Multiple choice

At 20 GHz, the gain of a parabolic dish antenna of 1 metre and 70% efficiency is

  1. 15 dB

  2. 25 dB

  3. 35 dB

  4. 45 dB
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$\lambda = \frac{c}{f} = \frac{3 \times 10^8}{20 \times 10^9} = \frac{3}{200} \\ \text{Gain} \hspace{1cm} G_P = \eta \pi ^2(\frac{D}{\lambda})^2 = 0.7 \times \pi^2 \bigg(\frac{1}{\frac{3}{100}}\bigg)^2 = 30705.4 \\ = 44.87 dB$

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