Measuring 3-port mixed-mode S-parameters

A balun is an important RF component used to convert between balanced and unbalanced electrical signals. Its input is single-ended and its output is differential. To ensure system performance, it is necessary to evaluate the balun structure, and the differential loss/gain is a critical parameter. Most test equipment is intended for single-ended devices, making the standard S-parameter easier to measure.

This article is a presentation of the transformation between standard S-parameters and mixed-mode S-parameters for 3-port scattering parameters. Using the ISL55016 from Intersil as an example, it will show how to get the differential gain by measuring a single-ended S-parameter.