Dielectric Resonator
Understanding Dielectric Resonators
Dielectric resonators offer a unique combination of high Q, small size, and temperature stability that makes them ideal for precision frequency sources and high-performance filters. A DR at 10 GHz may be only 5 mm in diameter, yet achieve Q values rivaling much larger metallic cavities.
DR Properties
- Dielectric constant: 20-100 (high). Concentrates fields, reducing size.
- Q factor: 5,000-50,000 unloaded. Limited by dielectric tan delta.
- Temperature stability: Near-zero temperature coefficient of frequency available (0 ppm/C).
- Size: DR diameter approximately lambda_0 / sqrt(er). Very compact at er=40.
Applications
- DRO (DR Oscillator): Low phase noise source, -100 to -120 dBc/Hz at 10 kHz offset at 10 GHz.
- DR filter: Multi-pole bandpass filters for satellite transponder multiplexers. Q of 10,000-30,000.
- DR antenna: The DR can radiate efficiently, serving as a compact wideband antenna.
Frequently Asked Questions
What is a dielectric resonator?
A DR is a ceramic element with high dielectric constant (20-100) that traps electromagnetic energy by total internal reflection. It achieves very high Q (5,000-50,000) in a compact size. Used in DROs (low phase noise sources) and high-Q filters.
What is a DRO?
A Dielectric Resonator Oscillator couples a DR to a negative-resistance device (transistor). The high Q of the DR stabilizes the oscillation frequency, providing very low phase noise. DROs are the preferred fixed-frequency source from 2-40 GHz.
How small is a dielectric resonator?
DR diameter is approximately lambda_0/sqrt(er). At 10 GHz with er = 40: diameter = 30mm/6.3 = 4.7 mm. Much smaller than a metallic cavity at the same frequency. This compactness is a key advantage over cavity resonators.