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The direction of the first minor lobe of 4 element isotropic broadside array separated by λ/2 is ___________(a) 41.4°(b) 30°(c) 60°(d) 90°I had been asked this question by my school principal while I was bunking the class.This intriguing question originated from Radiation Pattern for 4-Isotropic Elements in section Antenna Array of Antennas

Answer»

The CORRECT OPTION is (a) 41.4°

To explain I would say: The direction of the SECONDARY maxima (minor lobes) occur at θs

\(θ_s=cos^{-1} (\frac{λ}{2πd} \LEFT[-β±\frac{(2s+1)}{N} π\right])\)

⇨ \(θ_s=cos^{-1} (\frac{λ}{2π(λ/2)} \left[±\frac{3}{4} π\right])\) (s=1 for 1^st minor lobe)

⇨ \(θ_s=cos^{-1} (±\frac{3}{4})=41.4°\)



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