KAIRA LBA polarisation orientation

Last week, we showed the polarisation orientation of the High-Band Antenna (HBA) elements of the KAIRA array. And this week, it is the turn of the Low-Band Antenna (LBA) array.

KAIRA HBA polarisation orientation

Within each High-Band Antenna (HBA) tile there are sixteen elements comprising a crossed bowtie antenna. These are in "cells" which can be rotated to different orientations depending on the layout of the array and its location in the world. Following some requests from observers we have drawn up the layout of the elements in our tile and made it available for distribution. The result is as follows:

The circle represents the rotating part of the cell. In the centre of that circle is a representation of the printed-circuit board with the amplifiers, etc. The four "blades" of the antennas are connected to this. Two F-type connectors at the bottom of the boards take the signal out to the tile summators (but also bring power and control into the unit).

Polarisation testing on the LBA

Now that the cables are all connected, we need to test that they are all correct and working. We've already done the tests on the band-pass spectra, now we need to check that all polarisations are correctly connected. To do this, we modify the field pattern of each dipole using a large metal object (we had a loop antenna handy, so we used that).

Applying the loop antenna to the antenna. Is it just me, or does this look like Grindelwald's Sign?

We then go from X- to Y-polarisation on each antenna, applying the antenna to each, and look at the drop-out pattern, when plotting RCU (= channel number) versus time (= sequence number).

Progression of signal drops, going from dipole to dipole. Onwards and upwards, and not a single step back!

As you can see, there is a monotonically increasing progression, which means that the polarisation are correct. The slight wave in the line reflects the addition walking time between antennas at various parts of the process.

Yet another quality-assurance check complete!

Polarisation test aerial

In order to check that the polarisations have been correctly connected, we use a very low power signal, transmitted from a dipole on a test mast. We tried a number of locations in order to get sufficient power and contrast to verify the system.

Attaching the antenna to our P2P mast. (Photo: D. McKay-Bukowski)

The stand-alone mast. Note the test LBA aerial in the foreground. (Photo: D. McKay-Bukowski)