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

TL;DR

This paper introduces the A-Solver methodology, combining physical modeling and optimization, to accurately model the antenna aperture illumination pattern for improved radio interferometric imaging.

Contribution

It presents a low-order, physically motivated model for the antenna A-term that enhances correction accuracy in wide-bandwidth radio imaging.

Findings

The A-Solver captures dominant frequency-dependent antenna effects.

The methodology improves sensitivity and imaging performance.

The approach is adaptable to different antenna types.

Abstract

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