Vortex Beam Generation Using Ultrathin Huygens’ Metasurface with 360° Phase Control

Electromagnetic metasurfaces with spatial electromagnetic wave modulation have attracted great attention. Compared with the traditional planar electromagnetic wave, the vortex electromagnetic wave carrying orbital angular momentum (OAM) is a unique wave beam with helical phase structure and toroidal amplitude field, which is characterized by simple design and light weight. Due to the infinity of OAM modes and the orthogonality between different modes, it provides a new degree of freedom independent of time, frequency and polarization domains. In terms of channel capacity expansion and spectrum efficiency enhancement, OAM waves have great potential to alleviate the pressure caused by the growing demand for spectrum resources. In general, it is difficult to realize 360° phase control and high transmittance for a transmissive metasurface without vias at the same time when the number of cascaded layers is less than three.In this paper, we design an ultrathin Huygens’ metasurface with an antisymmetric split resonance ring placed on each side of the medium and a rectangular metallic stub placed on the middle of the resonance ring in both sides. Due to the antisymmetric design of the cell, the metasurface can simultaneously excite both electric and magnetic dipole resonances under x-polarized wave incidence, and the two resonances interact with each other to achieve 360° phase control. It shows that the designed unit cell can realize 360° phase control with a very small thickness of 0.035 wavelengths under the incident x-polarized wave at 14GHz. And based on the designed Huygens’ metasurface, the OAM-transmitting metasurfaces with modes 1 and −1 are designed by the phase compensation algorithm while ensuring the high transmittance.