Non-line-of-sight Millimeter Wave Radar High-precision 3D Imaging Technology Study

With the rapid development of global urbanization,urban environment imaging perception has great research and application value in the fields of urban warfare,disaster relief,automatic driving and so on.Due to the advantages of wave length,high resolution,low power consumption and strong penetration,millimeter wave imaging has important application prospects in all-weather perception of complex urban environment.However,in the complex urban environment,the traditional millimeter wave imaging technology adopts the visual echo detection mechanism,which can not realize the imaging of building masking area,resulting in a large number of sight distance blind areas in the urban environment.Therefore,a new technology of masking target perception is urgently needed.NLOS radar imaging is a new imaging technology rising in recent years.Its principle is to reconstruct the image of NLOS obscured target through imaging algorithm by using the diffraction and scattering propagation mechanism between illumination signal source and environment / target,so as to realize 'line of sight turning and seeing'.Focusing on the key problems of three-dimensional imaging of non line of sight radar,based on the theory of non line of sight imaging and millimeter wave propagation characteristics,this paper carries out the research on three-dimensional imaging technology of non line of sight millimeter wave radar.The main research contents and innovations of this thesis are as follows:1.The basic theory of three-dimensional imaging of non line of sight millimeter wave radar is studied.Firstly,the signal propagation model of millimeter wave radar under NLOS constraints is constructed,and the electromagnetic bidirectional reflection distribution and the main path characteristics of tertiary reflection are analyzed.Secondly,the geometric and signal models of three-dimensional imaging of Obscured Targets in non line of sight millimeter wave radar are constructed,and the characteristics of observation aperture,imaging area and imaging resolution under non line of sight constraints are explored.Finally,the typical three-dimensional imaging algorithm of line of sight millimeter wave radar is introduced,which lays a theoretical foundation for the design of non line of sight imaging algorithm.2.The three-dimensional imaging method of NLOS millimeter wave radar under the condition of ideal reflector is studied.In view of the fact that there is no prior wall layout information in practice,the method of extracting the structural features of reflective surface and shelter based on Hough transform of line of sight coarse imaging is studied,and the reflective wall layout is estimated from the results of line of sight coarse imaging.Aiming at the problem of NLOS target 3D imaging,a high-precision imaging algorithm based on wall mirror backward projection is proposed.Finally,the effectiveness of the millimeter wave imaging system is verified by the measured data.3.The three-dimensional self focusing imaging method of NLOS millimeter wave radar under the condition of non ideal reflector is studied.Firstly,the electromagnetic propagation characteristics of rough reflector and the influence of signal error are analyzed,and the phase error estimation model of NLOS millimeter wave radar 3D imaging under the condition of non ideal rough reflector is constructed.Secondly,two NLOS millimeter wave radar self focusing imaging algorithms under non ideal reflector are studied: image BP imaging algorithm based on minimum entropy(ME-MSBP)and image projection self focusing algorithm based on Bayesian learning minimum iteration(MEAFBRIM).The principles and processes of the two algorithms are described respectively.Finally,the effects of different reflection surfaces on NLOS millimeter wave radar are analyzed through simulation and measured data,and the effectiveness of the relevant algorithms is verified.