Abstract: A circularly polarized microstrip antenna with stable phase center is introduced. Theoretical analysis proves that a circular microstrip antenna, which is excited by three symmetrical feeds with equal amplitudes and 120° phase shifts, can obtain circularly polarized radiation characteristics. Due to a centrosymmetric feeding configuration, the stability of phase center for the proposed antenna is very high. The simulated results show that the stability is less than 1 mm in the half power beamwidth. The measured 3-dB axial-ratio bandwidth is 19.83% from 2.18 to 2.66 GHz.