A dual-band compact branch line coupler based on Γ-shaped transformer

This letter presents a dual-band branch-line coupler designed for dual-band operation. The proposed coupler is implemented by using a dual-band impedance transformer. The circuit features low loss (without couple lines or lumped elements) and a compact circuit size (all lines are 90° calculated at the center frequency of two operation bands). Explicit closed-form equations for the dual-band coupler parameters are derived analytically using the ABCD-matrix. In addition, simulation results of a coupler working at 1/2.5GHz was presents, which confirmed the design concept.