Worked with an engineer had some involvement in early oven design.
Apparently it took some serious work to radiate a magnetron into a closed metal box without destroying it from reflected power.
The first microwaves were actually called a radar range AND they were so heavy it was crazy!!
Raytheon was one of few companies that had the expertise to figure it out, thanks to WWII research with the MIT Radiation Labs, and fortunately owned Amana, which knew a lot about how to make consumer appliances. It took both to make the microwave oven a reality and even then, a decade of cost reductions to make it a true consumer item.
I always wondered about that. I’m an old ham radio operator and I have wondered how the standing waves don’t fry the transmitter in a microwave oven. Is there some weird trick with resonance or something?