A vector network analyzer (VNA) is used to measure what?

• A. Free-space path loss
• B. Complex impedance and S-parameters
• C. Noise figure of a receiver
• D. Modulation error rate

Answer: (B)

A vector network analyzer measures how a network responds to RF signals by showing how energy is reflected and transmitted through the device under test. It sends a swept RF signal into a port and records both the reflected signal and the transmitted signal, capturing their magnitude and phase. From these measurements, it computes S-parameters, which describe how incident waves at each port relate to outgoing waves at every port. This lets you see the complex impedance at a port and how the network behaves across frequency, which is essential for characterizing matching, insertion loss, and bandwidth.

Other options aren’t what a VNA is designed to measure: free-space path loss relates to propagation losses between transmitter and receiver in space, not the internal scattering of a network; noise figure of a receiver requires a different setup and a noise-figure meter; modulation error rate concerns digital signal quality and BER testers.