Broadband branch-line coupler with arbitrary power split ratio utilizing microstrip series stubs

This paper treats broadband branch-line couplers with arbitrary power split ratios utilizing microstrip series stubs as matching networks. Proposed series stubs are structurally integrated in input/output microstrip transmission lines. Based on the equivalent admittance approach, dual-band/wide-band characteristics with relative bandwidths of over 30 % can be obtained in the case of a coupler with a power split ratio of 1 to 5. Validity of this design procedure can be demonstrated by electromagnetic simulations and experiment.