Improving Conical Scanning for Satellite Tracking On-The-Move

Abstract

Mobile satellite antennas are gimbal-mounted with an active control system to keep the antenna pointed at the target satellite. Short time-scale antenna stabilization is achieved with gyroscope feedback. Long time-scale tracking of the satellite is maintained by scanning the antenna: The beam is intentionally nutated and the resulting change in signal strength is used to estimate how well the antenna is aligned to the satellite. We review the basic architectures for tracking with an outer control loop, assuming that the system is built upon a fast inner stabilization loop. The problem is formulated in a generic mathematical way, not specific to RF satellite communication. Approaches and nomenclature from other fields faced with the same problem of peak-seeking control are discussed. One common and simple technique for tracking is analyzed in detail to reveal the shortcomings that lead to degraded performance. An improvement is suggested and subjected to the same transient analysis to show the improvement. Implications to the overall closed-loop tracking systems are discussed.

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