In this paper, a novel compact planar antenna using the co-aperture concept is presented for CDMA/GPS/Zigbee applications. By simultaneously placing three antennas with different shapes and polarization directions in a small place and considering the coupling among them, the co-aperture with three ports and good in-band performance could be designed on a small PCB. In order to validate this design, the proposed antenna is simulated by HFSS simulator. The simulation shows that this antenna operates at three frequency bands (CDMA/GPS/Zigbee) with high gain of above 2 dBi and high isolations among input ports of above 28 dB within its impedance bandwidth, and the polarization direction of the GPS band is circular. Considering the three ports and small dimensions of 106.5 mm × 66 mm × 1.6 mm, it can be treated as an antenna-triplexer directly used in the hand-held terminals for both communication and positioning.