Analysis of the single tapered mode coupler

Broadband directional couplers in which the phase constants and coupling coefficients vary with distance along two coupled transmission lines as suggested in the two preceding papers are analyzed. A criterion is given for the allowed variations in the line parameters for a given bandwidth. Parameters which describe the performance of such couplers are given. It is found that such couplers give much greater bandwidth than conventional couplers of the distributed coupling type but they must be longer than conventional couplers.