Broadband low-loss impedance transforming rat-race coupler in suspended microstrip technique

Abstract

A broadband, impedance transforming rat-race coupler designed in a suspended microstrip technique has been presented. The proposed structure allows to transform input impedance to impedances on coupled ports with ratio 2:1. Furthermore, to improve operational bandwidth, additional, modified coupled-line sections have been added at input ports. The suspended microstrip technique has been chosen to minimize the coupler's losses. The described circuit has been theoretically analyzed, fabricated and measured.