Topic: Electromagnetics
The gain of a parabolic dish antenna of 1m diameter and 80% efficiency at 9.5 GHz is
- A. 39 dB
- B. 78 dB
- C. 40 dB
- D. 45 dB
Answer: A. 39 dB
Explanation: $Gain=\eta\frac{4\pi A_{e}}{\lambda^{2}}$. $c=f\lambda \Rightarrow \lambda=\frac{3\times10^{8}}{9.5\times10^{9}}=0.0315$. $A_{e}=\frac{\pi D^{2}}{4}=\frac{\pi}{4}$. $Gain=\frac{0.80\times4\pi\times\pi}{4\times(0.0315)^{2}}=7917.62$. Gain in $dB=10log_{10}(7917.62)=39~dB$.