A Low Sidelobe Level Along Direction of Propagation 4-Order OAM Beam Generated by Hexagonal Reflective Metasurface

As the potential of the OAM beam on wireless communication area was discovered by engineers, more and more attentions have been drawn into the OAM beam generating area. Metasurface as a two-dimensional resonant structure has become a popular method to generate the OAM beam efficiently. However, when the topologic number of the OAM beam comes to 4, the OAM beam generated by the metasurface has a high sidelobe level (SLL) appeared at the direction of propagation which will affect the distribution of the near-field and purity. In this paper, the reason why there is a large sidelobe at the propagation direction is analyzed through analysis method of array antenna. And then, based on the analysis, a hexagonal reflective meta-atom is designed and simulated. The designed meta-atom works at 10GHz and has a 2GHz bandwidth. And simulation results show that the phase range of the meta-atom manipulation can cover 0 to $2\pi$ . Finally, a reflective metasurface combined by the hexagonal meta-atom is designed and simulated. And the simulation results show that the sidelobe level along the propagation direction of a 4-order OAM beam generated by a hexagonal metasurface is 20dB lower than that of a quadrilateral metasurface.