A system for measuring residual phase noise of a device under test (DUT) includes first and second signal sources, first and second receivers, and a processor. The first signal source generates a first signal to be input to the DUT as a stimulus signal and provides a second signal that is phase coherent with the first signal. The second signal source receives the second signal and generates a reference signal based on the second signal, which is phase coherent with the stimulus signal. The first receiver measures an output signal from the DUT responsive to the stimulus signal, and the second receiver measures the reference signal from the second signal source. The processor mathematically suppresses a carrier of the output signal by determining a difference between the measured output signal and the measured reference signal, and determines the residual phase noise of the DUT based on the difference.