Circular Waveguide With DB-Boundary Conditions

A set of boundary conditions requiring vanishing of the normal components of the D and B vectors at the boundary surface was introduced recently and labeled as the DB-boundary conditions. Basic properties of the waveguide defined by circular cylindrical DB boundary are studied in this paper. It is shown that the circularly symmetric TE and TM modes coincide with those of the respective PEC and PMC waveguides. More general waveguide modes can be split in two groups, self-dual and anti-self dual modes with respect to a duality transformation and their dispersion properties differ from those of a PEC waveguide as there may exist backward-wave modes for certain ranges of frequencies.