What is the effective and equivalent isotropic radiated power?

Effective (or equivalent) isotropic radiated power (EIRP) is a measure of the best power that a specific transmitter antenna can radiate, usually in decibels (dB) or isotropic decibels (dBi). EIRP is used to measure the maximum amount of radiation that a radio frequency system can radiate in the establishment of standards or specifications. An isotropic radiator is a point radiation source that emits radiation in a spherical pattern. This means that the maximum radiated power at any point in the radiation pattern of the isotropic radiator is equal.

Effective (or equivalent) isotropic radiated power (EIRP) is a measure of the best power that a specific transmitter antenna can radiate, usually in decibels (dB) or isotropic decibels (dBi). EIRP is used to measure the maximum amount of radiation that a radio frequency system can radiate in the establishment of standards or specifications. An isotropic radiator is a point radiation source that emits radiation in a spherical pattern. This means that the maximum radiated power at any point in the radiation pattern of the isotropic radiator is equal.

What is the effective and equivalent isotropic radiated power?

EIRP has two main factors: total radiated power; and antenna gain based on the antenna pattern. When the same transmitter uses antennas with different antenna gains, different EIRP results will be produced. Conversely, transmitters with different power output values ​​operating on the same antenna will also produce different EIRP results. For example, a 100-watt transmitter with a gain of 4 (6dBi) and a 400-watt transmitter with a gain of 1 (0dBi) have the same EIRP. The important thing to note is that in the concept of EIRP, an isotropic radiating antenna is a hypothetical antenna whose antenna pattern cannot actually be realized. Therefore, EIRP is the theoretical maximum.

EIRP can sometimes be confused with the effective radiated power (ERP) defined by IEEE, which is the radiated power of the main lobe of a half-wave dipole antenna. The main lobe gain of the half-wave dipole antenna is 1.64 times (that is, 2.15dB) of the isotropic radiator antenna. Therefore, EIRP and ERP are interrelated values-for the same radio frequency system, EIRP is 1.64 times (or 2.15dB) of ERP.

In order to improve accuracy, other factors can be introduced into EIRP and ERP calculations. For example, losses caused by wiring, connectors, switches, circulators, etc. on the path from the transmitter to the antenna can be introduced. In addition, the degree of mismatch between antennas, interconnecting devices, and transmitter output stages can also be taken into account to achieve higher calculation accuracy.

Although polarization factors are not considered in EIRP or ERP, system designers must consider polarization loss during the actual antenna system installation process. Otherwise, the polarization loss of a linearly polarized antenna can be as high as 3dB, while the loss of a circularly polarized antenna is theoretically 100%.

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