Antenna Gain (dBi)

Antenna gain describes how effectively an antenna focuses transmitted (or received) radio energy in a particular direction rather than radiating it equally everywhere. It is most commonly expressed in dBi — decibels relative to an isotropic radiator, an idealised point source that radiates uniformly in all directions and is defined as 0 dBi. Antennas do not amplify power; they reshape where the existing power goes, much like a flashlight reflector concentrates the same bulb's light into a beam.

dBi versus dBd

A related unit, dBd, references gain against a half-wave dipole instead of an isotropic source. Because a dipole itself has roughly 2.14 dBi of gain, you convert by adding 2.14 to a dBd figure to get dBi, or subtracting it to go the other way. Manufacturers usually quote dBi, so a "3 dBi" whip and a "1 dBd" whip are nearly identical.

Practical impact on a mesh node

Higher gain extends range but narrows the radiation pattern. A 2-3 dBi rubber-duck antenna radiates a fat doughnut shape that tolerates a tilted or handheld node. A 5.8 dBi or 8 dBi collinear flattens that doughnut, pushing energy toward the horizon — excellent for a fixed rooftop relay reaching distant peers, but it can shoot over the top of a node sitting in a valley or directly below. Matching gain and pattern to your terrain matters more than chasing the biggest number.

Gain works together with clear line of sight to determine real-world reach on a LoRa link.