> Could it be there is some way to target a location with multiple radio beams such that the damaging effect occurs at the point of interference? Maybe just constructive interference from multiple weaker beams? Something like this would need to be aimed precisely of course.
Yes, a phased array [1], which is likely what the GGP was referring to by "What is unproven though, is how one would ever shrink the size of an electronic weapon like this."
Advanced radars work by creating a concentrated beam of RF with constructive interference and scanning it across the sky, but the installations are huge. A smaller directed microwave weapon would be meters across, hard to hide, and noisy.