Isotropic Radiator
An isotropic radiator is an ideal (theoretical) antenna operating without losses and having equal radiation in all directions.
This antenna is not available in the real world – but is used as a reference for all real-world antenna patterns.
The power density radiated from an isotropic radiator is homogeneously distributed over a spherical surface (with the radiator in the center of the spherical surface). With the power fed to the antenna, this leads to the following power density in a distance :