PHASE NOISE IN CRYOGENIC MICROWAVE HEMT AND MESFET OSCILLATORS

This paper addresses the influence of cooling on the phase noise of HE MT and MESFET oscillators. The initial measurements of the device dc c haracteristics and low frequency noise (0.1 kHz-100 kHz) under cooling give indications on the suitability of a given device for use in low phase noise cooled oscillators. Cooled pseudomorphic AlGaAs/GaInAs/GaA s HEMT's (PHEMT's) turn out to be particularly well-suited as they are free of collapse and they are free of g-r noise in the frequency rang e of interest. We report on 4 GHz oscillators operated at 110 K and fe aturing a phase noise below -100 dBc/Hz at 10 kHz from the carrier in spite of a very modest loaded Q (160). It is suggested that high tempe rature superconductor resonators could greatly enhance the spectral pu rity of PHEMT's oscillators.