New method of measuring low values of dielectric loss in the near millimetre wavelength region using untuned cavities

In the near millimetre wavelength region, which extends from 100 to 1000 GHz, low values of dielectric loss in a material can readily be measured by inserting a sample into an untuned cavity resonator. Most of the usual difficulties caused by reflection and standing waves are avoided by this method. This is demonstrated by some new measurements at 156 GHz on several polymeric materials whose low loss factors are of practical interest.