Sub-wavelength metallic waveguides loaded by uniaxial resonant scatterers

The dispersion properties of rectangular metallic waveguides periodically loaded by uniaxial resonant scatterers are studied with help of an analytical theory based on the local field approach, the dipole approximation and the method of images. The cases of both magnetic and electric uniaxial scatterers with both longitudinal and transverse orientations with respect to the waveguide axis are considered. It is shown that in all considered cases waveguides support propagating modes below cutoff of the hollow waveguide within some frequency bands near the resonant frequency of the individual scatterers. The modes are forward ones except the case of transversely oriented magnetic scatterers when the mode turns out to be backward. The described effects can be applied for the miniaturization of the guiding structures.