A New Branch-Line Hybrid Coupler with Arbitrary Power Division Ratio

This paper proposes a new branch-line hybrid coupler with controllable power ratio at the output ports. It is structured as two 90deg branch-line hybrid couplers connected by a variable impedance transmission line. The power division ratio is adjusted by controlling the impedance of the transmission line. Modeling the transmission line as series and parallel resonators shows that its impedance can be changed by changing the inductance and capacitance. In practice, using a varactor diode facilitates ease in dealing with the impedance of the transmission line and thus the power division ratio of the coupler.