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.
Toit et al. (Thu,) studied this question.