Densely-packed, all-digital aperture arrays form a key area of technology development
required for the Square Kilometre Array (SKA) radio telescope. The design of real-time
signal processing systems for digital aperture arrays is currently a central challenge
in pathfinder projects worldwide. We describe interim results of such work; an heirarchical,
frequency-domain beamforming architecture for synthesising a sky beam from the wideband
antenna feeds of digital aperture arrays.