Abstract: A microwave tunnel oven receives a series of packages each comprising a container and a load in the container to be heated by microwave energy. The oven has a conveyor with a series of carriers each for receiving one of the packages and conveying it through the oven. The improvement comprises modifying the microwave field in the load during its irradiation in the oven in a manner to generate higher order modes of microwave energy in the load to enhance the uniformity of heating throughout the load. The structure for achieving the field modification is divided into two parts, one part being formed on the conveyor and the other part being formed either on the package or on a subsidiary conveyor that extends parallel to the main conveyor.

Abstract: A product comprises a shallow container and a load located therein for heating by microwave energy. This product is designed either to be used with, or itself to incorporate, a structure for generating or enhancing at least one mode of the microwave energy of an order higher than a fundamental mode that is determined by boundary conditions resulting from the lateral dimensions of either the container of the load or both. The invention resides in controlling the depth of the load in the container in such a manner that, upon irradiation of the product with the microwave energy, the power absorbed by the load from a higher order mode is at or near a maximum value, while preferably the power absorbed by the load from the fundamental mode is at or near a minimum value.