Mode Matching Code

Hi,

Does anyone have a code to calculate the s-parameters of a waveguide discontinuity using mode matching.

I have used the following procedure but the solution does not converge:

1. Arrange the modes according to their cutoff.
2. Use certain number of modes in one of the waveguides then find the required number of modes in the second using a convergence technique (e.g. their area ratio)
3. calculate the inner & mutual products
4. use the relations between the inner & mutual products and the generalized scatternig matrix to calculate the s-paprameters.

do you think their is something missing in the algorithm or is it just some 'silly' mistake some where in the code.

Thanks in advance.

The procedure is sound. But tell us what is the discontinuity?

I am trying to model two types of discontinuities actually a rectangular to circular (which is the main part) and a rectangular to rectangular double step discontinuity.

But any code will be helpful.