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I got a Linksys AP, I noticed it has 2 antennas.
Is this called dipole antenna?

Why it has 2 antennas, not 1? what is the functionality of each one of them?


I read in the book that the length of an antenna should be equal or a multiple of the wavelength (2, 4, 1/2, 1/4 ...). What is the best multiplication to use?

I searched the net, all home made antennas had many parts of 1/2 size of wavelength (putting together parts of half the length of wavelength):
http://wireless.gumph.org/articles/homemadeomni.html


Wavelebgth of a 2.4GHz signal is:
3*10^8 / 2.4*10^9 = 0.125m = 12.5 cm

So, does every antenna of the AP has a 1/2 length of this wavelength (roughly 6 cm) ??


Thanks a lot !!

Why it has 2 antennas :
This is to reduce multipath effects for proper functioning of the link. It will work with one antenna also, two work together to reduce multipath effects.
Antenna Length
It is good to have antenna length of 1/2 the wavelength which is roughly 6 cms for 2.4 Ghz systems. The antenna length we see is different as the actual metallic antenna is covered with protective covering.

walid97 Escribi?3:

I got a Linksys AP, I noticed it has 2 antennas.
Is this called dipole antenna?

Why it has 2 antennas, not 1? what is the functionality of each one of them?


I read in the book that the length of an antenna should be equal or a multiple of the wavelength (2, 4, 1/2, 1/4 ...). What is the best multiplication to use?

I searched the net, all home made antennas had many parts of 1/2 size of wavelength (putting together parts of half the length of wavelength):
http://wireless.gumph.org/articles/homemadeomni.html


Wavelebgth of a 2.4GHz signal is:
3*10^8 / 2.4*10^9 = 0.125m = 12.5 cm

So, does every antenna of the AP has a 1/2 length of this wavelength (roughly 6 cm) ??


Thanks a lot !!

more info:

the two antennas will pick up two different signals if there is any kind of multipath happening and choose the strongest one (usually the direct signal or one with fewest bounces) to recieve, then use that antenna to send/recieve. some more expensive APs with two antennas can determine what antenna to send/recieve on based on the client it is connected to. the antennas unfortunately don't provide full duplex :(

more info part 2:

Its called antenna diversity if you want the books description :D

Im not sure if there is a "best" antenna length. I didn't see anything in the book. I think it may be a "you won't have any issues" with any of the given lengths (1/2, 1/2, etc.). I would assume that a 1:1 ratio would be technically best, but there most likely isn't any dissadvantage to using a different ratio in normal operating paramaters... but I also have nothing to back that up :D. also, each single antenna is considered an omni-directional/dipole antenna.

Thanks guys !
This helps :)

I don't know the Linksys AP but the Siemens AP has also 2 antennas - #1 is for "a" radio and #2 for "b/g" radio.

If you only use "a" or "b/g" then you could use the "spare" one for antenna diversity.