Mismatched Load Characterization for High-Power RF Amplifiers

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  • Author: Richard W. Brounley, P.E
Many applications for RF power amplifiers must deliver their power into loads with high Voltage Standing Wave Ratios (VSWRs). Among these applications are lasers, plasma chambers and ICP torches. It is impor-tant to characterize the RFPA in order to understand its performance regarding stabili-ty, dissipation, efficiency, voltage breakdown, and power developed into mismatched loads. This paper describes the techniques used to characterize an RFPA along with results obtained on a 45 MHz single transistor model. A multiple transistor RFPA at 80 MHz, used as a laser driver with a power output of 1200 watts peak, is also described. Protection meth-ods are also discussed, and a follow up article will add information on matching circuits and components for high power matching. The information in this article applies primarily to saturated amplifiers operating in class C, D, or E and capable of efficiencies in excess of 70%.