The radiation characteristics of a microstrip circularly-polarized aperture-patch $8 imes8$ array antenna are investigated at X-band. The radiator consists of a truncated square aperture on the ground plane with an inclined rectangular patch inside, and it is coupled by a microstrip line on the opposite side of the ground. The element spacing of the array was chosen as $0.8lambda_0$so as to minimize the mutual coupling and maximize the gain. A corporate feed network was employed to distribute the power to each element through four Wilkinson and two T-junction dividers. Measurement results for the $8 imes8$ array at 10 GHz showed a directivity of 26.3 dBi, a gain of 22.2 dBi, an axial ratio of 2.97 dB, and a side lobe level of -12.7dB. It was observed that when the array size increases, the directivity increases while the efficiency decreases.