| With the rapid development of wireless communication,the spectrum resources become increasing scarce.The scientists have found that the vortex electromagnetic waves carrying the orbital angular momentum have the orthogonality when the wave modes are not equal each other,and the modes can be set arbitrary values.Hence,the multi-channel signals modulated to different OAM modes can be transmitted in same frequency,theoretically,which can obtain infinite transmission capacity.Therefore,the orbital angular momentum technology is a powerful solution to solve the scarce spectrum resources.Among an important research subject is the formation of OAM vortex waves.As this time,with the advantage of high gain,easy manufacture and the capability of arbitrary modulating electromagnetic waves,the metasurface becomes a new method to generate vortex waves.In this paper,three kinds of metasurfaces are researched and designed to generate multifunctional OAM vortex waves.The main work of this article is as follows:(1)A high-efficiency miniaturized metasurface OAM antenna is designed.Firstly,a singlelayer dual-ring structure with small-size is proposed as the phase modulation unit,and the phase shift can cover 377 degrees.Secondly,the metasurfaces are designed by arranging the units periodically and compensating their phase,and generated the vortex beams with the OAM modes l = 1,2,3,4.And then the pattern purity and stability of vortex waves are analyzed.Furthermore,a kind of metasurfaces is designed to realize beam steering.The simulated results show that the vortex beam can be transmitted in discretionary direction.Finally,through the calculation,the aperture efficiency of designed metasurface is up to 22.6%.According to the comparison and analysis,the proposed metasurface in this paper has small size and high efficiency,and the generating OAM vortex beam has the merits of high purity,strong stability and narrow divergence angle.(2)A multi-beam dual-frequency dual-polarization metasurface OAM antenna is designed.Firstly,the dual-frequency dual-polarization unit by loading transmission lines is proposed,which can cover 425° phase shift at 10 GHz in x-polarized incidence and can cover 436° phase shift at 20 GHz in y-polarized incidence.The unit can be adjusted independently at two frequencies and its phase curve is not interfered each other.Secondly,three kinds of metasurfaces are designed,which can generate OAM vortex waves with different beam numbers,modes and directions.The simulation results show that the proposed metasurface can work at 10 GHz and 20 GHz,and four OAM vortex beams can be generated simultaneously even though the metasurface has a small size.Finally,a metasurface is manufactured and tested.The results show that the metasurface can simultaneously generate multi-beam,multi-mode and multi-direction OAM vortex waves in dual-frequency.In addition,the metasurface has the advantages of high gain and high aperture efficiency.(3)A metasurface OAM antenna with dual functions of reflection and refraction is designed.Firstly,a single-layer anisotropic unit is proposed.The reflection and refraction functions of the metasurface can be realized simultaneously by using the cross-polarization field of the anisotropic unit and the phase shift can cover 388° by adjusting one variable of the unit.Secondly,there kinds of dual-function measurfaces are proposed,which can respectively generate high-gain directional beams,dual-beam OAM vortex waves and four-beam OAM vortex waves.Finally,according to the simulated results,the designed single-layer metasurface can achieve reflection and refraction functions simultaneously. |
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