Sar multi-subarea imaging radio frequency simulation method and system based on coordinate system periodic reconstruction
The SAR multi-sub-region imaging RF simulation method based on coordinate system periodic reconstruction solves the problems of coordinate transformation error and large computational load in the SAR scene matching guidance RF simulation of aircraft, and achieves higher positioning accuracy and experimental efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BEIJING RESEARCH INSTITUTE OF MECHANICAL & ELECTRICAL TECHNOLOGY CO LTD CAM
- Filing Date
- 2023-03-08
- Publication Date
- 2026-07-03
AI Technical Summary
In the SAR scene matching guidance RF hardware-in-the-loop simulation of aircraft, traditional methods suffer from coordinate transformation errors, large computational load, and cumbersome processing, which affect positioning accuracy and test efficiency.
A SAR multi-sub-region imaging radio frequency simulation method based on coordinate system periodic reconstruction is adopted. The coordinate system is reconstructed, the ground center point of the radar beam is corrected, the sub-region is switched online and the scene transfer function is calculated through the SAR echo simulator, and the SAR echo is generated in real time, which simplifies the slant range calculation and beam illumination range processing.
It reduces the positional error introduced by the curvature of the Earth, improves the accuracy of radar beam slant range calculation and the consistency of simulation, simplifies the calculation process, and improves the accuracy and efficiency of simulation and experimentation.
Smart Images
Figure CN116224238B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of radio frequency simulation technology, and in particular to a radio frequency simulation method and system for SAR multi-sub-region imaging with coordinate system periodic reconstruction. Background Technology
[0002] Scene matching positioning technology is an important means to improve the homing accuracy of aircraft. Under satellite denial conditions, inertial navigation drift will cause the flight path to drift and the planned trajectory to be deviated. At this time, it is necessary to correct the aircraft's own position by using the ground point results after scene matching to obtain the accurate positioning of the trajectory and finally achieve accurate homing of the target.
[0003] The working principle of SAR scene matching guidance for aircraft is based on SAR imaging. According to multiple imaging matching points (called imaging sub-region centers) planned before flight, the airborne SAR is controlled to transmit broadband signals to the designated matching points during the imaging process to obtain high range resolution. The Doppler caused by the relative motion between the aircraft and the target in the azimuth direction achieves high azimuth resolution. After imaging processing, the SAR image of the sub-region is obtained and registered with the reference image. The slant range and Doppler information of the feature points are extracted to achieve auxiliary positioning correction and eliminate inertial navigation drift error caused by time.
[0004] In the SAR scene matching guidance RF hardware-in-the-loop simulation experiment of an aircraft, the traditional method requires pre-cropping, encoding, and parameter configuration of the reference map according to the planned matching points, and calculating the echoes of all sub-regions in a fixed coordinate system. This technology has two obvious drawbacks: First, the reference map is often in Gaussian plane coordinates and elevation information, while the aircraft position is in latitude, longitude, and altitude coordinates. For high-speed aircraft, the matching points are selected at large intervals. When calculating the slant distance between the aircraft and each sub-region in the same scene coordinate system, the curvature of the earth will introduce coordinate transformation errors, affecting the position of the sub-region center point on the reference map and the slant distance between the aircraft and the sub-region scattering point. Consequently, the beam illumination range deviates from the theory, and the SAR imaging center point shifts, thus increasing the matching and positioning error. Second, the simulator track configuration preparation workload is large, the calculation workload is large, and the usage method is fixed. The handling of switching between different sub-regions and beam illumination range calculation is relatively cumbersome. Therefore, how to achieve online automatic switching of sub-regions and accurate calculation of the slant distance between pixels within the radar beam illumination range and the aircraft in the SAR scene matching guidance radio frequency hardware-in-the-loop simulation test of aircraft is a key issue to improve the accuracy and test efficiency of the SAR scene matching guidance radio frequency hardware-in-the-loop simulation test of aircraft. Summary of the Invention
[0005] Based on the above analysis, this invention aims to disclose a coordinate system periodic reconstruction method and system for radio frequency simulation of SAR multi-sub-region imaging. It addresses the key issues of accuracy and experimental efficiency in the radio frequency hardware-in-the-loop simulation of SAR scene matching guidance for aircraft.
[0006] This invention discloses a radio frequency simulation method for SAR multi-sub-region imaging based on coordinate system periodic reconstruction, comprising the following steps:
[0007] The SAR echo simulator receives the aircraft's latitude, longitude, altitude, speed, and acceleration simulated by the simulator according to the communication cycle, as well as the center latitude, longitude, and altitude of the SAR imaged sub-area on the aircraft. It also receives the SAR's radio frequency excitation signal, clock signal, and radar pulse synchronization signal through the radio frequency cable, and receives the SAR's beam pointing angle sent by the bus fast-up device.
[0008] The SAR echo simulator simulates SAR echoes of a single sub-region by reconstructing the coordinate system, correcting the ground center point of the radar beam, switching the sub-region online, calculating the scene transfer function, generating SAR echoes and canceling the periodic coordinate system, and generating SAR echoes of a single sub-region in real time.
[0009] A single-sub-region SAR echo simulation method is adopted, and the SAR echo simulator generates SAR echoes of all sub-regions in real time during the simulation process.
[0010] Furthermore, the coordinate system reconstruction described in the SAR echo simulator for SAR echo simulation of a single sub-region includes:
[0011] When a radar pulse synchronization signal is detected and the coordinate reconstruction flag is invalid, coordinate reconstruction is performed to establish a periodic geographic coordinate system with the current imaging sub-region center as the origin and the three axes pointing north, sky, and east. The coordinate position of the aircraft in the periodic geographic coordinate system is calculated. The coordinate reconstruction flag is then set to valid. The coordinate reconstruction flag is set to invalid in the initial state and when the previously reconstructed coordinate system is canceled.
[0012] Furthermore, based on the latitude, longitude, and altitude coordinates of the aircraft The latitude, longitude, and altitude coordinates of the center of the sub-region The coordinates o of the aircraft in the periodic geographic coordinate system were calculated. t1 :
[0013]
[0014] in, (X,Y,Z) are the coordinates of the aircraft in the geocentric coordinate system;
[0015]
[0016] (X0, Y0, Z0) are the coordinates of the sub-region center point in the geocentric coordinate system:
[0017]
[0018] R eLet be the radius of the zonal circle, and e be the first eccentricity of the Earth.
[0019] Furthermore, the radar beam ground center point correction described in the SAR echo simulator for SAR echo simulation of a single sub-region includes:
[0020] 1) Calculate the beam center angle o based on the radar beam center elevation angle α1 and azimuth angle β1. m1 Coordinates in a periodic geographic coordinate system
[0021] 2) Based on the latitude and longitude of sub-region center o1 and the latitude and longitude of the scene center O The coordinates of the sub-region center o1 in the fixed Gaussian coordinate system OXZ are calculated as follows:
[0022] 3) Based on the coordinates of the sub-region center o1 in the fixed Gaussian coordinate system and the beam center o m1 The beam center o is obtained after the coordinates are corrected in the periodic geographic coordinate system. m1 Coordinates in a fixed Gaussian coordinate system
[0023] Furthermore, the beam center o m1 Coordinates in a periodic geographic coordinate system
[0024]
[0025] Where α1 is 0° in the horizontal direction and positive upwards, and β1 is 0° in the north direction and positive counterclockwise.
[0026] Beam center o m1 Coordinates in a fixed Gaussian coordinate system Approximate characterization is as follows:
[0027]
[0028] Furthermore, the online switching of sub-regions in the SAR echo simulator for SAR echo simulation of a single sub-region refers to switching the beam illumination area online based on the corrected ground center point of the radar beam to obtain the reference map data of the sub-region within the radar beam illumination range; specifically including:
[0029] 1) The SAR imaging echo simulator determines that the coordinate reconstruction flag is valid;
[0030] 2) Based on the Gaussian coordinates of the beam center Reference image resolution (δ) X ,δ Z Determine the radar beam center at the reference point. Figure 2 Index value of a dimensional matrix
[0031] 3) Based on the index value and the number of pixels in the sub-region, the reference map data within the radar beam illumination range is obtained in real time;
[0032] The reference map data includes the scattering coefficient, random phase, and position coordinates of each pixel in the beam-illuminated sub-region.
[0033] Furthermore, the scene transfer function calculation described in the SAR echo simulator for SAR echo simulation of a single sub-region includes:
[0034] 1) The simulator recursively calculates the aircraft's position according to the clock cycle to obtain the aircraft's position;
[0035] 2) Calculate the slant distance between the pixel and the aircraft pixel by pixel;
[0036] 3) Calculate the phase value introduced by the distance;
[0037] 4) Perform phase modulation and scattering coefficient amplitude weighting on each pixel;
[0038] 5) Coherently superimpose the pixels within the same distance gate to obtain the scene transfer function of that sub-region.
[0039] Furthermore, the slant range R between the k-th pixel and the aircraft k :
[0040]
[0041] t n The scene transfer function for this sub-region at time:
[0042]
[0043] M is the number of pixels falling within that distance gate, A k R k t k φ k Let T represent the amplitude, distance, delay, and random phase of the echo from the k-th pixel within the distance gate. s k is the sampling period of the system function; rw k is the pixel offset along the X-axis. cl H is the pixel offset along the Z-axis. k(cl,rw) Let λ be the coordinate of the k-th pixel on the Y-axis, and λ be the wavelength of the radar signal.
[0044] Furthermore, the SAR echo generation in the SAR echo simulator for SAR echo simulation of a single sub-region includes: generating the original time-domain baseband signal after down-conversion and AD transformation of the radar radio frequency excitation signal, performing FFT on the signal and the scene transfer function respectively, multiplying them in the frequency domain, and then performing IFFT to obtain the scene echo of each radar PRT signal.
[0045] The present invention also discloses a SAR multi-sub-region imaging radio frequency simulation system for coordinate system periodic reconstruction, including a simulator, SAR, bus fast-up device, SAR echo simulator, antenna array and feeding system;
[0046] The simulator performs real-time trajectory calculation and sends the aircraft's latitude, longitude, altitude, speed, acceleration, and the center latitude, longitude, and altitude of the sub-region to be imaged by the SAR on the aircraft to the SAR echo simulator according to the communication cycle.
[0047] The SAR injects radio frequency excitation signals, clock signals, and pulse synchronization signals into the SAR echo simulator through a radio frequency cable;
[0048] The bus fast-access device listens to communication data packets in real time and sends the SAR beam pointing angle to the SAR echo simulator.
[0049] The echo simulator generates simulated SAR echo signals by performing the SAR multi-sub-region imaging RF simulation method of coordinate system periodic reconstruction as described above. The SAR echo signals are radiated into a microwave anechoic chamber through an antenna array and a feeding system for SAR scene matching guidance RF hardware-in-the-loop simulation.
[0050] This invention can achieve one of the following beneficial effects:
[0051] The coordinate system periodic reconstruction SAR multi-sub-region imaging radio frequency simulation method and system disclosed in this invention reduces the relative position error introduced by the curvature of the earth when calculating the slant range in a fixed reference frame using traditional methods. This improves the accuracy of the slant range calculation between pixels within the radar beam illumination range and the aircraft, simplifies the process of calculating the SAR multi-sub-region illumination range and generating echo signals for the aircraft. Furthermore, during the radar beam illumination range calculation, the ground center point of the radar beam is calculated according to the actual radar position and the actual beam direction, ensuring consistency between the simulation and the real scene. This improves the accuracy and experimental efficiency of the SAR scene matching guidance radio frequency hardware-in-the-loop simulation for aircraft. Attached Figure Description
[0052] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.
[0053] Figure 1This is a flowchart of the SAR multi-sub-region imaging radio frequency simulation method in an embodiment of the present invention;
[0054] Figure 2 This is a flowchart of the SAR echo simulation method for a single sub-region in an embodiment of the present invention;
[0055] Figure 3 This is a coordinate system periodic reconstruction diagram of the SAR multi-sub-region imaging radio frequency simulation method for aircraft in this embodiment of the invention;
[0056] Figure 4 This is a schematic diagram of sub-region pixel slant distance calculation in an embodiment of the present invention;
[0057] Figure 5 This is a schematic block diagram showing the components and connections of the SAR multi-sub-region imaging radio frequency simulation system in an embodiment of the present invention. Detailed Implementation
[0058] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.
[0059] One embodiment of the present invention discloses a radio frequency simulation method for SAR multi-sub-region imaging based on coordinate system periodic reconstruction, such as... Figure 1 As shown, it includes the following steps:
[0060] Step S1: The SAR echo simulator receives the latitude, longitude, altitude, speed, and acceleration of the simulated aircraft, as well as the latitude, longitude, and altitude of the center of the SAR imaging sub-area on the aircraft, according to the communication cycle. It also receives the SAR's radio frequency excitation signal, clock signal, and radar pulse synchronization signal through the radio frequency cable, and receives the SAR's beam pointing angle sent by the bus fast-up device.
[0061] Step S2: The SAR echo simulator performs SAR echo simulation of a single sub-region through coordinate system reconstruction, radar beam ground center point correction, online sub-region switching, scene transfer function calculation, SAR echo generation, and periodic coordinate system cancellation, and generates SAR echo of a single sub-region in real time.
[0062] Step S3: Using the single-sub-region SAR echo simulation method in Step S2, the SAR echo simulator generates SAR echoes for all sub-regions in real time during the simulation process.
[0063] Specifically, the sub-region is the area where the imaging matching point is planned before flight; the simulator performs real-time calculations on the aircraft, sending the aircraft's latitude, longitude, altitude, velocity, acceleration, and the center latitude, longitude, and altitude of the sub-region to the imaging echo simulator at a 1ms communication cycle. The bus fast-access device monitors the SAR radar's communication data packets in real time and obtains the SAR beam pointing angle from the communication data packets.
[0064] like Figure 2 As shown, in step S2, the SAR echo simulation method for a single sub-region includes:
[0065] Step S201: Coordinate system reconstruction; Calculate the aircraft's position in the periodic geographic coordinate system by recreating the periodic geographic coordinate system.
[0066] The coordinate system reconstruction includes:
[0067] When the SAR echo simulator detects a radar pulse synchronization signal and the coordinate reconstruction flag is invalid, it performs coordinate reconstruction to establish a periodic geographic coordinate system with the current imaging sub-region center as the origin and the three axes pointing north, sky, and east; that is, the coordinate origin O1 is the current sub-region center, and the coordinate axes O1X... t Pointing north, coordinate axis O1Y t Pointing to the sky, coordinate axis O1Z t It can be determined using the right-hand rule;
[0068] like Figure 3 The image shown is a coordinate system periodic reconstruction diagram of the SAR multi-sub-region imaging RF simulation method for aircraft; O1 represents the actual flight position of the aircraft. t1 The coordinates of the current sub-region center are shown; the radar beam center elevation angle α and azimuth angle β are calculated by the aircraft's SAR based on the current inertial navigation sensing trajectory (with errors) and the current sub-region center. These are internal calculation results of the SAR and will not be explained in detail here. m1 The actual flight position of the aircraft is o t1 At that time, the coordinates of the radar beam ground illumination center are calculated based on the elevation angle and azimuth angle of the radar beam center.
[0069] Calculate the coordinate position of the aircraft in the periodic geographic coordinate system; set the coordinate reconstruction flag to active; the coordinate reconstruction flag is set to inactive in the initial state and when the previously reconstructed coordinate system is canceled.
[0070] More specifically, determining the coordinates of the spacecraft in the periodic geographic coordinate system. t1 hour,
[0071] Based on the latitude, longitude and altitude coordinates of the aircraft The latitude and longitude of the center of Hezi District The coordinates o of the aircraft in the periodic geographic coordinate system were calculated. t1 :
[0072]
[0073] in,
[0074] (X,Y,Z) are the coordinates of the aircraft in the geocentric coordinate system;
[0075]
[0076] (X0, Y0, Z0) are the coordinates of the sub-region center point in the geocentric coordinate system:
[0077]
[0078] R e Let be the radius of the zonal circle, and e be the first eccentricity of the Earth.
[0079] Step S202: Radar beam ground center point correction; The beam center point is corrected according to the radar beam center elevation angle and azimuth angle and the position of the aircraft to obtain the coordinates of the beam center in a fixed Gaussian coordinate system.
[0080] More specifically, the radar beam ground center point correction includes:
[0081] 1) Based on the elevation angle of the radar beam center α1 And the azimuth angle β1, the beam center o is calculated. m1 Coordinates in a periodic geographic coordinate system
[0082] Beam center o m1 Coordinates in a periodic geographic coordinate system
[0083]
[0084] Where α1 is 0° in the horizontal direction and positive upwards, and β1 is 0° in the north direction and positive counterclockwise.
[0085] 2) Based on the latitude and longitude of sub-region center o1 and the latitude and longitude of the scene center O The coordinates of the sub-region center o1 in the fixed Gaussian coordinate system OXZ are calculated as follows:
[0086] The coordinates of the sub-region center o1 in the fixed Gaussian coordinate system OXZ are as follows: When this is done, existing coordinate transformation methods can be used without affecting the scope of protection of this invention. The specific coordinate transformation methods will not be described in detail here.
[0087] 3) Based on the coordinates of the sub-region center o1 in the fixed Gaussian coordinate system and the beam center o m1 The beam center o is obtained after the coordinates are corrected in the periodic geographic coordinate system. m1 Coordinates in a fixed Gaussian coordinate system
[0088] Specifically, the beam center o m1Coordinates in a fixed Gaussian coordinate system It can be approximated as:
[0089]
[0090] Step S203: Online switching of sub-area; The beam illumination area is switched online according to the corrected ground center point of the radar beam to obtain the reference map data of the sub-area within the radar beam illumination range;
[0091] Specifically, the sub-area online handover process includes:
[0092] 1) The SAR imaging echo simulator baseband processing unit determines that the coordinate reconstruction flag is valid;
[0093] 2) Based on the Gaussian coordinates of the beam center Reference image resolution (δ) X ,δ Z Determine the index value of the radar beam center in the two-dimensional matrix of the reference map data.
[0094] 3) Based on the index value The reference map data within the radar beam illumination range is obtained in real time by combining the number of pixels in the sub-region;
[0095] The reference map data includes the scattering coefficient, random phase, and position coordinates of each pixel in the beam-illuminated sub-region.
[0096] Wherein, the scattering coefficient of the kth pixel is A k The amplitude of the echo corresponding to the k-th pixel; the coordinates of the k-th pixel are:
[0097] Among them, (k rw k cl ) represents the pixel offset of the k-th pixel relative to the beam center, k rw k is the pixel offset along the X-axis. cl H is the pixel offset along the Z-axis. k(cl,rw) Let be the coordinates of the k-th pixel on the Y-axis.
[0098] Step S204: Scene transfer function calculation; At the current PRT time, extract the reference map data and the aircraft position parameters, and calculate the sub-region scene transfer function;
[0099] Specifically, the scenario transfer function calculation process includes:
[0100] 1) The simulator recursively calculates the aircraft's position according to the clock cycle to obtain the aircraft's position;
[0101] The simulator recursively calculates the aircraft's position according to a clock cycle, using the following recursive formula:
[0102]
[0103] 2) Calculate the slant distance R between the pixel and the aircraft pixel by pixel. k and delay t k ;
[0104]
[0105] like Figure 4 The diagram shown illustrates the calculation of the slant distance of a sub-region pixel.
[0106] 3) Calculate the phase value introduced by the distance;
[0107] 4) Perform phase modulation and scattering coefficient amplitude weighting on each pixel;
[0108] 5) Coherently superimpose the pixels within the same distance gate to obtain the scene transfer function of that sub-region.
[0109] Specifically, t n The scene transfer function for this sub-region at time:
[0110]
[0111] M is the number of pixels falling within that distance gate, A k R k t k φ k Let T represent the amplitude, distance, delay, and random phase of the echo from the k-th pixel within the distance gate. s θ is the sampling period of the system function; θ is the wavelength of the radar signal.
[0112] Step S205: SAR echo generation; Based on the original radar time-domain baseband signal and the sub-region scene transfer function, time-frequency domain transformation is performed to obtain the scene echo of each radar PRT signal;
[0113] Specifically, the radar RF excitation signal is down-converted and AD-converted to generate the original time-domain baseband signal. This signal and the scene transfer function are then subjected to FFT, multiplied in the frequency domain, and then subjected to IFFT to obtain the scene echo of each radar PRT signal.
[0114] Step S206: Periodic coordinate system cancellation; when the radar pulse synchronization signal is detected to disappear, the imaging process ends, the coordinate reconstruction flag is set to invalid, and the periodic coordinate system is cancelled.
[0115] In step S3, steps S201-S206 are repeated to complete the real-time generation of SAR echoes for all sub-regions.
[0116] Another embodiment of the present invention discloses a SAR multi-sub-region imaging radio frequency simulation system with coordinate system periodic reconstruction, such as Figure 5 As shown, it includes a simulator, SAR, bus fast transfer device and SAR echo simulator;
[0117] The simulator performs real-time trajectory calculations and sends the aircraft's latitude, longitude, altitude, speed, acceleration, sub-region center latitude, longitude, altitude, and sub-region number to the SAR echo simulator according to the communication cycle.
[0118] The SAR injects radio frequency excitation signals, clock signals, and pulse synchronization signals into the SAR echo simulator through a radio frequency cable;
[0119] The bus fast-access device listens to communication data packets in real time and sends the SAR beam pointing angle to the SAR echo simulator.
[0120] The echo simulator generates simulated SAR echo signals by performing the SAR multi-sub-region imaging RF simulation method for coordinate system periodic reconstruction as described in the previous embodiment. The SAR echo signals are radiated into a microwave anechoic chamber through an antenna array and a feeding system for SAR scene matching guidance RF hardware-in-the-loop simulation.
[0121] In summary, the coordinate system periodic reconstruction SAR multi-sub-region imaging radio frequency simulation method and system disclosed in this invention reduces the relative position error introduced by the curvature of the earth when performing slant range calculation in a fixed reference frame using traditional methods. This greatly simplifies the process of calculating the SAR multi-sub-region illumination range and generating echo signals for aircraft. At the same time, during the calculation of the radar beam illumination range, the ground center point of the radar beam is calculated according to the actual radar position and the actual beam direction, ensuring the consistency between the simulation and the real scene, and improving the accuracy and experimental efficiency of the aircraft SAR scene matching guidance radio frequency hardware-in-the-loop simulation.
[0122] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.
Claims
1. A radio frequency simulation method for SAR multi-sub-region imaging based on coordinate system periodic reconstruction, characterized in that, Includes the following steps: The SAR echo simulator receives the aircraft's latitude, longitude, altitude, speed, and acceleration simulated by the simulator according to the communication cycle, as well as the center latitude, longitude, and altitude of the SAR imaged sub-area on the aircraft. It also receives the SAR's radio frequency excitation signal, clock signal, and radar pulse synchronization signal through the radio frequency cable, and receives the SAR's beam pointing angle sent by the bus fast-up device. The SAR echo simulator simulates SAR echoes of a single sub-region by reconstructing the coordinate system, correcting the ground center point of the radar beam, switching the sub-region online, calculating the scene transfer function, generating SAR echoes and canceling the periodic coordinate system, and generating SAR echoes of a single sub-region in real time. A single-sub-region SAR echo simulation method is adopted, and the SAR echo simulator generates SAR echoes of all sub-regions in real time during the simulation process; The coordinate system reconstruction described in the SAR echo simulator for a single sub-region SAR echo simulation includes: When a radar pulse synchronization signal is detected and the coordinate reconstruction flag is invalid, coordinate reconstruction is performed to establish a periodic geographic coordinate system with the current imaging sub-region center as the origin and the three axes pointing north, sky, and east. The coordinate position of the aircraft in the periodic geographic coordinate system is calculated. The coordinate reconstruction flag is then set to valid. The coordinate reconstruction flag is set to invalid in the initial state and when the previously reconstructed coordinate system is canceled. Based on the latitude, longitude and altitude coordinates of the aircraft The latitude, longitude, and altitude coordinates of the center of the sub-region The coordinates of the aircraft in the periodic geographic coordinate system were calculated. : ； in, ; ; These are the coordinates of the spacecraft in the geocentric coordinate system. ； The coordinates of the sub-region's center point in the geocentric coordinate system are: ； The radius of the circle is the area between the east and west. e This is the Earth's first eccentricity.
2. The SAR multi-sub-region imaging radio frequency simulation method according to claim 1, characterized in that, The ground center point correction of the radar beam described in the SAR echo simulator for a single sub-region includes: 1) Based on the elevation angle of the radar beam center and azimuth The beam center was calculated. Coordinates in a periodic geographic coordinate system ; 2) Based on the sub-region center latitude and longitude and scene center O latitude and longitude The center of the sub-region is calculated. In a fixed Gaussian coordinate system The coordinates are ; 3) Based on the sub-region center With fixed Gaussian coordinate system coordinates and beam center The beam center after the coordinates in the periodic geographic coordinate system are corrected. Coordinates in a fixed Gaussian coordinate system .
3. The SAR multi-sub-region imaging radio frequency simulation method according to claim 2, characterized in that, Beam center Coordinates in a periodic geographic coordinate system ; ； in, The horizontal direction is 0°, and upward is positive. North is 0°, and counterclockwise is positive. Beam center Coordinates in a fixed Gaussian coordinate system Approximate characterization is as follows: 。 4. The SAR multi-sub-region imaging radio frequency simulation method according to claim 2, characterized in that, The online switching of sub-regions in the SAR echo simulator for SAR echo simulation of a single sub-region refers to switching the beam illumination area online based on the corrected ground center point of the radar beam to obtain the reference map data of the sub-region within the radar beam illumination range; specifically including: 1) The SAR imaging echo simulator determines that the coordinate reconstruction flag is valid; 2) Based on the Gaussian coordinates of the beam center Reference image resolution Determine the index value of the radar beam center in the reference map two-dimensional matrix. ; 3) Based on the index value and the number of pixels in the sub-region, the reference map data within the radar beam illumination range is obtained in real time; The reference map data includes the scattering coefficient, random phase, and position coordinates of each pixel in the beam-illuminated sub-region.
5. The SAR multi-sub-region imaging radio frequency simulation method according to claim 4, characterized in that, The scenario transfer function calculations described in the SAR echo simulator for SAR echo simulation of a single sub-region include: 1) The simulator recursively calculates the aircraft's position according to the clock cycle to obtain the aircraft's position; 2) Calculate the slant distance between the pixel and the aircraft pixel by pixel; 3) Calculate the phase value introduced by the distance; 4) Perform phase modulation and scattering coefficient amplitude weighting on each pixel; 5) Coherently superimpose the pixels within the same distance gate to obtain the scene transfer function of that sub-region.
6. The SAR multi-sub-region imaging radio frequency simulation method according to claim 5, characterized in that, The slant distance between the kth pixel and the aircraft : ； The scene transfer function for this sub-region at time: ； M The number of pixels falling into the gate at that distance. A k , R k , t k and These represent the distances within the gate, respectively. k The amplitude, distance, delay, and random phase of the echo of each pixel. T s The sampling period of the system function; This represents the pixel offset along the X-axis. This represents the pixel offset along the Z-axis. For the first k The coordinates of each pixel on the Y-axis The wavelength of the radar signal.
7. The SAR multi-sub-region imaging radio frequency simulation method according to claim 1, characterized in that, The SAR echo generation described in the SAR echo simulator for SAR echo simulation of a single sub-region includes: generating the original time-domain baseband signal after down-conversion and AD transformation of the radar radio frequency excitation signal, performing FFT on the signal and the scene transfer function respectively, multiplying them in the frequency domain, and then performing IFFT to obtain the scene echo of each radar PRT signal.
8. A SAR multi-sub-region imaging radio frequency simulation system for coordinate system periodic reconstruction, characterized in that, This includes simulators, SAR, bus fast transfer devices, SAR echo simulators, and antenna arrays and feeding systems; The simulator performs real-time trajectory calculation and sends the aircraft's latitude, longitude, altitude, speed, acceleration, and the center latitude, longitude, and altitude of the sub-region to be imaged by the SAR on the aircraft to the SAR echo simulator according to the communication cycle. The SAR injects radio frequency excitation signals, clock signals, and pulse synchronization signals into the SAR echo simulator through a radio frequency cable; The bus fast-access device listens to communication data packets in real time and sends the SAR beam pointing angle to the SAR echo simulator. The echo simulator generates simulated SAR echo signals by performing the SAR multi-sub-region imaging radio frequency simulation method of coordinate system periodic reconstruction as described in any one of claims 1-7. The SAR echo signals are radiated into a microwave anechoic chamber through an antenna array and a feeding system for SAR scene matching guidance radio frequency hardware-in-the-loop simulation.