Building a model for antenna aperture illumination pattern

The sensitivity of modern radio telescopes is high enough that imaging is often limited by the effects of variations in the antenna primary beams as a function of frequency, polarization, time or antenna. The WB Full-polarization AW-Projection (WB-FP-AWP) algorithm offers a method to correct for the effects of antenna primary beams, which requires an accurate model of the antenna aperture illumination patterns (AIP), as a function of time, frequency, and polarization. The AIP is usually referred to in the literature as the A-term. This report details the development of an algorithm to model the antenna aperture illumination pattern. To model complex-valued aperture illumination patterns in full polarization an algorithm using Zernike Polynomials was tested against holographic measurements of the EVLA, ALMA and MeerKAT telescopes and demonstrated to achieve the required accuracy. Since this is a polynomial model, it is applicable to any type of antenna (as demonstrated by application to EVLA, ALMA and MeerKAT – which have very different type of antennas). The algorithm implementation was done in Python. More work is necessary to incorporate this work for use as part of the WB-FP-AW-Projection algorithm for imaging, which will enable its use for wide-field, wide-band, polarimetric imaging with MeerKAT.