Hm. They put in 700 watts of microwave energy, and got 20μN of force out. That's incredibly tiny. At that level, they have to try to eliminate sources of error such as attraction between the current-carrying conductors and anything conductive in the neighborhood.
They're working in a vacuum, because 700 watts will generate enough heat to move air. It's one of those things that's so close to the noise threshold that you can't tell if it's real. They write: "Our test campaign cannot confirm or refute the claims of the EM drive."
