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Measured DIGESTIF scanning compound beam

Submitter: APERTIF team (Wim van Cappellen)
Description: This animation is a follow-up of the measured DIGESTIF FPA patterns presented as Daily Image on 14-10-2008.

The left image shows the amplitude of the weights (in dB) with which the 56 X-polarized FPA element patterns are combined to obtain the compound beam in the right image. The weights have been determined for maximum sensitivity in the desired direction of observation. The right image shows the compound beam pattern. The beam is scanned over an area of 3 x 3 degrees, about the required field of view of the final APERTIF system (8 deg^2).

There are significant variations in the relative amplitudes of the weights when the beam is scanned. This can be explained by the complex behaviour of the element voltage beams presented on 14-10-2008. The weights include (and automatically compensate as good as possible for) mutual coupling in the antenna array, scattering of the struts, de-focussing, receiver gain and noise temperature differences, etc.

In contrast, the shape of the compound beam is very stable over the entire field of view: the mainlobe and the relative position and level of the sidelobes hardly change when the beam is scanned. It is very encouraging to see that the very distorted element patterns can be combined into such well-behaved beams.
Copyright: ASTRON, 2008.
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