SKA low frequency aperture array

The Square Kilometre Array, SKA is the next generation low frequency radio telescope and is described on its website [1]. The work performed in the European funded FP6 programme, SKA Design Studies, SKADS, [2] showed that an implementation of the SKA using phased aperture arrays, AAs, operating from 50MHz up to 1.4GHz with a dish based array covering ~1.2GHz to 10GHz represents the most capable design for the agreed SKA Phase 2 science case [3]. The deployment of the SKA starts with a ~10% instrument, Phase 1, commencing construction in 2018. This includes a low frequency sparse AA covering 50MHz to at least 350MHz. The development of the more technically challenging mid-frequency AA system will continue in parallel, preparing for deployment in SKA Phase 2 commencing in the mid 2020's. This schedule enables SKA Phase 1 to benefit from the experience gained with current low frequency AAs, LOFAR [4] and MWA [5] systems, followed by the more difficult higher frequency AA in Phase 2. A very large phased array, the Low Frequency AA, LFAA, will be deployed in only a few years time. The LFAA, illustrated in Figs. 1-3, covers the lowest frequency band for the SKA, from 50MHz up to 350MHz as described in the SKA Baseline Design or, as proposed up to ~650MHz. This is an aperture array consisting of ~131,000 (217) wide bandwidth antennas. The configuration will be very close packed with 95% of the antennas within a 3km radius core and the remaining collecting area situated on three spiral arms, extending out to a radius of 45km to enable higher spatial resolution observations. The overall system is organized as logical stations constituting correlatable entities. The signal processing design is to support 512 stations of ~35m diameter. The large bandwidths and low noise temperature levels required are a challenging requirement for a receiving antenna [6] with a 13:1 frequency range, well matched to a very low noise amplifier, ability to deploy quickly and cheaply, minimal self-induced radio frequency interference and able to withstand the harsh conditions of the Western Australia desert for decades.