Abstract: The nonlinear systems measurement system includes two signal generators generating different sinusoidal frequencies. A spectrum analyzer measures all signals. A single software program synchronizes the instruments. The fetched measurements are kept in data registers in correct sequence for feeding into two curve fitting routines. The sinusoidal signals are fed to a suitable combiner for the expected frequencies and dynamic range of the UUT. The combined signal is applied to the UUT. Via a software-controlled single-pole, triple-throw RF switch, the amplitude of the UUT output and the two input signals are measured at every power step as amplitude I1 and amplitude I2. The amplitude of the output component from the UUT at f1-f2 is measured as IMD2 and the output component at 2f1-f2 is measured as IMD3. The measured I1 and IMD2 are fed to the curve-fitting routine 1, yielding r1. The measured I2 and IMD3 are fed to curve-fitting routine 2, yielding r2.