X-to-K band broadband watt-level power amplifier using stacked-FET unit cells

A broadband watt-level stacked-FET power amplifier (PA) has been developed using 0.15 µm GaAs pHEMT's. A triple-stacked FET structure is used as a unit cell to combine RF voltage swings to achieve high output power and broad bandwidth at the same time. Special care has been taken to solve thermal and instability problems of stacked-FET cells for watt-level applications as well as to optimize the subsequent power combiner for bandwidth. The fabricated PA shows a peak power of 33.7 dBm with a power added efficiency (PAE) of 29.5% at frequency of 18 GHz, and higher than 32 dBm output power from 10 to 21 GHz. The fractional 3 dB output power bandwidth is 84%.