An oscillator that uses a Dielectric Resonator as the frequency determining element, to produce signals with excellent signal stability, high Q and very low micro-phonics is called as Dielectric Resonator Oscillator (DRO). The resonant frequency of a DRO depends upon the physical dimensions of the dielectric material used, its shape - rectangle or disc and its dielectric constant. 

The frequency of these oscillators is generally fixed but slight mechanical or electrical tuning can be achieved by using a self-locking screw or an integrated Varactor diode.

When using Mechanical tuning, if you bring a tuning screw close to the dielectric resonator, the resonant frequency can be modified.

In Electrical tuning or Varactor tuning, the DRO is coupled to a microstripline connected to the varactor, resulting in mutually coupled resonant circuits. Variation in bias voltage dependent capacitance of the varactor, varies the resonant frequency.

Features of a DRO:

• High Q-factor.
• Excellent temperature stability.
• Low cost and small size.
• Low phase noise.

Comparison with other types of oscillators:

• They have better stability than free-running cavity oscillators, Gunn diode oscillators and VCOs.
• They have better power efficiency in comparison to other oscillators like Gunn oscillator and VCO
• They exhibit less power variation over temperature
• They have high frequency pulling factor as compared to other free running oscillators. Pulling is an oscillator’s sensitivity to VSWR changes.

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