|Erik van der Wal
| Lately we have been busy with a cool subject in every sense of the word, maybe except for the protective gear, which is not up to the latest fashion.
Accompanied to the ever present goal of achieving lower and lower noise figures, is the demand to be able to measure these results accurately. The usual way is to a use a well calibrated diode noise source. Although these are pretty accurate, the uncertainty of the generated noise temperature is too large.
To improve the accuracy, we utilize the known temperature of boiling liquid nitrogen as a constant for calculating noise temperature. This mirrors the conceptual foundation of the noise standards used in virtually all national standards laboratories world-wide.
Furthermore, an analysis of the dominant uncertainty contributors was made. This allows us to add error bars to our noise figure measurements. The insert in the top-right shows a comparison of the uncertainties of noise sources for a room-temperature LNA measured at 1 GHz. The bottom line clearly shows the huge improvement in uncertainty when using liquid nitrogen.