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ASTRON RFoF towards AAVS0.5

Submitter: Pieter Benthem
Description: The Low Frequency Aperture Array (LFAA) covers the lowest frequency band of the SKA, from 50MHz up to 350MHz, as described in the Baseline Design. To transport the dual polarised antenna signals over the required distance of up to 10 kilometres towards the processing facilities, RF-over-Fibre (RFoF) technology is used.

For such long links, there are no real alternatives to RFoF technology, which offers the lowest cost and the lowest signal loss. Also, RFoF systems are highly immune to RFI pickup, static and lightning, as well as causing no electromagnetic interference themselves.

Commercially available RFoF links typically feed remote wireless transceivers and other antenna-systems for communication and CATV. The value added to these systems is large, and only a few links are typically required, so that the link itself is not very cost-constrained. Therefore, the price for off-the-shelf RFoF solutions is too high for the large number of links required for the LFAA.

Fortunately, the components required to build a customized, minimum-complexity and low-cost link for the LFAA are all commercially available. Furthermore, commodity applications like fibre-to-the-home drive volumes, and are bringing the cost of e.g. DFB lasers down to a few euros in volume. These devices work up to many GHz, so building a low frequency link is relatively straightforward.

Using such components, we have successfully realized and tested our RFoF link, and showed that it can meet the LFAA requirements that are derived from the Baseline Design Level 2 specifications.

The picture (top left) shows the most recent ASTRON deliverable (16 RFoF links) towards the Aperture Array Verification System0.5 (AAVS0.5), which is located on the Australian SKA site. The coaxial cables that are currently connecting all (16) antennas (bottom right) will soon be replaced by the RFoF links. The first field test is expected during January 2015.

Many thanks for all the work done by the ASTRON and ICRAR team!
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