There are some fascinating things you could do with one of those. You could, for example, make a "stick boiler"—like a "stick blender"—that you stick inside a cup of liquid to heat it up, without any part of the stick itself getting hot. (Presumably there'd be a waffle-grid cross-guard to block reflected RF.)

But, in the wrong hands, that's a directed-energy weapon, isn't it? (Hell, stick one of these in the right kind of tube and you've now got a coherent RF beam—a maser pointer. You could probably burn your name into a wooden building from across a football field with one.)