Focal field analysis of very large approximated parabolic multibeam reflector

This paper describes results of investigation into focal field distribution and beam capacity for a 300-meter diameter and 140.1 meter focal length paraboloid, which is designed for FAST (five-hundred-meter aperture spherical telescope). Two structure models are compared at different scales and frequencies. It is proven that flat unit with size of 10 meters can give a clear focal field vision suitable for simultaneous multidirectional observation, while for larger design size, spherical curved units are helpful in reducing surface and focal field aberration, and works with 15 meter unit at least. An estimation of beam capacity according to unit shapes, size and frequency is presented also.