On The Feasibility Of Near-field Target Detection With Orbital Angular Momentum Of Electromagnetic Wave

In recent years,the large applications potential of orbital angular momentum(OAM)electromagnetic(EM)waves in radio communications and radar domain appeals to scientists.It is a new topic that how to detect objects using the interaction between OAM EM beams and the objects and the information about OAM feature of scattered waves of the objects.This thesis,based on theoretical analysis and numerical simulation,study the OAM local spectrums that reflect the combinations of OAM states and discuss the feasibility of near-field target detection using EM vortex in several respects.The main work of the thesis can be summarized as follows:1.Systematically introduce the theory of OAM local spectrum.We begin with the receiving the signals of OAM EM radiation using the circular antenna array,and give the method of analyzing and calculating its OAM local spectrum.Then we show the distribution of OAM local spectrums in all direction via numerical simulations.2.Analyze and study the disturbance of simple objects acting on OAM local spectrums of OAM EM waves.The effects of objects in different positions and of different sizes on the spectral lines of OAM states are simulated,and the probability conclusions of sensing target response based on OAM local spectrum are given.3.The initial research of obtaining the target location information based on OAM local spectrums of target scattering waves is presented.The simulation results show that the method of processing spectral line of the OAM local spectrums can obtain the position information of the target from the scanning variation of spectral lines.4.Based on the rotational Doppler effect of OAM EM waves,the detection method of target rotational speed is preliminarily studied.The study reveals the close relation of scattering frequency spectrum,the incident frequency spectrum and the OAM local spectrum,which can extract the angular velocity information of the target.The conclusion shows that the near-field target detection based on the OAM electromagnetic waves has good feasibility.