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 ${S}_{i}$ 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 ${P}_{t0}$ fed to the antenna, this leads to the following power density ${S}_{i}$ in a distance $d$ :

(1) ${S}_{i}=\frac{{P}_{\text{\hspace{0.17em}}t0}}{4\text{\hspace{0.17em}}\pi \text{\hspace{0.17em}}{d}^{2}}$