Determining operating characteristics of signal generator using measuring device

A method determines operating characteristics of a signal generator. The method includes performing a first set of measurements of an output signal generated by the signal generator and corresponding reflected signal, where the first set of measurements is performed over multiple frequencies and amplitudes of the output signal; applying an external signal to the output port of the signal generator; performing a second set of measurements of the output signal and corresponding reflected signal while the external signal is being applied to the output port, where the second set of measurements is performed over frequencies and amplitudes of the output signal, the external signal having the same frequency as the output signal for each measurement of the second set of measurements. A set of coefficients describing the operating characteristics of the signal generator is determined by processing results of the first and second sets of measurements through a non-linear model.