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Low-sidelobe slot arrays for the Juno Microwave Radiometer

Juno is a NASA New Frontiers mission to Jupiter scheduled to launch in 2011. One of the instruments on board is called the Juno Microwave Radiometer (MWR), which will peer into the outer layers of Jupiter with the goal of determining the composition of ammonia and water in its atmosphere. This information will contribute to the knowledge of Jupiter's formation and evolution. The instrument uses six frequency bands, each requiring an antenna with very low sidelobes. Three of the antennas are 8×8 waveguide slot arrays with approximately 30dB Taylor slot amplitude distributions operating at 2.6GHz, 5.2GHz and 10GHz, and each requiring bandwidths of 4%. This paper presents a practical overview of the design and analysis of these antennas and compares measurements with the predictions, including those of finite element models on a finite ground plane using HFSS - a relatively large problem electrically. It was found that there was very good agreement between the HFSS predictions and the measured patterns down to at least −35dB. Due to limited time and space constraints, the paper will focus on the largest and most difficult to fabricate of these antennas, the 2.6GHz “A3” slot array.