This work is aimed at developing high power amplifier modules for multi-octave operation and high efficiency.  Initial efforts have focused on the use of travelling- wave amplifier (TWA) concepts.  TWAs offer wide bandwidth by incorporating the device Cgs into a synthetic transmission line.  Ordinarily the outputs are similarly combined into a synthetic line, but this results in low efficiency due to the excitation of a backward wave.  We have modified the TWA to include an efficient broadband output combiner circuit.  We also use capacitive division at the input of the devices to increase the bandwidth and equalize the drive levels.   Prototypes have demonstarted the idea using flip-chip mounting of GaAs FETs onto a thermally managed AlN substrate.