This Jet Engine Uses No Fuel – Only Microwaves and Air, According to Researchers

I don’t think this is a good article.

FTA: “This revolutionary new engine actually uses microwave and plasma technology as its foundation, which means it doesn't rely on traditional fuel or batteries as a source of power”

I doubt they have figured out how to create microwaves and plasma without using traditional fuel or batteries.

Also FTA: “The frequency of the microwaves is actually quite low, and on a comparable level with what you'd expect out of the microwave in your kitchen”

That doesn’t make sense to me. https://en.wikipedia.org/wiki/Microwave_oven: “Typically, consumer ovens work around a nominal 2.45 gigahertz (GHz)”. I wouldn’t call that “quite low”.