Machine Design

Smaller really is better

Last year MACHINE DESIGN reported that inventor Rob Vincent, an employee of the Physics Dept. at the Univ. of Rhode Island, had shrunk the size of dipole antennas, without compromising their performance.

Doubters of the claim were silenced recently when U.S. Navy tests gave similar results.

This March, Vincent and URI, with the help of the Naval Undersea Warfare Center and its antenna test range on Fishers Island, N. Y., put 14 versions of the Distributed Load Monopole (DLM) antennas through a battery of validation tests. The tests used the same methods and instrumentation as those for testing and certifying Navy antenna systems. The conclusion: smaller is better.

Vincent's Plano Spiral Top Hat 7-MHz antenna, for example, is half the size of a normal quarter-wave antenna operating at that frequency. The URI antenna gain matched that of the ideal quarter-wave antenna, and its bandwidth was nearly double. Such antennas have multiple uses, including military, marine, amateur radio communications and AM broadcasting.

The Top Hat DLM antenna — which incorporates a helix, a load coil, a capacitive top hat with radial spokes at the antenna top and a horizontal plane — had a gain nearly identical to an ideal quarter-wave antenna. Antenna bandwidth exceeded operating frequency by 5% and the antenna itself is about 30% the length of an ideal quarter-wave antenna. In addition, Vincent's DLM antennas with a standard helix and load coil were tested at various frequencies. All showed gains nearly equal to the ideal antenna with bandwidths of 3 to 10%. The antennas themselves are about 33 to 40% shorter than conventional designs.

Since last year's announcement, some 200 businesses and government agencies have sought information about the antennas for automotive, marine, and military applications. The technology is patent pending and Vincent has made the URI and its Physics Dept. partners that will benefit from any revenue his invention earns. URI is close to securing several license agreements as well, and has developed numerous prototypes.

The Navy's Fishers Island over-water range, the only one of its kind in the world, provides a better path for transmission and reception than over land. The far-field ground-wave antenna test range is capable of measuring performance of antennas over a frequency of 2 to 30 MHz. Gain measurements are done relative to an ideal quarter-wave monopole antenna. Industry often includes the center's data with products to assure customers of performance specs.

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