The measurement of the permittivity of sheet materials at microwave frequencies using an evanescent waveguide technique

Based on a method first proposed by Barlow (1962) the paper discusses how the complex permittivity of a sheet material can be determined by measuring the
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and frequency change produced by a sample when it is placed in a circular evanescent waveguide which is coupled to a resonant cavity. The method appears to be satisfactory for dielectric materials with loss tangents above about 0.01. Measurements on two mixtures of polystyrene and carbon, taken at 9 GHz, are reported.