Abstract: Improved miniaturized and low radar cross section (RCS） microstrip antenna is proposed for circularly polarized applications. The antenna scattering theory was given based on the theory of antenna radiation and scattering. The method of analyzing and controlling the scattering of circularly polarized microstrip antenna was also given. By the introduction of several circular and rectangular slots on the ground plane of the reference antenna, its RCS and size were reduced without effects on the circular polarization performances. The radiation and scattering characteristics were simulated and compared. The results show that the size of the proposed antenna is 50% smaller than the reference antenna, and the RCS of the reference antenna is also reduced.