Understanding Antenna Gain, Beamwidth, And Directivity

Antenna gain is a performance indicator gauged in comparison to a reference source. In compliance engineering, antenna gain is measured in decibels over isotropic (dBi), referring to an isotropic antenna — an “ideal” antenna that transmits/receives energy uniformly in all directions, exhibiting a gain of 0 dBi.  

In a transmitting antenna, gain describes the antenna’s ability to convert input power to radio waves sent in a specified direction. In a receiving antenna, gain describes the antenna’s ability to convert radio waves (incoming from a specified direction) into electrical power.