A new feedback method for power amplifier with unilateralization and improved output return loss

Given a device with a conventionally optimized P/sub 1 dB/ point, this paper proposes a new theory for feedback amplifiers to optimize gain and improves S/sub 22/ (ideally resulting in S/sub 22/=0). The design procedure only requires the small-signal S-parameters and the measured load-pull data of the transistor. To verify this theory, two 800-mW 2-GHz GaAs MESFET amplifiers with and without the lossless feedback were implemented and evaluated. The feedback amplifier achieved significant improvement in linear gain (6 dB), reverse isolation (12 dB), and output return loss (5 dB) with the same output P/sub 1/dB for both types of amplifiers.