射电天文中焦面阵或多波束馈源的应用

焦面阵技术或者多波束馈源系统已经日益广泛地应用于现代射电望远镜，因为它可以充分地利用同一射电望远镜反射面所能提供的信息，在观测比射电望远镜方向瓣大得多的展源时数倍乃至数十倍地提高观测的速度；当存在大气层或电离层的起伏或不均匀影响观测成像质量时，可消除这种影响，提高观测质量；利用焦面阵各单个馈源接收到的信息的互相关，则可以实时监控射电望远镜的反射面、二次反射面、指向精度，从而降低地面上大射电望远镜或空间射电望远镜的精度要求和造价。目前焦面阵已经愈来愈广泛地配置在毫米波射电望远镜和大型射电望远镜的主要波段。对此作了一个较新和全面的评述，对焦面阵应用中的限制，包括相位误差的限制和性能价格比的考虑和可能的前景作了简要的介绍。还分析了在计划中的大型主动球反射面射电望远镜（即FAST）上，配置焦面阵的相应限制、问题和难点，提出了初步的建议，并给出经中英双方讨论后初步拟定的FAST频段、波束及低噪声放大器的配置。

Applications of the Focus Plane Array or the Multi-beam Feed System in Radio Astronomy

The technique of the focus plane array (FPA) or the multi-beam feed system has been more and more widely applied in radio astronomy. Much more information of electric and magnetic field collected at the focus plane could be used to fasten the observational procedure several or even several tens times by scanning the telescope over the extended sources. The image quality observed can be improved by subtracting or removing effects of fluctuation or irregularity in the atmosphere or the ionosphere, and by monitoring or controlling the accuracy of the main reflector, the subreflector and the pointing of the telescope. Costs and requirements for the accuracy of huge radio telescopes or space radio telescopes might be much reduced by introducing the EPA in monitoring and adjusting telescopes in the future. The FPAs have been equipped widely on millimeter and sub-millimeter radio telescopes and main bands of large radio telescopes in the world. The paper will review the situation of that by listing operating feeds for the latter and describing briefly the FPAs equipped on the former. The restriction of applying the FPAs on telescopes and corresponding phase errors will be briefly analyzed in this paper. Consideration of the cost and prospect of application of the EPA are also shortly given. Finally tentative valuation and suggestion of applying the EPA on the FAST, a planned huge spherical radio telescope with active main reflector, are followed. Arrangement of frequencies, beams, LNAs and corresponding system temperature suggested by experts from China and Jodrell Bank Radio Observatory is listed at last.