Meaningful G/T Measurements – Made at Night

Abstract

The ratio of receive antenna gain to receive system noise temperature (G/T) is widely used throughout the satellite and telemetry communities, always appearing in the link budget in some manner. The conventional method of measuring G/T for directional antennas seems simple: measure received power while pointing the antenna at the sun, repeat the measurement while pointed at “cold sky”, and do a few simple calculations. This paper briefly summarizes the many sources of error in this technique and then presents an alternative approach using a calibrated signal source instead of the sun. Both theoretical and empirical results are presented. The proposed approach can be applied to any type of receiving system (including active antennas and multi-beam phased arrays) and yields G/T results that apply meaningfully to the link budget.