Question

The necessary condition for the direction of maximum first side lobe level of the 8-element isotropic array is _______

(a) \(\frac{3}{8} π\)

(b) \(\frac{3}{4} π\)

(c) \(\frac{1}{8} π\)

(d) \(\frac{5}{8} π\)

This question was posed to me during an interview.

The doubt is from Array of N-Isotropic Sources in division Antenna Array of Antennas

Answer 1

Right option is (a) \(\frac{3}{8} π\)

For explanation I would say: The secondary maxima occur when the numerator of the array factor equals to 1.

⇨ \(sin(\frac{Nᴪ}{2})=±1\)

⇨ \(\frac{Nᴪ}{2}=±\frac{2s+1}{2} π \)

⇨ \(ᴪ=±\frac{2s+1}{N}π=\frac{2+1}{8} π=\frac{3}{8} π.\)