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The effects of the antenna far-field power pattern limits the imagingperformance of modern wide-bandwidth, high-sensitivity interferometric radiotelescopes. Given a model for the aperture illumination pattern (AIP) of theantenna, referred to as the A-term, the wide-band (WB) A-Projection algorithmcorrects for the effects of its time, frequency, and polarization structure.The level to which this correction is possible depends on how accurately theA-term, represents the true AIP. In this paper, we describe the A-Solvermethodology that combines physical modeling with optimization to holographicmeasurements to build an accurate model for the AIP. Using a parametrizedray-tracing code as the predictor, we solve for the frequency dependence of theantenna optics and show that the resulting low-order model for the Karl G.Jansky Very Large Array (VLA) antenna captures the dominant frequency-dependentterms. The A-Solver methodology described here is generic and can be adaptedfor other types of antennas as well. The parameterization is based on thephysical characteristics of the antenna structure and optics and is thereforearguably a compact representation (minimized degrees of freedom) of thefrequency-dependent structure of the antenna A-term. In this paper, we alsoshow that the parameters derived from A-Solver methodology are expected toimprove sensitivity and imaging performance out to the first side-lobe of theantenna.

the astronomical journal

Direction Dependent Corrections in Polarimetric Radio Imaging II:  A-Solver Methodology A low-order solver for the A-Term of the A-Projection  algorithm