By Joseph H. Reisert
Icing is one of the most serious problems for antenna installations.
Ice buildup not only increases antenna wind load and weight but
often detunes an antenna to the point where it's no longer usable.
When ice first forms on an antenna, it is usually
wet and conductive. This is the most destructive
condition for electrically detuning an antenna.
Afterwards, ice build-up increases and eventually
will freeze solid. Detuning may not be as severe
after the ice dries but now the wind load has greatly
increased and the antenna may be stressed to the
When ice melts, it may do so in an asymmetrical
fashion so one side of the antenna may be more
affected than the other. Antennas can also be damaged
by flying ice from other nearby antennas often
found on a tower installation. This can often cause
catastrophic failures since ice is heavy and large
ice sheets often break loose with wind or melting.
The best way to handle ice is to not let it form
on the antenna in the first place. Over the years
many attempts have been made to protect against
ice build up by the use of various antenna coatings.
Hydrophobic agents are recommended for coating
antennas but they are expensive and must be periodically
reapplied. Other coatings such as teflon (RTM)
or PVC type materials have been tried but while
they may delay icing, they seldom prevent ice buildup
Another method of protection against ice buildup
is to enclose the antenna in a radome. Fiberglass
tubes or radomes are often used on vertical omni
directional antennas and are quite effective. However,
vertical omni antennas are not as vulnerable to
detuning and hence are less affected by ice. However,
icing will still increase windload significantly.
Yagi antennas have a special problem when coated
with ice. When the director elements become fat
(due to the ice), they electrically lengthen and
start to perform like reflectors. In extreme cases
of ice buildup, the maximum gain may be higher
off the rear of the antenna!
Some manufacturers have resorted to placing a
radome completely around a Yagi antenna or at least
over some of the elements (e.g. the driven element
and first few directors). While this may prevent
ice buildup on that part of the antenna, it significantly
increases cost and windload and may not completely
prevent performance degradation from ice on unprotected
One way to decrease the affects of icing is to
use larger (fatter) diameter elements. Fatter elements
have a lower Q and the percentage change with ice
buildup is decreased. These are available in our
heavy duty Yagi series.
Another technique is to tune Yagi antennas slightly
higher in frequency thus increasing the cutoff
frequency. If this technique is properly employed,
the gain drop over the band of interest is insignificant,
typically only tenths of a dB. However, when ice
begins to form, the cutoff frequency slowly decreases
and the gain gracefully degrades instead of completely
reversing direction. We feel that this approach
is more cost effective and apply this technique
to all our Yagi antennas whether they are the regular
or heavy duty type.
Still another possibility to decrease the effects
of icing is to use a stack of antennas. This not
only increases performance but when icing occurs,
if it is not identical on both antennas, the performance
may not be degraded completely.
Suffice it is to say that Astron Wireless Technologies,
Inc. is working on many aspects of icing and has
recommendations for your individual installation.
Let us know your problem and how we can best help
Wireless Technologies, Inc. and the author retain the rights
to all intellectual
This information should be used as a guideline
only to help you in the appropriate selection of an antenna.
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