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不到10%的有效视场，敏感区域之间的间隙很大。此外，单个组件不能有效地耦合到天线集中的能量上，这使望远镜在天空中的分辨率降低了20%，并且通常会损失大约一半的可用信号。由合作者提出的关键新发展。分别来自马萨诸塞大学和杨百翰大学的N. Erickson和B. Jeffs正在利用相控阵馈电技术构建焦平面阵列。这种方法与传统的馈源喇叭不同，它使用一组小天线馈源来合成主天线的单一馈源。这样的阵列收集了焦平面上所有的能量。该焦平面阵列各单元的相控组合可以合成最优尺寸和幅相分布的角，从而提高望远镜分辨率，补偿望远镜表面误差。与此同时，它们在天空中产生的光束几乎与阵列中的元素一样多。虽然相控焦平面阵列有望彻底改变射电天文学领域，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。Drs。Erickson和Jeffs计划测试以非常小的元件间距生产接收器前端的概念，展示现代数字信号处理器在波束矢量组合方面的效用，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年的项目的目标是在国家射电天文台的100米绿岸望远镜上安装一个覆盖70 - 95 GHz频率范围、100 MHz带宽的8 × 8阵列，进行低温冷却。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，埃里克森/杰夫斯项目还将涉及两所合作机构的工程和天文学研究生，并为五所学院天文学本科生实习计划中的有才华的本科生提供先进的研究课题。因此，它将教育新一代毫米波阵列仪器复杂艺术的研究人员。这项工作的资金由美国国家科学基金会天文科学部通过其先进技术和仪器项目提供。

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.