"John N9JG" wrote
This is useful information to know. I don't know why the section
about small
loops in the Antenna Handbook doesn't mention this. BTW, how far
does the
near-field extend?

======================================

It's because neither the authors nor the editors were aware of it.

The near-field on the surface of an antenna's conductors starts off at
a very high value. The far-field is zero at zero distance.

The near-field fades into the distance just the same as the
ar-field - only much faster. It also has a radiation pattern which
depends on an antenna's structure.

For argument's sake, for an isotropic antenna (which doesn't exist),
at a distance of 1/2/Pi = 1/6 of a wavelength from the antenna, the
near-fields and far-fields are equal to each other but differ in
phase. They both exist together and their effects on foreign bodies
are inseparable from a measurements point of view. They exist
seperately at all distances only as a mathematical fiction.

The near-field of open-wire transmission lines is sensibly zero at a
distance of 4 or 5 times the wire spacing but the radiation field is
finite and very small. The radiation field increases with wire spacing
and is a maximum when spacing is about 1/2-wavelength which nobody
ever uses. This accounts for the lack of use of low-loss open-wire
lines at UHF and higher frequencies.

Back to Magloops where the measurement unit is loop diameter rather
than wavelength and the near-field is mainly magnetic. The magnetic
field falls off at a rate proportional to the cube of distance. I
would be very happy with a distance of 1/2 the loop diameter or more
between the loop and large foreign bodies such as the ground.

Highly conductive metallic bodies merely slightly detune the loop with
little additional loss.
----
Reg.