Clutter Suppression Method Based on Dual-Based End-Fire Array Airborne Radar

Abstract

The present invention provides a clutter suppression method based on a dual-base end-fire array airborne radar. The method constructs raw clutter echo data for all range gates, extracts unambiguous clutter data at small elevation angles to construct an unambiguous clutter covariance matrix, and then calculates a transformation matrix to transform the raw clutter echo data. Maximum likelihood estimation is performed on the transformed clutter data to obtain a filter weight vector, and clutter suppression is performed on the raw clutter echo data. The method utilizes the difference between the clutter scattering point and the incident cone angle of the transceiver platform to select an appropriate elevation angle to construct a far-field stationary unambiguous clutter covariance matrix as a reference covariance matrix for RBC compensation, thereby ensuring the stationarity of the reference clutter. Subaperture smoothing is also used to expand samples to estimate the covariance matrix, ensuring that the number of samples meets the required sample number. Furthermore, the method eliminates the non-stationarity of the clutter, thereby enabling effective clutter suppression using a space-time adaptive algorithm.

Description

Technical Field

[0001] The present invention relates to the technical field of radar signal processing, and in particular to a clutter suppression method based on a dual-base end-fire array airborne radar. Background Art

[0002] Bistatic airborne radars utilize a split-transmitter / receiver system, with the transmitter positioned away from hazardous areas and the receiver located in the area of ​​interest. Compared to conventional monostatic detection systems, these systems offer advantages such as increased safety, longer range, and improved anti-interference capabilities. End-fire array antennas, whose maximum radiation direction points along the array's axis, have broad application prospects in the long-range detection field of airborne early warning radars due to their unique low profile, strong directional radiation characteristics, and high adaptability to the aerodynamics of high-speed moving platforms.

[0003] Xidian University has published a patent application titled "Robust Clutter Suppression Method for Airborne Non-Side-Looking Array Radar Based on Diagonal Loading" (authorization announcement number: CN112904289B). This patent application addresses the difficulty in effectively suppressing clutter due to the nonlinear space-time coupling characteristics of clutter, and solves the problem of difficulty determining the diagonal loading factor for airborne non-Side-Looking Array radars. However, this patent is applicable only to monostatic non-Side-Looking radar scenarios.

[0004] In their paper "Range Ambiguity Clutter Suppression Method for End-Fire Array Airborne Radar", Li Yongwei et al. compared the clutter compensation effects and clutter suppression performance of different compensation methods for end-fire array airborne radar, and concluded that under ideal conditions without errors, the RBC method is more suitable for end-fire array airborne radar.

[0005] Because the clutter characteristics of end-fire bistatic airborne radars are more complex than those of end-fire or bistatic airborne radars, with stronger range-dependence in the clutter Doppler frequency and greater non-stationarity, existing clutter suppression methods for end-fire or side-fire bistatic airborne radars are not highly applicable to end-fire bistatic airborne radars, and research on clutter suppression methods for bistatic end-fire airborne radars is lacking. Summary of the Invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a clutter suppression method based on a dual-base end-fire array airborne radar. Specifically, it includes:

[0007] The present invention provides a clutter suppression method based on a dual-base end-fire array airborne radar, comprising:

[0008] S100, constructing a coordinate system for a bistatic endfire array airborne radar system, and constructing an endfire array pattern using the coordinate system; constructing raw clutter echo data for all range gates using the endfire array pattern and the coordinate system;

[0009] S200, for a predetermined pitch angle, extracting unambiguous clutter data at the predetermined pitch angle using the original clutter echo data at the predetermined pitch angle;

[0010] S300, calculating a covariance matrix of unambiguous clutter data at a predetermined pitch angle, and constructing a clutter spectrum of any point on a normalized space-time-frequency plane using the covariance matrix;

[0011] S400, reconstructing the covariance matrix using the clutter spectrum of any point on the normalized space-time-frequency plane to obtain a reconstructed covariance matrix; performing diagonal loading on the reconstructed covariance matrix to obtain a loaded covariance matrix at a predetermined pitch angle;

[0012] S500, calculating a transformation matrix for transforming clutter data for each range gate using the loading covariance matrix at the predetermined pitch angle; transforming the original clutter echo data of all range gates using the transformation matrix to obtain transformed clutter data;

[0013] S600 , performing maximum likelihood estimation on the transformed clutter data to obtain a filtering weight vector of a space-time optimal filter, and performing clutter suppression on the original clutter echo data of each range gate based on the filtering weight vector of the space-time optimal filter.

[0014] Beneficial effects of the present invention:

[0015] First, the present invention uses end-fire arrays for both transmitting and receiving arrays, which can better adapt to the aerodynamics of the airborne radar and the width of the array beam coverage airspace. The dual-base airborne radar system also ensures the system's ability to resist electronic interference and survivability.

[0016] Second, the present invention uses the difference between the clutter scattering point and the incident cone angle of the transceiver platform to select the clutter covariance matrix from the appropriate far-field pitch angle and use it as the RBC compensation reference covariance matrix to ensure the stability of the reference clutter.

[0017] Third, the present invention uses sub-aperture smoothing to expand the sample in the case of small samples and estimates the far-field covariance matrix, thereby ensuring that the number of samples meets the requirements.

[0018] Fourthly, the present invention achieves compensation for the Doppler frequency-distance dependence of the bistatic end-fire airborne radar clutter, eliminates the non-stationarity of the clutter, and thus enables the space-time adaptive algorithm to effectively suppress the clutter.

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic flow chart of a clutter suppression method based on a dual-base end-fire array airborne radar provided by the present invention;

[0021] Figure 2 A schematic diagram of the geometric configuration of the airborne bistatic radar provided by the present invention;

[0022] Figure 3 Schematic diagram of the planar end-fire array provided by the present invention. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0024] like Figure 1 As shown, the present invention provides a clutter suppression method based on a dual-base end-fire array airborne radar, comprising:

[0025] S100, constructing a coordinate system for a bistatic endfire array airborne radar system, and constructing an endfire array pattern using the coordinate system; constructing raw clutter echo data for all range gates using the endfire array pattern and the coordinate system;

[0026] In a specific embodiment of the present invention, S100 includes:

[0027] S110, construct the coordinate system of the dual-base end-fire array airborne radar system;

[0028] refer to Figure 2 In this step, the ground projection point of the receiving array center is used as the coordinate origin O, the vertical direction upward is the z-axis, the projection of the line between the receiving and transmitting array centers on the ground is the x-axis, and the direction perpendicular to the xOz plane on the ground is recorded as the y-axis to construct a coordinate system.

[0029] S120, determining relevant parameters of the clutter point, the transmitting platform, and the receiving platform themselves or among themselves in the coordinate system;

[0030] Continue to refer Figure 2 ,exist Figure 2 The relevant parameters include: the height of the transmitting array H T , the height of the receiving array H R , the baseline length L between the transmitting array and the receiving array, the projection point O of the transmitting array on the ground, the projection point Q of the receiving array on the ground, the center O of the transmitting array T , receiving array center O R , the launch aircraft speed v T , the carrier speed v of the receiving arrayR , the velocity cone angle φ of the scattering point P relative to the launch platform VT , velocity cone angle φ of the scattering point P relative to the receiving platform VR , the slant distance R between the scattering point and the transmitting array T , the slant distance R between the scattering point and the receiving array R , the cone angle φ of the scattering point relative to the axial direction of the receiving platform antenna AR , the azimuth angle θ of the clutter point relative to the launch platform CT , the azimuth angle θ of the clutter point relative to the receiving platform CR , the angle δ between the launch platform axis and the flight direction of each carrier aircraft T , the angle δ between the receiving platform axis and the flight direction of each carrier aircraft R , the elevation angle of the clutter scatterer relative to the launch platform The elevation angle of the clutter scatterer relative to the receiving platform The line formed by the center point S of the ground double base equidistant curve and the clutter scattering point P, and the azimuth angle θ to the x-axis SP , the distance R from the center point S to the scattering point P SP , the distance R from the center point S to the projection point Q on the receiving array xOy surface SQ , the distance R from the center point S to the projection point O on the xOy plane of the transmitting array OS , the angle γ between the baseline and the x-axis;

[0031] The clutter equidistance ring (range gate) is a trajectory ring composed of ground clutter scattering points. The ring can be divided into several small clutter units, and the sum of the distances between each clutter unit and the transmitting and receiving platforms is equal. According to the knowledge of solid geometry, the sum of the distances between the two bases is R S The scattering points are distributed on the same ellipsoid, which is centered on the transmitting and receiving arrays. T and O R For the focus.

[0032] When the baseline length of the transmitting and receiving platform is less than a certain level, the effect of the earth's curvature on clutter modeling can be ignored. In this case, the equidistant loop curve is the intersection of the ellipsoid and the horizontal plane. The equidistant loop curve is an elliptical curve. In this case, the sum of the transmitting and receiving slant distances must satisfy:

[0033]

[0034] The cosine of the cone angle between the clutter point and the receiving array axis is:

[0035] The cosine of the cone angle between the clutter point and the transmitting and receiving platform velocities is:

[0036]

[0037] With variable θSP The slant ranges from the clutter scattering point P to the transceiver platform are constructed as follows:

[0038]

[0039] Among them, R SP Indicates the distance from the center point S to the scattering point P, R SQ Indicates the distance from the center point S to the projection point Q on the receiving array xOy surface, R OS Indicates the distance from the center point S to the projection point O of the transmitting array on the xOy plane.

[0040] Since, we can get about θ SP The quadratic equation of :

[0041]

[0042] Where: γ is the angle between the baseline and the x-axis.

[0043] The expressions of the azimuth and elevation angles of the transceiver platform relative to the clutter point are:

[0044]

[0045]

[0046] S130, constructing an endfire array pattern according to the planar endfire array;

[0047] A planar end-fire array with M rows and N columns is Figure 3 As shown. The subarray parallel to the X axis is defined as the row subarray, and the subarray parallel to the Y axis is defined as the column subarray. In addition, the row subarray and the column subarray operate in end-fire mode. The array element spacing of the row subarray and the column subarray is d r and d c The end-fire array pattern is then expressed as:

[0048]

[0049] in, is the directional pattern of the Lie sub-array, is the row array pattern, M is the total number of row elements, which also indicates the total number of channels, m is the row element number, N is the total number of column elements, which also indicates the total number of channels, n is the column element number, which also indicates the channel number, d r is the spacing of the row subarray, d c is the spacing of the column sub-array, λ is the emission wavelength, and the emission main lobe is pointed to

[0050]

[0051] Among them, I n Indicates the weight of the nth array element, I m Represents the weight of the m-th row element;

[0052] S140, determining the sum of the transmission signals of the M channels received by the nth (n=1, 2, ...., N) receiving channel;

[0053] In the presence of array element errors, the sum of the transmitted signals of the M channels received by the nth (n = 1, 2, ..., N) receiving channel is expressed as:

[0054]

[0055] Among them, θ R is the receiving azimuth;

[0056] In the absence of array element errors, the sum of the transmitted signals of the M channels received by the nth (n = 1, 2, ..., N) receiving channel is expressed as:

[0057]

[0058] S150: Determine original clutter echo data of all pulses received by all receiving channels on the lth range gate using the sum of the transmitted signals.

[0059] S150 of the present invention includes:

[0060] S151, determine the area of ​​the clutter unit,

[0061] In this step, the scattering coefficient σ0 is set to where σ m is the RCS when the signal is incident vertically, is the pitch angle, then the area of ​​a ground clutter unit is

[0062]

[0063] Among them, c represents the speed of light, τ represents the time width, Δθ R represents the receiving beamwidth, and β represents the bistatic angle;

[0064] S152, using the sum of the scattering coefficient and the transmitted signal, calculate the echo amplitude P of the i-th scattering unit on the l-th range gate received by the n-th receiving channel l,i , expressed as:

[0065]

[0066] Where P represents the transmit power, is the transmitting antenna gain, θ TiIndicates the azimuth angle of this scattering unit relative to the transmitting platform, Indicates the pitch angle of this scattering unit relative to the launch platform, is the receiving antenna gain, θ Ri represents the azimuth angle of the scattering unit relative to the receiving platform, represents the pitch angle of the scattering unit relative to the receiving platform, σ0 is the scattering coefficient, L s is the radar loss coefficient, k is the Boltzmann constant, T0 is the temperature at room temperature, T0 = 290K, B is the receiver operating bandwidth, and F is the receiver noise figure;

[0067] S153, using the echo amplitude P in S152 l,i Calculate the clutter echo data of all C scattering elements on the lth range gate of the kth pulse received by the nth receiving channel, which can be expressed as:

[0068]

[0069] in, φ AR,i Indicates the cone angle of this scattering unit relative to the axial direction of the receiving platform antenna, φ VT,i The cone angle of the scattering unit relative to the launch platform, φ VR,i represents the cone angle of the scattering unit relative to the receiving platform velocity, f r represents the pulse repetition frequency;

[0070] S154, using the clutter echo data in S153, determine the clutter echo data of all pulses received by all receiving channels on the lth range gate, expressed as:

[0071]

[0072] in, represents the echo data from the kth (k=1, 2, ...., K) pulse,

[0073] Then the clutter echo signals of all L range gates can be expressed as

[0074]

[0075] S200, for a predetermined pitch angle, extracting unambiguous clutter data at the predetermined pitch angle using the original clutter echo data at the predetermined pitch angle;

[0076] In a specific embodiment of the present invention, S200 includes:

[0077] S210, using the orthogonal projection theory, construct the i , Predetermined pitch angle The spatial domain projection matrix and temporal domain projection matrix of the corresponding clutter scattering unit;

[0078] The spatial and temporal angular frequencies of bistatic airborne radar clutter both contain pitch information, which can be used to completely distinguish clutter of different directions and distances. Therefore, the spatial and temporal two-dimensional angular frequency information of the unambiguous clutter of the bistatic airborne radar can be used to accurately extract the unambiguous clutter in each sampling range gate to form new clutter data, thereby eliminating ambiguous clutter and short-range clutter. Assume that the pitch angle of the clutter at a certain sampling range gate in the far field is The spatial domain projection matrix and the temporal domain projection matrix are expressed as:

[0079]

[0080] in, Indicates the Doppler frequency corresponding to this azimuth and elevation angle,

[0081] S220, extracting characteristic unambiguous clutter components from the original clutter echo data using the spatial domain projection matrix and the temporal domain projection matrix;

[0082] This step extracts the unambiguous clutter components that meet the characteristics from the original clutter data and is expressed as:

[0083]

[0084] in,

[0085] S230, summing the initial unambiguous clutter data corresponding to the range gate for the unambiguous clutter components of all azimuth angles at the predetermined pitch angle;

[0086] The sum of the clutter data processed by the space-time cascade OP in the (0, 2π) azimuth constitutes the unambiguous clutter data of this range gate, which is expressed as:

[0087]

[0088] S240 , expanding the initial unambiguous clutter data in S230 by using a sub-aperture smoothing method to obtain unambiguous clutter data at a predetermined pitch angle.

[0089] This step will Convert to Then, using the sub-aperture smoothing method, the spatial sub-aperture is taken as J, the temporal sub-aperture is taken as G, and the initial unambiguous clutter data in S230 is smoothed by the spatial and temporal sub-aperture to obtain the (N-G+1)(K-J+1) matrix Q r,t , respectively expressed as:

[0090]

[0091] Among them, r=1,....,N-G+1; t=1,....,K-J+1.

[0092] S300, calculating a covariance matrix of unambiguous clutter data at a predetermined pitch angle, and constructing a clutter spectrum of any point on a normalized space-time-frequency plane using the covariance matrix;

[0093] The covariance matrix of the unambiguous clutter data at the predetermined pitch angle in this step is expressed as:

[0094]

[0095] The covariance matrix is ​​used to construct the normalized space-time frequency plane at any point (ω s,u ,ω d,v ) is expressed as:

[0096]

[0097] in, Indicates that the aperture is smoothed in (ω s,u ,ω d,v ) is the space-time steering vector at .

[0098] S400, reconstructing the covariance matrix using the clutter spectrum of any point on the normalized space-time-frequency plane to obtain a reconstructed covariance matrix; performing diagonal loading on the reconstructed covariance matrix to obtain a loaded covariance matrix at a predetermined pitch angle;

[0099] The covariance matrix reconstructed in this step is expressed as:

[0100]

[0101] in, After reconstruction, (ω s,u ,ω d,v ), U represents the total number of points where the normalized spatial frequency is divided. V Indicates the total number of points after dividing the normalized Doppler frequency;

[0102] The loading covariance matrix under the pitch angle is expressed as:

[0103]

[0104] Here, σ represents the diagonal loading.

[0105] S500, calculating a transformation matrix for transforming clutter data for each range gate using the loading covariance matrix at the predetermined pitch angle; transforming the original clutter echo data of all range gates using the transformation matrix to obtain transformed clutter data;

[0106] The method based on the RBC principle is to achieve angle-Doppler two-dimensional compensation for each fuzzy range clutter in each range gate in the full frequency domain, compensating not only the mainlobe clutter but also the sidelobe clutter. The basic idea is to first use the original clutter echo data matrix to obtain samples through space-time sub-aperture smoothing to estimate the distribution of clutter power in each range gate, and then select the far-field stationary clutter covariance matrix R f As the covariance matrix of the reference distance unit, and through the transformation matrix T l This ensures that the noise characteristics of each training unit after transformation are consistent with the statistical characteristics of the remote reference distance unit.

[0107] In a specific embodiment of the present invention, S500 includes:

[0108] S510, bringing the loading covariance matrix at the predetermined pitch angle into the solution formula, and calculating the transformation matrix T for each range gate used to transform the clutter data l , the solution formula is expressed as:

[0109]

[0110] S520 uses the transformation matrix to transform the original clutter echo data of all range gates to obtain transformed clutter data, which is expressed as:

[0111]

[0112] S600 , performing maximum likelihood estimation on the transformed clutter data to obtain a filtering weight vector of a space-time optimal filter, and performing clutter suppression on the original clutter echo data of each range gate based on the filtering weight vector of the space-time optimal filter.

[0113] S600 of this step includes:

[0114] S610, converting the space-time adaptive processing algorithm into a mathematical optimization problem, expressed as:

[0115]

[0116] S620, solving a mathematical optimization problem based on the transformed clutter data to obtain a maximum likelihood estimate of the clutter covariance matrix, expressed as:

[0117]

[0118] S630: Determine a filter weight vector of a space-time optimal filter using the maximum likelihood estimate, expressed as:

[0119]

[0120] Where S is the space-time steering vector corresponding to the main lobe position;

[0121] S640 : Perform clutter suppression on the original clutter echo data of each range gate based on the filter weight vector of the space-time optimal filter.

[0122] The present invention provides a clutter suppression method based on a dual-base end-fire array airborne radar. The method constructs raw clutter echo data for all range gates, extracts unambiguous clutter data at small elevation angles to construct an unambiguous clutter covariance matrix, and then calculates a transformation matrix to transform the raw clutter echo data. Maximum likelihood estimation is performed on the transformed clutter data to obtain a filter weight vector, and clutter suppression is performed on the raw clutter echo data. The method utilizes the difference between the clutter scattering point and the incident cone angle of the transceiver platform to select an appropriate elevation angle to construct a far-field stationary unambiguous clutter covariance matrix as a reference covariance matrix for RBC compensation, thereby ensuring the stationarity of the reference clutter. Subaperture smoothing is also used to expand samples to estimate the covariance matrix, ensuring that the number of samples meets the required sample number. Furthermore, the method eliminates the non-stationarity of the clutter, thereby enabling effective clutter suppression using a space-time adaptive algorithm.

[0123] It should be noted 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 the technical features being referred to. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0124] 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 clutter suppression method based on a dual-base end-fire array airborne radar, characterized in that: include: S100, constructing a coordinate system of a bistatic endfire array airborne radar system, and constructing an endfire array pattern using the coordinate system; Use the end-fire array pattern and coordinate system to construct the raw clutter echo data of all range gates; S200, for a predetermined pitch angle, extracting unambiguous clutter data at the predetermined pitch angle using the original clutter echo data at the predetermined pitch angle; S300, calculating a covariance matrix of unambiguous clutter data at a predetermined pitch angle, and constructing a clutter spectrum of any point on a normalized space-time-frequency plane using the covariance matrix; S400, reconstructing the covariance matrix using the clutter spectrum of any point on the normalized space-time-frequency plane to obtain a reconstructed covariance matrix; Performing diagonal loading on the reconstructed covariance matrix to obtain a loaded covariance matrix at a predetermined pitch angle; S500, calculating a transformation matrix for transforming clutter data for each range gate using the loading covariance matrix at the predetermined pitch angle; transforming the original clutter echo data of all range gates using the transformation matrix to obtain transformed clutter data; S600, performing maximum likelihood estimation on the transformed clutter data to obtain a filter weight vector of a space-time optimal filter, and performing clutter suppression on the original clutter echo data of each range gate based on the filter weight vector of the space-time optimal filter; S100 includes: S110, constructing a coordinate system for the dual-base end-fire array airborne radar system; wherein the coordinate system has the ground projection point of the receiving array center as the coordinate origin O, the upward direction perpendicular to the ground as the z-axis, the ground projection of the line connecting the receiving and transmitting array centers as the x-axis, and the direction perpendicular to the xOz plane on the ground as the y-axis; S120, determining relevant parameters of the clutter point, the transmitting platform, and the receiving platform themselves or among themselves in the coordinate system; S130, constructing an endfire array pattern according to the planar endfire array; S140, using the endfire array pattern, determining the sum of the transmit signals of the M channels received by the nth, n=1, 2, ..., Nth, receiving channels with and without array element errors; S150: Determine original clutter echo data of all pulses received by all receiving channels on the lth range gate using the sum of the transmitted signals.

2. The clutter suppression method based on a dual-base end-fire array airborne radar according to claim 1, characterized in that: The relevant parameters in S120 include: the height H of the transmitting array T , the height of the receiving array H R , the baseline length L between the transmitting array and the receiving array, the projection point O of the transmitting array on the ground, the projection point Q of the receiving array on the ground, the center O of the transmitting array T , receiving array center O R , the launch aircraft speed v T , the carrier speed v of the receiving array R , the velocity cone angle φ of the scattering point P relative to the launch platform VT , velocity cone angle φ of the scattering point P relative to the receiving platform VR , the slant distance R between the scattering point and the transmitting array T , the slant distance R between the scattering point and the receiving array R , the cone angle φ of the scattering point relative to the axial direction of the receiving platform antenna AR , the azimuth angle θ of the clutter point relative to the launch platform CT , the azimuth angle θ of the clutter point relative to the receiving platform CR , the angle δ between the launch platform axis and the flight direction of each carrier aircraft T , the angle δ between the receiving platform axis and the flight direction of each carrier aircraft R , the elevation angle of the clutter scatterer relative to the launch platform The elevation angle of the clutter scatterer relative to the receiving platform The azimuth angle θ between the line formed by the center point S of the ground double base equidistant curve and the clutter scattering point P and the x-axis SP , the distance R from the center point S to the scattering point P SP , the distance R from the center point S to the projection point Q on the receiving array xOy surface SQ , the distance R from the center point S to the projection point O on the xOy plane of the transmitting array OS , the angle γ between the baseline and the x-axis; The end-fire array pattern in S130 is expressed as: in, is the directional pattern of the Lie sub-array, is the row array pattern, M is the total number of row elements, which also indicates the total number of channels, m is the row element number, N is the total number of column elements, which also indicates the total number of channels, n is the column element number, which also indicates the channel number, d r is the spacing of the row subarray, d c is the spacing of the column sub-array, λ is the emission wavelength, and the emission main lobe is pointed to Among them, I n Indicates the weight of the nth array element, I m Represents the weight of the m-th row element; S140, determining the sum of the transmission signals of the M channels received by the nth, n=1, 2, ..., N receiving channels, In the presence of array element errors, the sum of the transmit signals of M channels received by the nth, n=1, 2, ..., Nth receiving channels is expressed as: Among them, θ R is the receiving azimuth; In the absence of array element errors, the sum of the transmit signals of M channels received by the nth, n=1, 2, ..., Nth receiving channels is expressed as:

3. The clutter suppression method based on a dual-base end-fire array airborne radar according to claim 2, characterized in that: The S150 includes: S151, determine the area of ​​the clutter unit, expressed as: Among them, c represents the speed of light, τ represents the time width, Δθ R represents the receiving beamwidth, and β represents the bistatic angle; S152, using the sum of the scattering coefficient and the transmitted signal, calculate the echo amplitude P of the i-th scattering unit on the l-th range gate received by the n-th receiving channel l,i , expressed as: Where P represents the transmit power, is the transmitting antenna gain, θ Ti Indicates the azimuth angle of this scattering unit relative to the transmitting platform, Indicates the pitch angle of this scattering unit relative to the launch platform, is the receiving antenna gain, θ Ri represents the azimuth angle of the scattering unit relative to the receiving platform, represents the pitch angle of the scattering unit relative to the receiving platform, σ0 is the scattering coefficient, L s is the radar loss coefficient, k is the Boltzmann constant, T0 is the room temperature, T0 = 290K, B is the receiver operating bandwidth; F is the receiver noise figure; S153, using the echo amplitude P in S152 l,i Calculate the clutter echo data of all C scattering elements on the lth range gate of the kth pulse received by the nth receiving channel, which can be expressed as: in, φ AR,i Indicates the cone angle of this scattering unit relative to the axial direction of the receiving platform antenna, φ VT,i The cone angle of the scattering unit relative to the launch platform, φ VR,i represents the cone angle of the scattering unit relative to the receiving platform velocity, f r represents the pulse repetition frequency; S154, using the clutter echo data in S153, determine the clutter echo data of all pulses received by all receiving channels on the lth range gate, expressed as: in, represents the echo data from the kth, k=1,2,…,Kth pulse, 4. The clutter suppression method based on a dual-base end-fire array airborne radar according to claim 3, characterized in that: S200 includes: S210, using the orthogonal projection theory, construct the i , Predetermined pitch angle The spatial domain projection matrix and temporal domain projection matrix of the corresponding clutter scattering unit; S220, extracting characteristic unambiguous clutter components from the original clutter echo data using the spatial domain projection matrix and the temporal domain projection matrix; S230, summing the initial unambiguous clutter data corresponding to the range gate for the unambiguous clutter components of all azimuth angles at the predetermined pitch angle; S240 , expanding the initial unambiguous clutter data in S230 by using a sub-aperture smoothing method to obtain unambiguous clutter data at a predetermined pitch angle.

5. The clutter suppression method based on a dual-base end-fire array airborne radar according to claim 4, characterized in that: The spatial domain projection matrix and the temporal domain projection matrix in S210 are respectively expressed as: in, Indicates the Doppler frequency corresponding to this azimuth and elevation angle, The unambiguous clutter component in S220 is expressed as: in, The initial unambiguous clutter data in S230 is expressed as: S240 includes: Convert to Then, using the sub-aperture smoothing method, we take the spatial sub-aperture as J and the temporal sub-aperture as G, and perform spatial and temporal sub-aperture smoothing on the initial unambiguous clutter data in S230 to expand the sample size, and obtain (N-G+1)(K-J+1) matrices Q r,t , respectively expressed as: Where r = 1,…,N-G+1; t = 1,…,K-J+1.

6. The clutter suppression method based on a dual-base end-fire array airborne radar according to claim 5, characterized in that: S300 includes: S310, calculating the covariance matrix of the unambiguous clutter data at a predetermined pitch angle is expressed as: S320, constructing the normalized space-time frequency plane at any point (ω s,u ,ω d,v ) is expressed as: in, Indicates that after aperture smoothing (ω s,u ,ω d,v ) is the space-time steering vector at .

7. The clutter suppression method based on a dual-base end-fire array airborne radar according to claim 6, characterized in that: S400 includes: S410, reconstructing the covariance matrix using the clutter spectrum of any point on the normalized space-time-frequency plane to obtain a reconstructed covariance matrix, which is expressed as: in, Represents the reconstruction after (ω s,u ,ω d,v ), U represents the total number of points after the normalized spatial frequency is divided, and V represents the total number of points after the normalized Doppler frequency is divided; S420, performing diagonal loading on the reconstructed covariance matrix to obtain a loaded covariance matrix at a predetermined pitch angle, which is expressed as: Where σ represents the diagonal loading.

8. The clutter suppression method based on a dual-base end-fire array airborne radar according to claim 7, characterized in that: S500 includes: S510: Substitute the loading covariance matrix at the predetermined pitch angle into the solution formula to calculate the transformation matrix T for each range gate used to transform the clutter data. l , the solution formula is expressed as: S520 uses the transformation matrix to transform the original clutter echo data of all range gates to obtain transformed clutter data, which is expressed as:

9. The clutter suppression method based on a dual-base end-fire array airborne radar according to claim 8, characterized in that: S600 includes: S610, converting the space-time adaptive processing algorithm into a mathematical optimization problem, expressed as: S620, solving a mathematical optimization problem based on the transformed clutter data to obtain a maximum likelihood estimate of the clutter covariance matrix, expressed as: S630: Determine a filter weight vector of a space-time optimal filter using the maximum likelihood estimate, expressed as: Where S is the space-time steering vector corresponding to the main lobe position; S640 : Perform clutter suppression on the original clutter echo data of each range gate based on the filter weight vector of the space-time optimal filter.

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