Cylindrical capacitive obstacles in a waveguide

Scattering from a cylindrical metallic object placed centrally in a waveguide so that its axis is parallel to the transverse magnetic field of the dominant mode is shown to give rise to two field types in the scattered waves, which are dipole and isotropic in nature. On the other hand, a dielectric rod similarly placed shows only dipole scattering. A method is presented which uses a potential theory to describe dipole scattering from metallic, dielectric and magnetic obstacles, and it is further shown that the theory may be used to derive in a simple manner the dipole scattering from a coaxial obstacle which may consist of a metal rod with a dielectric or magnetic sleeve, or coaxial combinations of dielectric and magnetic materials. Isotropic scattering is important in a coaxial system only when the core is a good conductor, and it is shown by an electromagnetic solution that its magnitude is associated only with the radius of the metal core, any dielectric outer sleeve having negligible effect, provided that the overall radius is sufficiently small.