Project of a multibeam UHF receiver to improve survey capabilities

Abstract

The Institute of Radioastronomy (IRA-Bologna) of the National Institute for Astrophysics of Italy (INAF – Rome) joined the European group for the Square Kilometer Array Design Study (SKA-DS) in the frame of the FP6 program. One of the goals of the Design Study was the construction and test of a state of the art very small SKA prototype.A segment (1/8) of the N/S arm of the large Northern Cross array (408MHz+/−8MHz) was exploited to obtain a prototype array, made up by 8 cylindrical concentrators (23.5mt×7.5mt) equipped with 4 receivers each. In this way a 32 receivers array with a total collecting area of about 1400m2 was obtained. Signals are directly carried from the receivers, located on the focal lines, down to the back end, located in the processing room, via a very cost effective analog optical links. Here a fast back end, presently based on Field Programmable Gate Array (FPGA) Berkeley-Roach boards, takes care of running the required complex algorithms to perform (non-adaptive) multi-beamforming with a 2D FFT.The main advantage of such an already working array is to produce 21 independent 31’×104’ beams located inside a 38deg2 Field Of View (FoV). Our plan is to search for funds to refit the remaining 56 cylinders of the N/S arm, to dramatically increase both the sensitivity and number of beams (pixels) placed in the same FoV. In this way, it could be possible to perform a deep SETI survey in the UHF band by an about 11.200m2 antenna (equivalent to a 119m dish), a 37.6deg2 FOV and 189 independent beams. The system could be further expanded by installing more receivers on each N/S focal line, increasing the FOV and the number of pixels with the same sensitivity. Assuming that adequate funds could be found for refitting the giant E/W arm as well, an equivalent 180m dish could be obtained to perform a very deep SETI sky survey with a 120deg2 FOV at high sensitivity. This would allow a very fast and deep sky survey in the UHF band.