Question

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

(a) d < λ/2

(b) d < λ

(c) d > λ/2

(d) d=λ

I had been asked this question in an online interview.

My query is from Array of N-Isotropic Sources in division Antenna Array of Antennas

Answer 1

The correct option is (a) d < λ/2

To explain: 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=0)

⇨ \(\frac{d}{λ}\) < 1/2

⇨ d < λ/2