A dual-gain antenna option for GeoSTAR

GeoSTAR is a radiometer concept to provide high resolution microwave images of the Earth from geostationary Earth orbit (GEO) in bands from 50 to 183 GHz. The system consists of a Y-array of correlation interferometers, and uses aperture synthesis to achieve high resolution hemispheric coverage of the Earth. A ground-based 50 GHz demonstration instrument has been built and tested at the Jet Propulsion Laboratory which has now validated the calibration approach and error analysis. These analysis show that the antenna gain of the original design is marginal, since only about 42 percent of the received energy originates in the Earth disk as viewed from GEO. This degrades signal-to-noise (delta-T), and poses a problem for the 183 GHz bands where receiver noise and resolution requirements are greatest. This paper presents a new approach to the array geometry which solves this problem by arranging the majority of elemental antennas along two rows within each of the three array arms. The new geometry provides a factor of SQRT(3) times more distance between adjacent elements, and therefore enough physical space to raise the gain of the antenna elements by a factor of 3. The visibility sample grid and number of elements are unchanged. Only the shortest baselines retain the original design.