A Doherty Amplifier With Modified Load Modulation Scheme Based on Load-Pull Data

We present the design and development of a Ka-band Doherty power amplifier (DPA) that achieves high efficiency at power backoff (PBO) using a new load modulation scheme and a proposed load-pull-based design technique. Using the proposed technique, the device size of the peaking amplifier and the impedance of the quarter-wavelength (lambda/4) inverter are properly chosen to achieve high power-added efficiency (PAE) at a specific PBO level. The DPA is fabricated in a 0.15-mu m gallium arsenide pseudomorphic high-electron mobility transistor enhancement mode process and achieves a measured small signal gain of 10.5 dB, output power at 1-dB compression point (P-1 dB) of 27 dBm, and measured maximum PAE of 38%. The PAE at 6-dB PBO and 8-dB PBO are 32% and 28.5%, respectively. Furthermore, the PAE at 6-dB PBO maintains higher than 28.4% over a 1-GHz bandwidth from 29.25 to 30.25 GHz.