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Please read about this topic in an earlier thread on this forum: **broken link removed** where you can find url references too that hopefully still valid.
I do not know of a specific software focusing on the design of wideband RF impedance matching transformers, unfortunately.
You can model it in any good RF simulator software with an ideal transformer to which some paralel/series lumped capacitors/inductors are embedded. See also the Mini-circuits site (www.minicircuits.com)