In a method for the excitation of port groups of a multi-port device under test with coherent incident waves of the same frequency, which provide defined amplitude ratios and phase differences within each port group, the waves are generated respectively by one signal generator of a vectorial network analyzer per test port. The network analyzer has unbalanced test ports. A system-error correction of the unbalanced incident and reflected waves with reference to the ports of the device under test is implemented in order to obtain corrected waves. The amplitude and phase changes required in the signal generators to fulfill the desired amplitude and phase conditions are calculated from these corrected waves.