A Ka-band circular polarization planar array antenna with a scale of is 8×8 is designed in this paper, 2×2 subarray as a basic unit, its circular polarization characteristic is achieved by inserting polarized diaphragm into the subarray feed square waveguide. Using full-corporated E-plane power divider, the 16 subarrays are fed in the continuous phase. This way, the array antenna designed here fulfills good circular polarization and high gain feature.