Arraying performance of a 3-antenna demonstration array for Deep Space communications

NASA provides telecommunications services to its deep space scientific missions by way of its Deep Space Network (DSN) of large antennas. Currently this DSN consists of monolithic antennas (34 m and 70 m diameter) located equidistant in longitude around the earth. The use of arraying has been proposed as a cost effective way to replace large antennas and/or add capability to the DSN in the future. A demonstration array was constructed at JPL as part of the study of arraying possibilities. This array consisted of three elements, two of which were 6 m-diameter antennas and one of which was a 12 m-diameter antenna. The array included a real-time FPGA based signal processing system capable of simultaneously operating as an interferometer and a signal combiner. The signal combiner was designed to sum the entire received spectrum from all elements of the array with the resulting signal compatible with the downlink tracking and telemetry system used by the DSN. The system was used to track various spacecraft at both frequencies of interest (X-band near 8.4 GHz and Ka-band near 32 GHz) as well as natural radio sources over broader bandwidths around the same frequencies. Signals from the combiner system were provided to a telemetry receiver where performance measurements could be compared to a single DSN antenna. Detailed results of these demonstrations with the Mars Reconnaissance Orbiter (MRO) and the Cassini Orbiter at Saturn are presented.