Abstract: In this paper, an isoflux pattern antenna suitable for the Ka-band and an optimized design of septum circular polarizer is proposed. The antenna can be applied to low earth orbit satellites to enable TT&C (Tracking, Telemetry and Command). Satellites operating in low earth orbit generally require wider angle coverage and longer time visibility. And the pattern of this antenna can well compensate for the tilt angle between the satellite and the ground station, providing a uniform power density to the ground station while in orbit. The antenna uses a septum polarizer to achieve circular polarization, and the operating bandwidth of the antenna is further enhanced by optimizing the step size. The final optimized antenna pattern has isoflux characteristics, low side lobe level, and the relative operating bandwidth of the antenna can reach about 30%.