Definitions for "Isotropic Antenna"
A theoretical antenna that radiates equally in all directions and has zero gain by definition. An antenna is a passive device and so cannot amplify a signal. However, it can shape the signal to be stronger in one direction, leading to gain, which is often quoted relative to an isotropic.
This is a hypothetical one-directional point-source antenna that serves as a reference for the measurement of antenna gain for engineering calculations.
a hypothetical antenna radiating or receiving equally in all directions