2-PAD will be a dual polarisation, all-digital phased-array. The system will consist of two fully operational tiles plus ten dummy tiles for effective system tests. 2-PAD tiles are targeted to be system compatible with EMBRACE.

Infrastructural design of tile

The tile infrastructure is the mechanical structure and power supplies for a tile. The principle elements of the work are:

• mechanical design/drawing
• mounting and shielding of RF front-end
• modular, maintainable mounting of processing boards
• environmental packaging (appropriate for a test environment)
• electrical design (in particular power supplies)
• thermal design
• clock(/LO) distribution
• reliability analysis
• self test and reporting design

While full environmental protection and thermal design is not anticipated, a report of the methodology to be used will be included, since this is a major cost driver. Hence, this work package comprises a preliminary analysis of thermal and environmental considerations, drawing on the manufacturing experience of industry as appropriate. Design of self-test and reporting functions to aid long term maintenance of a major system. The tile will have an IP address to enable remote interrogation.

Fabricate active and dummy tiles

Sufficient modules and supporting infrastructure to prove the prototype tiles and the inter-tile communication will be manufactured. The requirement taken initially is:

• mechanical infrastructure for twelve tiles
• ~200 modules to fully populate two active tiles
• inexpensive dummy modules to fill the ten remaining tiles

Create tile test environment

The requirements of the antenna testing; including beam forming, beam steering, polarization etc., require a 12-tile array. In order to constrain costs, there will be two real modules and a further ten dummy modules around their edges, as shown in the figure at right.

Without the dummy modules, the electromagnetic environment of the active tile would be dominated by edge-effects not present in the full SKA. Following assembly and integration of the all-digital tiles, they will be evaluated against specification using functional testing of the system. The performance of the tiles is assessed with both laboratory based and astronomical tests. Importantly, the laboratory tests comprise full RF testing in a large calibrated anechoic chamber allowing fundamental data to be known to high precision. This includes for co-polarisation and cross-polarisation measurements. The output of this work package, a report which details the performance and flexibility of operation of the fully digital phased array concept, will provide essential input to the international SKA technology selection procedure.

System evaluation will be undertaken by groups other than the designers of 2-PAD. Industry (BAE Systems) will perform a formal design review.

Cost reduction studies

The tile will be the dominant cost item of the SKA; hence, production cost considerations are included throughout the design process. Clearly, some reasonable idea of what has to be built needs to be available before concluding any input from advanced manufacturing / assemble techniques. Accordingly this work package extends over the design/development cycle with effort back-end loaded and most effort is applied once realistic technical alternatives have been identified.

Reliability Analysis

With large numbers of complex tiles, a low failure rate is crucial to the viability of the SKA. Excessive failures increases running costs of the SKA potentially making it unviable. A formal theoretical reliability assessment will be performed on the tile design as projected for the SKA. Recommendations for improvement will be reported.

If the quality of the prototype tiles is high enough then initial reliability tests may be performed.

Objectives

Primary objectives:

1. Demonstrate an all-digital dual polarization tile.
2. Accurately estimate the cost of an all-digital tile for the SKA.
3. Estimate mean time between failures (MTBF) of an all-digital tile.

Secondary Objectives:

1. Demonstrate effective RFI mitigation techniques on an all-digital tile
2. Produce test environments for both the all-digital tile and a stand-alone beamformer.
3. Report on environmental and thermal management methodology.

Deliverables:

1. Dual polarization all-digital tile
2. Design documentation package for all-digital tile
3. Test environment for prototype all-digital tile.
4. Evaluation report of tile performance.
5. Tile cost estimates projected for SKA volumes and timescales.
6. Reliability analysis report.

Expected Outcome

The build, test and evaluation of a dual polarization all-digital tile, 2-PAD.