My understanding is that the Rf Designer program from ARRL has a
moderately complicated user interface and so it was not quite a popular as
originally hoped.

However, the Ansoft student version is just about as capable if not more
so and is a bit easier to learn.

http://www.ansoft.com/ansoftdesignersv/

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A long time ago I ran across a free S parameter simulator, RFSIMM99,
which handles most of the things I need. It also has a monte carlo
tolerance analysis which is convenient when I want to see what component
tolerances are going to do to me.

The company that originally made this program seem to not be there any
more, or at least my link to their website does not work, but the program
can be found on quite a lot of websites.


Jim Pennell N6BIU