A Universal Approach for Designing an Unequal Branch-Line Coupler With Arbitrary Phase Differences and Input/Output Impedances

For the first time, this paper presents a novel approach for designing a coupler with arbitrary division, optional phase difference, and alternative input/output impedances. In the section of theoretical analysis, rigorous closed-form design equations are derived, and explicit methodology for computer-aided design is given based on the equations. To validate the idea, several numerical examples extracted from the design procedure are constructed and demonstrated. Eventually, three prototypes of the coupler are fabricated, and experiments are carried out. The excellent agreement between the theoretical and experimental results sufficiently verifies the theoretical methodology. This proposed coupler is well applicable to the applications that require high flexibility in couplers' performances.