Ultrasmall, ultrawideband antennas

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

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.Bandwidth, by this definition, is ameasure of how much frequency canvary in an antenna and still have itmaintain an acceptable signal.Numerically, it is the upper frequencydivided by the lower. It may be possibleto extend that range to 100 to 1 for usein radar and communications systems,says the group.

The GTRI design takes advantage ofan electronic interaction betweenantenna elements called "mutualcoupling." For years, antenna designershave tried to minimize this interaction."But detailed computer modeling showsthat antennas with electricallyconnected elements have an extremelywide bandwidth," explains ResearchEngineer Jim Maloney. "Whateverybody used to avoid was actuallythe silver bullet that makes this work."Mahoney credits more powerfulcomputers with the discovery.

The 33 to 1 antennas are flat andinclude three layers of metal foil. Abackplane of foam and partiallyconductive films covers planarlaminated PC boards that sit behind theantenna. The backplane reflectselectromagnetic energy and protects thecircuitry. Simplified radiating structuresmeans supporting electronics becomethe driver of overall cost, explainresearchers.

A prototype that works down to300 MHz is 16-in. square and about3-in. thick, substantially smaller thanconventional "egg-crate" antennas. Theflat design conforms to surfaces so it iseasy to integrate. Potential applicationsinclude military ships, aircraft, vehicles,and tents, even wearable antennas thatsew into uniforms.