Low-loss design method for a planar dielectric-waveguide branch: effect of a taper of serpentine shape

A design method is proposed for a planar dielectric waveguide Y branch with low loss caused by radiation. In contrast to the usual design methods, in which the generation of the radiation wave is kept as small as possible, the present method positively uses, for the first time, the behavior of such a radiation wave. The radiation wave at any local position along a taper section of the Y branch is intentionally generated, and its power conversion and reconversion with the surface-wave mode are controlled to reduce the insertion loss for the surface-wave mode. A design example shows that the low-loss Y branch should have a serpentine-shaped taper, which is an unexpected shape compared to the usual design. The effectiveness of the design method presented is confirmed by comparing the numerical results with those of the usual types of Y branches and with measurements