A program for coupled modes equations for circular waveguide tapers

A FORTRAN90 program for solving the coupled modes equations for diameter variation in lossless smooth circular waveguide was written in order to assess the parameters of a suitable broadband taper for a reflectometer transmission line. General---purpose commercial software is too demanding in terms of computing resources for such a task, and this type of code, that used to be popular up to the 1980s, is perfectly suited for the purpose. The formulation was taken from and is briefly summarized here. The expressions for the coupling coefficients were checked whenever possible against the available literature, and results were compared with a few published ones. The program is available in the public domain as a .tar.gz archive at the same location as this report. Any users are kindly requested to cite this report in their papers.