Question
How much gain does an antenna have compared to a half-wavelength dipole if it has 6 dB gain over an isotropic radiator?
Answer Options
- A) 3.85 dB
- B) 6.0 dB
- C) 8.15 dB
- D) 2.79 dB
Correct Answer: A
Explanation
Antenna gain is measured relative to two primary references: an isotropic radiator (dBi) or a half-wavelength dipole (dBd). Since the half-wave dipole is a real-world antenna with measurable gain, it is inherently a better radiator than the theoretical isotropic source.
The gain of a half-wavelength dipole relative to an isotropic radiator is fixed at 2.15 dBi. To find the gain relative to a dipole (dBd) when given the gain in dBi, you simply subtract the fixed constant 2.15dB: Gain (dBd) = Gain (dBi) - 2.15 dB. The antenna has 6 dBi gain, so its gain relative to a dipole is 6.0 dBi - 2.15 dB = 3.85 dBd.
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