Antenna Design Goes from Computer Straight to Ship

Strong agreement between prototypes and numerical models in earlier work, plus the pressing demands of time, resulted in a decision to rely on computer modeling performed at SwRI to design and locate high-frequency (HF) communications antennas on a group of Canadian warships. Under an upgrade and modernization program for Tribal class destroyers, a large, new satellite-communications antennas must be modified so that eight transmitter circuits, operating in the 2-30 MHz range, can attain an optimum transmission pattern. Originally, the system's performance was to be measured and evaluated using scale models, an approach that can predict performance on shipboard installation, but which is time-intensive. The demands of time made it necessary to modify the antennas as soon as possible to avoid the possibility of diminished radio performance. Therefore, results derived from the numerical modeling were applied directly to the shipboard system, avoiding altogether the intermediate step of scale modeling.

In earlier projects, the agreement of both scale and numerical models had produced sufficient confidence to depend on numerical modeling to produce transmission patterns and impedance measurements for the antennas to assist in final design and location decisions. Computer models of the same type of ship had been constructed using Numerical Electromagnetics Code (NEC) software to analyze a similar frequency range for direction finding (DF) antennas.

For a communications antenna, the ideal surface wave transmission pattern should be as near to circular as possible so that transmission is uniform in all directions over a wide bandwidth. Modeling antenna performance for a full sweep of frequencies, from 2-30 MHz, can be accomplished literally overnight using NEC, with the computer requiring minutes to plot each frequency being modeled. The result is roughly equivalent to that of a three-week testing regime using scale models. In addition, numerical modeling can predict and estimate some performance parameters, such as near field radiation strength above the ship's deck or interactivity among different antenna systems on the same ship, which neither shipboard nor scale-model tests could do as safely or as reliably.

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Summer 1998 Technology Today SwRI Publications  SwRI Home