What is antenna gain and how is it measured?

Antenna gain is a measure of how well an antenna focuses or directs radiated power in a particular direction compared to a reference antenna. It's measured in dBi (relative to isotropic radiator) or dBd (relative to dipole antenna), where dBi = dBd + 2.15. Gain is achieved by focusing energy in specific directions rather than creating energy. A higher gain antenna has a narrower beam and longer range in the beam direction. For example, a parabolic dish antenna might have 30+ dBi gain, while a simple dipole has 2.15 dBi.