Abstract: There is a severe mutual coupling between any adjacent elements for a compact circularly polarized microstrip antenna array along E-plane and H-plane where each element is fed by two coaxial probes, which will bring remarkable performance reduction to the array. Thus, a two-element circularly polarized microstrip antenna array model is built by HFSS software, in which distance from one patch center to another and patch tangential substrate edge sizes on mutual coupling along E and H planes are simulated and analyzed. The result shows that there is a critical value for the distance. While the distance is less than the critical value, mutual coupling along E-plane is more severe than along the H-plane. Moreover,there is still another critical value for the edge size in the E-plane direction corresponding to a lowest mutual coupling along E-plane. Unfortunately, no optimal value for the edge size in the H-plane direction can bring minimum mutual coupling along the H-plane. At last, one test sample is designed, manufactured and tested, which is almost in consistent with the simulation result.