In this paper, an electromagnetic band gap structure is designed as a reflector for a dipole antenna which can transmit circular electromagnetic wave. The reflector comprises an array of 7? 5 triangular units, and the antenna works at 5.2GHz. The simulated results show that the proposed antenna radiate circular electromagnetic effectively, the impendence bandwidth is 0.65GHz, the polarization bandwidth is 0.13GHz, and the gain is 7.8dB.