Greg wrote:
"We would ideally like to put up an omnidirectional horizontally
polarized antenna like a loop."

FM and TV broadcasters do it and succeed amid adversity. In the US, TV
channel 2 is very near to 6 meters in wavelength. Now broadcasters may
opt for circular polarization, but in early times they used horizontal
polarization.

If crossed perpendicular dipoles are fed 90-degrees ouy-of-phase, the
combination is called a turnstile array.

The turnstile antenna produces a pattern that is nearly circular in the
plane of the turnstile. Due to the usual 1/2-wavelength of the turnstile
elements and coupling to their supports, there are often dimples in the
"circular" pattern which give an appearance of crossed figures of eight.
For practical purposes, the pattern circularity is usually good enough
for the turnstile to be accepted for VHF and UHF broadcasting.

Folded dipoles often make up the turnstile for the convenience of their
impedance when electrically connected in parallel and for the lightning
protection provided by closed-circuit antennas.

A single folded dipole is often wrapped into a halo shape with a small
gap between its ends for omnidirectional service and greater simplicity
than the turnstile. Capacitor plates are often added to the
short-circuited ends of the folded dipole to increase the capacitance
between its ends and thus improve current distribution which improves
pattern circularity. An array of such halos in a vertical stack can
provide gain by concentrating energy into a horizontal beam.

Phasing adjustments between elements stacked into the array of halos can
tilt the beam up or down from the horizontal.

High antennas often use a couple of degrees of downward beam tilt to
improve signals near the station and to reduce power loss in radiiation
toward the zenith.

Delaying the feed to each next higher element by an additional 4 or 5
degrees often depresses the elevation angle below the horizontal by a
degree or two.

Best regards, Richard Harrison, KB5WZI

Previously: "An array of such halos in a vertical stack can
provide gain by concentrating energy into a horizontal beam."
____________

N. B. A vertically stacked array of ANY kind of radiating element with ~ 1
lambda or less spacing can produce gain in the horizontal plane.

RF

Visit http://rfry.org for FM broadcast RF system papers.

"Richard Harrison" wrote in message
...
A single folded dipole is often wrapped into a halo shape with a small
gap between its ends for omnidirectional service and greater simplicity
than the turnstile. Capacitor plates are often added to the
short-circuited ends of the folded dipole to increase the capacitance
between its ends and thus improve current distribution which improves
pattern circularity. An array of such halos in a vertical stack can
provide gain by concentrating energy into a horizontal beam.
............................................

Richard,

For what it is worth, I ran EZNEC on a Squalo type 1/2 wave 6m antenna at 20
and 40 feet elevation. I made no attempt at matching or capacitive loading.
The gap at the ends was 2 inches.

1. Impedance at resonance was 10 Ohms. Reasonable for a 1:4 (12.5 : 50)
balun. I mention this, because it would be more rugged than a gamma match.

2. The azimuth plot was an ellipse, with a gain variation of 3 db between
the major and minor axis. Presumably capacitive loading would help this.

3. At 20 feet the lowest vertical lobe was at 14 degrees. At 40 feet, the
lowest vertical lobe was at 7 degrees, and it had many more lobes. I would
expect the M Squared antenna to have the same vertical, but not horizontal,
pattern.

Tam/WB2TT