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RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...
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Effective isotropic radiated power (sometimes also referred to as equivalent isotropic radiated power), is a commonly used unit when specifying antenna efficiency (gain).
In order to provide a common reference for radiated power, an ideal isotropic radiator is used as the standard. An isotropic radiator emits power from a singular point (dimensionless) whose wavefront is a perfect sphere of constant voltage (or power for equal impedances). Any gain specified for an antenna represents a concentration of the radiation pattern in a given direction. EIRP is calculated as follows:
where Power (dBm or dBW), Loss (dB), Gain (dBi)
Most antenna types; e.g., parabolic, Yagi, log periodic, have gains based on many physical parameters. A few common antenna types are fixed in physical dimensions and have well-known gains when positioned optimally above a ground plane; e.g.,1/4-wave monopole and 1/2-wave dipole antennas have gains of 2.15 dBi.
Sometimes, especially in the amateur radio world, antenna gains are expressed in units of dBd, which is decibels relative to a ½-wave dipole antenna. This is because the ½-wave dipole is thought of as a standard when discussing transmitter and receiver performance.