Full W-band GaN power amplifier MMICs using a novel type of broadband radial stub

In this paper, we describe the design of the first reported full W-band (75-110 GHz) power amplifier (PA) monolithic microwave integrated circuits (MMICs) based on gallium nitride technology. The discussed MMICs come in two versions. Over a bandwidth (BW) of 70-110 GHz, the three stage PA can deliver, on average, 25.6 dBm with a power-added efficiency (PAE) of 6.5%, while the four-stage PA is able to generate 27 dBm with a PAE of 6.1%. A peak output power of 28.6 dBm is achieved at 80 GHz with a PAE of 8.6%, which corresponds to a power density of 2.6 W/mm. The significant BW was achieved partially by incorporating a novel type of broadband radial stub into the design, which can provide nearly atwofold rejection-BW improvement over the conventional version. To the best of our knowledge, no other solid-state circuit can deliver such power levels over the complete W-band.