Basic Dielectric Resonator (DR) Material Properties
The most important material properties for a Dielectric Resonator (DR) are its dielectric constant (εr), Unloaded Quality Factor (Qu), and temperature coefficient of the resonant frequency (τf).
Dielectric Constant (εr)
The usual reason for choosing a DR as a resonating element is the size reduction afforded by the high εr of modern ceramics. But “dielectric constant” is a misnomer; not only does εr vary slightly for different temperature coefficient blends within the same material family, but lot-to-lot ceramic process variations cause εr to swing typically ±1 unit between lots. Within a given lot, the variation is much smaller. For example, the Trans-Tech, Inc. (TTI) catalog [reference 1] lists the εr of material D8371 as 35.5 ± 1.0.
TTI can help customers determine the proper resonator size for production (see “Ordering DRs to Frequency” on page 3). TTI measures the εr accurately using a Courtney fixture, as described in “Dielectric Constant Measurement” on page 2. TTI measures the εr of the ceramic lot, not of the individually-shaped DRs. Unless stipulated otherwise, TTI chooses a size for the test sample that resonates close in frequency to where the material is Qu specified.