Importance of Harmonic Terminations in Performances of a Class-C UHF Transistor Power Amplifier

The influence of 2nd harmonic on the performances of an UHF class-C transistor power amplifier was determined. A matching circuit was designed, in which the reactive impedance termination presented at the second harmonic can be varied without affecting the impedance presented at the fundamental frequency. The main performance characteristics of the transistor power amplifier (output power, efficiency, intermodulation) were then determined, using two such matching circuits at the input and the output ports of the transistor. A graphical presentation of the results facilitates the choice of the 2nd harmonic terminations which significantly improve the performances of the amplifier.