This paper presents the new method for mutual coupling reduction in closely-packed microstrip patch antenna. The structure includes of a single ground plane and it is consequently low cost and simple to fabricate. It is found that isolation of more than 40 dB can be achieved between two parallel microstrip patch antennas with using of one pair of slit two walls in air between microstrip antennas, inter-antenna spacing (center to center) is 0.257lambda0. Also we are investigated that with different shapes of EBG on the walls we can reduce S12 more than 4 dB. Ground plane size is (0.617lambda0times0.376lambda0). At 0.94 GHz it is shown that this translates into a center to center separation between antennas of just 20 mm. Similarly the structure can be applied to reduce mutual coupling between three or four radiating elements. A simulation result is used to confirm the suppression of mutual coupling between closely-packed antenna elements.