PURPOSE: To reduce the cost of a ground-station power amplification system by constituting a synthesizing circuit by combining filter combiners and units having waveguide switches connected to the output sides of the filter combiners.

CONSTITUTION: Many units connected to the outputs of filter combiners 2 through waveguide switches 3 are connected through waveguide switches 3, and those two units are further connected in parallel by a hybrid, a coupler, a filter, a combiner 1, etc., thereby obtaining a composite output. To one output of each filter combiner, a large-power dummy load 4 is connected directly. Consequently, the degree of freedom of frequency use increases and even if the frequency is varied after operation, filter combiners are replaced without stopping the function of a circuit, achieving the maintenance and adjustment of a power amplifier.