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Isotropic Radiation

Figure 1: An isotropic radiator has got a ball-shaped radiation

Kugel

Figure 1: An isotropic radiator has got a ball-shaped radiation

Some radiation sources radiate energy equally in all directions. Radiation of this type is known as isotropic radiation. We all know the Sun radiates energy in all directions. The energy radiated from the Sun measured at any fixed distance and from any angle will be approximately the same. Assume that a measuring device is moved around the Sun and stopped at the points indicated in the figure to make a measurement of the amounts of radiation. At any point around the circle, the distance from the measuring device to the Sun is the same. The measured radiation will also be the same. The Sun is therefore considered an isotropic radiator.

Figure 2: The dipole antennaes emission diagram is a slightly flattened torus

Figure 2: The dipole antennaes emission diagram is a slightly flattened torus

In antenna design the isotropic radiator is an hypothetic antenna. In reality this one antenna cannot exist. But it is used to compare real antennas each other. It is a hypothetical reference. All real antennas have a gain compared to this reference. This gain is a measure for the directivity of a given antenna.