ERP (Effective Radiated Power)

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ERP

Nederlands
Effective Radiated Power is the product of the power supplied to the antenna and the gain of the antenna, relative to a reference antenna, in agiven direction. So the ERP is the power that would be necessary at the input of the reference antenna to give the same amount of radiated power in the same direction. Usually, the antenne gain is relative to a half-wave dipole antenna.

If an isotropic antenna is used as reference antenna the term EIRP is used.

Because a haf wavelength dipole antenna has a antenna gain, relative to isotropic radiation. The ERP is smaller than the EIRP. The difference is:

ERP = EIRP/1.64 = EIRPdB - 2.15 dB.

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Effective Radiated Power (ERP)

There are several definitions of effective radiated power from an antenna. The most common definition of effective radiated power is the power supplied to an antenna multiplied by the antenna gain in a given direction, or as the product of the power supplied to the antenna and its gain relative to a half-wave dipole in a given direction:

ERP (dBm) = Power of transmitter (dBm) – loss in transmission line (dB) + antenna gain in dBd

Note that if the direction is not specified, the direction of maximum gain is assumed. The type of reference antenna also must be specified. A reference antenna can be real, virtual, or theoretical. Antenna examples are unit dipoles, half-wave dipoles, or isotropic, that is, omnidirectional antennas. If the cable loss is not specified, you should consider it zero.

The ERP value is frequently measured in watts.

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Effective Isotropically Radiated Power (EIRP)

Effective isotropically radiated power is the arithmetic product of the power supplied to an antenna and its gain relative to an isotropic source:

EIRP (dBm) = Power of transmitter (dBm) – loss in transmission line (dB) + antenna gain in dBi

dBm = 10 *log(power out / 1mW)

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Example: An antenna has a gain of 16 dBi, and the power delivered to the antenna is 100 milliwatts (0.1 watt). What is the effective isotropic radiated power?

100 mW equals to 20 dBm.

10 *log (100 mW/1 mW) = 10*2 = 20 dBm

EIRP = 20 + 16 = 36 dBm = 4 watts

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