Gunn Diode
Understanding Gunn Diodes
Gunn diodes were one of the first solid-state microwave sources and remain important for simple, low-cost oscillators at mmWave frequencies. Their simplicity (no external feedback circuit needed) makes them ideal for applications where a single-frequency source with moderate power and moderate noise is required.
Gunn Diode Properties
- Frequency range: 10-300+ GHz depending on material and device length.
- Output power: 10-500 mW (fundamental mode). Less at harmonics.
- Noise: Moderate phase noise. Better than IMPATT, worse than PLL-synthesized sources.
- Tuning: Mechanical (cavity tuning) or varactor bias. Limited tuning range.
Applications
- Motion sensors: 10.525 GHz (X-band) door openers, security.
- CW radar sources: Low-cost mmWave sources for range measurement.
- LO sources: Laboratory and test equipment LOs at mmWave.
Frequently Asked Questions
What is a Gunn diode?
A Gunn diode generates microwave oscillations from the bulk negative-resistance effect in GaAs or InP. It produces milliwatts of power at frequencies from 10 to 300+ GHz. It is used for motion sensors, radar, and mmWave LO sources.
How does a Gunn diode oscillate?
When biased above a threshold, electrons in GaAs transfer to a low-mobility energy valley, creating a high-field domain that transits the device. The transit time determines the oscillation frequency. No external feedback circuit is needed; the device oscillates inherently.
Are Gunn diodes still used?
Yes, for cost-sensitive applications requiring simple mmWave sources: motion sensors, police radar detectors, automotive radar, and some test equipment. They are being displaced by GaN and SiGe MMICs for more demanding applications.