Perspectives on Passive and Active Huygens’ Metasurfaces

We will describe the concept of the Huygens' metasurface which comprises co-located electric and magnetic dipoles forming an electrically dense array of Huygens' sources or scatterers. These engineered surfaces can be designed to control electromagnetic waves at will. Both passive and active Huygens' metasurfaces can be envisioned. Unlike traditional antenna transmitarrays, Huygens' metasurfaces can be made sub-wavelength thin and deprived of spurious Floquet modes, while preserving excellent matching characteristics. Huygens' metasurfaces can be used to manipulate the phase, magnitude and polarization of incident electromagnetic waves, including those from nearby elementary antennas, for a variety of applications. For example, Huygens' omega bi-anisotropic metasurfaces enable wave refraction at extreme angles without any reflections. They also allowed the demonstration of generalized flat reflectors having an arbitrary angle of reflection with respect to the angle of incidence and with 100% theoretical efficiency. Examples of Huygens' metasurface applications to be discussed include focusing and lensing, polarization control including chirality, active cloaking, high aperture efficiency/low-profile antennas, antenna aperture beamforming with simultaneous magnitude and phase control, and electronic beam steering.