Full-wave synthesis technique for the design of an optimized 0.5-18 GHz 90° hybrid coupler

Abstract

An optimization technique that can be used to design high performance, wideband 90° hybrid couplers is described. Optimization is performed not by using the traditional theoretical coupling factors, but rather by directly synthesizing the geometric dimensions of the hybrid in full-wave simulations. Simulated results thus include all secondary, nonideal transmission line and implementation effects, and can be optimized for the required equiripple results. The full-wave synthesis technique is explained in detail, and simulated results of a 2–18 GHz design with 0.5 dB magnitude imbalance improvement over any previous results are shown. It is also used to implement a unique 0.5–18 GHz 3 dB, 90° tandem hybrid, of which measurements are presented showing near optimally minimized magnitude imbalance of 1.47 dB, loss of less than 1.8 dB, and phase imbalance below 8°, over the complete ultrawideband bandwidth.