Gain of Directional Antennas

Gain is an antenna property dealing with an antenna's ability to direct its radiated power in a directed direction, or synonymously, to receive energy preferentially from a desired direction. However, gain is not a quantity which can be defined in terms of physical quantities such as the Watt, ohm or joule, but is a dimensionless ratio. As a consequence, antenna gain results from the interaction of all other antenna characteristics. This article explores these interactions using elementry definitions of antenna properties.