Skip to Main Content
Improvements both in accuracy and speed are described for the technique of measuring the microwave dielectric properties of low-loss materials by using a dielectric rod resonator short-circuited at both ends by two parallel conducting plates. A technique for measuring the effective surface resistance Rs of the conducting plates is proposed to allow the accurate measurement of the loss tangent tan delta. By means of the first-order approximation, the expressions are analytically derived for estimating the errors of the measured values of relative permittivity epsilonr, tan delta, and Rr, for measuring the temperature coefficient of epsilonr, and for determining the required size of the conducting plates. Computer-aided measurements are realized by using these expressions. It is shown that the temperature dependence of Rs, should be considered in the tan delta measurement. The copper plates used in this experiment have the relative conductivity of 91.0+-2.7 percent at 20°C, estimated from the measured Rs value. For a 99.9-percent alumina ceramic rod sample, the results measured at 7.69 GHz and 25°C show that epsilonr,= 9.687+-0.003 and tan delta = (1.6+-0.2)x 10-5. The temperature coefficients measured between 25 and 100°C are 112x10-6/°C for epsilonr, and 23x10-4/°C for tan delta.