Deflective Vortex Beam Generation based on Metasurfaces in the Terahertz Band

Abstract

Terahertz vortex beams can be used to improve the communication capacity of radar communication systems and the resolution of imaging systems. This paper presents a deflective vortex beam generation method based on a reflective metasurface working in the terahertz band. Without the limitations of traditional methods, metasurfaces are a good candidate to generate beams carrying an orbital angular momentum in the terahertz band. First, we designed and simulated a unit cell of the metasurface. The unit cell of our design consists of two metallic (gold) layers and one dielectric layer. An almost 360° phase shift was acquired by adjusting the length of the eight stubs of the top layer. The unit cell of the metasurface was simulated by CST Microwave Studio, and the simulation results showed that the co-polarization reflection efficiencies of the unit cells were more than 90%. To avoid performance degradation due to blockage of the feed horn, we controlled accurately the directions of vortex beams based on the concept of reflectarray. To verify the performance of our design, we simulated and measured five reflective metasurfaces. The results of simulation and measurement showed that these metasurfaces could generate five deflective vortex beams in the terahertz band. The topological charges of these beams are ±1, ±2, and 3, which account for the highest energy proportion in different vortex beams.