Not to be rude, but have you looked around on this
website? There are lots of good programs available.
I've never used it but here's one I saw on the homepage.
http://rfcafe.com/miscellany/press-rele ... 0-2010.htm
There are others. RF Cafe sells a spreadsheet
system analyzer. Have you looked at it?
http://rfcafe.com/business/software/rf- ... w-2005.htm
Another company makes some like CalcSys or SysCalc.
You couldlook them up.