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 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.

Progress on MFAA Front-End design

A true time-delay based beamformer has been developed through collaboration between the Station de Radioastronomie de Nançay and The University of Manchester. The integrated front-end system can process dual polarised array with 64 antenna elements per polarisation. The operational frequency band is 400MHz – 1450MHz. Two independent beams can be formed out of each polarisation. The integrated active finite array prototype and the corresponding beamformer is shown in Fig. 1.

Figure 1. The active antenna array prototype and the beamformer.

The response from each channel will be measured from man-made sources. The aims are to check the linearity of each channel and phase variations in the channel when different time delay parameters are introduced. The setup is shown in Fig. 2.

Figure 2. The setting up for the linearity testing.

A 2m2 Vivaldi antenna array with integrated receiver is under construction at Station de radioastronomie de Nançay in France. The arrays are composed of 256 vivaldi antenna with two polarizations. Each polarization contains also two beams. This phased antenna aperture array uses a full custom ASIC like LNA; Active Balun Filter and true time delay beamformer. All the ASICs was designed by microelectronic Nançay team for MFAA concept in order to have the best trade-off between performance/power consumption/ cost. The antenna array uses a set of PCB with different level of amplification, filtering and combination before the digitisation of the signal

Figure 3. 2m² Integrated Receiver Vivaldi antenna array with SATA cable connection.

The Bordeaux team has developed a digitiser board based on the AD9689-2000 from ADI. This board is composed by 4 digitisation channels. For each channel, a filter bank has been designed for frequency sub-band selection. The sampling clock is set at:

– 1600MHz to select either the DC-700MHz band or the 900MHz-1500MHz band,

– 1200MHz to select the 700MHz-1100MHz band.

The DC-400MHz band will be rejected by the active band pass filter of the analogue front-end designed by Nançay. This board could be connected to a digital platform as the Uniboard2 board with 4x40Gbps optic links. The board is now under test to measure the performance.

Figure 4: Digitiser board at University of Bordeaux

Simulating Arrays of Arrays for SKA MFAA

Figure 5: The Simulation arrays of arrays for MFAA

Dense or sparse?

This still remains an open question for the array configuration for the mid-frequency aperture array (MFAA) of the SKA. But what about sparse, dense arrays? This is a question Sarah Younes from University Antonine (UA) in Baabda, Lebanon, is helping the Netherlands Institute for Radio Astronomy (ASTRON) to answer. In collaboration with Université Catholique de Louvain (UCL) in Louvain-la-Neuve, Belgium, Sarah is implementing ASTRON’s Vivaldi antenna design in the Method of Moments based simulation software developed by Prof. Christophe Craeye (UCL) and Prof. Rémi Sarkis (UA). Ultimately this study will enable simulation of MFAA stations comprising disconnected tiles of dense connected Vivaldi antennas.

Report provided by the AAMID consortium