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An antenna in free space receives 4 μW of power when the incident electric field is 10 mV/m rms. The effective aperture of the antenna is:

An antenna in free space receives 4 μW of power when the incident electric field is 10 mV/m rms. The effective aperture of the antenna is: Correct Answer 15.07 m<span style="position: relative; line-height: 0; vertical-align: baseline; top: -0.5em;font-size:10.5px;">2</span>

Calculation:

RMS value of electric field = 10 mV

power density(Pd) is given by:
 
Pd = E2/377
 
Putting on the respective values, we get:
 

P = (10*10-3)2/377

P = 2.65*10-7

Received Power (Pr) = 4 × 10-6  W

Effective Aperture(Ac) = Received Power(Pr)/Power Density (Pd)

= (4*10-6)/(2.65*10-7)

= 15.07 m2 

Note: 

Here RMS value is given so we used the formula of Power density as E2/377 , if peak to peak Electric field or only Electric field is given then we use power density formula = 0.5*E2/377

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