Creeping wave propagation constants and modal impedance for a dielectric coated cylinder

The electromagnetic characteristics associated with the creeping waves supported by a dielectric coated cylinder are investigated. The propagation constants and wave impedances of the creeping waves are obtained numerically. Higher order modes which are significant for a thick coating are also investigated. The propagation constants and creeping wave modal impedance are compared with those obtained for a planar dielectric slab backed by a ground plane. It is found that, contrary to the planar configuration, no cutoff frequencies exist for the creeping waves associated with the coated cylinder. In fact, the coated cylinder supports an infinite number of modes. However, depending upon the thickness of the coating, only a few Elliott type creeping wave modes with low attenuation can exist. Furthermore, for each of the Elliott type creeping waves, there is a critical radius for the cylinder below which the Elliott type creeping wave cannot exist. The results are also compared with an impedance boundary cylinder, where the impedance is chosen to be purely imaginary.