Properties of NRD-guide and H-guide higher-order modes: physical and nonphysical ranges

New interesting modal properties are presented for the waveguiding structure constituted by a rectangular-section dielectric rod sandwiched between parallel conducting plates, which can represent either a non-radiative dielectric (NRD) guide or an H guide. A rigorous quantitative analysis of the dispersion properties indicates that higher-order modes can show different anomalous behaviors, as geometrical and electromagnetic parameters vary. A discussion of the physical nature of the waves related to complex wavenumbers allows us to illuminate the performance differences between NRD and H guides, as regards certain previously unexplored leakage effects.<>