Design of a frequency agile rat race coupler

A frequency reconfigurable 180° hybrid ring having wide tunability within 1.7 GHz - 3.2 GHz range is presented. Equivalent low-pass structures of transmission lines are used for original circuit modification and capacitors are replaced by varactor diodes for continuous tuning purpose. The proposed circuit can provide equal power division with 0°, 180° phase difference at different operating frequencies by simultaneously tuning six varactors. The circuit is designed on low cost FR-4 substrate and has also compact dimension (0.17λ×0.27λ×0.127λ) at 2.5 GHz, 50% less than conventional configuration.