How does a vector network analyzer work?

From RF Design Wiki · By the RF Design Wiki editorial team · Published October 21, 2026 · Last reviewed October 21, 2026 · How we research

A vector network analyzer measures the magnitude and phase of S-parameters. A swept source drives the device under test (DUT) through a test set with directional couplers or bridges that separate incident, reflected and transmitted waves; tuned receivers measure their ratios. Error correction (calibration) removes the systematic errors of the test set and cables.^[1]^[2]

What can a VNA measure?

Return loss, VSWR, impedance (Smith chart) from S₁₁/S₂₂.
Gain or insertion loss, phase, group delay from S₂₁.
Isolation from S₁₂.
Gain compression with power sweeps.
Time-domain response (TDR-like) via inverse FFT; see TDR.
With options: noise figure, mixer conversion, harmonics, and mixed-mode S-parameters.

Which settings matter most?

IF bandwidth: narrower lowers trace noise and increases dynamic range, at slower sweep speed; each 10× reduction lowers the noise floor 10 dB.
Source power: high enough for SNR, low enough to keep the DUT and receivers linear.
Number of points: enough to resolve resonances and avoid aliasing in time-domain or electrical delay.
Averaging and smoothing: use carefully, smoothing distorts narrow features.

^[1]

What is dynamic range?

The difference between maximum receiver power and the noise floor at a given IF bandwidth, often 100–140 dB on modern instruments. It limits how deep a filter stopband or how high an isolation can be measured.^[2]

Frequently asked questions

What is the difference between a scalar and vector analyzer?

A scalar analyzer measures magnitude only; a VNA also measures phase, enabling full error correction.

Can a VNA measure active devices?

Yes, with care for input power and DC bias through bias tees.

Are low-cost VNAs useful?

For learning and many hobby tasks, yes, within their dynamic range and accuracy limits.

References

Online sources accessed October 21, 2026; printed works cited by edition. See all sources.

“Understanding the Fundamental Principles of Vector Network Analysis (Application Note 1287-1)”. Keysight Technologies. application note.
“Fundamentals of Vector Network Analysis”. M. Hiebel, Rohde & Schwarz. 2007 and later editions.

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