We report on the development and characterization of novel 4.596 GHz and 6.834 GHz microwaveudfrequency synthesizers devoted to be used as local oscillators in high-performance Cs and Rb vapor-cell atomic clocks. The key element of the synthesizers is a custom module that integrates a highudspectral purity 100 MHz oven controlled quartz crystal oscillator frequency-multiplied to 1.6 GHzudwith minor excess noise. Frequency multiplication, division, and mixing stages are then implementedudto generate the exact output atomic resonance frequencies. Absolute phase noise performances of theudoutput 4.596 GHz signal are measured to be −109 and −141 dB rad2/Hz at 100 Hz and 10 kHz Fourierudfrequencies, respectively. The phase noise of the 6.834 GHz signal is −105 and −138 dB rad2/Hzudat 100 Hz and 10 kHz offset frequencies, respectively. The performances of the synthesis chainsudcontribute to the atomic clock short term fractional frequency stability at a level of 3.1 ×10−14 forudthe Cs cell clock and 2 ×10−14 for the Rb clock at 1 s averaging time. This value is comparable withudthe clock shot noise limit. We describe the residual phase noise measurements of key componentsudand stages to identify the main limitations of the synthesis chains. The residual frequency stabilityudof synthesis chains is measured to be at the 10−15 level for 1 s integration time. Relevant advantagesudof the synthesis design, using only commercially available components, are to combine excellentudphase noise performances, simple-architecture, low-cost, and to be easily customized for signaludoutput generation at 4.596 GHz or 6.834 GHz for applications to Cs or Rb vapor-cell frequencyudstandards.
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