The design of a circularly polarized (CP) microstrip antenna with wide beamwidth working at 1.268GHz is proposed. The wide beamwidth is achieved by introducing a substrate larger than the ground and an annular dielectric superstrate with a metal ring. The effects of the substrate, superstrate and ring on radiation pattern and circular polarization are discussed. Simulation results show the proposed antenna simultaneously has wide beamwidth, high low-elevation gain, symmetrical pattern and good CP characteristics. The minimum axial ratio is 0.34dB. 3dB beamwidth and 3dB axial-ratio beamwidth are 169.12° and 165° respectively.