Any time a charge is accelerated and electromagnetic field is produced.
Maxwells equations say this, and I am saying this from the James Clerk Maxwell
Telescope.
An RF current is constantly accelerating charge, sinusoidal acceleration at
the RF frequency.
Whatever conductor has RF current flowing in it will generate an EM field.
It does not matter whether it is terminated, open circuit, infinitely long,
shorted, grounded, insulated, red, blue, or if you call it an antenna or an
elephant. If RF current flows in it, it generates an electromagnic field.
The only way you can make it not radiate (or probably more accurately make it
radiate very little) is to have another conductor real close to it and parallel
to it that has an equal amplitude and opposite phase RF current flowing in it.
Yes there are variations of that, such as coax or a three wire three phase
transmission line. The principle is the same, the field produced by one
conductors current is canceled by the field(s) produced by the current(s)
flowing in the other conductor(s).
DE N6KB at JCMT
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