SKA field of view de-rotation using connected array beam scanning with constant beam shape invited paper

Image formation with high dynamic range is a crucial requirement of next-generation radio telescopes such as the Square Kilometer Array (SKA). Effects that may limit dynamic range include time variations of antenna beams against the celestial sphere during multiple measurements that decrease the effects of thermal noise and increase spatial resolution. Such beam variations must be small or known and resolved in the image computation. We investigate the feasibility of producing celestially invariant beams by varying in time the beamforming coefficients of phased array feeds (PAFs) in offset-fed reflector antennas on altazimuth mounts. Beams are optimized for maximum peak sensitivity of beam correlations subject to a prescribed upper bound on the time variations of correlation radiation patterns relative to the peak. The technique is illustrated by application to an SKA design where the PAF must also correct aberrations produced by shaped reflectors. The initial results indicate that -40dB pattern variations can be obtained over 10° rotations of the field of view with modest impact on sensitivity and duty cycle. Further work is required to determine the dynamic range expected using PAF image formation methods currently in development.