A Compact Ku-Band Broadband GaAs Power Amplifier Using an Improved Darlington Power Stage

In this article, a two-stage broadband GaAs power amplifier (PA) is presented, which consists of an improved Darlington power stage and a drive stage. As the most important part of the two-stage PA, the proposed Darlington power stage can simultaneously achieve large bandwidth and watt-level output power. The circuit analysis of the Darlington structure is carried out for large-size transistors. The bandwidth and gain of the Darlington structure are investigated in three cases with source peaking inductor, interconnection inductor, and compensation inductor. A design procedure for the total PA is developed to provide potential guideline. Furthermore, the total PA was fabricated using 0.15-μm GaAs pHEMT technology. The measured maximum gain in the case of a small signal is 25.9 dB, and the 3-dB bandwidth is from 10.7 to 16.7 GHz (43.8% fractional bandwidth). The maximum power of 36 dBm and the maximum power-added efficiency (PAE) of 46.8% are measured at 13 GHz. To the best of our knowledge, the proposed PA exhibits the highest figure of merit (FOM) when compared with the other previously published works.