Broadband and high-efficiency ultrathin Pancharatnam-Berry metasurfaces for generating X-band orbital angular momentum beam

Abstract Vortex beams have been extensively investigated for their major applications in wireless communications. To obtain practical applications, vortex beam generators with high performance and simple structure are of vital importance. Here, we present a novel metasurface-based device to generate high-performance vortex beams. This device is a four-layer Pancharatnam-Berry metasurface with ultrathin thickness. The unit cell of each metasurface is composed of a cross dipole and a square ring resonator. The simulated and experimental results show that the proposed meta-device can convert a right-hand circularly polarized wave into a left-hand circularly polarized vortex beam in a broadband from 9.3 to 12 GHz. Moreover, the device has high transmission efficiency up to 79% and ultrathin thickness of 0.2 λ ( λ is the central frequency of operation frequency band).