Mylinux wrote:
"Please."

The antenna pictured is a "grid dish" of the type practical below about
3 GHz. Its advantage is reduced wind loading.

Above about 3 GHz, the spacing between grid elements becomes so small
that advantage of the grid over a solid sheet of metal becomes
impractical.

Polarization of the reflector is in the direction of the length of its
elements. Polarization of the driven antenna element must agree with the
reflecting elements in the dish.

The ring-back construction is typical of a company, "Anixter Mark",
formerly "Mark Products".

Best regards, Richard Harrison, KB5WZI

Leon wrote:
"I guess that the black cylinder is just a waveguide."

Not exactly. At the frequencies used with grid dishes, the feedline is
usually coax. Waveguide would be too big.

The cylinder is a shield which allows a little dipole to illuminate the
dish but does not allow direct radiation in the same direction as that
reflected from the dish.

The rays reflected from the dish are parallel to each other and
perpendicular to the circumference of the dish. Parallel rays reflected
by the dish pass through its focal point where the dipole is located.

The transit time within the dish is long near its center and short near
its edges. Phase between direct feed radiation and reflected radiation
would be a mess were the direct radiation allowed, so the black cylinder
is used to clean up the dish pattern.

Best regards, Richard Harrison, KB5WZI

Jack wrote:
"The antenna you are asking for is built of helical antenna and dish."

The illostration on my screen was a dish constructed of parallel bars.
The dish will reflect a signal which has an electric field that
parallels the bars in the reflector. Cross-polarization of the signals
will not work. I`ve seen it tried.

A pickup dipole can be used to explore the field transmitted in the
maximum gain direction of a helical antenna. Regardless of the sense of
the pickup dipole, horizontal, vertical, or anywhere in-between,
throughout 360 degrees rotation, there is no change in amplitude due to
dipole polarization.

This characteristic of the helical antenna is called "circular
polarization". Off the axis of the helical antenna, signal strength
intercepted by a pickup dipole will vary with polarization, and the
field is said to be eliptically polarized.

To take full advantage of a helical antenna`s reflected energy requires
a solid-sheet reflector, or at least a cross-hatch conducting grid so
that more than one polarization of signal will be reflected. See the
RSGB "VHF-UHF Manual" for details. In my 3rd edition, this is found on
page 7.21.

As the dish il;lustration provided by the given URL has only parallel
reflector bars, it is nearly certain that the dish uses a single
polarization which agrees with the direction of the bars. The excitation
source is likely a dipole.

When a helix is teamed with a dipole, there is a 3 dB loss as compared
with a helix to helix or dipole to dipole. So, my bet is on a dipole
illuminating the reflector bars which share the same sense in the
antenna.

Best regards, Richard Harrison, KB5WZI