Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Reciprocity applied to complementary antennas

  1. Aug 14, 2005 #1
    Does reciprocity, the rule that electrical specifications of an antenna are essentially the same for receiving and transmitting [Wikipedia], apply to the following situation:

    Antenna Y transmits with power PY which antenna Z receives as power PZ. Does this mean if that antenna Z transmits with power PY, antenna Y receives it as power PZ? The antennae are assumed linear and well behaved.
     
  2. jcsd
  3. Aug 15, 2005 #2

    berkeman

    User Avatar

    Staff: Mentor

    I'm no antenna expert, but I believe that if the input Z of your two antennas are the same, then your statement will hold. The more general way that I've seen reciprocity derived (Stutzman & Theile, section 1.7) is in terms of the drive current into one antenna and the open circuit output voltage out of the other antenna:

    Voc,a / Ib = Voc,b / Ia

    If the two antennas have different input impedances at the drive frequency, then I think that your power statement may not hold. Like I said, though, I'm no expert on antennas....
     
  4. Aug 15, 2005 #3
    berkeman,

    Yours, the best explanation yet. One neat "power law" and more general than my original assertion, as you outline. Thank you.
     
  5. Aug 17, 2005 #4
    Luckily, I'm an actual antenna expert.

    Reciprocity is more interesting than that.

    It says that if Antenna 1 is driven with a current i1 which
    induces a voltage v2 at the terminals of antenna 2, then
    if antenna 2 is driven with i1, antenna 1 will have v2 volts
    at the terminals.

    This rather remarkable statement holds regardless of z1 and z2
    and regardless of the material configurations around or between
    the antennas. Only linearity and isotropy is required.

    What is amazing about this is that the transmitting and receiving
    current patterns of any given antenna are not generally the same, and
    reciprocity can be shown not to be a statement of energy
    conservation.
     
    Last edited: Aug 17, 2005
  6. Aug 17, 2005 #5
    Thanks, Antiphon. This may be what I had seen originally, years ago. Do you have any Internet references for the relation?
     
  7. Aug 17, 2005 #6
    Berkeman's Theile reference is a reliable textbook.

    As far as the internet goes, I cannot find a single technically correct reference.
    Most of them are flat out wrong and state that it means that an
    transmitting antenna has the same characteristics as a receiving antenna, etc.
    I will edit this post if I find one.

    As I mentioned the current patterns are different on an antenna which is
    transmitting than for the same antenna when receiving. Reciprocity would
    not be so unusual if this were not the case.


    Edit: The Navy has a decent link- start on page 42 of the slide show.
    http://www.nps.navy.mil/Faculty/jenn/EO3602/Vol2v1.3.pdf

    BTW, this is an oustanding executive summary slide show about antenna theory.
    I can recommend it to anyone looking for a decent antenna theory reference
    without having textbooks handy.
     
    Last edited: Aug 17, 2005
  8. Aug 17, 2005 #7
    Excellent reference, Antiphon - I appreciate your homework.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Reciprocity applied to complementary antennas
  1. Antenna Reciprocity (Replies: 12)

  2. Reciprocity theorem (Replies: 7)

  3. Antenna Duplexer (Replies: 7)

  4. Antenna Basics (Replies: 1)

Loading...