We have developed and tested a 21 element two-dimensional power-combining array, intended for transmitter applications in future deep space missions. The array uses MMIC phase shifters for beam scanning, MMIC power amplifiers and Vivaldi (Exponentially Tapered Slot Antenna) radiating elements. The measured combining efficiency, referred to the power amplifier output ports, is about 60%.
"Ka-band power-combining MMIC array", Proc. SPIE 1514, 15th International Conference on Infrared and Millimeter Waves, 15144R (1 December 1990); doi: 10.1117/12.2301581; https://doi.org/10.1117/12.2301581