Dense aperture arrays for the Square Kilometre Array

Aperture phased arrays operating up to 1.4 GHz are the most exciting receiver technology being developed for the Square Kilometre Array, SKA. The capabilities of a telescope using many phased array stations brings major scientific opportunities including very high survey speeds, flexibility for searching for transient phenomena, and multi-beaming capability which cannot be realized using any other technology. The very high level of control over each receiver element brings the ability of exquisite calibration as a function of frequency and pointing direction. The technological requirements to implement high frequency, astronomically capable phased arrays are severe in terms of power and cost due to the large numbers of channels and the amount of digital processing required. However, technological roadmapping shows that forthcoming technical developments make a large system deployment realistic from 2018 onwards. An aperture array covering this frequency range is the only instrument able to perform some of the most challenging science experiments planned for the SKA and is likely to make some transformational discoveries. The European based Aperture Array Verification Program, AAVP, is working on both the sparse low frequency array from 70MHz to 450MHz and a dense array from 400MHz to 1450MHz as the low frequency system for the SKA.