Patent ID: 8288694

Claim:
An apparatus for microwave heating of a planar product, said apparatus comprising a feeding waveguide having a rectangular cross-section with a first side of length b and a second side of length a, wherein a>b, for feeding a microwave apparatus, an elongated heating cavity having an enlarged rectangular cross-section with a first side of an extended length Cab and a second side of length a, wherein C>2 and C*b>a, a pair of lateral slots provided parallel in said opposite enlarged first walls of said elongated heating cavity and arranged to divide said elongated heating cavity into opposing first and second subcavities in the axial direction of said elongated heating cavity, said lateral slots permitting a planar product to be heated to traverse said elongated heating cavity via said lateral slots, a waveguide transition provided between the feeding waveguide and the heating cavity for transforming said standard rectangular cross-section at the input of the feeding waveguide into said enlarged cross-section of the heating cavity, and for feeding a fundamental mode from feeding waveguide to the first subcavity of the elongated heating cavity via an adjustable coupling iris, a frequency tuning device arranged to move an end wall of the second subcavity in the axial direction so as to tune the frequency of the elongated heating cavity and to move a maximum or minimum of an electric field in the axial direction at about a middle of a thickness of the planar product, a sensor for measuring a microwave power of the fundamental mode reflected from said heating cavity, and a coupling tuning device arranged to adjust a size of the coupling iris in a direction of the second side wall so as to minimize said reflected power from said heating cavity.