Non-cooperative signal perception system and multi-dimensional parameter estimation method for spaceborne passive SAR

Abstract

The invention relates to a non-cooperative signal perception system and a multi-dimensional parameter estimation method for spaceborne passive SAR, and belongs to the field of radar technology. The invention includes a non-cooperative SAR signal perception system and a non-cooperative SAR signal multi-dimensional parameter estimation method, wherein the non-cooperative SAR signal perception system includes a zenith sensing antenna, a direct signal array receiving unit, a ground detection antenna, and an echo signal array receiving unit, to realize the reception of non-cooperative SAR direct signals and echo signals; the non-cooperative SAR signal multi-dimensional parameter estimation method includes a direct signal time-frequency-space characteristic estimation unit and an antenna beam pointing parameter estimation unit, to realize multi-dimensional parameter estimation and antenna pointing estimation of non-cooperative SAR signals. Compared with traditional spaceborne SAR systems, the spaceborne passive SAR does not need to transmit any signals, and can sense and capture available non-cooperative SAR signal sources in space in real time, and use the non-cooperative SAR signal sources to perform dual-station SAR imaging detection.

Description

Technical Field

[0001] The present invention relates to a non-cooperative signal perception system and a multi-dimensional parameter estimation method for a spaceborne passive SAR, and belongs to the technical field of radar. Background Art

[0002] SAR satellites have been developed internationally for over 40 years, with over 40 satellites already in orbit. With the recent maturation of commercial miniaturized SAR satellite technology, nearly 1,000 miniaturized SAR satellites will be in orbit within the next 5 to 10 years. However, due to legal operating frequency restrictions, large-scale miniaturized SAR satellites will inevitably face electromagnetic interference issues. Research is urgently needed on a new type of SAR technology: spaceborne passive SAR systems. Spaceborne passive SAR systems do not require active transmission of high-power, broadband signals; instead, they simply sense and utilize signals from other SAR satellites to achieve Earth imaging observations.

[0003] Most existing spaceborne passive SAR systems employ cooperative detection, such as multi-satellite formations (one transmitter, multiple receivers, or multiple transmitters, one receiver), or medium- and high-orbit satellites transmitting and low-orbit satellites receiving. These systems utilize sufficient prior information and time-frequency and spatial synchronization between the transmitting and receiving SAR satellites, simplifying the complexity and technical difficulty of spaceborne SAR systems. However, cooperative detection systems can only sense and utilize signals from a limited number of SAR satellites, not from all in-orbit SAR satellites. This results in a low system imaging duty cycle. Summary of the Invention

[0004] The technical problem solved by the present invention is to overcome the shortcomings of the existing technology and provide a non-cooperative signal perception system and multi-dimensional parameter estimation method for spaceborne passive SAR. In order to realize imaging detection using space non-cooperative SAR signals, a hardware system consisting of a spaceborne passive SAR non-cooperative signal perception subsystem and a ground imaging detection subsystem is designed, and a multi-dimensional parameter estimation method is proposed to realize passive imaging. During the space non-cooperative SAR signal perception stage, a zenith sensing antenna is used to receive non-cooperative SAR signals in the corresponding detection frequency band. Since the signal parameters of the non-cooperative SAR cannot be predicted, a direct signal array receiving unit is required to perform rapid time-frequency two-dimensional estimation of the direct non-cooperative SAR signals, calculate the spatial position and flight trajectory of the non-cooperative SAR satellite, and input the available direct signal characteristic parameters into the radar ground imaging detection subsystem through signal availability analysis. To achieve Earth imaging, a planar multi-channel antenna is mounted on the underside of a passive SAR satellite to receive echo signals from non-cooperative SAR ground detection. Echo signal strength analysis reveals the non-cooperative SAR satellite's Earth observation beam pointing direction, which in turn determines the main lobe footprint of the non-cooperative SAR antenna beam and yields a complete estimate of the satellite's multi-dimensional parameters. Based on this, the ground detection antenna achieves Earth observation imaging through DBF rapid beam alignment.

[0005] The technical solution of the present invention is:

[0006] The non-cooperative signal sensing system of the spaceborne passive SAR includes a zenith sensing antenna, a direct signal array receiving unit, a ground detection antenna, and an echo signal array receiving unit;

[0007] The zenith sensing antenna is used to receive the sidelobe transmission signal of the non-cooperative SAR satellite antenna, generate a four-channel direct signal through a sum-and-difference network, and send it to the direct signal array receiving unit;

[0008] The direct signal array receiving unit is used to perform sum and difference beam angle measurement, differential Doppler positioning and time-frequency parameter search processing on the direct signal, generate non-cooperative SAR signal time-frequency estimation parameters and send them to the echo signal array receiving unit;

[0009] The ground detection antenna is used to receive the echo signal of the ground search area, generate the beam pointing area echo signal through DBF multi-channel processing, and send it to the echo signal array receiving unit;

[0010] The echo signal array receiving unit is used to perform parallel pulse compression and azimuth coherent accumulation processing on the ground echo signal, generate an echo energy distribution model and output a non-cooperative SAR antenna beam pointing, and finally complete the perception of the non-cooperative signal.

[0011] Furthermore, the zenith sensing antenna adopts an X-band two-dimensional planar array antenna, which is symmetrically divided into four-quadrant distributed sub-arrays, and realizes sum and difference beam amplitude ratio angle measurement through digital or analog methods.

[0012] Furthermore, the direct signal array receiving unit includes four independent down-conversion receiving channels, each of which includes a radio frequency bandpass filter, a variable gain amplifier, a mixer, an intermediate frequency bandpass filter, an intermediate frequency low noise amplifier and an analog-to-digital converter, for inputting the sampled digital signal into the processor module;

[0013] The processor module is used to complete signal parameter estimation and then feed back the center frequency to the programmable local oscillator source to produce a more matching local oscillator frequency, making the mixed intermediate frequency direct signal easier to be sampled by the analog-to-digital converter, thereby reducing the sampling frequency and data rate; the estimated parameters include the center frequency, bandwidth, and time width of the non-cooperative SAR signal.

[0014] Furthermore, the ground detection antenna adopts an X-band two-dimensional multi-channel array antenna.

[0015] Furthermore, the array aperture of the ground detection antenna is L×W, where L>6m and W>1m.

[0016] Furthermore, the number of channels of the ground detection antenna is P×Q, and the number of sub-array units corresponding to each channel is M. p ×M q , p=1,2,…,P,q=1,2,…,Q,the azimuth direction is realized by sub-array level digital beamforming Two-dimensional beam scanning in the range direction ±θ, where θ∈[10°~30°], the antenna pattern sidelobe is better than -13dB and the grating lobe is better than -15dB during scanning.

[0017] Furthermore, the echo signal array receiving unit includes P×Q independent receiving channels, each channel including a radio frequency bandpass filter, a variable gain amplifier, a mixer, an intermediate frequency bandpass filter, an intermediate frequency low noise amplifier, and an analog-to-digital converter, for inputting the sampled digital signal into the processor module;

[0018] The processor module completes I / Q demodulation, DBF, range pulse compression, and azimuth incoherent accumulation of the intermediate frequency echo signal to obtain an echo signal with a high signal-to-noise ratio, which is used for two-dimensional search and estimation of the non-cooperative SAR antenna beam pointing.

[0019] The method for estimating multidimensional parameters of non-cooperative signals of spaceborne passive SAR includes the following steps:

[0020] 1) The direct signal received by the zenith sensing antenna passes through the sum-difference network and is fed into the direct signal array receiving unit. The programmable array source is mixed with the direct sum signal. The non-cooperative signal time width Rough estimate; the bandwidth is obtained by fast Fourier transform (FFT) The center frequency is Doppler frequency Real-time estimation of multi-dimensional parameters;

[0021] 2) Build an optimization model that aims to optimize the impulse response width (IRW), peak sidelobe ratio (PSLR), and integrated sidelobe ratio (ISLR) of the compressed pulse signal. Utilizing global optimization techniques such as the particle swarm optimization algorithm, a rapid search is performed in the two-dimensional time-frequency support domain to obtain the optimal estimation of the time-frequency parameters of the non-cooperative SAR signal.

[0022] 3) In the direct signal array receiving unit, based on the time-frequency parameter estimation results of the non-cooperative SAR signal, amplitude comparison angle measurement and differential Doppler solution are performed on the direct signal of the sum and difference beam channels to obtain the relative spatial position estimation of the non-cooperative SAR satellite and the passive SAR. The non-cooperative SAR trajectory is fitted using an improved extended Kalman filter (EKF) tracking algorithm.

[0023] 4) The direct signal array receiving unit sends the non-cooperative SAR time-frequency estimation parameters to the echo signal array receiving unit;

[0024] 5) Based on the spatial relationship between the passive SAR and the non-cooperative SAR, the ground detection antenna directs the multi-channel antenna to the potential ground imaging area through DBF weighted synthesis of narrow beams to search and receive echo signals;

[0025] 6) In the echo signal array receiving unit, a parallel FPGA platform is used to perform I / Q demodulation, DBF beam scanning, range pulse compression, and azimuth coherent integration on the echo signal to obtain the echo signal power distribution of the ground imaging area.

[0026] 7) The echo signal array receiving unit modifies the echo power distribution model obtained by DBF beam scanning, compensates for the power attenuation difference of the echo caused by different paths in the pitch plane, and obtains the modified echo power distribution of the search area; selects the strongest power point as the center of the non-cooperative SAR imaging area, and thus solves the azimuth and range beam pointing estimation of the non-cooperative SAR

[0027] 8) At this point, the time-frequency and spatial parameter estimation of the non-cooperative SAR signal is complete, and the ground-based antenna directs the beam toward the corresponding area to achieve dual-station passive SAR imaging. The entire process is carried out in real time on orbit, completing continuous estimation and imaging processing.

[0028] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the non-cooperative signal perception system and multi-dimensional parameter estimation method of the spaceborne passive SAR.

[0029] A non-cooperative signal perception system and multi-dimensional parameter estimation device for a spaceborne passive SAR includes a memory, a processor, and a computer program stored in the memory and executable on the processor. The device is characterized in that when the processor executes the computer program, steps of the non-cooperative signal perception system and multi-dimensional parameter estimation method for the spaceborne passive SAR are implemented.

[0030] The advantages of the present invention compared with the prior art are:

[0031] 1) The present invention does not require pre-knowledge of radar signal parameters. It only requires the addition of a zenith array antenna to autonomously sense non-cooperative SAR signals in space. It can fully utilize all on-orbit SAR satellite signals for Earth imaging detection, and has high flexibility and a large imaging duty cycle.

[0032] 2) The present invention does not require the transmission of high-power signals, omits large-scale power amplifiers, significantly reduces system costs, and has excellent concealment;

[0033] 3) The present invention adopts parallel fast search optimization processing in the signal parameter estimation process, which not only ensures the parameter estimation accuracy but also takes into account the real-time performance of signal processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of the spaceborne passive SAR sensing and joint imaging scenario of non-cooperative SAR in space;

[0035] Figure 2 This is a block diagram of the spaceborne passive SAR non-cooperative signal intelligent perception system designed by the present invention;

[0036] Figure 3 This is a flowchart of the spaceborne passive SAR non-cooperative signal parameter estimation process designed by the present invention;

[0037] Figure 4 This is the structural diagram of the zenith sensing antenna subsystem of the spaceborne passive SAR;

[0038] Figure 5 This is a schematic diagram of the time-frequency-space parameter estimation of non-cooperative SAR signals;

[0039] Figure 6 This is a block diagram of the structure of the non-cooperative SAR direct signal array receiving unit;

[0040] Figure 7This is a schematic diagram of non-cooperative SAR antenna beam pointing parameter estimation;

[0041] Figure 8 It is a structural block diagram of a non-cooperative SAR echo signal array receiving unit. DETAILED DESCRIPTION

[0042] In order to better understand the above technical solution, the technical solution of the present application is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present application and the specific features in the embodiments are detailed descriptions of the technical solution of the present application, rather than limitations on the technical solution of the present application. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments can be combined with each other.

[0043] The following is a further detailed description of the non-cooperative signal perception system and multi-dimensional parameter estimation method of the spaceborne passive SAR provided by the embodiment of the present application in conjunction with the accompanying drawings. The specific implementation method may include (eg Figures 1 to 8 shown):

[0044] In the solution provided in the embodiment of this application,

[0045] a. In an exemplary embodiment of the present invention, a non-cooperative signal perception system and a multi-dimensional parameter estimation method for a spaceborne passive SAR are provided.

[0046] Figure 1 This is a schematic diagram of the joint imaging and detection scenario of spaceborne passive SAR and space non-cooperative SAR, including:

[0047] The main lobe of the non-cooperative SAR satellite antenna operating in space points to the ground observation area, and the signal leaks through the sidelobe radiation and is transmitted to the space-borne passive SAR; the low-orbit space-borne passive SAR zenith antenna receives and senses the direct signal, and obtains the position and signal parameters of the non-cooperative SAR satellite through time-frequency-space multi-dimensional parameter analysis; the main lobe footprint of the ground observation antenna is determined through range beam scanning search, and then the main lobe of the antenna is aimed at the area to realize passive imaging detection.

[0048] Figure 2 The non-cooperative signal intelligent perception system for spaceborne passive SAR proposed in an embodiment of the present invention includes:

[0049] The zenith sensing antenna subsystem 10 and the direct signal array receiving unit 20 receive and process the direct signal of the non-cooperative SAR, realize the reception of spatially available signals and intelligent perception of multi-dimensional information, and input the direct signal to the echo signal array receiving unit 30. Through the multi-channel ground detection antenna subsystem 40, the echo of the non-cooperative SAR beam illumination area is received and processed to realize non-cooperative SAR beam pointing estimation and ground imaging detection.

[0050] Figure 3 This is a flowchart of a non-cooperative signal parameter estimation technique for spaceborne passive SAR according to an embodiment of the present invention, including:

[0051] The side leakage signal from the non-cooperative SAR antenna is received by a four-subarray zenith antenna 100. A coarse estimate of the signal's time-frequency parameters is obtained through rapid time-domain analysis 101, and the signal availability is determined based on its time-frequency characteristics. Four-channel digital sum-and-difference reception processing is used to obtain a spatial angle estimate for the non-cooperative SAR 102. The Doppler variation rate of the sum beam received signal is used to estimate the spatial distance of the non-cooperative SAR 103. Combined with the signal angle estimate, spatial positioning is achieved, and an improved EKF algorithm is used to fit the satellite's motion trajectory 104. The operating mode of the non-cooperative SAR satellite is determined based on its orbital characteristics. Conventional SAR antennas have poor azimuth scanning capabilities. Based on the non-cooperative SAR operating mode determined in this manner, the azimuth scanning boundary of the non-cooperative SAR antenna beam can be determined, thereby achieving azimuth angle estimation for the non-cooperative SAR signal 105.

[0052] The passive SAR Earth observation antenna uses DBF processing to rapidly form a high-resolution narrow beam within the corresponding scanning area, performing beam scanning along the range direction within the estimated azimuth range 106. Based on the echo signal power model, the non-cooperative SAR antenna footprint is reconstructed and the two-dimensional pointing angle of its beam is determined, thereby estimating the non-cooperative SAR signal incidence angle 107. Based on the relative positions of the passive SAR satellite and the non-cooperative SAR satellite, DBF weighting is used to align the beam center with the non-cooperative SAR antenna pointing area, achieving bistatic radar imaging detection based on non-cooperative external radiation sources 108.

[0053] 1. Reference Figure 4 The zenith sensing antenna subsystem 10 includes: a four-subarray zenith antenna 101, which utilizes the principle of single-pulse sum-difference angle measurement to divide a two-dimensional planar antenna into four quadrant symmetrical subarrays. Amplitude-phase weighting is used to achieve a low-sidelobe sum-difference radiation pattern, ensuring that the sum beam of the four subarrays can scan within a 120° cone angle in the spatial domain without generating grating lobes. To improve the efficiency of searching for spatially available signals, the sum beamwidth is maintained at 8°-12°. A four-channel wideband signal receiver 102 has a receiving channel passband of 9-10.2 GHz, enabling effective reception of spatial non-cooperative SAR signals. A sum-difference beamformer 103 forms a sum signal channel and a two-dimensional difference signal channel through digital or analog means, performs down-conversion, filtering, amplification, and normalization, and achieves sum-difference amplitude ratios for the four subarray channels. The azimuth and elevation angles of the incident non-cooperative SAR signal are obtained from the angle detection curve 104. A sum signal processor 105 extracts sum signal channel data for accurate estimation of the time-frequency parameters, range estimation, and flight trajectory association processing of the non-cooperative SAR signal.

[0054] 2. Reference Figure 5The spatial parameter estimation process of the non-cooperative SAR includes: the zenith antenna and difference beam receiving signals can be used to estimate the azimuth and elevation angle of the non-cooperative SAR to achieve angle tracking; the sum beam receiving signals can realize the Doppler estimation and distance tracking of the non-cooperative SAR, and further obtain its radial velocity component; multiple groups of angles of the non-cooperative SAR are obtained through continuous observation. Since the SAR satellites operating in space have relatively stable motion trajectories, the improved EKF algorithm can be used to correlate the flight points of non-cooperative SAR satellites, fit their actual flight orbits, and realize satellite orbit determination.

[0055] 3. Reference Figure 6 The multi-dimensional parameter estimation of the direct signal of the space non-cooperative SAR is completed by the direct signal array receiving unit 20. According to the passive SAR satellite's own position 30, the signal parameters 40 and operating mode 50 of the non-cooperative SAR are obtained through FPGA processing. The four signals received by the four-subarray zenith antenna 10 are input into the direct signal array receiving unit 20. Each channel includes an RF bandpass filter 201 to filter out interference signals outside the 9-10.2GHz range; it is then connected to a variable gain amplifier 202, a mixer 203, an intermediate frequency bandpass filter 204, an intermediate frequency low noise amplifier 205, and an ADC 206. The sampled signal is fed into an FPGA or other processor 207. The programmable local oscillator source 208 outputs a matching local oscillator signal under the signal frequency estimation parameter fed back by the FPGA. After being selected by the multi-way switch 209, it is mixed with each received signal in turn to obtain the transmission characteristics of the four receiving channels. Amplitude and phase consistency correction is performed in the FPGA processor. Since space non-cooperative SAR usually transmits linear frequency modulation (LFM) signals for imaging detection, a rough estimate of the signal time width can be obtained by time domain processing. FFT can be used to obtain a rough estimate of the signal center frequency and bandwidth. At the same time, the Doppler frequency obtained by spatial position estimation is compensated, and the frequency-matched local oscillator signal is output to the four channels for down-conversion filtering. The frequency of the tuned local oscillator source is continuously received and fed back, making the down-converted intermediate frequency signal easier to be sampled by the ADC, thereby reducing the sampling rate. After obtaining the coarse estimated signal parameters, a two-dimensional time-frequency fine search model is established, and particle swarm optimization and other methods are used to perform a rapid random search of the signal parameters in the two-dimensional time-frequency domain to achieve the optimal parameter estimation of the direct signal.

[0056] 4. Reference Figure 7 (a) Since conventional SAR antennas have limited scanning angles in azimuth, the azimuth angle of the non-cooperative SAR transmission signal can be determined based on prior knowledge. Combined with the fitted flight trajectory and altitude, the ground scanning boundary of the non-cooperative SAR antenna beam can be calculated, thereby estimating the non-cooperative SAR antenna footprint. Figure 7(b) The spaceborne SAR ground detection antenna searches the footprint area of ​​the non-cooperative SAR antenna and uses DBF technology to quickly form a narrow beam and scan along the range direction. When the non-cooperative SAR signal encounters a ground target, it will scatter in other directions. Therefore, the ground detection antenna is used to receive the scattered echo and perform energy detection to determine the actual illumination area of ​​the non-cooperative SAR antenna, thereby realizing the beam pointing estimation of the non-cooperative SAR antenna.

[0057] 5. Reference Figure 8 The non-cooperative SAR echo signal is received by the two-dimensional multi-channel ground detection antenna 10 and fed into the echo signal array receiving unit 20. Based on the passive SAR satellite position 30, the non-cooperative SAR operating mode 40 and signal parameters 50 estimated by the direct signal array receiving unit, the FPGA 207 processes the non-cooperative SAR antenna beam to obtain the range direction 60 and azimuth direction 70 estimates. The multiple signals received by the ground detection antenna 10 are input into the echo signal array receiving unit 20. Each channel includes an RF bandpass filter 201 to filter out interference signals outside the 9-10.2 GHz range. The receiving channels include, but are not limited to, a variable gain amplifier 202, a mixer 203, an intermediate frequency bandpass filter 204, an intermediate frequency low-noise amplifier 205, and an ADC 206. The sampled signals are fed into an FPGA or other processor 207. A programmable local oscillator 208 estimates parameters based on the input non-cooperative SAR signal and outputs a frequency-matched local oscillator signal. This signal is then sequentially selected through a switch 209 and mixed with each received signal to obtain the transmission characteristics of the multiple receiving channels. Amplitude and phase consistency calibration is then performed in the FPGA processor. The multi-channel antenna beam scans the ground in the range direction. Through multi-channel reception and DBF processing, a model of the echo power distribution across the entire area is quickly derived. The point with the highest power is selected as the illumination center of the non-cooperative SAR beam. This point is then associated with the spatial position of the non-cooperative SAR and the range (60°) and azimuth (70°) beam pointing direction estimates are calculated.

[0058] b. Fast estimation method of two-dimensional time-frequency parameters of non-cooperative signals

[0059] In this embodiment, a two-step estimation strategy combining coarse estimation with local fine search is employed to rapidly estimate the time-frequency parameters of non-cooperative SAR signals. First, a coarse estimate of signal parameters such as time width, center frequency, and bandwidth is obtained using the time-domain sampled signal and FFT techniques. Since the signal frequency may be superimposed with instantaneous velocity Doppler components and other error factors, a particle swarm optimization algorithm is used to perform a rapid random search of the signal parameters in the time-frequency domain. This algorithm then establishes an optimization model to match the optimal estimate of the signal parameters.

[0060] 1. Reference Figure 4, the spaceborne passive SAR first senses the X-band signals available in space. Compared with ground systems, signals transmitted in space are less susceptible to clutter and multipath interference. The high-power signals emitted by non-cooperative SAR produce lateral leakage through the antenna side lobes. Through airspace search, a relatively pure non-cooperative SAR signal direct wave can be obtained. The spaceborne passive SAR is equipped with a top-mounted sensing antenna. The four-channel zenith antenna 101 forms a single-pulse array. During the flight of the passive SAR, the antenna and beam scan within a 120° cone angle range in the airspace to search for and receive X-band non-cooperative SAR signals; the received signal is fed into the four-channel broadband signal receiver 102 for filtering and down-conversion processing. The pulse duration of the sampled signal after down-conversion is estimated to be The bandwidth is The center frequency is After the sum and difference beamformer 103, the spatial relative position estimation of the incident SAR signal is completed: including azimuth and pitch angle distance Among them, the satellite angle information is obtained by measuring the angle by sum and difference beam amplitude ratio. Represents the antenna patterns corresponding to the four sub-arrays, and the zenith antenna and beam patterns are expressed as:

[0061]

[0062] The azimuth difference beam pattern is expressed as:

[0063]

[0064] The elevation difference beam pattern is expressed as:

[0065]

[0066] According to the echo amplitude ratio of different receiving beams, the corresponding two-dimensional spatial angle can be obtained through the angle detection curve:

[0067]

[0068]

[0069] Spatial distance between non-cooperative SAR satellites The Doppler frequency change rate of the direct wave signal is obtained. The Doppler frequency caused by the relative motion between the passive SAR and the non-cooperative SAR is roughly estimated as follows: When observing continuously, it is easy to get the rate of change of Doppler frequency

[0070]

[0071] represents the estimate of the center frequency of the direct signal, which can be further corrected by time-frequency two-dimensional search optimization. The relationship between the spatial position of the passive SAR and the Doppler change rate of the direct signal is expressed as

[0072]

[0073] Among them, the spatial coordinates of the non-cooperative SAR are (x0, y0, z0), and the spatial position of the passive SAR observation point is (x i ,y i ,z i ), Represents the spatial distance vector between the two; in the passive SAR spatial position and movement speed and acceleration Under known conditions, dynamic measurements are performed over a period of time. Based on the spatial angle measurements, unambiguous positioning of non-cooperative SAR satellites can be achieved. Direct wave signals are continuously received and the EKF algorithm is used to fit the non-cooperative SAR trajectory.

[0074] 2. Reference Figure 6 The direct signal array receiving unit 20 consists of a down-conversion RF receiving channel (including an RF bandpass filter 201, a variable gain amplifier 202, a mixer 203, an IF bandpass filter 204, an IF low noise amplifier 205, and an ADC 206) and an FPGA processor 207. During the down-conversion process, the channel signal is mixed with a programmable local oscillator 208. The RF bandpass filter has a passband of 9-10.2 GHz. The initial frequency of the programmable local oscillator is set to f LO , the pulse duration of the down-converted sampling signal is estimated to be The bandwidth is The center frequency is The instantaneous Doppler frequency obtained according to the above filtering process is The center frequency of the incident signal is corrected to The output frequency of the programmable local oscillator is updated, and the down-converted signal is sampled and analyzed. This process is repeated to obtain multiple sets of estimated values ​​of the signal frequency parameters, which are used to continuously update the spatial position of the target.

[0075] 3. Since the parameters of non-cooperative SAR signals are unknown, spatial measurement errors are inevitable. Based on the above time-frequency parameter estimation results, a two-dimensional local fine search is required in the estimated neighborhood. This paper proposes a fast search method for two-dimensional time-frequency parameters of signals based on particle swarm optimization. An optimization model is established. In the two-dimensional support domain of time and frequency opened by the above multiple sets of estimated parameters, the time unit Δt is used to calculate the number of time units. p , frequency unit Δf is used as the unit to randomly search the two-dimensional parameters. Establish the optimization objective function and use the rough estimation result of the signal as the received signal Random search for signal parameter configuration As a reference signal, the received direct signal is matched filtered:

[0076]

[0077] Calculate the impulse response width IRW, peak sidelobe ratio PSLR and integrated sidelobe ratio ISLR of the signal after pulse compression, and construct a multi-objective optimization model:

[0078]

[0079] Among them, w1~w3 are multi-objective optimization weights, which can be specified based on prior knowledge or dynamically adjusted. The parallelism of the particle swarm optimization algorithm can accelerate the calculation speed of two-dimensional parameter optimization and is easy to implement in an FPGA processor. Frequency-domain pulse compression only involves multiplication and addition operations, which is computationally simple. The two random parameters a and b are updated within a specified number of iterations, and the dimension of the optimization variables is low, so the optimal estimate of the signal time-frequency parameters can be quickly obtained50.

[0080] c. Non-cooperative SAR antenna beam pointing estimation method

[0081] In this embodiment, to quickly obtain the non-cooperative SAR antenna beam pointing, a ground detection search combining multi-channel reception and DBF technology is used. The azimuth of the non-cooperative SAR transmission signal and the center pointing of the antenna main lobe are determined based on the estimated satellite operating status. Since the pitch scanning angle of a typical spaceborne SAR is 20° to 60°, range-dimensional beam scanning is performed in the corresponding azimuth, and the beam pointing of the non-cooperative SAR is determined based on the echo energy distribution.

[0082] 1. Reference Figure 7 (a) According to the non-cooperative SAR flight trajectory obtained by the above fitting, its working mode is judged. Since the azimuth scanning capability of the satellite-borne SAR antenna beam is poor, the scanning range is usually Sometimes, there are Therefore, the azimuth angle θ of the beam s The range is well-defined; however, the range scan range is relatively wide. Within a ±θ scan range, θ ≤ 20°. Therefore, a detailed range search is required to determine the actual imaging observation area. First, the antenna footprint of the non-cooperative SAR is determined within the ground area corresponding to the satellite's flight path, using the principle of maximum area coverage in the two dimensions of azimuth and range.

[0083] 2. Reference Figure 7(b) Ground targets within the non-cooperative SAR signal beam's illumination area will scatter energy in other directions. The passive SAR ground detection antenna rapidly scans the beam in the range direction, and the actual beam direction of the non-cooperative SAR antenna is determined by comparing the signal energy of the received echoes. The aperture of a spaceborne passive SAR ground detection antenna is L × W, typically L > 6 m and W > 1 m. This is slightly larger than a conventional spaceborne SAR antenna in the same frequency band, facilitating the formation of a narrow beam with higher resolution. DBF technology and multi-channel reception allow for rapid detection of the scattered signal echo intensity within the area swept by the beam.

[0084] 3. Reference Figure 8 The echo signal array receiving unit 20 consists of a down-conversion RF receiving channel (including an RF bandpass filter 201, a variable gain amplifier 202, a mixer 203, an intermediate frequency bandpass filter 204, an intermediate frequency low noise amplifier 205, and an ADC 206) and an FPGA processor 207. During the down-conversion process, the channel signal is mixed with a programmable local oscillator 208. The local oscillator parameters are configured based on the estimated non-cooperative SAR signal parameters. The sampled multi-channel received echo signals are weighted by DBF to achieve optimal reception in different scanning areas. Based on the non-cooperative SAR signal parameters obtained from the zenith sensing antenna reception and signal analysis, a local reference signal s is constructed. r ; Implement pulse compression and azimuth coherent accumulation processing of multiple echoes in parallel in the FPGA processor, and establish the echo power distribution model of the entire scanning area Under the condition that the scattering characteristics of ground targets are relatively uniformly distributed, the point with the strongest echo power is used as the pointing center of the non-cooperative SAR antenna beam, thereby obtaining the range direction 60 and azimuth direction 70 estimates of the non-cooperative SAR antenna beam.

[0085] 4. When constructing the echo power distribution model Γ, in order to avoid estimation errors caused by inconsistent echo energy attenuation at different distances, the target echo power is accumulated in azimuth and the signal transmission path loss is compensated: According to the radar equation, the signal-to-noise ratio of the scattered echo signal can be expressed as

[0086]

[0087] Among them, the energy of the scattered echo of the non-cooperative SAR signal will be affected by the transmission path r R , the target scattering characteristics σ are different. In order to accurately invert the actual irradiation area of ​​the non-cooperative SAR beam, it is necessary to modify the scattering signal energy distribution model of the corresponding area: Assuming that the perigee slant distance of the ground detection antenna beam scanning area is r0, when the beam is scanned along the range direction, the pitch angle is The satellite height of the spaceborne passive SAR is h, and the echo energy obtained by the pulse pressure accumulation in the range and azimuth is P. After considering the path attenuation, the echo energy at this point is corrected to

[0088]

[0089] Considering the distribution of scattering characteristics of ground targets, in order to avoid the existence of strong scattering targets outside the non-cooperative SAR illumination area, which may cause the leakage signal echo to be received by the ground detection antenna and cause misjudgment, the scanning area can be partitioned and the scattering cross-sectional area parameter in formula (10) can be modified to σ′.

[0090] As can be seen from the examples above, this invention does not involve overly complex computations. The rapid two-dimensional time-frequency estimation of non-cooperative SAR direct signals, as well as echo-based non-cooperative SAR beam pointing estimation, offer high on-orbit processing efficiency. Compared to active bistatic detection, this system, by introducing a zenith antenna sensing system, effectively utilizes existing non-cooperative SAR signals in space for passive detection, resulting in excellent concealment. Furthermore, the perception of multidimensional spatial information involves a multi-objective particle swarm optimization algorithm, which, along with subsequent spatial search and imaging processing, can be implemented using parallel computing, offering advantages such as high computational efficiency and real-time performance.

[0091] The proposed intelligent sensing and multi-dimensional parameter estimation technology for non-cooperative SAR satellite signals does not require any prior information. Instead, it uses a zenith array antenna to autonomously sense non-cooperative SAR signals in space. It accurately estimates the multi-dimensional characteristics of non-cooperative SAR signals, including their time domain (including signal duration, pulse repetition period, etc.), frequency domain (including center frequency and bandwidth, etc.), and spatial domain (including non-cooperative SAR satellite trajectory, antenna beam pointing, etc.). It then guides the ground detection antenna beam toward the area illuminated by the non-cooperative SAR satellite's antenna beam to receive and process the echo signal, thereby enabling ground imaging observation. This new invention utilizes signals from all in-orbit SAR satellites, eliminating the need to transmit high-power signals, significantly reducing system costs and offering excellent concealment.

[0092] The present application provides a computer-readable storage medium storing computer instructions. When the computer instructions are executed on a computer, the computer executes Figure 3 The method described.

[0093] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage and optical storage, etc.) that contain computer-usable program code.

[0094] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0095] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0096] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 The steps for the function specified in one or more boxes.

[0097] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

[0098] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A non-cooperative signal sensing system for spaceborne passive SAR, characterized by: It includes zenith sensing antenna, direct signal array receiving unit, ground detection antenna, and echo signal array receiving unit; The zenith sensing antenna is used to receive the sidelobe transmission signal of the non-cooperative SAR satellite antenna, generate a four-channel direct signal through a sum-and-difference network, and send it to the direct signal array receiving unit; The direct signal array receiving unit is used to perform sum and difference beam angle measurement, differential Doppler positioning and time-frequency parameter search processing on the direct signal, generate non-cooperative SAR signal time-frequency estimation parameters and send them to the echo signal array receiving unit; The ground detection antenna is used to receive the echo signal of the ground search area, generate the beam pointing area echo signal through DBF multi-channel processing, and send it to the echo signal array receiving unit; The echo signal array receiving unit is used to perform parallel pulse compression and azimuth coherent accumulation processing on the ground echo signal, generate an echo energy distribution model and output a non-cooperative SAR antenna beam pointing, and finally complete the perception of the non-cooperative signal.

2. The non-cooperative signal sensing system for spaceborne passive SAR according to claim 1, characterized in that: The zenith sensing antenna adopts a two-dimensional planar array antenna of X band, which is symmetrically divided into four-quadrant distributed sub-arrays, and realizes sum and difference beam amplitude ratio angle measurement through digital or analog methods.

3. The non-cooperative signal sensing system for spaceborne passive SAR according to claim 1, characterized in that: The direct signal array receiving unit includes four independent down-conversion receiving channels, each of which includes a radio frequency bandpass filter, a variable gain amplifier, a mixer, an intermediate frequency bandpass filter, an intermediate frequency low noise amplifier and an analog-to-digital converter, and is used to input the sampled digital signal into the processor module; The processor module is used to complete signal parameter estimation and then feed back the center frequency to the programmable local oscillator source to produce a more matching local oscillator frequency, making the mixed intermediate frequency direct signal easier to be sampled by the analog-to-digital converter, thereby reducing the sampling frequency and data rate; the estimated parameters include the center frequency, bandwidth, and time width of the non-cooperative SAR signal.

4. The non-cooperative signal sensing system for spaceborne passive SAR according to claim 1, characterized in that: The ground detection antenna adopts an X-band two-dimensional multi-channel array antenna.

5. The non-cooperative signal sensing system for spaceborne passive SAR according to claim 4, characterized in that: The array aperture of the ground detection antenna is L×W, where L>6m and W>1m.

6. The non-cooperative signal sensing system for spaceborne passive SAR according to claim 4, characterized in that: The number of channels of the ground detection antenna is P×Q, and the number of sub-array units corresponding to each channel is M p ×M q , p=1,2,…,P,q=1,2,…,Q,the azimuth direction is realized by sub-array level digital beamforming Two-dimensional beam scanning in the range direction ±θ, where θ∈[10°~30°], the antenna pattern sidelobe is better than -13dB and the grating lobe is better than -15dB during scanning.

7. The non-cooperative signal sensing system for spaceborne passive SAR according to claim 1, characterized in that: The echo signal array receiving unit includes P×Q independent receiving channels, each of which includes a radio frequency bandpass filter, a variable gain amplifier, a mixer, an intermediate frequency bandpass filter, an intermediate frequency low noise amplifier, and an analog-to-digital converter, which is used to input the sampled digital signal into the processor module; The processor module completes I / Q demodulation, DBF, range pulse compression, and azimuth incoherent accumulation of the intermediate frequency echo signal to obtain an echo signal with a high signal-to-noise ratio, which is used for two-dimensional search and estimation of the non-cooperative SAR antenna beam pointing.

8. A method for estimating multidimensional parameters of non-cooperative signals of spaceborne passive SAR, characterized in that: The steps include: 1) The direct signal received by the zenith sensing antenna passes through the sum-difference network and is fed into the direct signal array receiving unit. The programmable array source is mixed with the direct sum signal. The non-cooperative signal time width Rough estimate; the bandwidth is obtained by fast Fourier transform The center frequency is Doppler frequency Real-time estimation of multi-dimensional parameters; 2) Build an optimization model that aims to optimize the impulse response width, peak sidelobe ratio, and integrated sidelobe ratio of the direct signal after pulse compression. Utilize the particle swarm optimization algorithm to perform a rapid search in the two-dimensional time-frequency support domain to obtain the optimal estimation of the time-frequency parameters of the non-cooperative SAR signal. 3) In the direct signal array receiving unit, based on the time-frequency parameter estimation results of the non-cooperative SAR signal, the direct signal of the sum and difference beam channels is subjected to amplitude angle measurement and differential Doppler solution to obtain the relative spatial position estimation of the non-cooperative SAR satellite and the passive SAR. The non-cooperative SAR trajectory is fitted using an improved extended Kalman filter tracking algorithm. 4) The direct signal array receiving unit sends the non-cooperative SAR time-frequency estimation parameters to the echo signal array receiving unit; 5) Based on the spatial relationship between the passive SAR and the non-cooperative SAR, the ground detection antenna directs the multi-channel antenna to the potential ground imaging area through DBF weighted synthesis of narrow beams to search and receive echo signals; 6) In the echo signal array receiving unit, a parallel FPGA platform is used to implement I / Q demodulation, DBF beam scanning, range pulse compression, and azimuth coherent accumulation processing on the echo signal to obtain the echo signal power distribution of the ground imaging area; 7) The echo signal array receiving unit modifies the echo power distribution model obtained by DBF beam scanning, compensates for the power attenuation difference of the echo caused by different paths in the pitch plane, and obtains the modified echo power distribution of the search area; selects the strongest power point as the center of the non-cooperative SAR imaging area, and thus solves the azimuth and range beam pointing estimation of the non-cooperative SAR 8) At this point, the time-frequency and spatial parameter estimation of the non-cooperative SAR signal is complete, and the ground-based antenna directs the beam toward the corresponding area to achieve dual-station passive SAR imaging. The entire process is carried out in real time on orbit, completing continuous estimation and imaging processing.

9. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method according to claim 8 are implemented.

10. A non-cooperative signal perception system and multi-dimensional parameter estimation device for spaceborne passive SAR, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to claim 8 are implemented.

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