A radion beam was a type of energy beam that could penetrate shields.
In 2372, Harry Kim modified the USS Voyager's main deflector to fire dozens of radion beams into the shields around a Mokra prison facility, where Tuvok and B'Elanna Torres were being held. One of the beams was to conceal a transporter signal for a rescue party, with the others being decoys. However, Voyager was driven off by the Mokra's phased ion cannons before the plan could be completed. (VOY: "Resistance")