Small dishes:
> Small dishes - Solid surface
> Small dishes - Mesh surface
> Small dishes + focal plane arrays

Aperture arrays:
> Aperture plane Array (AA)

Other concepts which have been considered:
> KARST - LAR - Cylindrical reflectors - Luneburg Lens

> Other possible design - Cylindrical reflectors

To build the SKA a significant reduction in costs is needed compared to current telescopes. Of the various components required only the electronics are getting cheaper. consequently, an exploration of designs which trade off the costs of mechanical structures for an increase in the electronics cost are required. One such approach is the cylindrical reflector.

In this design the reflector is in the shape of trough rather than the normal dish shaped antenna. Because of this the radio signals are not concentrated at single point but instead come to focus along a line.

To receive this signal the receptors and their associated electronics are needed at regular intervals along the line, which increases the electronics cost compared to a dish type antenna.

The advantage of the design is that any source can be brought into focus by rotating the trough about its long axis. This results in a considerable reduction in mechanical complexity compared to a dish antenna which needs to rotate about two axes. Because of this the cost of the mechanical structure for the cylindrical reflector is almost half that of a comparable fully steerable parabolic dish.

In the 1960’s cylindrical reflectors were built with collecting areas equivalent to ten of the largest parabolic dish antennas built to date. But the cost of electronics limited their operating frequency to below 1 GHz. Also a number of compromises, such as narrow band operation, were needed.

The improvement in the performance of electronics for a given cost, as is seen with computers, is breaking down these limitations and currently it is estimated that the cylinder reflector concept is fully competitive with other concepts at frequencies up to a 1 GHz. By the time the SKA is built this will increase to about 20 GHz allowing cylindrical reflector to cover the full SKA frequency range or for greatly reduced cost it could be used as the low frequency component of a hybrid or composite design.

In practice the area of sky seen by the cylinder is an order of magnitude greater. This allows surveys to be completed more rapidly and when the full field of view is not needed by the main observing program it allows other non time critical observing to take place. Thus the cylindrical reflector concept provides an SKA which can do a greater amount of astronomy than concepts with a limited field of view.


More about this design
White papers 2003 2002
Scientific presentation
Demonstrators:
Prototyping SKA Technologies at the Molonglo Radio Telescope
The BEST-1 SKA demonstrator

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