By Willem Esterhuyse, MeerKAT project office, Cape Town

The MeerKAT team has installed the last of the control system components on the MeerKAT prototype, and commissioned and tested the dish. A myriad of tests were performed, the most important of which were related to proof of the surface (accuracy and efficiency) and the pointing/tracking capability of the dish.

The surface was measured making use of photogrammetry as well as theodolites - the results from these two methods were consistent and therefore resulted in a high degree of confidence in the measurements.

Fig 1: Theodolite and Photogrammetry measurements.

Dr Mike Gaylard of HartRAO led the effort to build two receivers to test the flame-sprayed aluminum dish surface. The purpose was to test the efficiency of the antenna and check the integrity of the surface; as well as to verify the surface accuracy measurement results from the theodolites and photogrammetry.

Fig 2: The 1.42 GHz (left) receiver fitted on the dish. On the right Pieter Stronkhorst is busy fitting the 12 GHz receiver.

Adriaan Peens-Hough from the System Engineering team performed the tests and analyzed the results. Below is typical scan of a radio source done with the XDM.

Fig 3: Typical scan of a radio source.

The conclusion from all these tests were that the flame sprayed surface performs very well, the surface accuracy is better than 2mm RMS (the original spec were 4mm RMS) and that the dish efficiency is as expected.

IST also performed a number of pointing and tracking tests in order to refine the pointing model. Below is an example of the tests (this was done optically).

Fig 4: Optical pointing test.

The pointing and tracking performance of the antenna seems to be significantly better than the specified 0.04 deg. Some refinement on the pointing model will still be done after the XDM receivers have been fitted, but overall the MeerKAT team is very happy with the performance of the dish. The better than specified surface accuracy and pointing performance will allow operation to higher frequencies than originally specified, which may be important to SKA, depending on the SKA science case. The XDM dish is essentially complete and will be signed off after the final documentation has been completed.

The rest of the year will be spent on changing the design of the prototype to that of 12m (as that is the likely size of the dishes for MeerKAT); as well as to optimize the antenna structure for cost, since achieving the SKA cost target is the main remaining challenge.

View the latest pictures on the MeerKAT prototype.