MICROWAVE DEVICE FOR WARMING AND/OR DRYING FLAT MATERIALS PASSING THROUGH THE DEVICE

1. Apparatus for uniformly heating and/or drying wide, thin, sheet-like webs of paper, plastics, textiles or photographic materials using an energy transmitter supplied with microwaves which consists of waveguides which are arranged parallel to each other and are divided into two symmetric parts between which the material can be passed and which are interconnected and whose length is made to equal an integral number of half-waves (LAMBDA/2), the waveguide elements being alternately displaced by a quarter of a waveguide wavelength (LAMBDA/4) for the avoidance of undesired electromagnetic coupling between the waveguide elements and separate microwave generators being used, in conjunction with circulators, to supply each of the individual waveguide elements, characterised in that a) the individual waveguide elements (3) are, in their longitudinal direction, arranged parallel to or at a small angle (alpha) to the direction of travel of the web (2), b) the number of waveguide elements (3) is selected so as to be proportional to the width of the web (2), the proportionality factor being based on the required conditions, c) the width (b) of the individual waveguide elements (3) is of a size corresponding to the configuration of the H10 mode and d) magnetically-acting adjustable iris couplers (4) are provided for adjusting the microwave power acting in each waveguide element (3), which couplers allow a uniform or any desired pattern of the supplied microwave power transversely to the direction of travel of the web.