Abstract: A new design method of wideband Fabry-Perot resonator antenna (FPRA) is presented. A double-layered full-dielectric superstrate, which produces a reflection phase curve versus frequency with a positive slope, is used as a partially reflective surface ( PRS) to enhance the gain bandwidth of the FPRA. For a physical insight, the PRS is analyzed by using the transmission line theory and Smith Chart. The proposed method, as well as related analysis, is validated by a practical wideband FPRA design.