Phase drift effects in sampling microwave measurement systems

For the purpose of bounding sources of measurement uncertainty, we examine the effects of phase noise on measured wave-variables using sampling, downconvertor-based measurement systems. Utilizing an analytical description, we show that if the phase of the local oscillator is a time-varying quantity, then the downconverted signal appears as a phase-modulated signal. Furthermore, we discover that this error increases with increasing values of frequency and power level. We validate these claims with measurements. Finally, we propose a procedure for reducing this problem by employing nonlinear fitting routines.