This paper proposes on an effective mutual coupling suppression technique for planar phased array. This is achieved locating a metamaterial superstrate patch between radiation elements of phased array. The superstrate patch is realised by incorporating slots inside the patch, where the slots are arranged in 2×3 array column. The proposed mutual radiation decoupling technique is implemented on FR-4 substrate. Average coupling suppression of 5 dB is achieved on a low permittivity substrate over its operational frequency band. The proposed technique is (i) simple to implement; (ii) planar design; (iii) easily realised in practice; (iv) overcomes the shortcomings of poor front-To-back ratio previously reported in other radiation suppression techniques; and (v) applicable for densely packed microstrip. Furthermore, the proposed planar technique is highly versatile for various applications having stringent performance requirements.