I generally expect sub 100 MHz to be called radio rather than microwave, but I shouldn’t make assumptions. So you need a quarter wave to be longer than a build

I generally expect sub 100 MHz to be called radio rather than microwave, but I shouldn’t make assumptions. So you need a quarter wave to be longer than a building to make it not a concern, practically it needs to be much longer if you’re sending serious power and want to keep the density down. Let’s aim for a 1 km long antenna in space with voltage high enough that ohmic losses are not a concern, or a very large superconducting antenna and all of the apparatus that goes with it. Millions of volts likes to arc when you have debris just floating around everywhere in space. Superconducting is much more attractive regardless of the extra apparatus. I don’t see many points of concern, though you could still damage infrastructure if you aren’t constantly aligned. Blowing up terrestrial grids isn’t as bad as cooking people alive. It would still be the most dangerous thing we've ever put in space by a pretty wide margin. Keep space filled exclusively with small tin cans is not an accident and not entirely due to technical or economic limitations. It is a very sensitive political area. Putting anything that could be dangerous in orbit makes it dangerous to everyone. So your adversary across the ocean blows up a reactor? Cool. As long as they don't blow me up.