Dual-Drive Doherty

Ka-Band GaN Amplifier

Summary

Designed an efficient Doherty amplifier consisting of a main and auxiliary sub-amplifiers operating at 28GHz. Optimized for peak efficiency at 2W output power, with power-added efficiency retained through 6 dB backed-off output power (500 mW).

Drive-Up Performance

(9-10 dB maintained across combined PA drive up, with max PAE close to saturated output power)

Linear Stability

(Unconditional stability from DC through third harmonic @ 84GHz)

Matched Bandwidth

(Broadband match to 50 Ohms at output port)

Takeaways

Doherty topology can yield higher efficiency at saturated output power vs. a single PA
Designing for unconditional stability is challenging without sacrificing substantial gain performance.
Phase-delay lines can be added at output to adjust load contours for various parameters such that they overlap
Stubs and fractional wavelength lines can be used to reject undesired fundamentals and harmonics in bias tees