A long time ago, worked on a comm satellite program. It used a whack of tuned cans to combine high powered transmit signals with harmonics in each others' frequency bands to feed into the antenna. I once asked how they worked. The answer was 'magic'. I mean, they were physical RF filters, but no one could explain or reproduce how they worked. There was this one guy who could tighten the screws that adjusted the inside baffles so they 'worked'. No one else could.