Research On Vortex-electromagnetic-wave-based SAR Imaging Technology

The vortex electromagnetic(EM)wave carrying the orbital angular momentum(OAM),can distinguish the targets in one beam,which provides a new degree of freedom for target reconstruction and discrimination.Combined with the Doppler information provided by the motion radar platform,this paper applies vortex electromagnetic waves to SAR imaging technology,and is expected to achieve higher-resolution imaging.The main contents include the principle and resolution of the vortex-electromagnetic-wave-based SAR imaging,analysis of the echo characteristics and methods of two-dimensional(2D)imaging method and three-dimensional(3D)imaging.The research results in this paper can provide reference for vortex EM wave's theory and its application in SAR imaging technology.In the introduction,the background and significance of the proposed vortex-EM-based SAR are firstly described.Secondly,the origin and generation methods of vortex EM wave are summarized,the research status of vortex staring imaging technology and SAR imaging technology are reviewed.Finally,the main research contents and structure of the paper are introduced.Secondly,in the research of the proposed vortex-EM-based SAR imaging,the principle of utilizing vortex EM wave to achieve target azimuth imaging under staring condition is introduced.Secondly,according to the radiation characteristic,the mathematical model of the vortex-EM-based SAR imaging is derived,and the echo characteristics of the range,azimuth and cross-track dimension and the corresponding resolution are analyzed.In the research of 2D imaging method of the vortex-EM-based SAR,the imaging method in single OAM mode is studied firstly,and the influence of the amplitude term of Bessel function and the phase term of azimuth factor on target reconstruction are analyzed.The target imaging results under different OAM modes are obtained.Secondly,combined with the vortex EM wave radiation characteristics and the motion geometry of the radar platform,a imaging method based on multi-OAM modal design is proposed and the simulation results show that the higher-azimuth-resolution imaging can be realized.Finally,two types of 3D imaging methods based on azimuthal time-varying characteristics and back projection utilizing the unique phase wavefront structure of vortex EM waves are proposed.The resolution expression of the cross-track direction and its main influencing factors are derived and pointed,and the effectiveness of the proposed imaging method is verified by simulation experiments.