The transition region between bound-wave and leaky-wave ranges for 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 qualitatively, where some anomalous features are considered; then numerical values for a specific example, a recently proposed novel leaky-wave antenna structure, are presented