Design and realisation of a 100 MHz synthesis chain from an X-band reference signal

LPMO has undertaken the building of a cryogenic sapphire oscillator with the support of the french space and metrology agencies (CNES and BNM). The aim of this project is to provide a reference oscillator presenting short frequency stability better than 5.10^-14 in order to fulfill reference tests requirements for spatial and metrological applications. The cryogenic oscillator can operate on different frequencies ranging from 8 to 13 GHz depending on the sapphire resonator mode chosen as reference. The exact output signal frequency is not ´a priori´ known with a great accuracy due to the large relative uncertainties (of the order of 10^-4) affecting the resonator frequencies theoretical determination. Then a special synthesis chain has to be designed in order to transform the cryogenic oscillator performances to a reference signal whose frequency is fully compatible with most of time and frequency instrumentation. In this paper, we present the design, realization and preliminary tests of a synthesis chain generating a 100 MHz signal from an X-band reference. The performances of the two realized prototypes will enable to transform better than 5.10^-14 short term frequency stability.