Applications

A concept using a closely packed array (cluster) of transmit antennas for space-craft applications that require high effective isotropic radiated power (EIRP) is described and analyzed. The September 2003 baseline Jupiter Icy Moons Or-biter (JIMO) plan information provided to this study specifies that a data rate of 10 megabits per second (Mbps) be sent from Jupiter to Earth, at a maximum distance of 6.25 AU using a 32-GHz (Ka-band) downlink with a 3-dB margin, to be received by the equivalent of a DSN 70-m antenna. This requires a 250-MW EIRP, to be delivered by power combined from four 150-W power amplifiers into a 3-m-diameter antenna. The JIMO mechanical pointing error was specified to be ±0.003 rad, which results in an EIRP loss of between 10 dB and 15 dB if a single 3-m-diameter antenna is used without some additional form of beam steer-ing to correct for the mechanical pointing error. A cluster of four 1.5-m-diameter antennas can electronically steer a spatially combined beam to correct for the me-chanical pointing error and reduce the maximum pointing loss to 2.7 dB. Pointing information for electronic beam steering may be obtained by tracking an uplink microwave signal with the cluster or from infrared or optical Earth, Sun, or star trackers mounted with the antenna cluster. The results of a trade study comparing the single-antenna approach with the antenna-cluster approach are given, using a cluster of four antennas. The system architecture and the high-EIRP cluster concept are described. Advantages of the cluster concept over a single antenna include electronic beam steering, reduced antenna mass, higher antenna efficiency, lower power density in the transmit system components, spatial power combining, and graceful degradation