Fundamentals Of VNAs

By Bob Buxton, Anritsu Company

In our first column on vector network analyzers (VNAs), we discussed the importance of the instrument in today's RF/microwave designs. Today, we will review VNA fundamentals and how they have helped the analyzer become the instrument of choice in so many applications.

A VNA is essentially a combination of a source used to provide a stimulus to ports 1 and 2, and a set of receivers measuring both the source power (as a reference) and the transmitted or reflected signals from the device under test (DUT). S-parameters are derived by making "ratioed" measurements on the downconverted intermediate frequency (IF) of the incident, transmitted, and reflected signals. All of the components in the block diagram play a critical role in assuring the quality of the S-parameter results.