Waveguides and cavities with dielectric slab-loading that support uniform TEM modes

摘要

This dissertation provides a complete description of transverse electro-magnetic (TEM) waveguides and related resonant cavities so that they may be designed, constructed, and utilized with full knowledge of both their capabilities and limitations. A TEM waveguide consists of a rectangular waveguide containing dielectric loading slabs, configured to support propagation of TEM waves. TEM waveguides supply predictable, uniform electromagnetic fields suitable for a variety of applications, including microwave exposure, heating, and instrument calibration.;The primary design equations for the TEM waveguide are derived using a unique application of Snell's law. All possible modes of propagation and field distributions within the TEM waveguide are analyzed using closed-form transfer matrix and eigenvalue formulations. Measurements of cutoff frequency and several electric field distributions confirm the analysis. Secondary properties of the TEM waveguide, such as its characteristic impedance, are derived and measured. Additionally, coupling and termination strategies for TEM waveguides are examined.;A TEM waveguide is used as a sample exposure chamber to demonstrate its applicability. Both the simulations and measurements show that, while a waveguide may be designed for TEM operation at a particular frequency, the electrical properties of any sample inserted into the guide may profoundly affect the electromagnetic field distribution, resulting in non-TEM exposure. This research establishes that the design of a TEM waveguide must account for its intended application; otherwise, the system may not provide the desired TEM exposure.;This work also introduces a resonant structure called the quasi-TEM cavity. The structure consists of a rectangular cavity lined with dielectric loading slabs. When operated at its first resonant frequency, this structure may be applied in situations that require a compact exposure chamber with a nearly uniform field distribution. Adaptations of the theory used to analyze the TEM waveguide provide accurate descriptions of the cavity's resonant frequencies and electromagnetic field distributions, verified by experiment.