SKA-Low, to be constructed in outback Western Australia, will use a large number of linked antennas to study radio waves from the sky at low frequencies.
PHOTO BY: SKA Organisation
The SKA Telescope
The SKA telescope will be a radio “interferometer”, meaning that it will connect many small radio antennas together to act as a single larger telescope. By electronically combining the signals from the individual dishes, an interferometer produces the sharpness of vision equivalent to a single telescope equivalent in size to the maximum distance between individual small antennas. This approach is far more practical and flexible than building a single huge dish. For example, when needed, the SKA can be split into multiple, independent telescopes.
An individual dish of a radio telescope looks very much like a large version of the dishes used for satellite TV. However, the SKA will use thousands of dishes, each 15 metres in diameter, to produce a powerful radio telescope operating at intermediate radio frequencies, from 350 to 14000 MHz (“SKA-Mid”). These dishes will be spread across southern Africa.
While dishes are ideal for most radio waves, the SKA will separately use a different sort of antenna to catch signals at very lowest frequencies, from 50 to 350 MHz (“SKA-Low”). These antennas are carefully shaped metal conductors that are connected to sensitive electronics. This design is essentially a sophisticated version of a car’s radio antenna or an old-style “rabbit ears” television aerial. These antennas will then be spread across Australia. The antennas for SKA-Low will have no moving parts, but instead will use advanced signal processing to point the telescope to different parts of the sky.
The genius of interferometry is the way in which the signals from different individual dishes or antennas are brought together. The term “interferometry” refers to the wavelike properties of light (“interference”), and requires the radio waves from different individual antennas to be transported to a single location to be compared. Each antenna of the SKA will be connected to a central electronic “correlator” that correctly combines all the individual signals together and thereby constructs a picture of the sky. Sending these signals back to the correlator requires transporting a massive amount of information. The amount of data that will flow through the SKA every second will be larger than the current data rate of the entire Internet.