"Roy Lewallen" wrote
Reg Edwards wrote:

Ian, Oh yes they do.

Next to each half wavelength of line there is another half
wavelength
of line in which the current is in antiphase with it. And so, in
the
far field, the fields from adjacent half-wavelengths of line
cancel
each other out.
. . .

No, they don't. They cancel only in two directions, directly normal
to
the plane containing the wires. Radiation occurs in all other
directions, because the fields don't add in antiphase. An example of
an
antenna which uses two closely spaced elements carrying equal
out-of-phase currents is the W8JK.

Roy Lewallen, W7EL

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

Roy, I've never head of a W8JK. You are confusing the issue.

The problem is concerned with a LONG balanced transmission line and
its terminations which form part of the whole radiating system. And as
we can agree it is incorrect to consider parts of the system in
isolation.

To simplify the questions, wthout loss of rigor, it is best to
consider the line itself as being lossless with matched terminations.

I have stated that power radiated from the system is independent of
line length and nobody has disagreed. Indeed, a radiating power
calculating formula from reputable authors (of which I was unaware)
has confirmed this.

The power radiated from the system is identical to that radiated from
a monopole or short dipole, of length equal to wire spacing, with a
current equal to the current which flows in the terminations (ie., the
load). The terminations actually exist.

Radiated power = Load current-squared times calculated radiation
resistance.

That is obviously true down even to zero line length.

The implication is that radiation occurs only from the termination(s)
and that no radiation occus from the line. But, I repeat, we must NOT
consider the parts in isolation as do old wives.

You have stated that radiation from the line itself (in isolation)
must exist in the plane of the wires because of the finite spacing
between the line wires.

But we must consider only the far field. Not that in the immediate
vicinity of the line and its termination.

I suspect that the radiation pattern of a LONG-line SYSTEM converges
towards that from a monopole located in the position of the load.

Many of us are curious to acquire an idea of what the radiation
pattern looks like.

You are familiar with programs which produce far-field radiation
patterns. Do you know of a program which accurately produces the
radiation pattern of a very long close-spaced, zero resistance, pair
of wires terminated with a wire of length equal to wire spacing and
including a load resistance equal to Zo.

Patterns, of course, will change with frequency. It will be necessary
to statistically analyse results. Or just look at them from a common
sense point of view.

From a practical engineering viewpoint it is quite sufficient to know
what I innocently stated in the first place - the minute amount of
power lost is the load's radiation resistance times load current
squared and is independent of line length.
----
Reg, G4FGQ