On the electrically thick monopole: Part I--Theoretical solution

A new integral equation is formulated for the current distribution of an electrically thick, cylindrical antenna which is driven by a voltage across a finite gap on an infinitely large ground plane. Compared to the conventional integral equation of Hallen, this equation has an additional source term which can be expressed in terms of both the radius of the antenna and the width of the gap. A numerical solution of the integral equation has also been obtained by a so-called "approximate product-integration technique" and the results have been compared with the experimental data of a monopole antenna driven by a coaxial transmission line over an infinitely large ground plane. When the circumference of the antenna is comparable to a free-space wavelength, the experiment verifies that the theoretical model with finite gap excitation describes the experimental situation more properly than either the conventional model of a delta-function excitation on both outside and inside surfaces of the antenna, or the King-Wu model of a delta-fanction excitation only on the outside surface.