A method of determining true vector gain of an IF string on an RF network analyzer

A method of determining the true vector gain of an IF string in an RF network analyzer (101) (Fig. 1), the IF string having a plurality of cascaded amplifiers (2503 Fig. 26. 1) coupled to a parallel pair of synchronous detectors, the method comprising (a) turning off the gain (G1-G4) in all the amplifiers; (b) grounding (2502) the input to the amplifiers; (c) measuring (139) the outputs of the synchronous detectors at each of the four phase Fig offsets 0, 90, 180 and 270 degrees to determine the measured offsets of the IF string; and (d) averaging the four offset values for each of the detectors to calculate the true complex values of the offset of the IF string. The true complex gain is subsequently determined with amplifiers turned on, one at a time.