Microstrip decoupling networks for low-order multiport arrays with reduced element spacing

An array of monopole elements with reduced element spacing of λ/20 to λ/6 is considered for application in digital beam-forming and direction-finding. The small element spacing introduces strong mutual coupling between the array elements. This paper proposes that decoupling can be achieved analytically for arrays with three elements and describes Kuroda's identities in order to realize the lumped elements of the derived decoupling network. Design procedures and equations are proposed. The experimental results are presented. The decoupled array has a bandwidth of 1% and a superdirective radiation pattern.