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University of Hawaii

Electrical Engineering

Design and Optimization of Electrically Small Antennas for High Frequency (HF) Applications

Date: 2014-09-16           Add to Google Calendar
Time: 9:00 a.m. ** NOTE DATE/LOCATION CHANGE **
Location: Holmes Hall 287
Speaker: James Baker, candidate for PhD, advisor: Dr. Magdy Iskander

This dissertation presents a new design approach for the development and optimization of electrically small antennas (ESA) suitable for high frequency (HF) radio communications and coastal surface wave radar applications. For many ESA applications, the primary characteristics of interest (and limiting factors) are lowest self-resonant frequency achieved, input impedance, radiation resistance, and maximum bandwidth achieved. The trade-offs between these characteristics must be balanced when reducing antenna size in order to retain acceptable performance. Traditional methods of size reduction, including top-loading and folding, were employed to reduce antenna design ka below 0.5. When top-loading was applied, antenna Q was reduced by a factor of 10 with a corresponding increase in input resistance by a factor of 3. When folded arms were applied to various designs, Q was decreased by a factor of 2 with a corresponding increase in input resistance by a factor of 8. Antenna size was further reduced using innovative methods to more fully utilize the entire enclosed volume. Various methods for optimizing performance were investigated, including the utility of fractal geometries and genetic algorithms. The performance characteristics of fractal geometries were analyzed and compared with non-fractal designs of similar height, total wire length, and ka. Genetic algorithms were developed for optimizing antenna designs and used in custom programs, including a new cost function for better comparison of ESA performance. Several unique antenna designs were simulated and experimentally verified in field testing. Antenna performance was analyzed using Numerical Electromagnetics Code (NEC), an antenna modeling application based on the numerical solution of integral equations using the Method of Moments (MoM). Custom software applications were developed using National Instruments LabVIEW to extract impedance and other parameters from NEC output files for calculating performance values such as Q and effective radius. These applications were validated by reproducing published results for a variety of antenna designs. Experimentation was conducted using full-size prototypes with performance measured using vector network analyzers and HF transceivers. Experimental performance measurements were reproduced in simulation models with a high degree of correlation. Successful two-way radio communications were established with amateur radio stations around the world using prototype antennas.

Biography: James Baker received a B.G.S degree in history from Kansas University in 1978, a B.S. degree in electrical engineering from the University of Utah in 1995, and an M.S. degree in systems engineering from Johns Hopkins University in 2004. Between 1979 and 1991 he served in the United States Marine Corps, from 1995 to 1997 he worked as an applications engineer for National Instruments, from 1998 to 2008 he worked as an aircraft test engineer at Patuxent River Naval Air Station, and from 2008 to 2010 he worked as a research specialist at the Hawaii Center for Advanced Communications (HCAC). Since 2010 he has been working as senior principal engineer for the Test & Certification Group, Marine Corps Tactical Systems Support Activity, Camp Pendleton, CA. His research interests include HF antennas, electrically small antennas, and fractal geometries. During his studies, James has published five journal papers and twelve conference papers.