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

Antenna reactive field

  1. Aug 23, 2008 #1
    An antenna behaves like an RCL circuit.
    The R is the radiation resistance corresponding to energy actually radiate. Half come from the E field and half from the B field.

    The L and C are responsible for the reactive field close to the antenna. the C tells about the energy stored in the E field attached to the antenna.
    The L about the B field.

    Do the capacitative and inductive reactive fields store energy in the amount?
    Do some antennas have more energy in one or the other? Any example? Can we have an antenna with only inductive reactive field and no C field?
    Is it correct to say that the reactive field is time-varying (almost in phase with the source since it is so close) and looks like the electrostatic+magnetostatic field?
  2. jcsd
  3. Aug 23, 2008 #2
    Any structure that radiates electromagnetic energy can be considered an antenna in the context of your question. Therefore a (real, not ideal) capacitor is antenna, because any such structure can be made radiate to some degree; a real inductor is similarly a radiator.

    So clearly, for a given structure the capacitive and inductive fields do not have to be equal in terms of stored energy.

    Time varying charge densities and current densities give rise to time varying electrostatic and magnetostatic fields in addition to electromagnetic radiation.
  4. Aug 23, 2008 #3
    ak7948 you are very clear. But how about the simple Hertian dipole? It current is time changing (sinusoidally). Does its reactive field have more C reactive energy or L reactive energy? I guess the C and the L are distributed parameters and it is not easy to det. how much each one is.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook