Overmoded Rectangular Waveguide Components for a Multi-Moded RF Power Distribution System

We describe the design of several novel, passive waveguide devices being developed for the high-power rf distribution system of the Next Linear Collider (1). This system allows the combined power of several klystrons to be directed, by means of drive phase manipulation, to different accelerator feeds at different times during each pulse. The desire to reduce the amount of required low- loss, circular-waveguide delay line has led to the present multi-moded scheme, in which different modes travel through the same waveguide to different destinations. Components are needed for combining, launching, splitting, and directing hundreds of megawatts at X-band. For simplicity, manipulations are done primarily in overmoded rectangular guide, with the height increased to improve power-handling capacity. Features that invite breakdown, such as coupling slots and h-plane septa, are avoided. The components described here utilize TE 10 and TE20 as operating modes. They include a four-input superhybrid, a mode-selective extractor, mode-preserving bends, a rectangular mode converter, and a rectangular-to- circular taper (2), which converts between the above modes and the circular TE11 and TE01 modes, respectively.