VSWR protection of power amplifiers using BST components

A VSWR-protected ISM-band PA was realized using a BST based varactor for detuning of the input matching. Output VSWR levels of 30:1 can be tolerated by applying a varactor bias voltage of up to 20 V. The PA delivers 47.4 dBm output power at a maximum PAE of 49.5%. In case of high VSWR conditions the output power can be limited by detuning the varactor. It is shown that the concept protects the transistor efficiently with very low additional circuit complexity.