Dr. Chen Yue, Director of Commercial Satellite Technology for the China Academy of Space Technology (CAST) announced on December 10, 2016 that not only has China successfully tested EmDrives technology in its laboratories, but that a proof-of-concept is currently undergoing zero-g testing in orbit (according to the International Business Times, this test is taking place on the Tiangong 2 space station).
Unlike traditional engines (such as combustion and ion engines) that expel mass from the system to produce thrust, reactionless engines like the EmDrive use only electricity to generate movement. In the EmDrive, first proposed by Roger Shawyer, the microwave cavity is an asymmetric container, such as a truncated cone, with one end much larger than the other. At the narrower end, a source of electromagnetic energy (such as a magnetron) bombards the cavity with microwaves. These waves are contained and bounce off the cavity's walls, creating electromagnetic resonance. Due to the imbalanced resonance from the complex geometry of a truncated cone, the electromagnetic field in the EmDrive becomes directionally dependent (anisotropic). In this case, the anisotropic electromagnetic field 'pushes' the EmDrive away from the direction of the cavity's larger area end.