On the τ_f measurement of microwave dielectric ceramics

As a key parameter of microwave dielectric ceramics, the temperature coefficient of resonant frequency (τ_f) determines the temperature stability of microwave dielectric ceramics and relevant microwave devices. The τ_f of a microwave dielectric ceramic is typically calculated from the measured resonant frequencies of the system, consisting of the ceramic sample plus other dielectric elements, at two temperatures ∼60 – 70 °C apart. This measurement process assumes that τ_f is a constant; however, it is generally temperature-dependent based on both theoretical and experimental results. Furthermore, the as-measured τ_f is actually the τ_f of the dielectric resonator system, which is different from that of the sample itself. In this paper, these two overlooked problems during τ_f measurement are discussed in detail, and suggestions are given to avoid their possible misleading consequences and thus ensure the reliability of τ_f measurements.