Wire antenna near extended metal bodies

Abstract

The analysis of the properties of the wire antenna placed by an electrically large (with respect to the wavelength) metallic body is a hot problem in antenna engineering. Antenna mounting on the ship’s desk edge (on the bracket) and antenna mounting near a metallic body flush with it (as a conform component) are the examples. These particular problems are the special cases of the ones of the dipoles placed at the edge of the wedge and along a trough of finite length.

The research method in which the metallic body surface is substituted by a wire-grid model appears promising. In this formulation the problem is reduced to the computation (by the moment method) of the current distribution in a wire-grid model containing the arbitrarily placed wire segments. Determining currents along the wires makes it possible to calculate all electrical characteristics of the antenna.

Under the substitution of the continuous metallic surface to a wire-grid model the correct choice of the wire location and their number has the primary importance for the reduction of computation expenses. The wires of the model should be aligned along the most probable directions of the surface current flowing. The interval between the wires should not be more than 0.08λ, where λ is the wavelength.

The analysis of the properties of the monopole placed near the circular metallic cylinder of finite length shows that the minimum cylinder height, for which the antenna characteristics coincide with the characteristics of the same antenna placed near infinitely long cylinder, is equal to L₀ = L + 0.25 λ, where L is the monopole height. That’s why it is advisable to replace large metallic surface by the wires of length L₀.

By the example of these particular problems it is demonstrated that the proposed method makes it possible to take into account the structure details and provide the high accuracy within acceptable computation time.