This paper shows simple techniques to decouple multiple-input-multiple-output (MIMO) antenna. Different decoupling approaches are presented and demonstrated as effective methods to design MIMO antennas with high isolation and small element spacing. To decouple E- and H-plane coupled patch antennas, methods of using grounded stub and polarization conversion microstrip line can achieve high isolation of better than 30 dB and element spacing of 0.034λ at the center operating frequency. Such methods are suitable for narrowband operation MIMO. With respect to wideband operation MIMO antenna, the antenna size is generally large. Thus, shorting pins are inserted into the MIMO elements to avoid requiring additional space for decoupling the network. In this case, wideband and high isolation of about 30 dB can be achieved with zero spacing between the MIMO elements.