A compact broadband tapered slot antenna (TSA) array was designed, which can achieve a bandwidth of 4.5–18 GHz with scan angle up to 60°. Contrary to the conventional array design, the key to this design was taking advantage of mutual coupling between closely-spaced elements. A generic analytical-based method was developed to predict the mutual coupling between elements in the TSA array and the strong coupling between TSA elements was identified as being essential to the operation of arrays over broad bandwidth.