Abstract: A single feed circularly Polarized Antenna is proposed for GPS application. It is composed of four substrates. Thebottom layer of the antenna is a single-fed four-port hybrid ring in order to provide the required equal amplitudes and 90 ° phase shiftsignals for circular polarization. Other substrates, respectively, has a square patch to achieve the tri-band performance. The simulatedresults show that: the antenna can cover all GPS bands (L1\L2\L5), which has 24MHz bandwidth on each operating frequency. It hasgood impedance matching characteristics in (1.17-1.6) GHz band, because the VSWR is less than 2; In addition, the properties ofbeam width and circular polarization all can meet the demand.