An antenna system with reduced electromagnetic coupling exploiting the uniplanar compact photonic band gap (UC-PBG) structure to achieve higher isolation is presented in this paper to enhance the performance of MIMO antennas. Two closely-spaced monopole antennas operating in the frequency range 5-6 GHz is considered. It is shown that the use of UC-PBG is better than the existing methods in reducing the electromagnetic coupling. Other parameters of MIMO antennas like correlation co-efficient and diversity gain are also calculated.