Phase-Noise Analysis of an X-Band Ultra-Low Phase-Noise GaN HEMT Based Cavity Oscillator

This paper reports on an ultra-low phase-noise oscillator based on a GaN HEMT monolithic microwave integrated circuit reflection amplifier and an aluminum cavity resonator. It is experimentally investigated how the oscillator´s phase noise depends on the cavity coupling factor, phase matching, and bias condition of the reflection amplifier. For the optimum bias and cavity position phase noise of -145 dBc/Hz and -160 dBc/Hz at offsets of 100 and 400 kHz, respectively, from a 9.9-GHz carrier frequency is reached. This is, to the best of the authors´ knowledge, a record in reported performance for any oscillator based on a GaN HEMT device. The optimum performance at 400-kHz offset corresponds to a power normalized figure of merit of 227 and compensating for finite efficiency in the reflection amplifier, the achieved result is within 7 dB from the theoretical noise floor, assuming a linear theory.