Secondary lobes off the main sound beam that occur with linear arrays and can produce artifacts are called

• A. Side lobes
• B. Harmonics
• C. Grating lobes
• D. Speckle

Answer: (C)

Grating lobes are secondary beam directions that arise from the array’s periodic structure. When the spacing between elements is large relative to the wavelength, the array emits energy not just in the main direction but also at other angles, creating pronounced secondary maxima in the radiation pattern. These grating lobes can illuminate off-axis structures and send echoes back to the transducer, producing artifacts that appear at incorrect locations on the image.

Note that side lobes are weaker off-axis components from the single-element pattern and are typically reduced with apodization, but the term here specifically refers to the stronger, array-induced secondary lobes—grating lobes. Harmonics involve nonlinear frequency content, and speckle is the grainy texture from interference of echoes, not off-axis beam structure.