An Asymmetric Arbitrary Branch-Line Coupler Terminated By One Group Of Complex Impedances

Abstract

A novel arbitrary asymmetric branch-line coupler structure terminated by one group of complex impedances is proposed. Two left ports of the proposed branch-line coupler are terminated by equal arbitrary complex impedances, and the other two right ports are terminated by equal real impedances. Arbitrary power division ratios are feasible for the proposed structure. Using rigorous even- and odd-mode analysis and scattering parameters theory based on complex impedances, the closed-form design formulas for designing the proposed branch-line coupler is obtained. To validate the proposed structure and the given design equations, a microstrip branch-line coupler operating at the center frequency of 2.5GHz and terminated by 20 and 30 − 6j Ohm impedances is designed, simulated and measured. There is a good agreement between the simulated and measured results.