Zero-Doppler Centroid Steering for the Moon-Based Synthetic Aperture Radar: A Theoretical Analysis

Due to the earth and moon's revolutions, the Doppler centroid of the moon-based synthetic aperture radar (moon-based SAR) varies dramatically along the orbit of the moon when the SAR system is looking broadside (nonsquinted). However, the Doppler centroid should be kept as small as possible to avoid range ambiguity and to alleviate difficulty with focus. This letter presents the Doppler properties along the orbit of the moon in accordance with the antenna coordinate system. Based on the Doppler analysis and the phase scan, we propose a method for Doppler centroid steering to minimize the Doppler centroid frequency without rotating the platform. The new method can accurately compensate the Doppler centroid to zero, because it considers the effects of the lunar orbit and the relative motion between earth's target and moon-based SAR. To validate the proposed method, we also derived the lower and upper bounds of the look angle. Subsequently, we performed simulations in accordance with Jet Propulsion Laboratory Development Ephemeris 430 (JPL DE430). Finally, the performance requirement of the phase scan is analyzed so as to validate the proposed method.