Theoretical Study of Finite Dielectric-Coated Cylindrical Antenna

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Abstract
A finite cylindrical antenna which is imbedded in a concentric dielectric rod has been investigated by employing a rigorous formulation. When the antenna is relatively short, a numerical method is used; when the antenna is long, the Wiener‐Hopf technique is applied. In both cases the input admittance and the current distribution are obtained. It is found that the input conductances are larger than for the corresponding free‐space antennas, the field patterns tend to be more broadside and, as the antenna gets longer and longer, the locus of the input admittance becomes a circle instead of converging to one point as it does for a bare cylindrical antenna. The first method is applicable regardless of the thickness of the antenna and the dielectric rod; the second method can be applied only to a sufficiently long antenna. The minimum length is determined by the thickness of the dielectric rod. This study is limited to thin antenna in rather thick dielectric cylinders. However, the dielectric rod is still not thick enough to support a transverse magnetic (T.M.) mode.

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