RF and Microwave Measurement: VNA, Spectrum Analysis, Phase Noise, Load Pull and mmWave

This page collects AXMEAS Signal's field notes on RF and microwave measurement, from sub-GHz ISM bands to sub-THz links at 300 GHz: vector network analysis, spectrum and real-time signal analysis, phase noise, I/Q mixers, load pull, satellite and NTN emulation, mmWave frequency extenders and over-the-air measurement. Most articles come from European Microwave Week, electronica and other European shows, and read a real demo screen line by line.

Recurring themes: what a marker on a Smith chart says about reflection and loss; why calibration and the reference plane decide whether an S21 belongs to the connector or the demo board; what sweep speed and real-time bandwidth mean for probability of intercept; and why a phase-noise figure without an offset frequency is incomplete.

Frequently asked questions

What is the difference between real-time and swept spectrum analysis?

A swept analyser steps a resolution filter across the span and is blind outside the current frequency. A real-time analyser captures a band gap-free and computes overlapping FFTs, so short events inside its real-time bandwidth are caught with defined probability of intercept.

Why does VNA calibration matter so much at mmWave?

Cables, adapters and fixtures add loss, delay and mismatch that grow with frequency. Calibration and de-embedding move the reference plane to the device under test; without them the measured S-parameters describe the whole path.

Why does GaN load pull use pulsed or double-pulse stimulus?

GaN transistors show trapping and self-heating, so gain and efficiency depend on pulse width and history. Pulsed and double-pulse load pull separate these effects from the impedance being tuned.

How do I read EVM and MER together?

Both express modulation error. EVM is often normalised to peak constellation power, MER to average power, so for high-order QAM they differ by the constellation's peak-to-average ratio.

See also: Power electronics · Signal integrity and high-speed digital · About AXMEAS Signal