RADIATION DUE TO A CONVEX CURVATURE DISCONTINUITY OF A DIELECTRIC-COATED PERFECT CONDUCTOR

Surface waves radiate energy at discontinuities in the curvature of th e guiding structure. By reciprocity, surface waves will be excited by plane waves incident upon such a discontinuity. Here, the problem of t he radiation of a surface wave on a hat dielectric-coated perfect cond uctor incident upon an abrupt change to a dielectric-coated cylindrica l conductor with a large radius of curvature is considered. The proble m is formulated as an integral equation over the aperture of the disco ntinuity. Since the change in curvature is modest, an approximate pert urbation solution to the integral equation is derived and the radiated field due to the discontinuity is found. This radiated field reduces to published results for an impedance surface approximation when that approximation is valid. The problem of mode conversion and associated radiation near higher mode cutoffs is also studied. It is found that n ear mode cutoffs, the higher order mode dominates the radiation patter n and causes the overall radiation pattern due to the discontinuity in curvature to be narrow and end fire. Away from cutoff, when all of th e propagating bound modes are more tightly bound to the surface, the r adiation pattern is less narrow and less end fire. For very tightly bo und modes the pattern is nearly uniform. For dielectrics characterized by small permitivities, the changes in radiation pattern should be me asurable.