Question

A 1 km long microwave link uses two antennas each having 30dB gain. If the power transmitted by one antenna is 1 W at 3 GHz, the power received by the other antenna is approximately

Answer 1

Ans : (c)

R = 1000 m

$G_t=G_r=30dB=1000$

f = 3 GHz

$P_t=1W$

$\lambda =\frac{C}{f}=\frac{3\times {10}^{10}}{3\times {10}^9}=10cm$

Power density $P_{d}at1km$

$\frac{P_t{G}_t}{4\pi R^2}=\frac{1\times 1000}{4\pi ({10}^3{)}^2}=\frac{1}{4000\pi }$

$P_r=(A_e{)}_r{P}_d=\frac{G_r{\lambda }^2}{4\pi }\frac{1}{4000\pi }$

$=\frac{1000(0.1{)}^2}{4\pi }\times \frac{1}{4000\pi }$

$P_r=63.3\mu W$