Direct and Accurate Measurements of Mixer Equivalent Noise Temperatures

Abstract

A new measuring technique has been developed, which enables the effective noise temperature Teff and intrinsic conversion loss Li of a lossy 2-port network to be determined directly. This technique when applied to a mixer, yields results which are in agreement with theoretical predictions (0.5 5Teff5 To; To ambient temperature) and may be measured with greater accuracy than has previously been possible using other methods. Practical results will be presented together with theoretical predictions based on a new approach to mixer noise analysis. This approach gives greater insight into the noise generation mechanisms and is more readily interpreted than other methods published to date in the literature.

Accurate Noise Temperature Measurements on Mismatched Semiconductor Devices

“…Since the noise temperature can be measured with high precision, it is a sensitive indicator for the noise behaviour of the device. Although the experimental results are similar to those in [4], the results reported here have been obtained for mismatched devices without tuning. Furthermore, the input noise temperatures of low noise bipolar transistor preamplifiers have been measured for a number of samples in the frequency range of 20-40 MHz.…”

“…In practical devices, however, the series resistance has to be taken into account. The noise temperature TD of a real diode can be derived to be [8] TT RS + TB RB TD0 (4) RS + RB with RB as the dynamic resistance of the Schottky barrier as a function of the diode current ID n UT RB ---T -_ …”

“…isolators or circulators, to avoid measurement errors caused by the reverse noise radiation of the radiometer receiver, when reflected at a mismatched object under test [2]. In the MHz-range, where passive nonreciprocal components are not available with an acceptable performance, tuning procedures are required to account for mismatching effects [3,4]. The measurement system employed in this paper enables the direct noise temperature measurement without the use of passive nonreciprocal components and any tuning procedure.…”