This again transfers energy back to the antenna current.
2.
Note that, by the principle of Fourier or Hankel transform relationships between the antenna current distributions and the observed far-field patterns.
3.
This method can be used to compute the radiation resistance for any antenna whose far field radiation pattern has been found in terms of a specific antenna current.
4.
Station officials have confirmed it, as an unusual antenna current meter, one measuring in milli-amps, has been used by current owners to confirm.
5.
That current is in the same absolute direction as the actual antenna if the antenna is vertically oriented ( and thus vertically polarized ) but opposite the actual antenna if the antenna current is horizontal.
6.
It had been announced that the transmitter used for broadcasting would be rated at 3?kilowatts, producing an antenna current of 20 to 25 amperes, however, the actual transmitter ratings would be somewhat less.
7.
Also, in the particular case of a monopole antenna, the ground ( or an artificial ground plane ) serves as the return connection for the antenna current thus having an additional effect, particularly on the impedance seen by the feed line.
8.
The cause of these losses is related to the relatively low radiation resistance of an electrically short radiator with respect to the r-f resistance of the ground system and matching networks, all of which are in series with the antenna current.
9.
For example, current flowing in the antenna creates a purely magnetic component in the near field, which then collapses as the antenna current begins to reverse, causing transfer of the field's magnetic energy back to electrons in the antenna as the changing magnetic field causes a self-inductive effect on the antenna that generated it.
10.
The radiative near field ( sometimes called the "'Fresnel region "') does not contain reactive field components from the source antenna, since it is so far from the antenna that back-coupling of the fields becomes out of phase with the antenna signal, and thus cannot efficiently store and replace inductive or capacitive energy from antenna currents or charges.
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