antenna question

Discussion in 'Wireless & RF Design' started by jaygatsby, Jan 26, 2013.

  1. jaygatsby

    Thread Starter New Member

    Nov 23, 2011
    185
    23
    I once read on a forum that an antenna is basically an impedance matching network between the radio system and free space.

    I've believed this and thought about it since.

    Now I wonder, since an antenna radiates electromagnetic waves, and the impedance of free space presumably exists due to things like air, if this is not correct. If i understand this bit of physics correctly, the EM wave exists independently to molecules and atoms in the atmosphere.

    yeah?

    Thanks,
    J
     
  2. KnRele

    New Member

    Jan 7, 2013
    20
    8
    Yes, an electromagnetic wave exists in free space independent of air or any other detectable substance that might be there.

    The impedance, which is the ratio of the strengths of the electrical and magnetic component of the field as it propagates in empty space is approximately 377 Ohms, by the way this is not very different from what it is in air, since the relative dielectric and magnetic constants for air are very close to unity.

    It might indeed make sense to think of the antenna as an impedance matching device, matching the impedance at the end of the feeder cable to the impedance of space.

    However, there are several other practical issues that will be just as, if not more, important; typically issues having to do with the radiation pattern, such as the presence of intentional and unintentional parasitic elements and the size of the antenna compared to the wavelength of the radiation. The antenna will present some load impedance at its feeding terminals, which will depend on the particulars of its construction, and one will want to match the feeder cable's characteristic impedance to this.
     
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