Date of Graduation


Document Type


Degree Type



Statler College of Engineering and Mineral Resources


Lane Department of Computer Science and Electrical Engineering

Committee Chair

James E. Smith.


As with the fast-paced development of the communication industry, antennas have become an indispensable part of daily life. However, everyone may have experienced the malfunction of a communication system or radio due to a nearby human body or building or automobile. Then comes the question of how adjacent objects influence the antenna. This thesis has concentrated on the study of these effects on the impedance of the CTHA (contrawound toroidal helical antenna).;The results of this study indicate the CTHA's input impedance changes as a damped sinusoid function of the distance between it and the metallic ground plane. For equivalent distances between the antenna and the metallic ground plane, the CTHA's impedance has been shown to be less affected than the impedance of a vertical dipole, a horizontal dipole, or a horizontal loop antenna. This has been shown by both simulation and experiment and is demonstrated by the plot of the magnitude of the relative impedance change. It indicates that the CTHA will have a smaller increase of the SWR than the other antennas when foreign objects are in the vicinity of the antenna.;This study has also confirmed that NEC (numerical electromagnetic code) is an effective numerical tool for modeling dipoles and loop antennas. The inability for NEC to accurately model the CTHA seems to be caused by the inability to include effects of the core material with dielectric constant other than 1 of the CTHA. Another numerical method, XFDTD (X-window finite difference time domain method), has shown better accuracy in calculating the CTHA's impedance than NEC when comparing with the experimental results.