Question

Find the angle at which nulls occur for the two element array antenna with separation λ/4 and phase difference is 0?

(a) Doesn’t exist

(b) 0

(c) π/2

(d) π/4

I had been asked this question during an online exam.

My enquiry is from Factors topic in chapter Antenna Array of Antennas

Answer 1

Right answer is (a) Doesn’t exist

To explain I would say: The normalized array factor is given by \(AF_n=\frac{AF}{2}=cos(\frac{kdcosθ+β}{2})\)

⇨ AFn=0

⇨ \(cos⁡(\frac{kdcosθ+β}{2})=0\)

⇨ \(\frac{(\frac{2π}{λ})(λ/4)cosθ+0}{2}=\frac{π}{2}\)

⇨ cosθ=2

 No Nulls will occur for the given pattern.