Square Kilometer Array (SKA)-Low is the radio telescope operating in the lowest frequency band of the SKA, from 50 up to 350 MHz. It consists of 512 stations, each composed of 256 dual-polarization log-periodic antennas for a total of 262,144 independent signal paths. The low-frequency aperture array (LFAA) is the portion of the SKA-Low telescope including the antennas and the related electronics. Signal processing is hosted in a temperature controlled and shielded facility: the central processing facility (CPF), for all the core stations, or remote processing facilities (RPF), for stations in the array arms, to limit the maximum fiber length. Such a geographically distributed and interconnected radio telescope, spanning ∼65 km in diameter, requires that frequency and timing reference signals are distributed to the processing facilities with high stability and precision to ensure the required system performances. We present the realization of the clock and pulse per second distribution network inside the LFAA signal processing cabinet where subracks containing signal acquisition boards are housed. We describe the different parts of the chain, and we report on the total jitter introduced by this structure.
The SKA LOW telescope is an interferometer composed of 512 stations. Each station consists of 256 electronically steered antennas. The Low Frequency Aperture Array is the portion of the SKA-LOW telescope including the antennas and the related electronics. The LFAA signal processing chain amplifies, transports and combines the signals from the antennas composing each station into a coherent beam. Beamforming is performed in the frequency domain, with stringent requirements on bandpass flatness, linearity in a RFI contaminated spectral region, and allowed signal degradation. We adopted an architecture including a highly optimized oversampled polyphase filterbank for channelization, and a distributed network beamformer. The system has been validated as part of the Aperture Array Verification System, a single station operating at the SKA site in Western Australia.
KEYWORDS: Prototyping, Analog electronics, Signal processing, Electronic filtering, Digital filtering, Data conversion, Software development, Field programmable gate arrays, Polarization, Antennas
A novel version of digital hardware Italian Tile Processing Module (ITPM) 1.6 has been released for the Low-Frequency Aperture Array (LFAA) component of the Square Kilometre Array (SKA). This back-end includes two plugged-in main blocks, as an analog device , the Pre-ADU board, and an Analog to Digital Unit (ADU), a 6U board containing sixteen dual-inputs Analog to Digital Converters and two Field Programmable Gate Array (FPGA) devices, capable of digitizing and processing 32 RF input signals (50-650 MHz). We present the main features of the upgrade of the board compared to previous versions: there are new and high performance components improving processing capability, mechanical changes matching the design of the housing sub-rack and finally a general reduction of the overall power consumption. The ITPM ADU 1.6 version, now in engineering phase together with its sub-rack system, is currently the last prototype before the design of the industrial line for mass production, necessary for the LFAA deployment. Results of system performances will be presented.
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