Coarsely Discretized Huygens' Metasurface: Manipulating EM Waves with Simplicity

With the genesis of metamaterials and its 2D counterpart - metasurfaces, there is a paradigm shift in controlling electromagnetic (EM) waves. A special category of metasurfaces known as Huygens' metasurface - fundamentally based on equivalence principle, have demonstrated unprecedented capabilities for advanced wavefront engineering. In this paper, we provide current trends and progress in the area of Huygens' metasurfaces, particularly the coarsely discretized Huygens' metasurfaces, consisting of two to three meta-atoms per metasurface period. The basic design principle of coarsely discretized metasurface relies on the classical grating theory, where the undesired Floquet-Bloch (FB) modes are suppressed by engineering the individual meta-atom, and the desired ones are allowed to radiate in the far-field. Moreover, we briefly summarize the recent development in Huygens' box - a region of space surrounded by an active Huygens' metasurface, and its applications in antenna beam steering. Lastly, we provide a summary and brief outlook on the possible future research directions.