Design of reconfigurable dual-band branch-line coupler

This paper describes design of a reconfigurable dual-band branch-line coupler, consisting of conventional dual-band coupler associated with new type of tuning networks for individually adjusting coupling coefficient at two operation frequencies. The tuning network consists of transmission line, varactor diodes and lumped element components to achieve the variation of admittance of tuning network at different operating frequencies according to the given controlled voltages. In certain range of the control voltage, one can obtain the main change in coupling coefficient at upper frequency band. The dominant variation of coupling coefficient in lower frequency band will be obtained in the other range of the applied control voltages. The coupling coefficient of the coupler is almost invariant at the other operation band, while it is tuned at one of operation bands. An experimental prototype working at the two operating frequency bands of 1 and 2 GHz is constructed on a PCB substrate to validate the proposed reconfigurable dual-band coupler. The measurement results show good correspondence with the simulation results.