EFFICIENT ELECTROMAGNETIC MATERIAL CHARACTERIZATION VIA 2-D RECTANGULAR WAVEGUIDE REDUCTION

摘要

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.