A method and system for calibration and monitoring of phased array radar based on fiber optic time delay

Abstract

This invention discloses a phased array radar calibration and monitoring method and system based on fiber optic time delay, relating to the field of phased array weather radar data processing and calibration technology. It includes setting up a calibration system in the far field, comprising a fiber optic time delay module, a transceiver module, and a measurement module. A fixed time delay is introduced using fiber optics, making the distance of the echo in the radar base data much larger than the actual physical distance, thus avoiding interference from ground objects. A formula for calculating the reflectivity factor reference value considering atmospheric loss compensation error is derived, and absolute calibration is achieved by comparing the radar's measured values ​​with the theoretical reference value. The radar's mechanical elevation angle is adjusted so that beams with different normal deviation angles point towards the calibration system, and the echo intensity is extracted to assess the performance differences of each beam. Through long-term extraction of echo intensity in calibration mode or service mode, combined with system loss, stability parameters are calculated and time series are analyzed to achieve long-term monitoring and early warning of radar stability.

Description

Technical Field

[0001] This invention relates to the field of phased array weather radar data processing and calibration technology, and more specifically to a phased array radar calibration and monitoring method and system based on fiber optic time delay. Background Technology

[0002] Phased array weather radar, as one of the pillars of modern meteorological monitoring systems, plays a vital role in short-term weather forecasting, quantitative precipitation estimation, and severe weather assessment. Therefore, ensuring the accuracy of radar data is crucial. To ensure stable and reliable radar detection performance and accurate monitoring of meteorological targets in the target area, regular calibration of the phased array weather radar is essential.

[0003] Currently, the end-to-end absolute calibration method promoted by the China Meteorological Administration at various stations mainly uses metal sphere calibration. As an RCS-stable absolute calibration device, the metal sphere can provide a relatively good reference value. However, existing metal sphere calibration methods primarily involve suspending the metal sphere using a drone, which generally results in poor stability. The metal sphere is prone to swaying in the air, and operational calibration is easily constrained by airspace conditions, ground clutter, and drone endurance. Furthermore, phased array radars, based on beamforming technology, exhibit variations in antenna gain and other parameters in different directions, and currently, there are no effective beam assessment methods or long-term monitoring techniques.

[0004] Therefore, how to develop a phased array weather radar calibration system that can achieve calibration and long-term monitoring for operational radar calibration and monitoring, realize quantitative assessment of radar reflectivity factor, improve radar detection accuracy, and ensure the accuracy of weather forecasts is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of the above problems, the present invention is proposed to provide a method and system for calibration and monitoring of phased array radar based on fiber optic time delay that overcomes or at least partially solves the above problems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, embodiments of the present invention provide a phased array radar calibration and monitoring system based on fiber optic time delay, comprising:

[0008] Transceiver module: includes a horn antenna for receiving radar transmitted signals and transmitting echo signals to the radar, and a three-axis turntable for adjusting the direction of the horn antenna;

[0009] Fiber optic delay module: Connected to the transceiver module, it receives the electrical signal input from the transceiver module, converts it into an optical signal for delayed transmission in the optical fiber, then converts it back into an electrical signal and amplifies and attenuates the power, and finally feeds it back to the transceiver module to be transmitted back to the radar.

[0010] Measurement module: Used for real-time monitoring of internal system losses.

[0011] Furthermore, the fiber delay module includes a circulator, an optical transmitter, a main fiber, a tunable fiber, an optical receiver, a low-noise amplifier, an attenuator, and a high-precision non-directional coupler connected in sequence.

[0012] A high-precision non-directional coupler is connected to the measurement module to couple input and output signals for measurement.

[0013] After the radar signal is transmitted to the standard horn antenna, part of the signal is transmitted to the spectrum analyzer via a high-precision non-directional coupler, and the other part is transmitted to the circulator via a corresponding feeder. At this time, the circulator transmits the electrical signal to the optical transmitter. The optical transmitter converts the electrical signal into an optical signal, which is then transmitted in the main optical fiber, then through the tunable optical fiber, and finally to the optical receiver. The optical receiver converts the optical signal back into an electrical signal, amplifies the signal power through a low-noise amplifier, and then adjusts the signal strength to a suitable level through an attenuator. Finally, part of the signal is transmitted to the spectrum analyzer via the high-precision non-directional coupler, and the other part is transmitted to the horn antenna via the circulator, where it propagates towards the radar.

[0014] Furthermore, the measurement module includes a spectrum analyzer or a power meter;

[0015] Secondly, embodiments of the present invention provide a phased array radar calibration and monitoring method based on fiber optic time delay, comprising:

[0016] S1. The fiber optic delay module measures and records the actual physical distance between the horn antenna and the radar. The measurement module tests and records the total internal loss of the phased array radar calibration and monitoring system based on fiber optic delay. ;

[0017] S2. The radar and the transceiver module transmit continuous wave signals to each other, and the azimuth and elevation angles of the transceiver module are adjusted respectively to make the center of the radar beam main lobe aligned with the horn antenna; and the polarization axis of the transceiver module is rotated to make the isolation between the main polarization and the cross polarization greater than the preset threshold.

[0018] S3. After radar alignment, the radar continuously transmits signals and receives the echo signals from the fiber optic delay module, calculating the reflectivity factor detection value based on the actual physical distance. and total internal system losses The reflectivity factor reference value is calculated, and the overall deviation of the reflectivity factor of the radar system is obtained by comparing the detected reflectivity factor value with the reflectivity factor reference value.

[0019] Furthermore, the specific process of the radar continuously transmitting signals and receiving the echo signals from the fiber optic delay module in S3 is as follows:

[0020] After the radar signal is transmitted to the standard horn antenna, part of the signal is transmitted to the measurement module via a high-precision non-directional coupler, and the other part is transmitted to the circulator via a corresponding feeder. At this time, the circulator transmits the electrical signal to the optical transmitter. The optical transmitter converts the electrical signal into an optical signal, which is then transmitted through the main optical fiber to provide the basic time delay, and then through the tunable optical fiber to provide the micro-time delay variation, and finally to the optical receiver. The optical receiver converts the optical signal back into an electrical signal, amplifies the signal power through a low-noise amplifier, and then adjusts the signal strength to a suitable level through an attenuator. Finally, part of the signal is transmitted to the measurement module via the high-precision non-directional coupler, and the other part is transmitted through the circulator to the horn antenna, where it propagates towards the radar.

[0021] Furthermore, in S1, the total internal loss of the phased array radar calibration and monitoring system based on fiber delay was tested and recorded. The formula is:

[0022]

[0023] L1 represents the cable loss between the horn antenna and the high-precision non-directional coupler; L2 represents the loss of the fiber optic delay module by connecting the signal source to the input of the fiber optic delay-based phased array radar calibration and monitoring system, reading the output power of the calibration system through a spectrum analyzer, and calculating the loss of the fiber optic delay module.

[0024] Furthermore, the specific process in S2 to align the center of the radar beam's main lobe with the horn antenna is as follows:

[0025] S21. Set up a temporary signal source and a horn antenna next to the radar antenna to transmit continuous waves, control the three-axis turntable to continuously scan in the azimuth and elevation planes, obtain the azimuth and elevation angles corresponding to the maximum received power, and fix the three-axis turntable.

[0026] S22. The phased array radar calibration and monitoring system based on fiber optic time delay transmits continuous waves. The radar performs a fan-shaped scan with the theoretical alignment angle as the center to obtain the azimuth and elevation angles corresponding to the maximum received power, and then points the radar to that angle.

[0027] S23. Repeat steps one and two until the difference between the two maximum received power values ​​of the radar is less than 0.2dB, and complete the azimuth and elevation alignment.

[0028] S24. The radar transmits a single-carrier signal. By rotating the polarization axis of the horn antenna, the amplitude of the main polarization and cross-polarization signals on the spectrum analyzer is observed, and the polarization isolation is calculated. The antenna is rotated until the polarization isolation reaches its maximum value and is greater than 25dB.

[0029] Furthermore, the formula for calculating the reflectivity factor reference value in S3 is as follows:

[0030]

[0031] in and These are the receiving gain and transmitting gain of the horn antenna in a phased array radar calibration and monitoring system based on fiber optic time delay; Total internal loss of a phased array radar calibration and monitoring system based on fiber optic delay The value after converting to logarithm; R is the radar operating wavelength; R is the distance displayed in the radar base data as the echo from the calibration system. and These are the azimuth and elevation beamwidth of the radar antenna, respectively. The speed of light; This refers to the radar pulse width. The dielectric constant factor of water; For two-way atmospheric loss; R represents the distance in the base data corresponding to the echo generated by the phased array radar calibration and monitoring system based on fiber optic time delay.

[0032] Furthermore, it also includes performance evaluations for different beams:

[0033] The S2 method was used to complete the azimuth and polarization alignment between the radar normal beam and the phased array radar calibration and monitoring system based on fiber optic time delay.

[0034] Determine the beam deviation from the normal angle el3 to be tested, and calculate the required mechanical elevation angle el2 of the radar based on the true elevation angle el1 of the horn antenna relative to the radar in the calibration system: ;

[0035] The control radar performs an RHI scan at the required mechanical elevation angle of the radar and extracts the maximum value in the data as the alignment reflectivity factor at that elevation angle.

[0036] Change el3 and repeat the above steps to obtain the alignment reflectivity factor for multiple elevation angles;

[0037] By comparing the alignment reflectivity factor values ​​at different elevation angles, the differences in detection performance of different beams are evaluated; at the same time, the radiation patterns of the cascaded transceiver antennas are extracted and compared with the test data in the anechoic chamber.

[0038] Furthermore, this also includes calibration modes and business models:

[0039] Calibration mode: Keep the radar aligned with the fiber optic time delay-based phased array radar calibration and monitoring system, perform long-term RHI scanning, and statistically analyze the changes in reflectivity factor after alignment;

[0040] Business Model: During normal radar volume scan mode, extract the maximum value of data in the base data that corresponds to the azimuth and elevation angles of the phased array radar calibration and monitoring system based on fiber optic time delay and is calculated based on the time delay.

[0041] In both modes, the stability parameter is calculated by combining the system loss recorded by the measurement module. The stability parameter is the sum of the measured reflectivity factor and the system loss.

[0042] By analyzing the changes, standard deviations, and diurnal errors of stable parameters over long time series, the stability of radar systems can be assessed and early warnings can be provided.

[0043] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following:

[0044] This invention provides a method and system for calibration and monitoring of phased array radar based on fiber optic time delay. This system systematically solves the problems of insufficient stability, external rule constraints, and scanning time limitations in existing end-to-end operational calibration methods for phased array weather radars. Furthermore, it can assess the performance differences of different beams and monitor the long-term stability of the radar system. The calibration and monitoring system based on fiber optic time delay lines can provide stable echoes based on the radar's transmitted signals, thereby quantitatively calibrating the reflectivity factor. It evaluates beams at different elevation angles through a "mechanical servo + beamforming" method, without scanning time limitations. Through long-term radar operation, it statistically analyzes stable parameters and quantitatively assesses the stability of the radar system. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0046] Figure 1 This is a diagram of the overall system structure provided in the embodiments of the present invention;

[0047] Figure 2 This is a diagram illustrating the configuration of a phased array weather radar calibration and monitoring system based on fiber optic delay lines provided in an embodiment of the present invention.

[0048] Figure 3 This is a flowchart of the method provided in the embodiments of the present invention;

[0049] Figure 4 This is a graph showing the curve of echo intensity varying with distance library number and the comparison of theoretical values ​​provided in this embodiment of the invention;

[0050] Figure 5This is a diagram showing the elevation direction echo intensity distribution at the target distance library provided in this embodiment of the invention. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] This invention discloses a method and system for calibration and monitoring of phased array radar based on fiber optic time delay, such as... Figure 1 The following are included:

[0053] Transceiver module: includes a horn antenna for receiving radar transmitted signals and transmitting echo signals to the radar, and a three-axis turntable for adjusting the direction of the horn antenna;

[0054] Fiber optic delay module: Connected to the transceiver module, it receives the electrical signal input from the transceiver module, converts it into an optical signal for delayed transmission in the optical fiber, then converts it back into an electrical signal and amplifies and attenuates the power, and finally feeds it back to the transceiver module to be transmitted back to the radar.

[0055] Measurement module: Used for real-time monitoring of internal system losses.

[0056] The specific implementation of this invention is as follows:

[0057] (1) Preparations before calibration. Choose a day with clear skies and low wind speeds; select a mountain with higher elevation and lower surrounding elevations, based on the terrain around the radar location. Ensure there are no significant obstructions between the radar and the mountaintop.

[0058] (2) Equipment preparation. The specific equipment includes one absolute calibration system based on fiber optic delay module, one three-axis turntable (excluding the one used in the calibration system), one mobile power supply, two power meters, two signal sources, one spectrum analyzer (excluding the one used in the calibration system), one horn antenna (excluding the one used in the calibration system), and several cables.

[0059] (3) Instrument Calibration. Power on and preheat the signal source, spectrum analyzer, low-noise amplifier, power meter, and other equipment for at least 30 minutes to allow the temperature drift to stabilize. Then, calibrate the signal source, spectrum analyzer, and power meter. First, perform self-calibration on the power meter. Then, connect the signal source to the power meter and spectrum analyzer respectively, and calibrate the frequency response error of the spectrum analyzer by using the power meter reading as a reference. All equipment should be calibrated.

[0060] (4) Loss Test. Before the experiment, the loss of the entire fiber optic delay calibration system was tested, which mainly consisted of two parts. First, the cable loss L1 connecting the horn antenna and the high-precision non-directional coupler was tested. Second, after compensating for the cable loss, the cable was used to connect the signal source and the coupler, and the fiber optic delay module loss L2 was calculated by reading the signal input power and output power obtained from the spectrum analyzer. Therefore, the loss of the entire system was... .

[0061] (5) Direction Alignment. This step aims to align the radar with the calibration system and mainly consists of three steps. Step 1: Radar transmits, calibration system receives: At the calibration system installation location, a spectrum analyzer is connected, and a three-axis turntable is set up near the radar location. A feeder connects the horn antenna to the signal source, transmitting a continuous wave signal at a specified frequency. The turntable of the calibration system is controlled to continuously scan in the azimuth and elevation planes to obtain the maximum array value. Step 2: The direction of the horn antenna of the calibration system is fixed, and a signal source is connected to transmit a continuous wave signal at a specified frequency. The radar normal pointing is used to perform a fan-shaped scan of approximately ±5° in the azimuth and elevation angles according to the theoretically calculated alignment angle, obtaining the maximum value of the normal pointing. After obtaining the maximum value, the radar pointing is adjusted to the azimuth and elevation angles corresponding to the maximum value, and the data is read again. If the difference between the two maximum values ​​is less than 0.2dB, proceed to the next step; otherwise, repeat the scanning and positioning. Step 3: Polarization Alignment. The radar is set to alignment mode, transmitting a single-carrier signal with alternating polarization. The horn antenna at the calibration system is directly connected to the spectrum analyzer. The polarization axis of the horn is rotated using a three-axis turntable to observe the primary and cross-polarized signals. The planned isolation between the primary and cross-polarized signals is calculated, and the maximum planned isolation is found. The horn is then rotated 90° to verify if the isolation meets the requirement of being greater than 25dB. If not, the angle is fine-tuned until the requirement is met.

[0062] (6) Reflectivity factor calibration. After the radar is aligned, it continuously transmits signals and receives echo signals from the calibration system. By comparing the radar detection values ​​with the reference values, the overall deviation of the radar system's reflectivity factor is obtained.

[0063] The connection order of each module is as follows: Figure 2 As shown, the signal enters from the horn antenna and is transmitted in the direction of the arrow.

[0064] After the radar signal is transmitted to the standard horn antenna, part of the signal is transmitted to the spectrum analyzer via a high-precision non-directional coupler, and the other part is transmitted to the circulator via a corresponding feeder. At this time, the circulator transmits the electrical signal to the optical transmitter. The optical transmitter converts the electrical signal into an optical signal, which is then transmitted in the main optical fiber, then through the tunable optical fiber, and finally to the optical receiver. The optical receiver converts the optical signal back into an electrical signal, amplifies the signal power through a low-noise amplifier, and then adjusts the signal strength to a suitable level through an attenuator. Finally, part of the signal is transmitted to the spectrum analyzer via the high-precision non-directional coupler, and the other part is transmitted to the horn antenna via the circulator, where it propagates towards the radar.

[0065] Phased array radars exhibit variations in antenna radiation patterns at different elevation angles, leading to differences in detection performance. These differences typically require compensation within the radar system to bring the performance closer together at each elevation angle.

[0066] However, traditional methods are difficult to compare the performance of beams at different elevation angles: when using a fixed RCS period for calibration, ground interference cannot be avoided if the period is placed on the calibration tower using angle reflection or other methods; if a UAV is used to suspend a metal ball, the flight time is limited and the metal ball is subject to shaking, which reduces the accuracy of the comparison results.

[0067] The specific process of the calibration and monitoring method proposed in this invention is as follows: Figure 3 As shown:

[0068] The fiber optic delay module measures and records the actual physical distance between the horn antenna and the radar. The measurement module tests and records the total internal loss of the phased array radar calibration and monitoring system based on fiber optic delay. ;

[0069] By transmitting continuous wave signals between the radar and the transceiver module, the azimuth and elevation angles of the transceiver module are adjusted to align the center of the radar beam main lobe with the horn antenna; and by rotating the polarization axis of the transceiver module, the isolation between the main polarization and the cross polarization is made greater than a preset threshold.

[0070] After the radar is aligned, it continuously transmits signals and receives the echo signals from the circulator, calculating the reflectivity factor detection value based on the actual physical distance. and total internal system losses The reflectivity factor reference value is calculated, and the overall deviation of the reflectivity factor of the radar system is obtained by comparing the detected reflectivity factor value with the reflectivity factor reference value.

[0071] Case Study of a Wide-to-Narrow Pattern with 4x Widening (Normal Deviation +4°, Horizontal Polarization)

[0072] In this embodiment, the theoretical value calculation is based on the radar parameter formula, and the actual spatial distance between the time delay line testing device and the radar is determined sequentially. Total loss of delay line module Equivalent beamwidth Substituting the above parameters into the theoretical reflectivity factor calculation formula, the theoretical dBZ value of the wide-transmitting and narrow-receiving 4-fold widening mode is obtained.

[0073] 1. Actual spatial distance between the time delay line testing device and the radar calculate

[0074] The positions of the test antenna and the time delay line element are transformed to a geocentric rectangular coordinate system, and the spatial slant distance between the two points is obtained by comprehensively considering the Earth's curvature and the elevation difference between the two points. The actual spatial distance between the time delay line test device and the radar in this embodiment is calculated to be... =2424.22m. This distance is the actual spatial distance corresponding to the time delay line unit, used for subsequent theoretical value calculations.

[0075] 2. Calculation of the distance R displayed by the target in the radar base data

[0076] In this embodiment, the target is located in the 2094th range column, which is 12m long and has a zero-point distance of 174m. Therefore, the target's distance displayed in the radar base data is:

[0077]

[0078] The distance displayed by the target in the radar base data is used to interpret the echo position and atmospheric attenuation compensation term in the radar base data; while the actual spatial distance between the time delay line element and the radar is used for theoretical link calculation, and the two have different physical meanings.

[0079] 3. Total loss of delay line module calculate

[0080] To ensure stable operation of the delay module and accurately characterize signal energy changes in the delay line link, the overall link loss of the module was tested and evaluated. The loss from the horn antenna port to the LNA output was -3.29dB, and the loss from the LNA output to the horn antenna input was -6.06dB. The total loss of the fiber optic delay module was calculated by combining these two losses. =-9.35dB. This value is used in the theoretical formula to correct for link attenuation introduced by the delay line module.

[0081] 4. Equivalent beamwidth calculate

[0082] For phased array radars, the main lobe widths and combinations of the transmit and receive patterns may differ under different operating modes. To uniformly characterize the effective illumination range under different transmit and receive beam configurations, this embodiment uses the real fixed angle of the main lobe after combining the transmit and receive patterns and converts it into an equivalent beamwidth for theoretical echo intensity calculation. The real fixed angle of the main lobe of the combined transmit and receive patterns is converted into the product of the equivalent beamwidths to obtain... This parameter reflects the change in effective irradiation volume under the wide-range transmission and narrow-range reception mode, and is a key correction factor in the theoretical value calculation of this embodiment.

[0083] 5. Calculation of theoretical reflectivity factor dBZ

[0084] Substituting system parameters such as radar operating wavelength, equivalent gain of transmit and receive channels, pulse width, actual spatial distance between the delay line test device and the radar, total loss of the delay line module, and equivalent beamwidth into the radar parameter formula, the theoretical reflectivity factor corresponding to this embodiment is 65.727dB.

[0085] The formula for radar parameters is:

[0086]

[0087]

[0088] and These represent the azimuth and elevation beamwidth of the radar antenna, respectively.

[0089] Therefore, after the actual spatial distance, link loss and equivalent beamwidth between the delay line test device and the radar are all included in the calculation, the fiber delay line can form an equivalent echo with a clear theoretical reflectivity factor correspondence, which can be used for subsequent comparative analysis between the measured results and the theoretical values.

[0090] This embodiment uses measured radar base data to visualize and analyze the equivalent echo characteristics of a fiber optic delay line in a wide-transmit, narrow-receive, 4x widening mode. During processing, a specified radar base data file is read, an elevation angle layer close to the target is selected, and multiple azimuth data points within the same elevation angle layer are averaged to obtain a curve showing the echo intensity changing with a range library. Subsequently, the target's range library is determined based on this curve, and the average echo intensity at different elevation angles is extracted from this range library. Further analysis of the target echo distribution characteristics in the elevation direction and the 3dB beamwidth is then performed. Through joint analysis of the target peak intensity and elevation widening characteristics, the correspondence between the equivalent echo of the fiber optic delay line and the theoretical calculation results can be verified.

[0091] (1) Comparison of echo intensity variation curves with distance and library number and theoretical values

[0092] During the target range library determination process, an elevation angle layer close to the target is selected, and azimuth averaging is performed on multiple azimuth sampling data within this layer to obtain the corresponding curve between the range library index and the average echo intensity. To avoid the influence of near-range clutter, system leakage, or invalid range libraries on peak value interpretation, the program starts searching for valid peak values ​​after the set minimum search distance and compares the measured peak values ​​obtained from the search with the calculated theoretical values.

[0093] like Figure 4 As shown, the target echo peak is located at the 2094th distance cell, with a measured echo intensity of 64.777 dB and a theoretical value of 65.727 dB, a deviation of -0.950 dB. The results indicate that, under the 4x widening mode (wide transmit, narrow receive), the measured intensity of the equivalent echo of the fiber delay line shows good agreement with the theoretical calculation, and can be used for subsequent calibration result analysis.

[0094] (2) Echo intensity distribution in the pitch direction

[0095] After determining the target range library, the 2094th range library is fixed, and multiple azimuth data points at the corresponding range libraries in each elevation angle layer are averaged to obtain the distribution curve of echo intensity as a function of elevation angle. This curve can reflect the main lobe response characteristics of the target's equivalent echo in the elevation direction.

[0096] like Figure 5 As shown, the echo intensity in the elevation direction reaches its maximum value near 19.0°, with a peak intensity of 64.777 dB. Using a 3 dB decrease in peak intensity as the half-power criterion, the intersection point of the left and right 3 dB values ​​is determined through linear interpolation, and the 3 dB beamwidth in the elevation direction is calculated to be 1.683°. This result reflects the beamwidth characteristics of the target echo in the elevation direction under the wide transmit / narrow receive mode, providing a basis for further analysis of the transmit beamwidth effect and the applicability of equivalent echo calibration.

[0097] In summary, the echo intensity variation curve with range library number is mainly used to determine the target's range library location and verify the consistency between the measured peak value and the theoretical calculation value; the echo intensity distribution in the elevation direction is used to analyze the main lobe response and 3dB beamwidth of the target echo in the elevation direction. Both types of results are based on azimuth-averaged echo data, and the processing logic is consistent, enabling the verification of the equivalent echo characteristics of the fiber delay line in the 4x widening mode of wide transmission and narrow reception from both the range library number and elevation angle perspectives.

[0098] The calibration and monitoring system proposed in this invention can effectively delay radar signals. When the phased array radar receives the echo returned by the calibration system, it processes it according to the actual reception time. That is, the distance corresponding to the echo in the base data is much greater than the actual distance, thus avoiding the influence of ground objects. At the same time, since the system can be stably erected on the calibration tower without time limitations, it can test all elevation beams of the radar and simultaneously acquire the radiation patterns of the cascaded transmit and receive antennas.

[0099] To more accurately evaluate beam performance across different elevation angles, a set of evaluation procedures for different beams has been developed, with the specific steps as follows:

[0100] (1) Direction alignment. Direction alignment is achieved by following the above-mentioned direction alignment method, including azimuth, elevation (to align the normals) and polarization alignment.

[0101] (2) Elevation Angle Calculation. Based on actual beam requirements, mechanical servo and beamforming are used to align the elevation angle to be tested with the horn antenna of the calibration system. Specifically, let the elevation angle of the calibration system horn antenna relative to the radar be el1, the radar's reference mechanical elevation angle be el0 (i.e., at this mechanical elevation angle, the reference normal is 90°-el0; the elevation angle stored in the base data is the true elevation angle pointing; when the mechanical elevation angle changes, the elevation angle value stored in the base data does not actually point to that elevation angle; for example, if the mechanical elevation angle increases by 1°, the normal pointing decreases by 1°, and the true elevation angle pointing in the base data is the stored elevation angle value -1°), the radar's actual mechanical elevation angle be el2 (at this time, the radar's actual normal pointing is 90°-el2), and the normal deviation angle to be tested be el3. Then, there exists... The actual mechanical elevation angle of the radar can be calculated using this relationship.

[0102] (3) Adjust the elevation angle. Adjust the radar mechanical elevation angle according to the calculation results in (2) and perform RHI scanning.

[0103] (4) Data processing. After obtaining the data for all elevation angles that need to be tested, the data is processed to evaluate the performance of different beams: the maximum value in the data of different beams is extracted as the alignment reflectivity factor at that elevation angle, and the difference in detection performance of different beams is obtained by comparing the values ​​of the alignment reflectivity factor; by extracting the reflectivity factor of the same beam at different elevation angles, the radiation pattern of the cascaded transceiver antenna of the phased array weather radar is obtained and compared with the anechoic chamber data to obtain the difference between the actual far field and the anechoic chamber test.

[0104] This invention proposes two methods for long-term monitoring of radar stability, corresponding to calibration mode and operational mode, respectively.

[0105] In calibration mode, following the alignment method between the radar and the calibration system in different beam evaluation procedures, and maintaining the mechanical servo unchanged, RHI scanning is performed over a long period. The reflectivity factor after alignment is statistically analyzed.

[0106] In operational mode, the radar operates normally. The system selects the elevation layer closest to the calibration system relative to the radar elevation angle in volume scan mode, and selects all data within a 2° range before and after the theoretical azimuth angle. Based on the time delay, it calculates the range library containing the calibration system echo and extracts all data from the three libraries before and after this range library. Since there are no ground features at a relatively distant location, the reflectivity factor mainly comes from the calibration system echo. The maximum value extracted from each set of base data in the radar volume scan is statistically analyzed.

[0107] In both modes, the overall system loss is monitored using a spectrum analyzer, and the data is stored and transmitted to a computer. By aligning the spectrum analyzer recording time with the radial time of the radar base data, the loss of the entire calibration system at the echo moment of the radar receiving calibration system is approximately obtained, and the loss is added to the reflectivity factor value as a stability parameter. The stability of the radar system is evaluated by analyzing the variation, standard deviation, and diurnal error of this parameter over a long time series.

[0108] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0109] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for calibration and monitoring of phased array radar based on fiber optic time delay, wherein the method is implemented based on a phased array radar calibration and monitoring system based on fiber optic time delay, characterized in that, include: The phased array radar calibration and monitoring system based on fiber optic time delay includes: Transceiver module: includes a horn antenna for receiving radar transmitted signals and transmitting echo signals to the radar, and a three-axis turntable for adjusting the direction of the horn antenna; Fiber optic delay module: connected to the transceiver module, used to receive the electrical signal input by the transceiver module, convert it into an optical signal for delayed transmission in the optical fiber, then convert it back into an electrical signal and amplify and attenuate it, and finally feed it back to the transceiver module to be transmitted back to the radar; Measurement module: Used for real-time monitoring of internal system losses; The method includes: S1. The fiber optic delay module measures and records the actual physical distance between the horn antenna and the radar. The measurement module tests and records the total internal loss of the phased array radar calibration and monitoring system based on fiber optic delay. ; S2. The radar and the transceiver module transmit continuous wave signals to each other, and the azimuth and elevation angles of the transceiver module are adjusted respectively to make the center of the radar beam main lobe aligned with the horn antenna; and the polarization axis of the transceiver module is rotated to make the isolation between the main polarization and the cross polarization greater than the preset threshold. S3. After radar alignment, the radar continuously transmits signals and receives the echo signals from the fiber optic delay module, calculating the reflectivity factor detection value based on the actual physical distance. and total internal system losses Calculate the reflectivity factor reference value, and obtain the overall deviation of the reflectivity factor of the radar system by comparing the detected reflectivity factor value with the reflectivity factor reference value; In step S1, the total internal loss of the phased array radar calibration and monitoring system based on fiber optic delay is tested and recorded. The formula is: in L 1. To test the cable loss connecting the horn antenna and the non-directional coupler; L 2. To connect the signal source to the input terminal of the phased array radar calibration and monitoring system based on fiber optic time delay, the output power of the phased array radar calibration and monitoring system based on fiber optic time delay is read through the measurement module, and the loss of the fiber optic time delay module is calculated. The formula for calculating the reflectivity factor reference value in S3 is as follows: in and These are the receiving gain and transmitting gain of the horn antenna in a phased array radar calibration and monitoring system based on fiber optic time delay; Total internal loss of a phased array radar calibration and monitoring system based on fiber optic delay The value after converting to logarithm; The operating wavelength of the radar; R The distance displayed in the radar base data for the echo of a phased array radar calibration and monitoring system based on fiber optic time delay; and These are the azimuth and elevation beamwidth of the radar antenna, respectively. c The speed of light; This refers to the radar pulse width. The dielectric constant factor of water; This is for two-way atmospheric loss; R m This represents the actual physical distance between the horn antenna and the radar.

2. The method as described in claim 1, characterized in that, include: The fiber delay module includes a circulator, an optical transmitter, a main fiber, a tunable fiber, an optical receiver, a low-noise amplifier, an attenuator, and a non-directional coupler connected in sequence. The non-directional coupler is connected to the measurement module and is used to couple input and output signals for measurement. The specific process of the radar continuously transmitting signals and receiving the echo signals from the fiber optic delay module in S3 is as follows: After the radar signal is transmitted to the standard horn antenna, part of the signal is transmitted to the measurement module via a non-directional coupler, and the other part is transmitted to the circulator via a corresponding feeder. At this time, the circulator transmits the electrical signal to the optical transmitter. After the optical transmitter converts the electrical signal into an optical signal, the optical signal is provided with a basic time delay through the main optical fiber, and then with a micro-time delay variation through an adjustable optical fiber, and finally transmitted to the optical receiver. After the optical receiver converts the optical signal into an electrical signal, the signal power is amplified by a low-noise amplifier, and then the signal strength is adjusted to a suitable level by an attenuator. Finally, the signal adjusted by the attenuator is transmitted to the measurement module via the circulator and non-directional coupler, and the other part is transmitted to the horn antenna, which then propagates towards the radar.

3. The method as described in claim 1, characterized in that, The specific process for aligning the center of the radar beam's main lobe with the horn antenna in S2 is as follows: S21. Set up a temporary signal source and a horn antenna next to the radar antenna to transmit continuous waves, control the three-axis turntable to continuously scan in the azimuth and elevation planes, obtain the azimuth and elevation angles corresponding to the maximum received power, and fix the three-axis turntable. S22. The phased array radar calibration and monitoring system based on fiber optic time delay transmits a continuous wave. The radar performs a fan-shaped scan with the theoretical alignment angle as the center to obtain the azimuth and elevation angles corresponding to the maximum received power, and then points the radar to that angle. S23. Repeat S21 and S22 until the difference between the two maximum received power values ​​of the radar is less than 0.2dB, and complete the azimuth and elevation alignment. S24. The radar transmits a single-carrier signal. By rotating the polarization axis of the horn antenna, the amplitude of the main polarization and cross-polarization signals on the measurement module is observed and measured. The polarization isolation is calculated, and the polarization isolation is rotated until it reaches its maximum value and is greater than 25dB.

4. The method as described in claim 1, characterized in that, It also includes performance evaluations of different beams: Using the S2 method, the azimuth and polarization alignment between the radar normal beam and the fiber-optic time delay-based phased array radar calibration and monitoring system is completed. Determine the beam deviation normal angle el3 to be tested, and calculate the required mechanical elevation angle el2 of the radar based on the horn antenna of the fiber optic time delay-based phased array radar calibration and monitoring system relative to the radar's true elevation angle el1. ; The control radar performs an RHI scan at the required mechanical elevation angle of the radar and extracts the maximum value in the data as the alignment reflectivity factor at that elevation angle. Change el3 and repeat the above steps to obtain alignment reflectivity factors for multiple elevation angles; By comparing the alignment reflectivity factor values ​​at different elevation angles, the differences in detection performance of different beams are evaluated; at the same time, the radiation patterns of the cascaded transceiver antennas are extracted and compared with the test data in the anechoic chamber.

5. The method as described in claim 1, characterized in that, It also includes calibration mode and business mode: Calibration mode: Keep the radar aligned with the fiber optic time delay-based phased array radar calibration and monitoring system, perform long-term RHI scanning, and statistically analyze the changes in reflectivity factor after alignment; Business Model: During normal radar volume scan mode, extract the maximum value of data in the base data that corresponds to the azimuth and elevation angles of the phased array radar calibration and monitoring system based on fiber optic time delay and is calculated based on the time delay. In both modes, the system loss recorded by the measurement module is combined to calculate the stability parameter, which is the sum of the measured reflectivity factor and the system loss. By analyzing the changes, standard deviations, and diurnal errors of the stability parameters over long time series, the stability of the radar system is assessed and early warning is provided.

6. The method as described in claim 1, characterized in that, include: The measurement module includes a spectrum analyzer or a power meter.

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