Measurement Error of Temperature Coefficient of Resonant Frequency for Microwave Dielectric Materials by TE01δ-Mode Resonant Cavity Method

The temperature coefficient of resonant frequency of a microwave dielectric material (tau(f,s)) is defined as the tau(f) of an ideal resonant system that is homogeneously filled with this material, while it is usually measured as the tau(f) of a nonideal resonant system (tau(f),(r)) such as a cavity dielectric resonator. In the present work, finite element analysis is used to investigate degrees the measurement error of tau(f,s) by TE01 delta-mode resonant cavity method, for which the sample is placed on a support and far from the cavity walls. Several error sources contribute to the total measurement error, which is usually several ppm/C and decreases with the dielectric constant of the sample (epsilon(r,s)). Besides, the measurement error is strongly dependent on the cavity size. In comparison, the measurement error is much lower and usually within 1 ppm/degrees C for TE011-mode parallel plate method, where the sample is clamped between two metal plates. It is suggested to measure tau(f,s) by TE011-mode parallel plate method but not by TE01 delta-mode resonant cavity method if tau(f,s) is treated as tau(f,r), especially when epsilon(r,s) is low and high measurement accuracy is needed. If TE01 delta-mode resonant cavity method is used to measure tau(f,s), the result must be corrected with the aid of numerical calculation to improve the measurement accuracy.