The Cold Source Technique for Noise Figure Measurements

Noise figure is an important parameter that describes the noise contribution of an electronic device. A classical approach to measure the noise figure is to use a noise source which delivers two different input noise powers by switching between a “hot” and a “cold” state and a noise receiver (e.g. a spectrum analyzer).

In contrast to this approach, using a vector network analyzer with the “Cold Source” approach eliminates the need for a noise source. A cold source noise power measurement followed by an available gain measurement of the device under test is sufficient to determine the noise figure of the device. This application note describes the “Cold Source” technique for measuring noise figure on the R&S®ZNA family of vector network analyzers.

Background equations are provided for an analysis of noise factor, noise figure and noise temperature on a device under test and a cascade of devices.

Based on a measurement example the user will be guided through the process of setting up a noise figure channel and performing a noise figure measurement. In addition, various measurement options are reviewed, providing guidance as to when and how each option should be utilized to improve the noise figure results.