VSWR-protected 90 W L-band AlGaN/GaN power amplifier

Solid-state power amplifiers need protection against reflected power at the output caused by load mismatch. The standard method for protection is to include a ferrite-based isolator at the output. The isolator will redirect all reflected power to a dissipating load resistor and will ensure that the output of the amplifier always sees a 50 Ω load. Disadvantage of such isolator is the large size, weight and limited possibility for integration and miniaturization. In this work a protection circuit is presented that can replace the isolator and still offer full protection against any power reflection at the output of the amplifier. This protection circuit is based on measurement of the reflected power and a feedback loop to adjust the gain of a driver-stage, also known as fold-back protection. The driver-stage and output stage are implemented in AlGaN/GaN MMIC and power-bar technology. This protection circuit has been demonstrated on a 2-stage, 90 W L-band power amplifier, intended to be used in satellite payloads for various space applications.