This paper presents various designs for enhancing the radiation performance of a conventional Fabry-Perot cavity antenna (FPCA) by improving its aperture phase distribution using miniaturised convoluted frequency selective surfaces (FSS). The FSS behaves as a phase correcting surface (PCS) on electromagnetic (EM) rays as they are reflected inside the cavity of the FPCA. EM rays inside the cavity of the FPCA incur a phase change when reflected off the FSS PCS walls and base, making the aperture phase distribution more uniform, thereby increasing the directivity. To test the effectiveness of the FSS PCS in improving peak directivity, five models of FPCAs were designed to operate at 2 GHz. The first was a conventional FPCA with a polymethyl methacrylate (PMMA) partially reflective surface (PRS), no walls, a patch antenna emitter, and a copper base reflector. The second FPCA was designed so that the open sides of the conventional FPCA were fully enclosed with copper walls, The third FPCA had the copper walls replaced with FSS PCS walls. The fourth FPCA was designed by replacing the copper base reflector of the third FPCA with an FSS PCS base reflector. Finally, to make the antenna lighter and more cost-effective, a fifth FPCA was designed identically to the fourth FPCA, except that the PMMA PRS was replaced by a square-loop FSS PRS. The fifth FPCA design was fabricated and tested. Simulations and measurements demonstrate that the FSS PCS reflecting walls and FSS PCS reflective base significantly enhance the directivity radiation properties of the FPCA. The addition of the FSS PCS walls brought about greater aperture phase uniformity and a 2.06 dBi increase in peak directivity in both planes for the FPCA (PMMA PRS) when compared to the conventional FPCA (PMMA PRS) with no walls. When an FSS PCS base reflector was used instead of the conventional copper base reflector, there was a further increase in the aperture phase uniformity and peak directivity in both the FPCA with PMMA PRS and the FPCA with FSS PRS models. This increased aperture phase uniformity is brought about by the phase alteration of EM rays, as they are reflected off the FSS PCS structures surrounding the FPCA cavity. The maximum peak directivity in both the H and E Planes for the FPCA (PMMA PRS) with FSS PCS walls and an FSS PCS base reflector was 20.48 dBi, which is an increase in peak directivity of 8.3 dBi over the conventional FPCA. The maximum peak directivity in both the H and E Planes for the FPCA (FSS PRS) with FSS PCS walls and FSS PCS base reflector was 20.04 dBi, which is an increase in peak directivity of 7.86 dBi over the conventional FPCA. The high directivity (20.04 dBi) and thin PRS of the fifth FPCA design make it the most prominent. A major outcome of this fifth FPCA design is that its high directivity is achieved, not by adding additional components to a conventional FPCA, but by simply replacing its existing components with the FSS PCS.