Complex sentence: RF resonant cavity thrusters are a proposed type of electromagnetic thruster, such as the EmDrive and Cannae drive, which requires an electrical power source but unlike traditional electromagnetic thrusters, does not require reaction mass or propellant.
Split into simpler sentences: RF resonant cavity thrusters are a proposed type of electromagnetic thruster. Suc devices, including the EmDrive and Cannae drive, require an electrical power source but unlike traditional electromagnetic thrusters, are claimed not to require reaction mass or propellant.