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

Abstract

The delta gap model and the frill magnetic current model are often used as models for the feed point in numerical calculations for cylindrical antennas. When the delta gap model with finite gap width is used, the electrical field produced by the magnetic current of the feed point may be included in the excitation function of the integral equation so that a solution separated into the external and internal surface currents of a hollow cylindrical antenna can be derived. Such an analytic solution, however, has been obtained only for the case in which the cylindrical antenna has infinite length or is placed between two parallel conductive plates. This paper considers a cylindrical antenna of finite length using the same integral equation. As the first step, a numerical calculation of the excitation function for the feed 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 properties of the excitation function are examined. As the next step, the cylindrical antenna is numerically analyzed by the method of moments. In all of these analytical procedures, the current is represented by piecewise sinusoidal functions on the surface of the cylinder, and the Galerkin method is applied. The convergence of the input admittance thus obtained is compared to the results of various other methods, such as point matching without considering the magnetic current at the gap (approximation by the two-dimensional surface current and the one-dimensional axial current), and approximation of the axial current by the frill magnetic current feed model. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(3): 65–76, 2001