Antenna Theory Isotropic Radiation - Antenna Theory

What is Antenna Theory Isotropic Radiation?

In the preceding section, we have moved out through the radiation pattern. To have an improved examination concerning the radiation of an antenna, a referential point is essential. The radiation of an isotropic antenna fills this space.


Isotropic radiation is the radiation from a point source, radiating consistently in all directions, with identical strength irrespective of the direction of measurement.

The development of radiation pattern of an antenna is continuously measured using the isotropic radiation of that antenna. If the radiation is identical in all directions, then it is known as isotropic radiation.

  • The point source is an instance of isotropic radiator. On the other hand, this isotropic radiation is almost unmanageable, since each antenna radiates its energy with some directivity.
  • The isotropic radiation is nothing but Omni-directional radiation.
  • It has a doughnut-shaped pattern when viewed in 3D and a figure-of-eight pattern when viewed in 2D.

The figures given beyond display the radiation pattern of an isotropic or Omni-directional pattern. Figure 1 explains the doughnut shaped pattern in 3D and Figure 2 illustrates the figure-of-eight pattern in 2D.


The isotropic radiator has unity gain, which means having a gain factor of 1 in all directions. In terms of dB, it can be called as 0dB gain (zero loss).

Equivalent Isotropic Radiated Power

According to the standard definition, “The amount of power that an isotropical antenna radiates to create the peak power thickness experiential in the direction of maximum antenna gain is called as Equivalent Isotropic Radiated Power.”

If the radiated energy of an antenna is made to deliberate on one side or a specific direction, where the radiation is equal to that antenna’s isotropic radiated power, such a radiation would be called as EIRP i.e. Equivalent Isotropic Radiated Power.


Although isotropic radiation is an unreal one, it is the best an antenna can give. The gain of such antenna will be 3dBi where 3dB is a factor of 2 and ‘i’ represents factor of isotropic condition.

If the radiation is motivated in certain angle, then EIRP rises along with the antenna gain. Gain of the antenna is best attained by concentrating the antenna in certain direction.

Effective Radiated Power

If the radiated power is intended by taking half-wave dipole as the reference, rather than an isotropic antenna, then it can be termed as ERP (Effective Radiated Power).

E R P ( d B W ) = E I R P ( d B W ) 2.15 d B i

If EIRP is known, then ERP can be calculated from formula given above.

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