High-frequency power amplifier

A high-frequency power amplifier including an input terminal, an input matching circuit, an amplifying element, an output matching circuit, a coupling circuit, a detection circuit, and an output terminal, wherein

• either the input matching circuit or the output matching circuit has an active element,
• the input matching circuit receives a signal from the input terminal and outputs the signal to the amplifying element,
• the amplifying element receives and amplifies the signal outputted by the input matching circuit, and outputs the amplified signal to the output matching circuit,
• the output matching circuit receives the signal outputted by the amplifying element and outputs the signal to the coupling circuit,
• the coupling circuit receives and divides the signal outputted by the output matching circuit into signals, and outputs the signals to the detection circuit and the output terminal, respectively,
• the detection circuit receives one of the signals outputted by the coupling circuit, converts the one of the signals into a voltage, and outputs the voltage to the active element as a control voltage,
• and the active element receives the control voltage outputted by the detection circuit and changes impedance of the active element in accordance with the control voltage, thereby changing power exhibited by the signal outputted by either the input matching circuit having the active element or the output matching circuit having the active element, to change power of a signal which the coupling circuit outputs to the output terminal.