Generation of Narrow Divergence Angle OAM Beams for mmWave Communication Links Using Metasurface

This paper presents an efficient and fast strategy to generate single and multiple non-diffractive narrow divergence angle orbital angular momentum (OAM) beams for the 80 to 100 GHz millimeter wave band using a single circularly polarized (CP) feed and single layer reflectarray metasurface (RAMS). The proposed strategy is based on phase combination technique by superimposing different types of phase coding sequences on the RAMS aperture and using geometric phase theory for phase compensation. First the conventional OAM spiral phase distribution is combined with a focusing parabolic phase to generate a single OAM beam RAMS of reduced divergence angle and improved gain. Then to generate four OAM beams, a 1-bit binary coding sequence with 10101010 based on the chessboard configuration was added to achieve the phase distribution required for generation of four OAM beams each with small divergence angle. To demonstrate the feasibility of the proposed strategy, single and multiple OAM beams RAMS were designed and fabricated. Both simulation and measured results demonstrated that the proposed strategy is efficient and can reduce the divergence angle of conventional OAM beams from 32 degrees to 7 degrees. In addition, the OAM beam gain improved by 4 similar to 8 dB with mode purity greater than 91%. Furthermore, the proposed RAMS can simultaneously generate four OAM beams of stable divergence angle over a wide frequency range from 80 GHz to 100 GHz which can be used for future mmWave OAM communication links.