Fabry-Perot Antenna (FPA) is actually a one-dimensional resonant cavity to serve as a high gain radiator. This may consider as a replacement of large antenna array bearing some new features. Higher directivity is obtained through a uniform phase-front developed within the vertical cavity consists of a ground plane and a superstrate layer. The resonance condition of the cavity is maintained by adjusting its dimension as half of the wavelength of the radiating wave. A ‘primary-radiator’ indeed illuminates the Fabry-Perot cavity. Its high-gain characteristics are determined by this primary-radiator along with the superstrate layer. A grounded radiating aperture, a conventional microstrip patch, or a dielectric resonator antenna (DRA) having a broadside radiation pattern commonly serves as the primary-radiator in an FPA design. Traditionally, the superstrates were physically realized as partially reflecting surfaces (PRSs) such as thin dielectric slab, frequency selective surface (FSS), electromagnetic bandgap structure (EBG), artificial magnetic conductor (AMC), metamaterial, metal grid structure, etc. Their gain-enhancement mechanism used to be demonstrated in terms of reflection coefficients  or leaky-wave generation. Their basic concept was leakage of electromagnetic energy through the semitransparent superstrate. © 2019 URSI. All rights reserved.