Description
The SKA will combine the signals received from thousands of small antennas spread over a distance of more than 3000 km to simulate a single giant radio telescope capable of extremely high sensitivity and angular resolution. The SKA will also have a very large field-of-view (FOV) with a goal at frequencies below 1 GHz of 200 square degrees and of more than 1 square degree (about 5 full Moons) at higher frequencies. One innovative development is the use of Focal Plane Arrays using phased-array technology to provide multiple FOVs. This will greatly increase the survey speed of the SKA and enable multiple users to observe different pieces of the sky simultaneously. The combination of a very large FOV with high sensitivity means that the SKA will transform the exploration of the Universe.
The SKA will provide continuous frequency coverage from 70 MHz to 10 GHz in the first two phases of its construction. A third phase will then extend the frequency range up to 30 GHz.
- Phase 1: Providing ~20% of the total collecting area at low and mid frequencies by 2019.
- Phase 2: Completion of the full array at low and mid frequencies by 2024.
- Phase 3: Building of the high frequency array from 2022.
The frequency range from 70 MHz to 10 GHz, spanning more than two decades, cannot be realised using one design of antenna and so the SKA will comprise arrays of three types of antenna elements that will make up the SKA-low, SKA-mid and dish arrays:
- SKA-low array – A phased array of simple dipole antennas to cover the frequency range from 70 – 200 MHz. These will be grouped in 100m diameter stations each containing about 90 elements.
- SKA-mid array – This is likely to be a phased array of "tiles" to cover the medium frequency range from 200 to 500 MHz. The 3 metre x 3 metre tiles will be grouped into circular stations, 60 m in diameter.
- Dish Array – several thousand dish antennas to cover the frequency range 500 MHz to 10 GHz. It is expected that the antenna design will follow that of the Allen Telescope Array using an offset Gregorian design having a height of 15 metres and a width of 12 metres. It is hoped that the parabolic dishes will be equipped with focal plane arrays at their focus. This would allow the dishes to observe over a far wider field of view than that achieved with a single element feed. Prototypes of such multiple element feeds are now under development for the pathfinder arrays described below.
The area covered by the SKA – extending out to ~3000 km – will comprise three regions:
- A central region containing 5 km diameter cores of dish antennas, SKA-mid stations and SKA-low antennas. This central region will contain approximately half of the total collecting area of the three SKA arrays.
- A mid region extending out to 180 km. This will contain dishes and pairs of SKA-mid and SKA-low stations. In each case they will be randomly placed within the area with the density of dishes and stations falling off towards the outer part of the region.
- An outer region from 180 km to 3000 km. This will comprise five spiral arms along which dishes, grouped into stations of 20 dishes, will be located. The separation of the stations increases towards the outer ends of the spiral arms.
Read more about this topic: Square Kilometre Array
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