The Australian Square Kilometer Array Pathfinder (ASKAP) is
an array of thirty-six 12m diameter dishes located at the
Murchison Radio-astronomy Observatory in Western Australia.
Thirty of the dishes have now been fitted with
"chequerboard" Phased Array Feeds (PAFs),
the radio "cameras" like the one pictured above.
(The
first generation PAFs were green in colour,
with the Mk II PAFs being more muted shades.)
The dark squares are the copper "bow ties" of the dipole antennas
(under a conformal weather-protective coating).
Low noise active baluns connect between
adjacent corners of the chequerboard elements to amplify
the signals they receive,
and so each copper square can be part of up to four dipoles.
There are 112 copper squares on each PAF, and these are
used to form 188 active elements -- 94 for each of two
orthogonal polarisations. The squares are spaced 9cm apart,
and so the PAF sensitivity drops for wavelengths
shorter than 18cm (or frequencies higher than 1.8 GHz).
Signals from neighbouring dipoles are combined in
electronic beamformers in the central control building,
with up to 36 beams able to be synthesized for each PAF.
