Imagine a parallel connected LC circuit. Reduce the number of turns in the inductor until you have a single U shaped turn orientated horizontally. Reduce the capacitor plates until you have nothing left but the capacitance from one terminal end of the inductor to the other terminal end of the inductor. Essentially your LC circuit considered of a single, horizontally oriented, U shaped wire. Now put a large number of these U shaped wired in parallel with each other roataing about an axis line that passes perpendicularly though the wire end point terminals. You will have a resonant cavity shaped like a pillbox...The attraction of the EM thrustor technology is that the theory hints is ought to be possible to take the same RF energy and generate orders of magnitude more thrust by containing the rf energy within an resonant cavity instead of radiating it off into space.