In this work, an octagonal microstrip antenna is presented. The design formulas of it are introduced based on the circular microstrip antenna. After presenting the theory of it, a single octagonal patch antenna is designed and simulated. After that, the designed antenna is developed to a 2×2 planar array. To evaluate the performance of the single and array antennas, the designed antennas are simulated using HFSS and the obtained results are presented.