VNA Hardware Architecture
A Vector Network Analyzer measures S-parameters by injecting a known signal at one port and measuring the amplitude AND phase of signals at all ports. The key hardware components:
| Component | Function |
|---|---|
| Signal source | Swept RF source (50 MHz – 67+ GHz) |
| Directional bridge/coupler | Separates incident from reflected waves |
| Samplers/receivers | Measure amplitude and phase of waves |
| Reference receiver | Tracks source level for ratioed measurement |
| DSP/display | Computes S-parameters, Smith chart, etc. |
Directional Bridge Principle
The directional bridge separates the incident wave (a) from reflected wave (b): Incident port: a₁ = source_power / √2 Reflected port: b₁ = reflected_power / √2 S11 = b₁/a₁ (measured as complex ratio) Imperfect bridge → directivity error Ed (leakage into reflected port) SOLT calibration removes Ed: directivity typically improved to <−40 dB
From VNA to Touchstone
VNA measures complex S-parameters at each frequency sweep point:
S11_complex = Re{S11} + j·Im{S11} at each f
Export to Touchstone (# GHz S DB R 50):
f_GHz S11_dB S11_deg S21_dB S21_deg ...
1.000 -15.23 42.1 -1.83 -141.2 ...
Load in RF View → instant visualizationRF View: RF View is the analysis endpoint for all VNA measurements. Load any Touchstone file for Smith chart, matching design, simulation, and Monte Carlo. Free on Google Play.