Figure 1: Typical antenna pattern of an antenna with strong grating lobes
Grating lobes is the term for secondary main lobes (very strong sidelobes) in the antenna diagram. They have approximately the size of the main lobe and are distributed grid-like in the diagram. Grating lobes sometimes occur with phased array antennas (and also with ultrasound probes used in sonography). Grating lobes are a consequence of too large and uniform distances between the individual radiator elements in relation to the wavelength. With a good design of a phased array with optimal spacing of the radiating elements, they should not occur. However, this requirement is difficult to meet with very large bandwidths (e.g. with UWB Radar).