Numerical analysis of a cylindrical antenna with finite gap excitation based on realistic modeling

The delta gap model and the frill magnetic current model are often used as models for the feed point in numerical calculations for cylindrical antenna s. When the delta gap model with finite gap width is used, the electrical f ield produced by the magnetic current of the feed point may be included in the excitation function of the integral equation so that a solution separat ed into the external and internal surface currents of a hollow cylindrical antenna can be derived. Such an analytic solution, however, has been obtain ed only for the case in which the cylindrical antenna has infinite length o r is placed between two parallel conductive plates. This paper considers a cylindrical antenna of finite length using the same integral equation. As t he first step, a numerical calculation of the excitation function for the f eed point is considered. The excitation function is derived numerically by a method based on mode expansion in cylindrical coordinates and by a method based on the electric vector potential of the magnetic current ring. The p roperties of the excitation function are examined. As the next step, the cy lindrical antenna is numerically analyzed by the method of moments. In all of these analytical procedures, the current is represented by piecewise sin usoidal functions on the surface of the cylinder, and the Galerkin method i s applied. The convergence of the input admittance thus obtained is compare d to the results of various other methods, such as point matching without c onsidering the magnetic current at the gap (approximation by the two-dimens ional surface current and the one-dimensional axial current), and approxima tion of the axial current by the frill magnetic current feed model. (C) 200 0 Scripta Technica.