Design and metrological features of microwave synthesizers for atomic fountain frequency standard

In this paper we describe the improved redesign of the microwave frequency synthesizers for Laboratoire National d´Essais-Systemes de Reference Temps-Espace (LNE-SYRTE) atomic fountains. The synthesizers use a cryogenic oscillator to generate both Cs and Rb hyperfine frequencies based on a new distribution frequency of 1 GHz. The main metrological features (phase noise, long-term phase stability, and spectral purity) of the synthesizers have been measured in situ connected to an atomic fountain and are compatible with an accuracy goal of 10^-16 for the atomic fountains. The simultaneous test of two different synthesizers on the FO2 atomic fountain at the 10^-16 level also is reported