A 6-18-GHz GaN Reactively Matched Distributed Power Amplifier Using Simplified Bias Network and Reduced Thermal Coupling

Two-stage reactively matched gain cells are proposed to implement a high-gain multioctave distributed power amplifier (DPA). The proposed reactively matched distributed amplifier (RMDA) structure shows high gain and power in a small die size. Detailed analysis is presented to understand the design criteria for interstage matching of reactively matched cells. A shared dc bias network is proposed to simplify the biasing of each section to reduce the DPA die size. The thermal coupling effect of GaN high-power amplifier is minimized by optimizing the chip layout. The theoretical analysis is verified by the simulation and supported by the measured data. Two RMDAs are fabricated with a commercial 0.25- \mu \text{m} GaN HEMT process. The implemented RMDA with the compact transistor layout has been implemented in a small die size of 10.7 mm 2 and shows output powers reaching 40.3-43.9 dBm, power added efficiencies (PAEs) of 16-27%, and small-signal gains of 15.3-23.2 dB. The RMDA with the reduced thermal coupling achieves 40.6-43.4 dBm with a peak PAE of 29% in a slightly larger die size of 13.8 mm 2 . To the best of our knowledge, this is the first demonstration of a GaN DPA using reactively matched gain cells, showing very high gain and efficiency over multioctave bandwidth in a small die size.