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What is the direction of first null of broadside 4-element isotropic antenna having a separation of λ/4?(a) 0(b) 60(c) 30(d) 120The question was posed to me at a job interview.I'd like to ask this question from Radiation Pattern for 4-Isotropic Elements topic in section Antenna Array of Antennas

Answer»

Correct option is (a) 0

Easiest EXPLANATION: The nulls of the N- element ARRAY is GIVEN by

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

\(θ_n=cos^{-1}⁡(\frac{λ}{2π(λ/4)}\left[±\frac{2πn}{N}\right])=cos^{-1} (±\frac{4n}{4})=cos^{-1}(±n)=0\)



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