Abstract: A mobile satellite communication system including an artificial satellite which is situated in a satellite orbit and develops an active phased array antenna so as to accomplish a line to a terrestrial station using a portable terminal in a specific area. As a result, a service that satisfies a demand for communication in the specific area can be realized.

Abstract: A high-frequency power amplifier comprises a pair of FETs, a divider which supplies opposite-phase versions of a signal to be amplified to the FETs, distributed-parameter transmission lines connected respectively at one ends thereof to output electrodes of the FETs, and a combiner which combines signals appearing at another ends of the transmission lines into a signal of a common phase. Stubs which short-circuit for even harmonics included in output signals of the FETs are connected respectively to the transmission lines at positions distant from the output electrodes of the FETs by a multiple of a quarter wavelength of the fundamental wave included in the output signals of the FETs.