Research On Coded Aperture Imaging Based On Programmable Metasurface

Real aperture imaging systems and synthetic aperture imaging systems are mature radar systems,but both imaging systems have their own flaws.The performance of the real aperture imaging system is limited by the size of the aperture,while the synthetic aperture imaging system is subject to the relative motion of the target and the radar.therefor,a new radar system is need,which could achieve imaging within the beam under forward looking imaging geometry.Inspired by the idea of coded aperture in optics,coded aperture imaging in the microwave frequency has gradually entered people's field of vision.It obtains target distribution information through signals of different measurement modes,which realizes microwave imaging under gaze observation conditions.Recently,microwave metasurfaces have developed rapidly,which provide a new path to achieve coded aperture imaging.Through digital control,the electromagnetic response characteristics of the programmable metasurface antenna can be adjusted in real time,the amplitude and phase distribution of electromagnetic waves could be controlled and generating detection signals of different measurement modes.Based on the principle of coded aperture imaging,we analyze the characteristics of the programmable metasurface antenna and optimize its radiation field.Besides,the waveform is designed and a frequency domain computational imaging method is proposed.Finally,we analyze several errors which could occurred in practice.The realization of coded aperture imaging is based on differentially distributed detection signals,programmable metasurface are an ideal platform to realize coded aperture imaging due to their flexible electromagnetic wave adjusting capabilities.In this paper,the mathematical model of coded aperture imaging is established firstly.Then the incoherence of the generated random radiation field is analyzed through the effective rank and average column correlation coefficient of the reference matrix.And these two parameter are used to optimize the coding strategy and array spacing of the programmable metasurface antenna.The waveform of radar is an important factor affecting radar performance.In this paper,the single-frequency signal as the feed and the influence of noise on the imaging are analyzed.Then,the increase of the signal bandwidth is improved by the random frequency hopping signal,which improve the number of effective measurement modes and improve the imaging quality.When the feed signal is linear frequency modulation signal,a frequency domain computational imaging method is proposed,which combine the dechirping pulse compression method and computational imaging method.The simulation results show that the proposed method can significantly improve the coded aperture imaging quality under low SNR conditions.At the same time,the method can solve the targets in different distance imaging planes in parallel and achieve high-efficiency 3D target imaging.In practical applications,the performance of radar systems are influenced by various errors.In chapter 4,we analyze some kinds of errors in coded aperture imaging based on programmable metasurface,such as phase modulation error,imaging plane division distance error,echo signal phase error.Besides,phase retrieval algorithm is used to correct the echo signal phase error.Combining with computational imaging algorithm,the method perform well when there is phase error in the echo signal.The coded aperture imaging technology based on programmable metasurface reflects the development trend of software-based and intelligent imaging radar.At the end of this paper,the paper summarizes the whole thesis and proposes some in-depth research direction.