Analysis of an end junction between a coaxial waveguide, with a hollow inner, and a circular cylindrical waveguide

The paper describes an analysis of a junction between a composite region comprising a coaxial waveguide with a hollow inner conductor, and a circular cylindrical waveguide of diameter equal to that of the outer of the coaxial waveguide. Junctions of this description occur in a device termed the `Marcatili coupler¿¿, which provides an interesting solution to the problem of achieving efficient RF coupling into, or out of, a circularly symmetric fast-wave electron-beam tube such as the gyrotron. A step function is used to mathematically reduce the composite waveguide region to a single region, and the junction is then analysed by the moment method. It is shown that the predicted scattering characteristics of the junction are in good agreement with previously published measured results.