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→Decibel (dB)
=== Decibel (dB) ===
Again, it's not a characteristic of antenna but there is always a lot of confusion regarding this. Power in decibel is defined as,[[File:PowerDB.JPG|center|frame]]<ref>http://www.antenna-theory.com/definitions/decibels.php</ref>[[File:PowerDB.JPG|center|frame]]
Here the reference power is 1W when power is denoted in Watts. Hence the resultant decibel is known as dBW. When power is denoted in milliwatts, the resultant decibel is denoted by dBm. Here the reference power is 1 mW. <br \>
When decibels are used to describe gain, apart from dBW and dBm sometimes dBi and dBd are also used. dBi denotes gain of the antenna with respect to that of isotropic antenna. As the gain of an isotropic antenna is 1, nothing changes numerically. dBd denotes gain of antenna with respect to that of a standard half wave dipole antenna (gain is 2.15). Numerically, dBd = dB - 2.15. <br \>