Single-layer transmissive metasurface for generating OAM vortex wave with homogeneous radiation based on the principle of Fabry-Perot cavity

Abstract

In this paper, a single-layer transmissive metasurface (TMS) is designed to generate orbital angular momentum (OAM) vortex waves with homogeneous radiation at microwave frequencies (e.g., 10 GHz). A single-layer TMS with the thickness of 3 mm (0.1λ0) is designed by well connecting the phase shift range of two elemental TMS structures. Specifically, two TMS structures—meandering patch-double meandering rings and meandering patch-single meandering ring with the unit-cell size of 7.5 mm (0.25λ0)—are used together to achieve high transmission efficiency (>0.8) and a large phase coverage range (>360°). In order to address issues such as uneven circumferential radiation and posterior lobe radiation and further enhance the efficiency of the TMS, the modified principle of Fabry-Perot cavity (FPc) suited for realizing the TMS to generate OAM vortex waves is proposed, analyzed closely, and applied. Specifically, an improved rectangular microstrip antenna is employed as a feeding source and a double square ring array is used to construct the backplane. A prototype of the proposed TMS with a FPc is designed, simulated, manufactured, and measured. The simulated and experimental results agree well, which demonstrate the feasibility of the presented design methodology.