SMAP: Performance verification and testing of a challenging instrument antenna

NASA's Soil Moisture Active and Passive (SMAP) Mission will soon provide global measurements of soil moisture and its freeze/thaw state. These data will be used to enhance our understanding of the processes that link water, energy and carbon cycles, and to extend the capabilities of weather and climate prediction models. Accurate predictions of the antenna radiation pattern are needed for instrument calibration but measurements of the flight reflector will not be performed. Therefore, requirement verification was accomplished through a combination of RF model predictions, scale model measurements and flight feed measurements. This paper provides an overview of this complex instrument antenna with particular emphasis on the challenges overcome during the development phases. A description of the RF model used to predict the SMAP antenna performance is provided along with an overview of the scale model measurement campaign. The excellent agreement between the RF model predictions and the scale model measurements allowed the use of the former as a means of verifying that the antenna met its challenging requirements.