Roy said -
While a
short inductor can be modeled as a lumped load, that doesn't work
well
in cases like this where the current changes significantly from one
end
of the coil to the other due to radiation. The coil has to be
modeled as
a helix.

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The non-uniform current does not arise from radiation but from the
distributed capacitance of the wire turns on the helix to its
surroundings.

Distributed inductance and capacitance of the helix behave as a short
transmission line and there is a corresponding phase shift between one
end and the other in addition to the non-uniform current distribution.

The effects can be estimated by approximate calculations with an
adequate degree of accuracy but it requires the right type of computer
program (which probably doesn't exist) to provide exact answers.
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Reg.