Study On Generation And Manipulation Of Vortex Electromagnetic Wave Based On Metasurface

Vortex electromagnetic(EM)waves,namely EM waves with helical wave-front phase distribution,are expected to break through the bottleneck of the increasing shortage of communication spectrum resources owing to its capacity in improving communication capacity and data transmission rate.How to efficiently generate and manipulate vortex EM waves is the primary problem of vortex communication,and also the focus of research in recent years.The traditional methods of generating and controlling vortex EM wave suffer from issues of complex structure,low efficiency and band width,which greatly limit the application of vortex EM wave in modern wireless communication system.Metasurface is a two-dimensional planar structure composed of the deep subwavelength unit cells with a certain rule,which has a strong ability to manipulate the EM wave front.It has the advantages of low profile,simple design and low cost compared with traditional methods in generation and manipulation of vortex beams,and provides a simple and efficient way to generate and manipulate vortex EM wave.In this paper,a polarization-insensitive metasurface is designed to generate vortex EM waves and successfully reduce the divergence angle of vortex waves.And2-bit metasurfaces are designed to realize the directional control of vortex EM waves.The main research contents are as follows:1.A broadband polarization insensitive vortex metasurface is proposed by employing I-shaped unit cells.A complete 360° reflection phase range can be realized by rotating the meta-atom.The designed metasurface with vortex phase distribution is simulated under plane wave incidence.It can realize vortex EM wave within 12 GHz-20 GHz.In addition,the metasurface owes performance of polarization insensitive,which means that it can realize perfect vortex EM waves under circularly polarization(CP)and linearly polarization(LP)waves.2.A polarization insensitivity vortex-focus metasurface is designed,which can realize broadband vortex EM waves and reduce the divergence of vortex beams.The divergence angle of the vortex beam is successfully reduced by introducing the focusing phase to cancel the shear vector of the electromagnetic wave.Finally,a prototype is fabricated and measured.The simulation and measured results show that the designed vortex-focusing metasurface has the following advantages:(1)the design can realize wideband vortex beam from 12 GHz to 20 GHz(relative bandwidth of 50%),(2)the metasurface can generate narrow divergence angle vortex beam with high gain that is better than 15 d Bi in the working band,(3)the design is applicable to both circular polarization(CP)and linear polarization(LP)wave excitations,which provides an effective way to generate OAM beams.3.The 2-bit coding metasurfaces with different functions are designed using I-type unit structure,which realized generation and direction control of vortex EM waves with single and double OAM.Different deflection phases are superimposed on vortex phase with l=1 to design the metasurfaces with different EM response.Simulation results are consistent with the theoretical analysis,which show that single-beam and double-beam vortex waves are radiated in x and y directions.