In order to determine the operational parameters of a high-frequency power amplifier (1) (for example, complex forward and return voltage or power, complex load impedance, reflection or voltage standing wave ratio) on the connecting line (3) between the output of the high-frequency power amplifier (1) and a complex load, in particular, an antenna (4), an analog measured voltage Uu proportional to the complex voltage {right arrow over (U)} on the connecting line and an analog measured voltage Ui proportional to the complex current {right arrow over (I)} on the line (3) is determined by a Buschbeck coupling device. These measured voltages are digitized, and the required operational parameters can then be calculated in a computing unit (7) from these digital values.