It seems that NASA and some companies are spending time and money on so-called reactionless electromagnetic drives. See also: http://boingboing.net/2014/11/24/the-quest-for-a-reactionless-s.html
I would guess that well over 99% of physicists consider this bogus, no matter how often these things appear to produce a few micro Newtons of force, because they appear to violate conservation of momentum. The proponents nowadays claim some weird quantum mechanical vacuum effects are responsible.
Einstein once told the story of a conversation he supposedly had with another physicist who said: "I'm inclined to believe in ESP." Einstein reported that the conversation continued with him saying that: "This has more to do with physics than psychology" and his interlocutor replying "yes."
EM drives, if such things exist (and I very much doubt that they do, except in the case of Hogwarts brooms), similarly have more to do with physics than engineering. If you posit some kind of momentum violating funky quantum vacuum effect, you need to investigate it with methods of fundamental physics, not by building giant microwave pseudo engines.