Jan Verspecht
Jan Verspecht bvba, Belgium
http: //www.janverspecht.com
In the late 1980s a growing need was recognized by RF and microwave instrument manufacturers as well as several universities to "go beyond S-parameters." This resulted in significant development efforts for a new generation of vector network analyzers with nonlinear measurement capability. The challenge of going beyond S-parameters implied two things: first of all the development of a mathematical theory to describe well-defined classes of nonlinear device-under-test (DUT) behavior, and secondly the development of the instrumentation needed for applying the theory. The combined efforts of several industrial as well as academic research groups resulted in the theory of the scattering functions and in a new instrument called the large-signal network analyzer (LSNA). The combination of the two provides one possible way to "go beyond S-parameters." In this chapter the theory of the scattering functions is explained.
The theoretical concepts of the scattering functions are best introduced by an analysis of the chapter title. "Nonlinear" implies that, in principle, we will be working with general functional relationships between quantities. This is very different from S-parameters, which can only describe a linear relationship. The words "frequency domain" are present since the scattering functions approach, in the form presented here, is based on the assumption that all applied signals as well as the resulting device responses are discrete tone signals (often called multisines). The word "scattering" refers to the fact that we are working...
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