Multibeam Radiation And Polarization Control Based On Anisotropic Metasurface

Metamaterial is a kind of artificial material, which is composed of sub-wavelength unit cells arranged periodically or non-periodically. It can manipulate electromagnetic waves by adjusting the shape or size of the unit cell. Metasurface is a new research direction in metamaterials in recent years, which is a kind of super thin two-dimension (2D) metamaterials composed of sub-wavelength unit cells regularly arranged into plane array. It can be devided into reflection metasurface and transmission metasurface. Compared to the transmission metasurface, the reflection metasurface has a very high efficiency at the microwave frequency range, reaching nearly 100%, so our study is mainly based on the reflection metasurface in this paper. On the selection of the unit cell, we take a kind of anisotropic structure composed of two orthogonal I-shaped structures, which can manipulate the reflective phases of two orthogonal linearly-polarized waves independently by changing the dimensions of I-shaped structures in horizontal and vertical directions, respectively. We combine the designing concept of traditional multi-beam reflectarray antenna and anisotropic metasurface, to achieve the manipulation of the radiation directions and phases of multi-beams independently. When the orthogonal linearly-polarized beams are radiated to the same direction, we can control the polarization state of each beam by special design of phase different between horizontal and vertical polarizations. Based on this principle, three kinds of anisotropic metasurfaces with different functions working at Ku frequency band have been designed, simulated and tested. The measurement results agree very well with the simulation results, which verified the good capacity of anisotropic metasurface to manipulate the radiation and polarization of multi-beams independently. The main contents of this thesis are as follows:(1) The fundamental principles and designing methods of multi-beam radiation and polarization control based on anisotropic metasurface are studied. The anisotropic metasurface can manipulate the reflective phases of two orthogonal linearly-polarized waves in horizontal and vertical independently, so the directions and number of radiation beams also can be manipulated independently by combining with the designing method of multi-beam reflectarray antenna. When the orthogonal linearly-polarized waves are radiated to the same direction, we can control the polarization state of each beam independently by the special design of phase difference between horizontal and vertical polarized waves.(2) The basic unit structure of anisotropic metasurface is studied and the waveguide probe feed with equal E-plane and H-plane radiation patterns is introduced. In this paper, we take a kind of anisotropic unit cell composed of two cross I-shaped structures, which can manipulate the reflective phases of two orthogonal linearly-polarized waves independently by changing the dimensions of I-shaped structures in horizontal and vertical directions, respectively. Besides, we seclect a kind of waveguide probe feed with equal E-plane and H-plane radiation patterns as the feed of anisotropic metasurface, which has the advantage of small volume, low profile, good circularly symmetry radiation pattern, stable phase center and gain.(3) Three kinds of anisotropic metasurface with different functions have been designed, simulated and tested. We design one kind of two-beam polarization control anisotropic metasurface and two kinds of three-beam polarization control anisotropic metasurfaces, and each beam's polarization state can be designed and manipulated independently. The experimental results and the simulation results agree very well, which verified the good capacity of anisotropic metasurface to manipulate the radiation and polarization of multi-beams independently.