Compact Dual Band Varactor-Tunable Unequal-Length Branch-Line Hybrid

Abstract

We report a concurrent dual-band varactor-tuned branch-line coupler (BLC). It is based on an unequal-length dual-band BLC. A total of two varactors with single dc control voltage are used for tuning the dual-frequency-band. Meandering of both varactor-connected transmission lines pointing inward to the center of hybrid makes our coupler very compact in size. It has an overall dimension of 0.4 g x 0.22 g, where g is the guided wavelength corresponding to the lower band center frequency. Simulation and measurement results along with fabricated prototype of our proposed device are provided. Lower and upper frequency band tunable-bandwidth is 193- and 160- MHz, respectively.