TRANSMITTING ANTENNA

ANTENNE EMETTRICE

English Abstract

The invention relates to a transmitting antenna for navigation systems.
Antennae of this type are normally protected against mechanical and chemical
atmospheric influences by a radome. Antenna signals received by the monitor
probe are, however, corrupted by weather-related accumulations on the radome
such as rain, ice or snow. In order to prevent this influence to the greatest
possible extent, a combination consisting of a reflector and of an absorption
layer is applied to the inside of the radome in the area on which rain, ice or
snow is expected to accumulate.

French Abstract

La présente invention concerne une antenne émettrice pour systèmes de navigation. Ces antennes sont en règle générale protégées par un radôme contre les influences mécaniques et chimiques des intempéries. Mais lorsque l'antenne est soumise à la pluie, à la glace ou à la neige, le signal d'antenne reçu par des sondes de surveillance est faussé. Pour éliminer le plus largement possible cette influence, la face interne du radôme est couverte, dans la région exposée aux intempéries, par une combinaison d'un réflecteur et d'une couche absorbante.

Claims

Claims
1. Transmitting antenna for navigational systems whereby the monitoring
probe(s) receive(s) the transmitted signal and relay(s) it to an internal
evaluation
unit in which the signal received by the monitoring probe(s) is compared with
the
signal relayed by the transmitting antenna from the antenna feed arrangement,
and whereby the transmitting antenna is surrounded by a protective housing, a
so-called radome,
characterized in that reflectors and an absorption layer are attached to the
inside
of the radome, in those areas of the radome which can be covered by snow, ice
or rain, depending on weather conditions.
2. Transmitting antenna according to Claim 1,characterized in that the
reflectors consist of metal bars.
3. Transmitting antenna according to Claim 1, characterized in that the
reflectors are attached in the form of a conductive layer on the inside
surface of
the radome.
4. Transmitting antenna according to Claim 1,characterized in that the
conductive layer consists of a metal foil.
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Description

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CA 02390717 2002-05-08
Transmitting antenna
The invention relates to a transmitting antenna for navigation systems.
When such antennas are employed in air traffic navigation systems, in
particular for an instrument landing, a high degree of accuracy is obviously
required. This includes the requirement that the signals must be
transmitted with the necessary accuracy and without disturbance.
In prior art, a conventional measure for monitoring the transmitted signals
is to use monitor probes. With such monitor probes, which are provided
either for the overall antenna or for the individual antenna transmitter
groups, as the case may warrant, the signal transmitted by the
transmitting antenna is received and relayed to an evaluation unit. A
conventional method is also used to relay to this evaluation unit a signal
derived from the antenna feed signal. A comparison between these two
signals allows conclusions about possible deviations, so that appropriate
corrections can be made.
In most cases, the above named antennas are set up and operated ~'1
outdoors. To protect them against atmospheric damage, the antennas are
accommodated in protective housings which are also called radomes.
In practice, it has often been found that weather-related accumulations on
the outside of the radome, such as snow and ice as well as rain, can
cause undesirable reflections. These reflections cause the monitor probes
to produce wrong or disturbed signals, resulting in a false evaluation.
Since radomes are always three-dimensional structures, the accumulations
mentioned above can never be completely eliminated by means of design
features.
It is therefore the abject of the present invention to create a transmitting
antenna for navigation systems in which the monitoring probes)
receives) the transmitted signal and relays) it to an internal evaluation
unit in which the signal received from the monitoring probes) is/are
compared with the signal received from the antenna feed device, and the
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CA 02390717 2002-05-08
transmitting antenna is surrounded by a protective housing, a so-called
radome, which allows the transmission of undisturbed signals, i.e. in
which sensitivity to weather-related accumulations is greatly reduced.
According to the invention, this object is achieved by means of reflectors
arranged on the inside of the radome and an absorption layer in those
areas of the radome which are subject to weather-related accumulations
of snow, ice, or rain.
This combination of two measures has proven to be effective and easy to
accomplish.
Further details and advantages of the invention and its embodiments are
explained below by means of the single drawing.
The drawing shows a cross-sectional view of a transmitter group of a
navigation antenna system for instrument landing, in particular a so-called
glide-path antenna. Such antennas are operated in a frequency range of
328 to 335 MHz. Each of the above mentioned transmitter groups
consists of a double row of dipoles 1 and 2, which are arranged in front
of a conductive back 6. Also fastened to back 6 is a monitor probe, of
which parts 3 and 4 are shown in the drawing. This particular case
represents a loop probe. The signal transmitted by dipoles 1 and 2 is also
picked up by the monitor probe and relayed to the evaluation unit (not
shown here) in a manner not shown here. The antenna feed arrangement
is not shown either, since it does not contribute to the understanding of
the invention; at any rate, these are functional elements of an antenna
which are known in prior art. A radome 5 is provided to protect the
transmitting antenna. In this particular case, it consists of a tub-like
housing of an almost rectangular cross section, as the drawing shows.
Here, the transmitting antenna is shown in the position in which it is
operated. Therefore, an accumulation 9 of snow can form on he top side
of the radome in winter. When the transmitting antenna is operated,
certain parts of the transmission signal are reflected due to the physical
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~ CA 02390717 2002-05-08
properties of the snow cover. These reflected signal are received in the
same manner as the transmission signals coming from the dipoles and
impinging directly upon the monitor probe. This results in a signal
overlapped by the reflection signals which is relayed to the evaluation
unit. However, this signal does not correspond to the transmission signal
received by the aircraft.
According to the invention, a remedy is offered by attaching an additional
reflector 7 and an absorption layer 8 to the inside of radome 5, namely
where a snow accumulation 9 may normally be formed.
The reflector can be designed in a variety of ways. The drawing, for
example, shows reflector bars. Other solutions could include the use of a
conductive foil. To ensure that radiation reflected by rain or ice in the
front of radome 5, which in this case acts as a kind of corner reflector,
affects the monitor signal, reflector 7 is attached together with an
absorption layer 8 on the inside of radome 5. When such a combination is
applied, the transmitting antenna becomes largely insensitive to
atmospheric effects (rain, ice, snow).
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Representative Drawing