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

1. (A) 15 dB
2. (B) 25 dB
3. (C) 35 dB
4. (D) 45 dB

Correct answer: (D) 45 dB

Solution

At 20 GHz, lambda=0.015 m, so G=0.7*(pi*1/0.015)^2 about 30700, which is 10*log10(30700) about 44.9 dB ~ 45 dB. The stored 35 dB is wrong.

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