In order to increase the power available from solid-state sources, spatial combiners are being developed. Frequently the familiar waveguide or cavity combiners have serious disadvantages. In the past few years significant investigations have been carried out to develop planar arrays of solid-state oscillators or amplifiers in order to produce spatial combining. Some of these structures have used quasi- optical resonators for coupling the sources to provide feedback for frequency locking. Sources utilized have included Gunn, IMPATT, or resonant tunneling diodes, as well as three-terminal devices such as FETs or HEMTS, with the latter types being preferred because they offer higher efficiency, better control, and monolithic capability. This presentation will summarize progress to date.
James W. Mink,
"Progress in quasi-optical power combining", Proc. SPIE 1929, 17th International Conference on Infrared and Millimeter Waves, 192910 (14 December 1992); doi: 10.1117/12.2298153; https://doi.org/10.1117/12.2298153