Dielectric waveguide branching directional coupler

A dielectric waveguide branching directional coupler with curved transitions is presented and investigated by the method, which combines the building block approach of multimode network theory with rigorous mode matching procedure. The coupling problem is analyzed in terms of the scattering of incident surface wave by the nonuniform dielectric structure as a whole. Particular attention is directed to the effect of radiation due to bending of the curved transition waveguides on the performances of the coupler. Numerical results are given to establish useful guidelines for the design of directional couplers.