Abstract: The paper presents a microstrip antenna applied to global positioning system（GPS），have a greater beam width and good circular polarization characteristics. The slotted ground plane microstrip antenna and pyramidal horn structure are adopted，the ground plane embedded slots can excite circularly polarized（CP）radiation，then slotted ground plane microstrip antenna placed on the pyramidal horn structure can reached a wide-beam. The simulation results show that the antenna in the E plane and H plane to get wide beams，E plane beam width is greater than 123 °，and H plane beam width is greater than 136 °，while the circular polarization characteristics are remarkable within the beam width.