In a high-power transmitter, an input complex signal is multiplied in a complex multiplier by control signals. The output complex signal from the multiplier is converted to a high frequency signal and amplified by a power amplifier for transmission. The amplitude of the input complex signal is detected to access a memory where amplitude and phase correction values are stored. During a read mode of the memory, a set of amplitude and phase correction values is specified by the detected amplitude and supplied to the complex amplifier as the control signals. During a write mode of the memory, a set of amplitude and phase correction values is specified by a delayed version of the detected amplitude and rewritten with a set of new amplitude and phase correction values. The amplified high frequency signal is down-converted to a low frequency complex signal. The nonlinearity of the power amplifier is determined from a delayed version of the input complex signal and the down-converted complex signal and the new amplitude and phase correction values are produced from the detected nonlinearity and delayed versions of the amplitude and phase correction values which were supplied to the complex multiplier. At intervals, the memory is switched from the read mode to the write mode for updating its contents.