Research On The Generation Of Vortex Electromagnetic Wave Based On Reflective Metasurface

In recent years,orbital angular momentum has been attracted wide attention as a new degree of freedom.OAM has been paid attention to for its high spectrum efficiency and strong immunity to interference.There is a unique spatial distribution of electromagnetic wave wavefront carrying OAM.The capacity of the communication system can be improved by encoding the different topological modes,or combining the existing multiplexing technology.It reflects the potential application value of OAM in modulation and multiplexing technology.Metasurface is usually composed of sub-wavelength units,and has a good ability to control electromagnetic waves.Based on the reflective metasurface,the generation and divergence characteristics of vortex waves are studied.This thesis provides a new idea for the effective generation of vortex waves.The main contents and results of the thesis are as follows:1.A metasurface which can produce single-mode vortex wave in an ultra-wide frequency band is proposed.The metasurface consists of an array of arrow-shaped elements of different arm lengths.When a plane wave is perpendicularly irradiated onto the metasurface,the reflected wave is converted into a vortex wave.The simulation results show that the electromagnetic wave reflected by the designed metasurface is an ultra-wideband vortex wave from 18 GHz to 42 GHz,which is consistent with the theoretical analysis.2.Based on the design principle of single-mode vortex metasurface,a metasurface which can produce multi-mode vortex waves simultaneously is proposed.The metasurface is composed of arrow-shaped units with different arm length and equidistant circumferential arrangement.The plane wave is reflected by the metasurface and multi-mode vortex electromagnetic waves are obtained in the ultra-wideband from 18 GHz to 42 GHz.3.A metasurface which can generate vortex wave in the X-band and reduce the divergence of vortex wave is proposed.The vortex-focusing metasurface is composed of an orderly arrangement of double-layered rectangular units of different sizes.The compensation phase is formed by superposition of the vortex phase and the focusing phase.The simulation results show that in the frequency range from 8GHz to 12 GHz,the divergence angle of vortex wave generated by the vortex-focusing metasurface is reduced by about 40% compared with the divergence angle of the vortex wave generated by the vortex metasurface of the same scale.The designed vortex-focusing metasurface can converge vortex wave effectively,which verifies the correctness of the theoretical analysis,and provides an effective way to reduce the divergence of vortex waves.