Daily Image

13-08-2007
PreviousNext
Click here or on the picture for a full size image.

Interacting Antennas

Submitter: Stefan Wijnholds
Description: Mutual coupling is a free "bonus" coming with dense phased arrays. LOFAR's HBAs will not be an exception to this, so simulations are done to improve our intuition for this effect, and to see whether we can and/or should adjust LOFAR's station and array configuration to mitigate the effects of mutual coupling.

These images show the all-sky station beam voltage response expressed in terms of its Jones matrix after correcting for the antenna (element) voltage beam. Ideally this Jones matrix should be equal to the identity matrix over the entire sky, but in a more realistic scenario it will not, as shown in these images.
- The 1st column shows the real part of the elements of the Jones matrix (J11, J12, J21 adn J22) with a color scale from -1 to 1.
- The 2nd column shows the corresponding imaginary parts with color scale from -1 to 1.
- The 3rd column shows the absolute values (amplitudes) with color scale from 0 to 1.
- The 4th colum shows the phases with color scale from -180 to 180 degrees.

Elements J12 and J21 contain only numeric noise. This looks promising but is only true when the coupling between x- and y-dipoles can be neglected. Fortunately the size of the smallest features is physically restricted to the size of the main lobe and is thus comparable to the scale size of ionospheric fluctuations under observable conditions for which calibration strategies are already being devised.

Copyright: ASTRON/LOFAR
 
  Follow us on Twitter
Please feel free to submit an image using the Submit page.