Mid-Frequency Aperture Array

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Overview

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 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.

AIP Workshop

On June 8 and 9, 2017, the SKA Organisation, ASTRON, MFAA, PAF and WBSPF consortia had a meeting at ASTRON in Dwingeloo to consider new technologies that can improve the scientific capabilities of the SKA beyond Phase 1, and to discuss the structure and timescales of the SKA Advanced Instrumentation Program (AIP) and its successors.

Currently, the AIP includes consortia on Mid-Frequency Aperture Arrays (MFAA), Phased Array Feeds (PAF) and Wide-Band Single Pixel Feeds (WBSPF). These consortia are executing research and development programmes to demonstrate feasibility and increase maturity of their respective technologies for application in the SKA.

The workshop had 37 registered participants (see Figure 1) and included a series of talks on how new technologies will vastly improve the scientific prospects for SKA, a session on the SKA Observatory Development Programme, a session on the status and plans of the current MFAA, PAF and WBSPF consortia, and several technical talks by these consortia.

One of the main conclusions of the meeting is that, since the SKA Observatory is setup for a 50-year lifetime and will offer the world’s biggest radio telescope, continuous upgrades and expansions, enabling new capabilities, are essential for the future of the SKA. All presentations of the meeting, including a wrap-up of the discussions, can be downloaded from the meeting website: http://www.astron.nl/ska-aip2017/

Figure 1. Participants of the SKA AIP workshop at ASTRON, June 8 – 9, 2017.

Progress on MFAA Front-End Design

The University of Manchester has closely collaborated with Station de Radioastronomie de Nançay to test a true-time delay beamformer board (four 4:1 beamformer chips on each beamformer PCB). Two levels of beamforming hierarchy have been used to form two independent beams per polarisation out of the 8×8 dual polarised array (see Fig. 2 and 3). The time delay errors and the corresponding phase shift errors of the beamforming are shown in Fig. 4 and 5. It is indicated that the maximum phase error is approximately 10 degrees and time delay error of 50ps.

Figure 2. The beamformer PCB and the ORA feeding boards.

Figure 3. The beamformer PCB test at Station de Radioastronomie de Nançay.

Figure 4. The time delay errors of the beamformer chip.

Figure 5. The corresponding phase shift errors of the beamformer chip.

The University of Manchester has manufactured a 2m x 2m array for MFAA based on Crossed Ring Antenna Design (Fig. 6). The centre element in this array will exhibit the similar impedance characteristics across the frequency band as that in a large array such as at the station level. This measured impedance characteristics will be used for further study in the next phase of the project. This will include more in-depth investigation of matching performance with the LNAs and noise temperature rise caused by the mutual coupling.

Figure 6. The 16×16 finite array (the aperture size of 2mx2m) manufactured at the University of Manchester.

ASTRON has been developing the finite array based on Vivaldi and integrating the low noise front-end with the analogue beamformer boards. This is shown in Fig. 7. An improved LNA has been integrated closely with each Vivaldi element. The software to control the beamformer board has been developed and under testing at present. All the beamformer boards will be controlled by a centre board which is under development. An 2m x 2m array based on latest Vivaldi technology is under construction. The sub-tile for this array is shown in Fig. 8.

Figure 7. The Vivaldi antenna array and the beamformer boards.

Figure 8. The sub-tile for the 2m x 2m Vivaldi Antenna array at ASTRON.


Report provided by the AAMID consortium