Metallic and Goubau Waveguides with Eccentric Circular and Concentric Circular-Elliptic Cross-Sections

The cutoff wavenumbers knm and the field of three types of two-conductor metallic and two types of Goubau waveguides are determined analytically. The types are: Eccentric circular conductors of radii Rl, R2 and distance d between their axes, elliptic inner with circular outer and circular inner with elliptic outer conductor, while in the case of Goubau lines, dielectrically coated eccentric circular as well as concentric elliptic conductor are considered. For small eccentricities kd in the case of eccentric circular and h= ka/2 in the case of circular-elliptic(where a is the inter-focal distance of the elliptic conductor) exact, closed-form expressions are obtained for the coefficients gnm in the resulting relations knm(d or h)= knm(0)[1+gnm¿2+ ...], where ¿= knmd or h, for the cutoff wavenumbers of the corresponding waveguides. Similar expressions are obtained for the field. Numerical results for all types of modes and comparisons are also included.