Brief

S-parameters have a rich mathematical formalism in which there is no ambiguity. But when it comes to translating the mathematics of S-parameters into the practical interpretation of an interconnect’s electrical properties, confusion can slip in by way of an inexperienced user spreading misconceptions to a new user not sure what is important and what is not. In this article I reveal seven features of S-parameters that are confusing and how not to be confused.

Confusion #1

Fundamentally, an S-parameter, short for “scattering” parameter, is a measure of the ratio of the scattered voltage wave to the incident voltage wave to a device under test (DUT). The formalism was originally established in the frequency domain, where the voltage waves are sine waves.

The ratio of what comes out compared to what goes in, is basically a transfer function. It describes the response of the system to sine waves. A sine wave has only three figures of merit:

A frequency

An amplitude

A phase