Anisotropic Metasurface With Asymmetric Propagation of Electromagnetic Waves and Enhancements of Antenna Gain

An anisotropic metasurface that performs a reflectarray and transmitarray on each side is proposed. The proposed configuration comprises 15 x 15 unit cells that consist of polarization converters and a polarization filter. Two topologies are developed for the unit cells to meet five design goals simultaneously, including reflection magnitude, transmission magnitude, reflection phase difference, transmission phase difference, and polarization conversion ratio. By arranging the two topologies of unit cells according to a required phase distribution, in-phase reflection and transmission are achieved on each side. A prototype is designed, fabricated, and analyzed at 28.0 GHz. The feed is implemented as a quasi-Yagi antenna with gain of 8.0 dBi. When linearly-polarized electromagnetic waves impinge on the top, the proposed metasurface functions as a reflectarray and offers gain of 17.9 dBi. When the feed antenna illuminates the bottom, the proposed metasurface performs a transmitarray and depicts gain of 19.1 dBi. Moreover, when the both sides are arranged with feeds, a unidirectional pattern with power gain of 20.3 dBi is obtained. Such a "twin-feed mode'' demonstrates a highly-directed main beam with orthogonal polarization components, which is useful in dual-polarized communications. Thus, the proposed metasurface provides antenna applications with low-cost, low-complexity, and multifunctional wavefront manipulation.