Sapphire resonators + SiGe transistors based ultra low phase noise microwave oscillators

This paper reports on ultra-low phase noise microwave oscillators combining a room temperature high-Q whispering gallery mode (WGM) sapphire resonator and an ultra-low phase noise SiGe HBT based amplifier. An original symmetrical duralumin cavity has been designed in order to improve the thermal behavior of the resonator. Coupled to a high-precision electronic temperature controller, the structure presents a sensitivity to thermal fluctuations of -0.05 ppm/K. The non-linear and noise modelling of different microwave SiGe amplifiers have been realized in order to compute and optimize their phase noise performances. An original double stage amplifier, whose phase noise performances are very close of those of a single stage one, has been designed for X-band applications. C-band oscillators phase noise as low as -42 dB.rad².Hz¹at 1 Hz Fourier frequency and -135 dB.rad².Hz¹ at 1 kHz offset have been measured. X-band oscillators simulated phase noise results foresee very encouraging results