Theory of the terminated insulated antenna in a conducting medium

The general problem of the insulated antenna in an isotropic homogeneous medium of infinite extent is reviewed under the assumption that the medium is sufficiently conducting to permit the application of coaxial line theory. The currents and associated electromagnetic fields for the completely insulated antenna are obtained and the directional properties of the latter explained by comparison with a collinear array. An antenna in which only a central portion is insulated, while the ends are bare, is analyzed in terms of the theories of the insulated and bare antenna, both when the structure is driven by generators at the junctions of the bare and insulated sections and when it is driven by an internal coaxial feeder in the manner of a sleeve dipole. Finally, the center-driven insulated antenna with bare ends is investigated and its field is compared with that of the antenna driven at the junctions of the bare and insulated sections.