Question

The necessary condition for the direction of maximum second side lobe level of the 4-element isotropic array is _______

(a) \(\frac{5}{4} π\)

(b) \(\frac{3}{4} π\)

(c) \(\frac{1}{8} π\)

(d) \(\frac{5}{8} π\)

The question was posed to me in a job interview.

The question is from Array of N-Isotropic Sources in chapter Antenna Array of Antennas

Answer 1

The correct option is (a) \(\frac{5}{4} π\)

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

⇨ \(sin(\frac{Nᴪ}{2})=±1\)

⇨ \(\frac{Nᴪ}{2}=±\frac{2s+1}{2} π \)

⇨ \(ᴪ=±\frac{2s+1}{N}π=\frac{2(2)+1}{4} π=\frac{5}{4} π.\)