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USB WiFi Adapter Antenna

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bobcat2000:
Hi Guys,

I am looking at these USB WiFi adapters.  They seem to have 2 different type of antenna.  My understanding from my Physic class is that the piece of wire picks up the magnetic wave to generate electricity.  But these WiFi thingies are 2 ways.

It looks like the longer one has a bigger surface area.  Will the antenna with one piece of long wire better than the one with a small pads of copper? 

Thanks!



ataradov:
The first one looks like some artist rendition, it is likely not actually that complicated on the inside. In any case it is hard to tell without either simulation or proper characterization what is better.

More complex antennas may have weird radiation patterns and performance would depend on the orientation.

Generally the bigger the antenna, the better it would be provided it is still tuned to the target band.

bobcat2000:
Something likes this.  They printed the copper on the board.

When you say "Tune", you mean size doesn't matter?  I just assume bigger is better.


ataradov:
This is functionally no different than wire. It may be a bit worse, but not much. It is easier to manufacture, I guess.

The length of the wire is not arbitrary. It is calculated according to the frequency band (2.4 GHz or 5 GHz in this case). And when selecting the antenna it is important to match the used frequency band.

Note that the length of the squiggly line on the PCB is shorter than equivalent coil part on the wire one.  The coil or squiggly trace does not add anything, it is just a way to have antenna to be mechanically shorter while having the same electrical length.

David Hess:
Given the frequency and antenna length, I do not think that is a center-loaded dipole.  More likely it is the third type of colinear array described here; two or or more dipoles are placed in series with phase matching sections between them.  This gives greater gain and capture area by flattening the radiation pattern.

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