Design of wideband multi-layer quadrature hybrid couplers with butterfly shaped resonators

Abstract

In this paper, a wideband quadrature hybrid coupler is presented. The proposed structure has a multi-layer microstrip topology. In this topology, there are three substrate layers including prepreg material and four conductive layers. In order to achieve equal power division between through and coupled arms of the directional coupler while maintaining a 90 degrees phase shift, aperture coupling between the resonators located at both top and bottom layers is utilized. So as to avoid any unwanted effects of prepreg material in such multilayer topology, via shielding around resonators are inserted. In this study, coupling from input ports to output ports is accomplished by the shielded butterfly shaped slot etched to the ground layer of top and bottom layers. The proposed design operates within 3-12 GHz. The acquired phase imbalance between the coupled ports is <+/- 2.5 degrees. The results of the manufactured quadrature hybrid coupler agree well with the simulated results.