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What is the direction of first null of broadside 8-element isotropic antenna having a separation of \frac{λ}{4}?(a) 0(b) 60(c) 30(d) 120I got this question by my college professor while I was bunking the class.I need to ask this question from Radiation Pattern of 8-Isotropic Elements topic in portion Antenna Array of Antennas

Answer»

Right choice is (B) 60

Easy explanation: The nulls of the N- element array is GIVEN by

 \(θ_n=cos^{-1}⁡(\frac{λ}{2πd} [-β±\frac{2πn}{N}])=cos^{-1}⁡(\frac{λ}{2πd} [±\frac{2πn}{N}])\)

\(θ_n=cos^{-1}⁡(\frac{λ}{2π(\frac{λ}{4})}\LEFT[±\frac{2πn}{N}\right])=cos^{-1} (±\frac{4n}{8})=cos^{-1} (±\frac{n}{2})=cos^{-1} (±1/2)=60\)



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