| Description: | The above animation clearly demonstrates two major advantages of a Phased Array Feed (PAF) in the WSRT: The illumination of the reflector is much more efficient and the periodic 17 MHz variation that is observed with the MFFE L-band horn is significantly reduced.
The above results are measured with the APERTIF prototype installed in one of the WSRT dishes. A holographic measurement has been performed to obtain the magnitude of the aperture fields. For this measurement a reference telescope (in this case RT4) was tracking Cygnus A, while RT3 (MFFE) and RT5 (PAF) scanned a grid of 21 x 21 points around the source. From the correlation coefficients between the scanning telescopes and the reference telescope the complex voltage patterns of the scanning telescopes are determined. For convenience, the patterns were measured in rectangular coordinates in (RA,DEC) space. A rather inefficient DFT has been used to calculate the fields in the aperture planes. The weights applied to the PAF are optimized to maximize its sensitivity.
|
