Dielectric-waveguide branching directional coupler

A dielectric-waveguide branching directional coupler with curved transitions is presented, and is investigated by the use of a staircase approximation which combines the building block approach of multimode network theory with a rigorous mode matching procedure. The coupling problem is analysed from the viewpoint of the scattering of incident surface waves by the nonuniform dielectric structure as a whole. Particular attention is given to establishing the effect of radiation due to bending of the curved transition waveguides and other discontinuities on the performances of the coupler. Numerical results are given, from which guidelines for the design of directional couplers are derived.