Date of Award
Doctor of Philosophy (PhD)
Electrical Engineering and Computer Science
Jay K. Lee
Jun H. Choi
leaky-wave antenna, metamaterial transmission line, negative resistance, optic axis, rectangular waveguide, uniaxial medium
Two wave-guiding problems are treated in this work. The first part addresses the problem of a rectangular waveguide filled with a uniaxially anisotropic or uniaxial medium. Different orientations of the optic axis of the uniaxial medium are considered and the wave transmission and modal behaviors are investigated. When the optic axis is aligned with one of the coordinate axes, i. e., x, y, or z axis, the method of wave decomposition with respect to the optic axis orientation is proposed and the complete analytic solutions are presented and compared with conventional transverse-to-z solutions. When the optic axis is tilted but lying in one of the side wall planes, TE0n or TEm0 (transverse to z) modes are shown to be supported. Furthermore, the supported hybrid wave modes in these cases are numerically found from calculations using the proposed boundary condition matrix (BCM) method. Different from the conventional spectral domain calculation methods, the numerically found hybrid wave modes are expressed as a linear combination of ordinary and extraordinary waves. The algorithm is illustrated and numerical examples are given. The validity of the solution is verified by comparing its results with those of the aligned cases that are analytically solved.
The second wave-guiding structure is focused on a type of metamaterial realization. Analyses and experimental results of the negative resistance enhanced composite right/left-handed (NR-CRLH) transmission line are presented. As a demonstration of its unique amplitude and phase behaviors and its application, the detailed analysis of the structure is followed by an example of high-directivity leaky-wave antenna (LWA). In contrast to the conventional CRLH unit cell with via terminated stubs, the NR-CRLH unit cell is designed with negative-resistance (NR) terminated stub that compensates the power loss from the orthogonal direction with respect to the direction of guided-wave propagation. The NR is realized using the inverted common collector (ICC) configuration of an RF transistor, a common commercial product often seen for RF amplifier and oscillator applications. This implementation topology allows the active unit cell (AUC) to preserve all the CRLH properties including the unique dispersion relations, constant Bloch impedance in a broad operating frequency range, and bilateral operation. To highlight the advantages of the active metamaterial transmission line (TL), the NR-CRLH TL based LWA that permits the manipulation of the current distributions over the antenna surface is demonstrated. The NR-CRLH based active antenna allows the control of radiation performances including the patterns, beamwidth, and directivity. The measured results of the LWA prototype demonstrate enhanced directivity compared to the conventional CRLH LWA of the same lengths while minimally influencing all the preferable characteristics of full frequency scanning LWA.
Sun, Kepei, "Rectangular Waveguide Filled with Uniaxial Medium and Negative Resistance Enhanced Composite Right/Left-Handed Transmission Line" (2017). Dissertations - ALL. 814.
Available for download on Saturday, January 26, 2019