A Ka-Band GaAs Doherty Power Amplifier with Optimized Output Combiner

$A$ Ka-band power amplifier with Doherty architecture is designed in 0.15-μm GaAs pHEMT technology. The output combiner is optimized with II-type impedance inverting networks to replace λ/4 inverters for broadband characteristic from 23 to 27.5 GHz under large signal analysis. The design equations are provided. The proposed Doherty power amplifier realizes a gain of 12.5∼15.3 dB in small signal operation and a 25.6∼26.3 dBm saturation output power. The power added efficiency is 34.2∼38.4% at saturation and 18.5∼20.8% at 6-dB power back-off, over the whole 4.5-GHz bandwidth.