Abstract: A microwave apparatus injects microwave energy into a receptacle that is at least partially transparent to microwave energy. The receptacle has a window of microwave transparent material. The apparatus includes at least one microwave transmitter and one open microwave guide which is connected to the microwave transmitter and which is situated in the immediate vicinity of the receptacle. The open microwave guide has a plurality of parallel rungs and forming a slow - wave structure of the strapped bar type. The microwave guide is of a symmetrical V-shape, and at the apex of the V it is at a smaller distance from the window than at its feed point. A microwave feeder is disposed at at least both ends of the open microwave guide.