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

Abstract

Abstract-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.

Directivity enhancement and characteristics of space‐wave, leaky‐wave and creeping‐waves for an impedance cylinder coated with dielectric

“…They are characterized by the term f i (υ) = N(υ)/D(υ) [13,24] with the azimuthal summation replaced by the summation over the residues corresponding to the poles using Watson's transformation. The creepingwave poles for the current configuration are obtained from G 1 = 0 for ẑor ρ-directed source and G 2 = 0 for φ-directed source from Equation (19) for n ¼ υ ð ¼ υ 0 − jυ 00 Þ, υ 0 and υ 00 being the azimuthal propagation and attenuation constants, respectively for the creeping-wave. As a result, the creepingwave poles depend on the source polarization.…”

“…An approximate solution for the evaluation of the scattered field due to a , and ‐directed dipole source placed near the finite conducting and finite impedance cylinder was presented in [18]. A UTD‐based approach with the effective impedance boundary condition is used to compute the surface fields of a thin‐dielectric coated PEC circular cylinder in [19]. Scattering due to obliquely incident plane wave on an electrically large impedance cylinder was analysed using the UTD in [20].…”

“…Compared to the antenna configuration presented in [13], the current configuration achieves a much higher directivity for the space‐wave and leaky‐wave. Also, a much higher directivity is achieved compared to the case of the impedance cylinder/thin‐dielectric coated PEC cylinder in [17–20]. The large enhancement in the leaky‐wave directivity in the current case is due to the dominant leaky‐wave radiation contributed by the poles due to the reflections in the dielectric‐to‐impedance surface and dielectric‐to‐air interfaces, instead of the poles of the transmission matrix in [13].…”

Geometrical Theory of Diffraction Formulation for On-Body Propagation

“…The location of the observation point is then simply given by its coordinates. A similar approach for the impedance boundary conditions has been made in [12], [22], [23] and for a perfect electric conductor in [24]- [26]. The case with the source away from the cylinder is solved in [27].…”

“…A GTD/UTD formulation for the Impedance Boundary Condition (IBC) was done in [11], [12] and for dielectric coated cylinders in [13], [14]. These approximations would be more appropriate to use for on-body propagation than the PEC assumption.…”