To avoid grating lobe artifacts in a linear array, what is the typical maximum element spacing relative to wavelength?

• A. ≤ 0.4 λ
• B. ≤ 0.6 λ
• C. ≤ 0.5 λ
• D. ≤ 0.7 λ

Answer: (C)

Grating lobes appear when the element spacing in a linear array is too large, creating additional peaks in the radiation pattern that can look like true reflectors. The spacing determines where those lobes occur via the relation sin θ_g = m λ / d; as d grows, grating lobes can appear within the field of view.

To avoid them across typical steering angles, the spacing should be no more than half a wavelength. At d = λ/2, the first grating lobe would require sin θ_g = λ/d = 2, which is impossible within -90° to +90°, so no distinct grating lobes appear. This makes 0.5 λ the typical maximum spacing to prevent grating lobe artifacts.

So, the best choice is the spacing of 0.5 λ or less; spacings larger than that can produce grating lobes.