Mode filters for oversized transmission lines

Oversized waveguides allow to transmit high electromagnetic power, but require components able to filter the unwanted modal content unavoidably excited along their path. In this paper mode filters based on corrugations partially filled with absorbing materials are described; they have been studied aiming at optimizing their performance and overcoming their intrinsic limitations. More precisely the dependence of the filtering performance on various geometrical parameters is derived using analytical and numerical approaches. The problems related with the power handling capability of mode filters are shortly considered too. Finally the role of degenerate modes in deteriorating the filtering performance is explained and a solution to this problem is presented.