Flexible Unidirectional PTD-Symmetric Waveguide

The transmission and reflection characteristics of a bent square transverse electromagnetic waveguide constituted by two opposite perfect electric conductor and perfect magnetic conductor walls are analyzed. This waveguide exhibits a parity, timereversal, duality (PTD) symmetry with respect to both the diagonal axes. It is found that this property is maintained even when the structure is bent in a plane orthogonal to one of the two PTD symmetry axes (PTDbend). As a consequence, the transverse electromagnetic mode propagation is protected against backscattering by this class of discontinuities. The preservation of the PTD symmetry in presence of a geometric flexibility of the bend is also analyzed, thus introducing a new class of bendable waveguides that are largely immune to backscattering by bend discontinuities.