Multi-order OAM Generation Based On Metasurfaces And Waveguide Structures

This thesis studies the method of simultaneously generating multiple orders of orbital angular momentum(OAM)on the same structure.It is divided into two major directions:the special arrangement of the two-dimensional antenna array on the metasurface and the use of a special waveguide structure.According to the researches of our group,based on the periodic phase change of the bowtie unit,this paper proposes a dual-bowtie unit that can produce one cycle and two cycles of phase changes in two orthogonal directions.The feasibility of electromagnetic OAM multiplexing is further enhanced by the newly proposed unit.The array of cells can produce phase modes of different order OAM in these two directions with two orthogonal polarization incident waves,while maintaining a relatively uniform amplitude.Through theoretical analysis,unit simulation,metasurface array model simulation and experimental measurement,the obtained simulation and experimental data have a high degree of agreement,which verifies the correctness of the design.Compared to the OAM that previously produced an order using one metasurface,we further implemented an OAM mode that produces two orders simultaneously on one array.Combining the idea of simultaneously generating two orders of OAM on a model,we explored several special waveguide structures.One type is spoof surface plasmon(SSPP)structure with high confinement characteristics.The patch adjacent to the ring waveguide can be used to generate a certain order of OAM at a specific frequency.We designed and simulated the OAM generation of the single-circle SSPP waveguide and explained the feasibility of the double-circle SSPP waveguide.The other is to carve the surface of the closed waveguide to realize the leakage wave.We explored the rectangular waveguide and the substrate integrated waveguide(SIW),respectively,using continuous as well as discrete slotting methods.The simulation results also prove that OAM order can be controlled by the radius of the ring waveguide,and the interference between the two circular structures is negligible.In conclusion,we've designed and verified that both metasurface and waveguide can be adopted to generate two separate OAM modes,and can be further applied in OAM communication systems.