For some time, the xNTD project team, led by CSIRO, has been coordinating with the Low Frequency Demonstrator (LFD) team, led by Massachusetts Institute of Technology (MIT), with the expectation and intention to co-locate these instruments and share infrastructure in Western Australia (WA). Combining two different instruments on a common infrastructure platform enhances the science from both, and is a direct analogue to the plans for the Square Kilometre Array (SKA). This combined instrument is called MIRA — the Mileura International Radio Array. MIRA will be housed within the Murchison Radio Observatory, the area in WA's Murchison Shire that has been given protection for radio astronomy.

The component of MIRA implemented with focal plane arrays on dishes, formerly called the xNTD, is now called MIRA-NdA (pronounced "mir-an-da"): this stands for the MIRA-large-N (number), small-d (diameter) Array, and will have a large number of small parabolic dishes and "smart feeds".

Antenna feeds

As noted in the October 2006 issue of ATNF News, the ATNF is operating a two-element interferometer at Marsfield to test the performance of a Thousand Element Array (ThEA) tile made by the Netherlands Foundation for Research in Astronomy (ASTRON). The interferometer uses a 21-element input/one-beam output beamformer/correlator, controlled with a Python-based control system. Recent work by Doug Hayman, Tim Cornwell and a summer vacation student, Anthony Whelan, has concentrated on improving the calibration, mostly by using a noise source on the surface of the antenna.

The ATNF has also developed a new design for a linear connected phased array (i.e., connected dipole-like elements). We have undertaken extensive modelling, and built and measured a small prototype array, which has validated the modelling. We found that it was difficult to connect the array elements to the low-noise receivers without disturbing the radiation properties of the array.

We have now explored a variation on this design in which the dipole wires have been "fattened" to become square elements arranged in a checkerboard pattern. This solution turns out to have very good performance, as shown by modelled antenna beam patterns and gains, and good receiver-matching characteristics. Its checkerboard structure is also a "self-complementary screen", with predicted properties that are confirmed by our modelling. We are now building a prototype of such an array.

In collaboration with the Dominion Radio Astrophysical Observatory (DRAO) in Canada, we are continuing to measure and model phased array feeds based on Vivaldi elements. These and other designs for phased array feeds will be tested on a test antenna at Parkes, discussed below.

Antennas

CSIRO recently awarded a contract to Patriot Antenna Systems of Michigan, USA, to install a 12-m antenna at the Parkes Observatory. This antenna will be used to continue the study of phased array feeds. Site works have begun at Parkes. The antenna will be constructed by Patriot in Michigan in August 2007 and erected at Parkes in September of this year.

Studies for the MIRA-NdA antennas continue. On 12 December 2006 an antenna design working meeting was held at ATNF headquarters, with participants from CSIRO, DRAO and a team of five engineers from Connell Wagner. The DRAO team visited ATNF during 11 - 15 December 2006; meetings with them covered a range of MIRA-NdA activities. We are continuing to investigate novel antenna configurations for MIRA-NdA — those that will be able to achieve a wide field-of-view and high dynamic range. A number of options will be prepared for the MIRA-NdA antenna Critical Design Review in September 2007.

Staff

Five new staff members have joined the MIRA project at the ATNF in recent months. David DeBoer, formerly Project Manager with the Allen Telescope Array in the USA, has taken over from Colin Jacka in directing MIRA-NdA and SKA technical activities at the ATNF; however, Colin remains with the project on a part-time basis. Anthony Schinckel, formerly the Director of Operations for the Smithsonian Submillimetre Array in Hawai'i, has joined the project as a manager. Yuantu Huang and Juan-Carlos Guzman have been hired to work on the MIRA-NdA archive and central processor, respectively. Yuantu trained in China and the Australian National University (ANU) as a mathematician; Juan-Carlos worked for a number of years at La Silla Observatory in Chile in real-time control systems. Tim Bateman has joined us to program the Parkes digital beamformer, 192 inputs at tens of MHz bandwidth: he comes from industry and has had extensive experience in programming application-specific integrated circuits (ASICs).

Helen Sim and Dave DeBoer
(Helen.Sim@csiro.au)