A 1 km long microwave link uses two antennas each having

Home » Electromagnetic Theory » Electromagnetic theory miscellaneous » Question

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

1. 6.34 × 10^–2 watt
2. 6.34 × 10^–3 watt
3. 6.34 × 10^–1 watt
4. 6.34 × 10^–5 watt

Correct Option: D

P_R = P_T G_T G_R		λ		²
		4πd

where,
P_R = received power = ?
P_T = transmitted power = 1 watt
G_T = G_R = 30 dB = 1000
G_T = gain of transmitting antenna
G_R = gain of receiving antenna

λ =	c	=	3 × 10⁸	= 0.1
	f		3 × 10⁹

d = 1 km = 1000 m
Now,

P_R = 1 × 1000 × 1000 ×		0.1		²
		4π × 1000

= 6.34 × 10^–5 watts.