To the accuracy needed when planning observations, the primary beam of the VLA antennas can be taken to be a Gaussian with FWHM equal to arcsec or arcmin. If you must image a source, or a field of view, that is significantly larger than the FWHM of the VLA primary beam, then you should plan to make a mosaic from a number of pointings (see Lecture 14).

In standard VLA software, the primary beam correction
( , Lecture 2) is modeled by a power law expansion of the
form where and the coefficients are ,
, , , and
(Napier and Rots 1982). This correction is
usually not applied at small values of *X* for which the Napier-Rots
expansion gives 1. It is not well determined at large
values of *X* for which 0.15.

abridle@nrao.edu