An apparatus for heating a load with microwave energy is provided. The microwave energy is applied by the apparatus at frequencies wherein the load's dielectric constant is within a predetermined range. The apparatus may include a microwave power source configured to supply microwave energy at the applied frequencies; and a radiating plate. The radiating plate may include an electrically conductive structure that includes a plurality of radiating elements; and a feeding port, connecting the electrically conductive structure to the microwave power source. The radiating plate is configured so that most of the power fed from the microwave source through the feeding port returns towards the power source when no load is contacting the radiating plate, and most of the power fed from the microwave source through the feeding port is absorbed by the load to be heated by the apparatus when the load is contacting the radiating plate, even in absence of a microwave cavity that encloses the radiating plate and the load.