Design Of Quasi-optical System For Active Millimeter-wave Imaging

Millimeter-wave(MMW)imaging is of great value in the current security situation.Compared with infrared,X-ray and other imaging technologies,millimeter-wave imaging has better penetrability,higher image resolution and is harmless to human beings.Thus,it has obvious advantages in imaging technology.In terms of imaging system,it can be divided into active imaging and passive imaging.Compared with passive MMW imaging technology,active imaging can compensate for the weak radiation of MMW in natural environment by using the feed to illuminate the target area and receive the scattered echo signal to makes the imaging quality better and less affected by the environment.The quasi-optical system is the core of the whole MMW imaging system,and its performance affects the quality of imaging directly.The focus of this dissertation is to design a set of quasi-optical system for active MMW imaging,which is mainly divided into three parts,the design of overall structure,the design of feed array and the design of focusing antenna.The design of overall structure is the construction of the system framework,which determines the selection and parameter requirements of each element.The design of feed array includes the design of single feed and the arrangement of antenna,which is related to the imaging quality and samp ling rate.The design of the focusing antenna determines the spatial resolution and the imaging distance.Considering the coordination among all the parts and the relative position is of vital importance,so that all parts can make the most of them and the quasi-optical system designed is of practical value.In this Dissertation,based on the study of MMW imaging theory,the research scope of quasi-optical system is determined.Starting from the quasi-optical technology,the characteristics of several typical quasi-optical technologies are compared and analyzed,and the derivation of Gaussian beam method is emphatically studied.Two kinds of feed antennas commonly used in MMW imaging are studied,and the design methods and radiation characteristics of two fe ed antennas are summarized.According to the requirements of the system index,a multi-segment tapered dielectric rod antenna is used as the feed element.Combined with the sampling theorem,a single row feed array is designed and its mutual coupling characteristics are studied.The side-feed ellipsoid reflector with a working frequency of 94 GHz and a theoretical spatial resolution of 12 mm is designed by using the advantages of light mass and good focusing characteristics.The reflector is simulated with the feed antenna designed by using software FEKO,and the focusing characteristics are verified.Finally,the whole system structure is designed by introducing the rotating device,reflector and combining the feed array with the ellipsoid reflector.The field of view of 1 m×2 m is covered by the way of single line feeding and mechanical scanning,and the system requirements are completed.