Research On Active Milimeter Wave Imaging Technology

In recent years,with the increasing threat of terrorism,the security of public places,such as airports,stations,and large area of large-scale activities,has been paid more and more attention by the countries all over the world.Active millimeter wave imaging system can quickly and efficiently perform human imaging,and become one of the effective means to protect public safety.In this thesis,based on the background of human security imaging based on millimeter wave band,the image reconstruction algorithm under this system is studied for the system working mode of active millimeter wave circumferential scanning imaging.The main contents of this thesis include the following aspects:First,by analyzing the working environment of the imaging system,the linear frequency modulated continuous wave(LFMCW)signal is selected as the transmitting signal and the pulse compression process of the LFMCW signal is analyzed.According to the working principle and working mode of the active millimeter wave imaging system,the simulation model of the imaging system is set up according to the working flow of the imaging system,and the simulation data is obtained and verified.Aiming at the simulation data,two dimensional imaging algorithm and three dimensional imaging algorithm are studied and verified.Secondly,aiming at the more complex scanning mechanism of circumference scanning,the active millimeter wave circumferential scanning three-dimensional imaging algorithm based on frequency domain interpolation is studied,and the corresponding system sampling constraints and resolution parameters are given.In view of the nonuniform sampling problem in the spatial wave number domain of the imaging algorithm,four interpolation algorithms are studied,namely,the nearest Interpolation,the bilinear interpolation,the three spline interpolation and the bicubic interpolation.The experimental results of different interpolation algorithms are compared and analyzed to select the optimal interpolation algorithm in the active millimeter wave imaging system.Finally,in order to improve the imaging performance of the system,another more rigorous imaging algorithm,namely the iterative active millimeter wave circumferential scanning 3D imaging algorithm,is studied,and the system sampling constraint conditions and the resolution parameters are discussed.Through processing experimental data,we compare and analyze the active millimeter wave circumferential scanning three dimensional imaging algorithm based on interpolation in frequency domain.In this thesis,an active millimeter wave three dimensional imaging algorithm is proposed,which combines the synthetic aperture radar(SAR)imaging technology to reconstruct the target reflection distribution function.The active millimeter wave three-dimensional imaging algorithm proposed in this thesis is mainly aimed at the complexity of the scanning mechanism of the circumference scanning.By combining the synthetic aperture radar(SAR)imaging technology,the aim is to overcome the adverse factors of the near field environment imaging,to realize the reconfiguration of the target reflection distribution function and to obtain the three-dimensional imaging of the target in the observed area.