Propagation features of metamaterial NRD waveguides

Nonradiative dielectric (NRD) waveguides comprised of time-dispersive isotropic double-negative or singlenegative slabs sandwiched between metal plates are studied. Dispersion features of bound (surface) modes are considered, showing how to achieve ranges of unimodal backward propagation by means of epsilon-negative media. Such ranges allow us to relax the symmetry constraints, typical of ordinary double-positive NRD guides, aimed at avoiding the excitation of the undesired LSEo1 dominant mode. Complex proper leaky modes supported by double-negative NRD guides are also illustrated, which show physical ranges of radiation into the first higher-order TE1 mode of the background parallel-plate waveguide.