CN103033812B - Space pursing synchronization method of airborne bistatic synthetic aperture radar (SAR) beam - Google Patents
Space pursing synchronization method of airborne bistatic synthetic aperture radar (SAR) beam Download PDFInfo
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Abstract
The invention discloses a space pursing synchronization method of an airborne bistatic synthetic aperture radar (SAR) beam. The space pursing synchronization method of the airborne bistatic SAR beam particularly includes that a pursing radar sends an antenna beam, accurately calculating an azimuth angle of the antenna beam or a pitch angle of the antenna beam when an antenna beam of a receiving station is directed at a cover area of an antenna beam of a sending station, or meanwhile calculating the azimuth angle of the antenna beam and the pitch angle of the antenna beam simultaneously, and therefore the antenna beam of the receiving station can be accurately directed at the center of the antenna beam of the sending station, the accurate alignment of the antenna beam receiving and sending of an airborne bistatic SAR is achieved, and the space synchronization of the bistatic SAR is completed. The pursing space synchronization method of the airborne bistatic SAR beam solves the problem that in the prior method, an antenna directing control parameter has a big error, an enough coincided area of the received and sent antenna beams is guaranteed, and a security function for bistatic SAR imaging occurs.
Description
Technical Field
The invention belongs to the technical field of space synchronization in a Radar system, and particularly relates to a method for tracking and synchronizing space of a beam of an airborne bistatic Synthetic Aperture Radar (SAR).
Background
The bistatic SAR is a synthetic aperture radar with a new system of separate receiving and transmitting, and has the characteristics of different space geometric coordinate relations, strong anti-interference performance, concealment, anti-interception capability and the like. The bistatic SAR comprises satellite-borne bistatic SAR for satellite transmission and satellite reception, satellite-borne bistatic SAR for satellite transmission and airplane reception, airborne bistatic SAR for airplane transmission and airplane reception and the like.
Due to the separate receiving and transmitting, the airborne bistatic SAR has a new space geometry structure, and therefore the space synchronization problem of the airborne bistatic SAR is brought. The space synchronization requires that the antenna beams of the transmitting station and the receiving station have coincident irradiation areas for the same target area, so that the echo of the imaging area has enough signal-to-noise ratio, and the synthetic aperture radar imaging guarantee is provided. In the airborne bistatic SAR, because the receiving and transmitting carriers are in motion, the spatial position is constantly changed, and the difficulty of spatial synchronization is higher.
Aiming at the problem of space synchronization, a method proposed in bistatic forward-looking SAR synchronization technology research (Master thesis of electronic science and technology university, Sun Jia Xin, 2011) is to position a platform by using a GPS receiver, measure the attitude of the platform by using an inertial system, and derive pointing control parameters of an airborne bistatic SAR antenna through multi-coordinate system conversion, so that space synchronization is realized. However, because the positioning of the platform by the GPS receiver and the attitude measurement of the platform by the inertial system have certain errors, the calculated antenna pointing control parameter has certain deviation, and the overlapping area of the transmitting and receiving antennas is insufficient, which affects the imaging effect.
Disclosure of Invention
In order to solve the problem that the alignment of the receiving and transmitting antenna beams of the airborne bistatic SAR is not accurate enough, the invention provides a beam catch-up space synchronization method for an airborne bistatic SAR receiving station on the basis of the existing method, which is realized on the premise that the receiving and transmitting antenna beams all point to a target area, namely the receiving and transmitting station antenna beams complete the primary alignment, but the alignment accuracy is not enough, and the antenna beam pointing of the receiving station needs to be adjusted by the method provided by the invention, so that the receiving and transmitting antenna beams are aligned accurately.
For the convenience of describing the present invention, the following terms are first defined:
round probability error: the circle probability error is a measure for measuring the hit precision of the missile, and is also called as the circle common calculation deviation. The definition is to draw a circle by taking the target as the center of the circle. If the chance of a weapon hitting this circle is at least half, then the radius of this circle is the circle probability error.
The technical scheme of the invention is as follows: a beam catch-up space synchronization method of an airborne bistatic SAR specifically comprises the following steps:
s11, parameter initialization:
the parameters include: the radar transmits a chirp signal, the bandwidth B of the radar transmit pulse, the pulse width t of the radar transmit pulserFrequency modulation slope k of radar emission pulser＝B/trThe azimuth angle of the antenna beam when the receiving station antenna beam is initially aligned with the transmitting station antenna beam is beta0Azimuthal scan range-phi + beta0~+Φ+β0Phi is a first boundary angle, the range direction dimension N of the echo matrix and the azimuth direction dimension M of the echo matrix;
s12, recording radar echo after azimuth scanning:
when the bistatic SAR receiving and transmitting antenna wave beam points to the target area, the transmitting station starts to transmit radar transmitting pulse, the receiving station starts to control the antenna to carry out azimuth uniform scanning within the scanning range of-phi + beta0~+Φ+β0And the radar echo in the azimuth scanning range can be recorded after one-time scanning is finished, and a radar azimuth echo matrix Huibo1 is obtainedN×M；
S13, radar azimuth echo matrix distance direction pulse compression:
performing matched filtering on each row of the echo matrix, namely convolving each row of the echo matrix with the matched filtering matrix, namely obtaining a distance direction pulse compressed matrix H1;
s14, calculating an azimuth energy center:
according to the step S13, obtaining a matrix H1 after the radar azimuth echo matrix distance direction pulse compression, carrying out amplitude weighting on each column of H1 to obtain an amplitude weighting vector A1,
wherein,(i =0, 1, 2... M-1, j =0, 1, 2.. N-1), and then obtaining a position X where a peak of the vector a1 is located, where X is an energy center of the radar echo in the azimuth direction;
s15, adjusting the azimuth angle of the antenna, aligning the azimuth energy center:
the azimuth energy center X and the azimuth angle change delta beta of the antenna beam are in a linear relation, thenThe azimuth angle beta of the antenna beam when the antenna beam is aligned with the azimuth energy center can be obtained0And + delta beta, the antenna server completes the azimuth adjustment of the antenna pointing direction according to the beta, and catches up the radar transmitting antenna beam, so that the receiving station antenna beam is aligned to the azimuth energy center of the transmitting station antenna beam.
In order to solve the above problems, the present invention further provides a beam-catch-up space synchronization method for an airborne bistatic SAR, which specifically includes the following steps:
s21, parameter initialization:
the parameters include: the radar transmits a chirp signal, the bandwidth B of the radar transmit pulse, the pulse width t of the radar transmit pulserFrequency modulation slope k of radar emission pulser＝B/trThe pitch angle of the antenna beam when the antenna beam of the receiving station is initially aligned with the antenna beam of the transmitting station is theta0The pitch scan orientation is- Ψ + θ0~+Ψ+θ0Ψ is a second boundary angle, a range dimension N of the echo matrix, and an azimuth dimension M of the echo matrix;
s22, recording radar echoes after the pitching scanning:
when the bistatic SAR receiving and transmitting antenna beam points to the target area, the transmitting station starts to transmit radar transmission pulse, the receiving station controls the antenna to perform pitching uniform scanning within the scanning range of-psi + theta0~+Ψ+θ0The radar echo within the pitch scanning range can be recorded after one-time scanning is finished, and a radar pitch echo matrix Huibo2 is generatedN×M；
S23, radar pitch echo matrix distance direction pulse compression:
performing matched filtering on each column of the pitching echo matrix, namely convolving each column of the echo matrix with the matched filtering matrix to obtain a distance direction pulse compressed matrix H2;
s24, calculating a pitch energy center:
amplitude weighting is performed on each column of the distance-to-pulse-compressed matrix H2 to obtain an amplitude weighting vector a2, wherein, <math>
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further obtaining a position Y of a peak value of the vector A2, wherein Y is an energy center of the radar echo in the pitching direction;
s25, adjusting the pitch angle of the antenna, aligning the pitch energy center:
the pitching energy center Y and the antenna beam pitching angle change delta theta are in linear relation, thenTherefore, the antenna beam pitch angle theta can be obtained when the antenna beam is aligned with the pitch energy center0And + delta theta, the antenna servo completes the pitching adjustment of the antenna pointing direction according to theta, and catches up with the radar transmitting antenna beam, so that the receiving station antenna beam is aligned to the pitching energy center of the transmitting station antenna beam.
In order to solve the above problems, the present invention further provides a beam-catch-up space synchronization method for an airborne bistatic SAR, which specifically includes the following steps:
s31, parameter initialization:
the parameters include: the radar transmits a chirp signal, the bandwidth B of the radar transmit pulse, the pulse width t of the radar transmit pulserFrequency modulation slope k of radar emission pulser＝B/trThe flying height H of the receiving and transmitting platform, the width alpha of the antenna beam, and the azimuth angle beta of the antenna beam when the antenna beam of the receiving station is initially aligned with the antenna beam of the transmitting station0And a pitch angle of theta0Azimuthal scan range-phi + beta0~+Φ+β0The pitch scan orientation is- Ψ + θ0~+Ψ+θ0A range dimension N of the echo matrix and an azimuth dimension M of the echo matrix, wherein phi is a first boundary angle and psi is a second boundary angle;
s32, recording radar echoes after azimuth scanning and radar echoes after elevation scanning:
when bistatic SAR receiving and transmitting antenna wave beams point to a target area by the existing method, the transmitting station starts to transmit radar transmitting pulses, the receiving station starts to control the antenna to carry out azimuth uniform scanning within the range of-phi + beta0~+Φ+β0And the radar echo in the azimuth scanning range can be recorded after one-time scanning is finished, and a radar azimuth echo matrix Huibo1 is obtainedN×M；
The receiving station controls the antenna to perform pitching uniform-speed scanning within the range of-psi + theta0~+Ψ+θ0The radar echo within the pitch scanning range can be recorded after one-time scanning is finished, and a radar pitch echo matrix Huibo2 is generatedN×M；
S33, radar azimuth echo matrix and pitch echo matrix distance direction pulse compression:
performing matched filtering on each column of the azimuth echo matrix and the pitch echo matrix, namely convolving each column of the echo matrix with the matched filtering matrix to obtain an azimuth echo matrix H1 and a pitch echo matrix H2 after the range direction pulse compression;
s34, calculating an azimuth energy center and a pitch energy center:
respectively carrying out amplitude weighting on each column of the azimuth echo matrix H1 and the pitch echo matrix H2 after pulse compression to obtain amplitude weighting vectors A1 and A2,
wherein,(i =0, 1, 2... M-1, j =0, 1, 2.. N-1), and then the position X of the peak of the vector a1 is obtained, where X is the azimuth of the radar echoAn energy center;
(i =0, 1, 2... M-1, j =0, 1, 2.. N-1), and then obtaining a position Y where a peak value of the vector a2 is located, wherein Y is an energy center of a radar echo in a pitching direction;
s35, adjusting the pointing angle of the antenna, aligning the azimuth energy center and the elevation energy center:
the azimuth energy center X and the azimuth angle change delta beta of the antenna beam are in a linear relation, thenTherefore, the azimuth angle beta of the antenna beam when the antenna beam is aligned to the azimuth energy center can be obtained0+Δβ；
The pitching energy center Y and the antenna beam pitching angle change delta theta are in linear relation, thenTherefore, the antenna beam pitch angle theta can be obtained when the antenna beam is aligned with the pitch energy center0+Δθ；
And the antenna server finishes the adjustment of the antenna pointing direction according to the antenna beam azimuth angle beta and the antenna beam pitch angle theta, and catches up the radar transmitting antenna beam to enable the receiving station antenna beam to be aligned to the energy center of the transmitting station antenna beam.
In the above step, the matched filter matrix specifically includes:
The invention has the beneficial effects that: according to the method, the azimuth angle or the pitch angle of the antenna beam when the antenna beam of the receiving station is aligned to the area covered by the antenna beam of the transmitting station is accurately calculated in a mode of catching up the antenna beam emitted by the radar, or the azimuth angle and the pitch angle of the antenna beam are simultaneously calculated, so that the antenna beam of the receiving station can be accurately aligned to the center of the antenna beam of the transmitting station, the accurate alignment of the receiving and transmitting antenna beams of the airborne bistatic SAR is realized, and the space synchronization of the bistatic SAR is completed. The method solves the problem that the antenna pointing control parameters in the existing method have larger errors, ensures that the receiving and transmitting antenna beams have enough superposition area in the test process, and plays a role in guaranteeing the imaging of the bistatic SAR.
Drawings
FIG. 1 is a schematic flow diagram of the process of the present invention.
Fig. 2 is a system configuration diagram of an airborne bistatic SAR employed in an embodiment of the present invention.
Fig. 3 is a system parameter table of the airborne bistatic SAR employed in the embodiment of the present invention.
Fig. 4 is a schematic diagram of a radar echo matrix in an embodiment of the present invention.
Fig. 5 is a schematic diagram of distance-to-amplitude weighting vectors in the embodiment of the present invention.
Fig. 6 is a diagram illustrating simulation results of a circular probability error of an antenna pointing direction in the embodiment of the present invention.
Detailed Description
The invention is further described with reference to the following figures and specific embodiments.
The invention mainly adopts a simulation experiment mode to carry out verification, and a simulation verification platform is Matlab 2010. The invention is described in further detail below with reference to the figures and the detailed description.
From the description of the content of the invention, the method of the invention mainly calculates the azimuth angle or the pitch angle of the antenna beam when the antenna beam of the receiving station is aligned to the coverage area of the antenna beam of the transmitting station in a mode of catching up the antenna beam of the radar transmission antenna, or simultaneously calculates the azimuth angle and the pitch angle of the antenna beam, so that the antenna beam of the receiving station can be accurately aligned to the center of the antenna beam of the transmitting station, the accurate alignment of the receiving and transmitting antenna beams of the airborne bistatic SAR is realized, the space synchronization of the bistatic SAR is completed, and the structure of the bistatic SAR system is shown in figure 2.
It can be seen that calculating the azimuth angle and the elevation angle of the antenna beam simultaneously to achieve accurate alignment of the center of the antenna beam of the transmitting station is an optimal implementation manner, and the following mainly describes a specific implementation manner of the method of the present invention, and those skilled in the art can implement accurate alignment of the center of the antenna beam of the transmitting station by using the azimuth angle and the elevation angle of the antenna beam according to the implementation manner, and detailed description thereof is omitted.
The schematic flow chart of the beam catch-up space synchronization method of the invention is shown in fig. 1, and the specific process is as follows:
step 1, parameter initialization:
the initialized parameters are known and are as follows, as shown in fig. 3: bandwidth B =80MHz of radar transmission pulse, pulse width t of radar transmission pulser5us, chirp rate k of radar transmitted pulser＝B/tr16MHz/us, the flying height H of the receiving and transmitting platform is 6000m, the width alpha of the antenna beam is 3 degrees, and the azimuth angle of the antenna beam when the receiving antenna beam is initially aligned with the antenna beam of the transmitting station is beta0Angle of pitch theta is not less than 1 DEG0=46 °, azimuth scanning range- Φ + β0~+Φ+β0=9 ° -11 °, pitch scan range- Ψ + θ0~+Ψ+θ0= 36 ° -56 °, the range dimension N =2273 of the echo matrix, and the azimuth dimension M =4096 of the echo matrix.
The first boundary angle Φ and the second boundary angle Ψ can be obtained according to actual situations in a specific application.
The background noise used for the simulation was white gaussian noise with a signal to noise ratio of 0 dB.
It should be noted that, it is assumed here that the antenna beam azimuth width and the antenna beam elevation width are the same, and the transmit-receive platform flying height and the antenna beam width are only used for evaluating the calculation accuracy of the method of the present invention.
Step 2, recording the radar echo matrix after azimuth scanning and the radar echo matrix after pitch scanning:
when the bistatic SAR receiving and transmitting antenna beams all point to the target area by the existing method, the transmitting station starts to transmit the radar signal pulse in the step 1, the receiving station starts to control the antenna to carry out azimuth scanning, and the scanning range is-psi + theta0~+Ψ+θ0The angle ranges from minus 9 degrees to plus 11 degrees, radar echoes in an azimuth scanning range can be recorded after one-time scanning is finished, and a radar azimuth echo matrix Huibo1 is generatedN×MGenerating a radar azimuth echo matrix Huibo1 through simulationN×MThe echo matrix diagram is shown in fig. 4.
The receiving station controls the antenna to perform pitching uniform-speed scanning within the range of-psi + theta0~+Ψ+θ0= 36 DEG to 56 DEG, and radar echo Huibo2 in the range of pitching scanning can be recorded after one scanning is finishedN×M. Radar pitch echo matrix Huibo2 generated by simulationN×M。
Step 3, radar azimuth echo matrix and radar pitch echo matrix range pulse compression:
performing matched filtering on each column of the echo matrix obtained in the step 2 of the specific embodiment, that is, convolving each column of the echo matrix with a matched filtering matrix, where the matched filtering matrix is:
Here, rect represents a rectangular function, which can be defined herein asexp denotes an exponential function based on the natural logarithm e, the echo sampling frequency f of the receiving stations＝2B＝160MHz。
Those skilled in the art will appreciate that other forms of matched filter matrices may be used.
H1(i)＝ifft(fft(Huibo1N×M(i))·conj(fft(Re ferN×1) M-1), where i denotes the i-th column from the orientation of the compressed matrix, fft denotes the fast fourier transform, ifft denotes the inverse fourier transform, and conj denotes the conjugate.
In this way, the distance direction pulse-compressed matrix H2 can be obtained.
H2(i)＝ifft(fft(Huibo2N×M(i))·conj(fft(Re ferN×1))),（i＝0、1、2.....M-1)，
Step 4, calculating an azimuth energy center and a pitch energy center:
and (3) obtaining a matrix H1 after the radar azimuth echo matrix distance direction pulse compression according to the step 3, and performing amplitude weighting on each column of H1 to obtain an amplitude weighting vector A1, as shown in FIG. 5.
(i =0, 1, 2.. M-1, j =0, 1, 2.. N-1). This yields a position X =1881 at which the peak of vector a1 is located, X being the energy center in the azimuth direction of the radar echo.
Similarly, according to the step 3, a matrix H2 obtained after the radar pitch echo matrix distance direction pulse compression is obtained, and amplitude weighting is performed on each column of H2 to obtain an amplitude weighting vector a 2.
(i =0, 1, 2.. M-1, j =0, 1, 2.. N-1). This yields 1834 as the position Y of the peak of the vector a2, which is the energy center of the radar echo in the elevation direction.
Step 5, adjusting the pointing angle of the antenna, aligning the azimuth energy center and the pitching energy center:
because the antenna scans at uniform speed in the azimuth direction, the scanning range is-phi + beta0~+Φ+β0The angle is = -9 degrees to +11 degrees, and the value of the azimuth energy center X and the azimuth angle change delta beta of the antenna beam are in a linear relationThe azimuth angle beta of the antenna beam when the antenna beam is aligned with the azimuth energy center can be obtained0+ Δ β is 0.1855 °. The antenna servo unit completes the direction adjustment of the antenna direction according to the beta, so that the antenna beam of the receiving station is aligned to the direction energy center of the antenna beam of the transmitting station.
Because the antenna scans at a constant speed in the pitching direction, the scanning range is-psi + theta0~+Ψ+θ0The angle is = +36 degrees to +56 degrees, and the value of the pitching energy center Y and the pitch angle change delta theta of the antenna beam formLinear relationship ofThe antenna beam pitch angle θ = θ when the antenna beam is aligned with the center of the pitch energy can thus be derived0+Δθ=44.9561°。
And the antenna server finishes the adjustment of the antenna pointing direction according to the antenna beam azimuth angle beta and the antenna beam pitch angle theta, and catches up the radar transmitting antenna beam to enable the receiving station antenna beam to be aligned to the energy center of the transmitting station antenna beam.
Through the steps, the antenna beam of the receiving station can be accurately aligned to the antenna beam center of the transmitting station, so that the accurate alignment of the receiving and transmitting antenna beams of the airborne bistatic SAR is realized, and the spatial synchronization of the bistatic SAR is completed.
Based on the steps, 1000 Monte Carlo simulations are carried out on the simulation actual situation, namely 1000 experimental units under different pointing error influence conditions are taken, the value of the 500 th sample point (which is arranged according to the size) is extracted according to the idea of the circular probability error to serve as the effective value of the beam pointing in the antenna adjustment error interval of sigma (-0.002 degrees and 0.002 degrees, and the relation between the receiving antenna irradiation area and the transmitting antenna irradiation area is quantitatively analyzed by using the analysis method of the circular probability error.
The approximate distance r between the center of the irradiation area of the receiving antenna and the center of the irradiation area of the transmitting antenna can be determined as
Further, the maximum radius value r for allowing a circle with the center of the transmission antenna beam as the radius to fall within the reception beam irradiation region with a 50% probability can be determined0. Beta in this case1And theta1The antenna beam azimuth angle and the pitch angle of the receiving station antenna beam are theoretically accurately aligned with the antenna beam azimuth angle and the pitch angle of the transmitting station antenna beam, and the specific value is beta1=0°、θ1=45°。
The probability error of the circle pointing to the transmitter and receiver beam obtained by sequencing and taking out the 500 th point can be further calculated by the formula as follows: r is0=9.6417 m. The simulation results are shown in fig. 6.
Based on the beam width and the linear distance of the receiving station carrier platform to the target, the approximate diameter d of the beam coverage area can be calculated,
it can be seen that r & lt d, the beam catch-up space synchronization method provided by the invention is considered to have high synchronization precision.
Claims (6)
1. A beam catch-up space synchronization method of an airborne bistatic SAR specifically comprises the following steps:
s11, parameter initialization:
the parameters include: the radar transmits a chirp signal, the bandwidth B of the radar transmit pulse, the pulse width t of the radar transmit pulserFrequency modulation slope k of radar emission pulser=B/trThe azimuth angle of the antenna beam when the receiving station antenna beam is initially aligned with the transmitting station antenna beam is beta0Azimuthal scan range-phi + beta0～+Φ+β0Phi is a first boundary angle, the range direction dimension N of the echo matrix and the azimuth direction dimension M of the echo matrix;
s12, recording radar echo after azimuth scanning:
when the bistatic SAR receiving and transmitting antenna wave beam points to the target area, the transmitting station starts to transmit radar transmitting pulse, the receiving station starts to control the antenna to carry out azimuth uniform scanning within the scanning range of-phi + beta0～+Φ+β0And the radar echo in the azimuth scanning range can be recorded after one-time scanning is finished, and a radar azimuth echo matrix Huibo1 is obtainedN×M；
It is characterized by also comprising the following steps:
s13, radar azimuth echo matrix distance direction pulse compression:
performing matched filtering on each row of the echo matrix, namely convolving each row of the echo matrix with the matched filtering matrix, namely obtaining a distance direction pulse compressed matrix H1;
s14, calculating an azimuth energy center:
according to the step S13, obtaining a matrix H1 after the radar azimuth echo matrix distance direction pulse compression, carrying out amplitude weighting on each column of H1 to obtain an amplitude weighting vector A1,
wherein,i =0, 1, 2... M-1, j =0, 1, 2.. N-1, and then obtaining a position X where a peak of a vector a1 is located, where X is an energy center of a radar echo azimuth;
s15, adjusting the azimuth angle of the antenna, aligning the azimuth energy center:
the azimuth energy center X and the azimuth angle change delta beta of the antenna beam are in a linear relation, thenFrom this, the antenna beam azimuth angle β = β when the antenna beam is aligned with the azimuth energy center can be obtained0+ delta beta, the antenna servo performs the azimuth adjustment of the antenna pointing direction according to beta, catches up with the radar transmitting antenna beam, and makes the receiving station antenna beam align with the azimuth energy of the transmitting station antenna beamAnd (4) a heart.
2. The beam catch-up spatial synchronization method according to claim 1, wherein the matched filter matrix in step S13 is specifically:
3. A beam catch-up space synchronization method of an airborne bistatic SAR specifically comprises the following steps:
s21, parameter initialization:
the parameters include: the radar transmits a chirp signal, the bandwidth B of the radar transmit pulse, the pulse width t of the radar transmit pulserFrequency modulation slope k of radar emission pulser=B/trThe pitch angle of the antenna beam when the antenna beam of the receiving station is initially aligned with the antenna beam of the transmitting station is theta0The pitch scan orientation is- Ψ + θ0～+Ψ+θ0Ψ is a second boundary angle, a range dimension N of the echo matrix, and an azimuth dimension M of the echo matrix;
s22, recording radar echoes after the pitching scanning:
when the bistatic SAR receiving and transmitting antenna beam points to the target area, the transmitting station starts to transmit radar transmission pulse, the receiving station controls the antenna to perform pitching uniform scanning within the scanning range of-psi + theta0～+Ψ+θ0The radar echo within the pitch scanning range can be recorded after one-time scanning is finished, and a radar pitch echo matrix Huibo2 is generatedN×M；
It is characterized by also comprising the following steps:
s23, radar pitch echo matrix distance direction pulse compression:
performing matched filtering on each column of the pitching echo matrix, namely convolving each column of the echo matrix with the matched filtering matrix to obtain a distance direction pulse compressed matrix H2;
s24, calculating a pitch energy center:
amplitude weighting is performed on each column of the distance-to-pulse-compressed matrix H2 to obtain an amplitude weighting vector a2, wherein,i =0, 1, 2... M-1, j =0, 1, 2.. N-1; further obtaining a position Y of a peak value of the vector A2, wherein Y is an energy center of the radar echo in the pitching direction;
s25, adjusting the pitch angle of the antenna, aligning the pitch energy center:
the pitching energy center Y and the antenna beam pitching angle change delta theta are in linear relation, thenThe antenna beam pitch angle θ = θ when the antenna beam is aligned with the center of the pitch energy can thus be derived0And + delta theta, the antenna server completes the pitching adjustment of the antenna pointing direction according to theta, and catches up with the radar transmitting antenna beam, so that the receiving station antenna beam is aligned to the azimuth energy center of the transmitting station antenna beam.
4. The beam catch-up spatial synchronization method according to claim 3, wherein the matched filter matrix in step S23 is specifically:
5. A beam catch-up space synchronization method of an airborne bistatic SAR specifically comprises the following steps:
s31, parameter initialization:
the parameters include: the radar transmits a chirp signal, the bandwidth B of the radar transmit pulse, the pulse width t of the radar transmit pulserFrequency modulation slope k of radar emission pulser=B/trThe flying height H of the receiving and transmitting platform, the width alpha of the antenna beam, and the azimuth angle beta of the antenna beam when the antenna beam of the receiving station is initially aligned with the antenna beam of the transmitting station0And a pitch angle of theta0Azimuthal scan range-phi + beta0～+Φ+β0The pitch scan orientation is- Ψ + θ0～+Ψ+θ0A range dimension N of the echo matrix and an azimuth dimension M of the echo matrix, wherein phi is a first boundary angle and psi is a second boundary angle;
s32, recording radar echoes after azimuth scanning and radar echoes after elevation scanning:
when bistatic SAR receiving and transmitting antenna wave beams point to a target area by the existing method, the transmitting station starts to transmit radar transmitting pulses, the receiving station starts to control the antenna to carry out azimuth uniform scanning within the range of-phi + beta0～+Φ+β0And the radar echo in the azimuth scanning range can be recorded after one-time scanning is finished, and a radar azimuth echo matrix Huibo1 is obtainedN×M；
The receiving station controls the antenna to perform pitching uniform-speed scanning within the range of-psi + theta0～+Ψ+θ0The radar echo within the pitch scanning range can be recorded after one-time scanning is finished, and a radar pitch echo matrix Huibo2 is generatedN×M；
It is characterized by also comprising the following steps:
s33, radar azimuth echo matrix and pitch echo matrix distance direction pulse compression:
performing matched filtering on each column of the azimuth echo matrix and the pitch echo matrix, namely convolving each column of the echo matrix with the matched filtering matrix to obtain an azimuth echo matrix H1 and a pitch echo matrix H2 after the range direction pulse compression;
s34, calculating an azimuth energy center and a pitch energy center:
respectively carrying out amplitude weighting on each column of the azimuth echo matrix H1 and the pitch echo matrix H2 after pulse compression to obtain amplitude weighting vectors A1 and A2,
wherein,i =0, 1, 2... M-1, j =0, 1, 2.. N-1, and then the position X of the peak of the vector a1 is obtained, wherein X is the energy center of the radar echo azimuth;
i =0, 1, 2.... M-1, j =0, 1, 2... N-1, and then the position Y of the peak of the vector A2 is obtained, wherein Y is the energy center of the radar echo in the pitching direction;
s35, adjusting the pointing angle of the antenna, aligning the azimuth energy center and the elevation energy center:
the azimuth energy center X and the azimuth angle change delta beta of the antenna beam are in a linear relation, thenThe antenna beam azimuth angle β = β can thus be obtained when the antenna beam is aligned in azimuth towards the energy center0+Δβ；
The pitching energy center Y and the antenna beam pitching angle change delta theta are in linear relation, thenThe antenna beam pitch angle θ = θ when the antenna beam is aligned with the center of the pitch energy can thus be derived0+Δθ；
And the antenna server finishes the adjustment of the antenna pointing direction according to the antenna beam azimuth angle beta and the antenna beam pitch angle theta, and catches up the radar transmitting antenna beam to enable the receiving station antenna beam to be aligned to the energy center of the transmitting station antenna beam.
6. The beam catch-up spatial synchronization method according to claim 5, wherein the matched filter matrix in step S33 is specifically:
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