What is a DRO - Dielectric Resonator Oscillator?

An oscillator that uses a Dielectric Resonator as the frequency determining element, to produce signals with excellent signal stability, high Q and very low phase noise is called a Dielectric Resonator Oscillator (DRO). The DRO consists of a hollow metallic enclosed tube that exhibits resonance behavior when excited by an electromagnetic field. 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. DROs are typically constructed using low loss materials that have a high dielectric constant, to ensure that most of the electromagnetic fields will be contained within the dielectric medium.

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.

DROs are ideal for tuned amplifiers, frequency meters, antennas, bandpass filters, bandstop filters, frequency-selective limiters, and phased equalizer applications.

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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