Quite Universal Circuit Simulator (QUCS) is a great little Spice-like open-source tool that runs quickly, has a wide range of components, rather intuitie interface (but a so-so manual), and will execute S-parameter analysis. Available at qucs.sourceforge.net/.
NASA's Orion Flight Software Production Systems Manager Darrel G. Raines joins Planet Analog Editor Steve Taranovich and Embedded.com Editor Max Maxfield to talk about embedded flight software used on the Mars on EE Times Radio. Live radio show and live chat. Get your questions ready.