A thermal increase system includes one or more multi-level electrodes configured to radiate electromagnetic energy into a cavity in response to receiving a radio frequency (RF) signal from an RF signal source. Each multi-level electrode is positioned adjacent to a wall of the cavity, and each multi-level electrode includes a base portion coupled to an elevated portion. A radiating surface of the elevated portion is at a height of at least 0.5 centimeters (cm) from a radiating surface of the base portion.