Design of Dual-Band Coupler With Arbitrary Power Division Ratios and Phase Differences

This paper presents, for the first time, a directional coupler that allows for arbitrary power division ratios as well as arbitrary phase differences at dual frequencies of interest. Explicit design equations in terms of dual-band power-dividing ratios and phase differences will be given here and were derived based on the even- and odd-mode decomposition analysis. To illustrate the design procedure, examples will be provided and the relevant studies on the coupler's electrical parameters for a wide range of dual-band specifications and frequency ratios were conducted, by which the graphical solutions can be readily used as the further design tool. In addition, the resulting operational bandwidths are included and discussed for completeness. To validate our idea, four coupler prototypes were carried out according to the given guidelines. Excellent agreement is obtained between the measured and full-wave calculated results. The functional versatility of the proposed simple structure is well suited to applications in dual-band integrated modules, such as the beam-forming networks, for both loss and size reduction.