| In this Ph.D. research, several Ka-Band power amplifiers are designed and built for use in next generation mobile broadband communication systems. The Doherty power amplifier architecture is demonstrated as a possible solution to improving the back-off efficiency of millimeter-wave power amplifiers, since many mobile broadband communication systems employ modulation formats with large peak-to-average power ratios. This research also demonstrates some novel techniques to improve upon the Doherty architecture for millimeter-wave power amplifier design.;Two fully integrated Ka-Band Doherty power amplifiers are designed and developed using a 0.15-mum GaAs pseudomorphic high electron mobility transistor (pHEMT) process. The first uses the classic Doherty configuration with some previously developed modifications to resolve some practical issues and achieves a measured small signal gain of 10.3 dB, measured output power at 1-dB compression point (P1dB) of 25.1 dBm, measured peak power added efficiency (PAE) of 38%, and measured PAE of 27% at 6-dB back-off power. The bias network of this same Doherty was then modified by short circuiting some resistors in the gate bias path and it then achieves a measured small signal gain of 10.5 dB, measured output power at 1-dB compression point (P1dB) of 26.9 dBm, measured peak power added efficiency of 42%, and measured PAE of 32% at 6-dB back-off power. The second Doherty amplifier uses a novel load-pull based Doherty technique accounting for nonideal back-off impedance in millimeter-wave power amplifiers and achieves a measured small signal gain of 9 dB, simulated output power at 1-dB compression point (P1dB) of 29 dBm, simulated peak power added efficiency of 46%, and simulated PAE of 35% at 6-dB back-off power. The performance achieved with these power amplifiers makes them a promising candidate for use in next generation mobile broadband communication systems. |
