The South African MeerKAT radio telescope, currently being built
some 90 km outside the small Northern Cape town of Carnarvon,
is a precursor to the Square Kilometre Array (SKA) telescope
and will be integrated into the mid-frequency component of SKA
Phase 1. The SKA Project is an international enterprise to build
the largest and most sensitive radio telescope in the world, and
will be located in Africa and Australia.
Stratosat Datacom (Pty) Ltd, the primary industry partner on the
manufacturing of the MeerKAT antennas, leads a technology consortium
including international partners General Dynamics Satcom
(GDSatcom, USA) and Vertex Antennentechnik (Germany). At
least 75% of the components making up the MeerKAT dish will be
manufactured in South Africa by several sub-contractors. Key local
suppliers include Efficient Engineering (pedestals and yokes); Titanus
Slew Rings (azimuth bearings) and Tricom Structures (back-up
structure), all based in Gauteng.
In some cases foreign companies
will manufacture components for the first antenna - such as the first
set of reflector panels, first receiver indexer and first sub-reflector
- but the rest will be made locally. Suppliers from abroad include
the National Research Council of Canada, through the Herzberg,
Programs in Astronomy and Astrophysics (low-noise amplifiers and
first sub-reflector); Oxford Cryosystems Ltd. (cryogenic coldheads)
and Vertex Antennentechnik (control systems).
- March 2014: First antenna installed
- Mid 2014: First antenna qualified and critical design review
- End 2014: Four MeerKAT receptors will be fully assembled,
integrated and verified
- End 2015: Array of 16 antennas commissioned and ready to
- End 2016: All 64 antenna positioners will be in place.
- Mid 2017: Full array ready to do science.
- The MeerKAT telescope will be an array of 64 interlinked
receptors (a receptor is the complete antenna structure, with
the main reflector, sub-reflector and all receivers, digitisers and
other electronics installed).
- The configuration (placement) of the receptors is determined by
the science objectives of the telescope.
- 48 of the
in the core
area which is
1 km in diameter.
- The longest
any two receptors
is 8 km.
- Each MeerKAT receptor consists of three main components:
- The antenna positioner, which is a steerable dish on a
- A set of radio receivers;
- A set of associated digitisers.
- The antenna positioner is made up of the 13.5 m effective
diameter main reflector, and a 3.8 m diameter sub-reflector. In
this design, referred to as an 'Offset Gregorian' optical layout,
there are no struts in the way to block or interrupt incoming
electromagnetic signals. This ensures excellent optical
performance, sensitivity and imaging quality, as well as good
rejection of unwanted radio frequency interference from orbiting
satellites and terrestrial radio transmitters. It also enables
the installation of multiple receiver systems in the primary
and secondary focal areas, and provides a number of other
- The combined surface accuracy of the two reflectors is extremely
high with a deviation from
the ideal shape being no
more than 0.6 mm RMS
(root mean square). The
main reflector surface is
made up of 40 aluminium
panels mounted on a steel
- This framework is
mounted on top of a yoke,
which is in turn mounted
on top of a pedestal. The
combined height of the
pedestal and yoke is just
over 8 m. The height of the total structure is
19.5 m, and it weighs 42 tons.
- The pedestal houses the antenna's pointing control system.
- Mounted at the top of the pedestal, beneath the yoke, are an
azimuth drive and a geared azimuth bearing, which allow the
main and sub-reflectors, together with the receiver indexer, to
be rotated horizontally. The yoke houses the azimuth wrap, which
guides all the cables when the antenna is rotated, and prevents
them from becoming entangled or damaged. The structure
allows an observation elevation range from 15 to 88 degrees,
and an azimuth range from -185 degrees to +275 degrees, where
north is at zero degrees.
- The steerable antenna positioner can point the main reflector
very accurately, to within 5 arcseconds (1.4 thousandths of a
degree) under low-wind and night-time observing conditions,
and to within 25 arcseconds (7 thousandths of a degree) during
normal operational conditions.
- Electromagnetic waves from cosmic radio sources bounce off the
main reflector, then off the sub-reflector, and are then focused in
the feed horn, which is part of the receiver.
- Each receptor can accommodate up to four receivers and
digitisers mounted on the receiver indexer.
The indexer is a rotating support structure that allows the
appropriate receiver to be automatically moved into the antenna
focus position, depending on the desired observation frequency.
- The main function of the receiver is to capture the
electromagnetic radiation and convert it to an voltage signal that
is then amplified by cryogenic receivers that add very little noise
to the signal. The first two receivers will be the L-Band and UHFBand
- Four digitisers will be mounted on the receiver indexer, close to
the associated receivers. The function of the four digitisers is to
convert the radio frequency (RF) voltage signal from the receiver
into digital signals. This conversion is done by using an electronic
component called an analogue to digital converter (ADC). The
L-band digitiser samples at a rate of 1 712 million samples every
second. (The amount of data that is generated by the digitiser for
a receiver is equivalent to approximately 73 000 DVDs every day
or almost 1 DVD per sec.)
- Once the signal is converted to digital data, the digitiser sends
this data via buried fibre optic cables to the correlator, which is
situated inside the Karoo Array Processor Building (KAPB) at the
Losberg site complex.
- A total of 170 km of buried fi bre cables connect the receptors to
the KAPB, with the maximum length between the KAPB and a
single antenna being 12 km.
- Thefi bre cables run inside conduits buried 1 m below the ground
for thermal stability.
- At the KAPB, the signals undergo various stages of digital
processing, such as correlation - which combines all the signals
from all the receptors to form an image of the area of the sky
to which the antennas are pointing - and beam-forming, which
coherently adds the signals from all the receptors to form
a number of narrow, high sensitivity beams used for pulsar
science. The science data products are also archived at the
KAPB with a portion of the science archive data moved off site
via fi bre connection and stored in Cape Town (with possibilities of
reprocessing the data).
- Time and frequency reference signals are distributed, via buried
optical fi bres, to every digitiser on every receptor, so that they are
all synchronised to the same clock. This is important to properly
align the signals from all receptors.
- The control and monitoring system is responsible for monitoring
the health of the telescope and for controlling it to do what the
operators want it to do. A large number of internal sensors (more
than 150 000) monitor everything from electronic component
temperatures to weather conditions and power consumption.
The telescope was
originally known as the
Karoo Array Telescope
(KAT) that would consist
of 20 receptors. When
the South African
the budget to allow the
building of 64 receptors,
the team re-named it
"MeerKAT" - ie "more
of KAT". The MeerKAT
(scientific name Suricata
suricatta) is also a muchbeloved
that lives in the Karoo
The KAT-7 precursor array has been constructed and is being
used as an engineering and science prototype.