D. Dwyer, M. Havrilla, S. Dorey, M. Hastriter, and G. Simpson (USA)
2-D Stepped Waveguide Measurements, Electromagnetic Material Characterization, Modal Analysis _______________________________________________ * The views of the authors expressed in this article do not reflect the official policy of the U.S. Air Force, Department of Defense, or the U.S. Government.
Electromagnetic material characterization is the process of determining the complex permittivity and permeability of a material. Rectangular waveguide measurements involving frequencies greater than several giga-hertz require only a relatively small test sample. In an X-Band (8-12 GHz) waveguide, for example, sample dimensions in the cross sectional plane are only 0.9″ by 0.4″. However, for lower frequency applications waveguide dimensions become progressively larger. Consequently, larger quantities of materials are required leading to possible sample fabrication difficulties. Under these circumstances, a waveguide sample holder having a two-dimensional reduced aperture may be utilized to reduce the time and cost spent producing large precision samples. This type of holder, however, will cause a disruption in the waveguide wall surface currents, resulting in the excitation of higher order transverse electric (TE) and transverse magnetic (TM) modes. This paper will demonstrate how these higher-order modes can be accommodated using a modal analysis technique, thus resulting in the ability to measure smaller samples mounted in large waveguides and still extract the test sample’s constitutive parameters at the desired frequencies.
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