Machine Design

Ultrasmall, ultrawideband antennas

A novel phased-array antenna could dothe job of five conventional antennas,say engineers at the Georgia TechResearch Institute. Their FragmentedAperture Antenna, a computerdesignedplanar system, gives a 33 to1 bandwidth — well beyond the 10 to1 ratio of conventional designs.

GTRI researchers James Maloney (left) and Paul Friederich display prototype panels of a new ultrawideband antenna. Georgia Tech photo by Gary Meek

A novel phased-array antenna could do the job of five conventional antennas, say engineers at the Georgia Tech Research Institute. Their Fragmented Aperture Antenna, a computer designed planar system, gives a 33 to1 bandwidth well beyond the 10 to1 ratio of conventional designs.Bandwidth, by this definition, is a measure of how much frequency can vary in an antenna and still have it maintain an acceptable signal. Numerically, it is the upper frequency divided by the lower. It may be possibleto extend that range to 100 to 1 for use in radar and communications systems, says the group.

The GTRI design takes advantage of an electronic interaction between antenna elements called "mutual coupling." For years, antenna designers have tried to minimize this interaction."But detailed computer modeling shows that antennas with electrically connected elements have an extremely wide bandwidth," explains research engineer Jim Maloney. "What everybody used to avoid was actuallythe silver bullet that makes this work."Mahoney credits more powerful computers with the discovery.

The 33 to 1 antennas are flat and include three layers of metal foil. A backplane of foam and partially conductive films covers planar laminated PC boards that sit behind the antenna. The backplane reflectsel ectromagnetic energy and protects the circuitry. Simplified radiating structures means supporting electronics become the driver of overall cost, explain researchers.

A prototype that works down to300 MHz is 16-in. square and about 3-in. thick, substantially smaller than conventional "egg-crate" antennas. The flat design conforms to surfaces so it is easy to integrate. Potential applications include military ships, aircraft, vehicles,and tents, even wearable antennas that sew into uniforms.

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