Thursday, 23 August 2012

An odd numbering scheme

We've had a lot of feedback on our recent successes — thanks to everyone who commented or sent e-mails! However, there was one particular question which came up which probably wants some explanation. Paraphrased, it was:

How did you come up with your antenna numbering scheme?

Yes, I agree that it certainly looks a bit odd, so here's a recap of the reasons and a bit more explanation.

For the High-Band Antenna array, the logic is as follows:

  • The project has 48 'tiles' and we devised the 24+12+12 layout to suit our primary science objectives and environmental concerns.
  • However, we wanted to still keep the option of converting to a full-size LOFAR station one day. That has 96 tiles in a circular pattern, numbered by row, but with a "hole" in the centre (Tile ID = "HCC"). Sets of LOFAR layouts are shown here: http://kaira.sgo.fi/2011/02/hba-layout-part-1-lofar.html
  • So, we superimposed our layout on the standard full-size layout and used the numbering system that resulted. The one tile that would not be in the full size layout was originally referred to by Tile ID = "HXX", which later became "H96".
  • There is a diagram (which should help) here: http://kaira.sgo.fi/2011/06/hba-configuration.html

For the Low-Band Array, the layout (LINK) works like this:

  • A standard LOFAR remote station has 48 aerials in a scatter pattern.
  • We started with this layout for antennas "L00" to "L45".
  • These start "L00" in the centre, then increment anti-clockwise in rings.
  • However, there are two "out-rigger" antennas ("L46" and "L47") in the LOFAR setup which are 80-90 metres away. These could not be used at KAIRA owing to terrain issues.
  • So we made them "fit" somewhere in our array circle, but ran a massive simulation to find the spots where they would give the best beam performance. That's why these last two seem a bit oddly placed.

I hope that clears things up!

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