The transition region between bound-wave and leaky-wave ranges of a partially dielectric-loaded open guiding structure

Most modes on partially dielectric-loaded open guiding structures are purely bound in some frequency range and leaky in another. The transition region between them is complicated and interesting, including a section where the dispersion curve doubles back, because it connects a complex nonspectral (leaky-wave) solution with a real spectral (bound-wave or surface-wave) solution. The physical nature of this type of transition region is discussed in the context of a recently proposed novel leaky-wave antenna structure, and some anomalous features are described.<>