FASTL波段多波束馈源设计的初步分析

把抛物面天线的偏焦理论应用于FASTL波段多波束馈源系统的设计，分析了馈源喇叭横向偏焦距离与相应波束偏离角之间的关系，结合多波束射电望远镜扫描方式的要求，给出了FASTL波段多波束馈源的工作带宽、多波束馈源中相邻喇叭的间距以及喇叭口径大小的限制，并对正六边形阵列中处于不同位置的喇叭对应的波束的主瓣情况作了详细计算和分析。由此说明了FASTL波段多波束馈源采用19波束的可行性。另一方面，根据得到的工作频率带宽和喇叭口径大小的情况，对OMT和喇叭类型的选择进行了探讨。本文给出了FASTL波段多波束系统的大概轮廓，为进一步精确设计指明了方向。

A Preliminary Analysis of a Design of the L-Band Multi-Beam Feed for the FAST

In this paper, the theory of defocus is applied to the design of the L-Band Multi-Beam Feed for the FAST. By analyzing the relation between the defocus distance of a feed horn and the deflection angle of the corresponding beam and considering the requirement of the multi-beam radio-telescope scan method, we derive the working-frequency bandwidth, the distance between neighboring horns, and the limit on the aperture of a single horn. Futhermore, we give a detailed analysis of the gains of the main beams and the side beams from the horns at different positions in a regular-hexagon array. The results show the feasibility of adopting a 19-beam feed design for the FAST based on the working-frequency bandwidth and the aperture limit of a single horn. We additionally discuss the choices of the types of the OMT and the horns. This paper effectively provides an outline of the L-Band Multi-Beam Feed for the FAST, which indicates the direction for future work.