vfone said:Antenna gain is measured in either dBi or dBd
http://www.digi.com/support/kbase/kbaseresultdetl.jsp?id=2146
biff44 said:Because dBi is slightly larger number, data sheets almost always use dBi. dBi is simply dBd + 2.1 dB.
LvW said:biff44 said:Because dBi is slightly larger number, data sheets almost always use dBi. dBi is simply dBd + 2.1 dB.
That´s OK.
However, perhaps somebody is interested in the meaning of this abbreviation "dBi".
Background: dB corresponds to a simple number. As an antenna does not amplify a signal it does not multiply it with a number (as an amplifier does). Therefore the unit cannot be "dB".
But a directional antenna forms a beam and concentrates the power into one direction - leading to a gain figure if compared with the (theoretical case of an) isotropic antenna. Thus, it has x dB more power in that direction than for the isotropic case. That´s the meaning of "dBi".
LvW said:No, that´s definitely not correct.
You cannot radiate more power than available at the antenna input.
An isotropic radiator at the centre of a sphere will illuminate the surface of the sphere equally in all directions. If that radiator is replaced by, say, a dipole antenna then the surface of the sphere will not be illumnated evenly. Since the energy, assuming the same transmitted power, is distributed differntly in both cases then the dipole will have an apparent gain over the isotropic. This, numerically, is a gain of 1.64 or 2.16dBi. Some antenna manufacturers then reference their product against the radiation achieved from a dipole and then express this as a gain in dBd. A dipole has 0dBd gain. Hope this makes sense!saran7507 said:Hi All,
Can anybody tell me what is the unit for the antenna gain? We are using friis equation to get the gain value ....what would be the unit called ?
dBi or dBd.............
Waiting for your reply.
Thanx.
Regards,
Saran
mounika said:hi,
can anyone tell me what is the gain of antenna
engr_najam said:I am not sure, but if it is gain than it is the ratio of two same quantities, which means their units cancel out, hence no unit.
dB means the ratio is logarithmic form multiplied by 10 for power or 20 for voltage.
Aya2002 said:is there a relationship between dB, dBi, and dBm?
thanks
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