Wideband ring-hybrid with quadrature-phase outputs for high-power applications

This paper presents a 3-dB coupler providing 90° output phase-difference over wider bandwidth compared to other single-stage planar couplers. The proposed design is suited for the applications where high power RF signals need to be combined with quadrature phase. It uses a symmetric rat-race coupler to achieve wider bandwidth as compared to its asymmetric counterparts. The proposed coupler has a measured peak-to-peak phase-deviation of 16° and a magnitude-imbalance of lower than 0.5 dB over the entire bandwidth spanning 2 GHz to 3 GHz. The measurement results comparing the proposed coupler with a) a branch-line coupler, b) a rat-race coupler employing a Schiffman phase-shifter and c) a Wilkinson power-divider cascaded with the Schiffman phase-shifter, are also presented.