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Antenna identification

Discussion in 'Radio and Communications' started by Sceadwian, Aug 8, 2010.

  1. Sceadwian

    Sceadwian Banned

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    Attached are some images of two antennas that were removed from wi-fi type devices, they are both for 2.4ghz devices. The J one looks like a Jpole to me, (obviously), the I one looks like a whip with ground aerials on the reverse side, can someone properly characterize the two types of antennas used here? I'm a bit rough in the antenna department, are they both quarter wave?
     

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  2. RadioRon

    RadioRon Well-Known Member

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    The image on the left is an inverted F type antenna. This is a well known type of low profile antenna straight out of the text books. Something very similar was used back in the old days at VHF on top of train engines because it didn't get broken off and it fit easily through tunnels. It can be intuitively described as a monopole that has been bent over partway up and then impedance matched using a shunt inductance at the bend. The strip of holes is in metal that defines the upper part of a larger ground plane area. Without some additional metal or conductor of some sort, this one won't perform well, but usually it is attached to a module or package that provides this ground plane.

    The other antenna appears to be a planar version of a sleeve dipole. I think we can also refer to the coaxial form from which this derived as a bazooka dipole. The upper conductor is roughly a quarter wave (not exactly, due to tuning) monopole radiator, while the lower part is a planar balun that also acts as the other half of a half wave structure. The balun is effective at keeping the antenna currents from coupling back onto the feed line. It has pretty good bandwidth and doesn't want a ground plane beneath it.
     
    Last edited: Aug 9, 2010
  3. Sceadwian

    Sceadwian Banned

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    I looked up the Inverted F on Google images and found a diagram of it which agrees with you, a user on another forum agreed with it being a Jpole but I now see that the orientation of the ground plane is all wrong for that. There was a more extensive ground plane for it in the device but I don't remember exactly, my disassemble jobs are pretty much to turn a device into a pile of components rather than in depth understanding. I just keep the useful and interesting bits for later research.

    I did a Google search of sleeve dipole as well and it agrees as well, that one was taken out of a generic USB 802.11b module, there wasn't any kind of ground plane immediately near the antenna, I didn't look at the PCB too closely though so that's partially an assumption.

    Antenna design will likley always be a black art to me =) But thank you greatly for the information, I now can at least spot these types of designs
     
  4. dave

    Dave New Member

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  5. Ross Craney

    Ross Craney New Member

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    It is a "Black Art" even to the experts
     

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