Topic: Electromagnetics
Two isotropic antennas are separated 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 radiation pattern in the horizontal plane are
- A. 2
- B. 4
- C. 6
- D. 8
Answer: D. 8
Explanation: Phase difference, $\Psi=\alpha+\beta d\cos\theta$.
$\beta=\frac{2\pi}{\lambda}$, $d=2\lambda$.
$\Psi=\frac{2\pi}{\lambda} \times 2\lambda\cos\theta=4\pi\cos\theta$.
$E_T=2E_0\cos(\frac{\Psi}{2})=2E_0\cos(2\pi\cos\theta)$.
This term is maximum for $\theta=$ 0°, 60°, 120°, 180°, 240°, 270°, 300°. Thus, there is a total of 8 lobes.