GATE EC 1998 Electromagnetics Solution Q 10

GATE EC 1998 Electromagnetics Solution Q 10

An antenna in free space receives 2μW of power when the incident electric field is 20 mV/m rms. The effective aperture of the antenna is_____.

(a) 0.005 m^2

(b) 0.05\;m^2

(c) 1.885\;m^2

(d) 3.77\;m^2

Ans :- (c)

Explanation

Power density is given as,

P_d=\frac{E^2}\eta=\frac{\left(20\times10^{-3}\right)^2}{120\pi} =1.061\times10^{-6} A_e=\frac{P_r}{P_d}=\frac{2\times10^{-6}}{1.06\times10^{-6}}=1.885\;m^2

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