External radiation source radar target detection method based on satellite downlink communication signal

Abstract

The invention discloses an external radiation source radar target detection method based on a satellite downlink communication signal. The method comprises the following steps: S1, acquiring orbit parameters of satellites passing through an observation area and over a ground receiving station in a detection period according to a satellite ephemeris; s2, calculating orientation and motion parameters of the overhead communication satellite relative to the ground station through coordinate system transformation; s3, carrying out demodulation and modulation on the received reference signal; s4, compensating time delay and phase errors of the reference signal and the target echo signal based on the obtained motion parameters of the satellite relative to the ground station; s5, performing distance compression processing on the reference signal and the target echo signal after error compensation; s6, Doppler spread clutters are filtered out; s7, target motion compensation; and S8, performing distance Doppler processing on a signal processing result. The method improves the signal-to-noise ratio of the received signal and the detection accumulation time. And the obtained satellite relative motion parameters are respectively used for azimuth time delay and phase error compensation of received signals, Doppler spread clutter filtering and target motion compensation.

Description

Technical Field

[0001] The invention relates to the technical field of exo-radiation source radar, in particular to an exo-radiation source radar target detection method based on satellite downlink communication signals. Background Art

[0002] As a new type of target detection technology, external radiation source radar does not emit signals itself, but detects by receiving echo signals from non-cooperative radiation sources reflected by the target. It can detect various types of targets in a radio-silent manner. Currently, with the rapid construction and development of communication constellations, using communication satellites as radiation sources and realizing target detection based on radar signal processing has become an important research direction.

[0003] Due to the low orbital altitude and the need to achieve global coverage, communication satellites often have a very high movement speed. Therefore, the relative movement between the radar radiation source and the target and the radar receiving station is complex, resulting in strong Doppler spread clutter interference and range movement when the radar signal is accumulated. The hardware error of the receiving system and the atmospheric transmission will cause delay and phase error to the received signal, which will affect the subsequent energy accumulation processing and Doppler information estimation, reducing the detection probability and positioning accuracy of the target. Therefore, it is necessary to adopt a new method to suppress and correct Doppler spread clutter and range movement, compensate for signal delay and phase error, realize the effective accumulation of target echo signals, and improve the detection probability of the target.

[0004] The present application is different from the prior art as follows:

[0005] Technical comparison with patent CN115327530A "Reconstruction method of external radiation source radar reference signal based on Beidou satellite"

[0006] The radiation source used in patent CN115327530A is Beidou satellite, which belongs to the global satellite navigation system satellite, and the satellite orbit height is generally 21300~21500 kilometers, and the invention is mainly aimed at the Beidou signal structure, and the local ranging code of each Beidou navigation satellite is used for two-dimensional correlation and peak search to obtain the delay estimation value, Doppler estimation value and local ranging code, and the Doppler error estimation value is solved by combining the differential signal to realize the reference signal reconstruction. The radiation source used in the present invention is a low-orbit communication satellite, and the orbit height is generally 500~2000 kilometers. The radiation source signal has different transmission systems, modulation and coding modes, signal bandwidth and power, etc., mainly through satellite tracking to improve the signal-to-noise ratio of the received signal, demodulate and modulate the communication signal received by the reference channel to realize the reference signal reconstruction, and compensate for the azimuth time delay and phase error based on the acquired radiation source satellite motion parameters, and combine clutter filtering and motion compensation to improve the target signal accumulation strength.

[0007] Technical comparison with patent CN111948618A "A forward scatter target detection method and system based on satellite external radiation source"

[0008] Patent CN111948618A mainly processes the received signal based on the traditional satellite tracking loop, extracts the baseband signal, suppresses multipath signal interference based on linear canonical transformation, extracts the peak value as the detection quantity for target detection, and estimates the target speed and height in combination with the matched filtering algorithm. The present invention mainly improves the signal-to-noise ratio of the received signal through satellite tracking, combines reference signal reconstruction, azimuth time delay and phase error compensation, clutter filtering and motion compensation, and improves the target signal accumulation strength.

[0009] Technical comparison with patent CN112379360A "Coherence duration estimation method under background ionosphere effect of space-based external radiation source radar"

[0010] In patent CN112379360A, the space-based external radiation source uses high-orbit satellite signals, and the radar receiver is installed on a low-orbit satellite. Mainly under the influence of the ionosphere, based on the estimation model of the correlation coefficient with respect to time, the coherence time length for the correlation coefficient to drop to the correlation threshold is calculated according to the aircraft target echo signal and its center frequency. The radiation source of the present invention uses the downlink communication signal of the low-orbit satellite, and the radar receiver is installed on the ground. It mainly improves the signal-to-noise ratio of the received signal through satellite tracking, and combines reference signal reconstruction, azimuth time delay and phase error compensation, clutter filtering and motion compensation to improve the target signal accumulation strength.

[0011] Technical comparison with patent CN115932921A "A non-coherent joint accumulation processing method for multiple satellites and multiple carriers"

[0012] The radiation source used in patent CN115932921A is a synchronous orbit satellite, whose orbital altitude is about 35786 kilometers. It mainly calculates the Doppler frequency of the target under a certain carrier frequency by modeling the external radiation source radar system of the synchronous orbit satellite signal, and aligns the fuzzy function related accumulation results after different single-carrier motion compensation by multiple compensation and performs incoherent accumulation to obtain the target result. The radiation source used in the present invention is a low-orbit communication satellite, whose orbital altitude is generally 500 to 2000 kilometers. The radiation source signal has different transmission systems, modulation and coding methods, signal bandwidth and power, etc. It mainly improves the signal-to-noise ratio of the received signal through satellite tracking, and combines reference signal reconstruction, azimuth time delay and phase error compensation, clutter filtering and motion compensation to improve the target signal accumulation strength.

[0013] Technical comparison with patent CN110967675A "A passive detection method for satellite external radiation source targets based on neural network"

[0014] Patent CN110967675A mainly uses a delayed feedback network to purify the satellite direct wave signal in the reference channel containing sea clutter, uses a minimum mean square error filter to suppress the direct wave in the echo, and uses a decoupled echo state network to detect the target echo signal. The present invention improves the signal-to-noise ratio of the received signal through satellite tracking, demodulates and reconstructs the reference signal, compensates for the azimuth time delay and phase error based on the acquired radiation source satellite motion parameters, combines clutter filtering and motion compensation, improves the target echo signal accumulation strength, and performs target detection.

[0015] Technical comparison with patent CN117148393A "Fully polarized aerial target detection device and method based on GNSS external radiation source"

[0016] The radiation source used in patent CN117148393A is a GNSS satellite, which belongs to the global satellite navigation system satellite. It mainly detects and locates aerial targets based on the satellite direct signal received by the omnidirectional antenna and the satellite signal reflected by the target received by the left-hand circular polarization and right-hand circular polarization antennas. The radiation source used in the present invention is a low-orbit communication satellite. The radiation source signal has different transmission systems, modulation and coding methods, signal bandwidth and power, etc. The receiving antenna on the turntable is mainly controlled to align with the satellite radiation source according to the satellite tracking results to improve the signal-to-noise ratio and signal accumulation time of the received signal. Summary of the invention

[0017] In view of the above problems, the present invention proposes a method for detecting external radiation source radar targets based on satellite downlink communication signals to solve the problems raised in the above background technology.

[0018] To achieve the above object, the technical solution adopted by the present invention is:

[0019] A method for detecting external radiation source radar targets based on satellite downlink communication signals comprises the following steps:

[0020] S1. Obtaining the orbital parameters of the satellite passing over the observation area and the ground receiving station during the detection period according to the satellite ephemeris;

[0021] S2, calculate the position and motion parameters of the overhead communication satellite relative to the ground station through coordinate system transformation, so that the receiving antenna tracks the satellite and improves the signal-to-noise ratio of the received signal;

[0022] S3. Demodulate and modulate the received reference signal to reconstruct the reference signal;

[0023] S4, based on the obtained motion parameters of the satellite relative to the ground station, compensating the time delay and phase error of the reference signal and the target echo signal;

[0024] S5, performing distance compression processing on the reference signal and the target echo signal after error compensation;

[0025] S6, filter out Doppler spread clutter;

[0026] S7, target motion compensation;

[0027] S8. Perform range Doppler processing on the signal processing result to obtain the distance and speed information of the target and realize the detection of the target.

[0028] As a further improvement of the present invention, the specific process of S2 is: according to the satellite TLE ephemeris and the detection time combined with the orbit prediction model, the satellite state vector r in the ECI coordinate system is obtained. eci =[x eci y eci z eci ] T ; Combined with the earth orientation parameters, the satellite state vector r in the ECEF coordinate system is further obtained ecef =[x ecef y ecef z ecef ] T , the expression is:

[0029] r ecef =R eci_ecef r eci

[0030]

[0031] Among them, r eci is the satellite state vector in the ECI coordinate system; R eci_ecef is the Earth's rotation matrix; ω is the Earth's rotation angular velocity, t is the time from the reference time, is the earth orientation parameter at the initial moment;

[0032] Combined with the position of the ground receiving station, the satellite state vector r in the ENU coordinate system is further obtained enu =[x enu y enu z enu ] T , the expression is:

[0033] r enu =R ecef_enu (r ecef -k ecef )

[0034]

[0035] Among them, r ecef is the satellite state vector in the ECEF coordinate system; R ecef_enu is the transformation matrix, k ecef =[xgs_ecef y gs_enu z gs_enu ] T is the ECEF coordinate of the receiving station; φ and λ are the latitude and longitude of the receiving station respectively;

[0036] After spherical coordinate transformation, the satellite pitch angle θ is further obtained enu and azimuth α enu , the expression is:

[0037]

[0038] α enu =arctan2(x enu ,y enu )

[0039] Among them, x enu ,y enu and z enu is the coordinate of the satellite in the ENU coordinate system; the pitch angle θ enu Measured with reference to the horizontal plane; azimuth α enu Measured clockwise from due north;

[0040] Combined with the pitch angle and azimuth angle corresponding to the receiving antenna attitude in the ENU coordinate system, the satellite state vector r in the antenna body coordinate system is further obtained ante =[x ante y ante z ante ] T , the expression is:

[0041] r ante =R enu_ante r enu

[0042]

[0043] Among them, R enu_ante is the transformation matrix; r enu is the satellite state vector in the ENU coordinate system; θ atti and α ante are the elevation angle and azimuth angle corresponding to the receiving antenna attitude in the ENU coordinate system, respectively;

[0044] After spherical coordinate transformation and deflection calculation, the satellite azimuth angle α in the antenna body coordinate system can be further obtained. ante and the elevation angle θ ante , the expression is:

[0045]

[0046] α ante=arctan2(y ante ,x ante )

[0047] Among them, x ante ,y ante and z ante is the coordinate of the satellite in the antenna body coordinate system, and the polarization deflection angle is calculated from the polarization directions of the antenna and the satellite;

[0048] According to the satellite tracking results, the high-gain narrow-beam receiving antenna is aimed at the radiation source satellite by adjusting the angle of the antenna turntable.

[0049] As a further improvement of the present invention, the specific process of S4 is as follows: the hardware error of the receiving system and the atmospheric transmission etc. bring delay and phase error to the received signal, which are compensated by the acquired satellite relative motion parameters. The expressions of the reference signal and the target echo signal after two-dimensional division before compensation are respectively:

[0050]

[0051]

[0052] Among them, t f is the fast time, i.e. the distance time variable; t s is the slow time, i.e., the azimuth time variable; T a is the duration of the signal; S T (t) is the baseband signal transmitted by the satellite; τ ref (t s ) and τ sur (t s ) are the time delays caused by the propagation paths of the reference signal and the target echo signal at each azimuth moment; f c is the carrier frequency of the transmitted signal; f d-ref (t s ) and f d-sur (t s ) are the instantaneous Doppler frequencies of the reference signal and the target echo signal at each azimuth moment; Δτ(t s ) is the delay error caused by atmospheric transmission and satellite motion. Since the distance from the target to the receiving station is much smaller than the distance to the satellite, it is approximately assumed that the delay errors of the two channels are consistent; φ e (t s ) is the phase error caused by the frequency error of the receiver hardware. It is approximately assumed that the phase errors of the two channels are consistent after the receiver is calibrated;

[0053] Calculate the time delay τ at each azimuth according to the obtained satellite relative distance and Doppler frequency shift ref (t s) and the instantaneous Doppler frequency f d-ref (t s ), and perform delay and phase compensation on each azimuth moment of the reconstructed reference signal, and then cross-correlate the result with the signal received by the reference channel to obtain the delay error value of each azimuth moment Phase error value It is used to compensate the delay and phase error of the target echo signal, and its expression is:

[0054]

[0055] Among them, FFT f and IFFT f Respectively represent the fast time t f Do the Fast Fourier Transform and the Fast Inverse Fourier Transform.

[0056] Beneficial effects: Compared with the prior art, the present invention adopts the above technical solution and has the following advantages:

[0057] The present invention relates to the technical field of external radiation source radar, and in particular to an external radiation source radar target detection method based on satellite downlink communication signals. The specific steps are as follows: S1, obtaining satellite orbit parameters passing through the observation area and the ground receiving station during the detection period according to the satellite ephemeris; S2, calculating the azimuth and motion parameters of the overhead communication satellite relative to the ground station through coordinate system transformation, so that the receiving antenna tracks the satellite and improves the signal-to-noise ratio of the received signal; S3, demodulating and modulating the received reference signal and reconstructing the reference signal; S4, based on the acquired motion parameters of the satellite relative to the ground station, compensating the delay and phase errors of the reference signal and the target echo signal; S5, performing distance compression processing on the reference signal and the target echo signal after error compensation; S6, filtering out Doppler expansion clutter; S7, target motion compensation; S8, performing distance Doppler processing on the signal processing result, obtaining the distance and speed information of the target, and realizing the detection of the target. The method uses a high-speed moving communication satellite as a radiation source, and controls a high-gain narrow-beam receiving antenna to align with the satellite radiation source according to the satellite tracking result, so as to improve the signal-to-noise ratio of the received signal and the detection accumulation time. The acquired satellite relative motion parameters are used for azimuth time delay and phase error compensation of the received signal, Doppler spread clutter filtering and target motion compensation, which improves the accumulation intensity of the target echo signal and facilitates the detection of the target. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a schematic diagram of a target detection scenario of an external radiation source radar of the present invention;

[0059] Figure 2 It is a schematic diagram of coordinate system transformation;

[0060] Figure 3It is a flow chart of external radiation source radar detection based on satellite communication signals. DETAILED DESCRIPTION

[0061] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0062] The present invention provides an improved external radiation source radar target detection method based on satellite downlink communication signals. The technical solution of the present invention is aimed at the external radiation source radar target detection scenario, and its structure is as follows: Figure 1 As shown in the figure, a Cartesian coordinate system is established with the ground radar receiving station as the coordinate origin. The positions of the communication satellite and the target to be measured at the start measurement time and time t are P respectively. S0 , P T0 , P T and P S ; The distances from the satellite radiation source to the ground station and the target at the start of measurement and time t are l0 and r T0 , l(t) and r T (t); the distances of the target to be measured from the ground station at the start of measurement and at time t are r R0 and r R (t).

[0063] In this embodiment, the schematic diagram of the external radiation source radar target detection scene is as follows: Figure 1 As shown in the figure, the coordinate transformation process involved in calculating the satellite azimuth, elevation and deflection angle in the antenna body coordinate system is as follows Figure 2 shown.

[0064] The implementation process flow chart is as follows: Figure 3 As shown, the specific steps are as follows:

[0065] S1. Obtain orbital parameters of satellites passing over the observation area and the ground receiving station during the detection period according to the communication satellite ephemeris, wherein the satellite ephemeris in TLE format can be obtained by calling the external application programming interface of the ephemeris official website.

[0066] S2. In order to improve the signal-to-noise ratio and accumulation time of the received signal, the receiving antenna is combined with TLE ephemeris and coordinate transformation to track the satellite radiation source. The specific process is: According to the satellite TLE ephemeris and detection time combined with the orbit prediction model, the satellite state vector r in the ECI coordinate system is obtained. eci =[x eci y eci z eci ] T ; Combined with the earth orientation parameters, the satellite state vector in the ECEF coordinate system is further obtained

[0067] r ecef =[x ecef yecef z ecef ] T , the expression is:

[0068] r ecef =R eci_ecef r eci

[0069]

[0070] Among them, r eci is the satellite state vector in the ECI coordinate system; R eci_ecef is the Earth's rotation matrix; ω is the Earth's rotation angular velocity, t is the time from the reference time, is the earth orientation parameter at the initial moment.

[0071] Combined with the position of the ground receiving station, the satellite state vector r in the ENU coordinate system is further obtained enu =[x enu y enu z enu ] T , the expression is:

[0072] r enu =R ecef_enu (r ecef -k ecef )

[0073]

[0074] Among them, r ecef is the satellite state vector in the ECEF coordinate system; R ecef_enu is the transformation matrix, k ecef =[x gs_ecef y gs_enu z gs_enu ] T is the ECEF coordinate of the receiving station; φ and λ are the latitude and longitude of the receiving station, respectively.

[0075] After spherical coordinate transformation, the satellite pitch angle θ is further obtained enu and azimuth α enu , the expression is:

[0076]

[0077] α enu =arctan2(x enu ,y enu )

[0078] Among them, x enu ,y enu and z enuis the coordinate of the satellite in the ENU coordinate system; the pitch angle θ enu Measured with reference to the horizontal plane; azimuth α enu Measured clockwise from true north.

[0079] Combined with the pitch angle and azimuth angle corresponding to the receiving antenna attitude in the ENU coordinate system, the satellite state vector r in the antenna body coordinate system is further obtained ante =[x ante y ante z ante ] T , the expression is:

[0080] r ante =R enu_ante r enu

[0081]

[0082] Among them, R enu_ante is the transformation matrix; r enu is the satellite state vector in the ENU coordinate system; θ atti and α ante are the elevation angle and azimuth angle corresponding to the receiving antenna attitude in the ENU coordinate system, respectively.

[0083] After spherical coordinate transformation and deflection calculation, the satellite azimuth angle α in the antenna body coordinate system can be further obtained. ante and the elevation angle θ ante , the expression is:

[0084]

[0085] α ante =arctan2(y ante ,x ante )

[0086] Among them, x ante ,y ante and z ante is the coordinate of the satellite in the antenna body coordinate system, and the polarization deflection angle is calculated from the polarization directions of the antenna and the satellite.

[0087] According to the satellite tracking results, the high-gain narrow-beam receiving antenna is aligned with the satellite radiation source by adjusting the angle of the antenna turntable, thereby improving the signal-to-noise ratio of the received signal and the accumulation time of detection.

[0088] S3. The signal received by the reference channel is synchronized and demodulated after channel equalization, and the demodulation result is remodulated to obtain a reconstructed reference signal. The frame synchronization of the signal can be based on the cyclostationary characteristics of the satellite communication signal structure, and the peak value is obtained by cross-correlating the received signal with the locally generated synchronization sequence. The expression of the cross-correlation Corr(m) is:

[0089] N-1

[0090] Corr(m)=∑x ref (n+m)k syn (n)

[0091] n=0

[0092] Among them, x ref (n) is the signal received by the reference channel, k syn (n) is the zero-padded result of the locally generated synchronization sequence; N is the number of sampling points of the received signal of the reference channel.

[0093] S4, the hardware error of the receiving system and the atmospheric transmission etc. bring delay and phase error to the received signal, which can be compensated by the satellite relative motion parameters. ref (t f ,t s ) and the target echo signal S sur (t f ,t s ) are:

[0094]

[0095] Among them, t f is the fast time, i.e. the distance time variable; t s is the slow time, i.e., the azimuth time variable; T a is the duration of the signal; S T (t) is the baseband signal transmitted by the satellite; τ ref (t s ) and τ sur (t s ) are the time delays caused by the propagation paths of the reference signal and the target echo signal at each azimuth moment; f c is the carrier frequency of the transmitted signal; f d-ref (t s ) and f d-sur (t s ) are the instantaneous Doppler frequencies of the reference signal and the target echo signal at each azimuth moment; Δτ(t s) is the delay error caused by atmospheric transmission and satellite motion. Since the distance from the target to the receiving station is much smaller than the distance to the satellite, it is approximately assumed that the delay errors of the two channels are consistent; φ e (t s ) is the phase error caused by the frequency error of the receiver hardware. It is approximately assumed that the phase errors of the two channels are consistent after the receiver is calibrated.

[0096] Calculate the time delay τ at each azimuth according to the obtained satellite relative distance and Doppler frequency shift ref (t s ) and the instantaneous Doppler frequency f d-ref (t s ), and perform delay and phase compensation on each azimuth moment of the reconstructed reference signal, and then cross-correlate the result with the signal received by the reference channel to obtain the delay error value of each azimuth moment Phase error value It is used to compensate the delay and phase error of the target echo signal, and its expression is:

[0097]

[0098] Among them, FFT f and IFFT f Respectively represent the fast time t f Do the Fast Fourier Transform and the Fast Inverse Fourier Transform.

[0099] S5. Perform range compression processing on the reference signal and target echo signal after error compensation. Ignoring the influence of Doppler modulation in the cross-correlation processing, the result of range pulse compression processing on the target echo signal can be expressed as:

[0100]

[0101] Wherein, Corr(·) represents the cross-correlation result between the reconstructed reference signal and the target echo signal after error compensation; r(t s ) is the double base distance history, and its expression is:

[0102] r(t s )=r T (t s )+r R (t s )-l(t s )

[0103] Among them, t s is the slow time, i.e. the azimuth time; r T (t s ), r R (ts ) and l(t s ) are the distances from the satellite to the target, from the target to the ground receiving station, and from the satellite to the ground receiving station at each azimuth moment.

[0104] S6. According to the geometric relationship and motion parameters of the satellite radiation source relative to the ground receiving station, the Doppler frequency shift range of the clutter at different times and locations is calculated. Based on this clutter model, appropriate filtering methods can be used, such as space-time adaptive processing, time-frequency analysis filtering, etc., to effectively filter out Doppler spread clutter.

[0105] S7. Compensate for target motion. The distance movement can be corrected by methods such as keystone transformation to achieve effective accumulation of target echo signal energy. Based on the relative motion parameters of the satellite radiation source, the distance movement of the target echo can be calculated as reference information.

[0106] S8. Perform range Doppler processing on the target motion compensated signal, that is, continue to perform Doppler dimension fast Fourier transform on the range compression result. After obtaining the calculation result of the range Doppler map, the CFAR algorithm can be used to perform target detection, and the estimated values ​​of the dual-base range and speed of the detected target can be obtained to achieve target detection.

[0107] Through the above steps, the effective accumulation of target echo signal energy in the external radiation source radar signal processing based on the communication satellite downlink communication signal is achieved, the intensity of the target energy in the range Doppler processing result is improved, the detection of the target is facilitated, and the detection probability and accuracy are improved.

[0108] The above description is only a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent change made based on the technical essence of the present invention still falls within the scope of protection required by the present invention.

Claims

1. A method for detecting external radiation source radar targets based on satellite downlink communication signals, characterized in that: The following steps are involved: S1. Obtaining the orbital parameters of the satellite passing over the observation area and the ground receiving station during the detection period according to the satellite ephemeris; S2, calculate the position and motion parameters of the overhead communication satellite relative to the ground station through coordinate system transformation, so that the receiving antenna tracks the satellite and improves the signal-to-noise ratio of the received signal; S3. Demodulate and modulate the received reference signal to reconstruct the reference signal; S4, based on the obtained motion parameters of the satellite relative to the ground station, compensating the time delay and phase error of the reference signal and the target echo signal; S5, performing distance compression processing on the reference signal and the target echo signal after error compensation; S6, filter out Doppler spread clutter; S7, target motion compensation; S8. Perform range Doppler processing on the signal processing result to obtain the distance and speed information of the target and realize the detection of the target.

2. The method for detecting external radiation source radar targets based on satellite downlink communication signals according to claim 1, characterized in that: The specific process of S2 is: according to the satellite TLE ephemeris and the detection time combined with the orbit prediction model, the satellite state vector r in the ECI coordinate system is obtained. eci =[x eci y eci z eci ] T ; Combined with the earth orientation parameters, the satellite state vector r in the ECEF coordinate system is further obtained ecef =[x ecef y ecef z ecef ] T , the expression is: r ecef ＝R eci_ecef r eci Among them, r eci is the satellite state vector in the ECI coordinate system; R eci_ecef is the Earth's rotation matrix; ω is the Earth's rotation angular velocity, t is the time from the reference time, is the Earth orientation parameter at the initial moment; Combined with the position of the ground receiving station, the satellite state vector r in the ENU coordinate system is further obtained enu =[x enu y enu z enu ] T , the expression is: r enu =R ecef_enu (r ecef -k ecef ) Among them, r ecef is the satellite state vector in the ECEF coordinate system; R ecef_enu is the transformation matrix, k ecef =[x gs_ecef y gs_enu z gs_enu ] T is the ECEF coordinate of the receiving station; φ and λ are the latitude and longitude of the receiving station respectively; After spherical coordinate transformation, the satellite pitch angle θ is further obtained enu and azimuth α enu , the expression is: α enu =arctan2(x enu ,y enu ) Among them, x enu ,y enu and z enu is the coordinate of the satellite in the ENU coordinate system; the pitch angle θ enu Measured with reference to the horizontal plane; azimuth α enu Measured clockwise from due north; Combined with the pitch angle and azimuth angle corresponding to the receiving antenna attitude in the ENU coordinate system, the satellite state vector r in the antenna body coordinate system is further obtained ante =[x ante y ante z ante ] T , the expression is: r ante ＝R enu_ante r enu Among them, R enu_ante is the transformation matrix; r enu is the satellite state vector in the ENU coordinate system; θ atti and α ante are the elevation angle and azimuth angle corresponding to the receiving antenna attitude in the ENU coordinate system, respectively; After spherical coordinate transformation and deflection calculation, the satellite azimuth angle α in the antenna body coordinate system can be further obtained. ante and the elevation angle θ ante , the expression is: α ante =arctan2(y ante ,x ante ) Among them, x ante ,y ante and z ante is the coordinate of the satellite in the antenna body coordinate system, and the polarization deflection angle is calculated from the polarization directions of the antenna and the satellite; According to the satellite tracking results, the high-gain narrow-beam receiving antenna is aimed at the radiation source satellite by adjusting the angle of the antenna turntable.

3. The method for detecting external radiation source radar targets based on satellite downlink communication signals according to claim 1, characterized in that: The specific process of S4 is as follows: the hardware error of the receiving system and the atmospheric transmission etc. bring delay and phase error to the received signal, which are compensated by the acquired satellite relative motion parameters. The expressions of the reference signal and the target echo signal after two-dimensional division before compensation are respectively: Among them, t f is the fast time, i.e. the distance time variable; t s is the slow time, i.e., the azimuth time variable; T a is the duration of the signal; S T (t) is the baseband signal transmitted by the satellite; τ ref (t s ) and τ sur (t s ) are the time delays caused by the propagation paths of the reference signal and the target echo signal at each azimuth moment; f c is the carrier frequency of the transmitted signal; f d-ref (t s ) and f d-sur (t s ) are the instantaneous Doppler frequencies of the reference signal and the target echo signal at each azimuth moment; Δτ(t s ) is the delay error caused by atmospheric transmission and satellite motion. Since the distance from the target to the receiving station is much smaller than the distance to the satellite, it is approximately assumed that the delay errors of the two channels are consistent; φ e (t s ) is the phase error caused by the frequency error of the receiver hardware. It is approximately assumed that the phase errors of the two channels are consistent after the receiver is calibrated; Calculate the time delay τ at each azimuth according to the obtained satellite relative distance and Doppler frequency shift ref (t s ) and the instantaneous Doppler frequency f d-ref (t s ), and perform delay and phase compensation on each azimuth moment of the reconstructed reference signal, and then cross-correlate the result with the signal received by the reference channel to obtain the delay error value of each azimuth moment Phase error value It is used to compensate the delay and phase error of the target echo signal, and its expression is: Among them, FFT f and IFFT f Respectively represent the fast time t f Do the Fast Fourier Transform and the Fast Inverse Fourier Transform.

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