A compact dual band antenna operating simultaneously at 5.4 GHz and 15 GHz is presented in this paper. It is a planar array composed of a grid of 6×8 (48) patch antennas working at 5.4 GHz and 7×9 (63) patch antennas working at 15 GHz. The whole antenna array occupies an area of 150 mm × 180 mm which fits the ordinary size requirement of wireless access point. All the antenna patch antennas have a reflection coefficient lower than −6 dB across 320 and 2000 MHz bandwidth at 5 and 15 GHz. The electromagnetic coupling between any two antennas is lower than − 10 dB within the specified bandwidth. Measurement results show good agreement with the simulation of input matching, mutual coupling and radiation pattern. Compared to the ordinary antenna array design with half-wavelength spacing between two neighboring antennas, our proposed dual band array design accommodates 1.6 times more antennas at 5.4 GHz and extra 63 antennas at 15 GHz, while maintaining sufficient radiation efficiency, matching bandwidth and decoupling.