S-Parameters are good and still essential, but you need to be ready to go into the nonlinear regime
RF engineers know, and sometimes even love, their S-parameters. These parameters tell us a lot about the key characteristics of components and their behavior as it affects modeling, design, and debug. Many vendors offer vector network analyzers which provide the necessary fixtures, stimulus, and readouts of these vital perimeters, as well as analysis of the results and uploading to simulation tools.
But as RF performance demands have moved up in frequency and expectations, S-parameters are now being enhanced by nonlinear analysis. Agilent Technologies has been a leader in this area, with their X-parameter tools, while other RF test and measurement vendors have also done significant work individually and through groups such as the OpenWave Forum.
If you are not familiar with the trend towards nonlinear analysis, you should be. There's a lengthy technical tutorial with interesting historical R&D background, as well as the perspective of various vendors in the March 2010 issue of Microwave Journal, entitled "Fundamentally Changing Nonlinear Microwave Design". The article makes the transition beginning with well-established S-parameters, and also includes excellent references. It's worth your time to look into it, and maybe print it out for reading on your next trip, or vacation, that is, if you want to scare off those annoying fellow vacationers.♦