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.