Multiplicative and Additive Low-Frequency Noise in Microwave Transistors

The additive noise (i.e., noise figure) in the 1-Hz-1-GHz range and multiplicative noise (i.e., gain fluctuations) in the 1-Hz-100-kHz range have been measured for six different types of high electron mobility transistors and two heterojunction bipolar transistors. The instrumentation enables measurement of multiplicative noise as small as 10^-6 (1 ppm). Measurements were performed at 300 and 22 K and results are discussed with regard to transistor technology, coupling of additive and multiplicative effects, and bias circuit dependence. The results are applied to radiometers and the degradation in performance due to the gain fluctuation is presented.