Design of an aperturecoupled microstrip antenna array at 12 GHz is presented. The aperture used in this antenna structure is Hshaped, and all elements of the array are fed in parallel. To increase the antenna bandwidth, the radiating elements are separated from the feed network with an airgap. Based on the calculated results of a 4×4 element antenna array, an antenna array with 8×8 elements is designed, which has a 11.3~13.0 GHz bandwidth for S11<-10 dB and a maximum gain of 22.3 dBi.