The rectangular sections are attached as shown in the
illustration to prevent the circular waveguide from
operating in the wrong mode. Distance “O” is
so that a high impedance will be presented to any
unwanted modes. This is the most common design
used for rotating joints, but other types may be used
in specific applications.
WAVEGUIDE MAINTENANCE
The installation of a waveguide system presents
problems that are not normally encountered when
dealing with other types of transmission lines. These
problems often fall within the technician’s area of
responsibility.
A brief discussion of waveguide
handling, installation, and maintenance will help
prepare you for this maintenance responsibility,
Detailed information concerning waveguide mainte-
nance in a particular system may be found in the
technical manuals for the system.
Figure 3-53.—Choke joint.
Figure 3-54.—Rotating joint.
Since a waveguide naturally has a low loss ratio,
most losses in a waveguide system are caused by other
factors. Improperly connected joints or damaged inner
surfaces can decrease the efficiency of a system to
the point that it will not work at all. Therefore, you
must take great care when working with waveguides
to prevent physical damage. Since waveguides are
made from a soft, conductive material, such as copper
or aluminum, they are very easy to dent or deform.
Even the slightest damage to the inner surface of a
waveguide will cause standing waves and, often,
internal arcing. Internal arcing causes further damage
to the waveguide in an action that is often
self-sustaining until the waveguide is damaged beyond
use. Part of your job as a technician will be to inspect
the waveguide system for physical damage. The
previously mentioned dents are only one type of
physical damage that can decrease the efficiency of
the system.
Another problem occurs because
waveguides are made from a conductive material such
as copper while the structures of most ships are made
from steel. When two dissimilar metals, such as
copper and steel, are in direct contact, an electrical
action called ELECTROLYSIS takes place that causes
very rapid corrosion of the metals. Waveguides can
be completely destroyed by electrolytic corrosion in
a relatively short period of time if they are not isolated
from direct contact with other metals. Any inspection
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