In this communication, a wideband Fabry-Pérot resonator antenna (FPRA) is proposed. An optimized partially reflective surface (PRS) with a transverse permittivity gradient (TPG) composed of four nonrotationally symmetric sections is employed in the design of the antenna. The use of nonrotationally symmetric PRS results in more than 31% improvement of the 3 dB gain bandwidth compared with the traditional rotationally symmetric PRS. Furthermore, two types of nonresonant metamaterials (metallic-ring and etching-hole unit cells) are used to implement the equivalent permittivity of PRS. In this way, the equivalent permittivity value covers a broad range (3.5-9.5) for the same dielectric. As a result, the restrictions imposed by the use of only commercially available dielectrics and the errors that occur during the fabrication and assembly progress of different materials can be avoided. The primary radiator of FPRA is a double-ridge waveguide horn, which ensures wideband antenna operation. An FPRA prototype is fabricated and measured, which exhibits a broad bandwidth (5.2-11.5 GHz) with the return loss |S11| of less than -10 dB. The measured 3 dB gain bandwidth is 73.8% (in the frequency range of 5.3-11.5 GHz) with a peak gain of 17.1 dBi at 7.8 GHz.