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

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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.