Space-based radar clutter suppression method based on multi-domain cascade processing

Abstract

The invention discloses a space-based radar clutter suppression method based on multi-domain cascade processing. The method comprises the following steps: designing a linear frequency modulation signal and a phase coding signal; designing a first waveform signal based on pulse width frequency modulation polarity agility and linear frequency modulation by changing the frequency modulation polarity of the linear frequency modulation signal, and designing a second waveform signal based on phase coding, pulse width frequency modulation polarity agility and linear frequency modulation according to the phase coding signal and the first waveform signal; based on a minimum peak sidelobe energy criterion, designing an orthogonal waveform signal group about the second waveform signal by adopting an SQP algorithm; clutter space-time snapshot data are calculated according to the orthogonal waveform signal group; designing a matched filter according to the orthogonal waveform signal group and filtering clutter space-time snapshot data; calculating a weight coefficient of a space-time two-dimensional filter according to the filtered clutter space-time snapshot data by adopting a 3DT-STAP algorithm; and calculating a clutter suppression result according to the filtered clutter space-time snapshot data and the weight coefficient of the space-time two-dimensional filter.

Description

Technical Field

[0001] This invention belongs to the field of radar signal processing technology, specifically relating to a space-based radar clutter suppression method based on multi-domain cascaded processing. Background Technology

[0002] Space-based early warning radar is a core piece of equipment for achieving rapid, all-weather, 24 / 7 early warning of weak moving targets in wide-area air and near-space, possessing strategic advantages such as wide coverage, high power, and anti-stealth capabilities. However, due to its platform operating in satellite orbit at extremely high speeds and being affected by the Earth's rotation, the space-time coupling relationship of clutter varies with the range cell. Severe range ambiguity further exacerbates this phenomenon, resulting in an extremely complex and non-stationary clutter environment for space-based radar in moving target detection. This drastically degrades the space-time adaptive processing performance directly adapted from airborne radar. Therefore, clutter suppression is a core challenge in space-based radar systems.

[0003] Existing space-based radar carrier suppression schemes mostly suffer from a series of key technical challenges caused by non-stationary clutter and severe range ambiguity: 1) The problem of suppression mismatch caused by the variation of clutter space-time spectrum with distance cell needs to be addressed. Existing classical space-time adaptive processing techniques based on the stationarity assumption cannot adapt to the rapid changes in the severe non-stationarity of the clutter spectrum, resulting in a mismatch between the estimated clutter covariance matrix and the true clutter covariance matrix, and a significant decrease in clutter suppression performance.

[0004] 2) The challenge of clutter suppression in the short-range severe range ambiguity region—the area with the most severe non-stationarity—requires a breakthrough. The range ambiguity effect in the short-range region compresses and superimposes geographically incoherent clutter with varying statistical characteristics into the same observation data. This superposition not only amplifies the nonlinear modulation effect caused by the yaw angle but also introduces the most extreme clutter environment, becoming the main area where existing algorithms fail and severely limiting the ability to detect weak moving targets.

[0005] 3) The impact of clutter non-stationarity on system performance and reliability needs to be addressed. Complex and intense clutter severely obscures weak moving target signals, directly limiting the radar's detection capability in strong clutter backgrounds. Simultaneously, mismatched clutter suppression can trigger numerous false alarms, leading to unreliable radar output and impacting decision-making effectiveness. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, this invention provides a space-based radar clutter suppression method based on multi-domain cascaded processing. The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides a space-based radar clutter suppression method based on multi-domain cascaded processing, the space-based radar clutter suppression method comprising: Establish a clutter signal model for a planar array space-based early warning radar; Design linear frequency modulated signals and phase-coded signals with waveforms of different pulse widths; By changing the frequency modulation polarity of the linear frequency modulation signal, a first waveform signal based on pulse width modulation polarity agility and linear frequency modulation is designed, and a second waveform signal based on phase encoding, pulse width modulation polarity agility and linear frequency modulation is designed according to the phase encoding signal and the first waveform signal. Based on the criterion of minimizing peak sidelobe energy and using the SQP algorithm, an orthogonal waveform signal group for the second waveform signal is designed. Based on the clutter signal model of a planar array space-based early warning radar, clutter space-time snapshot data is calculated according to orthogonal waveform signal groups. Design a matched filter based on the orthogonal waveform signal group, and perform filtering processing on clutter space-time snapshot data based on the matched filter; The 3DT-STAP algorithm is used to adaptively calculate the weight coefficients of the 3DT-STAP space-time two-dimensional filter based on the filtered clutter space-time snapshot data, and to calculate the clutter suppression result based on the filtered clutter space-time snapshot data and the weight coefficients of the 3DT-STAP space-time two-dimensional filter.

[0007] The beneficial effects of this invention are: This invention proposes a clutter suppression method for space-based radar based on multi-domain cascaded processing. This method addresses the severe range ambiguity and clutter propagation problems caused by Earth's rotation and platform characteristics. It proposes a clutter suppression method based on a multi-domain cascaded approach involving the transmitted signal processing domain, Doppler domain, and spatial domain. Specifically, this method fully utilizes the flexibility of digital antenna arrays by introducing orthogonal waveform signals at the transmitting end to preprocess range-ambiguous clutter, thereby reducing the degree of freedom of received clutter. Then, 3DT-STAP (3D Space-Time Adaptive Processing) processing is performed in the Doppler-spatial domain. The orthogonal waveform signals are designed based on phase coding, pulse width modulation polarity agility, and linear frequency modulation, resulting in better orthogonality and suitability for space-based radar applications. Compared to existing technologies, this invention reduces the processing flow and algorithm complexity. The clutter preprocessing stage only requires matched filtering to significantly reduce the impact of range ambiguity. By leveraging the good orthogonality of the transmitted signal waveform, unwanted ambiguity clutter is suppressed to a certain level, improving the suppression performance of range ambiguity components in the clutter. Then, the data is directly fed into 3DT-STAP processing to suppress the remaining clutter, further enhancing clutter suppression performance. Therefore, this invention proposes a two-stage processing architecture. The first stage separates short-range ambiguity clutter by using the orthogonality of the transmitted signal to suppress unwanted ambiguity clutter. The second stage suppresses long-range ambiguity clutter by using 3DT-STAP processing. Without expanding the system dimension, this effectively separates short-range non-stationary clutter from long-range stationary clutter, eliminating the impact of range ambiguity and improving the estimation accuracy of the clutter covariance matrix. In summary, in the extremely complex environment of space-based radar with severe range ambiguity and non-stationary clutter, the key technological bottleneck to advance space-based early warning radar from concept to engineering application is to achieve efficient and robust clutter suppression by utilizing the limited computing resources on the satellite, so as to ensure reliable detection capability of weak moving targets.

[0008] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0009] Figure 1 This is a flowchart illustrating a space-based radar clutter suppression method based on multi-domain cascaded processing provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the geometric structure of the clutter signal model of the planar array space-based early warning radar provided in the embodiment of the present invention; Figure 3 This is a schematic diagram of the PWFMP-LFM-PC waveform provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the 3DT-STAP processing framework provided in an embodiment of the present invention; Figures 5(a) to 5(b)This is a schematic diagram comparing the PCCL values ​​of the orthogonal waveforms of PWFMP-LFM-PC optimized using the SQP method in this invention; Figures 6(a) to 6(b) This is a schematic diagram comparing the range-Doppler images of the received signal after clutter suppression using the traditional STAP algorithm and the method proposed in this invention. Figure 7 This is a schematic diagram comparing the SCNRloss results of the traditional STAP algorithm and the method proposed in this invention after clutter suppression of the received signal. Detailed Implementation

[0010] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0011] Please see Figure 1 This invention provides a space-based radar clutter suppression method based on multi-domain cascaded processing, specifically including the following steps: S10. Establish a clutter signal model for a planar array space-based early warning radar.

[0012] The geometric structure of the clutter signal model of the planar array space-based early warning radar established in this embodiment of the invention is as follows: Figure 2 As shown: The platform is located at a height At that location, and at a constant speed Movement. Assume there is a clutter block. The slant range between the radar clutter blocks is used Indicates. Point and points These correspond to the sub-satellite point and the Earth's center, respectively. Represents the radius of the Earth. Assume the space-based early warning radar uses a uniform planar array, which contains [variables] in the azimuth and elevation dimensions, respectively. One and Each array element. Point This represents the position of the planar array. The antenna array is placed in a Cartesian coordinate system. of On the plane, among which The axis is perpendicular to the array plane. The axis corresponds to the orientation of the array. The axis is determined by the right-hand rule. Furthermore, Represents azimuth. Represents the pitch angle.

[0013] For a uniform planar array, the time-domain steering vector corresponding to any clutter block or target... and azimuth spatial guidance vector They are respectively: (1); (2); in, This indicates the number of pulses during the coherent processing time. This indicates the transpose operation. These represent the azimuth and elevation angles of the clutter block or the target, respectively. and These are the normalized Doppler frequency and normalized azimuth spatial frequency corresponding to the clutter block or target, respectively: (3); (4); in, The operating wavelength of the radar; The pulse repetition frequency; The spacing between array elements; and These are the yaw angle and yaw magnitude, respectively, caused by the Earth's rotation, and are only related to the satellite's orbital inclination and current latitude.

[0014] according to Figure 1 The geometric structure of the space-based early warning radar system shown can be used to calculate the first... The clutter spacetime snapshot data for each distance gate is represented as follows: (5); in, and These represent the number of ambiguous range rings and the number of clutter blocks on a single range ring, respectively. Indicates the first On the fuzzy distance ring, the first The echo amplitude of each clutter block is related to factors such as radar transmit power, antenna gain, clutter block cross-section, terrain scattering coefficient, and slant distance between the radar and the clutter block. This represents the space-time steering vector corresponding to clutter. Indicates the first On the fuzzy distance ring, the first The time-domain steering vector of each clutter block, Indicates the first On the fuzzy distance ring, the first The azimuth spatial steering vector of each clutter block This represents the Kronecker product between matrices. Assume a noisy signal. It is zero-mean Gaussian white noise with variance of .

[0015] Since each clutter block is statistically independent, the corresponding clutter covariance matrix of this clutter data can be expressed as: (6); in, Indicates taking the expected value. This indicates the conjugate transpose operation. This indicates the modulo operation. Represents the identity matrix.

[0016] In practical engineering, clutter covariance matrix Maximum likelihood estimation is typically used. Instead, this estimate is obtained by averaging the distances between adjacent gates, as follows: (7); in, Indicates the number of doors at a distance.

[0017] By minimizing output noise and clutter power while maintaining the target energy, the weighting coefficients of the space-time two-dimensional filter can be obtained: (8); in, These are the azimuth and elevation angles corresponding to the target, respectively. This represents the space-time steering vector corresponding to the target, similar to clutter block calculation. , The time-domain steering vector corresponding to the target can be calculated using formula (1). The azimuth spatial steering vector corresponding to the target can be calculated using formula (2). express The conjugate transpose operation. This indicates the inverse operation.

[0018] S20. Design linear frequency modulated signals and phase-coded signals with waveforms of different pulse widths.

[0019] This invention first designs linear frequency modulated signals and phase-coded signals with waveforms of different pulse widths.

[0020] The designed linear frequency modulated signal is represented as: (9); in, express Time of the first The linear frequency modulated signal corresponding to each waveform. Indicates the first The pulse width corresponding to each waveform , Indicates the number of waveforms. Indicates the modulation phase number, Represents a rectangular window function; The designed phase-coded signal is represented as: (10); in, express Time of the first The phase-encoded signal corresponding to each waveform. Indicates the first The phase modulation sequence corresponding to the i-th waveform Phase modulation value of each symbol, , , This indicates the number of symbols in the phase modulation sequence corresponding to each waveform. , express Time of the first The waveform corresponds to the phase modulation sequence of the th wave An ideal rectangular pulse of one code element .

[0021] S30. Design a first waveform signal based on pulse width modulation polarity agility and linear frequency modulation by changing the frequency modulation polarity of the linear frequency modulation signal, and design a second waveform signal based on phase encoding, pulse width modulation polarity agility and linear frequency modulation according to the phase encoding signal and the first waveform signal.

[0022] The first waveform signal based on pulse width modulation polarity agility and linear frequency modulation designed in this embodiment of the invention is represented as follows: (11); in, express Time of the first The first waveform signal corresponding to each waveform is denoted as the PWFMP-LFM signal. , Indicates the number of waveforms. Indicates the first The pulse width of each waveform Indicates the first The random non-negative integers corresponding to each waveform are used to change the frequency modulation polarity, that is, to determine the polarity of the LFM signal's frequency modulation frequency. Odd numbers indicate a negative frequency modulation polarity, and even numbers indicate a positive frequency modulation polarity. Indicates bandwidth.

[0023] The embodiments of this invention design different pulse widths through two methods: pulse width sliding and pulse width jumping. The pulse width sliding method includes pulse width decreasing at equal intervals and pulse width that is larger in the middle and smaller at both ends. Specifically: Assuming the pulse width is constant, , This is the pulse width variation coefficient, and the range of pulse width variation is... , No. The actual pulse width of each waveform is The amount of pulse width variation at equal intervals Defined as , This indicates the waveform number. There are two common modes of pulse width slip: the first is where the pulse width decreases at equal intervals, i.e. The second type is characterized by a pulse width that is wider in the middle and narrower at both ends. The pulse width jump becomes the pulse width at... Randomly select a value from the middle, that is .

[0024] Furthermore, phase modulation of the PWFMP-LFM signal in the time domain yields a second waveform signal, denoted as the PWFMP-LFM-PC signal. The specifically designed second waveform signal, based on phase coding, pulse width modulation polarity agility, and linear frequency modulation, is expressed as: (12); in, express Time of the first The second waveform signal corresponding to each waveform. , Indicates the number of waveforms. express Time of the first The first waveform signal corresponding to each waveform. express Time of the first The phase-encoded signal corresponding to each waveform. Indicates the first The phase modulation sequence corresponding to the i-th waveform Phase modulation value of each symbol, , , This indicates the number of symbols in the phase modulation sequence corresponding to each waveform. , Indicates the modulation phase number, express Time of the first The waveform corresponds to the phase modulation sequence of the th wave An ideal rectangular pulse of one code element , Represents a rectangular window function. Indicates the first The pulse width corresponding to each waveform. Figure 3 This diagram illustrates a set of PWFMP-LFM-PC signals, where PRT is the pulse repetition frequency. Each waveform has a corresponding pulse width and frequency modulation polarity, and each waveform undergoes different phase-coded modulation. The phase-coded modulation function is... .

[0025] S40. Based on the criterion of minimizing peak sidelobe energy and using the SQP algorithm, design an orthogonal waveform signal group for the second waveform signal.

[0026] This invention, based on the criterion of minimizing peak sidelobe energy and employing the SQP (Sequential Quadratic Programming) algorithm, designs an orthogonal waveform signal set for a second waveform signal. The process includes: designing an orthogonal waveform optimization model for the second waveform signal; the optimization objective of the orthogonal waveform optimization model is to minimize the peak sidelobe energy of the orthogonal waveform signal; wherein the peak sidelobe energy includes autocorrelation peak sidelobe energy and peak cross-correlation energy; and solving the orthogonal waveform optimization model using the SQP algorithm to obtain the orthogonal echo signal set. More specifically: The autocorrelation function of the PWFMP-LFM-PC signal designed in this embodiment of the invention can be expressed as follows: (13); The cross-correlation function of the PWFMP-LFM-PC signal can be expressed as: (14); The autocorrelation peak sidelobe energies of orthogonal waveforms are defined as follows: (15); The peak cross-correlation energy of orthogonal waveforms is: (16); By applying constrained nonlinear programming, an optimization model is established for the orthogonal waveform design problem. Specifically, the optimization model for the orthogonal waveform with respect to the second waveform signal is expressed as follows: (17); in, This represents the peak sidelobe energy of the autocorrelation of orthogonal waveform signals. Indicates adjustment and The proportion of , Indicates the number of waveforms. This represents the peak cross-correlation energy of orthogonal waveform signals. , Indicates the first The waveforms correspond to... The autocorrelation function, Indicates time delay. Indicates the width of the main lobe. Indicates the first The waveforms correspond to... The cross-correlation function, This indicates the modulo operation.

[0027] The above problem is a typical nonlinear constraint problem. Many mathematical optimization software programs have modules that can be directly called during simulation. For example, in MATLAB, the fmincon function in the optimization toolkit can be used to obtain a near-optimal solution. This invention uses the SQP algorithm to solve the orthogonal waveform optimization model and obtains a set of orthogonal waveform signals related to the second waveform signal.

[0028] S50: Based on the clutter signal model of a planar array space-based early warning radar, calculate clutter space-time snapshot data according to orthogonal waveform signal groups.

[0029] In this embodiment of the invention, orthogonal waveform signals are transmitted in a time-division multiplexing manner at the transmitting end, meaning that the signals transmitted at each transmission time are mutually orthogonal, and a total of [number] signals are transmitted. The transmitted signal uses an orthogonal waveform signal group designed for PWFMP-LFM-PC using the S40 architecture. It is assumed that the number of transmitted orthogonal waveform signals is equal to the number of ambiguous range loops in the received clutter, i.e. = Then, based on the orthogonal waveform signal group, the clutter space-time snapshot data is calculated and converted from formula (5) to: (18); in, Indicates the first Spacetime snapshot data of clutter at a distance gate This indicates the number of clutter blocks on a single range ring. This indicates the number of orthogonal waveform signals in the orthogonal waveform signal group. Indicates the first On the fuzzy distance ring, the first The azimuth angle of each clutter block. Indicates the first On the fuzzy distance ring, the first The pitch angle of each clutter block, Indicates the first On the fuzzy distance ring, the first The echo amplitude of each clutter block, Indicates the clutter spacetime steering vector. Indicates the first On the fuzzy distance ring, the first The time-domain steering vector of each clutter block, Indicates the first On the fuzzy distance ring, the first The azimuth spatial steering vector of each clutter block Represents the Kronecker product between matrices. In the quadrature waveform signal group, the first... The second waveform signal, Indicates the first The distance to the door is the first The first clutter block A vague distance, Represents the speed of light. This indicates a noise signal.

[0030] S60. Design a matched filter based on the orthogonal waveform signal group, and perform filtering processing on the clutter space-time snapshot data based on the matched filter.

[0031] To distinguish echo signals at ambiguous locations at different distances, this embodiment of the invention selects the desired echo signal at the receiving end. This requires designing a suitable matched filter according to timing to filter the received signal. Specifically, this matched filter can be designed as follows: (19); in, This represents the initial time. After matched filtering by the matched filter, the [time value is missing]. The signal of a distance gate can be represented as: (20); in, Indicates the first The amplitude and phase information of a waveform after it has passed through a matched filter.

[0032] S70. The 3DT-STAP algorithm is adopted to adaptively calculate the weight coefficients of the 3DT-STAP space-time two-dimensional filter based on the filtered clutter space-time snapshot data, and calculate the clutter suppression result based on the filtered clutter space-time snapshot data and the weight coefficients of the 3DT-STAP space-time two-dimensional filter.

[0033] After matched filtering of the received signal at the receiving end, short-range clutter and some long-range clutter in the received signal are suppressed, and clutter non-stationarity is greatly reduced. However, due to the limited number of orthogonal waveform signals in the orthogonal waveform signal group... The number of ambiguity range rings is generally smaller than that of clutter. Therefore, there is still a significant amount of long-range clutter that needs further suppression. Here, 3DT-STAP is used to handle long-range stationary clutter.

[0034] In this embodiment of the invention, time-domain Doppler filtering is first performed on the received data from each channel to constrain clutter to a finite number of Doppler channels. Then, the outputs of several of these Doppler channels are selected for adaptive processing. A larger number of selected Doppler channels results in better clutter suppression, but also increases the computational load. Here, selecting three Doppler channels, i.e., 3DT-STAP, is the most suitable option considering both suppression effectiveness and computational complexity. Specifically, this embodiment of the invention employs the 3DT-STAP algorithm, adaptively calculating the 3DT-STAP space-time two-dimensional filter weight coefficients based on the filtered clutter space-time snapshot data. This includes: constructing a Doppler domain transformation matrix based on the number of Doppler channels; extracting three columns of data from the Doppler domain transformation matrix corresponding to the Doppler channel where the target is located and the multiple ordinary channels on both sides of the target to form a Doppler filter bank; designing the 3DT-STAP transformation matrix based on the Doppler filter bank; transforming the filtered clutter space-time snapshot data using the 3DT-STAP transformation matrix to obtain transformed clutter space-time snapshot data; calculating the target's 3DT-STAP space-time steering vector based on the 3DT-STAP transformation matrix; calculating the 3DT-STAP clutter covariance matrix based on the transformed clutter space-time snapshot data; and calculating the 3DT-STAP space-time two-dimensional filter weight coefficients based on the 3DT-STAP clutter covariance matrix and the target's 3DT-STAP space-time steering vector. More specifically: First, construct the Doppler domain transformation matrix. Time-domain filtering of the data involves processing the data in the Doppler domain, and its expression is as follows: (twenty one); in, This represents the number of Doppler channels. (In the context of using the...) When filtering the Doppler channel, the first Doppler domain transformation matrix should be selected. Columns are represented as: (twenty two); Next, the United Nations and Each Doppler channel forms a Doppler filter bank, from which the transformation matrix for 3DT-STAP can be obtained. : (twenty three); in, , This represents the data in the Doppler channel where the target is located within the Doppler domain transformation matrix. This represents the data from multiple ordinary channels on both sides of the target in the Doppler domain transformation matrix.

[0035] Then, after Doppler filtering, the first The distance gate data becomes: (twenty four); The space-time steering vector of 3DT-STAP is: (25); Finally, the weighting coefficients of the 3DT-STAP spatiotemporal two-dimensional filter are calculated and expressed as follows: (26); in, This represents the space-time two-dimensional filter weighting coefficients of 3DT-STAP. This represents the clutter covariance matrix of 3DT-STAP. , Indicates the first Clutter spacetime snapshot data after transformation by a range gate, This indicates the conjugate transpose operation. Indicates the number of doors at a distance. express The inverse operation, , Represents the transformation matrix of 3DT-STAP. express The conjugate transpose operation. , Indicates the Doppler filter bank. This represents the data in the Doppler channel where the target is located within the Doppler domain transformation matrix. This represents the data from multiple ordinary channels on both sides of the target in the Doppler domain transformation matrix. , This indicates the transpose operation. Indicates the number of Doppler channels. Describes the first element in the Doppler domain transformation matrix. Data from each Doppler channel, Denotes the Doppler domain transformation matrix. express The identity matrix, Represents the Kronecker product between matrices. Indicates the first Clutter spacetime snapshot data after filtering by a distance gate express The conjugate transpose operation.

[0036] Finally, the weighting coefficients of the space-time two-dimensional filter are... Applied to the The clutter suppression result after processing by the 3DT-STAP algorithm with a range gate can be expressed as follows: (27).

[0037] in, Indicates the first Clutter suppression results for each distance gate, express The conjugate transpose operation.

[0038] As can be seen, this embodiment of the invention designs mutually orthogonal pulse signals and transmits these signals sequentially at different slow moments at the transmitting end. Within a single receiving moment, the echo signal received by the two-dimensional phased array antenna is an incoherent superposition of different transmitted pulse echoes from ambiguous distance positions. After matching filtering the received superimposed signal for each channel, thanks to the orthogonality between the different pulse signals, some clutter energy from ambiguous distance positions can be effectively suppressed. Then, using... Figure 4 The 3DT-STAP algorithm shown processes spatial data from different slow reception times to obtain output data that can be used for weak moving target detection after clutter is fully suppressed.

[0039] To verify the effectiveness of the space-based radar clutter suppression method based on multi-domain cascaded processing provided in this embodiment of the invention, the following experiments were conducted.

[0040] Experiment 1: PWFMP-LFM-PC Waveform Design This invention verifies the performance of the designed waveform through simulation. The parameter settings are as follows: bandwidth of the LFM signal. When the pulse width is constant, the pulse width is The code length of the phase-coded signal , number of waveforms . Table 1 Performance of Orthogonal Waveform Signals

[0041] Figures 5(a) to 5(b) Figure 5(a) illustrates the comparison of PCCL (Pulse Compression Sidelobe Level) values ​​for the orthogonal waveforms of PWFMP-LFM-PC optimized using the SQP algorithm of this invention. Figure 5(a) shows the PCCL value for the traditional orthogonal encoding, and Figure 5(b) shows the PCCL value for the orthogonal waveforms of PWFMP-LFM-PC optimized using the SQP method of this invention. The PCCL value characterizes the cross-correlation of the waveforms. (From Table 1 and...) Figures 5(a) to 5(b)As can be seen, the PCCL value of the orthogonal waveform of the PWFMP-LFM-PC designed in this invention is 6.82dB lower than the PCCL value of the orthogonal coding. This indicates that the optimized PWFMP-LFM-PC signal has good orthogonal performance and can use the designed orthogonal PWFMP-LFM-PC waveform as a radar transmission signal, suppressing short-range clutter components and some long-range clutter components in the received signal through matched filtering.

[0042] Experiment 2: Analysis of Clutter Suppression Performance Assume the radar platform operates at an altitude of 506 km, has a transmit power of 1.25 GHz, a pulse repetition frequency of 4 kHz, a bandwidth of 4 MHz, an antenna array in a frontal side view, 288 antenna row elements, 12 antenna column elements, a main beam azimuth of 90°, a main beam elevation of 37°, and 64 pulses per CPI (Coherent Processing Interval).

[0043] like Figures 6(a) to 6(b) As shown in Figures 6(a) and 6(b), the received signals after clutter suppression are obtained using the traditional STAP (Space-Time Adaptive Processing) algorithm and the method proposed in this invention, respectively. It can be seen that the method proposed in this invention effectively suppresses short-range clutter and some long-range clutter to a certain extent. The range-Doppler images no longer show obvious short-range curved spectral lines, and some long-range ambiguity components are also suppressed.

[0044] The SCNR (Signal-to-Clutter-plus-Noise Ratio) loss result is as follows: Figure 7 As shown. From Figure 7 As can be seen, the traditional STAP algorithm (shown by the black line) suffers significant performance loss at both near-end and far-end ambiguity components, resulting in a wide notch in its SCNR loss curve. In contrast, the algorithm proposed in this invention (shown by the red line) exhibits better suppression performance at near-range clutter components and some far-range clutter components, with a much narrower notch width compared to the traditional algorithm.

[0045] In summary, the space-based radar clutter suppression method based on multi-domain cascaded processing proposed in this invention addresses the severe range ambiguity and clutter propagation problems caused by Earth's rotation and platform characteristics. This method proposes a clutter suppression approach based on a multi-domain cascaded transmission signal processing domain—Doppler domain—spatial domain. Specifically, this method fully utilizes the flexibility of digital antenna arrays by introducing orthogonal waveform signals at the transmitting end to preprocess range ambiguity clutter, thereby reducing the degree of freedom of received clutter. Then, 3DT-STAP processing is performed in the Doppler-spatial domain. The orthogonal waveform signals are designed based on phase coding, pulse width modulation polarity agility, and linear frequency modulation, resulting in better orthogonality and suitability for space-based radar applications. Compared to existing technologies, this invention reduces the processing flow and algorithm complexity. The clutter preprocessing stage only requires matched filtering to significantly reduce the impact of range ambiguity. By leveraging the good orthogonality of the transmitted signal waveform, unwanted ambiguity clutter is suppressed to a certain level, improving the suppression performance of range ambiguity components in the clutter. Then, the data is directly fed into 3DT-STAP processing to suppress the remaining clutter, further enhancing clutter suppression performance. Therefore, this invention proposes a two-stage processing architecture. The first stage separates short-range ambiguity clutter by using the orthogonality of the transmitted signal to suppress unwanted ambiguity clutter. The second stage suppresses long-range ambiguity clutter by using 3DT-STAP processing. Without expanding the system dimension, this effectively separates short-range non-stationary clutter from long-range stationary clutter, eliminating the impact of range ambiguity and improving the estimation accuracy of the clutter covariance matrix. In summary, in the extremely complex environment of space-based radar with severe range ambiguity and non-stationary clutter, the key technological bottleneck to advance space-based early warning radar from concept to engineering application is to achieve efficient and robust clutter suppression by utilizing the limited computing resources on the satellite, so as to ensure reliable detection capability of weak moving targets.

[0046] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0047] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art, by reviewing the specification and accompanying drawings, will understand and implement other variations of the disclosed embodiments in carrying out the claimed invention. In the specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. While certain measures are described in different embodiments, this does not mean that these measures cannot be combined to produce good results.

[0048] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A space-based radar clutter suppression method based on multi-domain cascaded processing, characterized in that, The space-based radar clutter suppression method includes: Establish a clutter signal model for a planar array space-based early warning radar; Design linear frequency modulated signals and phase-coded signals with waveforms of different pulse widths; By changing the frequency modulation polarity of the linear frequency modulation signal, a first waveform signal based on pulse width modulation polarity agility and linear frequency modulation is designed, and a second waveform signal based on phase encoding, pulse width modulation polarity agility and linear frequency modulation is designed according to the phase encoding signal and the first waveform signal. Based on the criterion of minimizing peak sidelobe energy and using the SQP algorithm, an orthogonal waveform signal group for the second waveform signal is designed. Based on the clutter signal model of a planar array space-based early warning radar, clutter space-time snapshot data is calculated according to orthogonal waveform signal groups. Design a matched filter based on the orthogonal waveform signal group, and perform filtering processing on clutter space-time snapshot data based on the matched filter; The 3DT-STAP algorithm is used to adaptively calculate the weight coefficients of the 3DT-STAP space-time two-dimensional filter based on the filtered clutter space-time snapshot data, and to calculate the clutter suppression result based on the filtered clutter space-time snapshot data and the weight coefficients of the 3DT-STAP space-time two-dimensional filter.

2. The space-based radar clutter suppression method based on multi-domain cascaded processing according to claim 1, characterized in that, The designed linear frequency modulated signal is represented as: ； in, express Time of the first The linear frequency modulated signal corresponding to each waveform. Indicates the first The pulse width corresponding to each waveform , Indicates the number of waveforms. Indicates the modulation phase number, Represents a rectangular window function; The designed phase-coded signal is represented as: ； in, express Time of the first The phase-encoded signal corresponding to each waveform. Indicates the first The phase modulation sequence corresponding to the i-th waveform Phase modulation value of each symbol, , , This indicates the number of symbols in the phase modulation sequence corresponding to each waveform. , express Time of the first The waveform corresponds to the phase modulation sequence of the th wave An ideal rectangular pulse of one code element .

3. The space-based radar clutter suppression method based on multi-domain cascaded processing according to claim 1, characterized in that, The first waveform signal designed based on pulse width modulation polarity agility and linear frequency modulation is represented as follows: ； in, express Time of the first The first waveform signal corresponding to each waveform. , Indicates the number of waveforms. Indicates the first The pulse width of each waveform Indicates the first A random non-negative integer corresponding to each waveform is used to change the frequency modulation polarity. Indicates bandwidth.

4. The space-based radar clutter suppression method based on multi-domain cascaded processing according to claim 1, characterized in that, Different pulse widths can be designed using two methods: pulse width sliding and pulse width jumping. The pulse width sliding method includes pulse width decreasing at equal intervals and pulse width being larger in the middle and smaller at both ends.

5. The space-based radar clutter suppression method based on multi-domain cascaded processing according to claim 1, characterized in that, The designed second waveform signal, based on phase coding, pulse width modulation polarity agility, and linear frequency modulation, is represented as follows: ； in, express Time of the first The second waveform signal corresponding to each waveform. , Indicates the number of waveforms. express Time of the first The first waveform signal corresponding to each waveform. express Time of the first The phase-encoded signal corresponding to each waveform. Indicates the first The phase modulation sequence corresponding to the i-th waveform Phase modulation value of each symbol, , , This indicates the number of symbols in the phase modulation sequence corresponding to each waveform. , Indicates the modulation phase number, express Time of the first The waveform corresponds to the phase modulation sequence of the th wave An ideal rectangular pulse of one code element , Represents a rectangular window function. Indicates the first The pulse width corresponding to each waveform.

6. The space-based radar clutter suppression method based on multi-domain cascaded processing according to claim 1, characterized in that, Based on the criterion of minimizing peak sidelobe energy and using the SQP algorithm, an orthogonal waveform signal set for the second waveform signal is designed, including: Design an orthogonal waveform optimization model for the second waveform signal; the optimization objective of the orthogonal waveform optimization model is to minimize the peak sidelobe energy of the orthogonal waveform signal; wherein, the peak sidelobe energy includes the autocorrelation peak sidelobe energy and the peak cross-correlation energy; The SQP algorithm is used to solve the orthogonal waveform optimization model to obtain the orthogonal echo signal group.

7. The space-based radar clutter suppression method based on multi-domain cascaded processing according to claim 6, characterized in that, The designed orthogonal waveform optimization model for the second waveform signal is expressed as follows: ； in, This represents the peak sidelobe energy of the autocorrelation of orthogonal waveform signals. Indicates adjustment and The proportion of , Indicates the number of waveforms. This represents the peak cross-correlation energy of orthogonal waveform signals. , Indicates the first The waveforms correspond to... The autocorrelation function, Indicates time delay. Indicates the width of the main lobe. Indicates the first The waveforms correspond to... The cross-correlation function, This indicates the modulo operation.

8. The space-based radar clutter suppression method based on multi-domain cascaded processing according to claim 1, characterized in that, Based on the orthogonal waveform signal group, clutter space-time snapshot data is calculated and expressed as follows: ； in, Indicates the first Spacetime snapshot data of clutter at a distance gate This indicates the number of clutter blocks on a single range ring. This indicates the number of orthogonal waveform signals in the orthogonal waveform signal group. Indicates the first On the fuzzy distance ring, the first The azimuth angle of each clutter block. Indicates the first On the fuzzy distance ring, the first The pitch angle of each clutter block, Indicates the first On the fuzzy distance ring, the first The echo amplitude of each clutter block, This represents the space-time steering vector corresponding to clutter. In the quadrature waveform signal group, the first... The second waveform signal, Indicates the first The distance to the door is the first The first clutter block A vague distance, Represents the speed of light. This indicates a noise signal.

9. The space-based radar clutter suppression method based on multi-domain cascaded processing according to claim 1, characterized in that, The 3DT-STAP algorithm is used to adaptively calculate the 3DT-STAP space-time two-dimensional filter weight coefficients based on the filtered clutter space-time snapshot data, including: Construct the Doppler domain transformation matrix based on the number of Doppler channels; The three columns of data corresponding to the Doppler channel where the target is located and the multiple ordinary channels on both sides of the target are extracted from the Doppler domain transformation matrix to form a Doppler filter bank; Design the transformation matrix of 3DT-STAP based on the Doppler filter bank; Based on the transformation matrix of 3DT-STAP, the filtered clutter space-time snapshot data is transformed to obtain the transformed clutter space-time snapshot data. Calculate the spacetime steering vector of the target's 3DT-STAP based on the transformation matrix of 3DT-STAP; Calculate the clutter covariance matrix of 3DT-STAP based on the transformed clutter space-time snapshot data; Based on the clutter covariance matrix of 3DT-STAP and the space-time steering vector of the target 3DT-STAP, calculate the space-time two-dimensional filter weighting coefficients of 3DT-STAP.

10. The space-based radar clutter suppression method based on multi-domain cascaded processing according to claim 1, characterized in that, The weighting coefficients of the space-time two-dimensional filter in 3DT-STAP are calculated as follows: ； in, This represents the space-time two-dimensional filter weighting coefficients of 3DT-STAP. This represents the clutter covariance matrix of 3DT-STAP. , Indicates the first Clutter spacetime snapshot data after transformation by a range gate, This indicates the conjugate transpose operation. Indicates the number of doors at a distance. express The inverse operation, , Represents the transformation matrix of 3DT-STAP. express The conjugate transpose operation. , Indicates the Doppler filter bank. This represents the data in the Doppler channel where the target is located within the Doppler domain transformation matrix. This represents the data from multiple ordinary channels on both sides of the target in the Doppler domain transformation matrix. , This indicates the transpose operation. Indicates the number of Doppler channels. Describes the first element in the Doppler domain transformation matrix. Data from each Doppler channel, Denotes the Doppler domain transformation matrix. express The identity matrix, Represents the Kronecker product between matrices. Indicates the first Clutter spacetime snapshot data after filtering by a distance gate These are the azimuth and elevation angles corresponding to the target, respectively. This represents the spacetime steering vector corresponding to the target. express The conjugate transpose operation.

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