LF: polarization of small loops]

[Bob Bruhns]

Rik,

A small loop (a loop less than 1/4 wavelength in circumference)
radiates outward in the plane of the loop.  Polarization is in the
plane of the loop and perpendicular to the outward direction.
Overall, very much like the pattern of a short vertical antenna, but
with the magnetic and electric lines of force swapped.

So a small horizontal loop will radiate horizontal polarization in
all compass directions toward the horizon.  Of course this will be
distorted by ground reflection and Brewster effects.  For a small
horizontal loop close to the ground, the takeoff angle will be
raised up from  the horizontal, then falling off in intensity at
higher angles approximately according to the cosine angle, until it
reaches a null straight up (90 degrees).

A small vertical loop will also radiate in the plane of the loop.
Toward the horizon this will be vertical and broadly directional
(approximately cosine again) in the plane of the loop, with nulls 90
degrees to the sides.  Toward the sky, radiation will be
horizontally polarized like a horizontal dipole in the plane of the
loop.

Two small vertical loops, at right angles to one another and fed 90
degrees out of phase, will be more or less omnidirectional.
Vertical polarization toward the horizon, circular polarization
straight up.

Check Terman "Radio Engineer's Handbook", McGraw-Hill, 1943.

  Bob, WA3WDR


----- Original Message -----
From: "Andre Kesteloot" <andre.kesteloot@verizon.net>
To: "lf-amrad" <lf@amrad.org>; "AMRAD Tacos" <tacos@amrad.org>
Sent: Wednesday, July 10, 2002 9:53 AM
Subject: [Fwd: LF: polarization of small loops]


> Rik Strobbe wrote:
>
> > Dear LF group,
> >
> > I have been looking for some information about the polarization
of small
> > loops, but no success.
> >
> > For full-size loops things are quite clear, a loop can be
polarized
> > horizontal or vertical depending on the feeding point.
> >
> > What about small loops ?
> > I found several descriptions of small transmitting loops close
to ground
> > and there loops were fed at different places (center horizontal
side, at
> > the edges). Polarization seems to be vertical in all cases.
> > And what about a small loop is free space ? Current distribution
is uniform
> > over the entire loop, regardless of the feeding point. So one
would expect
> > always the same polarization (but which one ?). Unless also the
voltage
> > distribution plays a role.
> >
> > Anyone who can point me to the right theory and/or has
experience with
> > feeding small loops at different points ?
> >
> > Thanks in advance,
> >
> > Rik   ON7YD
>
>
>
>
> _______________________________________________
> Tacos mailing list
> Tacos@amrad.org
> http://www.amrad.org/mailman/listinfo/tacos