Study Of Multi-antenna SAR Imaging Method On The Same Platform

In order to meet the increasing application demand,synthetic aperture radar(SAR)has been widely used in military and civil area.The coherent multi-antenna technique has been applied to SAR.The novel developing imaging technology based on multi-antenna is able to simultaneously improve the performance of SAR imaging by utilizing multiple antennas both at transmission and reception.Multi-antenna SAR system can provide more degrees of'freedom than traditional SAR.With the digital beamforming(DBF)technique,it shows a distinct advantage in moving target detection,high resolution and wide swath,and interference suppression based on the correlation characteristics of multiple transmit waveforms and equivalent array beam.It is received great attentions in remote sensing and radar imaging,and becomes one of research hotspots.Based on traditional SAR imaging technique,for the problems such as high resolution and wide swath,moving target detection and large amount of data,this dissertation focuses on imaging theory and method of coherent multi-antenna SAR.The key researches include multiple input and multiple output SAR(MIMO SAR)imaging method based on coprime array in range,imaging method of displaced phase center multiple azimuth beams(DPCMAB)based on fractional Fourier transform(FrFT)in azimuth and wide swath imaging of range-azimuth joint multi-antenna SAR based on compressed sensing(CS).The main works and innovation points are as follows.1.The SAR imaging method of high squint is studied.After a detailed derivation and analysis of the echo characteristics of the high squint mode,an extended Chirp scaling(ECS)imaging algorithm is proposed.The echo features are derived and analysed thoroughly,the range migration is removed in time domain,the imaging using the extended chirp scaling algorithm is carried out,and the implementation of this approach is demonstrated.The results show that the range migration is corrected by simple phase addition with appropriate arithmetic and the method is feasible.2.The SAR imaging method of multi-antenna in range is studied.Firstly the waveform of MIMO SAR based on linear frequency modulation pulse signal is designed.Waveform set based on LFM is analysised,and the ambiguity function expression is derived.The Costas encoding combined the LFM signal is designed,which called inter-pulse Costas hopping and intra-pulse slope coded LFM(IPC-SCLFM)signal.Secondly,MIMO-Cop SAR imaging method based on coprime array in range is proposed using IPC-SCLFM signals.The signal model of two kinds of Coprime receiving line array is studied.Echoes are separated by DBF and simple processing of multiply.The cross-correlation noise level is well suppressed and the amount of data is reduced effectively.Finally,the simulation experiments are performed and the results show that the imaging performance is good,and the noise level is well suppressed.3.The SAR imaging method of multi-antenna in azimuth is studied.SAR imaging of moving target from nonuniformly sampled signals with FrFT based on DPCMAB system is proposed.The problem of non-uniform sampling is caused by the dimension error of the antenna,the installation error,and the nonuniform motion of the platform.The nonuniformly sampled points in the fractional order Fourier transform domain are used to reconstruct the moving target detection of DPCMAB system.After the original data is compressed in range,the azimuth reconstruction is carried out,and the reconstructed data is obtained by FrFT,and the Doppler frequency estimation is obtained.Simulation results show that the method is effective.4.The SAR imaging method of multi-antenna in range-azimuth joint is studied.A MIMO SAR imaging based on compressed sensing(CS)is proposed.The sparse array is used in receiving antenna,and the mathematical model of this algorithm is given.The echoes are processed with equivalent DBF and the range resolution is improved.Zero point technique based on CS is proposed with DBF in receive and the range ambiguity is suppressed effectively.Resolution in azimuth is improved by DPCA technique.The simulation results show that the CS technique can effectively reduce the data of MIMO SAR system and the efficiency and validity of the new method is demonstrated.