Research On Antennas Design And Three-Dimensional Imaging Techniques For MIMO Sparse Array SAR

Array SAR technology can realize three-dimensional(3D)reconstruction of observation areas through a single flight with downward-looking imaging mode,which effectively solves the problem of the blind spot,geometric distortion and left and right fuzzy of traditional SAR technology.This technology has outstanding advantages and good application prospects in aspects of urban mapping,emergency mapping,topographical mapping,and harsh environment navigation.However,array SAR research field is still in its infancy.Now there is no open real array SAR system at home and abroad,and there is no open real three-dimensional echo data and imaging results.And now the study is mostly from the view of signal,which is little association with surveying and mapping.There are many technical gaps on the facts that how to use array SAR technology to transform the research results from the theory to the practical application,and how to effectively serve the surveying and mapping production.Therefore,it is necessary to study array optimization design,three-dimensional imaging algorithm and error compensation of array SAR system by simulation method.From the perspective of surveying and mapping,array SAR technology is combined with Multiple Input Multiple Output(MIMO)technology in the thesis.Which effectively reduces the hardware cost and system complexity on the basis of high-resolution three-dimensional imaging,and which provides the possibility of physical realization and development for array SAR system.In order to make up the technical gap using MIMO array SAR system to produce Digital Elevation Model(DEM),and promote the further development of array SAR technology,The thesis focuses on the optimal design of MIMO array SAR antenna,the array SAR imaging algorithm under non-ideal track,the error compensation of MIMO downward-looking array SAR,and MIMO side-looking array SAR interferometry.The main works and creations are as the following:1.The research status at home and abroad and working modes of array SAR technology were analyzed.And technical advantages for array SAR system compared with traditional SAR system,3D SAR system such as Multi-baseline Tomography SAR(MB-TomoSAR),near field 3D-SAR,Circular SAR(CSAR),Curvilinear SAR(CLSAR),and Li DAR system were summarized.The main problems of restricting the practicality of array SAR technology were pointed out.2.MIMO sparse array antennas schemes with aerial platform satisfying large scale mapping were designed,and MIMO antenna polynomial weighted average optimized method of downward-looking array SAR was proposed.Wave band,resolution,elevation precision and working height concerned by mapping applications were introduced,and the length of equivalent virtual array and actual physical array meeting the needs of large scale topographical mapping were solved.Then array numbers and position vectors of MIMO downward-looking array SAR for real aerial mapping platform(large aircraft and UAV)were optimized.Based on the idea of the spatial position convolution principle,MIMO antenna polynomial weighted average design method of downward-looking array SAR was proposed.The simulation results verified the correctness of the optimized array configuration.3.The non-ideal track motion error model of MIMO downward-looking array SAR was analyzed and constructed,and three-dimensional imaging algorithm of urban buildings MIMO downward-looking array SAR under non-ideal track was proposed.In order to verify the topographical mapping ability of array SAR technology in high-rise buildings,the non-ideal track motion error model of MIMO downward-looking array SAR is deduced with high-abrupt urban buildings.And 3D Range-Doppler(RD)imaging algorithm of urban buildings MIMO downward-looking array SAR under non-ideal track was proposed.Then the flight path and attitude modeling simulation technique of the aeronautical platform,and a fast and efficient echo simulation technique were used to verify the proposed algorithm.The correctness and effectiveness of the proposed method were verified by the comparison experiments.4.Combined with the real POS data form,elements of exterior orientation of traditional optical photogrammetry were introduced,and error compensation methods of MIMO downward-looking array SAR based on the inclination angle and the swirl angle were designed.The beam-independent phase error was compensated in the three-dimensional spatial domain firstly.Then the compensated echo data was transformed into the two-dimensional wavenumber domain in along-track and cross-track directions,and was equally divided into M and N segments.The MN subblocks were zeroed and extended to the original size,transformed into the two-dimensional spatial domain in along-track and cross-track directions and wavenumber domain in range direction,and the beam-dependent phase error was compensated.Finally,the subblock echo data were transformed into three-dimensional spatial domain,and added directly to the final data.And then the correct 3D imaging results could be obtained by 3D RD imaging algorithm.The effectiveness of the proposed method was verified by simulation experiments before and after compensation.5.A simple array vibrating error model was constructed,and the array vibrating error compensation method of MIMO downward-looking array SAR system was proposed,according to the mechanical vibration theory.The array vibrating error was decomposed into two parts,distance-independent and distance-dependent.Combined with the efficient 3D RD imaging algorithm,distance-independent vibrating error was compensated before range compression,and distance-dependent vibrating error was compensated between distance migration correction and azimuth compression,achieving 3D imaging of observation scene.The effectiveness of the proposed method was verified by simulation experiments before and after compensation.6.Zero intermediate frequency baseline estimation method assisted by DEM was proposed.In which,zero intermediate frequency as the criterion,the satellite orbit method and the FFT estimation method were used to iterate the baseline parameters,until the two-dimensional center frequency of differential interferogram is close to zero.Based on this,filtering method of InSAR interferogram based on sparse representation and phase unwrapping method of InSAR assisted by DEM were proposed.Interference processing scheme for MIMO side-looking array SAR was designed.The effectiveness of the proposed scheme was verified by experiments with satellite multi-baseline data.The research achievements in antennas design and three-dimensional imaging techniques for MIMO sparse array SAR are of great significance to promote the theoretical development of array SAR technology and physical realization.They pave the way for the scientific research to guide the engineering practice,and lay the foundation for the rapid acquisition and data updating of the basic geo-spatial information such as urban areas radar measurement,the 3D mapping of difficult mountainous areas and the disaster emergency mapping.