The Sapphire Whispering Gallery Mode Resonator technology enables the design of microwave oscillators presenting exceptional short term frequency stability. The resonator consists in a Al2O3 monocrystal disk where the electro-magnetical field is efficiently confined thanks to a process analog to the optical total reflection. Due to the low value of the sapphire dielectric losses, Q-factors as high as 200 000 at the ambient temperature and better than 10 millions at 77 K is currently obtained. The sapphire resonator constitutes then an ideal frequency reference that can be inserted in an oscillator loop. At the Laboratoire de Physique et de Métrologie des Oscillateurs, we implemented several sapphire resonator oscillators operating at the ambient temperature and at 77 K. We proposed original solutions to solve the main difficulties arising from the sapphire resonator, i.e. the large number of spurious resonances and the large temperature sensitivity.
