Definition
Antenna gain is the ratio of the power density in a given direction to the power density of a reference antenna (using an ideal radiation source) in the same direction. It is expressed in dBd or dBi.
Physically, a gain is the ratio of the signal output of a system to the signal input of the same system. If the transmit antenna is an ideal undirectional source, the input power should be 100 W. If the transmit antenna is a directional antenna with a gain of 13 dB (20 times), only 5 W (100/20) of input power is required. That is, an antenna's gain is the amplifier of input power of the undirectional ideal radiation source.
Antenna gain can be used to measure the capability of an antenna to receive and send signals in a specified direction, which is one of the most important parameters to consider when selecting an antenna. The antenna gain is related to the antenna radiation pattern. If the main lobe is narrow, the side lobe is small and the gain is high. Figure 2-2 shows the relationship between the main lobe width and antenna gain.
Under the same condition, a higher antenna gain indicates a longer transmission distance. In practice, select a proper antenna gain to ensure that beamwidth matches the target coverage area. If the coverage area is small, select a low-gain antenna with a wide vertical lobe.
Related Concepts
dBd: unit for measuring the balanced dipole's gain.
dBi: unit for measuring the radiation source antenna's gain, with equal signal radiation in all directions. The relationship between dBi and dBd is as follows: dBi = dBd + 2.15.
Lobe angle: defined as the angle between the points in the main lobe that are down from the maximum gain by 3 dB. For details, see Beamwidth.
Ideal radiation source: ideal isotropic antenna, that is, a simple point-shaped radiation source that provides the same radiation performance in all directions.
Formula
Antenna gain = 10lg(Power density of an antenna/Power density of a reference antenna)
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