In this letter, a compact circularly polarized microstrip antenna has been developed with a new type of feed structure. The key feature of the antenna is the integrated design of the quad-feed network coplanar with the driven patch, which makes the antenna simple in structure and has good circular polarization performance. A parasitic patch is used to expand the impedance bandwidth, while a round hole in the center of the driven patch is used to improve impedance matching. In addition, a cavity is utilized to reduce the transverse size of the antenna and improve the front-to-back ratio. The simulation and experimental results show that the VSWR of the antenna is lower than 1.5 and the average gain is higher than 8dBic in the L-band for International Maritime Satellite applications. Due to the centrosymmetric feed configuration, the antenna can also be used as a global positioning system antenna, which requires high stability of the phase center.