Modification to the scattering behavior of a sphere by reactive loading

The scattering of a plane electromagnetic wave by a metallic sphere loaded with a circumferential slot in the plane normal to the direction of incidence is investigated. The slot is assumed to be of small but nonzero width with a constant electric field across it, and under these assumptions the analysis is exact. The field scattered in any direction is then obtained by the superposition of the field diffracted by an unloaded sphere, and that radiated by an excited slot at the position of the load, with the radiation strength of the slot related to the loading characteristics in the combined problem. Numerical results are presented, primarily for the case of back scattering, and these are compared with experimental measurements made using a sphere with an equatorial slot backed by a radial cavity of adjustable depth. The agreement is excellent.