GATE EC 2021 Set 1 — Question 65
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Electromagnetics → Antennas → Gain, Directivity & Radiation Resistance
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Question
An antenna with a directive gain of is radiating a total power of . The amplitude of the electric field in free space at a distance of from the antenna in the direction of gain (rounded off to three decimal places) is ________ .
Correct answer
0.224 to 0.264
Solution
Given:
Directive gain
Total power radiated
Distance The power density at a distance in the direction of maximum gain is given by:In free space, the power density is related to the peak electric field amplitude by:where is the intrinsic impedance of free space.Equating the two expressions for :Substituting the values:Taking the square root:Rounding off to three decimal places, the amplitude of the electric field is .
Directive gain
Total power radiated
Distance The power density at a distance in the direction of maximum gain is given by:In free space, the power density is related to the peak electric field amplitude by:where is the intrinsic impedance of free space.Equating the two expressions for :Substituting the values:Taking the square root:Rounding off to three decimal places, the amplitude of the electric field is .
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