Cs frequency synthesis: A new approach

This paper describes a new approach to synthesizing the Cs hyperfine freque ncy of 9.192 GHz that is designed to be sufficiently rugged for use in spac e, specifically for the Primary Atomic Reference Clock in Space (PARCS) pla nned for the International Space Station, as well as ground applications. T his new approach requires no narrow band filters or frequency multiplicatio n, and the primary source of cooling is conduction. Instead of frequency mu ltiplication, it uses a custom regenerative divider stage followed by two c ommercial binary dividers and several mixing stages. A fractional frequency step of 2 x 10(-17) is achieved by mixing the output of a 48-bit numerical ly controlled oscillator with the microwave signal. Preliminary tests on th e new synthesizer design indicate an internal fractional frequency stabilit y of 1 x 10(-15) at 10 s and 1 x 10(-18) at 1 d, dominated by the daily roo m temperature variations. The phase and amplitude noise are similar to our previous designs that used frequency multiplication and narrow band filters . The temperature coefficient is less than 0.2 ps/K.