Suggested quasi Cassegrain system for multi-beam observation of FAST

TL;DR

This paper proposes a quasi Cassegrain system for FAST, a large radio telescope, enabling multi-beam observation from 0.5 to 8 GHz with improved image quality and a flexible number of feeds.

Contribution

It introduces a novel quasi Cassegrain design for FAST that simplifies the secondary reflector and enhances multi-beam capabilities across a wide frequency range.

Findings

Supports 7 to 217 feeds across 0.5-8 GHz

Achieves excellent image quality with a small secondary reflector

Enables integration with PAF technology for more feeds

Abstract

FAST, the largest single-dish radio telescope in the world, has a 500-meter diameter main reflector and a 300-meter diameter illumination area. It has a shape variable main reflector, which changes the shape of the illuminated area in the main reflector into a paraboloid continuously. In this article, we propose a quasi Cassegrain system to FAST. The detailed design results are given in this paper. Such a quasi Cassegrain system only needs to add a 14.6-meter diameter secondary reflector, which is close to the size of the feed cabin, the distance from the secondary reflector to the focus is only 5.08-meter, and it has excellent image quality. In this quasi Cassegrain system the shape of the illuminated area in the main reflector continuously changes into an optimized hyperboloid. Using this quasi Cassegrain system from frequency 0.5 G to 8 G, the multi-beam system can include 7 to 217 feeds. If this system is used in combination with PAF technology, more multi-beam feeds can be used.