POWER AMPLIFIER

PURPOSE:To eliminate the need for a changeover switch and a standby power amplifier element for the power amplifier and to obtain the power amplifier without causing using deterioration in performance attended with a fault of a changeover switch. CONSTITUTION:A communication signal received from input terminals 13 and separated to each channel is equally divided into (N+M) at a 3 dB hybrid. The divided communication signal is amplified up to 1/N of a power P desired to be outputted by optional N-sets of power amplifier elements 15 among (N+M) sets of the elements 15, and the resulting powers are synthesized by a power synthesizer 16 and outputs corresponding to the input terminals 13 of the power divider 14 are obtained at multi-port output terminals 11. Only N-sets of the power amplifier elements 15 are started and the remaining M-sets are stopped. Thus, a power amplifier element 15 in the stop state is properly started when the active power amplifier element 15 is faulty. An isolation characteristic change or the like attended with a change in the electric length is not caused when the standby power amplifier element 15 is selected and the amplification with high reliability is attained.