Abstract: A microwave oven having means defining an oven cavity, a magnetron microwave power source, a waveguide for coupling energy from the magnetron to the oven cavity and preferably a mode matching transformer for establishing primarily only the dominant mode in the oven cavity. A beam stirrer is disposed adjacent the waveguide feed into the cavity and is in the form of a resonant structure for coupling the energy to the cavity. The resonant structure is rotated in an eccentric manner to spread the energy beam to thereby provide a more uniform heating pattern. In one specific form the resonant structure is a cylinder of relatively short length and dimensioned to provide good matching with the magnetron source along with beam motion.