Steerable metasurface antennas Metasurface antennas are planar multi-layer configurations of sub-wavelength building blocks (i.e. unit cells) typically printed on grounded dielectric slab. Metasurfaces possess, among others, the ability to manipulate surface waves. Metasurface antennas radiation is well described in terms of a continuous slowly varying electric sheet tensorial reactance, interacting with a surface wave, which is gradually transformed into a leaky wave. Indeed, a leaky-wave antenna is a waveguiding structure which sustains a wave that radiates energy while propagating along the antenna itself. As for metasurface antennas, such radiating mechanism is achievable through Sinusoidally-Modulated Reactance Surface (SMRS) placed at the upper interface of a grounded dielectric slab.