Abstract: A microstrip antenna is designed of dual-band and dual circularly polarization (CP) with common apeture usingonly one probe feeding. The inside smaller circular patch operates at higher frequency and the outside circular ring patch operatesat the low frequency, while four narrow strip connect the two patches. The perpendicular perturbation segments at the side of theinside and outside patch are used for achieving CP radiation with LHCP and RHCP respectively . From the simulation andoptimization, the proposed antenna operates well impedance matching and dual CP performance.