Abstract

The invention presents a high efficiency linear power amplifier of plural frequency bands reduced in the number of parts and elements, simplified in the circuit construction, and saved in the circuit space, and in FIG. 1, signals entering from a common input terminal 1 in frequency bands A and B are matched in both frequency bands A and B in a wide band matching network 2, amplified in a pre-amplifier 3, put into a common terminal 4a of a switch circuit 4, and the signal in frequency band A is put into a changeover terminal 4b, matched in a matching network 5 and amplified in a post-amplifier 6, and its output is matched in a post-matching network 7 and sent out into an output terminal 8, while, similarly, the signal in frequency band B is put into other changeover terminal 4c of the switch circuit 4, matched in a matching network 9, amplified in a post-amplifier 10, and its output is matched in a post-matching network 11 and is sent out into an output terminal 12.The invention also presents a power amplifier capable of maintaining a similar high efficiency characteristic if the output power is lowered from the output power of maximum efficiency, and in FIG. 10, first and second power amplifiers 113, 114 are disposed in parallel, and a necessary number of power amplifiers are connected depending on a required output power by switch circuits 115 to 118, and the power source is turned on only in the connected power amplifiers, while the other power amplifiers are turned off, and therefore by the lowering portion of the output power, the current consumption decreases in proportion, so that the equivalent high efficiency operation same as in the case maximum efficiency is realized.