High frequency power amplifier is an important part of transmitting equipment in communication system. According to the width of its working frequency band, it can be divided into narrow-band high-frequency power amplifier and broadband high-frequency power amplifier. Narrow-band high-frequency power amplifier usually takes frequency selection circuit with frequency selection filtering function as output loop, so it is also called tuned power amplifier or resonant power amplifier. The output circuit of broadband high frequency power amplifier is transmission line transformer or other broadband matching circuit, so it is also called non-tuned power amplifier.

High-frequency power amplifier is an energy conversion device, which converts DC energy provided by power supply into high-frequency AC output. Amplifiers can be divided into Class A (conduction angle =360 degrees), Class B (conduction angle = 180 degrees) and Class A (conduction angle = 180 degrees ~360 degrees) according to different current conduction angles.