Satellite-borne interference SAR echo simulator and echo simulation method

Abstract

The invention discloses a spaceborne interference SAR echo simulator and an echo simulation method, and relates to the technical field of spaceborne interference SAR. The simulator comprises a radio frequency transceiver module, an intermediate frequency modulation module, an echo calculation module and a main control device. The radio frequency transceiver module realizes bidirectional frequency conversion and clock distribution of radio frequency and intermediate frequency signals; the intermediate frequency modulation module completes conversion and synchronous control of intermediate frequency and baseband signals; the echo calculation module adopts a CPU + GPU + FPGA architecture to efficiently generate scene echo data; the main control equipment realizes test case configuration, module control and state monitoring; the simulation method comprises the steps of constructing a space geometric model to calculate a phase difference, establishing a point target echo model, generating scene echo data, and performing intermediate frequency modulation and radio frequency conversion to form a signal closed loop. According to the invention, full-link closed-loop simulation is realized, the echo simulation precision and real-time performance are improved, multi-scene dynamic configuration is supported, and efficient test support is provided for satellite-borne InSAR load research and development.

Description

Technical Field

[0001] The present invention relates to the technical field of spaceborne interferometric synthetic aperture radar (SAR), and in particular to a spaceborne interferometric SAR (Synthetic Aperture Radar) echo simulator and an echo simulation method. Background Art

[0002] As an advanced remote sensing technology capable of acquiring three-dimensional surface information and monitoring deformation, spaceborne interferometric synthetic aperture radar (InSAR) plays an irreplaceable role in geological mapping, disaster monitoring, resource exploration, and other fields. With the development of satellite remote sensing technology, InSAR systems have placed higher demands on the simulation accuracy, real-time performance, and scene adaptability of echo signals. During the development and testing phase of spaceborne InSAR payloads, echo simulators are required to generate echo signals close to real scenes in order to verify the payload's imaging performance, interferometric processing accuracy, and system stability. However, actual satellite in-orbit testing is costly and time-consuming, and it is difficult to reproduce extreme operating conditions in complex scenarios. Therefore, the development of a high-performance spaceborne interferometric SAR echo simulator has become a key technical support for ensuring the efficiency of InSAR payload research and development.

[0003] Traditional SAR echo simulation technologies are mainly divided into two categories: point target simulation and simplified scene simulation. Point target simulation uses mathematical models to calculate the echo signals of single or multiple discrete targets. The method is simple and has low computational complexity, but it cannot reflect the continuous distribution characteristics of natural scenes, making it difficult to verify the imaging capabilities of the InSAR system for complex terrain. Simplified scene simulation generates uniform or piecewise uniform scene echoes based on empirical models. Although it can partially simulate natural scenes, it ignores the spatial heterogeneity and randomness of the surface scattering characteristics, resulting in insufficient authenticity of the echo signal. In addition, traditional simulators mostly use fixed parameter configurations and cannot flexibly adjust satellite orbit parameters, beam pointing, and target scattering characteristics. It is difficult to meet the needs of different test cases and has significant limitations.

[0004] In existing technologies, some SAR echo simulators attempt to improve simulation results by increasing hardware computing power or optimizing algorithms. For example, simulators based on general-purpose computers (CPUs) implement echo calculations through software programming. However, due to limitations in serial processing capabilities, they suffer from poor real-time performance when simulating large scenes and high resolutions. Application-specific integrated circuit (ASIC)-based simulators, while capable of high-speed computing, suffer from a fixed hardware structure that prevents flexible adaptation to parameter changes in different InSAR systems, resulting in limited scalability. Furthermore, existing simulators exhibit low simulation accuracy for interferometric phase differences and often ignore the effects of factors such as antenna baseline error and orbital offset. This results in significant deviations between the generated interferograms and the real scene, making it difficult to effectively verify the interferometric processing performance of InSAR systems. Summary of the Invention

[0005] Based on the above technical problems, the present application discloses a spaceborne interferometric SAR echo simulator and an echo simulation method, wherein a spaceborne interferometric SAR echo simulator specifically includes a radio frequency transceiver module, an intermediate frequency modulation module, an echo calculation module and a main control device; The RF transceiver module is connected to the SAR payload under test and the intermediate frequency modulation module respectively, and is used to receive the RF transmission signal of the SAR payload under test and transmit it to the intermediate frequency modulation module after down-conversion, receive the intermediate frequency echo signal of the intermediate frequency modulation module and transmit it to the SAR payload under test after up-conversion, and receive the synchronization clock of the SAR payload under test and distribute it to the intermediate frequency modulation module; The intermediate frequency modulation module is connected to the radio frequency transceiver module and the echo calculation module respectively, and is used to collect and process the intermediate frequency signal transmitted by the radio frequency transceiver module and send it to the echo calculation module, receive the baseband echo signal from the echo calculation module and process it into an intermediate frequency echo signal before transmitting it to the radio frequency transceiver module, and receive the PRT trigger signal of the test SAR payload and distribute it to the echo calculation module and itself; The echo calculation module is connected to the intermediate frequency modulation module and the main control device respectively, and is used to read the pre-stored baseband echo data and send it to the intermediate frequency modulation module in the echo playback mode to realize the delay processing of the baseband echo signal; The main control device is connected to the radio frequency transceiver module, the intermediate frequency modulation module, and the echo calculation module respectively, and is used to edit and configure test cases, control the operation of each module, monitor module status, and record operation logs.

[0006] Preferably, the radio frequency transceiver module includes a down-conversion unit, an up-conversion unit, a clock module and an antenna; The down-conversion unit is used to convert the RF input signal into an intermediate frequency output signal, and its RF input power range is selectable in multiple gears, the gain control range is selectable in multiple gears, the attenuation step is selectable in multiple gears, and the attenuation accuracy is selectable in multiple gears; The up-conversion unit includes two intermediate frequency input channels and two radio frequency output channels, which are used to convert the intermediate frequency input signal into a radio frequency output signal. The radio frequency output power range is multi-level optional, the output step is multi-level optional, and the attenuation accuracy is multi-level optional; The clock module receives an external reference clock and outputs multiple clocks, wherein the clock accuracy is selectable in multiple gears; The antennas are two linearly polarized antennas, the operating frequency is a specific band, the bandwidth is selectable in multiple gears, and the gain is selectable in multiple gears.

[0007] Preferably, the structure of the down-conversion unit includes a limiter, a first switch, a switch filter group, a bandpass filter, a mixer, a first amplifier, a digitally controlled attenuator, a low-pass filter and a second amplifier connected in sequence; The limiter input terminal is connected to an external radio frequency signal for limiting the input signal power; The first switch is a single-pole double-throw switch, one end of which is connected to the limiter output end, and the other end is selectively connected to the calibration input signal to achieve signal switching; The switch filter bank includes multiple filters with different bandwidths and corresponding amplifiers, and realizes the selection of different signal paths through switch switching; The mixer input end is connected to the bandpass filter output end and the specific frequency local oscillator signal respectively to down-convert the radio frequency signal into an intermediate frequency signal; The digitally controlled attenuator uses a specific type of chip to adjust the signal amplitude by controlling the attenuation; The low-pass filter is used to filter out high-frequency noise in the intermediate frequency signal, and the output end is connected to the intermediate frequency modulation module through the second amplifier.

[0008] Preferably, the up-conversion unit includes two channels with the same structure, and each channel is provided with a temperature-compensated attenuator, a third amplifier, a second digitally controlled attenuator, a mixer, a band-pass filter, a third digitally controlled attenuator and a second switch in sequence; The input end of the temperature compensation attenuator is connected to the intermediate frequency signal output by the intermediate frequency modulation module to compensate for the influence of temperature change on the signal amplitude; The mixer input terminal is connected to the output terminal of the third amplifier and the local oscillator signal of a specific frequency respectively, so as to up-convert the intermediate frequency signal into a radio frequency signal; The bandpass filter is used to filter out spurious components in the radio frequency signal; The second digitally controlled attenuator and the third digitally controlled attenuator are arranged in series to achieve wide range amplitude adjustment through multi-stage attenuation; The second switch is a single-pole single-throw switch that controls the output on and off of the radio frequency signal. The output ends of the two channels are connected to the antenna and the calibration interface respectively.

[0009] Preferably, the intermediate frequency modulation module includes an acquisition module, a playback module, an interface module, a time-frequency module and a PCIE interface module; The acquisition module performs ADC acquisition and digital down-conversion on the intermediate frequency transmission signal transmitted by the RF transceiver module to obtain a baseband transmission signal and send it to the echo calculation module through the optical fiber; The playback module receives the baseband echo signal from the echo calculation module, generates an intermediate frequency echo signal after delay modulation, digital up-conversion and DAC playback, and transmits it to the RF transceiver module; The interface module receives external PRT pulses as synchronization reference and outputs PRT pulses and echo envelope signals; The time-frequency module receives the 100MHz reference clock of the radio frequency transceiver module and distributes it to each internal unit after phase locking; The PCIE interface module realizes high-speed data communication with the echo calculation module.

[0010] Preferably, the echo calculation module adopts a CPU+GPU+FPGA architecture, including an interface unit, a GPU processing module and an ARM processing module; The interface unit receives the baseband transmission signal of the intermediate frequency modulation module through the optical fiber, checks and caches the data and transmits it to the ARM processing module, and at the same time receives the baseband echo signal of the ARM processing module and sends it to the intermediate frequency modulation module after processing; The GPU processing module calculates the impulse response sequence of the scene using a one-dimensional frequency domain algorithm, and convolves the baseband transmission signal with the impulse response sequence to generate echo data; The ARM processing module calculates the scene area illuminated by the satellite antenna beam, extracts the baseband transmission signal and sends it to the GPU processing module, and simultaneously reads the locally stored scene file and PVT table data.

[0011] Preferably, the main control device includes a use case editing and configuration module, a process control module, an interface display module and a communication module; The test case editing and configuration module is used to set overall parameters, scenario parameters, test device parameters, SAR parameters and wave position parameters, and supports the creation, opening, saving and association of test cases with instruction packages; The process control module realizes the operation control such as extension connection, system self-check, mode selection, initialization, start and stop; The interface display module displays test case information, extension status, system operation parameters and software operation messages; The communication module communicates with the echo calculation module through a network interface, and communicates with the radio frequency transceiver module and the intermediate frequency modulation module through a serial port.

[0012] A spaceborne interferometric SAR echo simulation method specifically includes: S1. Construct an interferometric SAR spatial geometric model to determine the geometric relationship between the radar antenna and the ground target, and calculate the echo phase difference based on the slant range difference between the target and the two antennas; S2. Establish a point target echo signal model and derive the mathematical expression of the baseband echo signal based on the radar platform motion parameters, transmission signal parameters and target slant range; S3. Generate scene echo data through the echo calculation module. The range-time superposition method is used for point target scenes, and the one-dimensional Fourier transform method is used for natural scenes to improve calculation efficiency. S4, the intermediate frequency modulation module performs delay modulation, digital up-conversion and digital-to-analog conversion on the baseband echo signal output by the echo calculation module to generate an intermediate frequency echo signal; S5. The RF transceiver module up-converts the intermediate frequency echo signal to the RF frequency band and sends it to the SAR payload under test. At the same time, it receives the transmission signal of the SAR payload under test and down-converts it to form a signal closed loop.

[0013] Preferably, the generating of the point target scene echo in S3 specifically includes: S301, determining the position and velocity information of the satellite according to the satellite orbit parameters and attitude file; S302, based on the satellite position and velocity, calculate the point target area illuminated by the satellite antenna beam at each PRT moment; S303, determining the scattering coefficient of each point target based on the scattering characteristics and position information of the point target; S304 , using a range-time domain superposition method, superimpose the echo signal of each point target in the range-time domain to generate baseband echo data of the point target scene.

[0014] Preferably, the natural scene echo generation in S3 specifically includes: S311. Calculate the scene area illuminated by the satellite antenna beam at each PRT time based on the satellite orbit parameters and attitude file; S312, performing grid processing on the target scattering coefficient in the scene area to generate point array scene data; S313, using the GPU to parallelly calculate the impulse response sequence of each point target, and obtain the overall impulse response function of the scene by superposition; S314 : Convolve the baseband transmit signal with the scene impulse response function to generate baseband echo data of the natural scene.

[0015] Compared with the prior art, the technical solution of this application has the following technical effects: The spaceborne interferometric SAR echo simulator of the present invention realizes a full-link closed-loop simulation from RF signal down-conversion, IF signal acquisition and processing to baseband echo signal generation through the coordinated work of the RF transceiver module, IF modulation module, echo calculation module and main control equipment. It ensures seamless transmission of signals between modules and can truly reproduce the complete signal flow of the InSAR system from transmission to reception. It provides a test environment close to the real scene for the tested SAR payload, and effectively verifies the payload's imaging performance and system stability.

[0016] This invention utilizes a heterogeneous computing architecture combining CPU, GPU, and FPGA, significantly improving echo data processing efficiency. The GPU's parallel computing capabilities significantly accelerate echo generation in large-scale scenarios, while the FPGA's high-speed data transmission ensures real-time acquisition and distribution of baseband signals. This architectural optimization not only meets the real-time computing requirements of complex scenarios but also provides powerful computing power for dynamic configuration of different orbital parameters and scenario types, enhancing the system's adaptability and scalability.

[0017] The IF modulation module of this invention utilizes high-precision ADC / DAC conversion and digital signal processing technologies to achieve precise delay modulation and up-conversion of baseband echo signals. This effectively improves the spectral purity and phase consistency of the IF echo signals, reduces signal distortion and spurious interference, and ensures high analog signal fidelity. Furthermore, the module's multi-channel design supports simultaneous processing of multiple echo signals, providing flexible configuration options for testing multi-channel InSAR systems.

[0018] The master control device of the present invention implements centralized control and parameter configuration of each hardware module through a unified software interface, greatly simplifying the system's operational process. Users can use the master control interface to monitor the operating status of each module in real time, dynamically adjust test parameters, and record and analyze test data. This design not only improves the system's usability and maintainability, but also facilitates test result traceability and data analysis, significantly enhancing testing efficiency and reliability.

[0019] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application so that it can be implemented in accordance with the contents of the specification, and to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following is a detailed description of the preferred embodiment of the present application in conjunction with the accompanying drawings.

[0020] Based on the detailed description of the specific embodiments of the present application in conjunction with the accompanying drawings below, those skilled in the art will become more aware of the above and other objects, advantages and features of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without inventive work. In all drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0022] According to the description of the drawings in the document and the corresponding technical content, the titles of the drawings are as follows: Figure 1 This is a schematic diagram of the overall structure of the spaceborne interferometric SAR echo simulator; Figure 2 This is a schematic diagram of the structure of a multi-channel SAR echo simulator; Figure 3 This is a structural diagram of the RF transceiver module of the SAR echo simulator; Figure 4 It is a schematic diagram of the down-conversion unit flow of the RF transceiver module structure; Figure 5 It is a schematic diagram of the up-conversion unit flow of the RF transceiver module structure; Figure 6 This is a schematic diagram of the intermediate frequency modulation module structure of the SAR echo simulator; Figure 7 This is a schematic diagram of the echo calculation module structure of the SAR echo simulator; Figure 8 This is a schematic diagram of the main control device structure of the SAR echo simulator; Figure 9 This is a flow chart of a spaceborne interferometric SAR echo simulation method; Figure 10 Schematic diagram of dual antennas and ground targets for spaceborne interferometric SAR echo simulation; Figure 11 Schematic diagram of the point target scenario echo generation process for the simulation method; Figure 12 Schematic diagram of the natural scene echo generation process for the simulation method. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. In the following description, specific details such as specific configurations and components are provided only to help fully understand the embodiments of the present application. Therefore, it should be clear to those skilled in the art that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present application. In addition, for clarity and brevity, the description of known functions and structures has been omitted in the embodiments.

[0024] It should be understood that references throughout this specification to "one embodiment" or "this embodiment" mean that a particular feature, structure, or characteristic associated with the embodiment is included in at least one embodiment of the present application. Therefore, the appearance of "one embodiment" or "this embodiment" throughout this specification does not necessarily refer to the same embodiment. Furthermore, these particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0025] In addition, the present application may repeat reference numerals and / or letters in different examples. This repetition is for the purpose of simplicity and clarity and does not in itself indicate the relationship between the various embodiments and / or settings discussed.

[0026] The term "and / or" in this article is only a description of the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist at the same time. The term " / and" in this article describes another type of association object relationship, indicating that two relationships can exist. For example, A / and B can mean: A exists alone, and A and B exist alone. In addition, the character " / " in this article generally indicates that the previous and subsequent associated objects are in an "or" relationship.

[0027] The term "at least one" in this article is merely a description of the association relationship between associated objects, indicating that three relationships may exist. For example, at least one of A and B can mean: A exists alone, A and B exist at the same time, and B exists alone.

[0028] It should also be noted that, in this document, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include," "comprises," or any other variations thereof are intended to cover non-exclusive inclusion.

[0029] Example 1 This embodiment mainly describes a spaceborne interferometric SAR echo simulator, such as Figure 1 As shown in Figure 1, the multi-channel SAR echo simulator mainly consists of a signal transceiver chassis, a main control laptop, a network switch and a cabinet; Figure 2 As shown, the signal transceiver chassis includes a radio frequency transceiver module, an intermediate frequency modulation module, an echo calculation module and a main control device; The RF transceiver module is connected to the SAR payload under test and the intermediate frequency modulation module respectively, and is used to receive the RF transmission signal of the SAR payload under test and transmit it to the intermediate frequency modulation module after down-conversion, receive the intermediate frequency echo signal of the intermediate frequency modulation module and transmit it to the SAR payload under test after up-conversion, and receive the synchronization clock of the SAR payload under test and distribute it to the intermediate frequency modulation module; The intermediate frequency modulation module is connected to the radio frequency transceiver module and the echo calculation module respectively, and is used to collect and process the intermediate frequency signal transmitted by the radio frequency transceiver module and send it to the echo calculation module, receive the baseband echo signal from the echo calculation module and process it into an intermediate frequency echo signal before transmitting it to the radio frequency transceiver module, and receive the PRT trigger signal of the test SAR payload and distribute it to the echo calculation module and itself; The echo calculation module is connected to the intermediate frequency modulation module and the main control device respectively, and is used to read the pre-stored baseband echo data and send it to the intermediate frequency modulation module in the echo playback mode to realize the delay processing of the baseband echo signal; The main control device is connected to the radio frequency transceiver module, the intermediate frequency modulation module, and the echo calculation module respectively, and is used to edit and configure test cases, control the operation of each module, monitor module status, and record operation logs.

[0030] like Figure 3 As shown in the figure, the RF transceiver module is the core unit of signal conversion, which includes a down-conversion unit, an up-conversion unit, a clock module and an antenna, realizing bidirectional conversion of RF and IF signals and clock synchronization; like Figure 4 As shown in the figure, the down-conversion unit can process RF input signals in a specific band (such as X-band 9.6±0.3GHz) and convert them into IF signals of 1.0±0.3GHz. The RF input power range covers 50~+10dBm. The gain adjustment of 10~+50dB is achieved through the digitally controlled attenuator, with an attenuation step of 0.5dB and an accuracy of ±0.5dB, ensuring stable conversion of signals within a wide dynamic range.

[0031] like Figure 5 As shown, the up-conversion unit contains two independent channels, which can reverse-convert the 1.0±0.3GHz intermediate frequency signal into a 9.6±0.3GHz radio frequency signal. The output power range is 60~0dBm, the amplitude consistency between channels is ≤1dB, and the phase consistency is ≤10°, meeting the strict requirements of interferometric SAR for dual-channel signal consistency.

[0032] The clock module receives a 100MHz or 10MHz external reference clock and outputs four 100MHz and one 10MHz clocks with an accuracy of ±0.1ppm, providing a high-precision time and frequency reference for the entire system.

[0033] The antenna uses two X-band linearly polarized antennas with a bandwidth of ≥600MHz and a gain of ≥2dBi to ensure efficient transmission and reception of RF signals.

[0034] Further, if Figure 6As shown in the figure, the intermediate frequency modulation module is responsible for the digital processing of the signal, including the acquisition module, the playback module, the interface module, the time-frequency module and the PCIE interface module, realizing the conversion between the intermediate frequency signal and the baseband signal and the high-speed data transmission.

[0035] The acquisition module collects the intermediate frequency signal through a 10-bit or higher ADC (the sampling rate is adapted to a maximum bandwidth of 600MHz), obtains the baseband transmission signal through digital down-conversion, and transmits it to the echo calculation module via optical fiber at a rate of ≥1GB / s.

[0036] After receiving the baseband echo signal, the playback module generates an intermediate frequency echo signal through delay modulation (delay adjustment accuracy reaches 0.5us), digital up-conversion and DAC conversion. The output power is 14±1dBm, the in-band flatness is ±0.5dB, and the spurious signal is ≤50dBc, ensuring signal fidelity.

[0037] The interface module receives the PRT trigger signal (pulse repetition period) of the SAR payload under test as the synchronization reference for the entire system, and simultaneously outputs the synchronization pulse and echo envelope signal to control the timing of the RF transceiver module.

[0038] The time-frequency module phase-locks the 100MHz reference clock and distributes it to each internal unit to ensure the synchronization of the ADC / DAC and baseband processing clocks.

[0039] Further, if Figure 7 As shown in the figure, the echo calculation module adopts a CPU+GPU+FPGA heterogeneous architecture to achieve efficient generation and processing of scene echoes. The interface unit receives the baseband transmission signal through optical fiber, and transmits it to the ARM processing module after verification and buffering. The GPU processing module uses a one-dimensional frequency domain algorithm to parallelly calculate the scene impulse response sequence, and convolve it with the baseband signal to generate echo data, supporting real-time calculation of millions of point targets per second. The ARM processing module accurately calculates the beam illumination area at each PRT moment based on the satellite orbit parameters (PVT table) and attitude file, extracts the scene scattering coefficient and drives GPU calculation.

[0040] Further, if Figure 8 As shown in the figure, the main control device realizes full system management and control through a unified interface. The use case editing module supports configuration of scenario parameters (such as mountainous areas and flat areas), SAR modes (strip and beamforming), and can save and call test cases. The process control module realizes operations such as extension connection, self-test, start / stop, communicates with the echo calculation module through the network, and controls the RF / IF module through the serial port. The interface displays the status of each module (such as PRT count and signal power) and operation log in real time to ensure the traceability of the test process.

[0041] This implementation describes in detail how a spaceborne interferometric SAR echo simulator builds a full-link closed-loop simulation system through the collaboration of RF transmission and reception, intermediate frequency modulation, echo calculation, and main control equipment. The system can realistically reproduce the complete signal transmission and reception process. The multi-module collaborative design improves the authenticity and flexibility of the echo simulation, can adapt to different scenarios and parameter configurations, and provide a near-realistic test environment for the test SAR payload, effectively verifying the payload performance and facilitating the development of spaceborne interferometric SAR technology.

[0042] Example 2 This embodiment describes in detail a method for simulating spaceborne interferometric SAR echoes. Figure 9 As shown, specifically including: S1. Construct an interferometric SAR spatial geometric model to determine the geometric relationship between the radar antenna and the ground target, and calculate the echo phase difference based on the slant range difference between the target and the two antennas; S2. Establish a point target echo signal model and derive the mathematical expression of the baseband echo signal based on the radar platform motion parameters, transmission signal parameters and target slant range; S3. Generate scene echo data through the echo calculation module. The range-time superposition method is used for point target scenes, and the one-dimensional Fourier transform method is used for natural scenes to improve calculation efficiency. S4, the intermediate frequency modulation module performs delay modulation, digital up-conversion and digital-to-analog conversion on the baseband echo signal output by the echo calculation module to generate an intermediate frequency echo signal; S5. The RF transceiver module up-converts the intermediate frequency echo signal to the RF frequency band and sends it to the SAR payload under test. At the same time, it receives the transmission signal of the SAR payload under test and down-converts it to form a signal closed loop.

[0043] Furthermore, the interferometric SAR spatial geometric model and phase difference calculation are built in S1, by clarifying the three-dimensional spatial relationship between the dual antennas and the ground target, such as Figure 10 As shown, the system consists of two antennas (transmitter and receiver), flying at a constant speed v along the azimuth direction, and the altitudes are and . Assume that the geographic coordinates of a ground point target P are , the positions of the antennas at zero Doppler time are and , then the slant distance between the target and the two antennas can be calculated using the spatial distance formula: Slant range from target to antenna 1: ; Slant range from target to antenna 2: ; Based on the "stop-and-go" assumption of spaceborne SAR (the antenna stops and waits for the echo after transmitting the pulse), the variation of slant range with azimuth time t can be expressed as: ,in, 、 is the slant range at zero Doppler, 、 For the corresponding time.

[0044] The echo phase difference is caused by the slant range difference. According to the propagation characteristics of electromagnetic waves, the phase difference Slope range difference The relationship is: ( is the radar wavelength), through geometric derivation, the slant range difference can be approximated as , where B is the baseline length of the two antennas, is the angle between the baseline and the target line of sight. Substituting into the phase difference formula, we get: ,The model accurately calculates the echo phase difference through baseline ,parameters and target orientation information, laying the foundation for interferogram ,generation, and can be extended to the phase superposition calculation of ,distributed target scenarios.

[0045] Furthermore, S2 describes in detail the establishment of the point target echo signal model and mathematical expression. Specifically, when establishing the point target echo signal model, the mathematical expression of the baseband echo is derived based on the radar platform motion characteristics and the transmission signal parameters, combined with the target slant range change. Assume that the radar moves in the azimuth direction with a speed of Flying at a constant speed, emitting linear frequency modulation signals, the slant range of point targets changes with azimuth time Change, the formula is: ,in, is the vertical distance between the target and the radar track (zero Doppler slant range), is the zero Doppler moment.

[0046] Linear frequency modulation signal transmitted by radar , the formula is: , where is the fast time variable, is a rectangular window function, is the pulse width, is the carrier frequency, The frequency is adjustable for distance.

[0047] The echo signal reflected by the point target experiences a propagation delay ( is the speed of light), after the received echo is down-converted and coherently demodulated, the baseband echo signal formula is: in, is the target complex scattering coefficient, is the signal wavelength.

[0048] Further simplify the slant range term and use Taylor expansion approximation , substituting into: , which fully describes the range frequency modulation characteristics and azimuth Doppler characteristics of point target echoes, providing a basic model for subsequent scene echo superposition and imaging processing.

[0049] Furthermore, in S3, generating a point target scene echo specifically includes: S301, determining the position and velocity information of the satellite according to the satellite orbit parameters and attitude file; S302, based on the satellite position and velocity, calculate the point target area illuminated by the satellite antenna beam at each PRT moment; S303, determining the scattering coefficient of each point target based on the scattering characteristics and position information of the point target; S304 , using a range-time domain superposition method, superimpose the echo signal of each point target in the range-time domain to generate baseband echo data of the point target scene.

[0050] When calculating the point target area illuminated by the satellite antenna beam at each PRT (pulse repetition time) in S302, the satellite orbit parameters (PVT table) and attitude file are used to determine the real-time position (three-dimensional coordinates) and velocity vector of the satellite. Suppose the position of the satellite at the PRT is , the speed is , the antenna beam pointing is determined by the attitude angle (azimuth, elevation angle), and the beam half-power angle is Combined with SAR imaging geometry, the beam illumination area on the ground is a rectangular area, and its distance range is determined by the satellite altitude. and pitch angle Decide, satisfy ($R$ is the slant range); the azimuth range is determined by the satellite speed and PRT duration Decide, satisfy The beam range in the satellite coordinate system is mapped to the ground coordinate system through coordinate transformation to determine the point target area covered by the beam at the PRT moment, that is, all slant ranges in And the position is The set of point targets within .

[0051] In S302, the range-time domain superposition method is used to generate baseband echo data of the point target scene. The range-time domain superposition method is based on the linear superposition principle of point target echo signals. The echoes of all point targets in the scene are directly superimposed in the range-time domain to generate scene echoes. According to the point target echo model, the baseband echo signal of a single point target is: ,in, For the The scattering coefficient of a point target, is the propagation delay, The target's position time The slope distance, is the signal wavelength, To adjust the frequency.

[0052] For the inclusion In a scenario with point targets, the baseband echo data is obtained by superimposing the echo signals of all point targets: By directly accumulating the echo signals of each point target in the range time domain, the delay and Doppler shift characteristics of each target are retained, which is suitable for scenarios with a small number of point targets.

[0053] Furthermore, the natural scene echo generation in S3 specifically includes: S311. Calculate the scene area illuminated by the satellite antenna beam at each PRT time based on the satellite orbit parameters and attitude file; S312, performing grid processing on the target scattering coefficient in the scene area to generate point array scene data; S313, using the GPU to parallelly calculate the impulse response sequence of each point target, and obtain the overall impulse response function of the scene by superposition; S314 : Convolve the baseband transmit signal with the scene impulse response function to generate baseband echo data of the natural scene.

[0054] In S311, the scene area illuminated by the satellite antenna beam at each PRT is calculated. According to the interferometric SAR spatial geometric model, when calculating the scene area illuminated by the satellite antenna beam at each PRT, the real-time position and attitude of the satellite are determined based on the satellite orbit parameters (PVT table) and attitude file. The position of the satellite at a certain PRT is set as the three-dimensional coordinates , the attitude is described by the roll angle, pitch angle, and yaw angle, and the azimuth half-power angle of the antenna beam is , the half-power angle in the range direction is .

[0055] Combined satellite speed and PRT duration , the azimuth illumination range is determined by the beam coverage width generated by the satellite movement, that is, ( is the ground projection length). The range of illumination is calculated based on the slant range formula. The slant range $R$ from the satellite to the ground scene satisfies , combined with the pitch angle , the slant range covered in the range direction is ( is the satellite altitude).

[0056] By converting the beam boundary in the satellite coordinate system to the ground coordinate system, it is finally determined that the scene area illuminated by the beam at the PRT moment is between , distance direction corresponds to slant distance The rectangular area provides the spatial range for the subsequent scattering coefficient gridding.

[0057] Furthermore, the intermediate frequency modulation module of S4 receives the baseband echo signal output by the echo calculation module through the playback module, performs delay modulation based on the PRT trigger signal, and adjusts the delay parameter (range is +2us~1.2ms, step size 0.5us, The target's range position is simulated using a pulse width (for pulse width). Digital upconversion then occurs, shifting the baseband echo signal from the baseband frequency to a 1.0±0.3GHz intermediate frequency (IF). Digital mixing and filtering are implemented in an FPGA to compensate for in-band amplitude and phase errors (amplitude error ≤±0.4dB, quadratic phase error ≤6°). DAC conversion (sampling bit count ≥10 bits) converts the digital signal into an analog IF echo signal. Output power is controlled to -14dBm, in-band flatness ±0.5dB, and spurious signals ≤-50dBc. The time-frequency module receives the 100MHz reference clock from the RF transceiver module and, after phase locking, provides a synchronous clock for the ADC / DAC to ensure consistent signal processing timing. The interface module distributes the PRT trigger signal, ensuring synchronization of delay modulation, upconversion, and digital-to-analog conversion. The resulting IF echo signal is then transmitted to the RF transceiver module.

[0058] Furthermore, the up-conversion unit of the RF transceiver module in the S5 receives the 1.0±0.3GHz intermediate frequency echo signal output by the intermediate frequency modulation module, and converts it into a 9.6±0.3GHz RF signal through the mixer and the 8.6GHz local oscillator signal. The up-conversion unit contains two independent channels. The temperature-compensated attenuator compensates for the influence of temperature on the signal amplitude. After the bandpass filter removes spurious signals, the output power is adjusted to the range of -60 to 0dBm by the digitally controlled attenuator. The signal is transmitted to the test SAR payload through the X-band linearly polarized antenna (bandwidth ≥ 600MHz, gain ≥ 2dBi). At the same time, the down-conversion unit of the RF transceiver module receives the 9.6±0.3GHz RF signal transmitted by the test SAR payload. After the power is limited by the limiter, the switch filter bank selects the appropriate bandwidth path and mixes it with the 8.6GHz local oscillator to obtain a 1.0±0.3GHz intermediate frequency signal. The signal is adjusted in amplitude by a digitally controlled attenuator (gain control range -10~+50dB), filtered out high-frequency clutter by a low-pass filter, and output to the intermediate frequency modulation module.

[0059] The clock module receives the 100MHz or 10MHz synchronous clock of the SAR payload under test and outputs four 100MHz and one 10MHz clock (with an accuracy of ±0.1ppm), providing a time and frequency reference for the entire system and forming a complete signal closed loop from payload transmission to echo reception.

[0060] This embodiment describes in detail a hybrid algorithm framework that uses the distance-time superposition method + one-dimensional Fourier transform method, which takes into account the simulation accuracy and computational efficiency of point targets and natural scenes, and improves the real-time processing capability of complex scenes through GPU parallel computing. It can flexibly adapt to different orbit parameters, scene types and payload indicators, and solves the problems of poor versatility and insufficient precision of traditional simulators.

[0061] The above are only preferred embodiments of the present invention, which do not limit the scope of protection of the present invention. For those skilled in the art, the present invention can be modified and varied in various ways. Any changes, modifications, replacements, integrations and parameter changes to these embodiments through conventional substitutions or that can achieve the same functions without departing from the principles and spirit of the present invention fall within the scope of protection of the present invention.

Claims

1. A spaceborne interferometric SAR echo simulator, characterized in that: It includes radio frequency transceiver module, intermediate frequency modulation module, echo calculation module and main control equipment; The RF transceiver module is connected to the SAR payload under test and the intermediate frequency modulation module respectively, and is used to receive the RF transmission signal of the SAR payload under test and transmit it to the intermediate frequency modulation module after down-conversion, receive the intermediate frequency echo signal of the intermediate frequency modulation module and transmit it to the SAR payload under test after up-conversion, and receive the synchronization clock of the SAR payload under test and distribute it to the intermediate frequency modulation module; The intermediate frequency modulation module is connected to the radio frequency transceiver module and the echo calculation module respectively, and is used to collect and process the intermediate frequency signal transmitted by the radio frequency transceiver module and send it to the echo calculation module, receive the baseband echo signal from the echo calculation module and process it into an intermediate frequency echo signal before transmitting it to the radio frequency transceiver module, and receive the PRT trigger signal of the test SAR payload and distribute it to the echo calculation module and itself; The echo calculation module is connected to the intermediate frequency modulation module and the main control device respectively, and is used to read the pre-stored baseband echo data and send it to the intermediate frequency modulation module in the echo playback mode to realize the delay processing of the baseband echo signal; The main control device is connected to the radio frequency transceiver module, the intermediate frequency modulation module, and the echo calculation module respectively, and is used to edit and configure test cases, control the operation of each module, monitor module status, and record operation logs.

2. A spaceborne interferometric SAR echo simulator according to claim 1, characterized in that: The radio frequency transceiver module includes a down-conversion unit, an up-conversion unit, a clock module and an antenna; The down-conversion unit is used to convert the RF input signal into an intermediate frequency output signal, and its RF input power range is selectable in multiple gears, the gain control range is selectable in multiple gears, the attenuation step is selectable in multiple gears, and the attenuation accuracy is selectable in multiple gears; The up-conversion unit includes two intermediate frequency input channels and two radio frequency output channels, which are used to convert the intermediate frequency input signal into a radio frequency output signal. The radio frequency output power range is multi-level optional, the output step is multi-level optional, and the attenuation accuracy is multi-level optional; The clock module receives an external reference clock and outputs multiple clocks, wherein the clock accuracy is selectable in multiple gears; The antennas are two linearly polarized antennas, the operating frequency is a specific band, the bandwidth is selectable in multiple gears, and the gain is selectable in multiple gears.

3. A spaceborne interferometric SAR echo simulator according to claim 2, characterized in that: The structure of the down-conversion unit includes a limiter, a first switch, a switch filter group, a band-pass filter, a mixer, a first amplifier, a digitally controlled attenuator, a low-pass filter and a second amplifier connected in sequence; The limiter input terminal is connected to an external radio frequency signal for limiting the input signal power; The first switch is a single-pole double-throw switch, one end of which is connected to the limiter output end, and the other end is selectively connected to the calibration input signal to achieve signal switching; The switch filter bank includes multiple filters with different bandwidths and corresponding amplifiers, and realizes the selection of different signal paths through switch switching; The mixer input end is connected to the bandpass filter output end and the specific frequency local oscillator signal respectively to down-convert the radio frequency signal into an intermediate frequency signal; The digitally controlled attenuator uses a specific type of chip to adjust the signal amplitude by controlling the attenuation; The low-pass filter is used to filter out high-frequency noise in the intermediate frequency signal, and the output end is connected to the intermediate frequency modulation module through the second amplifier.

4. A spaceborne interferometric SAR echo simulator according to claim 2, characterized in that: The up-conversion unit includes two channels with the same structure, each channel is provided with a temperature-compensated attenuator, a third amplifier, a second digitally controlled attenuator, a mixer, a band-pass filter, a third digitally controlled attenuator and a second switch in sequence; The input end of the temperature compensation attenuator is connected to the intermediate frequency signal output by the intermediate frequency modulation module to compensate for the influence of temperature change on the signal amplitude; The mixer input terminal is connected to the output terminal of the third amplifier and the local oscillator signal of a specific frequency respectively, so as to up-convert the intermediate frequency signal into a radio frequency signal; The bandpass filter is used to filter out spurious components in the radio frequency signal; The second digitally controlled attenuator and the third digitally controlled attenuator are arranged in series to achieve wide range amplitude adjustment through multi-stage attenuation; The second switch is a single-pole single-throw switch that controls the output on and off of the radio frequency signal. The output ends of the two channels are connected to the antenna and the calibration interface respectively.

5. The spaceborne interferometric SAR echo simulator according to claim 1, characterized in that: The intermediate frequency modulation module includes an acquisition module, a playback module, an interface module, a time-frequency module and a PCIE interface module; The acquisition module performs ADC acquisition and digital down-conversion on the intermediate frequency transmission signal transmitted by the RF transceiver module to obtain a baseband transmission signal and send it to the echo calculation module through the optical fiber; The playback module receives the baseband echo signal from the echo calculation module, generates an intermediate frequency echo signal after delay modulation, digital up-conversion and DAC playback, and transmits it to the RF transceiver module; The interface module receives external PRT pulses as synchronization reference and outputs PRT pulses and echo envelope signals; The time-frequency module receives the 100MHz reference clock of the radio frequency transceiver module and distributes it to each internal unit after phase locking; The PCIE interface module realizes high-speed data communication with the echo calculation module.

6. The spaceborne interferometric SAR echo simulator according to claim 1, characterized in that: The echo calculation module adopts a CPU+GPU+FPGA architecture, including an interface unit, a GPU processing module and an ARM processing module; The interface unit receives the baseband transmission signal of the intermediate frequency modulation module through the optical fiber, checks and caches the data and transmits it to the ARM processing module, and at the same time receives the baseband echo signal of the ARM processing module and sends it to the intermediate frequency modulation module after processing; The GPU processing module calculates the impulse response sequence of the scene using a one-dimensional frequency domain algorithm, and convolves the baseband transmission signal with the impulse response sequence to generate echo data; The ARM processing module calculates the scene area illuminated by the satellite antenna beam, extracts the baseband transmission signal and sends it to the GPU processing module, and simultaneously reads the locally stored scene file and PVT table data.

7. The spaceborne interferometric SAR echo simulator according to claim 1, characterized in that: The main control device includes a use case editing and configuration module, a process control module, an interface display module and a communication module; The test case editing and configuration module is used to set overall parameters, scenario parameters, test device parameters, SAR parameters and wave position parameters, and supports the creation, opening, saving and association of test cases with instruction packages; The process control module realizes the operation control such as extension connection, system self-check, mode selection, initialization, start and stop; The interface display module displays test case information, extension status, system operation parameters and software operation messages; The communication module communicates with the echo calculation module through a network interface, and communicates with the radio frequency transceiver module and the intermediate frequency modulation module through a serial port.

8. A spaceborne interferometric SAR echo simulation method, applicable to the spaceborne interferometric SAR echo simulator according to any one of claims 17, characterized in that: include: S1. Construct an interferometric SAR spatial geometric model to determine the geometric relationship between the radar antenna and the ground target, and calculate the echo phase difference based on the slant range difference between the target and the two antennas; S2. Establish a point target echo signal model and derive the mathematical expression of the baseband echo signal based on the radar platform motion parameters, transmission signal parameters and target slant range; S3. Generate scene echo data through the echo calculation module. The range-time superposition method is used for point target scenes, and the one-dimensional Fourier transform method is used for natural scenes to improve calculation efficiency. S4, the intermediate frequency modulation module performs delay modulation, digital up-conversion and digital-to-analog conversion on the baseband echo signal output by the echo calculation module to generate an intermediate frequency echo signal; S5. The RF transceiver module up-converts the intermediate frequency echo signal to the RF frequency band and sends it to the SAR payload under test. At the same time, it receives the transmission signal of the SAR payload under test and down-converts it to form a signal closed loop.

9. The method for simulating spaceborne interferometric SAR echoes according to claim 8, wherein: In S3, generating a point target scene echo specifically includes: S301, determining the position and velocity information of the satellite according to the satellite orbit parameters and attitude file; S302, based on the satellite position and velocity, calculate the point target area illuminated by the satellite antenna beam at each PRT moment; S303, determining the scattering coefficient of each point target based on the scattering characteristics and position information of the point target; S304 , using a range-time domain superposition method, superimpose the echo signal of each point target in the range-time domain to generate baseband echo data of the point target scene.

10. The spaceborne interferometric SAR echo simulation method according to claim 8, characterized in that: The natural scene echo generation in S3 specifically includes: S311. Calculate the scene area illuminated by the satellite antenna beam at each PRT time based on the satellite orbit parameters and attitude file; S312, performing grid processing on the target scattering coefficient in the scene area to generate point array scene data; S313, using the GPU to parallelly calculate the impulse response sequence of each point target, and obtain the overall impulse response function of the scene by superposition; S314 : Convolve the baseband transmit signal with the scene impulse response function to generate baseband echo data of the natural scene.

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