On Wed, 11 Aug 2004 18:59:22 -0700, John Larkin
wrote:

RFSIM99 does nice frequency-domain analysies, in all sorts of formats
- Smith, rectangular plots, polars, tabular s-param listings, stuff
like that. It does lumped parts, transmission lines, and some active
stuff. Free, too!

It's in a box here, near the bottom:

http://home.sandiego.edu/~ekim/e194rfs01/

That's certainly one highly useful piece of artillery for the RF
designer!
I don't think it actually allows one to *extract* S- parameters
through modling a BJT, for example.
I haven't had the chance to check it over in detail yet, but it seems
you have to insert already predetermined S-params from datasheets or
wherever and it will generate matching networks from there. So it
doesn't actually amount to a 'virtual VNA' - or does it??

p.
--

"What is now proved was once only imagin'd." - William Blake, 1793.