Isotropic Radiator as a Reference

The isotropic radiator is used as a reference for the computation of the resulting antenna pattern. It radiates the same power density in all directions.

As already mentioned, the isotropic radiator is a single point of radiation. The coordinates of this point are determined based on the coordinates of the single antennas used in the configuration. In a first step, the geometrical mean M g e o of the single antennas (each of them concentrated in a single point) is determined. Each antenna is weighted with its individual part of the Tx power (if power splitters are used). So, in power splitter mode, M g e o will be closer to the high power antennas.

The total Tx power P t 0 fed to the isotropic radiator is the sum of the powers fed to the individual antennas. With this power, the received power P r in a distance r can be computed with

(1) P r = P t 0 G t G r λ 0 2 ( 4 π r ) 2

For the computation of the resulting antenna pattern, the field strength and not the power is relevant. Therefore, the power density S r is computed with

(2) S r = P t 0 G t 4 π r 2 .


(3) S r = | E _ e f f | 2 Z F 0

the power density S r can be transformed to the effective electric field strength E eff ( Z F 0 is the free space impedance, and its value is 120   π   Ω ).