Abstract: A high-gain Fabry-Perot (F-P) cavity antenna with non-uniform frequency selective surface (FSS) superstrate and non-uniform electromagnetic band gap (EBG) reflecting ground is presented. Based on leaky wave theory model, a non-uniform FSS superstrate and EBG ground are proposed for large-aperture F-P cavity antenna to control the attenuation constant α and phase constant β. The uniformity of the amplitude and phase distribution on the aperture field can be improved, at the same time the deterioration of antenna performance is reduced when it deviates from the center frequency. So that the antenna can achieve high gain and high aperture efficiency when its bandwidth is maintained. The diameter of the proposed circular F-P resonant cavity antenna is 6.6λ₀. Simulation results show that the gain is 24.6 dBi, the aperture efficiency is 67.9%, the impedance bandwidth is 4.1% and the 3 dB gain bandwidth is 3.7%; the measured gain is 23.9 dBi, and the aperture efficiecy is 56.9%. The proposed antenna overcomes the limit on aperture efficiency and gain of conventional F-P cavity antennas due to the uniform distribution of the aperture field.