Study On Imaging Method Of High Resolution Millimeter Wave SAR

Because of its small size and light weight,millimeter wave SAR(MMW SAR)is more suitable for small and flexible platforms such as unmanned aerial vehicle(UAV).However,Platforms such as UAV have complex flight paths and easy to produce large motion error,which is easy to have negative effects on imaging.At the same time,With the improvement of target detection,recognition and cognition ability,in order to obtain more detailed and richer target scattering information,higher requirements are put forward for SAR imaging resolution.With the improvement of target detection ability,recognition ability and cognition ability,in order to obtain more detail information and scattering information of targets,higher image resolution requirements are put forward to SAR.The long synthetic aperture is basis for achieving high resolution in azimuth of monopulse SAR.However,in the case of a long synthetic aperture,serious spatially variant phase error and continuous motion errors will be introduced.At the same resolution,due to the shorter wavelength and smaller antenna aperture of MMW SAR,the influence of motion error is more prominent,which will have a negative impact on the imaging quality.It is difficult for high resolution imaging to suppress serious space variant error.Aiming at high precision motion compensation,the main contents and contributions of this thesis include the following aspects:In view of spatially variant phase error caused by long synthetic aperture,the motion error geometric modeling and signal modeling are carried out under the condition of arbitrary platform motion trajectory.At the same time,the influence of different motion errors on imaging quality is analyzed,and motion compensation requirements under typical imaging parameters are given.On this basis,the time domain imaging motion error compensation method is deeply studied,and corresponding processing flow is given.By compensating nonlinear phase caused by motion error,the high precision focusing imaging is realized.The influence of motion error on imaging quality is verified by point target simulation experiment,and the correctness and effectiveness of the proposed processing process are verified.Aiming at motion error caused by the platform deviating from ideal track,this thesis analyzes the influence of non-ideal trajectory of radar platform and also analyzes the influence of different trajectory estimation methods on the accuracy of trajectory reconstruction based on the actual trajectory data.On this basis,a motion compensation method based on moving least squares is proposed.The moving least squares method is used to reduce the influence of higher order error of the platform trajectory on imaging focusing,and avoids the decline of trajectory estimation accuracy caused by conventional smoothing processing.The effectiveness and correctness of the proposed method are verified by the simulation and the measured data processing.In order to estimate the residual phase error,a high resolution Autofocus motion compensation method is studied,and an improved maximum norm motion compensation method is proposed.An improved maximum norm motion compensation method is used to compensate the random initial phase of multiple special points.On this basis,the residual phase error is estimated and compensated by integrating several special points,which enhances the stability and adaptability of motion error estimation,and greatly improves estimation accuracy of residual phase error.The point target simulation experiment and measured data processing confirm the effectiveness of the proposed method.