What Is a Vector Network Analyser? A Practical Guide to VNAs and How to Choose One

A Vector Network Analyser (VNA) is the instrument RF and microwave engineers reach for when they need to know exactly how a component behaves at frequency — not just whether a signal gets through, but how much is reflected, how much is lost, and how the phase shifts along the way. This guide explains what a VNA measures, how it works, and how to match one to your application. If you already know what you need, you can jump straight to Telonic’s range of vector network analysers.

What a VNA actually does

A VNA sends a known signal into a device under test (the DUT), then measures both what reflects back and what passes through. Because it measures magnitude and phase — not just signal level — it can fully characterise how a device treats RF energy. That is the “vector” in the name, and it is the dividing line between a VNA and simpler scalar instruments such as a VSWR meter, which capture amplitude only and so cannot describe impedance completely.

This matters because a complete picture of a component’s behaviour requires phase. Knowing that a filter passes 90% of power at a frequency is useful; knowing the phase relationship as well lets you design matching networks, predict group delay, and plot results on a Smith chart.

S-parameters: what a VNA reports

VNA measurements are expressed as scattering parameters, or S-parameters. For a 2-port device the four common ones are:

When you test an antenna, S11 is usually the headline figure — it shows how much signal is reflected instead of radiated. When you test a filter, S21 matters more, because it shows which frequencies pass and which are blocked.

From these raw S-parameters a VNA derives the numbers most engineers work with day to day: return loss (how little signal a well-matched device reflects), VSWR (another expression of match quality against a 50 Ω system), insertion loss (how much signal a device costs you as it passes through), and phase / group delay (how timing changes across the band).

How a VNA works

Inside, a VNA combines a signal source with multiple receivers. The sequence is straightforward:

1. The instrument generates a known swept-frequency signal.
2. That signal is driven into the DUT.
3. Directional couplers separate the incident, reflected, and transmitted waves.
4. The receivers measure magnitude and phase of each, normalised against the source so absolute output power doesn’t matter.
5. Error correction (from calibration) removes the contribution of cables, adaptors, and fixtures.
6. The result is displayed as S-parameters, return loss, VSWR, impedance, and phase.

A 1-port VNA can measure reflection only — enough for basic antenna matching. A 2-port VNA measures reflection and transmission, which covers the large majority of RF components. Higher-end 4-port instruments handle differential and multi-port devices.

VNA vs spectrum analyser

These two RF instruments are often confused, but they answer different questions. A spectrum analyser is a passive receiver: it measures signals that already exist — power, harmonics, noise, interference, occupied bandwidth. A VNA is active: it generates its own known stimulus and measures how a device responds to it.

Put simply, a spectrum analyser looks at signals; a VNA tests how a device behaves when a signal passes through it. Use a VNA for return loss, VSWR, impedance, insertion loss, gain, phase, and S-parameters. Use a spectrum analyser for signal power, spurious emissions, and interference. Most RF labs keep both on the bench.

How to choose a VNA

Four specifications do most of the deciding. Price follows from them rather than the other way around.

Frequency range

Your VNA must cover the highest frequency you need to measure, including relevant harmonics. The most affordable entry point for sub-3 GHz work is the Siglent SNA5003-E (9 kHz–3 GHz); broader sub-6 GHz development — most antenna, Wi-Fi, Bluetooth, and IoT work — is well served by a Rigol DNA5042 (5 kHz–4.5 GHz) or Siglent SNA5006-E (6.5 GHz). Radar, 5G mmWave, and satellite work need the higher-frequency 20 GHz or 26.5 GHz models. Higher frequency raises cost steeply, so don’t pay for range you’ll never use.

Number of ports

A 2-port VNA is the workhorse: reflection and transmission for filters, amplifiers, cables, and antennas. Choose a 4-port analyser when you work with differential or balanced devices, or want to characterise a multi-port module in a single setup.

Dynamic range

Dynamic range is how well the VNA distinguishes very small signals from large ones — essential for deep filter notches, isolation, and high-loss devices. Across Telonic’s range this is the main practical difference between the entry series and the wider-dynamic-range Rigol DNA6000 and Siglent SNA6000 bench instruments at equivalent frequencies.

Calibration

A VNA is only as accurate as its calibration. Cables, adaptors, and fixtures all introduce phase shift and loss; calibration baselines and removes them. Common methods include SOLT (Short-Open-Load-Through) and faster electronic calibration kits. Treat the calibration kit as part of the measurement, not an accessory — and note that Telonic includes calibration with supported instruments.

Form factor

Bench VNAs suit lab and production work. Handheld VNAs such as the Siglent SHN900A series (up to 26.5 GHz) are built for field antenna checks, site testing, and distance-to-fault work where portability outweighs the broadest capability. If you only need an instrument occasionally, renting avoids tying up capital.

Quick reference

• Antenna / IoT / sub-6 GHz development: 2-port, up to ~4.5–6 GHz.
• Filters, amplifiers, broadband components: 2-port with strong dynamic range, frequency to suit the device.
• Differential / balanced / multi-port modules: 4-port.
• Field and site work: handheld.
• Occasional or one-off projects: rental.

Frequently asked questions

What does VNA stand for?

Vector Network Analyser (Vector Network Analyzer in US spelling).

Is a VNA the same as a network cable tester?

No. A VNA measures RF and microwave electrical performance. It is unrelated to an Ethernet/LAN cable tester.

Can a VNA test antennas?

Yes — return loss, VSWR, and impedance matching are among the most common VNA measurements.

Do I need a 1-port or 2-port VNA?

Use 1-port for simple reflection only. Choose 2-port if you need to measure transmission through a device, which most applications require.

Why does calibration matter so much?

Without it, cables and adaptors corrupt the reading. Calibration removes their effect so the result reflects the device itself.

Ready to specify an instrument? Browse Telonic’s vector network analysers, compare the bench and handheld ranges, or request a quote.