Abstract: A microwave heating apparatus is designed to improve distribution of the microwaves introduced into a multi-mode microwave cavity for heating or other selected applications. The microwave heating apparatus includes a microwave signal generator and a waveguide to convey microwave power to the cavity. A perforated metal plate disposed within the cavity encloses a volume adjacent to the waveguide opening, forming a leaky multimode subcavity. Through multiple processes of reflection, transmission, diffraction, and scattering, the leaky subcavity serves to smooth the microwave power distribution in the near-field region adjacent to the waveguide to better disperse the energy throughout the main applicator cavity. A more uniform level of microwave power is thereby applied to the workpiece.