Comparison between measurements made on an iris filter structure (see reference below) and calculations made with the mode matching method used on this site.

Red and blue traces are calculated (30 modes) with the mode matching method used on this site. The black traces are borrowed from the reference below.

Reference:
Alessandra Esposito, Frederico Malucelli, Luciano Tarricone.
"An Optimized Parallel Admittance Matrix Approach Using the Adjacence-Graph Recursive-Thresholding Technique", IEEE Trans. Microwave Theory Tech. vol. 50, no 9, p.  2105, September 2002