Improving Design of Symmetrical Six-Port Microstrip Coupler

Abstract

It is possible to broaden the bandwidth of the symmetrical six-port microstrip coupler by incorporating various elements into the original structure. A consolidated eigenmode-based model has also been developed to predict the performance of such a coupler (when implemented in various novel forms). Laboratory tests have confirmed that the prototype coupler thus obtained is able to meet all the design specifications over a 44% bandwidth. Introduction After Riblet [1] reported the use of a symmetrical six-port coupler as a five-way power divider, other researchers [2]-[4] have demonstrated that this new coupler can also be utilized as the core component of a six-port reflectometer capable of yielding optimum measurement performance. For the latter application, analysis [3] has shown that the coupler’s characteristics may be represented by the following scattering matrix [5]: S =   γ α β τ β α α γ α β τ β β α γ α β τ τ β α γ α β β τ β α γ α α β τ β α γ   (1) where for the ideal case [3] we need to impose the following design specifications for the four scattering coefficients defined in Eqn. 1: