Dynamic Noise Figure Measurements

Dynamic noise figure (NF) measurements are essential for accurately characterizing the performance of devices like amplifiers and converters in real-world scenarios, especially in radar and communication systems. Traditional methods, such as the Y-factor technique, use a spectrum analyzer and calibrated noise source to evaluate additive noise under small-signal conditions. While sufficient for receivers, these measurements fail to reflect the true performance of amplifiers operating near their 1 dB compression point—common in transmitters.

The R&S®FSWP phase noise analyzer and VCO tester address this limitation by enabling dynamic, large-signal NF measurements based on phase noise analysis. Unlike small-signal approaches, this method accounts for the flicker noise and wideband noise that dominate at higher input power levels. By measuring phase noise across varying drive levels, the FSWP accurately captures the additive/residual phase noise and calculates a more realistic NF. The analyzer uses the equation:
NF = L(f) – Nth + Pin,
where L(f) is phase noise at a specified offset, Nth is thermal noise (–177 dBm/Hz), and Pin is the input power.

Experimental results show that as input levels increase toward 0 dBm, the noise figure worsens significantly, proving that traditional small-signal NF underestimates true system behavior. This makes the FSWP approach particularly valuable for link budget calculations in practical systems. With features tailored for precise measurement under operational conditions, the R&S®FSWP is a superior tool for engineers needing accurate NF data for high-frequency and high-performance designs.