Generalized dual-band branch-line coupler with arbitrary power division ratios

In this paper, a novel design of generalized dual-band quadrature hybrid with arbitrary power division ratios is presented and investigated. This coupler has a simple structure and can cover a wide range of power division ratios at the two designated frequencies. Exact closed-form equations are derived based on the even-odd-mode analysis method. The proposed structure offers some special features, encompassing: (1) a generalized structure of some recently published papers; (2) isolation in vertical and horizontal directions in the two-dimensional structure; (3) the same sign of the output phase difference for the structure with horizontal isolation and the opposite sign for the structure with vertical isolation; (4) large power division ratios for both vertical and horizontal isolation conditions; (5) large frequency band ratio for both vertical and horizontal isolation conditions; (6) capability of the bandwidth improvement by exploiting coupled lines with small coupling coefficient. For demonstration, a microstrip implementation of a 16:1 dual-band coupler working on 2.45/5.8 GHz is developed. Consistency between simulation and measurement results justifies the proposed design method and its equations.