Four MOSFETs deliver 600 W of RF power

The scheme outlined does not require even one power combiner, and the amplifier circuit is capable of operating at an efficiency of 50%. Supply voltages of 40 to 50 VDC can be used, depending on the linearity requirements. Since the bias for each device is independently adjustable, no matching is required for the gate threshold voltages. In view of the fact that the power gain of a MOSFET is largely dependent on the drain bias current, only transconductance matching within + or - 10% is required. The stability of the amplifier is tested in a 3.0:1 load impedance mismatch at all phase angles. It is found to be completely stable, even at reduced supply voltages. It is pointed out that a properly designed FET circuit should be inherently more stable than a bipolar circuit, especially under varying load conditions.