A novel circularly polarized microstrip antenna that incorporates a decagonal slot in the ground plane is presented in this paper. The antenna is based on a 0.762-mm-thick Rogers RO3203 substrate with dimensions 5 cm × 8 cm, and employs a Wilkinson power divider as a feeder. The proposed antenna is designed and simulated using Ansoft HFSS, a Finite-Element-Method based EM solver. The computed return loss is better than 10 dB over the 2.4-2.484 GHz frequency range. A prototype of the designed antenna is fabricated and measured. A good analogy between measured and simulated S11 plots is witnessed. The axial ratio, peak gain and radiation pattern of the antenna are included herein. It is shown that the antenna has a less-than-3dB axial ratio, a 0.5dB peak gain variation, and an acceptably omni-directional radiation pattern over the frequency range of interest.