Research On The Generation Of Vortex Electromagnetic Waves For Radar Imaging

Vortex Electromagnetic(EM)waves carrying orbital angular momentum(OAM)have abundant degree of information modulation and unique ability of information acquisition,which have attracted intensive attention recently.When irradiated by vortex beam carrying orbital angular momentum,the radar echoes may carry more target information,which has the potential to improve imaging resolution with signal processing.In this thesis,we mainly focus on the generation of vortex EM waves for radar imaging.The main contents include: analyzing characteristics of vortex EM waves and the effect of different array settings to radiation field,studying the radiation optimization for radar imaging,investigating array error contribution on radiation and demonstrating the generation of vortex beam with a system.This work can benefit the generation design of vortex EM waves in radar imaging,as well as in wireless communication.Chapter 1 describes the background about this research and overviews the the study progress of OAM and generation of vortex EM waves.Finally,the structure arrangement of this thesis is introduced in this chapter.In Chapter 2,the characteristics of vortex EM waves based on uniform circular array(UCA)and the reasons of superposition are mainly analyzed.Also,the primary application issues are figured out in this part.Subsequently,the effects of array factors on radiation field are conducted by theory and simulation.In addition,the pure state region is derived with array settings.In Chapter 3,the beam optimum and side-lobe energy suppression are investigated for radiation optimization.Theory analysis and numerical simulation results validate that the incoherent main-lobe direction question can be solved with beam forming technique and concentrated UCAs.Two circular arrays can depress the side-lobe level by the design of array radius and array antennae.And Multi-UCAs can also suppress the side-lobe energy with window function design.Subsequently,the mathematical models with different array errors are derived and the effects on radiation field are evaluated by numerical simulations.In Chapter 4,the generation of vortex beam is demonstrated by a phased array system.Firstly,the system scheme and the structure are introduced.Secondly,the vortex radiation field measurement is devised based on the planar near-field measurement.After near-field data calibration,planar near-field to far-field transformation and characteristics analysis,the experimental results verify that uniform circular array can generate vortex EM waves carrying different OAM states within a certain extent array errors and the radiation quality can be evaluated by above analysis.The main innovative contributions about this thesis are concluded in Chapter 5,and next steps of the work are discussed.