Question

The necessary condition for maximum of the second side lobe of n element array is __________

(a) \( \frac{Nᴪ}{2}=±\frac{5π}{2}\)

(b) \( \frac{Nᴪ}{2}=±\frac{3π}{2}\)

(c) \( \frac{Nᴪ}{2}=±\frac{π}{2}\)

(d) \( \frac{Nᴪ}{2}=±\frac{4π}{2}\)

I had been asked this question during an internship interview.

Enquiry is from Radiation Pattern for 4-Isotropic Elements in chapter Antenna Array of Antennas

Answer 1

Right answer is (a) \( \frac{Nᴪ}{2}=±\frac{5π}{2}\)

The explanation is: The secondary maxima occur when the numerator of the array factor equals to 1.

⇨ \(sin(\frac{Nᴪ}{2})=±1\)

⇨ \(\frac{Nᴪ}{2} =±\frac{2s+1}{2}π\)

⇨ \(\frac{Nᴪ}{2}=±\frac{5π}{2}\)  [s=2 for second minor lobe].