An S-parameter measurement technique allows measurement of devices under test (DUTs), such as power amplifiers, which require a modulated power tone drive signal for proper biasing, in combination with a probe tone test signal, wherein both the modulated and probe tone signals operate in the same frequency range. The technique uses a stochastic drive signal, such as a CDMA or WCDMA modulated signal in combination with a low power probe tone signal. A receiver in a VNA having a significantly narrower bandwidth than the modulated signal bandwidth enables separation of the modulated and probe tone signals. VNA calibration further improves the measurement accuracy. For modulated signals with a significant power level in the frequency range of the probe tone signal, ensemble averaging of the composite probe tone and power tone signals is used to enable separation of the probe tone signal for measurement.
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