Evaluation of the complex permittivity of layered dielectric materials with the use of an open-ended coaxial line

Open-ended co-axial lines have been investigated extensively for their application in the nondestructive characterization of materials. However most of these studies are based on the assumption that the sample medium is large enough to contain the aperture fields within its volume. A few recent reports do consider a finite thickness of the material in their formulation. However, these models still suffer from one or the other limitation. In the present work, we compare the performance of a variational expression for the aperture admittance, as well as a full-wave formulation based on the method of moments, with those of experimental data. A procedure is then developed for the characterization of stratified dielectric samples with the use of this formulation. The results thus obtained are compared with those generated by other techniques. Limitations of the procedure are summarized. (C) 1996 John Wiley & Sons, Inc.