8-42 GHz GaN non-uniform distributed power amplifier MMICs in microstrip technology

This paper reports on two wide bandwidth monolithic power amplifiers suitable for electronic warfare (EW) systems and other wide bandwidth applications up to the Q-band. The MMICs are based on a 100nm AlGaN/GaN T-gate HEMT microstrip transmission line MMIC technology with an fT>80 GHz. Both designed and fabricated amplifiers use the non-uniform distributed power amplifier (NDPA) topology and cover a frequency range from 8 GHz to 42 GHz, whereas the lower band edge is limited by the on-chip DC bias network. The first MMIC is a single-stage topology with a measured S21 of 6+-1 dB, the second a dual-stage topology with a measured S21 of 14+-2 dB, both over the entire frequency range. By choosing adequate device geometries and a low interstage impedance of 32 in the dual-stage design, the wide bandwidth and high saturated output power of >0.5W of the single-stage design are maintained. A large-signal state-space model was used in the design process. A large-signal methodology for the broadband design of the amplifiers given soft compression of the FETs and low PAE over large bandwidth is proposed and verified.