Question

Two isotropic antennas are seperated by a distance of two wavelengths. If both the antennas are fed with currents of equal phase and magnitude, the number of lobes in the rdiation pattern in the horizontal plane are

Answer 1

Ans : (d)

Given that: d = $2\lambda and\alpha =0$

$\Psi =\alpha +\beta dcos\theta$

$\Psi =0+\frac{2\pi }{\lambda }\cdot 2\lambda \cdot cos\theta =4\pi cos\theta$

When $\Psi =0,2\pi ,-2\pi ,4\pi ,-4\pi$ maxima occurs in that direction.

Maximum at $\theta =0,\frac{\pi }{3},\frac{\pi }{2},\frac{2\pi }{3},\pi ,\frac{4\pi }{3},\frac{3\pi }{2},\frac{5\pi }{3}$

So, number of lobes in the radiation pattern in the horizontal plane = 8.