A quasi-optics perturbation technique for measuring dielectric constants

A method of measuring dielectric constants of materials in sheet form by insertion in a Fabry-Perot resonator is described. By tilting the dielectric sheet at a slight angle with respect to the system axis, the reflected wave can be eliminated. The working formula for determing the dielectric constant then reduces to a simple linear relation involving the ratio of the mirror motion required to restore resonance to the thickness of the dielectric. The method is applicable at all frequencies where Fabry-Perot resonators can be used and for materials with loss tangents less than one. A table of measured values of common dielectrics is presented for 143 Gc/s and 343 Gc/s.