A 4-GHz band low-noise measurement system

A 4-GHz-band noise measurement system has been built for calibrating microwave low-noise sources accurately. The system reduces the contribution of several errors occurring in conventional systems. The system is composed of a highly stable and sensitive Dicke-type comparison radiometer, whose front end is cooled with liquid nitrogen, and two highly stable standard noise sources: one using liquid nitrogen and the other operating at the ice point. It is also computerized to provide automatic measurement operation and real-time data processing. The ultimate calibration error is within about ±0.4 K, for all temperatures up to 350 K, and is within ±0.2 K near 80 K and 273 K.