Date of Award

Spring 2002

Project Type

Dissertation

Program or Major

Engineering: Electrical

Degree Name

Doctor of Philosophy

First Advisor

Kondagunta U Sivaprasad

Abstract

As antenna sizes on portable wireless devices decrease to the dimensions of the device itself and to that of the operating wavelength, the system begins to operate in the near-resonant frequency range. Currently, a straightforward synthesis approach for determining optimal antenna placement within such near-resonant range systems does not exist. Previously, characteristic mode analysis had only been applied to systems with constant geometry that operated in the near-resonant range and the system had constant characteristic modes independent of the probe location. Successful application of characteristic mode analysis to radiating systems with a constant characteristic mode response suggest that a similar technique may be useful for antenna placement in systems that exhibit a variable characteristic mode response to antenna position.

In this research, we investigate system characteristic mode response to variable antenna placement in systems operating in the near-resonant frequency range where the dimensions of the antenna and wireless device are both comparable to a wavelength. To achieve this, new characteristic mode software was developed and a number of dynamic systems composed of a driven dipole antenna positioned close to either a wire or planar arrangement of parallel wires, simulating the antenna/wireless device system, were studied and their computational and experimental results were obtained. The results clearly demonstrate, that as expected, the dominant system characteristic modes are dependent upon antenna position due to the interaction between the antenna and the device. Additionally, these results suggest that a knowledge of the isolated characteristic modes, the geometry of the antenna, and the non-driven portion of the structure may be sufficient to predict the behavior of the characteristic mode response of the system to an antenna repositioned above the non-driven structure. In conclusion, this work establishes the foundation for the development of an antenna placement algorithm for systems operating in the near-resonant range with variable antenna placement by examining the relationship between antenna position and the variation of the system characteristic modes.

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