Research On Key Technology Of Three-Dimensional Imaging Of Terahertz Radar

Terahertz radar has high carrier frequency and the capability to realize broad band and narrow wave beam.Besides,the features of harmlessness to human body and good penetration to non-polar materials make terahertz radar have wide application prospect in security check,medical detection,and so on.On the other hand,three-dimensional(3D)radar imaging can reconstruct the 3D targets distribution and provide more feature in-formation for the subsequent processing of target detection and recognition.Combining terahertz radar with 3D imaging can effectively improve the imaging resolution and ex-pand the application of 3D radar imaging.Imaging model and corresponding imaging algorithm are the key techniques of 3D terahertz radar imaging.However,the 3D imaging models and imaging algorithms cannot be generalized,but need to be analyzed specifically.In this dissertation,the 3D terahertz radar imaging for CSAR model,for array CSAR model and for the drone fleet-borne radars are discussed and researched.The main work and contributions are summarized as follows:1.Based on the researched terahertz radar prototype,the signal model is introduced.For the non-linearity problem of the frequency modulated rate,correction method through reference signal compensation is proposed.Furthermore,the 2D and 3D scattering char-acteristics of terahertz radar targets are measured and studied.Then,two commonly used3 D radar imaging models,which are CSAR and LASAR are introduced,and their 3D imaging mechanism,resolution and basic imaging algorithms are analyzed.2.Further researches are carried out for the 3D imaging of terahertz CSAR.First,on the basis of 2D FFBP for CSAR imaging,the coordinate partition format of the 3D space scene is obtained by rotating the polar coordinate plane,and the 3D FFBP algorithm for CSAR is proposed.Comparing with 3D BP algorithm,the 3D FFBP improves the com-putational efficiency.Second,the PFA based CSAR 3D imaging algorithm is analyzed.In this algorithm,the echoes are projected to each plane and imaged with PFA.Consid-ering the range approximation error in PFA,the applicable constraints of the algorithm is analyzed.At last,the CZT based sub-aperture algorithm for CSAR cylindrical imaging is proposed,and the computational efficiency is improved comparing with the STOLT interpolation based algorithm.3.For the security check application of terahertz radar,the array CSAR 3D imaging model is proposed.In this model,with the basis of CSAR geometry,the linear array an-tenna is used in the height dimension to form the aperture,and the problem that the height direction resolution relies on the pitch angle of radar in CSAR is solved.The 3D imag-ing algorithm in wavenumber domain is proposed and the sampling criteria is analyzed.To solve the problem that the wavelength of terahertz radar is too short for the antenna array elements to meet the sampling requirements,sparse antenna array is designed.Fur-thermore,the SBL based sparse recovery imaging method is proposed to reconstruct the scatterering distribution of target in the height direction.4.Researches for small drone borne radar 3D imaging are carried out.Based on the application scenario and platform conditions of small drone borne radar,a drone-fleet borne radar imaging mode is proposed.To improve the availability of drone fleet borne radar,the simultaneous transmission and receiving mode is proposed.The transmitted signal with frequency-division model and the corresponding echo model are analyzed.Based on the echo model,the drone fleet borne radar 3D imaging method is studied.In this dissertation,a series of work on terahertz radar 3D imaging are carried out.Considering the characteristics of terahertz radar and the specific application scenarios,the corresponding 3D imaging models and imaging algorithms are studied.These studies provide technical support for the applications of terahertz radar imaging.