A new type of circularly polarized antenna based on Substrate Integrated Waveguide (SIW) is introduced. HFSS simulation software is used for the optimization of the antenn The maximum gain is 7. 3 dB, and the Axial Ratio (AR) is 1. 03 dB when central frequency is 12 GHz. The simulation result shows that the new antenna has high gain and low AR, and also has the advantages of cheap and easy to fabricate.