Beam Patterns of the Five-hundred-metre Aperture Spherical Telescope: Optimisation

TL;DR

This paper explores optimal parameters for the spherical panels of FAST to enhance beam shape and gain, demonstrating that precise adjustments in curvature, focal distance, and panel positioning significantly improve observational performance.

Contribution

It identifies optimal curvature radius and focal shift for spherical panels, and emphasizes the importance of precise control for stable, high-quality beam patterns.

Findings

Optimal curvature radius around 300 m improves beam shape.

Small focal shifts (~a few cm) increase aperture efficiency by ~10%.

Panel shifts of a few mm enhance beam pattern stability.

Abstract

The Five-hundred-metre Aperture Spherical Telescope (FAST) uses adaptive spherical panels to achieve a huge collecting area for radio waves. In this paper, we try to explore the optimal parameters for the curvature radius of spherical panels and the focal distance by comparison of the calculated beam patterns. We show that to get the best beam shape and maximum gain, the optimal curvature radius of panels is around 300 m, and a small shift in the focal distance of a few cm is needed. The aperture efficiency can be improved by ~10% at 3 GHz by this small shift. We also try to optimise the panel positioning for the best beam, and find that panel shifts of a few mm can improve the beam pattern by a similar extent. Our results indicate that accurate control of the feed and panel positions to the mm level is very crucial for the stability of FAST's observational performance.