Over the past several years, discussions have been occurring in several countries about the next logical step in radio astronomy following the construction of the large millimetre array ALMA. An initiative has emerged to develop a telescope to provide two orders of magnitude increase in sensitivity over existing facilities at metre to centimetre wavelengths. To achieve this goal will require a telescope with one square kilometre of collecting area - providing 50 times the sensitivity compared to the Very Large Array (VLA).

Credit: Canadian glactic plane survey
The Square Kilometre Array (SKA) will probe the gaseous component of the early Universe, thereby addressing fundamental questions in research on the origin and evolution of the Universe. The SKA will complement planned facilities at other wavelengths, such as ALMA and James Webb Space Telescope (JWST). HI, CO and continuum radiation would be observed from the interstellar medium of most of the galaxies the JWST will discover in the infrared at large redshifts.

Extensive discussion of the science drivers and of the evolving technical possibilities has led to a concept for the Square Kilometre Array and a set of design goals. The SKA will be an interferometric array of individual antenna stations, synthesizing an aperture with diameter of up to several 1000 kilometers. A number of configurations are under consideration to distribute the 1 million square metres of collecting area. These include 150 stations each with the collecting area of a 90 m telescope and 30 stations each with the collecting area equivalent to a 200 metres diameter telescope.


Approximately 50% of the collecting area is to be contained within a centrally-condensed inner array of 5km diameter to provide ultrahigh brightness sensitivity at arc-second scale resolution for studies of the faint spectral line signatures of structures in the early Universe. Another 25 % of the collecting area will be located within a diameter of 150 km, and the remainder out to 3000 km or more. This high angular resolution capability will allow imaging of faint emission from the interstellar medium of distant galaxies, as well as the surface of stars, and the active nuclei of galaxies.

+ more about design proposals
+ Design concept / demonstrator white papers

The SKA Science requirements list the goals for the basic system parameters.

SKA Design Goals

Parameter Design Goal
Frequency range 100 MHz - 25 GHz Goal: 60 MHz - 35 GHz
Simultaneous independent observing bands2 2 pairs (2 polarizations at each of two independent frequencies,with same FoV centers)
Max. freq. separation of observing bands Factor of 3 between observing band center frequencies (same FoV centers)
Instantaneous bandwidth of each observing band Full width = 25% of observing band center frequency, up to a maximum of 4 GHz BW for all frequencies above 16 GHz
Sensitivity at 45 degrees elevation (A/T) Goal: 2500 at 60 MHz
5000 at 200 MHz, 20000 between 0.5 and 5 GHz, 15000 at 15 GHz,and 10000 at 25 GHz Goal: 5000 at 35 GHz
Configuration Minimum baselines 20 meters, 20% of total collecting area within 1 km diameter, 50% of total collecting area within 5 km diameter, 75% of total collecting area within 150 km diameter, maximum baselines at least 3000 km from array core (angular resolution < 0.02 / fGHz arcsec)
Image quality Dynamic range > 10^6 and image fidelity > 10^4 between 0.5 and 25 GHz, over a range of 90 degrees in declination and 100 in angular resolution
Contiguous imagingfield of view (FoV)

1 square degree within half power points at 1.4 GHz, scaling as , 200 sq.
deg. within half power points at 0.7 GHz, scaling as between 0.5-1.0 GHz

Number of separated
fields of view 		1 with full sensitivity Goal: 4 with full sensitivity 10 simultaneous sub-arrays
Correlator and post-correlation processing Input bandwidth 25% of center frequency for frequencies below 16 GHz and
4 GHz for frequencies above 16 GHz (per observing band) Imaging of 1 square degree at 1.4 GHz with 0.1 arcsec angular resolution Imaging of 200 sq. degrees at 0.7 GHz with 0.2 arcsec angular resolution Imaging of 10^4 separate regions within the FoV, each covering at least 10^5 beam areas at full (maximum baseline) angular resolution Spectral resolution of 10^4 channels per observing band per baseline Minimum sampling interval 0.1 ms for wide-field pulsar searches
Beamformer capability 50 simultaneous summed (phased array) beams within FoV, inner 5 km diameter of array. No time averaging, 8 bits/sample.
Survey speed
Antenna pointing and slewing Blind pointing < 0.1 HPBW, move between adjacent sky positions separated by 0.5 HPBW in 3 sec, move between sky positions sep. by 90 deg. in < 60 s
Instrumental polarization Polarization error / total intensity –40 dB at FoV center, -30 dB out to FoV edge (after routine calibration)
Spectral dynamic range 10^4 (flatness of bandpass response after calibration)
Total power calibration Total power (zero-spacing) flux density measured with 5% error within 1 hr.




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