Abstract—A high gain circular polarized radial line slot antenna (CP-RLSA) is reported in the design with Matlab and HFSS interface technology to achieve the slot array model modified adjusted automation. In this paper, we find that proper adjustment of the frequency offset can get a higher gain and a lower return loss. A new material with the relative dielectric permittivity of 1.06 can help to reach the purpose of grating lobe suppression. The designed antenna achieves a high gain more than 30 dB at the frequency of 12 GHz with a coaxial probe feed in the simulation. While the measured gain is 30.818 dB at the frequency of 11.8 GHz, and the trend of the measurement result coincides well with the simulation one.