Direct Evaluation of Complex Permittvity from Transmission Line Discontinuity Measurements

A new way to determine the complex permittivity of liquid or solid dielectric material samples is proposed. The method makes use of a discontinuity in a rectangular waveguide. The discontinuity is either a rectangular post or a cylinder containing a dielectric sample. A mode mode-matching method is first used to find the reflection and transmission coefficients from a knowledge of the permittivity. Graphs of ¿ vs S are presented and a simple analytical expression is then obtained to solve the inverse problem. This expression is easy to use and much more rapid than iterative methods. It can also be applied to other types of discontinuities.