The measurement of dielectric constants in a Fabry-Perÿt resonator

A resonant method for the accurate measurement of low-loss dielectric materials is described in which pieces of the material are themselves used to form the resonator. The arrangement is that of the Fabry-Perÿt interferometer, which can be used with either plane or bounded waves. The measurement involves the substitution of a half-wave piece of the material into a resonant arrangement of quarter-wave pieces. ¿r(1 ¿ j tan ¿) is evaluated from the Q-factors and the difference between the insertion losses. Any desired sensitivity can be obtained by using additional quarter-wave pieces. The method has been checked by making measurements in 3 cm waveguide on titanium-dioxide ceramic and on polystyrene. The loss tangents for both materials were found to be of the order of 0.0005 with an experimental accuracy of ±30%. Only three pieces of the titanium dioxide were required to obtain this accuracy.