Square Kilometre Array Developments

Russ Taylor, University of Calgary
Sean Dougherty, Herzberg Institute of Astrophysics

This year has seen very significant developments in the Square Kilometre Array project. Early in the year, the International Square Kilometre Array Steering Committee (ISSC) agreed on a reference design for the SKA, consisting of a square kilometre of 10 to 15 metre class antennas with “smart” receivers, combined with a smaller central array of aperture plane receivers for operation at the very lowest frequencies (see Figure 1.) In the 300 MHz to 3 GHz range phased-array systems at the focus of the parabaloids will be used to obtain very large instantaneous field-of-view, enabling the SKA key science through surveys of the line and continuum emission from large volumes of the Universe.

Figure 1. A concept drawing of a portion of the SKA showing the reference design, consisting of 10-15 metre diameter parabolic reflectors with “smart” feeds for large field-of-view, along with a compact core of aperture plane array receivers for all-sky imaging and monitoring at the lowest frequencies.

SKA site proposals were submitted to the ISSC from Australia, Argentina/Brazil, China, and South Africa. All the site proposals were subjected to technical review this year. Ernie Seaquist served on the International SKA Site Advisory Committee that provided external expert advise to the process. At the August ISSC meeting in Dresden, the potential sites for the SKA were short-listed to two; the Mileura site in Western Australia and the Karoo site in South Africa (see Figure 2). The sites in Argentina and China suffered from ionospheric instability due to their locations with respect to the geomagnetic equator. In addition the Chinese site, which depends on formations in the karst mountains of south-central China, was too restrictive to allow an optimal array configuration over the 3000 km extent required for the SKA.

Figure 2. The two short-listed sites for the SKA; the Karoo region of South Africa (top) and Mileura, West Australia (bottom)

Following the adoption of the SKA reference design, the Canadian SKA Consortium Board, the Canadian SKA Science Advisory Committee and HIA explored several options for the direction of the Canadian SKA program. In June 2006 they recommended that Canada collaborate with Australia in research and design leading to the construction of an SKA pathfinder telescope at the Mileura site that is based on the international SKA reference design. This pathfinder, called the Mileura International Radio Array, will be an expansion to the Australia xNTD program to create a scientifically capable telescope that will begin early science around 2012. On November 30, the President of the National Research Council of Canada and the Chief Executive Officer of the Australia Commonwealth Science and Industrial Research Organization (CSIRO) confirmed their intent to cooperate on the realization of the Mileura International Radio Array. The Agreement recognizes the Australian and Canadian national priorities to participate in the Square Kilometre Array and declares our intention to jointly develop MIRA in a manner that is consistent with the first 1% of the SKA. The Canadian role in MIRA is contingent on further LRP funding as recommended by the LRP Mid-term Review Committee.

The Canadian SKA Science Advisory Committee (CSKASAC), chaired by Norbert Bartel, is working on a Canadian MIRA science specifications document in preparation for a joint Australia-Canada science meeting in March 2007.

Since mid 2005, a seven-member working group of funding agency representatives has been meeting to discuss the funding and governance mechanisms for the International SKA project. Greg Fahlman, Director General of NRC-HIA, represents Canada on this working group. At its meeting in Prague in August 2006, the Funding Agency Working Group recommended that an International SKA Forum be established to develop the international governance model for the SKA. In the meantime the international MOU to establish the International SKA Steering Committee has been extended to 2007. The Canadian members on the ISSC are Peter Dewdney and Russ Taylor.

On October 19, the European Strategy Forum for Research Infrastructure (ESFRI) published it roadmap for new large-scale research infrastructure for the next 10-20 years, which includes the SKA. As a result the European Union has invited the International SKA project to submit an FP7 preparatory phase proposal for implementation of the SKA. Canada is participating along with the other members of the International SKA project in the development of this proposal.

Meanwhile, the US SKA Consortium has submitted a TDP (Technology Development Program) proposal to the NSF in November for approximately $10 M USD. This proposal had been held up until the completion of the NSF Senior Review. The TDP is primarily a technology study on the cost/performance of 10-15m class antennas. Canada and Australia are participating as collaborators in aspects that are aligned with MIRA technology development.

Canadian SKA Technology Research and Development

Technical collaboration on MIRA between the HIA radio astronomy technology group (led by Peter Dewdney) and R&D teams at CSIRO is well advanced. Canadian technology development builds upon the expertise in focal-plane phased-arrays and advanced materials engineering that is the legacy of the Large Adaptive Reflector project. The refocusing of the SKA project, Canada is now concentrating on two key technologies for the Reference Design.

Phased Focal Plane Arrays.

Development of focal plane arrays based on broad-band Vivaldi antennas continues apace at HIA DRAO in Penticton. The Phased Array Demonstrator (PHAD) project aims to build a 180-element array using commercial off-the-shelf (COTS) receivers and digital signal processor (DSP) to expedite design and provide an array for engineering tests. All components of the system, from array elements to receiver boards, to the analogue signal transmission system and to the DSP beam former have now been prototyped. These components are currently being put through qualification testing, before fabrication of the full 180-element array.
 
Many PHAD tests will be made in the new anechoic chamber at DRAO with a state-of-the-art spherical near-field scanner. A renewed effort in systems simulations of phased arrays on radio telescopes is underway currently, to prepare for placing the PHAD array on a radio telescope.

At the University of Calgary Department of Computer and Electrical Engineering, recent successful prototyping of an uncooled, low-noise, broad-band amplifier promises to provide a solution to the integration of high-performance, inexpensive receivers into the very large number of receiver array elements that will be required for the SKA.

Figure 3. The proto-type 24-element PHAD phased-array feed and receiver system. The Vivaldi elements are visible on the left with the COTS receivers on the right. This system is being used for end-to-end system tests prior to fabrication of the full 180-element array.

Composite Applications to Radio Telescopes

Before the announcement of the SKA reference design, some exploratory design studies of composite parabolic reflectors had been carried out at DRAO as an alternative to the LAR for addressing the challenge of designing cost-effective collecting area for the SKA, which remains one of the outstanding technology challenges facing the SKA project. The results of those studies showed great promise and resources were redirected toward a new project, Composite Applications to Radio Telescopes (CART), targeting the fabrication of antennas for the SKA Reference Design.

CART is being carried out in two phases. The first phase, near completion, is the investigation of preliminary designs and cost estimates, fundamental material properties testing, culminating in the construction a small (~1-m diameter) reflector to verify RF performance of composite reflectors.

Figure 4. A 1-metre CART prototype reflector under test in the near-field scanner range at HIA DRAO.

The second phase is the design and construction of a prototype 10-m diameter radio telescope to demonstrate the complete concept feasibility of composite antennas and verify cost estimates. This phase has been in progress since summer 2006 and a Preliminary Design Review was held in October at DRAO, with a board of reviewers from the Australia Telescope National Foundation, the Allen Telescope Array, AMEC Dynamic Structures and DIAB (composite core materials manufacturer). The panel was impressed with the project concept and objectives, the progress to date and the team’s expertise. They provided constructive feedback and gave a strong positive endorsement to continue with the prototype development for this competitive antenna technology. Currently the team is hard at work preparing to build the 10-m prototype. The necessary mold is on order and the LAR aerostat hangar is being converted into a production facility for the prototype. In parallel, the reflector design is nearing completion and several options are being explored for the telescope mount. The aim is to commission the 10-m prototype in the late spring of 2007 for assessment during the summer months.

Figure 5. Rendering of a 12-m CART antenna currently under development at HIA DRAO.