An apparatus (10) for generating ultraviolet radiation includes a pair of magnetrons (12) coupled to a longitudinally extending microwave chamber (14) for generating standing microwave energy waves within the chamber (14). Microwave energy from the magnetrons (12) is directly coupled to the microwave chamber (14) without the use of coupling slots, antennas or other coupling structures. A longitudinally extending electrodeless plasma bulb (20) is mounted within the microwave chamber (14) and is operable to emit ultraviolet radiation (24) in response to excitation by the microwave energy generated by the pair of magnetrons (12). The microwave chamber (14) includes a pair of longitudinally extending tuning walls (42) positioned on opposite sides of the plasma lamp bulb (20) and capable of overlapping the standing microwave energy waves generally along the longitudinal length of the plasma bulb (20).