antenna mismatch!

Discussion in 'Wireless & RF Design' started by aj_silverthunder, Nov 19, 2009.

  1. aj_silverthunder

    Thread Starter Active Member

    Jun 6, 2009
    116
    0
    what is antanne mismatch!how to solve this mismatch!
    guys can a transmitter be connected directly to a di-pole antanna!
     
  2. ELECTRONERD

    Senior Member

    May 26, 2009
    1,146
    16
    aj_silverthunder,

    Google is your friend; I googled "Antenna Mismatch" just for kicks and found several great resources in an instant. Next time, try and exert some effort and research your questions on your own, then if you have remaining questions you can ask the forum.

    Consider an RF transceiver and a isotropic antenna (theoretical antenna; doesn't actually exist-google it!). Since we have an "isotropic" antenna, there is theoretically no mismatch between our transceiver and antenna. A mismatch occurs when the impedance of the RF transceiver and the antenna doesn't match (usually they should both have an impedance of 50Ω) and there is too high of an SWR (Standing Wave Ratio-always want a 1:1 match; google it!). So for our application we may assume the RF transceiver has an impedance of 50Ω and so does the isotropic antenna. We may also assume that the SWR is 1:1. Since an isotropic antenna is ideally the "perfect" antenna, those matching conditions won't come to a perfect match; thus, you have a mismatch. Actually, a mismatch is generally referred to being a significant mismatch. In other words, if my antenna impedance were 56Ω and my SWR was 1:2, then we can say the antenna is matched. But, if I have an antenna impedance of 82Ω and an SWR of 1:3.4, then you can definitely say that we have a mismatch occuring-and quite a big one at that!

    That's quite a mouthful, but I'm sure you'll soak it in. ;)

    Austin
     
  3. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,040
    287

    Hi AJ:

    This is probably more than you'll ever need to know about the subject, but this has been my specialty for about 37 years.


    Eric
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Hi Austin,

    For a 50Ω system I think the VSWR with a 56Ω load would be 1.12:1 and with a 82Ω load it would be 1.64:1.

    Rgds,

    t_n_k
     
  5. ELECTRONERD

    Senior Member

    May 26, 2009
    1,146
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    I do believe your correct, t_n_k. ;) Thank you very much for your comment, I'm glad you brought that to my awareness. In truth, I wasn't quite sure how to calculate that, but your explanation does make sense.

    Austin
     
  6. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Hi Austin,

    It's fairly simple really ....

    VSWR=(ZL/Zo):1


    Rgds,

    t_n_k
     
  7. ELECTRONERD

    Senior Member

    May 26, 2009
    1,146
    16
    Hi t_n_k,

    Yes I came to that conclusion when you suggested the VSWR in your first post.

    Thanks,

    Austin
     
  8. rotson80

    New Member

    Feb 2, 2009
    2
    0
    Hello, i am new to RF, fresh graduate. I have a job now. Wat does this formula means.

    Thank you.
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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