A set of preliminary specifications were agreed at the Sydney Workshop in December 1997, to provide some uniformity in the technical goals for the instrument. This document has been drawn from a more extensive document maintained at the SKAI web site.

Preliminary specifications for SKA science case

• Aeff/Tsys: 2 x 10⁴ m²/K
• Sky coverage: 2 sterad
• Frequency range 0.03 - 20 GHz
• Imaging Field of View: 1 square deg. @1.4 GHz
• Number of instantaneous pencil beams: 100
• Maximum primary beam separation:
  • low frequency: 100 deg
  • high frequency: 1 deg @1.4 GHz
• Number of pixels: 10⁸
• Angular resolution: 0.1 arcsec @1.4 GHz
• Surface brightness: 1K @0.1 arcsec (continuum)
• Instantaneous bandwidth: 0.5 + f/5 GHz
• Number of spectral channels: 10⁴
• Number of widely spaced, simultaneous frequency bands: 2
• Clean beam dynamic range: 10⁶ @1.4 GHz
• Calibratable polarisation purity: -40 dB

Square-Kilometer Array Specifications Glossary

• Aeff/Tsys: The effective collecting area divided by the system temperature. This is the proportional to lambda² * G / T. Aeff/Tsys may be a function of frequency.
• Sky Coverage: The solid-angle area of the celestial sphere that can be seen by the array with Aeff/Tsys greater than half of its maximum value. This does not say anything about tracking time or about UV coverage when used in VLBI.
• Total Frequency Range: The total frequency tuning range of the instrument. This may be divided into sub-ranges with different antenna technologies, and it is not necessarily contiguous.
• Imaging Field-of-View: The instantaneous, contiguous solid-angle area of the sky that can be imaged, given a sufficiently capable correlator. This area will be a function of frequency.
• Number of Instantaneous Pencil Beams: The number of "phased array" pencil beams that can be placed simultaneously within the Imaging Field-of-View for point source observations such as pulsars, stars (including SETI), and VLBI.
• Maximum Primary Beam Separation: This spec assumes that the square-kilometer array will have at least two levels of beam forming. Signals from small antennas (dipoles, small dishes, etc.) are combined to form an array element primary beam, and signals from array elements can be combined in a correlator to make a map within the primary beam or combined directly to form one or many pencil beams within the primary beam. More than one primary beam could be formed within the pattern of the small antennas. The Maximum Primary Beam Separation specifies how far apart these primary beams can be formed simultaneously.
• Number of Pixels: The number of spatial resolution elements in a map synthesized within the Imaging Field-of-View.
• Angular Resolution: The maximum angular resolution of the array as determined by its largest linear extent (longest baseline).
• Time Resolution: The time interval between independent intensity outputs from the array. For example, this may be detected samples from a phased array for pulsar work or a time series of maps for solar or planetary observations.
• Surface Brightness Sensitivity: The minimum detectable (5-sigma) continuum surface brightness for a specified resolution, e.g., 1K @0.1 arcsec. This may be a function of frequency.
• Instantaneous Bandwidth: The widest contiguous frequency range that may be observed simultaneously given enough correlator or other processing capability. Typically this means the widest selectable IF filter bandwidth before the digitizer.
• Number of Spectral Channels: The number of independent frequency samples from the array after all signal processing.
• Number of Simultaneous Frequency Bands: The number of widely spaced frequency ranges that may be observed simultaneously. For example, a stellar flare study might want to observe at 1.4 and 5.0 GHz at the same time, each with instantaneous bandwidths of 0.3 GHz.
• Clean Beam Dynamic Range: The best intensity dynamic range that may be obtained in a fully processed synthesized map, as limited by unknown errors in the array or its environment.
• Calibratable Polarization Purity: The error in Q, U, and V Stokes parameters as a fraction of I for a strong radio source after all data processing, as limited by unknown errors in the array or its environment.

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