Date of Award

5-14-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical Engineering and Computer Science

Advisor(s)

Jay Lee

Keywords

Antennas, Electrically Small, Matching Network, Non-Foster, Tunable, Wideband

Abstract

This dissertation reviews the application of non-Foster circuits for wideband antenna matching, and introduces a novel, rapid means of “tuning” the circuit to accommodate variations in antenna loadings. The tuning is accomplished via the judicious addition of a common transistor.A detailed literature search is provided, and non-Foster circuits are discussed in detail, including the myriad of implementations with focus on tuning. A comparison between different tuning methods is presented. The novel tuning method is evaluated via the normalized determinant function to ensure stability. Evaluations include simulations using commercially available software and experimentation to ensure not only stability but also that noise added by the active circuitry is manageable. Wideband stable operation is confirmed by pairing the tunable non-Foster matching circuit with an electrically small, resistively loaded dipole, and performance gains are demonstrated using the tunability feature. The resistively loaded dipole alone demonstrates reasonable performance at higher frequencies, but performance degrades considerably at lower frequencies, when the dipole is electrically small. The tunable non-Foster circuit is shown to alleviate some of this degradation. Additionally, applications other than wideband antenna matching can benefit from tunable non-Foster circuits such as tunable filters and phase shifters, and these are discussed as well. Finally, practical limitations of non-Foster circuits are presented.

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Open Access

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