Distortion measurements with a vector network analyzer

A distortion measurement method uses alternative measurements to determine the distortion of a DUT, depending on the ratio of the distortion at an output of the DUT to distortion of a source stimulating the DUT. The method includes calibrating the VNA at a distortion frequency, measuring a first gain of the DUT with the source and the receivers of the VNA set to the distortion frequency, and measuring a second gain of the DUT with the source of the VNA set to a fundamental frequency and the receivers of the VNA set to the distortion frequency. When the second gain is less than a predesignated threshold, a match-corrected source signal is acquired and used with the first gain and the second gain to determine the distortion of the DUT. When the second gain is not less than the predesignated threshold, a match-corrected DUT output signal is measured and used with the first gain and the second gain to determine the distortion of the DUT.