Improved directional couplers for overmoded waveguide systems

Multihole couplers showing insufficient suppression of single modes or insufficient directivity can be improved by adding holes of a shifted coupler structure of the same kind. A shifted structure improving the directivity also enhances suppression of unwanted modes propagating in backward direction. On the other hand marked suppression of a single unwanted backward mode also improves suppression of the other backward modes as well as directivity. (orig./AH)