Before the network analyzer, determining the reflection coefficient of a circuit required you to manually calculate the phase of the reflection coefficient one frequency at a time on a piece of paper. This manual process required you to first find the maxima and minima of the standing voltage wave in a slotted line and repeat this process for all frequencies of interest. It is safe to say that if the vector network analyzer (VNA) had not been created, the highfrequency community would look very different today.
Today, the VNA characterizes high-frequency passive and active devices in their linear mode of operation by measuring their network parameters, called S-parameters, as a function of frequency. Over time, VNAs have been extended in hardware and in capability to also measure noise parameters and nonlinear characteristics, including compression, intermodulation, and hot S22 measurements1. As a result, the VNA evolved into an instrument enabling multiple measurements with a single connection.