Wireless Communication Basics
Which describes the antenna gain unit dBi?
- AThe degree to which an antenna takes power from a supply and amplifies the signal, as the ratio of output power to input power
- BThe width of the frequency range an antenna can transmit and receive, as a ratio to the center frequency
- CThe strength of the power radiated in a particular direction, as a ratio relative to a hypothetical isotropic antenna that radiates equally in all directions
Show answer and explanation
Answer: C. The strength of the power radiated in a particular direction, as a ratio relative to a hypothetical isotropic antenna that radiates equally in all directions
An antenna does not amplify power; it strengthens radio waves in a particular direction by concentrating the radiated power in that direction. dBi is gain relative to an isotropic antenna that radiates equally in all directions, and a half-wave dipole antenna has about 2.15 dBi. The higher an antenna's gain, the narrower its beam and the weaker its radiation in other directions. Gain relative to a half-wave dipole antenna is expressed in dBd.
- A. An antenna is a passive component and does not amplify power. It only changes how the radiated strength is distributed over directions.
- B. The width of the frequency range is the bandwidth (fractional bandwidth), a different property from gain.
- C. Correct. It expresses the radiated strength in a given direction relative to an isotropic antenna.