Summary form only given, as follows. Design and performance of power amplifiers that have established new benchmarks for 2 to 20 GHz power are reported. The Dual Field Plate amplifier achieved P3dB of 26.3 Watts max., 15.4 Watts average, with 38.3% max 19.8% average PAE. Using an improved device, the No FP amplifier achieved P3dB of 21.6 Watts max., 16.0 Watts average, with 35.7% max 25.9% average PAE. This output power, bandwidth, and efficiency is superior to the best previously reported results for GaN HEMT power amplifiers.