Mid-Frequency Aperture Array



The AAMID Consortium, working on the Mid-Frequency Aperture Array (MFAA), an Advanced Instrumentation Work Package, aims to demonstrate the feasibility, competitiveness and cost-effectiveness of MFAA technology for SKA2. The key advantage of Aperture Arrays (AAs) is the capability of realising a very large Field of View and sensitivity, which results in an unsurpassed survey speed. Furthermore, AAs are capable of generating multiple independent FoVs, enhancing the efficiency of the system, for calibration and for multiple concurrent observations.

Aperture Array Summit

The SKAO and CETC-38/KLAASA organised an Aperture Array Summit in Hefei (China) in the last week of October. The summit was well attended and included a broad representation from industry, universities, the local government, AA consortium partners and the SKAO. At the Summit, progress on MFAA technology development and plans for future directions have been discussed (Figure 1).

Figure 1. Aperture Array Summit in Hefei, China.

Progress on MFAA Front-End Design

The University of Manchester is closely collaborating with Station de Radioastronomie de Nançay in France to test a true-time delay beamformer board (four 4:1 beamformer chips on each beamformer PCB). The board is currently being integrated into a beamformer rack (Figure 2) that can handle a 64-elements dual polarised tile.

Figure 2. Beamformer rack.

CETC-38/KLAASA has developed a next iteration of their Vivaldi antenna tile for MFAA. The tile has 9x8x2=144 antenna elements operating in the 300 – 1500 MHz frequency range and uses extrusion techniques to reduce the costs.

Figure 3. Vivaldi tile (144 antenna elements) by KLAASA.

November has been a busy month for the Maltese team, who have been focused on the arrival of more than 100m2 of mid-frequency antennas to be assembled in the field and tested. Figure 4 shows the print-screen of the antennas and the sheets of antennas being printed.

Figure 4: Print screen of the FR-ORA array to be deployed in Malta.

The assembly of the antennas onto a polystyrene base is shown in Figure 5. This is done to provide a mechanical support for the antenna array, which is then placed onto a chicken-wire ground plane and assembled on top of metallic frame.

Figure 5: Antennas assembled onto polystyrene base to give support to the structure.

The assembly of the structure is shown in Figure 6. The entire array is then placed within a dome structure to protect the array from wind and rain (Figure 7). The team then carried out electromagnetic simulations on the metallic frame and the dome structure to understand the effect of these support structures on the array’s electromagnetic performance.

Figure 6. Antenna array assembled inside the dome structure with the ground plane (chicken wire) visible.

Figure 7. Dome structure being erected to protect antenna array from the elements.

Throughout December, the team will be working on taking beam measurements of the array using a UAV system, coupled with GPS, to determine the array’s exact performance and compare it with the electromagnetic simulations.

Station de Radioastronomie de Nançay has assembled and tested several new integrated custom IC’s and circuit board for MFAA. Figure 8 show a feed module of a Vivaldi antenna using two ASIC’s (an LNA and an active balun filter) of which 270 pieces are now available for integration. Figure 10 shows a Vivaldi array of ASTRON with the feed modules from Nancay. Also, 20 BeamFormer boards have been assembled and ready for testing. These board use the latest true-time delay custom integrated circuits.

Figure 8 (left). Feed module with MFAA ASIC’s by Nancay. Figure 9 (right). BeamFormer board containing 4 custom true time delay chips.

Figure 10. Integrated feed module and Vivaldi array.

Report provided by the AAMID consortium