Patent ID: 8558622

Claim:
A radio frequency power amplifier, comprising: an amplifying element that amplifies a radio frequency signal having a first frequency; an input matching circuit connected to an input terminal of the amplifying element; an output matching circuit connected to an output terminal of the amplifying element; and a reactance control circuit having one end connected to an output terminal of the amplifying element, and the other end connected to an input terminal of the output matching circuit and to a direct current power source terminal, wherein the amplifying element is a field effect transistor including a gate electrode, a drain electrode, and a source electrode, at least one of the gate electrode or the source electrode has a field-plate structure, the reactance control circuit has a reactance which resonates at a second frequency with a parasitic capacitance of the amplifying element at the output terminal of the amplifying element, the parasitic capacitance of the amplifying element is a parasitic capacitance held by the amplifying element calculated from inter-electrode parasitic capacitances between the gate electrode, the drain electrode and the source electrode, a parasitic capacitance C of the amplifying element is expressed by an equation C = Cds + Cgs × Cdg Cgs × Cdg where Cgs is a parasitic capacitance between the gate electrode and the source electrode, Cdg is a parasitic capacitance between the drain electrode and the gate electrode, and Cds is a parasitic capacitance between the drain electrode and the source electrode, and the second frequency is identical or close to the first frequency.