SAR Satellite Azimuth Agile Observation Mode Scanning Pointing Detection Method and System

Abstract

This invention provides a method and system for detecting the scanning direction of a SAR satellite in an agile azimuth observation mode. The method includes: setting up a microwave probe in front of the onboard SAR antenna array to meet the far-field testing conditions and signal energy requirements of the radiating element; disconnecting the port connection between the antenna array calibration network and the internal calibrator; connecting the internal calibrator port to the microwave probe antenna via a ground-based high-frequency test cable; setting the onboard SAR system to a single-TR calibration test mode; performing normal-state single-TR calibration tests and specified-scan state single-TR calibration tests; powering on the entire satellite and recording echo data; performing pulse compression and interpolation processing on the echo data acquired from the two tests to obtain the phase value at the peak value; performing phase difference calculation and reference mapping conversion on the corresponding TR channels to generate a two-dimensional phase difference cloud map; and determining the correctness of the SAR antenna pattern scanning direction based on the two-dimensional phase difference cloud map. This invention reduces the satellite development process and improves the efficiency of integrated SAR testing of the entire satellite.

Description

Technical Field

[0001] This invention relates to the field of SAR ground-based satellite integration and testing technology, specifically to a SAR satellite azimuth agile observation mode scanning pointing detection method and system. Background Technology

[0002] Spaceborne active phased array synthetic aperture radar (SAR) is an all-weather, all-time Earth observation method. With the continuous development of spaceborne active phased array SAR technology, large two-dimensional scanning and broadband signals are becoming essential conditions for SAR satellites to obtain high-resolution, wide-bandgap observations. In particular, the azimuth scanning capability not only achieves high azimuth resolution but also allows for the observation of a large number of targets during a single SAR satellite flight. Especially in situations where the azimuth distance is close and the distance is far, the azimuth scanning capability of the SAR antenna can be used to achieve dense observation of multiple target clusters in a single flight through forward-looking, side-looking, and backward-looking methods. This has led to a new application mode of agile azimuth observation, greatly improving the observation efficiency of SAR satellites. At the same time, as SAR satellites are developing towards high integration, lightweight design, and mass production, the requirements for efficient functional testing of new SAR satellite observation modes are becoming increasingly stringent. During SAR satellite ground integration testing, the correctness of the SAR antenna pattern scanning direction directly affects the reachability of target detection in the azimuth-agile observation mode. Incorrect scanning direction leads to mismatch between the satellite system and the ground application processing system, making it impossible to acquire images of the desired targets. To achieve rapid testing and verification of the SAR satellite's azimuth-agile observation mode function, it is necessary to improve and develop the traditional testing methods for SAR patterns using onboard active phased array systems. This will allow the methods to adapt to the overall satellite testing conditions and environment, while also meeting the requirements for high-efficiency SAR satellite testing.

[0003] Currently, the testing method for the azimuth-agile observation mode of spaceborne active phased array SAR is the near-field testing method. Generally, during the integration of the SAR antenna subsystem, the SAR antenna is pushed into a microwave anechoic chamber, and the precise channel radiation characteristics are obtained through the near-field testing system, thus yielding the pattern test results (including pattern shape and scanning angle), which can verify the correctness of the SAR antenna scanning direction. Since the SAR antenna subsystem needs to be integrated into the satellite platform, the beam control of the SAR antenna must receive commands from the satellite system to achieve azimuth-agile observation functionality. Therefore, it is necessary to further verify the correctness of the SAR pattern scanning direction in the azimuth-agile observation mode under the condition of the entire satellite. However, the near-field system requires a high-precision scanning rig, which cannot be quickly deployed in a conventional satellite integration facility. Transporting the entire SAR satellite system to the microwave anechoic chamber for testing requires a long testing time and complex testing fixtures. Moreover, the transfer of the SAR satellite between a conventional integration facility and the microwave anechoic chamber can also pose unpredictable safety risks to the satellite product.

[0004] Currently, the pointing test of SAR pattern scanning in azimuth-agile observation mode can also be performed using an internal calibration system. The main functions of internal calibration include measuring the amplitude and phase distribution of the TR channel, extracting the system reference function, and monitoring its stability. In most known spaceborne SAR systems using active phased array antennas, a wired antenna calibration network is constructed using a power distribution network and couplers, which, together with an internal calibrator, completes the calibration of the SAR system's active transmit and receive channels. The internal calibration system can be used to test the amplitude and phase characteristics of the array channels, obtain pattern data at different scanning angles through inversion, and then check the correctness of the SAR pattern scanning pointing in azimuth-agile observation mode. However, the calibration link has the following drawbacks:

[0005] a. The calibration network can only cover up to the output port of the TR component, but cannot cover the connection joint between the TR component and the radiating array, nor can it cover the radiating array. Therefore, it cannot fully obtain the antenna characteristics.

[0006] b. The final calibrated amplitude and phase data is the transmission effect of the calibration network and the feed network together. The error introduced by the temperature change characteristics of the calibration network itself cannot be easily removed.

[0007] c. The test data acquired by the internal calibration system is collected within the closed loop of the system and requires inversion processing. Compared with the near-field system, there is no direct reference, and the intuitiveness of the direction pattern scanning detection decision is not strong.

[0008] Based on research, the following are some publicly available domestic patents related to efficient detection of SAR satellite multi-target observation pattern scanning:

[0009] Chinese patent document CN103344847A discloses an antenna pattern testing method based on spherical near-field scanning extrapolation. This invention obtains the far-field pattern by extrapolating the data obtained from near-field testing using an algorithm. This not only reduces the testing distance but also eliminates the plane wave condition required for cylindrical wave testing. The resulting three-dimensional antenna pattern allows for clearer and more intuitive analysis of antenna performance, possessing significant engineering practical value. This invention enables effective near-range antenna testing, saving testing costs and reducing testing difficulty. Furthermore, it provides a more accurate analysis of antenna performance by obtaining the three-dimensional pattern of the antenna under test. While the previous invention still required complex near-field scanning equipment, this invention eliminates the need for such equipment.

[0010] Chinese patent document CN104101786B discloses a full-space active multi-beam spherical phased array antenna pattern measurement system. This patent mainly targets full-space active multi-beam spherical phased array antennas and aims to provide a measurement system that is flexible in control, has high pointing accuracy, low cost, and uses electrical scanning instead of mechanical scanning. This invention still requires complex scanning equipment to achieve antenna pattern testing and is specifically designed for spherical phased array antennas rather than planar phased array antennas, which is significantly different from this invention.

[0011] Chinese patent document CN103344847A discloses a method for simultaneous multi-beam precise scanning sampling in near-field measurements of a phased array antenna. This method first involves a probe locator sliding at a constant speed in a predetermined direction. Upon passing a sampling position, it sends an electrical pulse to an encoding controller. The encoding controller, according to a predetermined precise working cycle, command timing, and number of operations, coordinates the phased array antenna's beam control system and RF measurement system to complete multiple beam switching and RF sampling measurements. This achieves simultaneous multi-beam precise scanning sampling RF measurements at a single sampling position, ensuring that the sampling data for each beam has a fixed positional offset across all sampling positions. This maintains a consistent near-field measurement sampling interval for each beam, facilitating near-field to far-field mathematical calculations. This invention still relies on a near-field measurement system to achieve beam scanning testing.

[0012] Chinese patent document CN106546827B discloses a method, circuit, and system for testing the radiation pattern of a phased array direction finding device. This patented method connects the RF output of a vector network analyzer to the RF input of a power divider network. Each RF output of the power divider network is connected via cables to a specific transceiver channel of the phased array direction finding device under test. Each transceiver channel of the phased array direction finding device under test is connected to a microwave switch via a channel cable, an elevation difference channel cable, and an azimuth difference channel cable. The common terminal of the microwave switch is also connected to the RF input of the vector network analyzer. The controller has signal connections to the wave control system of the phased array direction finding device under test, the microwave switch, and the vector network analyzer. This invention primarily targets the lateral direction of a phased array, using a vector network analyzer for testing, and differs significantly from the purpose and specific technical method of this invention.

[0013] Chinese patent document CN107329003B discloses a method for optimizing SAR antenna pattern testing. This patent first establishes a mathematical model for calculating the pattern of an active phased array antenna based on electromagnetic field theory; secondly, it acquires and calculates the basic data of the active phased array antenna, and calculates and stores the amplitude and phase weighting coefficients of all wave positions of the SAR antenna according to design requirements and engineering feasibility; finally, in a planar near-field testing system environment, it uses near-field testing methods to obtain the antenna subarray patterns at different positions on the antenna array surface. This patent mainly optimizes antenna pattern testing based on near-field testing methods, while this invention does not use near-field testing equipment, greatly simplifying the testing equipment. Summary of the Invention

[0014] To address the shortcomings of existing technologies, the purpose of this invention is to provide a SAR satellite azimuth agile observation mode scanning pointing detection method and system.

[0015] A SAR satellite azimuth-agile observation mode scanning pointing detection method according to the present invention includes the following steps:

[0016] Step S1: Fix the microwave probe on the adjustable bracket and place the adjustable bracket in front of the SAR antenna array. The microwave probe points to the center of the front area to be measured. The microwave probe and the SAR antenna array maintain a set distance, and the half-power main lobe region of the microwave probe and the half-power main lobe region of the radiating element intersect.

[0017] Step S2: Disconnect the high-frequency cable from the SAR antenna array calibration network to the internal calibrator, and connect the external calibration port of the internal calibrator to the microwave probe through the ground test high-frequency cable;

[0018] Step S3: Lay absorbing material in front of the SAR antenna array, on both sides, and on the adjustable support;

[0019] Step S4: Set the SAR subsystem to normal state single TR calibration test mode, set the corresponding working bandwidth, power on the satellite and record the transmitted calibration echo data;

[0020] Step S5: Set the SAR subsystem to the specified scanning state single TR calibration test mode, where the fixed scanning angle matches the target observation center pointing angle of the azimuth agile observation mode, and set the same working bandwidth as the normal state. Power on the satellite and record the transmitted calibration echo data.

[0021] Step S6: Perform pulse compression and interpolation processing on the calibration echo data obtained from the two test records respectively, and take the phase value at the peak value after pulse compression of each TR channel to form two sets of phase value data results;

[0022] Step S7: Subtract the two sets of phase values ​​according to the one-to-one correspondence of the TR channels, and convert the one-dimensional phase difference data into a two-dimensional phase difference cloud map for display based on the mapping relationship between the TR channels and the array layout. Use the two-dimensional phase difference cloud map to determine the correctness of the direction of the radiation pattern scan.

[0023] Preferably, step S1 includes:

[0024] Step S1.1: Fix the microwave probe on the adjustable bracket and set the microwave probe to point to the center of the area to be tested;

[0025] Step S1.2: Based on the assumption that the radiating element corresponding to any TR channel of the SAR antenna under test meets the far-field test conditions, calculate the distance from the microwave probe to the array of the SAR antenna under test;

[0026] Step S1.3: Based on the requirement that the 3dB beam of the microwave probe and the 3dB beam of the radiating element intersect, adjust the distance between the microwave probe and the SAR antenna array under test.

[0027] Preferably, step S4 includes:

[0028] Step S4.1: Select the single TR calibration mode of the SAR subsystem as the system working mode during detection. Only one TR channel is turned on at each pulse moment, and the acquisition of the radiation element signals of all TR channels in the area to be tested is completed one by one.

[0029] Step S4.2: Set the SAR antenna to operate in normal mode with a scanning angle of 0°;

[0030] Step S4.3: Select and set the working bandwidth, power on the satellite, start the SAR subsystem, and record the transmitted test echo data.

[0031] Preferably, step S5 includes:

[0032] Step S5.1: Select the single TR calibration mode of the SAR subsystem as the system working mode during detection. Only one TR channel is turned on at each pulse moment, and the acquisition of the radiation element signals of all TR channels in the area to be measured is completed one by one in sequence.

[0033] Step S5.2: Set the SAR antenna to scan mode and use the center pointing angle of the target observation in the azimuth agile observation mode as the fixed scanning angle of the radiation pattern;

[0034] Step S5.3: Select and set the same working bandwidth as in step S4.3;

[0035] Step S5.4: Power on the satellite, start the SAR subsystem and record the transmitted test echo data.

[0036] Preferably, step S6 includes:

[0037] Step S6.1: Perform pulse compression processing on the calibration echo data obtained from the two test records respectively, and each pulse compression result data corresponds to the corresponding TR channel;

[0038] Step S6.2: Interpolate the processed data after pulse compression and take the phase value at the peak value;

[0039] Step S6.3: Save the phase values ​​of all TR channels in the area to be tested to form two sets of phase value data.

[0040] Preferably, step S7 includes:

[0041] Step S7.1: Subtract the two sets of phase value arrays and untangle the subtraction result;

[0042] Step S7.2: Based on the single TR calibration order and the TR channel arrangement relationship of the array surface in the region to be measured, generate a two-dimensional phase difference cloud map from the subtracted one-dimensional phase difference array according to the mapping relationship;

[0043] Step S7.3: Generate a theoretical scanning phase cloud map based on the set scanning angle;

[0044] Step S7.4: Based on the principle of whether the measured two-dimensional phase difference cloud map is consistent with the theoretical scanning phase cloud map, complete the detection and confirmation of the SAR pattern scanning direction.

[0045] A SAR satellite azimuth-agile observation mode scanning pointing detection system according to the present invention includes the following modules:

[0046] Module M1: Fix the microwave probe on the adjustable bracket, place the adjustable bracket in front of the SAR antenna array, point the microwave probe towards the center of the area to be measured, maintain a set distance between the microwave probe and the SAR antenna array, and there is an intersection between the half-power main lobe region of the microwave probe and the half-power main lobe region of the radiating element.

[0047] Module M2: Disconnect the high-frequency cable from the SAR antenna array calibration network to the internal calibrator, and connect the external calibration port of the internal calibrator to the microwave probe via a ground-based test high-frequency cable;

[0048] Module M3: Absorbing material is placed in front of the SAR antenna array, on both sides, and on the adjustable support.

[0049] Module M4: Set the SAR subsystem to normal state single TR calibration test mode, set the corresponding working bandwidth, power on the satellite and record the transmitted calibration echo data;

[0050] Module M5: Set the SAR subsystem to a specified scanning state single TR calibration test mode, where the fixed scanning angle matches the target observation center pointing angle of the azimuth agile observation mode, and set the same working bandwidth as the normal state. Power on the satellite and record the transmitted calibration echo data.

[0051] Module M6: Performs pulse compression and interpolation processing on the calibration echo data obtained from the two test records, and takes the phase value at the peak of each TR channel after pulse compression to form two sets of phase value data results;

[0052] Module M7: Subtracts the two sets of phase values ​​according to the one-to-one correspondence of the TR channels, and converts the one-dimensional phase difference data into a two-dimensional phase difference cloud map for display based on the mapping relationship between the TR channels and the array layout. The correctness of the direction of the radiation pattern scan is judged by the two-dimensional phase difference cloud map.

[0053] Preferably, the module M1 includes:

[0054] Module M1.1: Fix the microwave probe on the adjustable bracket and set the microwave probe to point to the center of the area to be tested;

[0055] Module M1.2: Based on the assumption that the radiating element corresponding to any TR channel of the SAR antenna under test meets the far-field test conditions, calculate the distance from the microwave probe to the array of the SAR antenna under test;

[0056] Module M1.3: Adjust the distance between the microwave probe and the SAR antenna array under test according to the requirement that the 3dB beam of the microwave probe and the 3dB beam of the radiating element intersect.

[0057] Preferably, the module M4 includes:

[0058] Module M4.1: Select the single TR calibration mode of the SAR subsystem as the system working mode during detection. Only one TR channel is turned on at each pulse moment, and the acquisition of the radiation element signals of all TR channels in the area to be tested is completed one by one in sequence.

[0059] Module M4.2: Set the SAR antenna to operate in normal mode with a scanning angle of 0°;

[0060] Module M4.3: Select and set the working bandwidth, power on the satellite, start the SAR subsystem, and record the transmitted test echo data.

[0061] Preferably, the module M5 includes:

[0062] Module M5.1: Select the single TR calibration mode of the SAR subsystem as the system working mode during detection. Only one TR channel is turned on at each pulse moment, and the acquisition of the radiation element signals of all TR channels in the area to be tested is completed one by one in sequence.

[0063] Module M5.2: Set the SAR antenna to operate in scanning mode, and use the center pointing angle of the target observation in azimuth agile observation mode as the fixed scanning angle of the radiation pattern;

[0064] Module M5.3: Select and set the same operating bandwidth as in module M4.3;

[0065] Module M5.4: When the satellite is powered on, the SAR subsystem starts working and records the transmitted test echo data.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] 1. The efficient detection method for scanning pointing in the SAR satellite azimuth agile observation mode of the present invention is for testing the scanning pointing of the two-dimensional large-scan SAR antenna pattern, especially for testing the scanning pointing in different azimuth directions in the azimuth agile observation mode. It can make up for the shortcomings of the internal calibration system test that cannot cover the connection joint between the TR component and the radiating array and cannot cover the radiating array.

[0068] 2. The SAR satellite azimuth agile observation mode scanning pointing high efficiency detection method of the present invention realizes simple and efficient testing through standard microwave probe antenna, without the need for complex test fixtures for near-field testing in an anechoic chamber, and the time consumption is also greatly reduced. At the same time, the use of pulse compression technology ensures the detection accuracy.

[0069] 3. The SAR satellite azimuth agile observation mode scanning pointing high efficiency detection method of the present invention can acquire the full-link amplitude and phase characteristic data of the array under test by selecting only the single TR test calibration mode function of the SAR subsystem itself without changing the design of the SAR subsystem.

[0070] 4. The SAR satellite azimuth agile observation mode scanning pointing high efficiency detection method of the present invention solves the problem of high efficiency and universality of SAR antenna pattern scanning pointing test. The time required for one test is in the minute range, which greatly saves the test time compared with the time required for one near field test of several hours.

[0071] Other beneficial effects of the present invention will be explained in detail through the introduction of specific technical features and technical solutions in specific embodiments. Those skilled in the art should be able to understand the beneficial technical effects brought about by these technical features and technical solutions through the introduction of these technical features and technical solutions. Attached Figure Description

[0072] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0073] Figure 1 This is a flowchart of the efficient detection method for scanning pointing in the SAR satellite azimuth agile observation mode of the present invention;

[0074] Figure 2 This is a schematic diagram illustrating the principle of efficient scanning pointing detection in the SAR satellite azimuth agile observation mode of the present invention;

[0075] Figure 3 This is a schematic diagram illustrating the alignment principle of the microwave probe of the present invention.

[0076] Figure 4 This is a schematic diagram of the overall layout of the detection method of the present invention;

[0077] Figure 5 This is a schematic diagram of the agile orientation observation mode of the present invention;

[0078] Figure 6 This is the theoretical phase value required for the azimuth scan to point at -5° and the range scan to point at 0° in this invention;

[0079] Figure 7 This is a two-dimensional display diagram of the measured phase values ​​of the azimuth scanning direction pointing to -5° and the range scanning direction pointing to 0° according to the present invention.

[0080] Figure 8 This is a three-dimensional display diagram of the measured phase values ​​of the azimuth scanning direction pointing to -5° and the range scanning direction pointing to 0°, according to the present invention. Detailed Implementation

[0081] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0082] This invention relates to ground-based integrated testing of spaceborne SAR, and more particularly to a highly efficient and universal high-efficiency detection technology for the scanning pointing of spaceborne active phased array SAR. It relates to the testing and processing of the amplitude and phase characteristics of the SAR antenna TR channel during the ground-based integrated testing of spaceborne SAR. Based on far-field testing principles, a standard microwave probe antenna and support, and single-TR test calibration working modes with different scanning states, this method provides a highly efficient detection method for the scanning pointing of SAR satellites in an agile observation mode. The method includes fixing the microwave probe to the support; adjusting the support to achieve the required position and distance between the microwave probe and the antenna array under test, ensuring that the radiating elements corresponding to each TR channel meet the remote testing conditions and that the main beam of the radiating element intersects with the main beam of the microwave probe; and disconnecting the antenna array. The calibration network is connected to the port of the internal calibrator. The port of the internal calibrator is connected to the microwave probe antenna via a high-frequency cable for ground testing to achieve full-link characteristic testing of the SAR antenna TR channel. The spaceborne SAR system is set to single TR test calibration mode in normal state (no scanning) and specified scanning state (fixed scanning angle) respectively, and the whole satellite is powered on and the echo data of each test is recorded. The echo data obtained from the two tests are processed by pulse compression and interpolation, the phase value at the peak is taken, and the phase difference and unwrapping processing of the corresponding TR channel are performed. A two-dimensional phase difference cloud map is generated using the calibration order and array TR channel arrangement rules. The trend is compared with the theoretical two-dimensional phase difference cloud map to obtain the detection result of the SAR pattern scanning pointing correctness. The purpose of this invention is to provide an efficient detection method for scanning pointing in the SAR satellite azimuth agile observation mode, to realize the testing of the scanning pointing of the spaceborne SAR antenna pattern, and at the same time realize the efficiency and universality of the testing method.

[0083] Reference Figure 1 As shown, the SAR satellite azimuth agile observation mode scanning pointing detection method provided by this invention is described as follows:

[0084] Step S1: Fix the microwave probe on the adjustable bracket, place the adjustable bracket directly in front of the SAR antenna array, point the microwave probe towards the center of the area to be tested, and keep a certain distance between the microwave probe and the antenna array so that the radiating elements corresponding to each TR channel in the area to be tested meet the far-field test conditions. At the same time, it is required that the half-power main lobe region of the microwave probe and the half-power main lobe region of the radiating element have an intersection.

[0085] Let's elaborate further:

[0086] Step S1.1: Fix the microwave probe on the bracket, and set the microwave probe to point towards the center of the area to be tested by moving the bracket and adjusting the height of the bracket;

[0087] Step S1.2: Due to space limitations in the factory, far-field testing conditions cannot be achieved for the SAR antenna array area under test. However, far-field testing conditions can be achieved for the radiating element corresponding to any TR channel on the SAR antenna array area under test due to its small size. Using the basic principle of far-field testing, the distance from the microwave probe to the SAR antenna array under test is calculated based on the fact that the radiating element corresponding to any TR channel of the SAR antenna under test meets the far-field testing conditions.

[0088] Step S1.3: To ensure measurement accuracy, the main lobe power signal is acquired under far-field conditions. Therefore, it is required that the 3dB beam of the microwave probe and the 3dB beam of the radiating element have an intersection. Theoretically, the 3dB main lobe of the microwave probe antenna should coincide with the 3dB main lobe of the radiating element at the outermost edge of the SAR antenna array area under test. Based on this requirement, the distance from the microwave probe to the SAR antenna array under test is calculated.

[0089] Step S1.4: In order to reduce spatial propagation attenuation and increase signal power, the distance value calculated in steps 102 and 103 is used as a reference to set the distance from the microwave probe to the array surface under test.

[0090] Step S2: Disconnect the high-frequency cable from the SAR antenna array calibration network to the internal calibrator, and connect the external calibration port of the internal calibrator to the microwave probe via a ground-based test high-frequency cable.

[0091] Let's elaborate further:

[0092] Step S2.1: Disconnect the high-frequency cable between the SAR antenna calibration network and the internal calibrator to eliminate the amplitude and phase error introduced by the calibration network;

[0093] Step S2.2: Connect the internal calibrator to the microwave probe antenna via a ground test high-frequency cable, and use the microwave probe to replace the calibration network to acquire the full-link amplitude and phase characteristic data of each TR channel in the area under test.

[0094] Step S3: Install absorbing materials in the relevant areas in front of and on the left and right sides of the SAR antenna array and on the adjustable support to reduce radial reflection and interference.

[0095] Let's elaborate further:

[0096] Step S3.1: To ensure detection accuracy, absorbent materials are placed in the relevant areas in front of and on the left and right sides of the SAR antenna array to reduce radial reflection and interference during electromagnetic radiation of the SAR system. Movable and splicable absorbent walls are erected in front of and on the left and right sides of the SAR antenna array. Absorbent materials are placed on the ground and marble platform between the SAR antenna array and the microwave probe.

[0097] Step S3.2: To ensure detection accuracy, the microwave probe bracket is wrapped with absorbing material, leaving only the microwave probe exposed to reduce radial reflection and interference from electromagnetic radiation of the SAR system.

[0098] Step S4: Set the SAR subsystem to normal mode (non-scanning) single TR calibration test mode, set the corresponding working bandwidth, power on the satellite and record the transmitted calibration echo data.

[0099] Let's elaborate further:

[0100] Step S4.1: Select the single TR calibration mode of the SAR subsystem as the system working mode during detection. Only one TR channel is turned on at each pulse moment, and the other TR channels are in the load state (do not radiate or receive signals). The acquisition of the radiation element signals of all TR channels in the area to be tested is completed one by one.

[0101] Step S4.2: Set the SAR antenna to operate in normal mode (no scanning), i.e., the scanning angle is 0°;

[0102] Step S4.3: Select and set the working bandwidth;

[0103] Step S4.4: Power on the satellite, start the SAR subsystem and record the transmitted test echo data.

[0104] Step S5: Set the SAR subsystem to the specified scanning state (fixed scanning angle) single TR calibration test mode, where the fixed scanning angle matches the target observation center pointing angle of the azimuth agile observation mode, and set the same working bandwidth as the normal state. Power on the satellite and record the transmitted calibration echo data.

[0105] Let's elaborate further:

[0106] Step S5.1: Select the single TR calibration mode of the SAR subsystem as the system working mode during detection. Only one TR channel is turned on at each pulse moment, and the other TR channels are in the load state (do not radiate or receive signals). The acquisition of the radiation element signals of all TR channels in the area to be tested is completed one by one.

[0107] Step S5.2: Set the SAR antenna to scan mode and use the center pointing angle of the target observation in the azimuth agile observation mode as the fixed scanning angle of the radiation pattern;

[0108] Step S5.3: Select and set the same working bandwidth as in step 4;

[0109] Step S5.4: Power on the satellite, start the SAR subsystem and record the transmitted test echo data.

[0110] Step S6: Perform pulse compression and interpolation processing on the calibration echo data obtained from the two test records respectively, and take the phase value at the peak of each TR channel after pulse compression to form two sets of phase value data results.

[0111] Let's elaborate further:

[0112] Step S6.1: Perform pulse compression processing on the calibration echo data obtained from the two test records respectively, and each pulse compression result data corresponds to the TR channel of the test array region;

[0113] Step S6.2: Interpolate the processed data after pulse compression and take the phase value at the peak value;

[0114] Step S6.3: Save the phase values ​​of all TR channels in the area to be tested to form two sets of phase value data.

[0115] Step S7: Subtract the two sets of phase values ​​according to the one-to-one correspondence of the TR channels, and convert the one-dimensional phase difference data into a two-dimensional phase difference cloud map for display based on the mapping relationship between the TR channels and the array layout. Use the two-dimensional phase difference cloud map to determine the correctness of the direction of the radiation pattern scan.

[0116] Let's elaborate further:

[0117] Step S7.1: Subtract the two sets of phase value arrays according to the one-to-one correspondence of TR channels, and unwrap the subtraction result;

[0118] Step S7.2: Based on the single TR calibration order and the TR channel arrangement relationship of the array surface in the region to be measured, generate a two-dimensional phase difference cloud map from the subtracted one-dimensional phase difference array according to the mapping relationship;

[0119] Step S7.3: Generate a theoretical scanning phase cloud map based on the set scanning angle;

[0120] Step S7.4: The judgment principle is whether the measured two-dimensional phase difference cloud map is consistent with the theoretical scanning phase cloud map. If the trend is consistent, it means that the SAR pattern scanning direction is consistent with the design value. Otherwise, it is determined that the SAR pattern scanning direction is inconsistent with the design value and needs to be corrected and changed.

[0121] More specifically, the main contents of this invention are as follows:

[0122] 1. Agile directional observation mode

[0123] To fully utilize the two-dimensional large scanning angle characteristics of planar active phased array antennas, especially the large azimuth scanning, continuous multi-target observation can be achieved through forward-looking, side-looking, and backward-looking imaging. (See also...) Figure 5 During a single flight, there are a large number of targets to be observed. Given that the targets are close in azimuth and far in distance, the SAR antenna's azimuth scanning capability can be utilized to achieve dense observation of multiple target clusters during a single flight by using forward-looking, side-looking, and backward-looking methods.

[0124] 2. Detection Principle

[0125] An active phased array antenna is composed of many small array elements. Each element corresponds to a TR (transient current) module channel and a radiating element. The TR module channel serves to shift the phase and attenuate power, while the radiating element radiates electromagnetic waves. (Refer to...) Figure 2 When the antenna is not scanning, the amplitude and phase values ​​of any array element to the microwave probe can be expressed as: in The power amplitude value (including spatial propagation attenuation), α i The phase value (including the phase value corresponding to the spatial propagation distance); during antenna scanning, the beam scanning angle position is set to... According to the principle of phased array antenna radiation patterns, the amplitude and phase values ​​of any array element to the microwave probe can be expressed as:

[0126]

[0127] in λ is the wavelength. phase value and The phase value set for scanning can be obtained by subtracting the phase values. Furthermore, the theoretical phase value set for scanning exhibits a clear linear relationship based on the array element distribution. Therefore, if the amplitude and phase data of each array element in both the normal and scanning states to the waveguide probe are obtained, the phase value set for scanning can be calculated in reverse. Comparing this value with the theoretical value can then be used to verify the correctness of the scanning direction. For specific experimental verification results, refer to... Figures 6 to 8 .

[0128] 3. Microwave probe antenna deployment

[0129] The microwave probe antenna layout should meet the requirements of far-field testing conditions and testing accuracy, referring to... Figure 3 First, the distance between the microwave probe antenna and the radiating elements corresponding to each TR channel in the area of ​​the array under test should meet the far-field condition, and the distance should be greater than 2L. 2 / λ, where L is the size of the radiating element and λ is the wavelength; secondly, the main lobe of the microwave probe antenna pattern must be located within the main lobe of any radiating element in the area to be tested of the SAR antenna array. Theoretically, the main lobe 3dB of the microwave probe antenna should coincide with the main lobe 3dB of the radiating element at the outermost edge of the area to be tested of the SAR antenna array.

[0130] 4. Test Environment Setup

[0131] The SAR satellite integration facility does not meet electromagnetic environment requirements; unlike a microwave anechoic chamber, it lacks absorbing walls on all sides. Therefore, it is necessary to configure the testing environment around the SAR antenna array to ensure testing accuracy. (Refer to...) Figure 4 SAR satellites are typically placed on marble platforms, with microwave probes mounted directly in front of the SAR antenna array under test. To achieve this, firstly, movable and modular absorbing walls need to be erected in front of and on both sides of the SAR antenna under test; secondly, absorbing materials need to be deployed on the exposed marble platform and ground in front of the SAR antenna array under test; and thirdly, absorbing materials need to be wrapped around metal supports and other metal products, leaving only the microwave probe exposed.

[0132] 5. System operating mode and antenna scanning state settings

[0133] To improve testing efficiency, firstly, a single TR test calibration working mode is selected, which allows each single TR channel to work in a time-division manner, and the amplitude and phase characteristics of each single TR channel across the entire link and bandwidth are tested one by one; secondly, the SAR antenna is set to work in normal state (i.e., no scanning) and specified scanning state respectively, and the same working bandwidth is set.

[0134] 6. Signal Body Type Selection

[0135] To ensure and improve test accuracy, a linear frequency modulated signal was selected, and pulse compression processing technology was used to process the broadband signal acquired for the test to improve test accuracy.

[0136] 7. Data Processing

[0137] First, the recorded calibration echo data is converted to obtain echo complex data, and then FFT transformation is performed. The frequency domain data of each TR channel in the two tests are as follows:

[0138] S 11_int (f), S 12_int (f)……S 1N_int (f)

[0139] and

[0140] S 21_int (f), S 22_int (f)……S 2N_int (f),

[0141] Where N represents the number of TR channels;

[0142] Next, matched filtering is performed on each test data point. The matched filtering function is H(f). The outputs after matched pulse compression of the two test data points are as follows:

[0143] S 1_out (f)=[S 11_int (f)·H(f); S 12_int (f)·H(f); ...;S 1N_int (f)·H(f)]

[0144] and

[0145] S 2_out (f)=[S 21_int (f)·H(f); S 22_int (f)·H(f); ...;S 2N_int [(f)·H(f)],

[0146] Next, the pulse compression data of each TR channel from both tests was interpolated to obtain the phase value at the peak value. The phase values ​​at the peak value of each TR channel from the two tests are as follows:

[0147] P1 = [P 11_max ,P 12_max ,……,P 1N_max ]

[0148] and

[0149] P2 = [P 21_max ,P 22_max ,……,P 2N_max ],

[0150] Phase change test value ΔP = P1 - P2;

[0151] Finally, based on the single TR calibration order and array channel arrangement rules, the one-dimensional phase change value is converted into a two-dimensional phase change value cloud map, and the trend is compared with the theoretical two-dimensional phase change value cloud map.

[0152] In summary, the efficient detection method for SAR satellite azimuth agile observation mode scanning pointing in this invention mainly completes the detection and confirmation of antenna pattern scanning pointing during SAR satellite integration testing. It solves the problem of flexible deployment in nearby sites, achieves the same accuracy as near-field testing in a microwave anechoic chamber, and also makes up for the shortcomings of the internal calibration system, which cannot cover the connection joint between the TR component and the radiating array, nor can it cover the radiating array. It realizes efficient and fast antenna pattern scanning pointing calibration test verification in the whole satellite state, meets the requirements of high efficiency and universality of the spaceborne SAR ground installation and integration test system, and greatly improves the efficiency of whole satellite integration testing.

[0153] The present invention also provides a SAR satellite azimuth agile observation mode scanning pointing detection system. The SAR satellite azimuth agile observation mode scanning pointing detection system can be implemented by executing the process steps of the SAR satellite azimuth agile observation mode scanning pointing detection method. That is, those skilled in the art can understand the SAR satellite azimuth agile observation mode scanning pointing detection method as a preferred embodiment of the SAR satellite azimuth agile observation mode scanning pointing detection system.

[0154] A SAR satellite azimuth-agile observation mode scanning pointing detection system includes the following modules:

[0155] Module M1: Fix the microwave probe on the adjustable bracket, place the adjustable bracket in front of the SAR antenna array, point the microwave probe towards the center of the area to be measured, maintain a set distance between the microwave probe and the SAR antenna array, and there is an intersection between the half-power main lobe region of the microwave probe and the half-power main lobe region of the radiating element.

[0156] Module M2: Disconnect the high-frequency cable from the SAR antenna array calibration network to the internal calibrator, and connect the external calibration port of the internal calibrator to the microwave probe via a ground-based test high-frequency cable;

[0157] Module M3: Absorbing material is placed in front of the SAR antenna array, on both sides, and on the adjustable support.

[0158] Module M4: Set the SAR subsystem to normal state single TR calibration test mode, set the corresponding working bandwidth, power on the satellite and record the transmitted calibration echo data;

[0159] Module M5: Set the SAR subsystem to a specified scanning state single TR calibration test mode, where the fixed scanning angle matches the target observation center pointing angle of the azimuth agile observation mode, and set the same working bandwidth as the normal state. Power on the satellite and record the transmitted calibration echo data.

[0160] Module M6: Performs pulse compression and interpolation processing on the calibration echo data obtained from the two test records, and takes the phase value at the peak of each TR channel after pulse compression to form two sets of phase value data results;

[0161] Module M7: Subtracts the two sets of phase values ​​according to the one-to-one correspondence of the TR channels, and converts the one-dimensional phase difference data into a two-dimensional phase difference cloud map for display based on the mapping relationship between the TR channels and the array layout. The correctness of the direction of the radiation pattern scan is judged by the two-dimensional phase difference cloud map.

[0162] In a preferred embodiment, the module M1 includes:

[0163] Module M1.1: Fix the microwave probe on the adjustable bracket and set the microwave probe to point to the center of the area to be tested;

[0164] Module M1.2: Based on the assumption that the radiating element corresponding to any TR channel of the SAR antenna under test meets the far-field test conditions, calculate the distance from the microwave probe to the array of the SAR antenna under test;

[0165] Module M1.3: Adjust the distance between the microwave probe and the SAR antenna array under test according to the requirement that the 3dB beam of the microwave probe and the 3dB beam of the radiating element intersect.

[0166] In a preferred embodiment, the module M4 includes:

[0167] Module M4.1: Select the single TR calibration mode of the SAR subsystem as the system working mode during detection. Only one TR channel is turned on at each pulse moment, and the acquisition of the radiation element signals of all TR channels in the area to be tested is completed one by one in sequence.

[0168] Module M4.2: Set the SAR antenna to operate in normal mode with a scanning angle of 0°;

[0169] Module M4.3: Select and set the working bandwidth, power on the satellite, start the SAR subsystem, and record the transmitted test echo data.

[0170] In a preferred embodiment, the module M5 includes:

[0171] Module M5.1: Select the single TR calibration mode of the SAR subsystem as the system working mode during detection. Only one TR channel is turned on at each pulse moment, and the acquisition of the radiation element signals of all TR channels in the area to be tested is completed one by one in sequence.

[0172] Module M5.2: Set the SAR antenna to operate in scanning mode, and use the center pointing angle of the target observation in azimuth agile observation mode as the fixed scanning angle of the radiation pattern;

[0173] Module M5.3: Select and set the same operating bandwidth as in module M4.3;

[0174] Module M5.4: When the satellite is powered on, the SAR subsystem starts working and records the transmitted test echo data.

[0175] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0176] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for detecting the pointing of a SAR satellite azimuth agile observation mode scan, characterized in that, Includes the following steps: Step S1: Fix the microwave probe on the adjustable bracket and place the adjustable bracket in front of the SAR antenna array. The microwave probe points to the center of the front area to be measured. The microwave probe and the SAR antenna array maintain a set distance, and the half-power main lobe region of the microwave probe and the half-power main lobe region of the radiating element intersect. Step S2: Disconnect the high-frequency cable from the SAR antenna array calibration network to the internal calibrator, and connect the external calibration port of the internal calibrator to the microwave probe through the ground test high-frequency cable; Step S3: Lay absorbing material in front of the SAR antenna array, on both sides, and on the adjustable support; Step S4: Set the SAR subsystem to normal state single TR calibration test mode, set the corresponding working bandwidth, power on the satellite and record the transmitted calibration echo data; Step S5: Set the SAR subsystem to the specified scanning state single TR calibration test mode, where the fixed scanning angle matches the target observation center pointing angle of the azimuth agile observation mode, and set the same working bandwidth as the normal state. Power on the satellite and record the transmitted calibration echo data. Step S6: Perform pulse compression and interpolation processing on the calibration echo data obtained from the two test records respectively, and take the phase value at the peak value after pulse compression of each TR channel to form two sets of phase value data results; Step S7: Subtract the two sets of phase values ​​according to the one-to-one correspondence of the TR channels, and convert the one-dimensional phase difference data into a two-dimensional phase difference cloud map for display based on the mapping relationship between the TR channels and the array layout. Use the two-dimensional phase difference cloud map to determine the correctness of the direction of the radiation pattern scan.

2. The SAR satellite azimuth agile observation mode scanning pointing detection method according to claim 1, characterized in that, Step S1 includes: Step S1.1: Fix the microwave probe on the adjustable bracket and set the microwave probe to point to the center of the area to be tested; Step S1.2: Based on the assumption that the radiating element corresponding to any TR channel of the SAR antenna under test meets the far-field test conditions, calculate the distance from the microwave probe to the array of the SAR antenna under test; Step S1.3: Based on the requirement that the 3dB beam of the microwave probe and the 3dB beam of the radiating element intersect, adjust the distance between the microwave probe and the SAR antenna array under test.

3. The SAR satellite azimuth agile observation mode scanning pointing detection method according to claim 1, characterized in that, Step S4 includes: Step S4.1: Select the single TR calibration mode of the SAR subsystem as the system working mode during detection. Only one TR channel is turned on at each pulse moment, and the acquisition of the radiation element signals of all TR channels in the area to be tested is completed one by one. Step S4.2: Set the SAR antenna to operate in normal mode with a scanning angle of 0°; Step S4.3: Select and set the working bandwidth, power on the satellite, start the SAR subsystem, and record the transmitted test echo data.

4. The SAR satellite azimuth agile observation mode scanning pointing detection method according to claim 3, characterized in that, Step S5 includes: Step S5.1: Select the single TR calibration mode of the SAR subsystem as the system working mode during detection. Only one TR channel is turned on at each pulse moment, and the acquisition of the radiation element signals of all TR channels in the area to be measured is completed one by one in sequence. Step S5.2: Set the SAR antenna to scan mode and use the center pointing angle of the target observation in the azimuth agile observation mode as the fixed scanning angle of the radiation pattern; Step S5.3: Select and set the same working bandwidth as in step S4.3; Step S5.4: Power on the satellite, start the SAR subsystem and record the transmitted test echo data.

5. The SAR satellite azimuth agile observation mode scanning pointing detection method according to claim 1, characterized in that, Step S6 includes: Step S6.1: Perform pulse compression processing on the calibration echo data obtained from the two test records respectively, and each pulse compression result data corresponds to the corresponding TR channel; Step S6.2: Interpolate the processed data after pulse compression and take the phase value at the peak value; Step S6.3: Save the phase values ​​of all TR channels in the area to be tested to form two sets of phase value data.

6. The SAR satellite azimuth agile observation mode scanning pointing detection method according to claim 1, characterized in that, Step S7 includes: Step S7.1: Subtract the two sets of phase value arrays and untangle the subtraction result; Step S7.2: Based on the single TR calibration order and the TR channel arrangement relationship of the array surface in the region to be measured, generate a two-dimensional phase difference cloud map from the subtracted one-dimensional phase difference array according to the mapping relationship; Step S7.3: Generate a theoretical scanning phase cloud map based on the set scanning angle; Step S7.4: Based on the principle of whether the measured two-dimensional phase difference cloud map is consistent with the theoretical scanning phase cloud map, complete the detection and confirmation of the SAR pattern scanning direction.

7. A SAR satellite azimuth agile observation mode scanning pointing detection system, characterized in that, Includes the following modules: Module M1: Fix the microwave probe on the adjustable bracket, place the adjustable bracket in front of the SAR antenna array, point the microwave probe towards the center of the area to be measured, maintain a set distance between the microwave probe and the SAR antenna array, and there is an intersection between the half-power main lobe region of the microwave probe and the half-power main lobe region of the radiating element. Module M2: Disconnect the high-frequency cable from the SAR antenna array calibration network to the internal calibrator, and connect the external calibration port of the internal calibrator to the microwave probe via a ground-based test high-frequency cable; Module M3: Absorbing material is placed in front of the SAR antenna array, on both sides, and on the adjustable support. Module M4: Set the SAR subsystem to normal state single TR calibration test mode, set the corresponding working bandwidth, power on the satellite and record the transmitted calibration echo data; Module M5: Set the SAR subsystem to a specified scanning state single TR calibration test mode, where the fixed scanning angle matches the target observation center pointing angle of the azimuth agile observation mode, and set the same working bandwidth as the normal state. Power on the satellite and record the transmitted calibration echo data. Module M6: Performs pulse compression and interpolation processing on the calibration echo data obtained from the test records on both sides, and takes the phase value at the peak of each TR channel after pulse compression to form two sets of phase value data results; Module M7: Subtracts the two sets of phase values ​​according to the one-to-one correspondence of the TR channels, and converts the one-dimensional phase difference data into a two-dimensional phase difference cloud map for display based on the mapping relationship between the TR channels and the array layout. The correctness of the direction of the radiation pattern scan is judged by the two-dimensional phase difference cloud map.

8. The SAR satellite azimuth agile observation mode scanning pointing detection system according to claim 7, characterized in that, The module M1 includes: Module M1.1: Fix the microwave probe on the adjustable bracket and set the microwave probe to point to the center of the area to be tested; Module M1.2: Based on the assumption that the radiating element corresponding to any TR channel of the SAR antenna under test meets the far-field test conditions, calculate the distance from the microwave probe to the array of the SAR antenna under test; Module M1.3: Adjust the distance between the microwave probe and the SAR antenna array under test according to the requirement that the 3dB beam of the microwave probe and the 3dB beam of the radiating element intersect.

9. The SAR satellite azimuth agile observation mode scanning pointing detection system according to claim 7, characterized in that, The module M4 includes: Module M4.1: Select the single TR calibration mode of the SAR subsystem as the system working mode during detection. Only one TR channel is turned on at each pulse moment, and the acquisition of the radiation element signals of all TR channels in the area to be tested is completed one by one in sequence. Module M4.2: Set the SAR antenna to operate in normal mode with a scanning angle of 0°; Module M4.3: Select and set the working bandwidth, power on the satellite, start the SAR subsystem, and record the transmitted test echo data.

10. The SAR satellite azimuth agile observation mode scanning pointing detection system according to claim 9, characterized in that, The module M5 includes: Module M5.1: Select the single TR calibration mode of the SAR subsystem as the system working mode during detection. Only one TR channel is turned on at each pulse moment, and the acquisition of the radiation element signals of all TR channels in the area to be tested is completed one by one in sequence. Module M5.2: Set the SAR antenna to operate in scanning mode, and use the center pointing angle of the target observation in azimuth agile observation mode as the fixed scanning angle of the radiation pattern; Module M5.3: Select and set the same operating bandwidth as in module M4.3; Module M5.4: When the satellite is powered on, the SAR subsystem starts working and records the transmitted test echo data.

Images