Phased Array Feed: Development of a Cryogenic 19 Element System for Radio Astronomy

在厘米波长工作的射电望远镜历史上只使用一个馈电系统，相当于天空中的一个空间像素。这造成了一个非常缓慢和费力的数据收集过程。相比之下，光学和红外波长的现代仪器，以及最近的毫米和亚毫米波长的仪器，能够同时从多个(在某些情况下是许多)独立的像素并行收集数据。观测效率和科学能力方面的收益可能是巨大的。多像素提高了去除信号背景的能力，大大提高了进行大面积调查的速度。21厘米波长的第一步是阿雷西博天文台7像素的阿雷西博L波段馈电阵列，该阵列于2004年安装在305米长的望远镜上。未来对观测能力影响更大的方向是计划为阿雷西博提供低温冷却的40光束相控阵馈电，也在L波段工作。可行性研究表明，阿雷西博光学系统可以支持天空中的所有40束光束，一个将容纳19个单元阵列的演示杜瓦系统即将完成。为了进一步开发建造未来大型阵列所需的技术，康奈尔大学的G.Cortes-Medellin博士和D.Campbell博士计划在低温杜瓦上增加低噪声放大器，并部署整个系统用于阿雷西博望远镜。目标是证明使用多像素阵列可以实现低于35K的系统噪声温度，研究阿雷西博光学系统的最佳波束形成算法，并确定系统的整体时间稳定性。该项目正在推进的新一代更高效的多元L波段接收器将与杨百翰大学正在开发的相控阵馈电信号处理后端相结合。总而言之，这些研究将使设计更大的全尺寸相控阵馈源成为可能，这将极大地加快厘米波长测量的能力。在整个项目中受雇的学生和年轻科学家将帮助增强下一代精通硬件的研究人员，为重要的无线电方案提供信号检测和传播方面的专业知识。这项工作的资金由NSF的天文科学部通过其先进技术和仪器计划提供。

Radio telescopes operating at centimeter wavelengths have historically used just a single feed system, equivalent to a single spatial pixel on the sky. This makes for a very slow and laborious data-gathering process. In contrast, modern instruments at optical and infrared wavelengths, and more recently those at millimeter and sub-millimeter wavelengths, are able to gather data in parallel from multiple (and in some cases many) independent pixels at once. The gains in observing efficiency and scientific capability can be enormous. Multiple pixels improve the ability to remove signal background and greatly increase the speed at which large-area surveys can be carried out. An initial step at the wavelength of 21 centimeters is the Arecibo Observatory 7-pixel Arecibo L-band Feed Array (ALFA), installed on the 305-meter telescope in 2004.A future direction with even more impact on observing power is a planned cryogenically-cooled 40-beam phased array feed (PAF) for Arecibo, also operating at L-band. Feasibility studies have shown that Arecibo optics can support all 40 beams on the sky, and a demonstration dewar system that will house a 19-element array is nearly complete. To further develop the technology needed to build large arrays of the future, Drs. G. Cortes-Medellin and D. Campbell of Cornell University plan to add low noise amplifiers to the cryogenic dewar and deploy the full system for use on the Arecibo telescope. The goals will be to demonstrate that a system noise temperature of less than 35 K can be achieved with a multipixel array, investigate optimal beam-forming algorithms for Arecibo's optics, and determine the system's overall temporal stability. The new, more efficient generation of multi-element L-band receivers being advanced by this project will mesh with phased array feed signal-processing backends under development at Brigham Young University. Together, the studies will enable the design of a larger, full-scale phased array feeds that will greatly accelerate the capabilities of cm-wavelength surveys. Students and young scientists employed throughout the project will help augment the next generation of hardware-savvy researchers with expertise in signal detection and propagation for the important radio regime.Funding for this work is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.