performance antennas have asymmetrical patterns
with lower side lobe levels on one side. For
these antennas, radiation pattern envelopes
are prepared for the full 360°. The
frequency coordinator can use the better
half of the radiation pattern on either
the right or left side of the antenna to
reduce potential interference. Half of the
UXH feed hub is painted red to identify the
better side. This side can be placed either
to the right or left of boresight. Therefore,
it is necessary for the frequency coordinator
to specify feed "red left" or "red right." The
installer must be advised of the proper feed
orientation on all ultra high performance
antennas and the proper polarization for
plane-polarized antennas.
Dual-polarized feeds for the following standard
and focal plane antennas must be positioned with
the waveguide bends in the vertical plane, as
shown in Figure 9:
Positions with Waveguide Bends in Vertical Plane
(applies to specific antennas-see text)
protective covers from the feed input flange and
the connector flange of the transmission line.
Connect the flanges together with screws, lock
washers, and nuts (if supplied), using the proper
O-ring or O-rings.
Fingertighten all of the screws. Then tighten first
the screws at or near the center of the long dimension
of the flange and then those on the short dimension.
Tighten the screws in pairs; that is, screws located
180° apart. If the gap between connector flanges
is not uniform after tightening, loosen the screws
and retighten them.
antenna and proceeds to the transmitter or receiver.
The lines must be anchored with hangers along the
supporting structure to prevent any strain at flange
connections.
5. Pressurize Line and Feed. Connect a
dehyrdrator to the gas port of the flange connector
closest to the transmitter or receiver. The dehydrator
is used to purge the system of moisture and provide a
constant supply of dry air at a specified gauge
pressure above atmospheric pressure. This supply
is maintained to prevent moist air from entering the
system and impairing performance. A source of dry
nitrogen can be used instead of dry air.
Remove the gas port plug on the connector at the
antenna end of the transmission line and purge the
line continuously until it is dry. Then replace
the plug and pressurize the line.
The dehydrator used depends on the pressure
requirements of the waveguide transmission line
and the feed. A gauge pressure of 8 psi (55 kPa)
is adequate for most systems. However, no more than
10 psi (70 kPa) should be used.
Caution: Excessive pressure can damage the
feed window. Some feeds may have lower maximum
pressure ratings because they are limited by the
size of the feed pressure window. Check to see if
there is a pressure specification label on the feed
to be certain that you are using the correct pressure --
only those feeds that have a maximum rating of less than
10 psi are labeled with the maximum pressure rating.
Example: For feeds connected to WR229 waveguide,
use only 4 psi (28 kPa) pressure; the maximum
pressure rating in 5 psi (35 kPa).
A. Replacement of Improved Hub Design Feed
General Note: Some feeds have a feed horn,
illuminator ring, and waveguide bends that cannot be
passed through the 8-inch (203 mm) diameter opening
in the seating ring. When this is the case, the feed
must be removed from the front side of the antenna. The
following feeds cannot be removed from the rear side of
the antenna:
When replacing a feed, you should also consider
replacing the new parts included in the kit; seating ring,
vertex plate, spacer plate, and guy wires. If these parts
are to be replaced, they must be installed from the
front side of the antenna as given in Steps 1, 2,
and 3 for new installations.
To remnove the feed from the rear of the antenna for
either replacement or inspection of the feed horn and
window, proceed as follows.