FET vs. bipolar - Which oscillator is quieter

A comparison of bipolar transistors and GaAs FETs, in similar oscillator circuits, revealed significant differences in C-band noise behavior. The FET oscillators generated higher single sideband phase noise than their bipolar counterparts, and were much more sensitive to tuning losses. The evaluation pitted a high-quality bipolar transistor against two types of MESFETS; all devices were commercially available samples. Although the bipolar transistor is still the best performer, the FET oscillators show greater performance improvements: 14-dB compared with only 2-dB enhancement for the bipolar. Since phase noise is related to Q, the higher Q of the simpler bipolar oscillator circuit may explain the difference.