The invention relates to a bi-ioop transmitting and/or receiving
antenna, intended to be installed on a vehicle that may be submerged and
operates at high frequency in order to transmit and/or to receive highfrequency
waves between said vehicle and a terrestrial base, for example.
The antenna is used for transmissions in the frequency bands 1.5 to 30 MHz,
for example, the transmission of data taking place via the ionosphere.
it relates to an antenna system allowing data of any format, audio,
images or video, to be transmitted between a submersible vehicle and a
terrestrial base, for example.
Submersible vehicles generally transmit and receive signals via
wire antennas towed or drawn by these submersible vehicles. These
antennas are positioned so as to float on the surface of the water while the
submersible vehicle is submerged at a greater depth.
When the submersible vehicle has to move from one location to
another, the cable of the antenna must be wound in and wound onto a
support, which may cause mechanical and electrical damage.
On the other hand, since the antenna floats on the surface, it is
easy to repair.
As an example of an antenna according to the prior art, the patent
application FR 2962854 discloses a wire antenna, for high-frequency
submarine transmissions, comprising a coaxial cable and a radiating
element, one end of which is connected to the coaxial cable, and which is
dimensioned so as to transmit high-frequency waves.
The patent application FR 3003388 discloses an antenna
comprising a coaxial cable and a radiating element, in which the antenna is
towed behind a submersible vehicle and rises to the surface of the water, to
the dioptre, in order to allow data exchanges and, in particular, HF
transmissions.
2
The known antennas of the prior art are prone in particular to
breakage of the connecting cable and mechanical problems during
deployment or when winding the cable of the antenna onto a support. From a
radiofrequency perspective, they offer low performance and may not be used
as high-power transmission antennas, the transmission power typically being
limited to a few watts.
The architecture of the antenna according to the invention is
original in the sense that it comprises a double loop that is symmetric with
respect to a support axis and which is isolated from the water in which it may
be submerged by means of a dielectric enclosure, each loop being supplied
with power in phase opposition so that the resultant of return currents to
ground (water) cancel each other out, thereby substantially decreasing ohmic
losses in the water.
The invention relates to a transmitting and/or receiving antenna
intended to be borne by a submersible vehicle characterized in that it
comprises at least one of the following elements:
« a support element made of a conductive material and adapted to
distance the loops from the ground of the submersible vehicle and to
electrically connect the assembly to this ground of the carrier;
• a first loop of a given shape comprising a first end connected to a first
point and a second end connected to a common point;
• a second loop comprising a first end connected to a second point and
a second end connected to the common point, having a shape similar
to the shape of the first loop;
• the two loops are symmetric with respect to an axis of symmetry A and
are supplied with power in phase opposition so that the return currents
to the common point balance each other out;
• the first and the second loop being protected by an enclosure.
According to one embodiment, each of the second ends of the
antenna is mechanically and electrically connected to the support
3
. corresponding to the axis of symmetry, the two other first ends of the antenna
are adapted to be connected to the outputs of two identical tuning boxes.
An antenna loop is, for example, circular in shape, or else
quadrilateral in shape.
5 The shape and the dimensions of an antenna loop are adapted for
the antenna to operate in a frequency range [1.5 MHz, 30 MHz],
The antenna may also comprise a ferromagnetic core positioned
in the centre of the two loops, which allows the size of the antenna to be
decreased while maintaining a high level of performance.
10 The invention also relates to an antenna system characterized in
that it comprises at least one antenna having one or more of the features
mentioned above, said antenna being positioned on a ground referencesupport
and being supplied with power by a device comprising:
• a first tuning box having an output connected to the first end of the first
15 loop;
• a second tuning box having an output connected to the first end of the
second loop;
• said reference-support is made of a conductive material and is
adapted to distance the loops from the ground of the submersible
20 vehicle and to electrically connect the assembly to this ground of the
carrier;
• a power divider receiving, as input, a signal S transmitted by a
transceiver and delivering a first signal Si supplying the first loop with
power and a second signal $2 in phase opposition with the first signal
25 supplying a second loop* with power.
The first tuning box, the second tuning box and the power dividermay
be integrated within one and the same assembly.
The antenna system is, for example, positioned on a submersible
vehicle.
30* Other features and advantages of fhe present invention will
become more clearly apparent upon reading the description of exemplary
4
embodiments given by way of wholly non-limiting illustration, alongside the
appended figures which show:
• Figure 1, an example of an antenna according to the invention;
• Figure 2, a functional representation of the antenna according to the
5 invention;
• Figure 3, an example of the use of an antenna system according to
the invention on a submersible vehicle;
• Figure 4A and Figure 4B, a variant embodiment for the tuning boxes
installed in the system;
10 • Figure 5, a variant of an antenna comprising a ferromagnetic core; and
• Figure 6A and Figure 6B, examples of the geometry of watertight
enclosures.
In order to gain a better understanding of the structure of the
antenna according to the invention, the description is provided for an antenna
15 positioned on a submersible vehicle that can be submerged in seawater, the
vehicle being located at a shallow depth. The antenna operates, for example,
in a frequency range [1.5 MHz, 30 MHz],
Figure 1 shows an example of an antenna according to the
invention intended to be positioned on a submersible vehicle (Figure 3, for
20 example). The antenna 1 comprises a first antenna element in the shape of a
loop 2 comprising a first end 21 connected to a first point corresponding to
the output 4s of a tuning box 4 and a second end 22 connected to a common
point M, the loop having a given shape, a second antenna element in the
shape of a loop 3 that is symmetric with the first ioop-shaped antenna
25 element'2 with respect-: to an axis of symmetry A, the second loop 3->'
comprising a first end > 31 connected to a second point corresponding, for
example, to the output 5s of a second tuning box 5 and a second end 32
connected to the common point M, having a shape similar to the shape of the
first loop, a power supply device, shown in detail in Figure 2, is designed to
30 supply the two loops with power in phase opposition so that the ground return
currents balance each other out. The second symmetric ends 22 and 32 are
5
mechanically and electrically connected to a support 10 made of a
conductive material corresponding to the axis of symmetry, thereby making it
possible to distance the loops from the ground of the carrier (submersible
vehicle) on which the antenna system is installed, and to fix and electrically
5 connect the assembly to this ground of the carrier. The other first ends 21
and 31 are connected to the outputs of the two identical tuning boxes 4 and 5
(Figure 2), respectively, having the same operating characteristics.
The design and operation of the tuning boxes 4 and 5 are known
to those skilled in the art and will not be described in detail in order to
10 facilitate understanding of the invention.
As shown in Figure 1, the ground return currents i1 and i2 flow
through the antenna elements or loops in opposite directions.
A loop may be a section piece made of a conductive material
folded in order to form a first rectangular loop 2, which shape is used by way
15 of example, and its symmetric counterpart, the second rectangular loop 3.
When used underwater (submarine equipment), the interior of the
enclosure is filled, for example with a dielectric material, preferably
polyurethane foam, for the purpose of providing resistance to hydrostatic
pressure. When used on the surface, the interior of the enclosure is left filled
20 with air.
The first end 21 of the first loop 2 is connected to the output 4s of
the first tuning box 4, itself connected to one of the outputs 7s of a power
divider 7 by means of a coaxial connecting cable 40. The input 7e of the
power divider will be connected to a transceiver 11 by means of a coaxial
25 cable 12 (Figure-2);. - ,. :-,.-.••
The first end 31 of the second loop 3 is connected to the output §s
of the second tuning box 5, itself connected to the other output 7s' of the
power divider 7 by means of a second coaxial connecting cable 50.
The assembly is surrounded by a dielectric enclosure 8,
30 composed/for example, of a radome made of reinforced plastic 81 and a
foam filling 82.
6
The dielectric enclosure 8 is fixed to a metai fastening base 9.
comprising holes 90 through which fastening screws are passed according to
means known to those skilled in the art.
The protected antenna could thus be fixed to a submersible
5 vehicle, as shown in Figure 3.
The shape, geometry and dimensions of an antenna element will
be chosen in particular according to the operating frequency range of the
antenna. These dimensions could also be chosen according to potential
space constraints. The shape and the size of the assembly formed by the
10 antenna and the watertight housing correspond, for example, to a
parallelepipedal solid of approximately 2mx2mx1m.
The antenna system thus formed may be installed in water on a
submersible vehicle, on a surface vessel or else on land vehicles. It may be
directly installed on the carrier without any offset, unlike the known structures
15 of the prior art.
The antenna operates, for example, in the frequency range from
1.5 to 30 MHz and preferably between 2 and 12 MHz. The chosen radiation
mode will be, for example, of near-vertical incidence ionospheric radio wave
type, better known by the abbreviation NVIS for near-vertical incidence
20 sky wave.
Figure 2 shows a functional diagram of the antenna according to
the invention.
The antenna 1 is connected to a transceiver 11 by means of a
coaxial cable 12. The radiofrequency signal S delivered by the coaxial cable
25 is divided!by