A compact and simple shape of defected ground structure (DGS) is applied to reduce the mutual coupling between array elements in a microstrip array design. The proposed DGS with its low width is inserted between the adjacent E-plane coupled elements in the array to suppress the surface waves. Parametric studies of DGS parameters for a transmission line loaded with unit cell DGS are presented. A two-element array loaded with this DGS is then shown to provide a relative reduction in mutual coupling of 23 dB as compared to the same structure without the DGS. Simulation and measured results are provided and discussed.