Primary Beam

The ultimate factor limiting the field of view is the diffraction-limited response of the individual antennas. An approximate formula for the full width at half power in arcminutes is: $\theta_{\rm PB} = 45/ \nu_{\rm GHz}$. More precise measurements of the primary beam shape have been derived and are incorporated in the AIPS task PBCOR to allow for correction of the primary beam attenuation in wide-field images. Objects larger than approximately half this angle cannot be directly observed by the array. However, a technique known as `mosaicing', in which many different pointings are taken, can be used to construct images of larger fields. Refer to References 1 and 2 for details, or contact Debra Shepherd.