Multiple choice

A mast antenna consisting of a 50 metre long vertical conductor operates over a perfectly conducting ground plane. It is base-fed at a frequency of 600 kHz. The radiation resistance of the antenna in Ohms is

  1. $\dfrac{2\pi^2}{5}$
  2. $\dfrac{\pi^2}{5}$
  3. $\dfrac{4\pi^2}{5}$
  4. $20\pi^2$
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C Correct answer
Explanation

Since antenna is installed at conducting ground,

$$ R_rad = 80 \pi^2 (\dfrac{dl}{\lambda})^2 = 80 \pi^2 \left( \dfrac{50}{0.5 \times 10^3} \right)^2 = \dfrac{4\pi^2}{5} \Omega$$

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