Phase noise of signal generators with multichannel digital synthesizers

Abstract

Wide use of a direct digital synthesizer (DDS) and digital to analog converters (DAC) in digital antenna arrays permits for fast modulation parameters variations and beam positioning, and also improves the quality of beam forming due to high accuracy of signal generation. However, any systematic and random phase deviations of array channels not only lead to distortion of radiation pattern but also cause deterioration of signal processing at receiver end. Phase noise is one of critical parameters of such systems. Traditional theory and empirical methods assumes small or zero phase deviation of phase of channel output signal when combining these signals. We have proposed the model in which coupling of AM and PM noise persists for any arbitrary phase deviation of channels in multistage circuits comprising multichannel digital synthesizers. Absolute phase noise measurements of combined DACs outputs for zero phase offset and antiphase modes with two values of DAC output signal amplitude difference permit for estimation of residual phase noise of DAC and clock receiving and distribution circuitry and demonstrate good compliance of results of calculation.