Consider the Friis' transmission equation $P_R=\left(P_T G_T G_R \lambda^2\right) /(4 \pi D)^2$, where $P_R$ and $P_T$ are the received and the transmitted powers, respectively.

$G_T$ and $G_R$ are the gain of transmitting and receiving antennas, respectively, $D$ is the distance between the transmitting and receiving antennas, and $\lambda$ is the wavelength in free space.

Given: $G_T=G_R=1.0, \lambda=0.30 \mathrm{~m}$ and $P_T=+10 \mathrm{dBm}$.

Choose the distance (D), in km , from the following options at which the received power, $P_R=-90 \mathrm{dBm}$ ?

An antenna with a directive gain of 6 dB is radiating a total power of 16 kw . The amplitude of the electric field in free space at a distance of 8 km from the antenna in the direction of 6 dB gain(rounded off to three decimal places is$\_\_\_\_$ $\mathrm{V} / \mathrm{m}$.

Column
1. Point electromagnetic source
2. Dish antenna
3. Yagi-Uda antenna

Column
P. Highly directional
Q. End fire
R. Isotropic