[KarlInOhio]

I’m an old ham radio operator and I have wondered how the standing waves don’t fry the transmitter in a microwave oven.

That's why you never run it empty. You need something with water in it to absorb the energy.

[Wilhelm Tell]

I understand not running it empty. All that energy has to go somewhere. A microwave has to deal with widely varied loads, from heating a bagel to cooking a whole meal.