Space-based early warning radar range ambiguity clutter suppression method and system based on secondary phase coding

Abstract

The invention discloses a space-based early warning radar range ambiguity clutter suppression method and system based on secondary phase coding, and mainly solves the problems that an existing range ambiguity clutter suppression technology is high in complexity and poor in clutter suppression performance. The implementation scheme comprises the following steps of: performing phase modulation on each transmitted pulse of the planar array space-based early warning radar by adopting a secondary phase coding technology; the planar array receives the phase modulation echo signal scattered by the ground clutter block and preprocesses the phase modulation echo signal to obtain clutter echo data; carrying out secondary phase decoding on the clutter echo data, and constructing an integral echo data vector by using the decoded clutter echo data vector; performing main clutter angle and Doppler spectrum center alignment on the overall echo data vector to obtain an aligned overall echo data vector; and filtering clutter components in the aligned overall echo data vector to obtain an output signal after clutter suppression. According to the method, the range ambiguity clutter suppression performance in the medium-orbit space-based early warning radar can be improved, the complexity is low, the hardware resource overhead is small, and the method can be used for detecting a low-speed moving target.

Description

Technical Field

[0001] The present invention belongs to the field of radar signal processing technology, and specifically relates to a method and system for suppressing range ambiguity clutter in a space-based early warning radar. The method and system are applicable to clutter suppression scenarios in a moving target detection system of a medium-orbit space-based early warning radar, and can effectively suppress range ambiguity clutter and improve the detection performance of low-speed moving targets. Background Art

[0002] Due to the long detection range of medium-orbit space-based early warning radars, clutter signals suffer from significant range ambiguity. Furthermore, due to the equivalent yaw effect caused by the Earth's rotation, clutter exhibits significant range dependence, known as clutter inhomogeneity. When range ambiguity and clutter range dependence interact, clutter components in different ambiguity range regions exhibit different frequency characteristics in the Doppler domain, resulting in a significant broadening of the mainlobe clutter spectrum in the Doppler dimension. This phenomenon makes it difficult for medium-orbit space-based early warning radar systems to obtain sufficient training samples that approximately satisfy the independent and identically distributed (IID) property, significantly reducing the clutter suppression performance of traditional space-time adaptive processing (STAP) techniques.

[0003] To address these issues, two representative range-ambiguous clutter suppression technologies have been proposed based on elevation-azimuth multi-channel space-based early warning radar systems: three-dimensional STAP (3D-STAP) and waveform diversity-based technologies. 3D-STAP combines elevation, azimuth, and Doppler information for adaptive processing, theoretically effectively suppressing range-ambiguous clutter. However, this technology relies heavily on the system's degrees of freedom, requiring the simultaneous use of multiple elevation and azimuth channels for adaptive processing. This significantly increases the number of independent and identically distributed training samples required, and the computational complexity is high, making it difficult to meet the real-time processing requirements of spaceborne systems. To alleviate these issues, some studies have proposed dimensionality reduction 3D-STAP technology to reduce the number of samples and computational burden. However, due to the loss of system degrees of freedom associated with dimensionality reduction, its mainlobe clutter suppression performance is significantly reduced.

[0004] Waveform diversity-based technologies achieve range-ambiguous clutter separation and suppression by modulating the carrier frequency, delay, and phase characteristics of the transmit waveform. Multiple-input, multiple-output (MIMO) technology effectively creates virtual transmit degrees of freedom and is suitable for new radar architectures, including frequency-diversity (FDA) arrays and element pulse coding (EPC) arrays. FDA-MIMO systems use frequency stepping to introduce range dependence into the signal phase, resulting in a larger spatial frequency separation of clutter at different ambiguity ranges within the transmit elevation spatial frequency domain. This allows elevation beamforming to extract and suppress clutter signals in specific range-ambiguous regions. EPC-MIMO systems, on the other hand, effectively separate range-ambiguous clutter components within the transmit spatial frequency domain by applying Fourier basis coding to the element pulse dimension, thereby achieving clutter suppression. However, waveform diversity-based technologies are limited by the non-ideal orthogonality of the transmit waveforms. Cross-correlation interference between waveforms can degrade subsequent clutter suppression performance. Furthermore, these technologies typically rely on MIMO systems for implementation, resulting in complex hardware architecture and processing flows, posing significant challenges in engineering applications.

[0005] Patent document CN202210967045.0 discloses a "Method and System for Non-Stationary Clutter Suppression in Space-Based Early Warning Radar." Its implementation steps include: transmitting signals from each azimuth transmitting element and encoding them in different pulses and azimuth transmitted signals; incrementally increasing the frequency of the antenna transmitting signals from each elevation element; performing down-conversion and analog-to-digital conversion, and storing the digitized echo data; synthesizing the digitized echo signal data into a single-channel receiving channel through elevation sub-arrays, and simultaneously synthesizing the echo signal receiving data in azimuth sub-arrays into a multi-channel receiving channel; performing matched filtering on each azimuth receiving channel to decode the transmitted signal for each azimuth; and designing an elevation spatial domain filter to perform space-time adaptive processing to filter out clutter. While this technology can solve the problem of range ambiguity clutter suppression in space-based early warning radar systems, it requires the transmitted code division waveform to have good orthogonality to ensure that the receiving end can effectively separate the transmitted signal through matched filtering. However, in real-world scenarios with densely distributed clutter scatterers, the integrated sidelobe ratio, resulting from the cross-correlation energy between code-divided signal echoes, degrades waveform separation and reduces range-ambiguous clutter suppression performance. Furthermore, this technical solution must be implemented within a MIMO system architecture, increasing the difficulty of system hardware design and the complexity of the signal processing process.

[0006] Patent application number CN201910604078.7 discloses a "range-ambiguity clutter suppression method based on extended azimuth phase coding." Its implementation steps include: using extended azimuth phase coding to phase-modulate the transmitted signal from each transmitting antenna to separate the spatial spectra of different ranges in the transmit spatial frequency domain; designing an EAPC offset factor and performing transmitter filtering to independently extract target and clutter echoes in each range-ambiguity region; applying azimuth de-skew to the extracted echoes to focus the energy of moving targets to the desired region; and employing an adaptive matched filtering algorithm to suppress clutter and detect moving targets. While this technique can suppress the interference of range-ambiguity clutter on moving target detection, its implementation still relies on a MIMO system. Due to the non-ideal orthogonality between the transmitted signals, it is difficult to achieve complete waveform separation at the receiver, resulting in insufficient extraction of the transmit dimensional degrees of freedom, thus reducing the effectiveness of range-ambiguity clutter separation. Furthermore, since this technique requires constructing filters for all range bins and transmitted pulses to extract echo signals from different range-ambiguity regions, it increases signal processing time. Summary of the Invention

[0007] The purpose of the present invention is to address the defects in the above-mentioned prior art and provide a method and system for suppressing range ambiguity clutter in space-based early warning radar based on secondary phase coding, so as to reduce the complexity of clutter suppression and improve the suppression performance of range ambiguity clutter.

[0008] The technical concept of the present invention is as follows: by designing secondary phase coding to phase modulate the coherent transmission pulse signal, the clutter echo signals in different range ambiguity zones have distinguishable characteristics in the transmission pulse dimension. This design does not require the use of a MIMO system architecture to distinguish different range ambiguity clutter in the transmission spatial frequency domain, which can reduce the complexity of clutter suppression; the receiving end implements secondary phase decoding processing matched with the transmission coding, which can achieve the shift and alignment of the clutter spectra of different range ambiguity in the Doppler dimension, significantly reducing the clutter spectrum broadening caused by multiple range ambiguities; the angle-Doppler clutter compensation algorithm is used to alleviate the distance dependence of clutter, thereby improving the range ambiguity clutter suppression performance; finally, a space-time adaptive processing algorithm is used to suppress clutter and detect moving targets.

[0009] According to the above ideas, the technical solution of the present invention includes:

[0010] 1. A method for suppressing range ambiguity clutter in a space-based early warning radar based on secondary phase coding, comprising:

[0011] Secondary phase coding is used to phase modulate each transmitted pulse signal of the planar array space-based early warning radar.

[0012] The planar array antenna receives the phase modulated echo signal scattered by the ground clutter block, and sequentially performs sub-array beamforming, down-conversion and matched filtering processing to obtain clutter echo data;

[0013] performing secondary phase decoding processing on the clutter echo data, and constructing an overall echo data vector using the decoded clutter echo data vector;

[0014] aligning the main clutter angle and the Doppler spectrum center of the overall echo data vector using a clutter alignment technique to obtain an aligned overall echo data vector;

[0015] The space-time adaptive processing technology is used to filter out the clutter components in the aligned overall echo data vector to obtain the clutter-suppressed output signal.

[0016] Furthermore, the method of using secondary phase coding to perform phase modulation on each transmitted pulse signal of the planar array space-based early warning radar includes:

[0017] Obtaining the linear frequency modulation signal emitted by each array element in the planar array space-based early warning radar

[0018] Perform secondary phase coding design on the kth transmit pulse to generate the corresponding secondary phase coding factor Ψ k ;

[0019] Using the quadratic phase coding factor Ψ k Linear frequency modulation signal Perform phase modulation to generate the phase modulation signal emitted by each array element in the planar array space-based early warning radar in the kth pulse period:

[0020] Further, performing secondary phase decoding processing on the clutter echo data and constructing an overall echo data vector using the decoded clutter echo data vector includes:

[0021] According to the expected distance area p0 and Doppler shift factor ε, the secondary phase decoding design is performed to generate the secondary phase decoding factor

[0022] Using the quadratic phase decoding factor Clutter echo data Decode and obtain the clutter echo data of the expected distance area p=p0 after decoding and the clutter echo data of the remaining p≠p0 distance areas

[0023] The decoded noise data Arrange along the receiving channel dimension and pulse dimension in sequence to obtain the clutter echo data vector after decoding the lth range unit

[0024] The target's echo data vector is constructed using the target's time steering vector and space steering vector as well as the target's complex amplitude after matched filtering.

[0025] Using the decoded clutter echo data vector Moving target echo data vector and white Gaussian noise Construct the overall echo data vector of the lth range unit

[0026] 2. A space-based early warning radar range ambiguity clutter suppression system based on secondary phase coding, characterized by comprising:

[0027] The transmission modulation module is used to phase modulate each transmission pulse signal of the planar array space-based early warning radar using secondary phase coding;

[0028] The echo pre-processing module is used to receive the phase-modulated echo signal scattered by the ground clutter block, and perform sub-array beam synthesis, down-conversion and matched filtering to obtain clutter echo data;

[0029] The decoding and data construction module is used to perform secondary phase decoding on the clutter echo data and construct the overall echo data vector to obtain the overall echo data vector containing clutter, target and noise;

[0030] The clutter alignment module is used to construct an angle-Doppler compensation matrix corresponding to the range unit to be processed, and use the matrix to correct the overall echo data vector so that the main clutter angle and the Doppler spectrum center are aligned with the range unit to be detected, thereby obtaining the aligned overall echo data vector;

[0031] The space-time adaptive clutter suppression module is used to construct a space-time adaptive processing filter weight vector using the minimum variance distortion-free response criterion, and perform an inner product between the weight vector and the aligned overall echo data vector to obtain an output echo vector after clutter is filtered out.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] First, the present invention introduces a quadratic phase-coded modulation and demodulation mechanism to suppress clutter range ambiguity without limiting the transmitted waveform. Compared with the existing waveform diversity technology based on the MIMO system, it can not only improve the suppression performance of space-based early warning radar range ambiguity clutter, but also reduce hardware resource overhead.

[0034] Secondly, since the present invention only implements space-time adaptive processing in the receive-Doppler two-dimensional domain, compared with the existing full-dimensional 3D-STAP technology, it can effectively suppress range-ambiguous clutter while significantly reducing the complexity of clutter suppression and the number of training samples required, thereby improving the real-time performance of range-ambiguous clutter suppression in space-based early warning radars. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a flow chart of the method for suppressing range ambiguity clutter in space-based early warning radar based on secondary phase coding according to the present invention;

[0036] Figure 2 Schematic diagram of the geometric model of the positive side-looking medium-orbit planar array space-based early warning radar in the method of the present invention;

[0037] Figure 3 This is a block diagram of the space-based early warning radar range ambiguity clutter suppression system based on secondary phase coding of the present invention;

[0038] Figure 4 This is a clutter Capon power spectrum diagram of the range ambiguity clutter simulated by the present invention;

[0039] Figure 5 The range-Doppler spectrum is a simulation of suppressing range ambiguity clutter using the present invention and the prior art respectively;

[0040] Figure 6 This is a graph showing how the signal-to-noise ratio loss varies with the normalized Doppler frequency when the range ambiguity clutter is simulated and suppressed using the present invention and the prior art respectively. DETAILED DESCRIPTION

[0041] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention and not all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0042] Reference Figure 2 The implementation scenario of the present invention includes a planar array radar and a mid-orbit space-based platform. The planar array radar is placed on the mid-orbit space-based platform and works in a positive side-view mode. The scenario parameters are defined as follows:

[0043] The flight altitude of the medium-orbit space-based platform is H, and the flight speed is v p And along the y-axis direction. Each column of the planar array radar contains M array elements, each row contains N array elements, and the distance between the array elements is d e , the row element spacing is d aIn the transmitting mode, the planar array uses full aperture transmission. In the receiving mode, the planar array is evenly divided into N R non-overlapping sub-matrices, corresponding to N R The size of each sub-array is M rows × N r Column, N r =N / N R , the distance between the equivalent phase centers of adjacent sub-arrays is d R =N r d a The planar array radar transmits pulses at a constant pulse repetition rate f within a coherent processing interval. r =1 / T r Send J pulses, T r is the pulse repetition period.

[0044] Divide the ground into N a Range ambiguity areas, each range ambiguity area is divided into L range units, each range unit is divided into N along the azimuth direction c For the ground clutter block located in the pth range ambiguity area, the lth range unit, and the qth azimuth, its slant range R l,p Defined as the distance between the clutter block and the geometric center of the planar array radar, the pitch angle Defined as the angle between the line connecting the clutter block and the geometric center of the planar array radar and the Z axis, the azimuth angle θ q It is defined as the angle between the projection of the line connecting the clutter block and the geometric center of the planar array radar on the XOY plane and the Y axis, where p∈{1,2,…,N a} is the distance fuzzy number index, l∈{1,2,…,L} is the distance unit number index, q∈{1,2,…,N c} is the index of the number of clutter blocks.

[0045] Example 1: A method for suppressing range ambiguity clutter in space-based early warning radar based on secondary phase coding.

[0046] Reference Figure 1 , the implementation steps of this embodiment include:

[0047] Step 1: Use secondary phase coding to phase modulate each transmitted pulse signal of the planar array space-based early warning radar.

[0048] In a specific embodiment, the implementation includes:

[0049] 1.1) Each array element of the planar array space-based early warning radar transmits a total of I pulse signals within a coherent processing interval, and each pulse signal adopts a linear frequency modulation pulse signal. Its form is:

[0050]

[0051] in, is the baseband complex envelope, is a rectangular pulse function, t is the fast time, T p is the pulse duration, μ=B / T p is the modulation frequency, B is the baseband bandwidth, and f0 is the carrier frequency;

[0052] 1.2) Perform secondary phase coding design on the k-th pulse signal to generate the corresponding secondary phase coding factor Ψ k :

[0053]

[0054] Where k = 1, 2, ..., I, ε > 0 is the frequency offset factor;

[0055] 1.3) For the secondary phase coding factor Ψ k Optimize, that is, select the optimal Doppler shift factor ε′ to obtain the secondary phase coding factor Ψ′ k :

[0056] 1.3.1) Given the spatial position parameters of the desired target in represents the slant range of the desired target in the p0th range zone and the l0th range unit, θ0 and are the azimuth and elevation angles of the desired target respectively;

[0057] 1.3.2) Based on the given desired target spatial position parameters, determine the slant range of the close-range fuzzy clutter superimposed within the range unit l0 where the target is located. Slant range to distant ambiguity clutter Where p0-j and p0+j represent the near-range fuzzy zone before and far-range fuzzy zone after the target range p0, respectively, j = 1, 2, ... J, J is the difference in fuzzy distance between the farthest or closest fuzzy zone and the desired range zone;

[0058] 1.3.3) Calculate the clutter in the close-range ambiguity zone at the slant range The close-range mainlobe clutter Doppler frequency f D,-j and long-range ambiguity clutter at slant range The far-range mainlobe clutter Doppler frequency at

[0059]

[0060]

[0061] Among them, H and v pare the height and speed of the medium-orbit space-based platform respectively, λ0 is the wavelength, is the spatial cone angle in the main beam direction, R e is the radius of the Earth; ρ c is the equivalent yaw amplitude, θ c is the equivalent yaw angle, and the two reflect the deviation between the actual heading and the ideal heading of the space-based early warning radar caused by the rotation of the earth, which are expressed as:

[0062]

[0063]

[0064] Among them, v e is the Earth's rotation speed at the equator, α is the latitude of the subsatellite point, and β is the orbital inclination;

[0065] 1.3.4) Based on the close-range mainlobe clutter Doppler frequency f D,-J and the far-range mainlobe clutter Doppler frequency f D,+J , when j=J, determine the optimal Doppler shift factor ε′:

[0066]

[0067] 1.3.5) Based on the optimal Doppler shift factor ε′, the optimized secondary phase coding factor Ψ can be obtained k ′:

[0068]

[0069] 1.4) Using the optimized secondary phase coding factor Ψ k ′ for linear frequency modulation pulse signal Perform phase modulation to generate the phase modulation signal s emitted by each element in the planar array space-based early warning radar in the kth pulse period k (t):

[0070]

[0071] Step 2: The planar array antenna receives the phase modulated echo signal scattered by the ground clutter block and performs preprocessing to obtain clutter echo data.

[0072] In a specific embodiment, the preprocessing of this step includes but is not limited to sequentially performing subarray beamforming, down-conversion, and matched filtering on the phase modulated echo signal, which is implemented by:

[0073] 2.1) Sub-array beam combining is performed on the phase modulated echo signal received by the planar array space-based early warning radar after being scattered by the ground clutter block to generate channel-level receiving data, and the nth RThe clutter block echo data received by the receiving channel in the kth pulse period

[0074] 2.1.1) For the ground clutter block at the pth range ambiguity zone, the lth range unit, and the qth azimuth, calculate the time it takes for the kth transmitted pulse to propagate to the nth ground clutter block after being scattered by the clutter block. R The round-trip delay of the receiving channel

[0075]

[0076] Among them, n R =1,2,…,N R , N R is the total number of receiving channels, c is the speed of light, R l,p 、 and θ q are the slant range, elevation angle and azimuth angle of the ground clutter block at the pth range ambiguity zone, the lth range unit and the qth azimuth angle respectively;

[0077] 2.1.2) Based on round-trip delay The phase modulated echo signal corresponding to the ground clutter block at the pth range ambiguity area, the lth range unit, and the qth azimuth angle is calculated.

[0078]

[0079] Among them, ξ l,p,q is the complex amplitude of the ground clutter block at the pth range ambiguity zone, the lth range unit, and the qth azimuth, is the azimuth angle θ q and pitch angle The full array transmit gain at ;

[0080] 2.1.3) Phase Modulation Echo Signal Perform subarray beamforming to obtain the nth R The clutter block echo data received by the receiving channel in the kth pulse period

[0081]

[0082] in, is the azimuth angle θ q and pitch angle The sub-array receiving gain at ;

[0083] 2.2) Echo data of clutter block Perform down-conversion and matched filtering to obtain the clutter block echo data after matched filtering

[0084]

[0085] in, is the down-conversion function, is the matched filter function,

[0086] is the normalized received spatial frequency of the clutter block,

[0087] is the normalized Doppler frequency of the clutter block,

[0088] is the complex amplitude of the ground clutter block at the pth range ambiguity area, the lth range unit, and the qth azimuth after matched filtering, is the convolution operation, the superscript * is the conjugate operation, and sinc[·] is the sinc function;

[0089] 2.3) According to the Ward clutter model, the clutter echo data of multiple clutter blocks from different range ambiguity areas in the same range unit are superimposed to obtain the clutter echo data of the lth range unit.

[0090]

[0091] Among them, N a is the total number of distance fuzzy areas, N c Count the total number of independent clutter blocks within each distance unit;

[0092] According to the clutter echo data under the range ambiguity situation It can be seen that when considering the presence of the p-th range ambiguity clutter echo in the k-th receiving pulse, it means that the current receiving window receives the signal located at R l,p The clutter block echo at position 1 actually originates from the k-p+1th transmitted pulse. Therefore, the receiving window of the kth pulse will simultaneously receive different range-ambiguous clutter echoes corresponding to different previous transmitted pulses. However, these range-ambiguous clutter block echoes carry different QPC modulation phases, and their phase characteristics are related to the index of the range ambiguity region. This shows that by designing quadratic phase encoding to modulate the transmitted pulse, the present invention can make clutter echoes from different range ambiguity regions have distinguishable characteristics in the pulse dimension. This distinguishing characteristic is the basis for resolving the range-ambiguous clutter problem.

[0093] Step 3: In order to realize the shift of clutter spectrum along the Doppler dimension in different range ambiguity areas, thereby reducing the broadening of clutter spectrum caused by multiple range ambiguities, the echo data obtained above need to be Perform secondary phase decoding and use the decoded clutter echo data vector Constructing the overall echo data vector This facilitates the subsequent alignment of the main clutter angle with the Doppler spectrum center, which is achieved by:

[0094] 3.1) Design the secondary phase decoding based on the expected distance region p0 and the Doppler shift factor ε, and obtain the secondary phase decoding factor

[0095]

[0096] Wherein, k-p0+1 represents the index of the number of transmitted pulses corresponding to the desired distance area p0;

[0097] 3.2) Using the quadratic phase decoding factor Clutter echo data Decode and obtain the clutter echo data of the expected distance area p=p0 after decoding and the clutter echo data of the remaining p≠p0 distance areas

[0098]

[0099]

[0100] 3.3) Based on the decoded echo data above, the clutter echo data when p=p0 is obtained respectively The corresponding residual coding phase And the clutter echo data when p≠p0 The corresponding residual coding phase

[0101]

[0102]

[0103] From the above residual phase, we can see that after the secondary phase decoding, the residual coding phase of the p0th expected range zone where the target is located is zero, while the remaining range ambiguity regions with p≠p0 still have non-zero coding phases. According to the frequency shift characteristics of the Fourier transform, for the range ambiguity clutter with p≠p0, its spectrum will be shifted by (p-p0)εf in the Doppler domain. r The movement direction is analyzed as follows:

[0104] When p>p0, the clutter spectrum in the long-range ambiguity zone before secondary phase decoding is distributed on the left side of the expected clutter spectrum in the range-Doppler domain. After secondary phase decoding, the frequency shift (p-p0)εf r >0, indicating that the clutter spectrum of the pth far-range ambiguity zone moves rightward along the Doppler frequency axis to the vicinity of the expected clutter spectrum;

[0105] When p<p0, the clutter spectrum in the close-range ambiguity zone before secondary phase decoding is distributed to the right of the expected clutter spectrum in the range-Doppler domain. After secondary phase decoding, the frequency shift (p-p0)εf r <0, indicating that the clutter in the pth close-range ambiguity zone moves leftward along the Doppler frequency axis to the vicinity of the expected clutter spectrum;

[0106] In summary, secondary phase decoding can move the clutter spectrum of other range ambiguity areas along the Doppler dimension to the clutter spectrum of the desired area where the target is located, thereby significantly reducing the broadening of the clutter spectrum caused by multiple range ambiguities.

[0107] 3.4) Arrange the clutter data decoded in step 3.2) along the receiving channel dimension and pulse dimension to obtain the decoded clutter echo data vector of the lth range unit

[0108]

[0109] in, is the clutter time steering vector,

[0110] is the clutter space steering vector,

[0111] is the clutter Doppler offset vector,

[0112] The superscript T is the transpose operation, ⊙ is the Hadamard product, is the Kronecker product;

[0113] 3.5) Construct target echo data vector

[0114] Since the target echo signal and the clutter echo signal undergo the same processing flow at the receiving end, including subarray beamforming, downconversion, and matched filtering, a detailed description of the target echo signal reception process is omitted. The following directly provides the three key parameters required to construct the target echo data vector: the target's complex amplitude after matched filtering, the target's time steering vector, and the target's spatial steering vector, and describes their calculation methods. Based on these three key parameters, the target echo data vector can be constructed. Its implementation includes:

[0115] 3.5.1) Calculate the complex amplitude of the target after matched filtering

[0116]

[0117] in, is the azimuth angle θ0 and the elevation angle The full array transmission gain at

[0118] is the azimuth angle θ0 and the elevation angle The sub-array receiving gain at

[0119] ξ0 is the complex amplitude of the target before matched filtering, R0 is the slant range of the target;

[0120] 3.5.2) Calculate the time-oriented vector of the target and the space-direction vector

[0121]

[0122]

[0123] in, is the normalized Doppler frequency of the target,

[0124] is the normalized spatial frequency of the target,

[0125] v0 is the target radial velocity;

[0126] 3.5.3) Time-oriented vector according to the target and the space-direction vector and the complex amplitude of the target after matched filtering Construct target echo data vector

[0127]

[0128] 3.6) According to the clutter echo data vector decoded in step 3.4) Target echo data vector in step 3.5) and white Gaussian noise vector Calculate the overall echo data vector of the lth range unit

[0129]

[0130] in, is a Gaussian distribution, N R K×N R K-dimensional identity matrix, is the noise power.

[0131] Step 4: Use clutter alignment technology to align the overall echo data vector Align the main clutter angle with the Doppler spectrum center to obtain the aligned overall echo data vector xl .

[0132] In a specific embodiment, the implementation includes:

[0133] 4.1) Calculate the angle-Doppler compensation matrix h corresponding to the lth range unit l :

[0134] 4.1.1) Calculate the distance between the lth distance unit and the distance unit to be detected c The main clutter Doppler frequency deviation between and main clutter spatial frequency deviation

[0135]

[0136]

[0137] in, is the distance unit to be detected l c The pitch angle of the inner clutter block;

[0138] 4.1.2) Based on the Doppler frequency deviation of the main clutter and main clutter spatial frequency deviation Get the lth distance unit and the distance unit to be detected l respectively c The Doppler frequency deviation vector between and the spatial frequency deviation vector

[0139]

[0140]

[0141] 4.1.3) According to the Doppler frequency deviation vector and the spatial frequency deviation vector Calculate the angle-Doppler compensation matrix h corresponding to the lth range unit l :

[0142]

[0143] Where diag[·] is the vector diagonalization operation;

[0144] 4.2) Using the angle-Doppler compensation matrix h l For the overall echo data vector in step 3.6) Correction is performed so that the overall echo data vector The main clutter angle and Doppler spectrum center in the distance unit to be detected c Align to obtain the aligned overall echo data vector x l :

[0145]

[0146] After the above compensation processing, the space-time distribution characteristics of the main clutter in the overall echo data vector corresponding to each range unit are basically consistent with those of the range unit to be detected. That is, the clutter data in each range unit approximately satisfies the independent and identically distributed characteristics, and the clutter range dependence is alleviated, which is more conducive to improving the clutter suppression performance of subsequent space-time adaptive processing.

[0147] Step 5: Use space-time adaptive processing technology to filter out the aligned overall echo data vector x l The clutter component in the output signal y after clutter suppression is obtained l .

[0148] In a specific embodiment, the implementation includes:

[0149] 5.1) For the first c The distance unit to be detected is selected, and the overall echo data vector x after the two sides are aligned is selected. l As a training sample, calculate the clutter plus noise covariance matrix R of the range unit to be detected:

[0150]

[0151] Among them, L s is the total number of training samples, is the conjugate transpose operation;

[0152] 5.2) Time-oriented vector according to the target and the space-direction vector Calculate the target's space-time steering vector

[0153]

[0154] 5.3) According to the clutter plus noise covariance matrix R and the target's space-time steering vector The space-time adaptive processing filter weight vector w is constructed using the minimum variance distortion-free resounding criterion. l :

[0155]

[0156] Among them, the superscript -1 is the inversion operation;

[0157] 5.4) Space-time adaptive weight vector w l The overall echo data vector x after alignment in step 4.2) l Perform inner product and filter out the overall echo data vector x after alignment lThe clutter component in the filter is used to obtain the output echo vector after filtering out the clutter component:

[0158]

[0159] The flowchart representation or method representation of the above embodiment can be understood as: representing a module, fragment or part that includes one or a group of executable instruction codes configured to implement specific logical functions or process steps. The step numbers are only for a clear description of the implementation scheme of the present invention to facilitate understanding, and the order of the serial numbers is not limited, that is, the implementation may not be carried out in the order shown or discussed.

[0160] Example 2: Space-based early warning radar range ambiguity clutter suppression system based on secondary phase coding,

[0161] Reference Figure 3 This example includes a transmit modulation module 1, an echo preprocessing module 2, a decoding and data construction module 3, a clutter alignment module 4 and a space-time adaptive clutter suppression module 5, wherein the transmit modulation module 1 includes a linear frequency modulation signal generation submodule 11, a frequency offset factor calculation submodule 12, a coding factor generation submodule 13 and a phase modulation submodule 14, and the decoding and data construction module 3 includes a decoding factor calculation submodule 31, a clutter data decoding submodule 32, a target echo vector construction submodule 33 and an overall echo vector construction submodule 34.

[0162] The whole system works as follows:

[0163] The transmitting modulation module 1 is used to perform phase modulation on each transmitted pulse signal of the planar array space-based early warning radar using quadratic phase coding. The linear frequency modulation signal generation submodule 11 is used to generate a linear frequency modulation signal transmitted by each array element in the planar array space-based early warning radar; the frequency offset factor calculation submodule 12 is used to calculate the frequency offset factor of the quadratic phase coding factor; the coding factor generation submodule 13 is used to use the frequency offset factor to generate a quadratic phase coding factor corresponding to each transmitted pulse; the phase modulation submodule 14 is used to use the quadratic phase coding factor to perform phase modulation on the linear frequency modulation signal to obtain a phase modulation signal transmitted by each array element in the planar array space-based early warning radar during each pulse period, and transmit it to the echo preprocessing module 2 via the ground.

[0164] The echo pre-processing module 2 is used to receive the phase modulated echo signal after being scattered by the ground clutter block, and perform sub-array beam synthesis, down-conversion and matched filtering in sequence to obtain clutter echo data, and transmit it to the decoding and data construction module 3;

[0165] The decoding and data construction module 3 is used to perform secondary phase decoding on the clutter echo data and construct an overall echo data vector to obtain an overall echo data vector containing clutter, target, and noise. The decoding factor calculation submodule 31 is used to calculate the secondary phase decoding factor; the clutter data decoding submodule 32 is used to decode the clutter echo data using the secondary phase decoding factor to obtain a decoded clutter echo data vector; the target echo vector construction submodule 33 is used to construct the target echo data vector using the target's time steering vector and spatial steering vector and the target's complex amplitude after matched filtering; and the overall echo vector construction submodule 34 is used to construct an overall echo data vector using the clutter echo data vector, the target echo data vector, and the white Gaussian noise vector, and transmit it to the clutter alignment module 4.

[0166] The clutter alignment module 4 is used to construct an angle-Doppler compensation matrix corresponding to the range unit to be processed, and use the matrix to correct the overall echo data vector so that the main clutter angle and the Doppler spectrum center are aligned with the range unit to be detected, thereby obtaining the aligned overall echo data vector and transmitting it to the space-time adaptive clutter suppression module 5;

[0167] The space-time adaptive clutter suppression module 5 is used to construct a space-time adaptive processing filter weight vector using the minimum variance distortion-free response criterion, and perform an inner product between the weight vector and the aligned overall echo data vector to obtain an output echo vector after clutter is filtered out.

[0168] It should be noted that the above-mentioned functional modules can be implemented in whole or in part through software, hardware, firmware, or any combination thereof. When implemented using software, they can be implemented in whole or in part in the form of a program instruction product. The program instruction product includes one or a group of program instructions. When the program instructions are loaded and executed on a computer, the process or function described is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The program instructions can be stored in a computer-readable and writable storage medium, or transferred from a computer-readable and writable storage medium to another computer-readable and writable storage medium.

[0169] The direct coupling or communication connection between the modules shown or discussed in this embodiment can be achieved through indirect coupling or communication connection of some interfaces, devices or modules. The various functional modules and submodules in this embodiment can be dynamically located in a processing component, or each module can exist physically separately, or two or more modules can be dynamically located in a processing component. When the above-mentioned dynamic components are implemented in the form of software functional modules and sold or used as independent products, they can also be stored in a computer-readable and writable storage medium. The storage medium can be a memory, a magnetic disk, an optical disk, etc.

[0170] The beneficial effects of the present invention are further illustrated below through simulation experiments.

[0171] 1. Experimental conditions:

[0172] The hardware platform of the simulation experiment of this embodiment is: processor Intel(R) Core(TM) i7-10700 CPU, main frequency 2.90GHz, memory 96GB.

[0173] The software platform for the simulation experiment of this embodiment is: MATLAB R2021b.

[0174] The space-based early warning radar system based on the front side-viewing planar array has an array element size of 17 rows × 448 columns and an azimuth dimension array element spacing d. a =0.12m, pitch dimension array element spacing d e = 0.12m. In transmit mode, the planar array uses full-aperture transmission. In receive mode, the planar array is evenly divided into 32 non-overlapping subarrays along the azimuth dimension. These 32 non-overlapping receive subarrays correspond to 32 receive channels after subarray synthesis. Each subarray has 17 rows × 14 columns of elements. The specific settings for other relevant simulation parameters are shown in Table 1.

[0175] Table 1 Simulation parameters of space-based early warning radar system

[0176]

[0177] 2. Simulation content and results analysis:

[0178] Simulation 1, based on the above simulation conditions, 1448 discrete points are selected in the spatial frequency domain [-0.5, 0.5] and the normalized Doppler frequency domain [-0.5, 0.5] respectively, and the two-dimensional clutter Capon spectrum is estimated for each spatial frequency point and normalized Doppler frequency point using the method of the present invention. After obtaining the clutter power value, the clutter Capon power spectrum simulation diagram is drawn. The results are shown in Figure 1. Figure 4 As shown. Among them, Figure 4 (a) is the clutter Capon power spectrum obtained based on the unprocessed raw clutter data, which is used as a comparison benchmark; Figure 4 (b) is the clutter Capon power spectrum after secondary phase decoding obtained by the present invention, Figure 4 (c) is the clutter Capon power spectrum after angle-Doppler compensation obtained using the present invention.

[0179] Depend on Figure 4 (a) It can be seen that due to the coexistence of range ambiguity and clutter range dependence, the angle-Doppler characteristics of each range-ambiguous clutter are significantly different, resulting in the clutter Capon power spectrum obtained from the original clutter data being severely broadened in the space-time domain.

[0180] Depend on Figure 4 (b) It can be seen that by introducing secondary phase coding at the transmitter and performing secondary phase decoding at the receiver, the clutter spectra from different range ambiguity areas are effectively aligned in the Doppler dimension, thereby significantly reducing the space-time spread of the clutter spectrum. This verifies the effectiveness of the secondary phase coding technology proposed in this invention in alleviating the range ambiguity problem.

[0181] As shown in Figure 4(c), based on the secondary phase decoding, the angle-Doppler compensation technology of the present invention can effectively correct the distance dependence of the clutter, achieve further focusing of the main lobe of the clutter Capon power spectrum, and help improve the minimum detectable speed performance of the radar system.

[0182] Simulation 2, based on the above simulation conditions, within 2667 range cells, the echo data of each range cell is discretized into 724 frequency points within the normalized Doppler frequency range of [-0.5, 0.5]. The conventional STAP method and the method of the present invention are used to perform space-time adaptive filtering on each range cell and each normalized Doppler frequency point, and the output amplitude is obtained and the range-Doppler spectrum is plotted. The results are shown as follows: Figure 5 As shown. Among them, Figure 5 (a) is the range-Doppler spectrum result of the conventional STAP method, Figure 5 (b) is the range-Doppler spectrum result of the method of the present invention, Figure 5 (c) is the local amplification result of the range-Doppler spectrum of the conventional STAP method. Figure 5 (d) is the local amplification result of the range-Doppler spectrum of the method of the present invention.

[0183] Depend on Figure 5 (a) It can be seen that after using the conventional STAP method for space-time adaptive filtering, the remaining mainlobe clutter in the range-Doppler spectrum is relatively high in intensity and occupies a wide Doppler frequency range, seriously affecting the detection of weak and slow-moving targets. This shows that the conventional STAP method is difficult to effectively deal with range ambiguity and clutter range dependence.

[0184] Depend on Figure 5 (b) It can be seen that after the space-time adaptive filtering method of the present invention is used, the mainlobe clutter is effectively suppressed. This is because the present invention effectively alleviates the range ambiguity and clutter range dependence problems by performing secondary phase encoding and decoding and angle-Doppler compensation on the clutter, making the space-time characteristics of the clutter of the training samples and the unit to be detected more consistent, thereby improving the estimation accuracy of the clutter plus noise covariance matrix and significantly enhancing the clutter suppression performance.

[0185] contrast Figure 5 (c) and Figure 5As shown in Figure (d), the target is located at a normalized Doppler frequency of -0.2 and a range bin number of 1040. Although the target itself is located within the mainlobe clutter region, after processing by the method of the present invention, the remaining mainlobe clutter spectrum width is significantly narrowed, and the output signal-to-noise ratio of the target at the corresponding frequency and range bin is significantly improved, indicating that the present invention can effectively suppress non-uniform range ambiguity clutter and greatly improve the detection performance of weak moving targets.

[0186] Simulation 3, based on the above simulation conditions, select 724 discrete frequency points in the normalized Doppler frequency range [-0.5, 0.5], and use the conventional STAP method and the method of the present invention to calculate the output signal-to-noise ratio loss value corresponding to each frequency point, that is, the ratio of the output signal-to-noise ratio under the clutter background to the output signal-to-noise ratio under the noise background. Connect all the discrete output signal-to-noise ratio loss values to draw a curve of the output signal-to-noise ratio loss versus Doppler frequency. The results are shown in the figure. Figure 6 The dashed line shows the curve of the output noise-to-noise ratio loss as a function of the normalized Doppler frequency after processing by the conventional STAP method, the dotted line shows the curve of the output noise-to-noise ratio loss as a function of the normalized Doppler frequency after processing by the method of the present invention, and the solid line shows the curve of the output noise-to-noise ratio loss as a function of the normalized Doppler frequency when the covariance matrix of the clutter plus noise is precisely known, which serves as the upper bound of the performance.

[0187] Depend on Figure 6 It can be seen that in both the mainlobe clutter region and the sidelobe clutter region, the output signal-to-noise ratio loss of the proposed method is basically better than that of the conventional STAP method, and the notch of the loss performance curve is significantly narrowed, which is closer to the optimal performance curve. This shows that the proposed method has a better suppression effect on non-uniform clutter under range ambiguity and can effectively improve the slow-moving target detection capability.

[0188] In summary, the present invention uses quadratic phase encoding technology to phase-modulate the transmitted pulses at the transmitter end, effectively distinguishing clutter from different range ambiguity zones in the pulse dimension. Secondary phase decoding, matching the transmitted encoding, is performed at the receiver end to shift and align clutter from the remaining range ambiguity zones along the Doppler dimension to the desired range zone, significantly reducing the clutter spectrum expansion caused by multiple range ambiguities. Furthermore, angle-Doppler compensation technology is employed to effectively mitigate the range dependence of clutter and improve the accuracy of the clutter-plus-noise covariance matrix estimation. Finally, through space-time adaptive processing, the present invention effectively suppresses the range-ambiguous non-uniform clutter encountered by medium-orbit space-based early warning radars, significantly improving the detection performance of weak, slow-moving targets. Simulation results verify the correctness, effectiveness, and reliability of the present invention.

[0189] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for suppressing range ambiguity clutter in space-based early warning radar based on secondary phase coding, characterized in that: include: Secondary phase coding is used to phase modulate each transmitted pulse signal of the planar array space-based early warning radar. The planar array antenna receives the phase modulated echo signal scattered by the ground clutter block, and sequentially performs sub-array beamforming, down-conversion and matched filtering processing to obtain clutter echo data; performing secondary phase decoding processing on the clutter echo data, and constructing an overall echo data vector using the decoded clutter echo data vector; aligning the main clutter angle and the Doppler spectrum center of the overall echo data vector using a clutter alignment technique to obtain an aligned overall echo data vector; The space-time adaptive processing technology is used to filter out the clutter components in the aligned overall echo data vector to obtain the clutter-suppressed output signal.

2. The method according to claim 1, characterized in that The method of using secondary phase coding to phase modulate each transmitted pulse signal of the planar array space-based early warning radar includes: (2a) Obtaining the linear frequency modulation signal emitted by each array element in the planar array space-based early warning radar in, is the baseband complex envelope, is a rectangular pulse function, t is the fast time, T p is the pulse duration, μ is the modulation frequency, and f0 is the carrier frequency; (2b) Perform secondary phase coding design on the kth transmitted pulse to generate the corresponding secondary phase coding factor Ψ k : Where k = 1, 2, ..., I, I is the number of pulses in the coherent processing interval, and ε>0 is the frequency offset factor; (2c) Using the quadratic phase coding factor Ψ k Linear frequency modulation signal Perform phase modulation to generate the phase modulation signal s emitted by each element in the planar array space-based early warning radar in the kth pulse period k (t):

3. The method according to claim 2, characterized in that The frequency offset factor ε in step (2c) is calculated as follows: (2c1) Calculate the slant range of the main beam in the closest range ambiguity area respectively The close-range mainlobe clutter Doppler frequency f D,-J and the slant range within the farthest distance ambiguity zone The far-range mainlobe clutter Doppler frequency at in, is the equivalent yaw amplitude caused by the Earth's rotation, is the equivalent yaw angle, l0 is the target principal value distance, p0 is the target ambiguity range number, p0-J and p0+J are respectively the closest ambiguity zone before and the farthest ambiguity zone after the target range p0, J is the difference in ambiguity range number between the farthest or closest ambiguity zone and the expected range zone, λ0 is the wavelength, ψ0 is the main beam space cone angle, α is the latitude of the sub-satellite point, β is the orbital inclination, v p is the satellite speed, H is the satellite orbit height, R e is the radius of the Earth; (2c2) According to the close-range main lobe clutter Doppler frequency f D,-J and the far-range mainlobe clutter Doppler frequency f D,+J , the Doppler shift factor ε is calculated as: Among them, f r is the pulse repetition rate.

4. The method according to any one of claims 1 to 3, characterized in that The planar array antenna receives the phase modulated echo signal scattered by the ground clutter block, and sequentially performs subarray beamforming, down-conversion and matched filtering processing to obtain clutter echo data, including: (4a) The planar array antenna receives the phase modulated echo signal scattered by the ground clutter block located in the pth range ambiguity area, the lth range unit, and the qth azimuth. in The kth transmission pulse is scattered by the pth range ambiguity area, the lth range unit, the ground clutter block at the qth azimuth and then propagates to the nth R The round-trip delay of the receiving channel, n R =1,2,…,N R , N R is the number of receiving channels after the planar array is divided into sub-arrays along the azimuth dimension, c is the speed of light, R l,p is the slant range of the ground clutter block in the pth range ambiguity zone and the lth range unit, d R is the distance between the equivalent phase centers of adjacent sub-arrays, is the pitch angle of the ground clutter block in the pth range ambiguity zone and the lth range unit, θ q is the azimuth of the qth clutter block, l=1,2,…,L, L is the total number of range gates, T r is the pulse repetition period, ξ l,p,q is the complex amplitude of the ground clutter block at the pth range ambiguity zone, the lth range unit, and the qth azimuth, is the azimuth angle θ q and pitch angle The full array transmit gain at ; (4b) Phase modulated echo signal After performing sub-array beamforming, channel-level receiving data is formed to obtain the nth R The echo data of the clutter block received by the receiving channel in the kth pulse period in, is the azimuth angle θ q and pitch angle The sub-array receiving gain at ; (4c) The clutter block echo data Perform down-conversion and matched filtering to obtain the clutter block echo data after matched filtering in, is the down-conversion function, is the matched filter function, is the convolution operation, the superscript * is the conjugate operation, is the complex amplitude of the ground clutter block at the pth range ambiguity area, the lth range unit, and the qth azimuth after matched filtering, is the azimuth angle θ q and pitch angle The normalized received spatial frequency of the clutter block at , The running speed is v p The planar array space-based early warning radar system is used to calculate the azimuth angle θ q and pitch angle The normalized Doppler frequency generated by the clutter block at (4d) According to the Ward clutter model, the clutter echo data of multiple clutter blocks from different range ambiguity areas in the same range unit are superimposed to obtain the clutter echo data of the lth range unit. Among them, P is the total number of range fuzzy areas, N c Count the total number of independent clutter blocks within each distance unit.

5. The method according to any one of claims 1 to 4, characterized in that Performing secondary phase decoding processing on the clutter echo data and constructing an overall echo data vector using the decoded clutter echo data vector includes: (5a) According to the expected distance region p0 and the Doppler shift factor ε, a secondary phase decoding design is performed to generate the secondary phase decoding factor Wherein, k-p0+1 represents the index of the number of transmitted pulses corresponding to the desired distance area p0; (5b) Using the quadratic phase decoding factor Clutter echo data Decode and obtain the clutter echo data of the expected distance area p=p0 after decoding and the clutter echo data of the remaining p≠p0 distance areas (5c) The decoded noise data Arrange along the receiving channel dimension and pulse dimension in sequence to obtain the clutter echo data vector after decoding the lth range unit in, is the time-oriented vector of the clutter block, is the spatial steering vector of the clutter block, Φ(p) is the Doppler shift vector, the superscript T is the transpose operation, ⊙ is the Hadamard product, is the Kronecker product; (5d) Construct the target's echo data vector using the target's time steering vector and space steering vector as well as the target's complex amplitude after matched filtering in, is the complex amplitude of the target after matching filtering, v0 is the target radial velocity, θ0 is the target azimuth, is the target pitch angle; (5e) Using the decoded clutter echo data vector Target echo data vector and white Gaussian noise Construct the overall echo data vector of the lth range unit 6. The method according to claim 1, characterized in that The method of aligning the main clutter angle and the Doppler spectrum center of the overall echo data vector using the clutter alignment technology to obtain the aligned overall echo data vector includes: (6a) Construct the angle-Doppler compensation matrix h corresponding to the lth range unit l : in, is the distance between the lth distance unit and the distance unit to be detected c The main clutter Doppler frequency deviation between is the Doppler frequency deviation vector, is the distance between the lth distance unit and the distance unit to be detected c The main clutter spatial frequency deviation between is the spatial frequency deviation vector, diag[·] is the vector diagonalization operation; (6b) Using the angle-Doppler compensation matrix h l For the overall echo data vector Correction is performed so that the main clutter angle and Doppler spectrum center are consistent with the distance unit to be detected l c Align to obtain the aligned overall echo data vector x l :

7. The method according to claim 1, characterized in that The method of filtering out the clutter components in the aligned overall echo data vector using a space-time adaptive processing technique to obtain a clutter-suppressed output signal includes: (7a) Using the minimum variance distortionless responsivity criterion, we construct the space-time adaptive processing filter weight vector w l : Where R is the clutter plus noise covariance matrix, is the target space-time guidance vector, v0 is the target radial velocity, θ0 is the target azimuth, is the target pitch angle, the superscript -1 is the inverse operation, the superscript is the conjugate transpose operation; (7b) For the space-time adaptive weight vector w l The aligned overall echo data vector x l Perform inner product and filter out the overall echo data vector x after alignment l The clutter component in the filter is used to obtain the output echo vector y after filtering out the clutter component. l :

8. A space-based early warning radar range ambiguity clutter suppression system based on secondary phase coding, characterized in that: include: The transmission modulation module is used to phase modulate each transmission pulse signal of the planar array space-based early warning radar using secondary phase coding; The echo pre-processing module is used to receive the phase-modulated echo signal scattered by the ground clutter block, and perform sub-array beam synthesis, down-conversion and matched filtering to obtain clutter echo data; The decoding and data construction module is used to perform secondary phase decoding on the clutter echo data and construct the overall echo data vector to obtain the overall echo data vector containing clutter, target and noise; The clutter alignment module is used to construct an angle-Doppler compensation matrix corresponding to the range unit to be processed, and use the matrix to correct the overall echo data vector so that the main clutter angle and the Doppler spectrum center are aligned with the range unit to be detected, thereby obtaining the aligned overall echo data vector; The space-time adaptive clutter suppression module is used to construct a space-time adaptive processing filter weight vector using the minimum variance distortion-free response criterion, and perform an inner product between the weight vector and the aligned overall echo data vector to obtain an output echo vector after clutter is filtered out.

9. The system according to claim 8, characterized in that The transmission modulation module includes: The linear frequency modulation signal generation submodule is used to generate the linear frequency modulation signal emitted by each array element in the planar array space-based early warning radar; A frequency offset factor calculation submodule, used to calculate the frequency offset factor of the secondary phase coding factor; A coding factor generation submodule is used to generate a secondary phase coding factor corresponding to each transmit pulse using a frequency offset factor; The phase modulation submodule is used to phase modulate the linear frequency modulation signal using the quadratic phase coding factor to obtain the phase modulated transmission signal of each array element in the planar array space-based early warning radar within each pulse period.

10. The system according to claim 8, wherein: The decoding and data construction module includes: A decoding factor calculation submodule, used to calculate the secondary phase decoding factor; Clutter data decoding submodule: used to decode the clutter echo data using the secondary phase decoding factor to obtain the decoded clutter data echo data vector; Target echo vector construction submodule: used to construct the echo data vector of the moving target using the time steering vector and space steering vector of the target and the target complex amplitude of the target after matching filtering; Overall echo vector construction submodule: used to construct an overall echo data vector using clutter echo data vector, target echo data vector and white Gaussian noise.

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