G/T measurement techniques for MUOS on orbit testing

On-orbit testing of G/T for MUOS is complicated by the satellite automatic level control (ALC) which compensates for Ka rain fades to achieve high link availability. Because the satellite is commanded to operate in a non-standard mode for testing, the uplink transmitting terminal broad-band noise contribution is nearly equal to the expected level of satellite noise being measured! The antenna size constraint of the UHF receiving test terminal further contributes to the total unwanted noise in the test. In this paper, we describe a technique which uses a sequence of measurements to systematically isolate the two noise sources (transmitting and receiving terminal) which potentially contribute to satellite G/T measurement error. Using the link equations provided, power levels measured by a spectrum analyzer which properly determine satisfactory performance of the satellite under test can be predicted. Once the satellite has launched, the technical approach described in this paper will be used to demonstrate the G/T ratio of the MUOS communications payload is consistent with pre-launch measurements.