Research On Operating Modes And Imaging Algorithms Of High-resolution Terahertz Radar Systems

Terahertz radars can easily facilitate transmitting wideband signals to obtain highresolution radar imagery of targets because of their extremely high carrier frequencies.Reasonable design of operating modes and imaging algorithms of terahertz radars can acquire more target information and improve signal processing efficiency respectively,which can effectively enhance the capacity for automatic target recognition and classification.Therefore,design of operating modes and imaging algorithms of high-resolution terahertz radar systems has extremely important research significance.With the development of terahertz imaging radars,an important trend towards enhancing the system detection range and resolution.The long-range high-resolution terahertz imaging radars extend the application range of terahertz radar technology,but they also pose new challenges to design of operating modes and imaging algorithms of terahertz radar systems.In this dissertation,two kinds of extremely potential applications of terahertz radar imaging technology: near-earth security screening and imaging of space targets are studied.Compared with traditional imaging scenarios,the aforementioned imaging scenarios exhibit the characteristics of varying imaging geometric models,field of view(FOV)enlargement,and non-cooperation target.Thus,the existing operating modes and imaging algorithms of terahertz radar systems can not meet the requirements for high-resolution radar imaging.In view of the aforementioned problems,this dissertation presents several operating modes and the corresponding imaging algorithms of highresolution terahertz radar systems suitable for the above imaging scenarios on the basis of summarizing and analyzing the existing operating modes and imaging algorithms of terahertz radar systems.The proposed operating modes accurately represent the geometric relationship between a target and radar and fully exploit aperture synthesis technology.The main work and contributions of this dissertation are given as follows:1.For near-earth security screening,two-dimensional(2D)operating mode and imaging algorithm of high-resolution terahertz radar is studied.The operating mode of distributed multi-static terahertz radars is proposed to solve the problems that the quasioptical scanning mode has small FOV,short imaging distance,and cooperative targets.On the basis of the proposed operating mode,a rapid high-resolution 2D imaging algorithm is given,and it improves imaging rate.2.For 2D radar imaging of low-maneuvering space targets with complex motion,a high-resolution 2D imaging algorithm of low-maneuvering space targets is studied.2D imaging algorithm based on second-order keystone transform(SKT)is proposed to solve the problems of first-order range migration(FRM)and second-order range migration(SRM)caused by complex motion of space targets during coherent processing interval,achieving high-resolution imaging of low-maneuvering space targets.3.For three-dimensional(3D)radar imaging of space debris,3D operating modes and imaging algorithms of high-resolution terahertz radar systems are studied.A novel operating mode of high-resolution terahertz radar systems,i.e.,spiral inverse synthetic aperture radar(S-ISAR),is proposed,which solves the problem that the height resolution depends on the angle between radar line-of-sight(RLOS)and the space debris' s major axis in the traditional mono-static ISAR operating mode and realizes high-resolution 3D imaging of space debris.On the basis of proposed operating mode,the characteristics of the instantaneous distance between the target and the imaging radar are analyzed.According to the analyzed results,3D imaging algorithm based on the distance approximation is proposed.The theoretical analysis and experimental results demonstrate that 3D imaging algorithm based on the distance approximation has the characteristics of low computational complexity and high-resolution.4.For 3D radar imaging of space debris,3D operating modes and imaging algorithms of high-resolution terahertz radar systems are studied.A novel operating mode of high-resolution terahertz radar systems,i.e.,spiral circular synthetic aperture radar(SCSAR),is proposed,which solves the problem that S-ISAR cannot utilize full azimuth aperture and realizes high-resolution 3D imaging of space debris.On the basis of proposed operating mode,The 3D imaging algorithm based on Green's function decomposition is proposed.The theoretical analysis and experimental results demonstrate that the3 D imaging algorithm based on Green's function decomposition efficiently improves the azimuth resolution.