中国科学院南京天文光学技术研究所机构知识库

FAST, the largest single-dish radio telescope in the world, has a 500-meter diametermain reflector and a 300-meter diameter illuminated area. It has amain reflector that can vary its shape, which continuously changes the shape of the illuminated area in reflector into a paraboloid. In this article, we propose a quasi-Cassegrain system for FAST. The detailed design results are provided. 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 5.08m, 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 0.5GHz to 8GHz, the multi-beam system can include 7 to 217 feeds. If this system is used in combination with Phased Array Feed (PAF) technology, more multi-beam feeds or a higher working frequency can be used.