Method and device for calibrating ultra-long baseline distributed radar transceiver local oscillator frequency
By performing Doppler processing on the echo signal of a stationary target selected by an ultra-long baseline distributed radar, extracting and compensating for the local oscillator frequency difference, the problem of the frequency difference between the transmitter and receiver affecting the detection performance is solved, and efficient frequency calibration and performance improvement are achieved.
Patent Information
- Application Number
- CN202310782737.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-06-29
- Publication Date
- 2026-05-15
- Estimated Expiration
- 2043-06-29
AI Technical Summary
The transmit and receive local oscillators of ultra-long baseline distributed radar are difficult to achieve the same clock source, which affects the system's detection performance. In addition, microwave photonics technology solutions are complex, costly, and have unstable signal quality.
By performing Doppler processing on the echo signal of stationary targets, the local oscillator frequency difference of the ultra-long baseline distributed radar is extracted, and the echo signals of other targets are compensated based on this frequency difference. Frequency calibration is performed using linear frequency modulated signals and Fourier transform techniques.
It effectively eliminates the influence of the local oscillator frequency difference between the transmitter and receiver on the measurement results, improves the detection performance of ultra-long baseline distributed radar, and reduces system complexity and cost.
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Figure CN116774172B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of radar detection technology, specifically relating to a method and device for calibrating the local oscillator frequency of an ultra-long baseline distributed radar transceiver. Background Technology
[0002] Ultra-long baseline distributed detection radar boasts advantages such as long detection range and high measurement accuracy. However, the transmitting and receiving antennas of distributed ultra-long baseline radars are typically distributed over a distance of tens or even hundreds of kilometers, making it difficult to ensure that the transmitting and receiving local oscillators are synchronized, thus affecting the system's detection performance. Theoretically, using microwave photonics technology to distribute the clock local oscillator can solve the problem of synchronized transmitting and receiving local oscillators. However, this method significantly increases system complexity and cost. Furthermore, the clock local oscillator signal transmitted over long distances via optical fiber is susceptible to environmental factors (temperature, vibration, etc.), making it difficult to guarantee signal quality. Therefore, eliminating the frequency difference between the transmitting and receiving local oscillators is crucial for achieving ultra-long baseline distributed detection. Summary of the Invention
[0003] The purpose of this invention is to provide a method and device for calibrating the local oscillator frequency of an ultra-long baseline distributed radar, which can meet the local oscillator frequency calibration requirements of ultra-long baseline distributed detection radar, reduce the impact of frequency differences in the local oscillator frequency of the distributed radar on the system's detection performance, and reduce the complexity of the ultra-long baseline distributed detection system.
[0004] Specifically, on the one hand, the present invention provides a method for calibrating the local oscillator frequency of an ultra-long baseline distributed radar, comprising: selecting a target that is stationary relative to the ultra-long baseline distributed radar; extracting the local oscillator frequency difference of the ultra-long baseline distributed radar by performing Doppler processing on the echo signal of the stationary target; and compensating for the echo signals of other targets based on the local oscillator frequency difference of the ultra-long baseline distributed radar.
[0005] Furthermore, the step of selecting a target that is stationary relative to the ultra-long baseline distributed radar, extracting the local oscillator frequency difference of the ultra-long baseline distributed radar through echo Doppler processing of the stationary target, and compensating for the echo signals of other targets based on the local oscillator frequency difference of the ultra-long baseline distributed radar includes:
[0006] S1: Select a stationary high-elevation target for the ultra-long baseline distributed radar, and set the linear frequency modulated (LFM) signal bandwidth B, LFM signal pulse width τ0, and LFM signal repetition frequency f. p ;
[0007] S2: Perform pulse compression on the received static high-elevation target echo signal to form N spikes;
[0008] S3: According to 1 / f pThe time width divides the received static high elevation angle target echo signal into N equal segments, and aligns them according to the position of each pulse compression peak to form a two-dimensional matrix of pulse number-range unit;
[0009] S4: Perform a Fourier transform on the sequence of N pulse pressure peaks in the two-dimensional matrix of the pulse number-distance unit, and use the obtained Doppler value as the local oscillator frequency difference Δf;
[0010] S5: When detecting a moving target, the received moving target echo signal is compensated using the local oscillator frequency difference Δf, that is, the received moving target echo signal s r (t) Perform local oscillator frequency difference compensation according to the following formula to obtain the compensated moving target echo signal u. r (t):
[0011] u r (t)= s r (t)×exp(-j2πΔft) (4)
[0012] S6: The compensated moving target echo signal u r (t) Perform pulse compression operation to form N spikes; according to 1 / f p The time width is divided into N equal segments of the compensated moving target echo signal, and aligned according to the position of each pulse pressure peak to form a two-dimensional matrix of pulse number-distance unit; Fourier transform is performed on the sequence of N pulse pressure peaks in the two-dimensional matrix of pulse number-distance unit to obtain the Doppler frequency of the real target.
[0013] Furthermore, the selection of stationary high-elevation targets for ultra-long baseline distributed radar includes:
[0014] 1) According to 2D 2 / λ calculates the far-field region of an ultra-long baseline distributed radar, where D is the baseline length and λ is the radar operating wavelength.
[0015] 2) Select a high elevation target that is stationary relative to the ultra-long baseline distributed radar in the far field region of the ultra-long baseline distributed radar to ensure that the elevation angle of the target observed by the radar is high enough to avoid ground clutter entering the radar main lobe.
[0016] Furthermore, the high-elevation targets of the ultra-long baseline distributed radar include large targets in geosynchronous orbit on the equatorial plane or calibration targets at a certain altitude at a distance.
[0017] Furthermore, the bandwidth B of the linear frequency modulated signal is such that the distance unit corresponding to the pulse compression distance resolution c / 2B is larger than the size of the selected stationary target, where c is the speed of light.
[0018] Furthermore, the pulse width τ0 of the linear frequency modulated signal is such that the pulse compression gain Bτ0 satisfies the condition that the target signal-to-noise ratio after single pulse compression is greater than a set threshold, where B is the bandwidth of the linear frequency modulated signal.
[0019] Furthermore, the threshold is calculated from the detection probability and false alarm rate in constant false alarm rate detection.
[0020] Furthermore, the repetition frequency f of the linear frequency modulated signal p Make c / 2f p Greater than the target distance, where c is the speed of light.
[0021] On the other hand, the present invention also provides an ultra-long baseline distributed radar transceiver local oscillator frequency calibration device, the device including a memory and a processor; the memory stores a computer program for implementing an ultra-long baseline distributed radar transceiver local oscillator frequency calibration method, and the processor executes the computer program to implement the steps of the above method.
[0022] In another aspect, the present invention also provides a computer-readable storage medium having a computer program stored thereon, characterized in that the computer program, when executed by a processor, implements the steps of the above-described method.
[0023] The beneficial effects of the ultra-long baseline distributed radar transceiver local oscillator frequency calibration method and equipment of the present invention are as follows:
[0024] The ultra-long baseline distributed radar transceiver local oscillator frequency calibration method and device of the present invention utilizes the spatial stationary target measurement environment to meet the local oscillator frequency calibration requirements of ultra-long baseline distributed detection radar, reduce the impact of frequency difference in distributed radar local oscillator on system detection performance, and reduce the complexity of ultra-long baseline distributed detection system. Attached Figure Description
[0025] Figure 1 This is a flowchart of an embodiment of the present invention.
[0026] Figure 2 This is a schematic diagram of typical stationary target echo information detected by ultra-long baseline distributed radar according to an embodiment of the present invention.
[0027] Figure 3 This is a schematic diagram of the pulse Doppler echo processing results according to an embodiment of the present invention.
[0028] Figure 4 This is a schematic diagram of the frequency difference extraction results of ultra-long baseline distributed radar according to an embodiment of the present invention.
[0029] Figure 5 This is a schematic diagram of the Doppler processing results of other target pulses after local oscillator frequency difference compensation in an embodiment of the present invention. Detailed Implementation
[0030] The present invention will now be described in further detail with reference to the embodiments and the accompanying drawings.
[0031] Example 1:
[0032] One embodiment of the present invention is a method for calibrating the local oscillator frequency of an ultra-long baseline distributed radar transceiver.
[0033] In the ultra-long baseline distributed radar transceiver local oscillator frequency calibration method of the present invention, the reasons for the error in radar measurement results caused by the frequency difference between the local oscillator signals at the transmitting and receiving ends are first analyzed.
[0034] Assume the local oscillator signal at the transmitting end is:
[0035] L t (t)=exp(j2πf0t) (1)
[0036] Where j is the imaginary unit, f0 is the carrier frequency at the transmitting end, and t is time. The local oscillator signal L at the transmitting end... t (t) is a continuous signal.
[0037] If the baseband signal is B(t), then the transmit excitation signal is:
[0038] s t (t)=B(t)Lt(t)
[0039] Where τ is the pulse width of the baseband signal, and T is the repetition period of the baseband signal, which is the reciprocal of the repetition frequency, 1 / f. p .
[0040] The local oscillator signal at the receiving end is:
[0041] L r (t)=exp[j2πf′0(t-τ0)] (2)
[0042] Where f′0 is the carrier frequency at the receiving end, and L is the local oscillator signal at the receiving end. r (t) is a continuous signal.
[0043] The delay τ0 introduced at the receiver is because the transceiver of the ultra-long baseline distributed detection radar is not synchronized. If the time reference is the start of signal transmission at the transmitter, the receiver may be delayed by time τ0.
[0044] The signal received by the receiver of the ultra-long baseline distributed sounding radar is:
[0045] s r (t)=B(t-T0)L t (t-T0)L r *(t-T0)=B(t-T0)exp(j2πΔft-j2πΔfT0+j2πf′0τ0)(3)
[0046] Where T0 represents the delay corresponding to the target echo signal, Δf=f0-f′0 represents the frequency difference between the local oscillator signals at the transmitting and receiving ends, and L r * (t-T0) is L r The conjugate signal of (t-T0).
[0047] If the received signals are arranged in pulse order, then the initial phase of each pulse is as follows: Where T is the repetition period of the transmitted signal.
[0048] Therefore, it can be seen that due to the frequency difference between the local oscillator signals at the transmitting and receiving ends, in addition to a fixed value, the initial phase of each pulse of the received signal also has a phase that increases linearly with the pulse sequence number. If the pulse Doppler processing method is used to perform coherent accumulation on the target, due to the existence of the linear phase, a stationary target will be judged as a target with velocity, resulting in measurement errors.
[0049] The main input data of this invention are echo data from stationary targets detected by an ultra-long baseline distributed radar (ULD-DAR) and echo data from other moving targets. To eliminate the influence of the frequency difference between the local oscillator signals at the transmitting and receiving ends on the measurement results, a target stationary relative to the ULD-DAR is selected. The ULD-DAR local oscillator frequency difference is extracted by performing PD (pulse Doppler) processing on the echo of the stationary target. Based on this ULD-DAR local oscillator frequency difference, compensation is performed for the echo signals of other targets, thereby obtaining accurate measurement results. Figure 1 As shown, the specific steps of the ultra-long baseline distributed radar transceiver local oscillator frequency calibration method of the present invention are as follows:
[0050] S1: Select a stationary high-elevation target for the ultra-long baseline distributed radar, and set the linear frequency modulated (LFM) signal bandwidth B, LFM signal pulse width τ0, and LFM signal repetition frequency f. p .
[0051] 1) According to 2D 2 / λ calculates the far-field region of an ultra-long baseline distributed radar, where D is the baseline length and λ is the radar operating wavelength.
[0052] 2) Select high elevation targets that are stationary relative to the ultra-long baseline distributed radar in the above-mentioned long-range areas, such as large targets in geosynchronous orbit on the equatorial plane or calibration targets at a certain altitude in the distance, to ensure that the elevation angle of the radar observation target is high enough to avoid ground clutter entering the radar main lobe.
[0053] 3) Set the linear frequency modulated signal bandwidth B to ensure that the distance unit corresponding to the pulse compression distance resolution c / 2B is larger than the size of the selected stationary target, where c is the speed of light. This operation ensures that the target's energy is concentrated at a single point of pulse compression.
[0054] 4) Set the linear frequency modulated signal pulse width τ to ensure that the pulse compression benefit Bτ satisfies the requirement that the target signal-to-noise ratio after single-pulse pulse compression is greater than the set threshold, where B is the linear frequency modulated signal bandwidth. This threshold is calculated from the detection probability and false alarm rate in constant false alarm rate detection. For example, in constant false alarm rate detection, the detection probability is 0.8 and the false alarm rate is 10. -6 The calculated threshold is 13dB.
[0055] 5) Set the repetition frequency f of the linear frequency modulated signal according to the target distance. p Ensure c / 2f p The distance is greater than the target distance, where c is the speed of light, to avoid aliasing when receiving signals.
[0056] S2: Perform pulse compression on the received echo signal from a stationary high-elevation target to form N spikes. N is typically chosen to be a multiple of 8 to facilitate Fast Fourier Transform. The received echo signal from a stationary high-elevation target is as follows: Figure 2 As shown.
[0057] S3: According to 1 / f p The time width divides the received stationary high-elevation target echo signal into N equal segments, aligns them according to the position of each pulse compression peak, and forms a two-dimensional matrix of pulse number-range units, such as... Figure 3 As shown.
[0058] S4: Perform a Fourier transform on the sequence of N pulse compression peaks in the two-dimensional matrix of the pulse number-distance unit, and use the obtained Doppler value as the local oscillator frequency difference Δf. Figure 4 As shown.
[0059] S5: When detecting a moving target, the received moving target echo signal is compensated using the local oscillator frequency difference Δf, that is, the received moving target echo signal s r (t) Perform local oscillator frequency difference compensation according to the following formula to obtain the compensated moving target echo signal u. r (t):
[0060] u r (t)= s r (t)×exp(-j2πΔft) (4)
[0061] S6: The compensated moving target echo signal u r (t) Perform pulse compression operation to form N spikes; according to 1 / f pThe time width divides the signal into N equal segments, which are aligned according to the position of each pulse pressure peak to form a two-dimensional matrix of pulse number-distance units. A Fourier transform is performed on the sequence of N pulse pressure peaks in the two-dimensional matrix of pulse number-distance units. The Fourier transform yields the Doppler frequency of the real target, such as... Figure 5 As shown.
[0062] Through derivation, this invention discovers that due to the frequency difference between the local oscillator signals at the transmitting and receiving ends, in addition to a fixed initial phase, each pulse of the received signal also has a phase that increases linearly with the pulse sequence number. If pulse Doppler processing is used to perform coherent accumulation on the target, due to the existence of the linear phase, a stationary target will be judged as a target with velocity, resulting in measurement errors.
[0063] In order to eliminate the influence of the local oscillator signal frequency difference between the transmitting and receiving ends on the measurement results, this invention selects a target that is stationary relative to the ultra-long baseline distributed radar. The local oscillator frequency difference of the ultra-long baseline distributed radar is extracted by processing the echo PD (pulse Doppler) of the stationary target. Based on the local oscillator frequency difference of the ultra-long baseline distributed radar, compensation is completed for the echo signals of other targets, thereby obtaining accurate measurement results.
[0064] The present invention relates to a method and device for calibrating the local oscillator frequency of ultra-long baseline distributed radar, which utilizes the spatial stationary target measurement environment to complete the calibration of the local oscillator frequency of ultra-long baseline distributed radar, thereby improving the detection performance of ultra-long baseline distributed radar.
[0065] While the present invention has been disclosed above with reference to preferred embodiments, these embodiments are not intended to limit the invention. Any equivalent changes or modifications made without departing from the spirit and scope of the invention are also within the scope of protection of the invention. Therefore, the scope of protection of the present invention should be determined by the claims of this application.
Claims
1. A method for calibrating the local oscillator frequency of an ultra-long baseline distributed radar, characterized in that, include: A stationary target relative to the ultra-long baseline distributed radar is selected. The local oscillator frequency difference of the ultra-long baseline distributed radar is extracted by Doppler processing of the echo signal of the stationary target. Based on the local oscillator frequency difference of the ultra-long baseline distributed radar, compensation for the echo signals of other targets is completed. The specific steps include: S1: Select a stationary high-elevation target for the ultra-long baseline distributed radar, and set the linear frequency modulated (LFM) signal bandwidth B, LFM signal pulse width τ0, and LFM signal repetition frequency f. p ; S2: Perform pulse compression on the received static high-elevation target echo signal to form N spikes; S3: According to 1 / f p The time width divides the received static high elevation angle target echo signal into N equal segments, and aligns them according to the position of each pulse compression peak to form a two-dimensional matrix of pulse number-range unit; S4: Perform a Fourier transform on the sequence of N pulse pressure peaks in the two-dimensional matrix of the pulse number-distance unit, and use the obtained Doppler value as the local oscillator frequency difference Δf; S5: When detecting a moving target, the received moving target echo signal is compensated using the local oscillator frequency difference Δf, that is, the received moving target echo signal s r (t) Perform local oscillator frequency difference compensation according to the following formula to obtain the compensated moving target echo signal u. r (t): u r (t)= s r (t)×exp(-j2πΔft) (4) S6: The compensated moving target echo signal u r (t) Perform pulse compression operation to form N spikes; according to 1 / f p The time width is divided into N equal segments of the compensated moving target echo signal, and aligned according to the position of each pulse pressure peak to form a two-dimensional matrix of pulse number-distance unit; Fourier transform is performed on the sequence of N pulse pressure peaks in the two-dimensional matrix of pulse number-distance unit to obtain the Doppler frequency of the real target.
2. The ultra-long baseline distributed radar transceiver frequency calibration method according to claim 1, characterized in that, The selected stationary high-elevation targets for ultra-long baseline distributed radar include: 1) According to 2D 2 / λ calculates the far-field region of an ultra-long baseline distributed radar, where D is the baseline length and λ is the radar operating wavelength. 2) Select a high elevation target that is stationary relative to the ultra-long baseline distributed radar in the far field region of the ultra-long baseline distributed radar to ensure that the elevation angle of the target observed by the radar is high enough to avoid ground clutter entering the radar main lobe.
3. The ultra-long baseline distributed radar transceiver local oscillator frequency calibration method according to claim 2, characterized in that, The ultra-long baseline distributed radar stationary high elevation targets include large targets in geosynchronous orbit on the equatorial plane or distant calibration targets at a certain altitude.
4. The ultra-long baseline distributed radar transceiver frequency calibration method according to claim 2, characterized in that, The bandwidth B of the linear frequency modulated signal is such that the distance unit corresponding to the pulse compression distance resolution c / 2B is larger than the size of the selected stationary target, where c is the speed of light.
5. The ultra-long baseline distributed radar transceiver frequency calibration method according to claim 2, characterized in that, The pulse width τ0 of the linear frequency modulated signal is such that the pulse compression gain Bτ0 satisfies the condition that the target signal-to-noise ratio after single pulse compression is greater than a set threshold, where B is the bandwidth of the linear frequency modulated signal.
6. The ultra-long baseline distributed radar transceiver local oscillator frequency calibration method according to claim 5, characterized in that, The threshold is calculated from the detection probability and false alarm rate in constant false alarm rate detection.
7. The ultra-long baseline distributed radar transceiver frequency calibration method according to claim 2, characterized in that, The repetition frequency f of the linear frequency modulation signal p Make c / 2f p Greater than the target distance, where c is the speed of light.
8. A calibration device for the local oscillator frequency of an ultra-long baseline distributed radar transceiver, characterized in that, The device includes a memory and a processor; the memory stores a computer program for implementing a method for calibrating the local oscillator frequency of an ultra-long baseline distributed radar transceiver, and the processor executes the computer program to implement the steps of the method according to any one of claims 1-7.
9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1-7.