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To increase gain of a parabolic reflector antenna by 6dBi, the correct statement is:

(Assuming efficiency 70%)


1. Diameter is to be increased to 6 folds
2. Diameter is to be increased to 4 folds
3. Diameter is to be increased to 2 folds
4. None of above

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Correct Answer - Option 3 : Diameter is to be increased to 2 folds

Gain of parabolic reflector

\(G = 6{\left( {\frac{d}{\lambda }} \right)^2}\)

d → diameter

λ → wavelength

in dB G(dB) \( = 10\log \left[ {6{{\left( {\frac{D}{\lambda }} \right)}^2}} \right]\)

i.e. G(dB) ∝ 20 log (D)

To increase gain of the parabolic reflector

The diameter should be increased by 2 fold.

i.e. D’ = 2D

G’(dB) ∝ 20 log (2D)

G’(dB) 20 log 2 + 20 log D

G’(dB) 6.02 + G(dB)

G(dB) → initial gain

More information:

For parabolic reflector:

\(HPBW = \frac{{70\lambda }}{D},\;BWFN = \frac{{140\lambda }}{D}\)

λ → wavelength

D → diameter

Directivity \( = \frac{{41200}}{{\theta {^\circ _E} \times \theta {^\circ _H}}}\)

General formula for gain of Antenna

\(G = \frac{{4\pi {A_e}}}{{{\lambda ^2}}}\)

Ae → effective area

λ → wavelength

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