Microwave Measurements of the Loss in Low Loss Dielectrics

Abstract

A technique has been developed which offers a significant improvement in the measurement of the loss in low loss materials having dielectric constants ≥4. The device consists of a cutoff section of circular waveguide concentrically loaded with a rod of the dielectric to be measured. The principal advantage of the technique is that by proper choice of sample and waveguide dimensions one can minimize the effect of resistive losses due to the metal walls. This is achieved by using the sample rod essentially as a section of dielectric waveguide in which the major fraction of the energy is confined to the rod. Both the reduction in wall losses and the simplicity of the design make the use of the waveguides fabricated from lower conductivity, high melting point metals much more attractive for measurement of low loss ceramic dielectrics at high temperatures. Results are reported for single crystal sapphire.