---
title: "Vector Network Analyzer Interactive Lab | Sandbox Physics"
description: "How can a network analyzer separate a device from its cables?"
canonical_url: "https://sandboxphysics.com/labs/vector-network-analyzer/"
language: "en"
page_type: "lab"
alternate_languages:
  zh-CN: "https://sandboxphysics.com/zh/labs/vector-network-analyzer/"
last_modified: "2026-10-29"
---

IN15 · Where does the cable end?

# Vector Network Analyzer

**How can a network analyzer separate a device from its cables?** A network analyzer compares outgoing RF waves with the incident wave, keeping both amplitude and phase. Known standards reveal the instrument and cable errors at a chosen reference plane. Reflection and transmission corrected to that plane describe the connected device; moving the plane requires a model of the intervening line.

Follow incident and reflected RF waves, calibrate two ports and move a known reference plane before retaining complex reflection and transmission.

> Interactive simulation: open this page in a web browser to change the parameters and run the model.

Model assumptions

A real 50-ohm RMS traveling-wave model uses coherent receiver ratios, passive reciprocal error boxes and matched TEM cables. SOL standards at both ports plus a known through calibrate a reduced two-port model, including source and load mismatch. Isolation and switch terms are zero; this is not a commercial full SOLT uncertainty model. Separate check standards never enter the fit. Receiver ratios do not establish absolute power. Frequency is assumed calibrated; noise is bounded complex receiver noise. Known port extension removes only the specified matched spacer. No dispersive, connector-mode, temperature or nonlinear effects are modeled.

### A saved sweep, at its saved plane

$f/\mathrm{MHz}\quad;\quad20\log_{10}|S_{ij}|/\mathrm{dB}$

Turquoise: corrected reflection; violet: corrected transmission. Amber: raw receiver ratios at the instrument, before correction. Dashed grey: separate ideal device reference at the saved reporting plane. No noisy or nonpassive result is clipped into the unit circle.

Raw waves, calibration and check standards

Kept sweeps

| Record | Device | Calibration | Check error | Valid |
| --- | --- | --- | --- | --- |

Raw receiver channels

| Channel | Real part | Imaginary part |
| --- | --- | --- |

Measured standard wave ratios

| Channel | Real part | Imaginary part |
| --- | --- | --- |

Coefficients fitted from saved standards

| Channel | Real part | Imaginary part |
| --- | --- | --- |

JSON and CSV retain raw complex incident/outgoing waves for both excitations, standards, coefficient snapshots, exact geometry, processing plane, bounded noise, seed and version. Touchstone uses real fifty-ohm reference and the declared RI column order; invalid sweeps cannot be exported as corrected Touchstone.

Physics tutorial

## Choose the boundary before naming the device

**Background** At radio frequencies, a cable stores phase delay and can carry waves in both directions. The analyzer measures wave ratios at its receivers, including its own imperfections.

**Why it matters** A smooth trace can include an excellent cable and a poor device, or the reverse. Calibration specifies which boundary the reported device begins at.

Start with the essentials

- **Focus question**: How can a network analyzer separate a device from its cables?
- **One-sentence intuition**: Known standards define a reference plane; a separate check tests whether the correction predicts something it did not fit.

### Core mathematical model

#### Real-reference RMS power waves

$$
\begin{aligned}a&=\frac{V+Z_0 I}{2\sqrt{Z_0}},\qquad b=\frac{V-Z_0 I}{2\sqrt{Z_0}}\\P&=|a|^2-|b|^2,\qquad Z_0=50\,\Omega\end{aligned}
$$

Current points into each device port. Voltage and current are RMS phasors with positive complex time convention. Net power is incident wave magnitude squared minus outgoing wave magnitude squared. Receiver ratios alone do not calibrate absolute watts.

#### A reflection travels through a line twice

$$
\Gamma_{\mathrm{plane}}=\Gamma_{\mathrm{device}}e^{-2\gamma\ell},\qquad\gamma=\alpha+\mathrm i\frac{2\pi f}{v}
$$

A known matched spacer adds an outward and return path to reflection. Transmission accumulates the sum of the two one-way spacer lengths. Extension removes that specified propagation; it cannot guess an unknown connector.

### Common difficulties

#### A matched load has no resolved reflection phase

**Typical misconception** Every reflection must have a meaningful angle.

**Better mental model** At a reflection null, noise determines the angle. The phase is withheld when the wave ratio falls below the stated floor.

#### One-port correction is not full two-port calibration

**Typical misconception** Correcting two reflections also corrects transmission.

**Better mental model** The two receivers need a through relation, and both mismatch feedback paths enter the matrix inverse. This reduced model explicitly omits switch terms and isolation.

### Run the experiment

1. 01

   #### Follow both directions

   Compare the filter and through presets, then reverse the source.

   **What to observe:** Incident and reflected markers follow the physical coaxial paths. The stored sweep contains both excitation directions.

2. 02

   #### Move the cable end

   Drag the device carriage to change cable length, then acquire fresh standards.

   **What to observe:** The old calibration becomes incompatible when the actual cable changes. Old saved records keep their original geometry.

3. 03

   #### Move only the reporting plane

   Choose the reference-plane preset and increase the extension.

   **What to observe:** The pink rings move along the known spacer. Corrected phase changes by round-trip reflection or one-way transmission propagation.

4. 04

   #### Test the calibration

   Compare the defined and wrong-kit presets. Inspect the withheld checks and export a sweep.

   **What to observe:** Open and short parasitics matter. The independent load and series-resistor checks never contribute to the calibration fit.

Physical conclusion

Keep raw forward and reverse waves, standard definitions, cable geometry and calibration together.

## Related experiments and articles

How physics instruments measure · Reading path

### How physics instruments measure

Articles on this path that use this experiment, followed by the other experiments they suggest.

1. [Article **How a network analyzer separates the cable from the device**](https://sandboxphysics.com/stories/instruments/vector-network-analyzer/)

Fields & matter · Starter path

## From a field to an electron microscope

Map an electric field and steer a charged particle. Then find the electron's wavelength and use electron beams to see a crystal and a surface.

[Start here → **Make an Electric Field Visible** Move the probe around a dipole and check that the field always points downhill on the potential landscape. Observe · 8 min](https://sandboxphysics.com/labs/electric-field/)

1. [1 Make an Electric Field Visible](https://sandboxphysics.com/labs/electric-field/)
2. [2 A Charge Bending through Fields](https://sandboxphysics.com/labs/charged-particle/)
3. [3 Electron Wavelength & Voltage](https://sandboxphysics.com/labs/electron-wavelength/)
4. [4 Electron Diffraction & Reciprocal Space](https://sandboxphysics.com/labs/electron-diffraction/)
5. [5 TEM Bright Field, Dark Field & SAED](https://sandboxphysics.com/labs/tem-mode-selector/)
6. [6 SEM Secondary-Electron Topography](https://sandboxphysics.com/labs/sem-topography/)

[View the full path →](https://sandboxphysics.com/topics/fields-and-matter/#starter-path)