Question

If the distance between the transmitting and receiving antenna is decreased by a factor 2 while other factors remain same, then the new power received by the antenna _______

(a) increases by factor 2

(b) decreases by factor 2

(c) increases by factor 4

(d) decreases by factor 4

This question was posed to me during an interview.

I want to ask this question from Friis Transmission Equation topic in division Antenna Parameters of Antennas

Answer 1

Right option is (c) increases by factor 4

The explanation: From Friss transmission equation, \(P_r=P_t\frac{G_t G_r \lambda^2}{(4πR)^2}\)

\(\frac{P_{r1}}{P_{r2}} = \frac{R_2^2}{R_1^2} = \frac{(R/2)^2}{R^2} = \frac{1}{4}\)

Pr2=4Pr1.