Research On Transmitting And Receiving Principles Of Multi-mode OAM Beams Based On Antenna Arrays

Orbital Angular Momentum(OAM)of an electromagnetic wave is a physical form in which equal phase plane of electromagnetic wave is spiral along the propagation direction.OAM has attracted wide attention in the field of radio frequency and optical communication due to the orthogonality between different integer eigenstates.As a new degeree of freedom,the most critical issue is the generation of multi-mode OAM beams.In this thesis,based on the multi-mode OAM beams generated from time modulated uniform circular array(TMUCA),the theory of OAM beam steering and multi-mode OAM multiplexing in TMUCA are studied.The main contents are summarized as follows:This thesis first establishes the theoretical model of TMUCA to generate OAM beams on harmonic frequency and gives a time sequence design criterion for generating OAM beam.Furthermore,the characteristic of OAM beams on each harmonic are analyzed.This method can generate multi-mode OAM beams by controlling switches connected to the array elements while avoiding the use of expensive phase-controlled devices.The amplitude and phase characteristics of each harmonic are analyzed by simulation,and it is proved that the method can generate different OAM modes on different harmonics,which verifies the effectiveness of the giving method.Secondly,this thesis presents an OAM beam steering method based on TMUCA.OAM beams can be generated on the harmonics and the direction of OAM beam on the harmonics can be steered by designing the time sequence loaded onto the switch.Furthermore,this thesis designs a patch antenna operating at 3.5 GHz to verify the effectiveness of OAM beam steering for time modulation.The results show that the method is effective not only on isotropic antenna elements,but also can achieve OAM beam steering on actual patch antenna arrays.In addition,compared with beam steering in phased arrays,this method has the advantages of low cost and low complexity.Finally,based on the simultaneous generation of multi-mode OAM beams,this thesis establishes and analyzes the OAM multiplexing communication system model based on TMUCA and compares it with the traditional LOS MIMO system.When the number of multiplexing channels is equal,the TMUCA system can provide same channel capacity at a lower cost.In addition,as the signal-to-noise ratio and the number of antenna elements increase,the system capacity of both systems increases.The TMUCA-based OAM multiplexing communication system uses the natural orthogonality between different OAM modes to perform efficient demultiplexing of OAM without complicated digital signal post-processing techniques to eliminate inter channel interference at the receiving end.