CN113253230A - Sub-aperture processing-based space-based early warning radar aerial moving target detection method and system - Google Patents

Abstract

The invention provides a sub-aperture processing-based space-based early warning radar air moving target detection method and system, which comprises the following steps: preprocessing multi-channel echoes of the space-based early warning radar to obtain preprocessed radar echo data; performing Keystone transformation on the preprocessed radar echo data to finish distance walking correction; dividing the echo data after the distance walk correction along the azimuth sub-aperture to ensure that Doppler diffusion does not occur in the sub-aperture; clutter suppression is completed in each sub-aperture by using a post-Doppler space-time adaptive processing technology, preliminary accumulation is completed in each sub-aperture, and then a target to be detected is extracted through constant false alarm detection of a low threshold; and performing phase compensation on the extracted targets to be detected one by one, performing Fourier transform along the direction of the sub-apertures to realize coherent accumulation among the sub-apertures and further improve the output signal-to-noise-ratio of target signals, and finally rejecting false alarms and reserving real target points through high-threshold detection.

Description

A method and system for detecting airborne moving targets in space-based early warning radar based on sub-aperture processing

technical field

The present invention relates to the field of radar signal processing, in particular, to a method and system for detecting airborne moving targets of space-based early warning radar based on sub-aperture processing, and more particularly, to a space-based method and system based on sub-aperture coherent accumulation transform (SCA). Early warning radar AMTI method.

Background technique

Space-based early warning radar has the advantages of continuous global coverage, strong anti-stealth capability and high security, and plays a very important role in national defense construction. With the rapid development of aerospace technology, advanced air flight targets often exhibit small radar cross-sectional area (RCS), high speed, and high maneuverability, resulting in weak echo signal energy. The moving objects of are often submerged in the extended ground/sea clutter background, making object detection extremely challenging. Space-time adaptive processing (STAP) technology can be applied in the multi-channel space-based early warning radar system to achieve effective clutter suppression and improve the output signal-to-noise ratio (SCNR) of the target.

Exchanging energy by prolonging the accumulation time is an effective way to improve the detection performance of weak and small targets. However, under long-term observation, due to the maneuvering characteristics of non-cooperative targets, it will cause cross-distance walking and cross-Doppler frequency walking, which will reduce the output SCNR. . The methods to solve this problem include three schemes: coherent accumulation, non-coherent accumulation and mixed accumulation. Among them, the coherent accumulation method improves the output SCNR by coherent accumulation of multiple azimuth pulses, but usually needs to set up a multi-dimensional parameter matched filter, which is not suitable for engineering real-time processing; the non-coherent accumulation transformation faces the defect of insufficient output SNR. . The hybrid accumulation method can deal with the contradiction between the low gain of the traditional non-coherent accumulation and the large calculation of the coherent accumulation. This kind of method divides the accumulation time into segments, completes the coherent accumulation in the segment, and then further completes the incoherent accumulation result of the coherent accumulation in each segment. Accumulation means intra-segment coherent accumulation and inter-segment incoherent accumulation. Typical methods include combining Hough transform, dynamic programming, and tracking before detection (TBD). However, in the background of space-based radar AMTI, due to the large distance of the target echo, the direct coherent accumulation pulses in the segment are few, and the accumulation gain is small, which is not conducive to the detection of weak air-moving targets of the space-based early warning radar. Increasing the coherent accumulation time as much as possible, and then making full use of the target energy accumulation in the track to obtain the maximum accumulation gain is the direction of the space-based early warning radar for weak air moving target detection.

Patent document CN102288948B (application number: 201110123779.2) discloses a STAP-based high-speed platform high-speed air moving target detection method. The invention belongs to the technical field of aerial moving target detection. Detection steps: (1) Keystone transformation is performed on the space-time two-dimensional data received by the high-speed platform phased array radar to correct the clutter distance movement; (2) The clutter covariance is estimated according to the data of the reference unit for the corrected data of the clutter movement. (3) The inverse matrix of the clutter covariance matrix is multiplied by the data after Keystone transformation to achieve clutter suppression; (4) The suppressed data is transformed into the distance frequency domain to prepare for the target distance walking compensation; (5) According to the air movement The target speed range and radar system parameters construct a fuzzy number set; (6) construct a filter bank according to the fuzzy number set; (7) Step 4 data passes through the filter bank to realize the target distance walking correction and perform space-time two corrections on the correction results. Dimensional beamforming achieves target accumulation. Through parallel processing, the invention simultaneously detects multiple targets with different fuzzy numbers, and has the advantages of high operation speed, convenient engineering realization, and the like.

SUMMARY OF THE INVENTION

In view of the defects in the prior art, the purpose of the present invention is to provide a method and system for detecting airborne moving targets of space-based early warning radar based on sub-aperture processing.

According to a method for detecting air moving targets of space-based early warning radar based on sub-aperture processing provided by the present invention, the method includes:

Step S1: preprocessing the multi-channel echoes of the space-based early warning radar to obtain preprocessed radar echo data;

Step S2: Perform Keystone transformation on the preprocessed radar echo data to complete distance walking correction;

Step S3: Divide the echo data after the distance walking correction along the azimuth sub-aperture to ensure that Doppler diffusion does not occur in the sub-aperture;

Step S4: use post-Doppler space-time adaptive processing technology in each sub-aperture to complete clutter suppression, complete the preliminary accumulation of coherence in each sub-aperture, and then extract the to-be-detected through low-threshold constant false alarm detection. Target;

Step S5: Perform phase compensation on the extracted targets to be detected one by one, and then perform Fourier transform along the sub-aperture direction to complete the coherent accumulation between sub-apertures, further improve the output signal-to-noise ratio of the target signal, and detect through a high threshold. Eliminate false alarms and keep true target points.

Preferably, the preprocessed radar echo data in the step S1 includes: echoes of moving targets in the air, clutter and noise;

The air moving target echo of the mth channel after preprocessing is expressed as:

表示目标幅度，P_t，τ，B，G_T(θ_Azi,t,θ_El,t)，G_{R_Sub}(θ_Azi,t,θ_El,t)，λ，L_s和σ分别表示峰值功率，脉宽，带宽，发射天线全孔径增益，接收天线子通道增益，信号波长，雷达系统损失和目标RCS；R₀为最近斜距；θ_El,t和θ_Azi,t分别为目标的下视角和方位角；且cos(θ_Cone,t)＝cos(θ_El,t)cos(θ_Azi,t)；θ_Cone,t表示空间锥角；t_r和t_a分别表示距离快时间和方位慢时间变量；T_a表示积累时间，rect(·)和sinc(·)分别表示矩形窗函数和sinc函数；c表示光速；j表示虚数单位；R_0t,m(t_a)为利用平台参数经过deramp补偿后的斜距：in,

represents the target amplitude, P _t , τ, B, G _T (θ _Azi,t ,θ _El,t ), G _{R_Sub} (θ _Azi,t ,θ _El,t ), λ, L _s and σ represent the peak power, respectively, Pulse width, bandwidth, full aperture gain of transmit antenna, sub-channel gain of receive antenna, signal wavelength, radar system loss and target RCS; R ₀ is the closest slant range; θ _El,t and θ _Azi,t are the down-angle and θ of the target, respectively. Azimuth; and cos(θ _Cone,t )=cos(θ _El,t )cos(θ _Azi,t ); θ _Cone,t represents the spatial cone angle; _tr and t _a represent the distance fast time and azimuth slow time, respectively Variable; T _a represents the accumulation time, rect( ) and sinc( ) represent the rectangular window function and sinc function respectively; _c represents the speed of light; _j represents the imaginary unit; Slope distance after:

Among them, R ₀ is the nearest slant distance; D is the antenna size, and d _m is the channel spacing;

v _e =v _y sinθ _Azi,t sinθ _El,t -v _rx cosθ _Azi,t sinθ _El,t denotes the equivalent radial velocity; v _rx =vv _x is the relative platform velocity; v denotes the platform velocity, v _x denotes the Target azimuth velocity; v _y represents target radial velocity;

表示等效的加速度。

represents the equivalent acceleration.

Preferably, the step S1 includes: preprocessing the multi-channel echoes of the space-based early warning radar, including range compression, platform motion parameter compensation, frequency reduction, and clutter Doppler center compensation operations.

Preferably, the step S2 includes: using the Keystone transform to complete the distance movement correction before the sub-aperture division, and simultaneously remove the distance movement within the sub-aperture and between the sub-apertures.

Preferably, the step S5 includes: performing phase compensation on the extracted targets to be detected one by one, deriving and compensating the phase relationship between the sub-aperture echoes, performing Fourier transform along the sub-aperture direction, and completing the inter-sub-aperture echoes. Coherent accumulation to further improve the output signal-to-noise ratio of the target signal;

The phase compensation for the extracted targets to be detected one by one includes:

表示搜索的等效加速度；λ表示信号波长；j表示虚数单位；l表示子孔径数；T_c表示子孔径内的积累时间；τ_a,1表示参考子孔径的时间变量；in,

represents the equivalent acceleration of the search; λ represents the signal wavelength; j represents the imaginary unit; l represents the number of sub-apertures; T _c represents the accumulation time in the sub-aperture; τ _a,1 represents the time variable of the reference sub-aperture;

The echo signal is coherently accumulated in each sub-aperture by the azimuth Fourier transform, and the coherent accumulation is completed between the sub-apertures by the sub-aperture Fourier transform; after the sub-aperture coherent accumulation, the echo signal is finally expressed as :

表示积累后的幅度；M表示通道数；P_av表示雷达平均功率；G_T表示发射天线全孔径增益；G_R-Sub表示接收天线子通道增益；f_a和f_l分别表示多普勒频率和子孔径频率变量；L表示子孔径数；B表示信号带宽；t_r表示距离快时间变量；R₀表示最近斜距，c表示光速，T_c表示子孔径积累时间，λ表示信号波长，v_e表示等效径向速度，N_c表示子孔径内的方位脉冲数，D表示天线方位尺寸，θ_El,t表示目标下视角,θ_Azi,t表示目标方位角。in,

represents the accumulated amplitude; M represents the number of channels; P _av represents the average radar power; G _T represents the full aperture gain of the transmitting antenna; G _R-Sub represents the sub-channel gain of the receiving antenna; f _a and f _l represent the Doppler frequency and sub-channel, respectively Aperture frequency variable; L represents the number of sub-apertures; B represents the signal bandwidth; t _r represents the distance fast time variable; R ₀ represents the closest slope distance, c represents the speed of light, T _c represents the sub-aperture accumulation time, λ represents the signal wavelength, and _ve represents the Equivalent radial velocity, N _c represents the number of azimuth pulses in the sub-aperture, D represents the azimuth size of the antenna, θ _{El, t} represents the viewing angle of the target, θ _{Azi, t} represents the azimuth angle of the target.

A kind of space-based early warning radar air moving target detection system based on sub-aperture processing provided according to the present invention includes:

Module M1: Preprocess the multi-channel echo of the space-based early warning radar to obtain the preprocessed radar echo data;

Module M2: Perform Keystone transformation on the preprocessed radar echo data to complete distance walking correction;

Module M3: Divide the echo data after distance walking correction along the azimuth sub-aperture to ensure that Doppler diffusion does not occur in the sub-aperture;

Module M4: Use post-Doppler space-time adaptive processing technology to complete clutter suppression in each sub-aperture, complete initial coherent accumulation in each sub-aperture, and then extract the target to be detected through low-threshold constant false alarm detection ;

Module M5: Perform phase compensation on the extracted targets to be detected one by one, and then perform Fourier transform along the sub-aperture direction to complete the coherent accumulation between sub-apertures, further improve the output signal-to-noise ratio of the target signal, and detect through a high threshold Eliminate false alarms and keep true target points.

Preferably, the preprocessed radar echo data in the module M1 includes: echoes of moving targets in the air, clutter and noise;

The air moving target echo of the mth channel after preprocessing is expressed as:

表示目标幅度，P_t，τ，B，G_T(θ_Azi,t,θ_El,t)，G_{R_Sub}(θ_Azi,t,θ_El,t)，λ，L_s和σ分别表示峰值功率，脉宽，带宽，发射天线全孔径增益，接收天线子通道增益，信号波长，雷达系统损失和目标RCS；R₀为最近斜距；θ_El,t和θ_Azi,t分别为目标的下视角和方位角；且cos(θ_Cone,t)＝cos(θ_El,t)cos(θ_Azi,t)；θ_Cone,t表示空间锥角；t_r和t_a分别表示距离快时间和方位慢时间变量；T_a表示积累时间，rect(·)和sinc(·)分别表示矩形窗函数和sinc函数；c表示光速；j表示虚数单位；R_0t,m(t_a)为利用平台参数经过deramp补偿后的斜距：in,

represents the target amplitude, P _t , τ, B, G _T (θ _Azi,t ,θ _El,t ), G _{R_Sub} (θ _Azi,t ,θ _El,t ), λ, L _s and σ represent the peak power, respectively, Pulse width, bandwidth, full aperture gain of transmit antenna, sub-channel gain of receive antenna, signal wavelength, radar system loss and target RCS; R ₀ is the closest slant range; θ _El,t and θ _Azi,t are the down-angle and θ of the target, respectively. Azimuth; and cos(θ _Cone,t )=cos(θ _El,t )cos(θ _Azi,t ); θ _Cone,t represents the spatial cone angle; _tr and t _a represent the distance fast time and azimuth slow time, respectively Variable; T _a represents the accumulation time, rect( ) and sinc( ) represent the rectangular window function and sinc function respectively; _c represents the speed of light; _j represents the imaginary unit; Slope distance after:

Among them, R ₀ is the nearest slant distance; D is the antenna size, and d _m is the channel spacing;

v _e =v _y sinθ _Azi,t sinθ _El,t -v _rx cosθ _Azi,t sinθ _El,t denotes the equivalent radial velocity; v _rx =vv _x is the relative platform velocity; v denotes the platform velocity, v _x denotes the Target azimuth velocity; v _y represents target radial velocity;

表示等效的加速度。

represents the equivalent acceleration.

Preferably, the module M1 includes: preprocessing the multi-channel echoes of the space-based early warning radar, including range compression, platform motion parameter compensation, frequency reduction, and clutter Doppler center compensation operations.

Preferably, the module M2 includes: using the Keystone transform to complete the distance movement correction before sub-aperture division, and simultaneously remove the distance movement within and between sub-apertures.

Preferably, the module M5 includes: performing phase compensation on the extracted targets to be detected one by one, deriving and compensating the phase relationship between the sub-aperture echoes, performing Fourier transform along the sub-aperture direction, and completing the inter-sub-aperture echoes. Coherent accumulation to further improve the output signal-to-noise ratio of the target signal;

The phase compensation for the extracted targets to be detected one by one includes:

表示搜索的等效加速度；λ表示信号波长；j表示虚数单位；l表示子孔径数；T_c表示子孔径内的积累时间；τ_a,1表示参考子孔径的时间变量；in,

represents the equivalent acceleration of the search; λ represents the signal wavelength; j represents the imaginary unit; l represents the number of sub-apertures; T _c represents the accumulation time in the sub-aperture; τ _a,1 represents the time variable of the reference sub-aperture;

The echo signal is coherently accumulated in each sub-aperture by the azimuth Fourier transform, and the coherent accumulation is completed between the sub-apertures by the sub-aperture Fourier transform; after the sub-aperture coherent accumulation, the echo signal is finally expressed as :

表示积累后的幅度；M表示通道数；P_av表示雷达平均功率；G_T表示发射天线全孔径增益；G_R-Sub表示接收天线子通道增益；f_a和f_l分别表示多普勒频率和子孔径频率变量；L表示子孔径数；B表示信号带宽；t_r表示距离快时间变量；R₀表示最近斜距，c表示光速，T_c表示子孔径积累时间，λ表示信号波长，v_e表示等效径向速度，N_c表示子孔径内的方位脉冲数，D表示天线方位尺寸，θ_El,t表示目标下视角,θ_Azi,t表示目标方位角。in,

represents the accumulated amplitude; M represents the number of channels; P _av represents the average radar power; G _T represents the full aperture gain of the transmitting antenna; G _R-Sub represents the sub-channel gain of the receiving antenna; f _a and f _l represent the Doppler frequency and sub-channel, respectively Aperture frequency variable; L represents the number of sub-apertures; B represents the signal bandwidth; t _r represents the distance fast time variable; R ₀ represents the closest slope distance, c represents the speed of light, T _c represents the sub-aperture accumulation time, λ represents the signal wavelength, and _ve represents the Equivalent radial velocity, N _c represents the number of azimuth pulses in the sub-aperture, D represents the azimuth size of the antenna, θ _{El, t} represents the viewing angle of the target, θ _{Azi, t} represents the azimuth angle of the target.

Compared with the prior art, the present invention has the following beneficial effects:

The invention proposes a space-based early warning air moving target detection method based on sub-aperture coherent accumulation. By adopting the method, the coherent accumulation in sub-apertures and between sub-apertures can be realized at the same time, and the shortage of output SCNR of the existing hybrid accumulation algorithm is overcome. Compared with the maximum-likelihood-based coherent accumulation algorithm, the proposed method has more advantages in computational complexity; therefore, the proposed method guarantees output SCNR with relatively high computational efficiency, which is very suitable for long-term use under the background of space-based early warning. Observation improves detection of weak targets in the air.

The invention can simultaneously realize the coherent accumulation detection between sub-apertures and within the sub-apertures, effectively improve the output SCNR, and is very suitable for completing air moving target detection under the background of space-based early warning.

Description of drawings

Other features, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments with reference to the following drawings:

1 is a main implementation step diagram of a space-based early warning AMTI method based on sub-aperture coherent accumulation provided by the present invention;

Figure 2 is a multi-channel observation model for space-based radar to observe moving targets in the air;

Fig. 3 is the flow chart of the air moving target detection method of space-based early warning radar based on sub-aperture processing;

Figure 4 is a schematic diagram of the clutter spectrum of the space-based early warning radar;

Figure 5 is a schematic diagram of the results of directly using STAP for clutter suppression and moving target detection;

FIG. 6 is a schematic diagram of clutter suppression results using sub-aperture STAP (divided into 8 sub-apertures in total);

FIG. 7 is a schematic diagram of the result of low-threshold CFAR detection (8.5dB);

Figure 8 is a schematic diagram of the search curves of targets 1 to 3 and false alarm points; f

FIG. 9 is a schematic diagram of the comparison results of the mixed accumulation and sub-aperture coherent accumulation of target 1;

Figure 10 is a schematic diagram of the comparison results of the mixed accumulation and sub-aperture coherent accumulation of target 2;

Figure 11 is a schematic diagram of the comparison results of the mixed accumulation and sub-aperture coherent accumulation of target 3;

FIG. 12 is a schematic diagram of detection results obtained by coherent accumulation of sub-apertures;

FIG. 13 is a schematic diagram of the result after high-threshold CFAR detection.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the inventive concept. These all belong to the protection scope of the present invention.

The purpose of the present invention is to overcome the defect of the traditional hybrid accumulation method that the output SCNR is limited, the phase relationship between the sub-apertures is not fully utilized, and therefore the moving target detection performance is not ideal, and a sub-aperture coherent accumulation (SCA)-based method is proposed. Space-based early warning radar AMTI method.

Example 1

According to a method for detecting air moving targets of space-based early warning radar based on sub-aperture processing provided by the present invention, the method includes:

Step S1: preprocessing the multi-channel echoes of the space-based early warning radar to obtain preprocessed radar echo data;

Step S2: Perform Keystone transformation on the preprocessed radar echo data to complete distance walking correction;

Step S3: dividing the echo data corrected by the distance movement along the azimuth sub-apertures, and the basis of the division is that Doppler frequency movement does not occur in each sub-aperture to ensure that Doppler diffusion does not occur in the sub-aperture;

Step S4: Use Post-Doppler Space-Time Adaptive Processing (STAP) in each sub-aperture to complete clutter suppression, complete the preliminary accumulation of coherence in each sub-aperture, and then pass the low-threshold constant false alarm (CFAR) Detect, extract the target to be detected;

Step S5: Perform phase compensation on the extracted targets to be detected one by one, and then perform Fourier transform along the sub-aperture direction to complete the coherent accumulation between sub-apertures and further improve the output signal-to-noise ratio (SCNR) of the target signal. High-threshold CFAR detection rejects false alarms and preserves true target points.

Specifically, the preprocessed radar echo data in the step S1 includes: echoes of moving targets in the air, clutter and noise;

The air moving target echo of the mth channel after preprocessing is expressed as:

表示目标幅度，P_t，τ，B，G_T(θ_Azi,t,θ_El,t)，G_{R_Sub}(θ_Azi,t,θ_El,t)，λ，L_s和σ分别表示峰值功率，脉宽，带宽，发射天线全孔径增益，接收天线子通道增益，信号波长，雷达系统损失和目标RCS；R₀为最近斜距；θ_El,t和θ_Azi,t分别为目标的下视角和方位角；且cos(θ_Cone,t)＝cos(θ_El,t)cos(θ_Azi,t)；θ_Cone,t表示空间锥角；t_r和t_a分别表示距离快时间和方位慢时间变量；T_a表示积累时间，rect(·)和sinc(·)分别表示矩形窗函数和sinc函数；c表示光速；j表示虚数单位；R_0t,m(t_a)为利用平台参数经过deramp补偿后的斜距：in,

represents the target amplitude, P _t , τ, B, G _T (θ _Azi,t ,θ _El,t ), G _{R_Sub} (θ _Azi,t ,θ _El,t ), λ, L _s and σ represent the peak power, respectively, Pulse width, bandwidth, full aperture gain of transmit antenna, sub-channel gain of receive antenna, signal wavelength, radar system loss and target RCS; R ₀ is the closest slant range; θ _El,t and θ _Azi,t are the down-angle and θ of the target, respectively. Azimuth; and cos(θ _Cone,t )=cos(θ _El,t )cos(θ _Azi,t ); θ _Cone,t represents the spatial cone angle; _tr and t _a represent the distance fast time and azimuth slow time, respectively Variable; T _a represents the accumulation time, rect( ) and sinc( ) represent the rectangular window function and sinc function respectively; _c represents the speed of light; _j represents the imaginary unit; Slope distance after:

Among them, R ₀ is the nearest slant distance; D is the antenna size, and d _m is the channel spacing;

v _e =v _y sinθ _Azi,t sinθ _El,t -v _rx cosθ _Azi,t sinθ _El,t denotes the equivalent radial velocity; v _rx =vv _x is the relative platform velocity; v denotes the platform velocity, v _x denotes the Target azimuth velocity; v _y represents target radial velocity;

表示等效的加速度。

represents the equivalent acceleration.

Specifically, the step S1 includes: preprocessing the multi-channel echoes of the space-based early warning radar, including range compression, platform motion parameter compensation, frequency reduction, and clutter Doppler center compensation operations.

Specifically, the step S2 includes: using the Keystone transform to complete the distance movement correction before the sub-aperture division, and simultaneously remove the distance movement within the sub-aperture and between the sub-apertures.

Specifically, the step S5 includes: performing phase compensation on the extracted targets to be detected one by one, deriving and compensating the phase relationship between the sub-aperture echoes, performing Fourier transform along the sub-aperture direction, and completing the inter-sub-aperture echoes. Coherent accumulation to further improve the output signal-to-noise ratio of the target signal;

The phase compensation for the extracted targets to be detected one by one includes:

表示搜索的等效加速度；λ表示信号波长；j表示虚数单位；l表示子孔径数；T_c表示子孔径内的积累时间；τ_a,1表示参考子孔径的时间变量；in,

represents the equivalent acceleration of the search; λ represents the signal wavelength; j represents the imaginary unit; l represents the number of sub-apertures; T _c represents the accumulation time in the sub-aperture; τ _a,1 represents the time variable of the reference sub-aperture;

The echo signal is coherently accumulated in each sub-aperture by the azimuth Fourier transform, and the coherent accumulation is completed between the sub-apertures by the sub-aperture Fourier transform; after the sub-aperture coherent accumulation, the echo signal is finally expressed as :

表示积累后的幅度；M表示通道数；P_av表示雷达平均功率；G_T表示发射天线全孔径增益；G_R-Sub表示接收天线子通道增益；f_a和f_l分别表示多普勒频率和子孔径频率变量；L表示子孔径数；B表示信号带宽；t_r表示距离快时间变量；R₀表示最近斜距，c表示光速，T_c表示子孔径积累时间，λ表示信号波长，v_e表示等效径向速度，N_c表示子孔径内的方位脉冲数，D表示天线方位尺寸，θ_El,t表示目标下视角,θ_Azi,t表示目标方位角。in,

represents the accumulated amplitude; M represents the number of channels; P _av represents the average radar power; G _T represents the full aperture gain of the transmitting antenna; G _R-Sub represents the sub-channel gain of the receiving antenna; f _a and f _l represent the Doppler frequency and sub-channel, respectively Aperture frequency variable; L represents the number of sub-apertures; B represents the signal bandwidth; t _r represents the distance fast time variable; R ₀ represents the closest slope distance, c represents the speed of light, T _c represents the sub-aperture accumulation time, λ represents the signal wavelength, and _ve represents the Equivalent radial velocity, N _c represents the number of azimuth pulses in the sub-aperture, D represents the azimuth size of the antenna, θ _{El, t} represents the viewing angle of the target, θ _{Azi, t} represents the azimuth angle of the target.

The space-based early warning air moving target detection method based on sub-aperture coherent accumulation provided by the present invention first uses Keystone transform to perform distance walking correction, and then completes clutter suppression and preliminary detection through sub-aperture division and sub-aperture STAP, and then compensates for the moving target return. The phase relationship between the sub-apertures and the coherent accumulation of sub-apertures further improve the output SCNR, and finally identify the real target through high-threshold CFAR detection.

A kind of space-based early warning radar air moving target detection system based on sub-aperture processing provided according to the present invention includes:

Module M1: Preprocess the multi-channel echo of the space-based early warning radar to obtain the preprocessed radar echo data;

Module M2: Perform Keystone transformation on the preprocessed radar echo data to complete distance walking correction;

Module M3: Divide the echo data corrected by the distance movement along the azimuth sub-aperture, and the basis of the division is that the Doppler frequency movement does not occur in each sub-aperture to ensure that Doppler diffusion does not occur in the sub-aperture;

Module M4: Use Post-Doppler Space-Time Adaptive Processing (STAP) in each sub-aperture to complete clutter suppression, complete the initial accumulation of coherence in each sub-aperture, and then pass the low-threshold constant false alarm (CFAR) Detect, extract the target to be detected;

Module M5: Perform phase compensation on the extracted targets to be detected one by one, and then perform Fourier transform along the sub-aperture direction to complete the coherent accumulation between sub-apertures and further improve the output signal-to-noise ratio (SCNR) of the target signal. High-threshold CFAR detection rejects false alarms and preserves true target points.

Specifically, the preprocessed radar echo data in the module M1 includes: air moving target echo, clutter and noise;

The air moving target echo of the mth channel after preprocessing is expressed as:

表示目标幅度，P_t，τ，B，G_T(θ_Azi,t,θ_El,t)，G_{R_Sub}(θ_Azi,t,θ_El,t)，λ，L_s和σ分别表示峰值功率，脉宽，带宽，发射天线全孔径增益，接收天线子通道增益，信号波长，雷达系统损失和目标RCS；R₀为最近斜距；θ_El,t和θ_Azi,t分别为目标的下视角和方位角；且cos(θ_Cone,t)＝cos(θ_El,t)cos(θ_Azi,t)；θ_Cone,t表示空间锥角；t_r和t_a分别表示距离快时间和方位慢时间变量；T_a表示积累时间，rect(·)和sinc(·)分别表示矩形窗函数和sinc函数；c表示光速；j表示虚数单位；R_0t,m(t_a)为利用平台参数经过deramp补偿后的斜距：in,

represents the target amplitude, P _t , τ, B, G _T (θ _Azi,t ,θ _El,t ), G _{R_Sub} (θ _Azi,t ,θ _El,t ), λ, L _s and σ represent the peak power, respectively, Pulse width, bandwidth, full aperture gain of transmit antenna, sub-channel gain of receive antenna, signal wavelength, radar system loss and target RCS; R ₀ is the closest slant range; θ _El,t and θ _Azi,t are the down-angle and θ of the target, respectively. Azimuth; and cos(θ _Cone,t )=cos(θ _El,t )cos(θ _Azi,t ); θ _Cone,t represents the spatial cone angle; _tr and t _a represent the distance fast time and azimuth slow time, respectively Variable; T _a represents the accumulation time, rect( ) and sinc( ) represent the rectangular window function and sinc function respectively; _c represents the speed of light; _j represents the imaginary unit; Slope distance after:

Among them, R ₀ is the nearest slant distance; D is the antenna size, and d _m is the channel spacing;

v _e =v _y sinθ _Azi,t sinθ _El,t -v _rx cosθ _Azi,t sinθ _El,t denotes the equivalent radial velocity; v _rx =vv _x is the relative platform velocity; v denotes the platform velocity, v _x denotes the Target azimuth velocity; v _y represents target radial velocity;

表示等效的加速度。

represents the equivalent acceleration.

Specifically, the module M1 includes: preprocessing the multi-channel echoes of the space-based early warning radar, including range compression, platform motion parameter compensation, frequency reduction, and clutter Doppler center compensation operations.

Specifically, the module M2 includes: using the Keystone transform to complete the distance movement correction before sub-aperture division, and simultaneously remove the distance movement within and between sub-apertures.

Specifically, the module M5 includes: performing phase compensation on the extracted targets to be detected one by one, deriving and compensating the phase relationship between the sub-aperture echoes, performing Fourier transform along the sub-aperture direction, and completing the inter-sub-aperture echoes. Coherent accumulation to further improve the output signal-to-noise ratio of the target signal;

The phase compensation for the extracted targets to be detected one by one includes:

表示搜索的等效加速度；λ表示信号波长；j表示虚数单位；l表示子孔径数；T_c表示子孔径内的积累时间；τ_a,1表示参考子孔径的时间变量；in,

represents the equivalent acceleration of the search; λ represents the signal wavelength; j represents the imaginary unit; l represents the number of sub-apertures; T _c represents the accumulation time in the sub-aperture; τ _a,1 represents the time variable of the reference sub-aperture;

The echo signal is coherently accumulated in each sub-aperture by the azimuth Fourier transform, and the coherent accumulation is completed between the sub-apertures by the sub-aperture Fourier transform; after the sub-aperture coherent accumulation, the echo signal is finally expressed as :

表示积累后的幅度；M表示通道数；P_av表示雷达平均功率；G_T表示发射天线全孔径增益；G_R-Sub表示接收天线子通道增益；f_a和f_l分别表示多普勒频率和子孔径频率变量；L表示子孔径数；B表示信号带宽；t_r表示距离快时间变量；R₀表示最近斜距，c表示光速，T_c表示子孔径积累时间，λ表示信号波长，v_e表示等效径向速度，N_c表示子孔径内的方位脉冲数，D表示天线方位尺寸，θ_El,t表示目标下视角,θ_Azi,t表示目标方位角。in,

represents the accumulated amplitude; M represents the number of channels; P _av represents the average radar power; G _T represents the full aperture gain of the transmitting antenna; G _R-Sub represents the sub-channel gain of the receiving antenna; f _a and f _l represent the Doppler frequency and sub-channel, respectively Aperture frequency variable; L represents the number of sub-apertures; B represents the signal bandwidth; t _r represents the distance fast time variable; R ₀ represents the closest slope distance, c represents the speed of light, T _c represents the sub-aperture accumulation time, λ represents the signal wavelength, and _ve represents the Equivalent radial velocity, N _c represents the number of azimuth pulses in the sub-aperture, D represents the azimuth size of the antenna, θ _{El, t} represents the viewing angle of the target, θ _{Azi, t} represents the azimuth angle of the target.

The space-based early warning air moving target detection method based on sub-aperture coherent accumulation provided by the present invention first uses Keystone transform to perform distance walking correction, and then completes clutter suppression and preliminary detection through sub-aperture division and sub-aperture STAP, and then compensates for the moving target return. The phase relationship between the sub-apertures and the coherent accumulation of sub-apertures further improve the output SCNR, and finally identify the real target through high-threshold CFAR detection.

Example 2

Embodiment 2 is a preferred example of Embodiment 1

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and provides a detailed implementation manner and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

A space-based early warning AMTI method based on sub-aperture coherent accumulation provided by the present invention specifically includes the following steps: as shown in Figure 1 and Figure 3:

Step 1: Establish an on-board multi-channel observation model, and complete preprocessing such as distance compression, platform parameter phase compensation and frequency reduction.

2, in the three-dimensional coordinates O-XYZ, the height of the satellite platform is H, the speed of the platform is v, and the direction is along the X-axis; the three-dimensional coordinates of the moving target in the air are (x ₀ , y ₀ , z ₀ ), along the The track speed and the vertical track speed are respectively v _x and _vy ; the transmitting antenna adopts full-aperture transmission, the receiving antenna is divided into M sub-arrays, and the channel spacing is d _m =m d, m = 0, 1, ... , M-1, where d represents the adjacent channel interval; θ _El,t , θ _Azi,t and θ _Cone,t are the lower viewing angle, azimuth angle and spatial cone angle, respectively.

According to Fig. 2, the equivalent spontaneous self-retraction slope distance of the mth channel can be expressed as

In the formula, _ta represents the azimuth slow time, and D=Md represents the antenna azimuth size. According to the second-order Taylor expansion and the use of platform parameters for deramp processing, the slope distance can be further expressed as the following form:

为最近斜距，v_rx＝v-v_x为相对平台速度，v_e＝v_ysinθ_Azi,tsinθ_El,t-v_rxcosθ_Azi,tsinθ_El,t表示等效的径向速度，

表示等效的加速度。In the formula,

is the nearest slope distance, v _rx =vv _x is the relative platform velocity, v _e =v _y sinθ _Azi,t sinθ _El,t -v _rx cosθ _Azi,t sinθ _El,t denotes the equivalent radial velocity,

represents the equivalent acceleration.

In this way, the echo signal of the mth channel can be expressed as

表示目标幅度，P_t，τ，B，G_T(θ_Azi,t,θ_El,t)，G_{R_Sub}(θ_Azi,t,θ_El,t)，λ，L_s和σ分别表示峰值功率，脉宽，带宽，发射天线全孔径增益，接收天线子通道增益，信号波长，系统损失和目标RCS。t_r表示距离快时间，rect(·)和sinc(·)分别表示矩形窗函数和‘sinc’函数。In the formula,

represents the target amplitude, P _t , τ, B, G _T (θ _Azi,t ,θ _El,t ), G _{R_Sub} (θ _Azi,t ,θ _El,t ), λ, L _s and σ represent the peak power, respectively, Pulse width, bandwidth, transmit antenna full aperture gain, receive antenna sub-channel gain, signal wavelength, system loss and target RCS. t _r represents the distance fast time, rect( ) and sinc( ) represent the rectangular window function and the 'sinc' function, respectively.

Step 2: Use Keystone transform to complete the distance system correction.

Keystone transform (KT) is widely used in radar field because it does not require any prior information of moving targets and is suitable for multi-target scenarios. The echo signal corrected by KT can be expressed as

In the formula, τ _a represents the new azimuth time variable after KT is performed. It should be emphasized that the purpose of using KT to perform distance correction before sub-aperture division is to remove the distance movement of the target within and between sub-apertures at the same time. d _m is the channel spacing, _{ve is the equivalent radial velocity, and a e is} the equivalent radial acceleration.

Step 3: Divide the echo data into sub-apertures along the azimuth direction.

Specifically, sub-apertures are divided in the azimuth direction, the coherent accumulation time T _a is equally divided into L sub-apertures, and the accumulation time and sampling points of each sub-aperture are T _c =T _a /L and M _c =T _c /PRT . At this time, the echo signal can be written as

In the formula, the echo of the lth sub-aperture can be written as

In the formula, τ _a,l represents the azimuth time variable of the lth sub-aperture. Since KT has corrected the distance walk, it is enough to ensure that the Doppler walk does not occur in each sub-aperture; the azimuth FT of the segmented echo can be obtained.

表示子孔径内积累的幅度，P_av表示雷达平均功率，f_a表示多普勒频率变量。In the formula,

represents the magnitude of accumulation within the subaperture, _Pav represents the radar average power, and _fa represents the Doppler frequency variable.

Step 4: Use the space-time adaptive processing technology to complete clutter suppression in each sub-aperture, and extract the target to be detected through low-threshold CFAR detection.

Specifically, the multi-channel space-based early warning radar echo in the range-Doppler domain can be expressed as the following form after sub-aperture division

In the formula, it is assumed that H ₁ and H ₀ represent the existence of targets and the absence of targets, respectively; S _t,l (t _r0 ,f _a0 ), S _c,l (t _r0 ,f _a0 ) and n _l (t _r0 ,f _a0 ) represent the multi-channel moving target echo, clutter and noise, respectively; the multi-channel target echo S _t,l (t _r0 ,f _a0 )=[S _t,1,l (t _r0 ,f _a0 ),... ,S _t,M,l (t _r0 ,f _a0 )] ^T , the multi-channel clutter S _c,l (t _r0 ,f _a0 ) can be obtained by setting the along-track and vertical-track speeds to zero.

Clutter suppression is performed within each sub-aperture, and the process can be expressed as

为从第l个子孔径中估计的杂波协方差矩阵。最优权矢量为In the formula, S is the target steering vector, W _l is the weight vector,

is the clutter covariance matrix estimated from the lth subaperture. The optimal weight vector is

The output signal after clutter suppression can be expressed as

In the formula, X _l (t _r0 , f _a0 ) represents the echo signal of the lth sub-aperture in the range-Doppler domain including the clutter signal, the target signal and the noise signal. Next, low-threshold CFAR detection is performed on the reference sub-aperture to extract potential target points, while there are some false alarm points; this process is expressed as

where V _LT represents the low detection threshold.

Step 5: For the extracted targets to be detected, perform phase compensation one by one and then perform Fourier transform along the sub-aperture direction to complete the sub-aperture coherent accumulation to further improve the output SCNR. Finally, false alarms are raised through high-threshold CFAR detection and the real targets are retained. point.

Specifically, it is assumed that s′ _t,l (t _r ,τ _a,l ) represents the two-dimensional time domain signal after sub-aperture clutter suppression, and the sub-aperture azimuth time variable satisfies τ _a,l =τ _a,1 + l·T _c , therefore, the lth sub-aperture echo and the reference sub-aperture echo have the following relationship

In the formula, the phase difference is related to the target motion parameters and the number of sub-apertures, which can be expressed as

In the formula, there is a fixed initial phase difference and a Doppler translation term related to the equivalent acceleration between the lth sub-aperture and the reference sub-aperture. A compensation function is constructed as follows to cancel the Doppler translation term associated with the phase term associated with the target acceleration, i.e.

Next, the echo signals can be preliminarily accumulated in each sub-aperture by the azimuth FT, and then the secondary coherent accumulation between the sub-apertures can be completed by the sub-aperture FT. After sub-aperture coherent accumulation, the echo signal can finally be written as

表示最终经过空域合成和子孔径相参积累的幅度。可见，目标在其对应的斜距、多普勒和子孔径处形成峰值。最后，通过高门限CFAR进行虚警剔除和真实目标点提取。该过程可表示为In the formula,

Indicates the magnitude of the final spatial synthesis and sub-aperture coherent accumulation. It can be seen that the target forms peaks at its corresponding slant range, Doppler and sub-aperture. Finally, false alarm rejection and real target point extraction are performed by high-threshold CFAR. This process can be expressed as

where _VHT represents the high detection threshold. The processing flow chart of this method is shown in FIG. 3 .

The effect of the present invention can be further illustrated by the following simulation:

(1) Simulation conditions

The parameters of the simulation experiment platform and the moving target are given in Table 1 and Table 2, respectively. The implementation steps of this embodiment are all performed on the MATLAB2016 simulation platform.

Table 1 Simulation parameter table

Table 2 Air moving target parameters

(2) Simulation content

This section presents the results of the simulation processing to verify the proposed algorithm. The simulation is carried out by adding 3 fast moving targets to the space-based early warning radar echo.

Figure 4 is the clutter spectrum of the space-based early warning radar; Figure 5 is the result of directly using STAP for clutter suppression and moving target detection; Figure 6 and Figure 7 are the results of using sub-aperture STAP and low-threshold CFAR detection (8.5dB) respectively ; Figure 8 is the search curve of targets 1 to 3 and a certain false alarm point; Figure 9 to Figure 11 are the comparison results of the mixed accumulation and sub-aperture coherent accumulation of targets 1 to 3 respectively; Threshold CFAR (13.2dB) detection result.

It can be seen from Figure 4 that the moving target is submerged in the severely expanded space-based clutter spectrum and cannot be effectively detected; Figure 5 shows the range Doppler spectrum after clutter suppression. It can be seen that although the clutter is effectively suppressed, the target has Range walking and Doppler frequency walking lead to defocusing in both the range dimension and Doppler dimension, which cannot be effectively detected; Figure 6 and Figure 7 are the sub-aperture STAP (divided into 8 sub-apertures) clutter suppression and low threshold, respectively (8.5dB) CFAR detection results, it can be seen that there are many false alarm points while the clutter is effectively suppressed; Figure 8 shows the search curves of targets 1 to 3 and false alarm points. It can be seen that the search curve of the real target will increase with the acceleration. The search curve will have peaks, but the false alarm points will not; Figures 9 to 11 are the comparison results of the hybrid accumulation and sub-aperture coherent accumulation of target 1 to target 3 respectively. It can be seen that the proposed method has better performance than the traditional hybrid accumulation detection method. Low side lobes, that is, better output SCNR. Figure 12 and Figure 13 respectively show the final processing results after sub-aperture coherent accumulation and high-threshold CFAR detection. It can be seen that all three weak targets can be effectively detected.

To sum up, the simulation experiment verifies the correctness, effectiveness and reliability of the present invention.

It should be understood that those skilled in the art can make many modifications and changes according to the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the prior art according to the concept of the present invention shall fall within the protection scope determined by the claims.

Those skilled in the art know that, in addition to implementing the system, device and each module provided by the present invention in the form of pure computer readable program code, the system, device and each module provided by the present invention can be completely implemented by logically programming the method steps. The same program is implemented in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, and embedded microcontrollers, among others. Therefore, the system, device and each module provided by the present invention can be regarded as a kind of hardware component, and the modules used for realizing various programs included in it can also be regarded as the structure in the hardware component; A module for realizing various functions can be regarded as either a software program for realizing a method or a structure within a hardware component.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above-mentioned specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essential content of the present invention. The embodiments of the present application and features in the embodiments may be combined with each other arbitrarily, provided that there is no conflict.

Claims (10)

1. A space-based early warning radar air moving target detection method based on sub-aperture processing is characterized by comprising the following steps:

step S1: preprocessing multi-channel echoes of the space-based early warning radar to obtain preprocessed radar echo data;

step S2: performing Keystone transformation on the preprocessed radar echo data to finish distance walking correction;

step S3: dividing the echo data after the distance walk correction along the azimuth sub-aperture to ensure that Doppler diffusion does not occur in the sub-aperture;

step S4: clutter suppression is completed in each sub-aperture by using a post-Doppler space-time adaptive processing technology, preliminary accumulation of coherent signals is completed in each sub-aperture, and then a target to be detected is extracted through constant false alarm detection of a low threshold;

step S5: and performing phase compensation on the extracted targets to be detected one by one, and performing Fourier transform along the direction of the sub-apertures to complete coherent accumulation among the sub-apertures, further improving the output signal-to-noise ratio of target signals, eliminating false alarms through high threshold detection and reserving real target points.

2. The subaperture-processing-based space-based pre-warning radar airborne target detection method of claim 1, wherein the preprocessing of the radar echo data in step S1 comprises: echoes, clutter and noise of moving targets in the air;

the preprocessed moving target echo in the air of the mth channel is represented as:

wherein,

representing the target amplitude, P_t，τ，B，G_T(θ_Azi,t,θ_El,t)，G_{R_Sub}(θ_Azi,t,θ_El,t)，λ，L_sAnd sigma respectively represents peak power, pulse width, bandwidth, transmitting antenna full aperture gain, receiving antenna subchannel gain, signal wavelength, radar system loss and target RCS; r₀Is the nearest slope distance; theta_El,tAnd theta_Azi,tRespectively a lower viewing angle and an azimuth angle of the target; and cos (theta)_Cone,t)＝cos(θ_El,t)cos(θ_Azi,t)；θ_Cone,tRepresenting a spatial cone angle; t is t_rAnd t_aRespectively representing the fast distance time and slow direction time variables; t is_aRepresenting the accumulation time, rect (-) and sinc (-) respectively representing a rectangular window function and a sinc function; c represents the speed of light; j represents an imaginary unit; r_0t,m(t_a) In order to utilize the slope distance of the platform parameter after deramp compensation:

wherein R is₀Is the nearest slope distance; d represents the size of the antenna square dimension D_mRepresenting the channel spacing;

v_e＝v_ysinθ_Azi,tsinθ_El,t-v_rxcosθ_Azi,tsinθ_El,trepresents the equivalent radial velocity; v. of_rx＝v-v_xRelative platform velocity; v denotes the platform velocity, v_xRepresenting the target azimuth velocity; v. of_yRepresenting a target radial velocity;

representing the equivalent acceleration.

3. The subaperture-processing-based space-based pre-warning radar airborne target detection method of claim 1, wherein the step S1 comprises: and preprocessing multi-channel echoes of the space-based early warning radar, including distance compression, platform motion parameter compensation, frequency down-modulation and clutter Doppler center compensation.

4. The subaperture-processing-based space-based pre-warning radar airborne target detection method of claim 1, wherein the step S2 comprises: distance walk rectification is completed before sub-aperture division by using Keystone transformation, and distance migration in sub-apertures and between sub-apertures is removed.

5. The subaperture-processing-based space-based pre-warning radar airborne target detection method of claim 1, wherein the step S5 comprises: phase compensation is carried out on the extracted targets to be detected one by one, the phase relation among the sub-aperture echoes is deduced and compensated, Fourier transform is carried out along the sub-aperture direction, coherent accumulation among the sub-apertures is completed, and the output signal-to-noise ratio of target signals is further improved;

the step of performing phase compensation on the extracted targets to be detected one by one comprises the following steps:

wherein,

representing the equivalent acceleration of the search; λ represents a signal wavelength; j represents an imaginary unit; l represents the number of subapertures; t is_cRepresenting the accumulation time within the sub-aperture; tau is_a,1A time variable representing a reference sub-aperture;

the echo signals are subjected to coherent accumulation in each sub-aperture by azimuth Fourier transform, and are subjected to coherent accumulation among the sub-apertures by sub-aperture Fourier transform; after sub-aperture coherent accumulation, the echo signal is finally expressed as:

wherein,

representing the accumulated amplitude; m represents the number of channels; p_avRepresents the radar average power; g_TRepresenting the transmit antenna full aperture gain; g_R-SubRepresenting receive antenna subchannel gains; f. of_aAnd f_lRespectively representing the Doppler frequency and the sub-aperture frequency variables; l represents the sub-aperture number; b represents the signal bandwidth; t is t_rRepresenting a distance fast time variable; r₀Representing nearest slope, c light speed, T_cDenotes the sub-aperture integration time, λ denotes the signal wavelength, v_eRepresenting the equivalent radial velocity, N_cIndicating the number of azimuth pulses within the sub-aperture, D indicating the azimuth dimension of the antenna, theta_El,tRepresenting the target down-viewing angle, theta_Azi,tRepresenting the target azimuth.

6. A space-based early warning radar air moving target detection system based on sub-aperture processing is characterized by comprising:

module M1: preprocessing multi-channel echoes of the space-based early warning radar to obtain preprocessed radar echo data;

module M2: performing Keystone transformation on the preprocessed radar echo data to finish distance walking correction;

module M3: dividing the echo data after the distance walk correction along the azimuth sub-aperture to ensure that Doppler diffusion does not occur in the sub-aperture;

module M4: clutter suppression is completed in each sub-aperture by using a post-Doppler space-time adaptive processing technology, initial coherent accumulation is completed in each sub-aperture, and then a target to be detected is extracted through constant false alarm detection of a low threshold;

module M5: and performing phase compensation on the extracted targets to be detected one by one, and performing Fourier transform along the direction of the sub-apertures to complete coherent accumulation among the sub-apertures, further improving the output signal-to-noise ratio of target signals, eliminating false alarms through high threshold detection and reserving real target points.

7. The subaperture-processing-based space-based pre-warning radar airborne target detection system of claim 6, wherein the pre-processing of the radar echo data in module M1 comprises: echoes, clutter and noise of moving targets in the air;

the preprocessed moving target echo in the air of the mth channel is represented as:

wherein,

representing the target amplitude, P_t，τ，B，G_T(θ_Azi,t,θ_El,t)，G_{R_Sub}(θ_Azi,t,θ_El,t)，λ，L_sAnd sigma respectively represents peak power, pulse width, bandwidth, transmitting antenna full aperture gain, receiving antenna subchannel gain, signal wavelength, radar system loss and target RCS; r₀Is the nearest slope distance; theta_El,tAnd theta_Azi,tRespectively a lower viewing angle and an azimuth angle of the target; and cos (theta)_Cone,t)＝cos(θ_El,t)cos(θ_Azi,t)；θ_Cone,tRepresenting a spatial cone angle; t is t_rAnd t_aRespectively representing the fast distance time and slow direction time variables; t is_aRepresenting the accumulation time, rect (-) and sinc (-) respectively representing a rectangular window function and a sinc function; c represents the speed of light; j represents an imaginary unit; r_0t,m(t_a) In order to utilize the slope distance of the platform parameter after deramp compensation:

wherein R is₀Is the nearest slope distance; d represents the size of the antenna square dimension D_mRepresenting the channel spacing;

v_e＝v_ysinθ_Azi,tsinθ_El,t-v_rxcosθ_Azi,tsinθ_El,trepresents the equivalent radial velocity; v. of_rx＝v-v_xRelative platform velocity; v denotes the platform velocity, v_xRepresenting the target azimuth velocity; v. of_yRepresenting a target radial velocity;

representing the equivalent acceleration.

8. The subaperture-processing-based space-based pre-warning radar airborne target detection system of claim 6, wherein the module M1 comprises: and preprocessing multi-channel echoes of the space-based early warning radar, including distance compression, platform motion parameter compensation, frequency down-modulation and clutter Doppler center compensation.

9. The subaperture-processing-based space-based pre-warning radar airborne target detection system of claim 6, wherein the module M2 comprises: distance walk rectification is completed before sub-aperture division by using Keystone transformation, and distance migration in sub-apertures and between sub-apertures is removed.

10. The subaperture-processing-based space-based pre-warning radar airborne target detection system of claim 6, wherein the module M5 comprises: phase compensation is carried out on the extracted targets to be detected one by one, the phase relation among the sub-aperture echoes is deduced and compensated, Fourier transform is carried out along the sub-aperture direction, coherent accumulation among the sub-apertures is completed, and the output signal-to-noise ratio of target signals is further improved;

the step of performing phase compensation on the extracted targets to be detected one by one comprises the following steps:

wherein,

representing the equivalent acceleration of the search; λ represents a signal wavelength; j represents an imaginary unit; l represents the number of subapertures; t is_cRepresenting the accumulation time within the sub-aperture; tau is_a,1A time variable representing a reference sub-aperture;

the echo signals are subjected to coherent accumulation in each sub-aperture by azimuth Fourier transform, and are subjected to coherent accumulation among the sub-apertures by sub-aperture Fourier transform; after sub-aperture coherent accumulation, the echo signal is finally expressed as:

wherein,

representing the accumulated amplitude; m represents the number of channels; p_avRepresents the radar average power; g_TRepresenting the transmit antenna full aperture gain; g_R-SubRepresenting receive antenna subchannel gains; f. of_aAnd f_lRespectively representing the Doppler frequency and the sub-aperture frequency variables; l represents the sub-aperture number; b represents the signal bandwidth; t is t_rRepresenting a distance fast time variable; r₀Representing nearest slope, c light speed, T_cDenotes the sub-aperture integration time, λ denotes the signal wavelength, v_eRepresenting the equivalent radial velocity, N_cIndicating the number of azimuth pulses within the sub-aperture, D indicating the azimuth dimension of the antenna, theta_El,tRepresenting the target down-viewing angle, theta_Azi,tRepresenting the target azimuth.

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