We are now at the half-way point of the final research and design phase of the SKA, which is coordinated within the international consortium under European Commission’s SKA Preparatory Phase Program (PrepSKA). Canada is a signatory to the PrepSKA agreement, and the Canadian contribution to the international R&D effort is underway at NRC-HIA and a group of Canadian universities, with participation by key industries. This year additional funding of $1.25M for the university-based R&D component of the Canadian SKA Program was secured through the NSERC SRO program, augmenting funding from other sources to provide $2.4M in support of university R&D over the next three years. Participating universities are Calgary, McGill, UBC and Victoria.
For the last two years an Informal Funding Agency Group (IFAG) has met twice per year to discuss “issues that or of mutual interest to the funding agencies and to the SKA program, and to facilitate a full and open exchange among SKA and Funding Agency representatives”. At the last meeting of the IFAG, as part of the SKA Forum held in South Africa in February 2009, the IFAG became the Agencies SKA Group. The intent of the evolution from IFAG to ASG is “the formation of a Group of funding bodies with the aim of delivering a non-binding Joint Agreement on the Implementation of the SKA”.
A Canadian SKA Program workshop is taking place in Calgary on 7-8 October. The workshop brings together the R&D teams at universities and HIA, Canadian industries, and representatives of provincial and federal government programs to review international developments and Canadian strategic priorities, assess progress and plan for the coming year, and further develop industrial partnerships and opportunities. Attendance at the workshop is capped at 50. Further information on the workshop, in the program and list of participants, is available at www.ucalgary.ca/ras/cskaworkshop.
The SKA has been called an ICT telescope. Information and communication technologies are central to the power of the telescope. Furthermore, the manner in which the SKA executes its key science projects introduces a significant “sociological” element to the operation of the SKA. Most of the early key science will be achieve by major surveys using very large amounts of observing time and carried out by global collaborations of research centres. These observations may be “commensal” in the sense that a major observing block will serve several science programs simultaneously – i.e. several projects will accept the same output data stream, or multiple streams may be created from different “back ends”. International teams will be responsible for securing and managing the data, the specialized processing to create the various science products, and the visualization, post-processing analysis and knowledge extraction from the products. Challenges to be met include:
These requirements drive the need for a global and national cyber-infrastructure for SKA key science. A group of Canadian universities (Calgary, McGill and UBC and UBC-Okanagan are working with NRC and international partners on a project called Cyber SKA Canada to define and begin developing the cyber-infrastructure required.
Figure 1 The Mk2 10-m composite reflector complete with the PHAD array at the focus
The Composite Applications for Radio Telescopes (CART) project at the National Research Council Canada Herzberg Institute of Astrophysics (NRC-HIA) Dominion Radio Astrophysical Observatory (DRAO) is investigating the radio frequency (RF) and structural properties of composite radio telescopes. To demonstrate the feasibility and performance of composite reflectors, two 10-m diameter prototypes have been built. The second reflector, the Mk2, was designed and built after the experience of a Mk1 prototype, and has exhibited outstanding performance with a surface rms of 0.54 mm , which can operate up to 27 GHz with excellent efficiency, though the conductive materials used limit the maximum frequency to around 15 GHz. At 1000US/m2, this design represents an excellent cost-performance value. This reflector is currently being used to test a prototype phased-array receiver system (a radio “camera”) (Fig. 1).
Most recently, a manufacturing study of an SKA-scale composite reflector production has been completed by Profile Composites of Sidney BC, a company with extensive composite production experience. This study demonstrates that when producing reflectors for the SKA (which requires total of ~3000 15-m reflectors) the costs for a 12-m reflector using a Mk2-type design can be as low as $371USD/m2. This has significant implications in the cost analysis for the SKA, and the study has already been accepted by the SKA Project Development Office at the University of Manchester, UK as an SKA Memo (see SKA Memo 116)
Looking to advance a reflector design for the SKA, HIA is now examining 15-m offset reflector designs that are required for an SKA Dish Verification Programme that is being developed to demonstrate the reflector technology required for the SKA. Using optical designs that have been developed as part of the US SKA Technology Development Programme (TDP), HIA have produced a novel “shell-style” design that builds on some of the design features in the UC Berkeley Allen Telescope Array dishes at Hat Creek, California. This new design is not only optimal for large-volume production, it addresses a number of issues related to differential thermal expansion and wind loading that further improves reflector performance over that attained to date (Fig. 2)
In recognition of the advances the CART team at HIA-DRAO has
made in the past two years in the area of composite design and engineering, they
have recently won a JEC ASIA 2009 Innovation Award under the Aerospace category
for their development of the Mk2 10m radio telescope. The award will be
presented Wednesday October 14 at the JEC Asia show in Singapore. This is a
prestigious international award in a highly competitive R&D field. For more
info on these awards see http://www.netcomposites.com/news.asp?5499
Figure 3. Images of the Sun (left) and Cas A (right) made using the PHAD array and the 10-m MK2 CART antenna. Each pixel in these images represents a single beam formed from simultaneous data.
The Phased-Array Feed Demonstrator (PHAD) project is motivated by the need to provide expanded field-of-view for future radio telescopes, especially the SKA. PHAD aims to characterize and explore the performance of phased-array feeds for astronomy, which has high performance demands than typical commercial applications of this technology.
The PHAD array has been mounted on the Mk2 prototype CART reflector at DRAO since last Fall, and over the winter has been doing on-the-sky tests using observations of satellites and strong astronomical sources, and subsequent beam forming and analysis of data. While not sensitive to most astronomical sources, images have been made of the Sun and Cas A (Fig. 3).
An important SKA specification is to attain polarization observations with a high degree of polarization purity. Experiments have included incorporating cross-polarization into the beam-forming algorithms, with the aim of correcting polarization impurities through appropriate choice of beamformer weights. The PHAD array is the first array of this type in the world that is capable of these measurements. To date, the team have demonstrated that it is possible to reduce instrumental polarization through processing of both element polarizations, attaining a level of a few percent. Ultimately, this performance is dependent on system stability.
To enable direct measure of the system performance of new receiver systems being developed for phased-arrays, a new hot-cold test facility has been built at HIA-DRAO. The HCTF system consists of a metal ground shield, to isolate the receiver placed inside from ambient ground noise. The receiver is then exposed to either an ambient temperature radiation field from the microwave absorber on the underside of the roof, or cold sky by moving the roof off the ground shield. Once done, it is a simple matter to calculate the receiver noise using the Y-factor method. The HCTF will be very important as we make progress on development of antenna elements with integrated low-noise amplifiers.
This facility has already been used to successfully test the performance of a wide-bandwidth, low-frequency (300-900 MHz) antenna built at HIA-DRAO for implementation on the Parkes 64-m telescope
In parallel with the construction and testing of PHAD,
HIA-DRAO have carried out simulations of the performance of Phased-Array Feeds
from the viewpoint of carrying out astronomical observations, particularly
calibration and data correction issues that will have to be resolved to attain
high-fidelity, wide-field, full-polarization imaging capability. This work has
taken advantage of the flexibility of the MeqTrees package for describing and
solving a Measurement Equation that incorporates various instrumental effects.
This work is fully described in a series of memos, the first of which is now SKA
Figure 4. The Hot-Cold Test Facility at HIA-DRAO. Structure of the left is the ground shield. The elevated tracks support the ambient absorber load, which is partially covering the ground shield in this photograph.
At the University of Calgary Institute for Space Imaging Science the worlds best performing low noise amplifiers are being designed and fabricated. The noise temperatures of these devices are so low that conventional techniques to measure noise power have insufficient accuracy to yield a precise measure of the noise. A new measurement facility has been designed and constructed (Figure 5). This system used cryogenic noise sources and is inside a shielded enclosure to isolate the electronics from intefering RF signals. The measurements of Calgary amplifiers in comparison to European devices have been confirmed by a controlled comparison experiment between ASTRON and ISIS using Canadian and European designed LNAs.
Over the next year the new amplifies will integrated into a receiver system on the synthesis telescope at HIA-DRAO and the PHAD phased-array demonstrator for testing and measurement in astronomical systems.
Figure 5. Shielded Cryogenic Noise Measurement System at the University of Calgary Institute for Space Imaging Science for accurate measurement of sub- 0.2dB noise figures.