An In-depth Analysis of Antenna Gain

From a professional perspective, antenna gain is defined as the ratio of the square of the field strength produced by an actual antenna to that of an ideal radiating element (typically an isotropic radiator, which radiates energy uniformly in all directions) at the same point in space, under equal input power conditions. Simply put, it represents the power ratio, as illustrated in the figure below.

Antenna gain is closely related to the antenna radiation pattern, which serves as a “map” depicting the distribution of signal strength in different directions. The narrower the main lobe of the pattern, the more concentrated the signal is in a specific direction. Additionally, smaller side lobes and back lobes indicate reduced energy leakage in undesired directions. Consequently, the antenna’s gain increases as a result.
When describing antenna gain, we often encounter two parameters: dBd and dBi. They are like two different “rulers” for measuring antenna gain.

dBi represents the antenna’s maximum directional field strength relative to an isotropic radiator (an ideal point-source antenna that radiates energy uniformly in all directions, with a radiation pattern resembling a perfect sphere). For example, an antenna with a gain of 5dBi means its radiation intensity in the maximum direction is 5dB stronger than that of an ideal isotropic radiator.

On the other hand, dBd represents the antenna’s maximum directional field strength relative to a half-wave dipole (a common basic antenna form consisting of two quarter-wavelength conductors, shaped like a “dumbbell”). Unlike an isotropic radiator, a half-wave dipole has inherent directionality and does not radiate uniformly in all directions.

Antenna gain plays a critical role in the operational quality of mobile communication systems in real-world scenarios, as it directly determines the signal level at the cell edge. In various communication environments, antenna gain serves as an indispensable factor.
In base station communications, the typical gain of a directional base station antenna is around 18 dBi, while that of an omnidirectional base station antenna is approximately 11 dBi. Directional antennas, with their higher gain, concentrate signals toward specific areas, effectively covering key zones such as urban business districts and residential areas. Omnidirectional antennas, on the other hand, rely on their relatively lower but uniformly distributed gain to provide signal coverage for users within a certain range in open suburban or rural areas.

Satellite communication heavily depends on high-gain antennas. Due to the vast distance between satellites and Earth, signals experience significant attenuation during transmission. To ensure stable signal transmission between ground stations and satellites, high-gain antennas are essential for concentrating signal energy and reducing path loss. For instance, parabolic antennas—commonly used in satellite communications—function like large “signal-collecting bowls,” focusing weak satellite signals for reception while also concentrating signals transmitted from ground stations to achieve long-distance communication. In satellite TV reception, the familiar “dish” antenna is a type of parabolic antenna that uses high gain to receive satellite signals, allowing us to enjoy programs from around the world in our homes.