Collaborative Research: Development of a Millimeter-wave Phased Focal Plane Array

目前，一个典型的大型毫米波射电望远镜的成本超过1亿美元，但最先进的焦平面外差接收器阵列覆盖的有用视场不到10%，敏感区域之间有很大的差距。此外，单独的组件不能有效地耦合到天线集中的能量，使望远镜在天空中的分辨率降低20%，通常会失去大约一半的可用信号。马萨诸塞州大学的N·埃里克森博士和杨百翰大学的B·杰夫斯博士分别提出的关键新发展是利用相控阵馈电技术构建焦平面阵列。这种方法不同于传统的馈电喇叭，它使用一簇小天线馈电来合成主天线的单一馈电。这样的阵列收集了焦平面内的所有能量。这种焦平面阵元的相位组合使人们能够合成具有最佳大小和幅度/相位分布的喇叭，以提高望远镜分辨率并补偿望远镜表面误差。与此同时，它们在天空中产生的波束几乎与阵列中的元素一样多。虽然相控焦平面阵列有望给射电天文学领域带来革命性的变化，但成功部署大型二维阵列仍需数年时间，因为它需要克服制造、加工和封装方面的障碍。埃里克森博士和杰夫斯博士计划测试用非常小的单元间隔生产接收器前端的概念，演示现代数字信号处理器在波束矢量组合方面的实用性，并开发用于组合波束、校准阵列和处理最终数据流的计算算法。这个为期3年的项目的目标是一个覆盖70-95 GHz频率范围和100 MHz带宽的8 x 8阵列，经过低温冷却并安装在国家射电天文台100米绿岸望远镜上。除了为未来大型、高效的二维毫米波接收器阵列铺平道路外，Erickson/Jeffs项目还将涉及两个合作机构的工程和天文学研究生，并为五所大学天文学本科生实习计划中有才华的本科生提供高级研究课题。因此，它将教育新一代研究人员在毫米波阵列仪器的复杂艺术方面的成员。这项工作的资金是由NSF的天文科学部通过其先进技术和仪器计划提供的。

Presently, a typical large mm-wave radio telescope costs more than $100M but state-of-the-art arrays of focal-plane heterodyne receivers cover less than 10% of the useful field of view with large gaps between sensitive areas. Moreover, individual components are not efficiently coupled to the energy concentrated by the antenna, reducing the telescope's resolution on the sky by 20% and typically losing about half of the available signal. The key new development proposed by collaborators Drs. N. Erickson and B. Jeffs of the University of Massachusetts and Brigham Young University, respectively, is the construction of focal-plane arrays utilizing phased array feed techniques. This approach differs from traditional feed horns by using a cluster of small antenna feeds to synthesize a single feed for the main antenna. Such an array collects all of the energy in the focal plane. Phased combination of the elements of this focal plane array allows one to synthesize horns of optimal size and amplitude/phase distribution to enhance the telescope resolution and compensate for telescope surface errors. At the same time they produce nearly as many beams on the sky as elements in the array.While phased focal-plane arrays hold great promise for revolutionizing the field of radio astronomy, successful deployment of large two-dimensional arrays is still several years off, for it requires hurdles to be overcome in manufacturing, processing, as well as packaging. Drs. Erickson and Jeffs plan to test concepts for producing receiver front-ends with very small element spacings, demonstrate the utility of modern digital signal processors to do the vector combination of beams, and develop computational algorithms for combining the beams, calibrating the array, and processing the final data stream. The goal of this 3-yr project is an 8 x 8 array covering the frequency range 70 - 95 GHz with 100 MHz bandwidth, cryogenically cooled and installed on the 100-m Green Bank Telescope of the National Radio Astronomy Observatory.In addition to paving the way for future large, efficient, two-dimensional mm-wave receiver arrays, the Erickson/Jeffs project will involve engineering and astronomy graduate students at the two collaborative institutions and provide advanced research topics for talented undergraduate students in the Five College Astronomy Undergraduates Internship Program. It will thereby educate members of a new generation of researcher in the complex art of mm-wave array instrumentation. Funding for this work is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.