GATE EC 2019 Set 1 — Question 33
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Electromagnetics → Antennas → Dipole & Monopole Antennas
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Question
Radiation resistance of a small dipole current element of length at a frequency of 3 GHz is 3 ohms. If the length is changed by 1%, then the percentage change in the radiation resistance, rounded off to two decimal places, is ______%.
Correct answer
1.98 to 2.02
Solution
The radiation resistance of a small dipole is given by:This shows that . Let the initial length be and the initial radiation resistance be .
If the length is changed by 1%, the new length is either (increase) or (decrease).
Case 1: 1% increase ()Percentage change .
Case 2: 1% decrease ()Percentage change .
The magnitude of the percentage change is approximately 2.00%.
If the length is changed by 1%, the new length is either (increase) or (decrease).
Case 1: 1% increase ()Percentage change .
Case 2: 1% decrease ()Percentage change .
The magnitude of the percentage change is approximately 2.00%.
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