Question

Which of the following is the necessary condition to avoid grating lobes in N-Isotropic element broadside array?

(a) d < λ

(b) d > λ

(c) d=λ

(d) d < 2λ

The question was posed to me in an online quiz.

My enquiry is from Array of N-Isotropic Sources in portion Antenna Array of Antennas

Answer 1

The correct choice is (a) d < λ

The explanation is: Grating lobes are the minor and unnecessary lobes other than the major lobe.

To avoid grating lobes, kd(cosθ-cosθm)≤2π

\(\frac{d}{λ}≤\frac{1}{1+|cosθ_m |} \)

For broadside to avoid grating lobes (θm=90)

⇨ \(\frac{d}{λ}\) < 1

⇨ d < λ