An Asymptotic Solution for Surface Fields on a Dielectric-Coated Circular Cylinder With an Effective Impedance Boundary Condition

An effective surface impedance approach is introduced for determining surface fields on an electrically large dielectric-coated metallic circular cylinder. Differences in analysis of rigorously-treated coated metallic cylinders and cylinders with an impedance boundary condition (IBC) are discussed. While for the impedance cylinder case a single constant surface impedance is considered, for the coated metallic cylinder case two surface impedances are derived. These are associated with the TM and TE creeping wave modes excited on a cylinder and depend on observation and source positions and orientations. With this in mind, a uniform theory of diffraction (UTD) based method with IBC is derived for the surface fields by taking into account the surface impedance variation. The asymptotic expansion is performed, via the Watson transformation, over the appropriate series representation of the Green's functions, thus avoiding higher-order derivatives of Fock-type integrals, and yielding a fast and an accurate solution. Numerical examples reveal a very good accuracy for large cylinders when the separation between the observation and the source point is large. Thus, this solution could be efficiently applied in mutual coupling analysis, along with the method of moments (MoM), of large conformal microstrip array antennas.