Which statement describes grating lobes in relation to array transducers?

• A. They are the same as side lobes but occur with array transducers
• B. They arise only in single-element transducers
• C. Grating lobes
• D. They are a type of color artifact

Answer: (C)

Grating lobes are secondary beam maxima that appear in the radiation pattern of an array transducer due to the regular spacing of its multiple elements. When the spacing between elements is large relative to the wavelength, interference from the array creates additional directions in which the beam is strong—these extra lobes are the grating lobes. They are a property of array geometry, not a single-element device, and they are distinct from the usual side lobes that come from having a finite aperture. They are not color artifacts.

The best descriptor here is that grating lobes are the extra, unintended lobes that arise from the array’s element spacing. To reduce them, designers keep spacing at or below about half the wavelength and use apodization to suppress sidelobe levels.