| Description: | The right panel shows the calculated response beam of a single LOFAR LBA dipole, as the Earth rotates for 24 hours. The image is centered on the position of the bright radio source Cygnus A. The black lines intersect at the North celestial pole, i.e. roughly the position of the North Star. The maximum response (orange) is always towards the zenith. The purple hemisphere is below the horizon. Note that path of Cygnus A passes close to the horizon, but not quite below it.
The left panel shows the calculated response beam of (half) a LOFAR station, consisting of 48 dipoles spread over about 25m. A beamformer adds the 48 signals in such a way that the maximum response is pointed at the position of Cygnus A. Of course the response is multiplied with the dipole beam (right panel), which remains pointed at the zenith. Note that the main lobe changes shape, and even its position, especially when Cygnus gets close to the horizon. Also note the changing pattern of sidelobes, which extends all over the sky. Care is taken in the design of LOFAR to minimize the effective sidelobe sensitivity, so that sources outside the field-of-view (i.e. the main lobe)do not contaminate the observations. |
