OPEN-ENDED COAXIAL-LINE TECHNIQUE FOR THE MEASUREMENT OF THE MICROWAVE DIELECTRIC-CONSTANT FOR LOW-LOSS SOLIDS AND LIQUIDS

A system which enables fast and reliable measurements of the dielectric constant over continuous microwave frequency ranges for both solid and liquid low-loss materials is described. The main thrust of this work is the application of the open-ended coaxial-line probe technique, which has been used previously for soft biological materials, to low-loss solid samples. Using the instrumentation and procedure presented here, the dielectric constant for low-loss solids can be measured absolutely to +/-2%-3% with routine care. The uncertainty can be reduced by about a factor of 2 by averaging several measurements. It is also smaller for liquid samples. This application features the use of relatively simple and readily available microwave components. Also, it is shown that a simple empirical relationship can be used to obtain the bulk dielectric constant from samples of a material in the form of thin slabs. The experimental results which are presented here for kapton, Teflon, Coming glass No. 021 1, soda lime glass, magnesium oxide, sapphire, silicon, alumina, and lanthanum aluminate, as well as carbon tetrachloride, compare favorably with existing literature values.