Research On Multi-antenna SAR Imaging

Synthetic Aperture Radar(SAR)which is a high-resolution imaging radar technology plays an important role in military reconnaissance,remote sensing observation and other fields.However,nowadays conventional SAR systems with a single transmit and receive antenna are not capable of fulfilling the increasing demands for high-resolution wide-swath imaging.The technology which combined SAR and Multi-Input Multiple-Output(MIMO)can make full use of waveform diversity and antenna diversity to attain much more spatial degree of freedom than conventional SAR systems.MIMO-SAR with the capability to achieve highresolution wide-swath imaging had turned into an attractive field.The MIMO-SAR radar orthogonal waveform sets and MIMO-SAR fundamental imaging processing methods is investigated based on SAR imaging processing methods.The primary contents of the dissertation include:(1)Design MIMO-SAR radar orthogonal transmit waveform sets.The orthogonal waveform sets using orthogonal frequency division multiplexing(OFDM)modulation technique are studied according to the orthogonality principle of radar transmit signal.Firstly,the orthogonal signals which using the linear frequency modulation(LFM)in sub-carrier are studied,and their autocorrelation,cross correlation and ambiguity function are simulated and analyzed.Secondly,the orthogonality of Phase Coded(PC)OFDM signals is studied.The new phase coded signals are generated by chaotic map sequence,which have the superiority of strong confidentiality and low probability of intercept.The autocorrelation,crosscorrelation,ambiguity function and Doppler tolerance of chaotic PC-OFDM signals are simulated and analyzed,and the advantages and disadvantages of these signals are discussed.(2)Research on conventional single-antenna SAR imaging method.Firstly,the SAR imaging principle is analyzed and the SAR signal echo model is established.Secondly,the Range-Doppler(R-D)algorithm is simulated,and the RADARSAT-1 radar data are used to verify the effectiveness of the R-D algorithm.Finally,in terms of SAR imaging on sparse scenes,SAR echo signal focusing imaging by compression sensing theory is studied.The simulation analysis shows that the compression sensing has a great advantage in sidelobes suppression on SAR imaging.(3)Research on MIMO-SAR imaging processing methods.Firstly,the minimum SAR area constraint of conventional SAR is analyzed,and the tri-input tri-output SAR imaging model based on OFDM-LFM signals is established.Secondly,in combination with the requirements to achieve high-resolution in range,large bandwidth signal is synthesized in SAR range with sub-band synthesis method.Finally,in accordance with the requirements of high-resolution wide-swath imaging in SAR azimuth,SAR signal is transmitted with low pulse repetition frequency.In SAR azimuth,multi-channel reconstruction method is used to eliminate spectral aliasing.The simulation results demonstrate the effectiveness of the method.The method compares with the focus images of the conventional SAR imaging algorithm,which shows that the MIMO-SAR can realize high-resolution wide-swath imaging.