The gridding requires at least Nyquist sampling of the plane to avoid
the artifact known as aliasing. For the signal, the Nyquist sampling in the
plane is obtained with a size of the grid cells equal to half the
size of the antenna diameter (this is the smallest spatial frequency that
the interferometer can be sensitive to, i.e. the natural resolution in the
plane). In the image plane, this implies to make an image at least
twice as large as the primary beam size (see Fourier transform property #2
in appendix). Unfortunately, the spatial frequencies of the noise are not
bounded: Noise aliasing can not be avoided, i.e. the noise increases at the
edges of the produced image.