Reconfigurable microwave couplers with dynamic performance control

Two kinds of reconfigurable microwave couplers are presented in this paper. The first one is a 90-degree branch-line coupler with a wide range of tunable coupling ratios. Especially, when its coupling ratio is tuned to be 1, this coupler becomes a crossover. The second one possesses a reconfigurable performance between a rat-race coupler and a 90-degree coupler. Both of the devices have a symmetrical structure, and varactors are loaded to the couplers as the tuning elements. By applying suitable control voltages, the reconfigurable performance is realized. Closed-form equations are derived to theoretically analyze the proposed devices. To further verify the design theory, both structures are simulated. Moreover, the first coupler is fabricated and characterized. Good performance is achieved in both simulation and measurement results.