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Test & Measurement System

Vector Network Analyzer (VNA)

VECTOR NETWORK ANALYZER (VNA) S-PARAMETER MEASUREMENT: MAGNITUDE AND PHASE SOURCESynthesizer POWERSplitter REFCoupler REF RXa1/a2 TO DUT PORT 1 PORT 2 FROM DUT DUT TESTCoupler TEST RXb1/b2 LOAD50Ω DSPS-parameter Calculation S11 = b1/a1 | S21 = b2/a1 S22 = b2/a2 | S12 = b1/a2
Component Descriptions

Signal Chain Walkthrough

A Vector Network Analyzer measures the S-parameters (scattering parameters) of RF components and networks by injecting a known signal and measuring the reflected and transmitted waves in both magnitude and phase.

Signal Source

A synthesized signal source sweeps across the measurement frequency range. Modern VNAs cover DC to 110+ GHz with sub-Hz frequency resolution.

Directional Couplers

Reference and test couplers separate the incident wave (a) from the reflected/transmitted wave (b). The reference coupler samples the incident power; the test coupler samples the response from the DUT.

Receivers

Coherent receivers (tuned to the source frequency) measure the magnitude and phase of the reference and test signals. The ratio b/a gives the S-parameter at each frequency point.

Calibration

Error correction using known standards (open, short, load, thru) removes systematic errors from cables, connectors, and the VNA's own imperfections.

Typical Specifications

Component Specifications

ComponentParameterTypical Value
FrequencyRangeDC to 110+ GHz
Dynamic RangeTypical100 - 140 dB
PortsConfiguration2 or 4 port
IF BandwidthRange1 Hz - 1 MHz
Trace Noise@10 kHz IFBW0.002 dB RMS
Design Note: VNA dynamic range is limited by the directional coupler directivity, receiver noise floor, and source power. Calibration is essential: a 2-port SOLT calibration corrects 12 error terms. For on-wafer MMIC measurements, TRL (Thru-Reflect-Line) calibration using fabricated on-wafer standards provides the best accuracy.
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