AbstractAssembling polarization conversion metasurface (PCM) and a simple patch antenna to realize a circularly polarized (CP) antenna with over 10% fractional bandwidth (BW) is a challenging task. A kind of PCM composed of S‐ring and grating structure that converts linearly polarized (LP) wave into CP wave in a broadband frequency from 8.74 to 12 GHz can address the challenge. The universality of the PCM in realizing antenna polarization conversion is verified by using a standard LP horn antenna. Then, we design a broadband LP rectangular patch antenna to demonstrate that the present PCM can be integrated with small antenna devices to achieve CP antenna. A broadband CP patch antenna with a 12.4% −10 dB BW and 11.3% 3 dB axial ratioBW is obtained. The antenna gain reaches 8.1 dB with the enhancement gain of 4.1 dB. The findings are very attractive for wireless communication, radar monitoring, and satellite systems because the proposed antenna has excellent broadband CP performances, simple structure, and easy fabrication.