data 1 and Data 2 are coherent. After merging, the coherence of the signal can be fully utilized to improve the signal-to-noise ratio. The processing of the front and back two steps is coherent integration processing.

[0025] Further, step S5 specifically includes the following steps: The detection method that determines whether there is a target at this position while keeping the false alarm probability unchanged is called Constant False Alarm Rate (CFAR) detection. Specifically, the decision threshold is adaptively adjusted through background signals such as clutter and noise around the target to ensure that the false alarm probability remains unchanged. The first step is to obtain the surrounding noise power through various estimation methods, determine the threshold according to the Neyman-Pearson criterion, and if the power exceeds the threshold, it is considered that there is a target at this point, otherwise there is no target at this point, etc.

[0026] Further, step S6 specifically includes the following steps: Determine the position of the target on the range-velocity spectrum through CFAR detection, and compare the phase differences at the positions of the target in Data One and Data Two;

[0027] If the phase difference is less than ±π / 2, then the velocity range of this target does not exceed the velocity measurement range of the signal with a period of T, and the velocity is calculated according to the following formula:

[0028] v = Δ θ λ / 4πT

[0029] where Δ θ represents the phase difference at the positions of the target in Data One and Data Two;

[0030] If the phase difference is greater than ±π / 2, then the velocity of this target exceeds the velocity measurement range and velocity ambiguity needs to be considered, and the velocity is calculated according to the following formula:

[0031] v = Δ θ λ / 4πT + v max

[0032] where v max is the maximum velocity measurement velocity of the signal with a period of T.

[0033] The beneficial effects of the present invention are as follows: The present invention can expand the radar velocity measurement range, can perform reasonable parameter design according to actual needs, and achieve velocity measurement. This method eliminates the phase change caused by scanning, realizes the full utilization of signals, fully utilizes time accumulation for signal gain, and has a high time utilization rate compared with traditional velocity ambiguity resolution algorithms. This method performs coherent processing on Data One and Data Two, and there is no need to perform CFAR detection on Data Two and Data One separately, saving hardware resources. This method fully utilizes the received signals, realizes the maximum signal gain processing, thereby obtaining the highest signal-to-noise ratio, ensuring the accuracy of CFAR detection, and ensuring the robustness of the system.

[0034] Other advantages, objectives, and features of the present invention will be described in the subsequent specification, and to some extent, they are obvious to those skilled in the art, or those skilled in the art can obtain teachings from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] To make the objectives, technical solutions and beneficial effects of the present invention clearer, the following drawings are provided for description of the present invention:

[0036] Figure 1 For the multi-frequency operation mode;

[0037] Figure 2 For the flowchart of the multi-frequency velocity ambiguity resolution algorithm;

[0038] Figure 3 For the emission antenna scanning mode diagram under amplitude comparison angle measurement;

[0039] Figure 4 For the schematic diagram of velocity measurement expansion under amplitude comparison angle measurement;

[0040] Figure 5 For the signal processing flowchart;

[0041] Figure 6 For the principle of the two-constant false alarm detector;

[0042] Figure 7 (a) in is the range-velocity spectrum diagram at scanning position 1, and (b) is the velocity spectrum diagram at scanning position 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] Aiming at the problems existing in the current traditional multi-PRF velocity ambiguity resolution algorithm, the present invention proposes a signal processing algorithm for velocity expansion in the case of amplitude comparison angle measurement.

[0044] First, the operating mode of the radar transmitter is introduced. Since amplitude comparison angle measurement is used for elevation angle measurement. The transmitting antenna first transmits a linear frequency modulated continuous wave with a sweep period of T at scanning position 1, and then transmits a linear frequency modulated continuous wave with a sweep period of T at scanning position 2. The linear frequency modulated continuous wave signals are alternately transmitted with the same sweep period at scanning positions 1 and 2 respectively, as Figure 3 shown.

[0045] Assume that there is a target with a velocity of v at a distance of R in the direction of the radar. Then the far-field envelope signal received by the radar from scanning position 1 at time t can be expressed as: where x k (t) is the input envelope signal of antenna element k, is the pattern of antenna element k, is the time delay of antenna element k in the direction. N is the number of antenna arrays. After the radar goes through a sweep period, that is, at time t + T, the far-field envelope signal received from scanning position 2 can be expressed as: As can be seen from the formula, the received signals at radar scan position one and scan position two mainly differ in amplitude due to the radiation pattern Therefore, amplitude comparison can be used to measure the angle and determine the angle where the target is located. The key point is that the phase difference is caused by the time delay due to velocity and the difference in the radiation pattern pointing. It is found that in the case of continuous scanning at different angles in the scanning mode, the initial phases at different scanning angles are inconsistent. Therefore, this phase is eliminated before velocity ambiguity resolution based on phase where Δ(k) is the phase of the signal of the k-th array element.

[0046] Once the scanning mode is fixed, the phase difference caused by the antenna direction pointing is a constant term and can be eliminated during velocity ambiguity resolution. After eliminating the constant Δ1, the phase difference between scan position one and scan position two only contains velocity spread.

[0047] As Figure 4 shown, the maximum unambiguous velocity with a sweep frequency period of T is λ / 4T. In the amplitude comparison angle measurement mode, the maximum unambiguous velocity is λ / 2T, which expands the velocity measurement range and subsequent amplitude comparison angle measurement can be performed.

[0048] The specific signal processing flow is as Figure 5 shown.

[0049] After collecting data one and data two at M scan positions one and M scan positions two, the constant phase difference caused by the change in antenna direction pointing in the phases of data one and data two is eliminated;

[0050] Then coherent processing is performed, so that only one two-dimensional FFT is carried out after data one and data two are combined, making full use of time and signals to achieve maximum signal gain processing; specifically including: First, two windowed Fourier transforms are respectively performed on the received multiple echo signals to obtain the two-dimensional images of range-Doppler of data one and data two. Then the range-Doppler of data one and the range-Doppler of data two are combined. Since the constant phase difference has been eliminated in step S3, all the phases of data one and data two are coherent, and the coherence of the signals can be fully utilized after combination to improve the signal-to-noise ratio. The processing of the previous and subsequent two steps is coherent integration processing;

[0051] Then CFAR detection is performed on the target. As Figure 6 shown, the detection method of determining whether there is a target at this position while ensuring that the false alarm probability remains unchanged is called constant false alarm rate (CFAR) detection. Specifically, the decision threshold is adaptively adjusted according to the clutter, noise and other background signals around the target to ensure that the false alarm probability remains unchanged. The first step is to obtain the surrounding noise power through various estimation methods, determine the threshold according to the Neyman-Pearson criterion, and if the power exceeds the threshold, it is considered that there is a target at this point, otherwise there is no target at this point, etc.;

[0052] Velocity ambiguity resolution is performed based on the phase difference on the range-velocity spectrum after the two-dimensional FFT of Data 1 and Data 2 respectively, specifically including: determining the position of the target on the range-velocity spectrum through CFAR detection, and comparing the phase differences at the positions of the targets in Data 1 and Data 2;

[0053] If the phase difference is less than ±π / 2, the velocity range of the target does not exceed the velocity measurement range of the signal with a period of T, and the velocity is calculated according to the following formula:

[0054] v = Δ θ λ / 4πT

[0055] where Δ θ represents the phase difference at the positions of the targets in Data 1 and Data 2;

[0056] If the phase difference is greater than ±π / 2, it is necessary to consider that the velocity of the target exceeds the velocity measurement range and ambiguity occurs, and the velocity is calculated according to the following formula:

[0057] v = Δ θ λ / 4πT + v max

[0058] where v max is the maximum velocity measurement velocity of the signal with a period of T.

[0059] As shown in (a) and (b) of Figure 7 , Scan Position 1 and Scan Position 2 are at the same position on the range-velocity spectrum. Just looking at the range-velocity spectrum diagram, the velocity of the target is 10 m / s. However, due to the phase difference between Scan Position 1 and Scan Position 2 being 212.45°, the velocity of the target is determined to be 23.6 m / s.

[0060] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A sawtooth wave radar speed measurement extension method based on the amplitude comparison angle measurement mode, characterized in that: including the following steps: S1: The transmitting antennas of the radar transmitter alternately transmit linear frequency-modulated continuous wave signals with the same sweep period of T at scan position 1 and scan position 2; S2: For a target located in the direction, at a distance R and with a velocity v, first collect data one from M scanning positions one and data two from M scanning positions two; the far-field envelope signal received by the radar from scanning position one at time t is expressed as: where x k (t) is the input envelope signal of antenna element k, is the radiation pattern of antenna element k, is the delay of antenna element k in the direction , and N is the number of the antenna arrays; After the radar goes through one sweep period, that is, at time t + T, the far-field envelope signal received from scan position 2 is expressed as: S3: Eliminate the constant phase difference caused by the change in the antenna direction pointing in the phases of data 1 and data 2 for each received echo signal; the constant phase difference Δ1 caused by the change in the antenna direction pointing in the phases of data 1 and data 2 is: where Δ(k) is the phase of the k-th array element signal. After eliminating the constant phase difference Δ1, the phase difference between scan position 1 and scan position 2 only contains velocity spread; The maximum unambiguous velocity is λ / 2T; S4: Perform coherent accumulation processing through two-dimensional FFT; specifically including the following steps: S41: First, perform two-windowed Fourier transforms on the received multiple echo signals respectively to obtain two-dimensional images of range-Doppler of data 1 and data 2; S42: Then, merge the range-Doppler of data 1 and the range-Doppler of data 2. Since the constant phase difference has been eliminated in step S3, all the phases of data 1 and data 2 are coherent. After merging, the coherence of the signal can be fully utilized to improve the signal-to-noise ratio; the processing of the previous and subsequent two steps is coherent accumulation processing; S5: Perform constant false alarm rate CFAR detection on the target; the constant false alarm rate CFAR detection is to adaptively adjust the decision threshold through the background signal around the target to ensure that the false alarm probability remains unchanged, specifically including the following steps: S51: First, obtain the surrounding noise power; S52: Determine the threshold according to the Neyman-Pearson criterion; S53: Judge whether the noise power exceeds the threshold. If the power exceeds the threshold, it is considered that there is a target at this point, otherwise there is no target at this point; S6: Perform velocity ambiguity resolution according to the phase difference on the range-velocity spectrum after two-dimensional FFT of data 1 and data 2 respectively; including the following steps: Determine the position of the target on the range-velocity spectrum through CFAR detection, and compare the phase differences of the positions of the target in data 1 and data 2; If the phase difference is less than ±π / 2, the velocity range of this target does not exceed the velocity measurement range of the signal with a period of T, and the velocity is calculated according to the following formula: v = Δ θ λ / 4πT where, Δ θ represents the phase difference between the positions of the targets of the first data and the second data; If the phase difference is greater than ±π / 2, the velocity of this target exceeds the velocity measurement range and velocity ambiguity needs to be considered, and the velocity is calculated according to the following formula: v = Δ θ λ / 4πT + v max where v max is the maximum speed measurement speed of a signal with a period of T.

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