A novel 3dB directional coupler with reconfigurable performance

In this paper, a novel reconfigurable 3-dB directional coupler is presented. Varactors and inductors are loaded to the device to realize the performance of reconfiguration. By adjusting the voltage applied to the varactors, the proposed coupler can be reconfigured from a branch-line coupler (90-degree coupler) to a rat-race coupler (180 or 0 degree coupler) and vice versa. During the tuning, good isolation and matching (small reflections) are obtained. To facilitate the design, rigorous theoretical analysis is carried out. Based on the analysis, general design equations are derived. Furthermore, a prototype working at 1 GHz is simulated to prove the design theory. Good agreement is achieved between the simulation and theoretical results.