Target Detection And Imaging Based On Vortical Electromagnetic Waves

Vortical electromagnetic waves are electromagnetic waves that carry orbital angular momentum.Compared with traditional plane waves,vortical electromagnetic waves have a higher degree of freedom in information modulation because their wave-front phase are helical structure,which have great application potential in wireless communication,target detection,imaging and other fields.In recent years,the application research of vortical electromagnetic waves is mainly concentrated in the field of wireless communication,and there is little research in the field of target detection and imaging which is still in the preliminary research stage.In this paper,the application of vortical electromagnetic waves in the field of target detection and imaging is preliminarily explored.The beam characteristics of vortical electromagnetic waves,the design of a new electromagnetic vortex generator,the scattering characteristics and imaging of vortical electromagnetic waves hava been researched in depth.Based on the existing basic theoretical knowledge of vortical electromagnetic waves,this paper takes the characteristics and applications of the spiral phase and beam-hollowing of vortical electromagnetic waves as the main research objects.The main work of this paper includes the following aspects:Firstly,the beam characteristics of vortical electromagnetic waves used for detection and imaging.Through the research of the radiation field characteristics of the vortical electromagnetic wave,based on the theory of spectral analysis,the feasibility and defects of the vortical electromagnetic wave used for target detection and imaging have been initially explored.However,the application of vortical electromagnetic waves in the field of target detection and imaging will be limited by the beam-hollowing characteristics.The hollowness of the beams means that the beam propagation center of the vortical electromagnetic waves has a depression,and the hollowness appears near the beam propagation axis.Therefore,the influencing factors of beam-hollowing characteristics have been continued to research,including preliminary research on the bunching methods.Secondly,the design of beam-convergence multi-mode electromagnetic vortex generator.Aiming at the existing electromagnetic vortical generators,most of them generate single or few mode vortical electromagnetic waves,and there is no improvement in the beam-hollowing characteristics.In this chapter,a beam-convergence multi-mode electromagnetic vortical generator is designed based on X-band,but it is not limited to X-band.The electromagnetic vortex generator is composed of a radiating structure,a feeding structure,a parabolic reflecting surface structure and a supporting structure,which can generate negative-five-step to positive-five-step vortical electromagnetic waves,and greatly improve the beam hollowing characteristics,besides effectively reducing the beam opening angle and increasing the gain.Third,the scattering characteristics and imaging research of vortical electromagnetic waves.Based on the vortical electromagnetic wave generated by the OAM ideal field source,through the scattering effect with PEC plane,combined object target,random rough surface,the amplitude and phase characteristics of the backscattered echo have been researched.Some regular explorations have been made on the receiving array of scattered echo,the active application of beam-hollowing characteristics,and the judgment method of roughness of the rough surface.Finally,based on the existing research of beam characteristics and scattering characteristics,the imaging potential of vortical electromagnetic waves in the OAM dimension has been derived and verified,comparing the ISAR imaging theory of ideal scattering points based on plane waves.