Manipulation Of Vortex And Directive Beams Based On Metasurfaces

Metasurfaces(MSs)have unique electromagnetic properties by elaborately designing subwavelength elements,which are hard to be obtained by natural materials.Owing to the powerful manipulation of electromagnetic(EM)waves based on the MSs,this thesis focus on news schemes toward beam generation and polarization control for orbital angular momentum(OAM)beams and highly directive beams.A series of new applications are put forward and implemented in our work.The contents and contributions of this thesis are summarized as below:(1)A new strategy of OAM beam generation and the relevant polarization control is investigated and experimentally validated.We show the feasibility to convert a linearly polarized wave from a single point source to an OAM wave with arbitrary polarization via an anisotropic MSs.By controlling the initial phase differences between two orthogonal polarization waves,the polarization state of an OAM wave can be efficiently customized.Moreover,the phase differences caused by different propagation paths can be compensated by MSs.Finally,a single OAM beam with customized topological charge and polarization state can be generated in a simple manner.(2)A shared aperture theory of multiple OAM beams is presented to enable independent control of beam numbers,polarizations,orientations,and topological charges of OAM beams,respectively.It has shown the comprehensive capabilities of anisotropic MSs in wave fronts and polarization control.Due to merits of simple structure,low processing cost,excellent performance,this method provides opportunities for polarization multiplexing and spatial multiplexing in microwave OAM communication systems.(3)A folded reflectarray antenna(FRA)is proposed with the virtue of the high gain,low profile,planar structure.Based on the polarization sensitivity of the meta-atom,we realize wave transmission and reflection for two polarizations separately,thereby devising the propagation path with multiple folds.On this basis,a MS-based folded reflectarray antenna(FRA)is designed,simulated,and measured.The experimental results show that the FRA achieved 31%matching bandwidth from 9 to 12.1 GHz,a high aperture efficiency of 50.3% and the peak gain of 28.08 d Bi at 10.8 GHz.(4)To further reduce the height between the feeding source and the MS we propose a novel circularly polarized folded transmitarray antenna(CPFTA).The CPFTA can realize outstanding performances of broadband,ultralow profile,planar structure,easy integration and circular polarization.By carefully synthesizing the phase distributions,the CPFTA is also employed to generate OAM waves with circular polarization.The proposed CPFTAs are promising for applications in low profile,high gain antenna,circular satellite communications and vortex wave communications.(5)The nonlinear OAM wave generation method is proposed based on the space-time coding Ms.By controlling the initial phase in space domain and the delay time from time domain,we can generate OAM waves at high order harmonics,and realize independent control of OAM properties at arbitrary two harmonics,which is confirmed by simulation and experiment simultaneously.