Discrete Huygens' Metasurface: Realizing Anomalous Reflection and Diffraction Mode Circulation with a Robust, Broadband and Simple Design

Metasurfaces composed of subwavelength unit cells usually require a large number of unit cells which leads to complicated design and optimization. Aggressive discretization in a metasurface can significantly reduce the number of unit cells within a period, resulting in lower requirement for phase and/or surface impedance coverage. Additionally, the enlarged unit cells will encounter negligible mutual couplings when combined together, hence making straightforward the process of metasurface design. These advantages combine to allow the design of a novel class of metasurfaces which support the high efficiency redirection of electromagnetic (EM) waves over a wide bandwidth and operation angle. Moreover, an aggressively discretized metasurface may realize functionalities such as diffraction mode circulation, which are unsupported in its continuous counterparts. In this paper we propose a simple transmissive metasurface which can realize diffraction mode circulation by refracting plane waves with incident angles of -45, 0, 45 degrees to plane waves with refraction angles of 0, 45, -45 degrees respectively. The power efficiency of each anomalous refraction is more than 80% at the design frequency of 28 GHz, and the 3-dB power efficiency bandwidth is 11%. We fabricated and measured the metasurface, the experiment results agree well with simulation results.