What is antenna gain?

Antennas are passive devices, meaning they cannot magically create additional electrical power. Instead, antenna "gain" is achieved by focusing the transmitter's existing power into a specific direction, much like the reflector in a flashlight focuses the bulb's light into a narrow, bright beam. Because the energy is concentrated in one direction, the signal appears stronger in that specific direction compared to a standard reference antenna (usually a theoretical isotropic antenna or a standard half-wave dipole). This directed energy concentration is what hams refer to when they say a directional antenna has high gain. Distractors claiming the antenna "adds power" are physically impossible, as they would violate the law of conservation of energy. It merely shapes and directs the radiation pattern.