EXTERNAL INSTRUMENT

The Aperture Array Verification System

The Aperture Array Verification System (AAVS) is the testbed for the SKA consortium, to evaluate equipment and confirm the performance of antennas before the rollout of the full SKA_LOW.

SKA_LOW will consist of 500 ‘field nodes’ (equivalent to MWA tiles), each containing 256 antennas sitting on a mesh ground-plane about 40m in diameter. The log-periodic style antennas under consideration are called SKALA. The SKALA are arranged in a pseudo-random pattern on the field node. The antennas currently deployed on a field node at the MRO are the second revision; SKALA-2. There are a few singular SKALA-4 antennas also under test on site. The SKALA antennas are best tuned to a frequency range of 50-350MHz, similar to MWA dipoles. The main difference between the MWA and SKA_LOW is the immediate transfer of analog signal to fiber (RFoF) in the SKALA antennas. This reduces signal loss, but introduces additional antenna complexity and cost.

Power is distributed to the antennas via a large box that sits in the center of the station, called the Antenna Power Interface Unit (APIU). The cables between the APIU and the SKALAs are a hybrid copper and fibre, to both deliver power to the antennas and transfer RFoF signal. Once the data reaches the control building, it enters Tile Processing Modules (TPMs) which are similar in function to MWA receivers. Only one field node on site is currently populated, and is called AAVS1.1, but there is infrastructure in place for four stations.