Radiation and guided waves

Abstract

An analysis is carried out of the field radiated by a dipole in an arbitrary medium separated from others by parallel plane interfaces. The resulting solution in the form of a contour integral is then examined in relation to the intrinsic properties of the media involved and the position of the antenna. The solution is obtained by splitting the integral into pole residues and branch-cut-integral; the latter is evaluated by developing it into a suitable asymptotic series. It is shown that depending on conditions modal-type propagation can take place between the parallel interfaces in addition to radiation field. Distinction is drawn between proper modes, quasimodes, surface waves, leaky waves and radiation field. All these waves are needed in the complete description of the field, and their relative intensities are evaluated. Extreme cases are considered in which the media involved pass into good conductors on one hand and perfect dielectrics on the other. Surface waves appear as a particular case of the more general problem considered (or as a part of the solution) and they form just one piece of a complete jig-saw, though under certain specifically simple conditions these waves appear to have some rather unique properties. In general (with the exception of perfectly conducting tubular waveguides) it is shown that no mode can exist on its own but rather in conjunction with other modes (including surface waves) and the radiation field.