Question

For an isotropic antenna, the average power Pav  can be expressed in terms of radiated power Pr as ____

(a) Pav=Pr/4π

(b) Pav=Pr/2πr^2

(c) Pav=Pr/2π

(d) Pav=Pr/4πr^2

The question was asked in an online interview.

I'm obligated to ask this question of Directive Gain topic in chapter Antenna Parameters of Antennas

Answer 1

Right option is (d) Pav=Pr/4πr^2

For explanation I would say: Average power is the total power radiated in the unit area. Here for isotropic radiation, area is spherical (say with radius r) and the area is 4πr^2.

∴ Pav=Pr/4πr^2