Unifying G/T and Noise Figure Metrics for Receiver Systems

The conventional method of comparing system performance of SatCom transceivers is the classical G/T method. The G/T method consists of determining the gain of the system divided by the noise temperature of the system. G/T is a useful metric for comparing systems as this metric sets the system's signal-to-noise ratio (SNR). A close cousin to the G/T metric, is the noise figure metric. Typically, noise figure is defined for a circuit topology, and not for a system which is a hybrid topology, consisting of field density characteristics on its input, and voltage-current circuit characteristics on its output. (e.g. antenna-receiver systems). It will be shown that the G/T characterization is only valid for pure signals (no thermal noise contamination from the transmit source), and the Friis noise figure calculation is only accurate for systems whose input noise levels are of the same value as those used to measure the receiver's stated noise figure. This paper presents a variation of the application of the IEEE noise figure definition (in terms of effective input noise temperature) which has been expanded to include systems that are a hybrid of wave and circuit characteristics such as the integration of an antenna with a receiver.