Dual-Frequency Vortex Beam Generation Using Coding Metasurface

This paper presents a dual-frequency coding metasurface (CM) for vortex beam generation. The metasurface unit cell is realized with two symmetric metal layers separated by a dielectric substrate. Each metal layer consists of an outer square ring, a middle square ring, and an inner rhombus patch. Two out-of-phase transmitting states in two bands are achieved by rotating the inner rhombus patch by 90 °. Two 1 = + 2 vortex beams are then realized in two different bands by properly distributing the two states on the metasurface aperture. A metasurface with $30 \times 30$ elements is designed, simulated, and experimentally demonstrated. The experimental results agree well with the simulating ones, showing that the metasurface achieves a high transforming efficiency in both Ku (13.6-14.8GHz) band and Ka (26.7-27.7 GHz) band.