New method of measuring low values of dielectric loss in the near millimetre wavelength region using untuned cavities
Abstract
In the near millimeterwavelength region, low values of dielectric loss in a material can be readily measured by inserting a sample into an untuned cavity resonator. The highQ values of the cavities give the technique great sensitivity to low values of loss tangent and, in contrast to other techniques, place very few restrictions on the shape, size, and position of the sample. The technique is demonstrated by measurements at 156 GHz on several polymer materials whose low loss factors are of practical interest. It is shown that the loading of an untuned cavity by a solid sample of low loss is proportional to its absorption cross section, which is the product of its volume and its linear absorption coefficient in the trivial case of n = 1. In the usual case of n greater than 1, reflection at the boundaries will affect the measured cross section in a way that has been investigated experimentally for a number of shapes, both simple and complex, and theoretically for the specific cases of slabs and cubes.
 Publication:

IEE Proceedings: Physical Science Measurement and Instrumentation Management and Education Reviews
 Pub Date:
 November 1980
 Bibcode:
 1980IPPSM.127..535L
 Keywords:

 Cavity Resonators;
 Dielectric Properties;
 Electrical Measurement;
 Microwave Resonance;
 Millimeter Waves;
 Q Values;
 Absorption Cross Sections;
 Absorptivity;
 Energy Dissipation;
 Microwave Oscillators;
 Polymers;
 Q Factors;
 Instrumentation and Photography