In precision measurements, phase noise can introduce measurement errors that reduce the precision and accuracy of the system. Due to the presence of phase noise, the phase of the signal changes over time, and this change can interfere with the stability of the measurement results, leading to measurement errors.

Frequency converters are often used in the transformation of frequency. The basic function of an RF frequency divider is to reduce the frequency of the input signal to the output frequency corresponding to its crossover ratio. In this process, the phase information of the signal is also affected. Due to the non-ideal characteristics of the internal circuitry of the frequency divider, such as component non-linearity, thermal noise, current noise, etc., random changes in the phase of the output signal can occur, resulting in phase noise.

The figure below shows the single sideband phase noise plot of a commercial 10GHz crossover, which is seen to be around -155dBc/Hz in the region beyond 100kHz off the carrier.

Taking the Tianqiong TQSRO-R10 sapphire signal source as a reference, the reference generates a 10GHz signal with ultra-low phase noise, which is dichroic through a commercial frequency divider, and is tested with a Rhodes phase noise meter. The output phase noise is shown in the figure below, where the blue line is the phase noise of the 10GHz signal and the yellow line is the phase noise of the 5GHz signal.

Phase noise change after crossover

It can be seen that in this case, the frequency divider can improve the phase noise at the near end, while the phase noise beyond 10kHz away from the carrier is deteriorated due to its own noise floor.