Analysis of an arbitrarily excited – loaded dipole antenna with a derived expression for the field in the feed gap

Abstract

Expressions are derived for the aperture time-harmonic electromagnetic fields in the feed gap of a solid infinite antenna along the z axis. This is done by matching the Fourier representation of the external electromagnetic fields to the Fourier representation of the fields inside the feed gap. The Fourier expansion is built up by superposition of basic sets of [Formula: see text]-independent cylindrical waves that are obtained from the solution of Helmholtz equations governing z-directed electric Hertzian potentials. The z-directed electric field, which is in the form of a Fourier–Bessel series, is then used to calculate the input admittance of an infinitely long antenna excited across a practically wide feed gap. This is done using the axial field discontinuity method, which is based on the Wiener–Hopf type analysis. The method treats the dipole antenna as a series combination of longitudinal electric-field surface functions that may exist owing to feeding and (or) loading. A comparison is made between the radiation characteristics based on the Fourier-series field inside a wide gap and those obtained using the delta-function excitation for a finite-length dipole antenna with various excitation and loading conditions.