Compact Antenna Structure for Satellite Telecommunications
The present invention relates to an antenna structure for telecommunications, a
platform comprising the antenna structure and a method for communication by satellites
between two stations using the antenna structure.
5 In the field of broad band satellite communications (that is to say, not transmitting
not only voice), obtaining good quality communication involves specific performance .
aspects for the electromagnetic waves produced by the antenna structure used in the
communication in terms of gain and level of side lobes (ratio between the intensity of the
side lobes and the intensity of the main lobe).
10 For this, a known technique is to use, for example, a parabolic dish type antenna
structure comprising a source that produces electromagnetic waves and a parabolic dish
arranged in order to focus the electromagnetic waves produced by the source. The source
is positioned at a focal point of the parabolic dish.
In order to obtain the best performance levels in respect of the criteria mentioned
15 above in terms of gain and level of side lobes, the parabolic dish must have a diameter of
at least 40 centimetres so as to avoid significant masking of the transmitting source.
However, in the previous case, in order to point the radiated beam in a particular
direction, two motors are needed. Also, the antenna structure may present a large
dimensional footprint that is inconvenient in certain applications involving in particular the
20 installation of the antenna structure on an aerial platform, for example, on a helicopter.
It is also a known technique to use an electronic scanning antenna structure using
phase shifting. Such an antenna structure involves using elementary sources that are
most often in the form of patches (in particular superposed) in order to obtain a relatively
wide bandwidth. Verification of the criterion in terms of gain for the antenna structure
25 imposes the requirement, in addition, of applying the networking of a certain number of
elementary sources.
However, this leads to an increase in the overall dimensional footprint of the
antenna structure. In addition, where the transmission of a circular polarisation is desired,
the use of an electronic scanning antenna structure may entail using an additional
30 polarizer, which may slightly degrade the gain of the radiating structure including the
antenna structure and the polariser. In addition, in order to point the beam in a particular
direction, at least one motor unit is essential.
On the basis of the overall dimensional footprint of the antenna structure, strong
constraints in terms of motor torque are needed at the level of the motorisation device to
35 be used.
2
There is therefore a need for an antenna structure for telecommunications, in
particular satellite telecommunications, that has a reduced dimensional footprint (that is,
having a diameter less than 10 times the wavelength relative to the operating frequency)
while also making it possible to obtain high quality broadband communication, particularly
5 in terms of gain and reduction of side lobes.
To this end, the invention provides an antenna structure for telecommunications, in
particular by satellite, comprising at least one elementary antenna having a helical shape
and dimensioned so as to transmit andlor receive at least one electromagnetic wave
having a frequency higher than 4 GHz, preferably between 4 GHz and 50 GHz, in
10 particular comprised within a spectral band selected from among the X band and the Ku
band.
According to particular embodiments, the antenna structure includes one or more of
the following characteristic features, taken into consideration or in accordance with all
technically possible combinations:
15 - the antenna structure includes a transmitting-receiving surface, with each
elementary antenna extending between a first near end that is adjacent to the
transmitting-receiving surface and a second distal end that is at a distance from the
transmitting-receiving surface;
- the antenna structure includes a housing the base surface of which is the
20 transmitting-receiving surface which delimits an electromagnetic wave feed cavity for
feeding electromagnetic waves to the elementary antennas, arranged to be in contact with
the transmitting-receiving surface;
- the elementary antennas are devoid of an insertion loop for inserting the
magnetic field and include moreover an insertion element for inserting the electric field;
25 - the insertion element is a metal rod and the elementary antennas include a
dielectric insulation device inserted between the rod and the housing;
- the antenna structure additionally also includes a radome capable of being
attached to the housing and comprising a positioning cavity that is able to receive the
dielectric device in an inserted position;
30 - the housing includes an first interior wall that is parallel to the transmittingreceiving
surface, the transmitting-receiving surface being comprised between the first
interior wall and the radome, with the dielectric device being supported against the first
interior wall when the radome is attached to the housing and the dielectric device is in its
inserted position;
35 - the dielectric device includes a receiving cavity for receiving the rod;
3
- the rod includes a first rectilinear cylindrical portion with a circular base, the
dielectric device includes a first end portion and a second cylindrical end portion with a
circular base, and the receiving cavity comprises an axial cavity capable of receiving the
first rectilinear portion, the first rectilinear portion having a fourth diameter, the second end
5 portion having a sixth diameter and the axial cavity having a second depth that is equal to
half of the sum of the fourth diameter and the sixth diameter;
- the dielectric device includes a cylindrical crown ring having a circular base
presenting a seventh diameter, the transmitting-receiving surface comprises a coaxial
access port capable of receiving the dielectric device, the coaxial access port is cylindrical
10 with a circular base and presents a first diameter that is greater than the seventh
diameter;
- the antenna structure has a generally circular form and includes at least two
assemblies of a plurality of elementary antennas, the elementary antennas of each
assembly being arranged along a circle having a given radius that is specific to this
15 particular assembly, with all the said circles being concentric;
-the antenna structure includes a transmitting-receiving surface having a generally
rectangular form;
- the antenna structure includes power supply sources and at least two assemblies
of a plurality of elementary antennas, the elementary antennas of each assembly being
20 arranged along a supply line specific to this particular assembly, with each line being
parallel to the other specific supply lines and being powered by a respective power supply
source. '
In addition, the invention also relates to a platform, in particular an aerial platform,
comprising at least one antenna structure as described previously.
25 The object of the present invention also relates to a method for
telecommunications, in particular by satellite, between two stations comprising a
transmission or reception step for transmitting or receiving electromagnetic waves having
a frequency higher than 4 GHz, preferably between 4 GHz and 50 GHz, in particular
comprised within a spectral band selected from among the X band and the Ku band, by an
30 antenna structure as described previously.
Other characteristic features and advantages of the invention will become apparent
upon reading the detailed description that follows, embodiments of the invention, provided
purely by way of example and with reference made to the drawings that include the
following:
35 - Figures 1 to 3, diagrams of an antenna structure according to a first embodiment
as viewed respectively from the top, in perspective, and from the side;
4
- Figure 4, a graph showing the evolution of the adaptation of the antenna
structure from the first embodiment as a function of the frequency (in the case of
a structure adapted by the satellite bands in the X band);
- Figure 5, a gain radiation pattern of the antenna structure from the first
5 embodiment;
- Figures 6 and 7, diagrams of an antenna structure according to a second
embodiment in perspective view and side view;
- Figure 8, a gain radiation pattern of the antenna structure from the second
embodiment;
10 - Figures 9 and 10, diagrams of an antenna structure according to a third
embodiment shown in perspective view from the top and in perspective view
from the bottom; and
- Figure 11, a graph showing the evolution of the gain as a function of the angle of
transmission considered for the antenna structure of the third embodiment;
15 - Figures 12 and 13, partial cross sectional views along a transverse plane of the
antenna structure shown in Figure 1, the antenna structure being provided with a
dielectric insulation device capable of maintaining the straightness of the
elementary antenna and ensuring optimal radiation performance levels.
An antenna structure 10 for telecommunications, in particular by satellite, is
20 represented in Figure 1.
The antenna structure 10 includes an elementary antenna 12, a transmittingreceiving
surface 14 and a radome 16.
The elementary antenna 12 has a helical shaped form. Thus, the elementary
antenna 12 includes a transmitting part constituted of a metal wire defining a spiral that
25 winds around an axis. In this case, this axis is the normal to the transmitting-receiving
surface 14. The projection of the spiral over the transmitting-receiving surface 14 is a
circle whose diameter is denoted as D. In a manner known as such, the diameter of the
projection of the spiral, the number of coils of the spiral, the spacing between these coils
make it possible to determine the frequency or frequencies that the elementary antenna
30 12 is capable of transmitting or receiving.
The elementary antenna 12 may be appropriately dimensioned so as to transmit
andlor receive an electromagnetic wave having a frequency higher than 4 GHz for
applications in the context of satellite communications. This signifies that such an
elementary antenna 12 presents an extension along the direction Z that is less than 20
35 millimetres (mm) and a diameter that is less than 30 mm. t
5
Advantageously,the elementary antenna 12 is appropriately dimensioned so as to
transmit and/or receive an electromagnetic wave having a frequency comprised between
4 GHz and 50 GHz. This signifies that such an elementary antenna 12 presents an
extension along the direction Z that is comprised between 1.5 mm and 20 mm and a
5 diameter that is comprised between 2 mm and 30 mm.
Preferably, the elementary antenna 12 is appropriately dimensioned so as to
transmit andlor receive an electromagnetic wave having a frequency comprised in a
spectral band selected from among the X band and the Ku band.
By definition, an electromagnetic wave in the field of satellite communications
10 belongs to theX band when the wave has a frequency comprised between 7.2 GHz and
8.4 GHz. Thus, an elementary antenna 12 is capable of transmitting and/or receiving an
electromagnetic wave belonging to the X band if the elementary antenna 12 presents an
extension along the direction Z comprised between 9 mm and 10 mm and a diameter
comprised between 14 mm and 15 mm.
15 By definition, an electromagnetic wave in the field of satellite communications is a
Ku-band when the wave has a frequency range 10.7 GHz to 14.25 GHz. Thus, a
elementary antenna 12 is capable of transmitting andlor receive an electromagnetic wave
belonging to Ku-band if the elementary antenna 12 presents an extension along the
direction Z comprised between 6 mm and 8 mm and a diameter comprised between 10
20 mm and 12 mm.
The elementary antenna 12 extends between a first end 18 supplied through a
coaxial access port present on the transmitting-receiving surface 14 and a second distal
end 20 that is at a distance from the transmitting-receiving surface 14. The first end 18 is
adjacent to the transmitting-receiving surface 14. The elementary antenna 12 thus
25 projects outward from the transmitting-receiving surface 14.
The transmitting-receiving surface 14 is circular in shape.
The transmitting-receiving surface 14 presents an area A that is less than or equal
to 100"AZ where "*" refers to the mathematical operation of multiplication, and A denotes
the average wavelength of the different wavelengths of the waves that the elementary
30 antennas 12 are dimensioned to transmit and/or receive.
For example, according to the example shown in Figure 1, the area A is less than
7600 mmz.
The antenna structure 10 includes, in addition, a cylindrical housing 22 the base
surface of which is the transmitting-receiving surface 22.
6
The housing 22 delimits an electromagnetic wave feed cavity for feeding
electromagnetic waves to the elementary antenna 12 arranged so as to have the coaxial
access ports present on the transmitting-receiving surface 14.
The housing 22 includes an injection inlet 24 for injecting an electromagnetic
5 wave, with the electrical field of the electromagnetic wave then propagating in the radial
cavity.
The elementary antenna 12 is equipped with an insertion element for inserting the
electric field. This means that elementary antenna 12 is devoid of an insertion loop for
inserting the magnetic field.
10 In one example, the electric field insertion element is a metal rod that is able to be
in contact or not with the housing 22. In the event of there being no contact, a dielectric
insulation device is inserted between the rod and the housing 22 which makes it possible
to maintain the straightness of the rod and incidentally that of the elementary antenna 12.
Ideally this dielectric device has dielectric characteristics less than 4 in order to ensure
15 optimal performance levels of the antenna structure.
The radome 16 has a cylindrical shaped form, whose base is the transmittingreceiving
surface 14.
The radome 16 presents a diameter of less than 50 millimetres (mm). The radome
16 has an extension along the direction Z, which is less than 14 mm and is positioned at a
20 distance greater than 1 mm from the elementary antennas 12.
The antenna structure 10 may be made of metallised plastic, in particular the
housing 22 and the elementary antenna 22 are made of such a material so as to limit the
overall weight thereof. Ideally however, the material should be a conductive metal.
In operation, the antenna structure 10 is fed by an electromagnetic wave. The
25 elementary antenna 12 captures the electric field originating from this electromagnetic
wave in order to transmit a wave in the desired frequency band.
Figure 4 shows that over the entire band of interest (in this case, it is the X band)
the adaptation is less than -20 dB. This attests to the good adaptation in terms of
impedance of the antenna for operation in the X band.
30 It appears in Figure 5 that the antenna structure 10 presents gain in the order of 13
dB.
The helical elementary source presents a broad band, that is, a band higher than
25% around the centre operating frequency, with circular polarization and very good
radiation efficiency (in particular the axial ratio for a similarly small antenna is better than
35 that in the state of the art and apodization of the transmitted wave is facilitated).
7
As a result, the antenna structure 10 presents better performance levels than a
small sized parabolic dish, greater compactness, and reduced weight (this effect being
accentuated in other embodiments discussed here below). This reduced weight provides
the ability to reduce the constraints in particular in case of the antenna structure 10 being
5 accompanied by a mechanical positioner. The antenna structure 10 is capable of
transmitting a circular polarized wave without the use of an additional polarizer.
Figures 6 and 7 illustrate a second embodiment of the antenna structure 10
according to the invention. The elements that are identical to the first embodiment shown
in Figure 1 have not been described again. Only the differences have been highlighted.
10 In the second embodiment, instead of a single elementary antenna 12, the
antenna structure 10 includes a plurality of elementary antennas 12.
Each elementary antenna 12 shown in Figures 6 and 7 is identical to the
elementary antenna 12 described in reference to Figure 1.
By way of a variant, some antennas are different.
15 The antenna structure 10 includes at least two assemblies of a plurality of
elementary antennas 12. According to the example shown in Figure 6, the antenna
structure 10 includes four assemblies 30, 32, 34, 36 of a plurality of elementary antennas
12.
The elementary antennas 12 in each assembly 30, 32, 34, 36 are arranged along
20 a circle having a given radius that is specific to this particular assembly 30, 32, 34, 36,
with all the said circles 30, 32, 34, 36 being concentric.
Thus, in the case of Figure 6, the first assembly 30 includes six elementary
antennas 12 arranged along a first circle having a first radius R1; the second assembly 32
includes fourteen elementary antennas 12 arranged along a second circle having a
25 second radius R2; the third assembly 34 includes twenty elementary antennas 12
arranged along the third circle having a third radius R3 and the fourth assembly 36
includes twenty-six elementary antennas 12 arranged along the fourth circle having a
fourth radius R4. The four radii R1, R2, R3 and R4 are such that the first radius R1 is
smaller than the second radius R2, the second radius R2 is smaller than the third radius
30 R3, and the third radius R3 is smaller than the fourth radius R4.
The elementary antennas 12 are equipped with insertion elements for inserting the
electric field. According to the example represented, the insertion elements for. inserting
the electric field are in the form of metal rods. This signifies that the elementary antennas
12 are devoid of an insertion loop for inserting the magnetic field.
35 The antenna structure 10 includes, in addition, a cylindrical housing 22 the base
surface of which is the transmitting-receiving surface 22.
8
The rods that feed the elementary antennas 12 may or may not be in contact with
the housing 22. In the event of there being no contact, a dielectric insulation device is
inserted between the rod and the housing 22 which makes it possible to maintain the
straightness of the rod and incidentally that of the elementary antenna 12.
5 The housing 22 delimits a wave feed cavity for feeding electromagnetic waves to
the elementary antennas 12, arranged to be in contact with the transmitting-receiving
surface 14.
The radome 16 has a cylindrical shaped form, whose base is the transmittingreceiving
surface 14.
10 The radome 16 has a diameter of less than 350 mm and a height of less than 30
mm.
The operation of the antenna structure 10 according the second embodiment is
similar to the operation of the antenna structure 10 according the first embodiment.
It appears from Figure 8 that the antenna structure 10 has a gain in the order of 28
15 dB.
In the case of the embodiment with a radial cavity for feeding (transmittingreceiving
surface 14 in circular format), the fabrication of the antenna structure 10 is
simplified since the feed cavity is not complex.
In addition, the antenna structure 10 presents a broad band, higher than 10%
20 around the centre operating frequency and very good radiation efficiency (better than
70%) with low losses.
The optimisation of the antenna structure 10 to improve the reduction of side lobes
is also easy to implement since they depend only on the position and orientation of the
elementary antennas 12.
25 The size of the antenna structure 10 is reduced, in particular in the direction Z. As
a result thereof there is a greater degree of compactness in the antenna structure 10.
The gain of the antenna structure 10 is easily controllable since the increase in the
number of elementary antennas 12 leads to an increase in the gain of the antenna
structure 10.
30 The antenna structure 10 presents a lower mass than the parabolic dish of a
parabolic antenna structure 10 whose source is remote, particularly if the material is
metalised plastic.
In addition, in the event the antenna structure 10 is made of metalized plastic, this
could lead to reductions in the cost of manufacturing of the antenna structure 10.
9
Figures 9 and 10 illustrate a third embodiment of the antenna structure 10. The
elements that are identical to the first embodiment shown in Figure 1 have not been
described again. Only the differences have been highlighted.
In the third embodiment, instead of a single elementary antenna 12, the antenna
5 structure 10 includes a plurality of elementary antennas 12.
Each elementary antenna 12 shown in Figure 9 is identical to the elementary
antenna 12 described with reference to Figure 1.
By way of a variant, certain antennas are different.
The antenna structure 10 includes at least two assemblies of a plurality of
10 elementary antennas 12. According to the example shown in Figure 9. the antenna
structure 10 includes twelve assemblies 50 of a plurality of elementary antennas 12.
In addition, each assembly 50 includes twelve elementary antennas 12 fed in
propagating mode in a linear guide.
The elementary antennas 12 in each assembly 50 are arranged along a supply
15 line specific to this particular assembly 50.
Each specific line is parallel to the other specific lines.
It appears from Figure 11 that an assembly 50 presents a gain in the order of 23
dB.
The antenna structure 10 includes a plurality of elementary sources 52. The
20 number of elementary sources 52 is the same as the number of assemblies 50 that the
antenna structure 10 includes. In this case, the antenna structure 10 includes twelve
elementary sources 52. Each elementary antenna 12 is fed by a respective feed source
52.
The radome 16 presents a parallelepipedic form whose base is the transmitting-
25 receiving surface 14.
In the case of the X band, the radome 16 has a length that is less than 300 mm
and a width less than 200 mm.
The operation of the antenna structure 10 according to the third embodiment is
similar to the operation of the antenna structure 10 according the first embodiment.
30 In the case of the embodiment with a guide in propagative mode for the feed
(transmitting-receiving surface 14 in planar format), the losses are reduced, in particular in
the context of scanning antenna.
In addition, the elementary antenna 12 being compact, the possibilities of precise
pointing of an axis are increased.
35 The fabrication of the antenna structure 10 is also simplified.
10
Thus, in all embodiments, due to the fact of the elementary antenna 12 being
broad band, with circular polarisation and presenting good radiation efficiency, the
antenna structure 10 presents a reduced dimensional footprint in comparison to antenna
structures of the state of the art for identical performance levels in terms of radiation. The
5 antenna structure 10 is capable of transmitting a circular polarised transmission without
the use of an additional polariser. This greater compactness is accompanied by a gain in
lightness and a gain in radiation performance (broad band) as compared to a parabolic
dish of small size (diameter less than 40 cm for operation in X band). In addition, the
antenna structure 10 is easy to implement and can be manufactured at low cost.
10 Thus, the proposed antenna structure 10 may possibly be used as a substitute for
a parabolic antenna of smaller dimensions andlor for a scanning antenna for applications
related to telecommunications between two stations, in particular by satellite. It is worth
noting that in this case, the radiation pattern of the antenna structure 10 thus created is in
conformity with the templates specified for being used with certain satellites.
15 Such an antenna structure 10 is advantageously usable in a platform, in particular
an aerial type platform such as a helicopter. In the context of this use, the compactness of
the antenna structure 10 provides the ability to reduce the constraints on the installation
and location of equipment units in the platform.
Figure 12 illustrates a fourth embodiment of the antenna structure 10 according to
20 the invention. The elements that are identical to the first embodiment shown in Figure 1
have not been described again. Only the differences have been highlighted.
In the remainder of this description, the reference-coordinate system used is the
one defined in Figure 1, in which the direction Z is the normal to the transmitting-receiving
surface 14.
25 In the fourth embodiment, the elementary antenna 12 includes an insertion
element for inserting the electric field 100.
The housing 22 presents a first interior wall 102 and a second interior wall 104
which delimit the electromagnetic wave feed cavity along the direction 2.
At least one coaxial access port 106 is provided in the transmitting-receiving
30 surface 14.
The radome 16 includes a third interior wall 108 and 110 a positioning cavity. The
radome 16 is configured so as to be attached to the housing 22.
A dielectric insulation device 112 is inserted between the rod and the housing 22.
The dielectric device 112 is provided in order to maintain the straightness of the
35 elementary antenna 12. The dielectric insulation device 112 also provides the ability to
prevent contact between the elementary antenna 12 and the housing 22.
11
According to the example shown in Figure 12, insertion element for inserting the
electric field 100 is a rod. In addition, the rod 100 is made of metal.
In the case of Figure 12, the rod 100 is bentlangled in a manner such that the rod
100 comprises two rectilinear parts 114, I I 6 connected by an elbow 118.
5 The first interior wall 102 is parallel to the transmitting-receiving surface 14. In
Figure 12, the first interior wall 102 has a disk-shaped form. The first bottom wall 102 is
removed, by a first distance HI along the direction Z, from the transmitting-receiving
surface 14.
The second interior wall 104 is parallel to the transmitting-receiving surface 14.
10 The second interior wall 104 is borne by the same component piece as the transmittingreceiving
surface 14. In Figure 12, the second interior wall 104 has a disk-shaped form.
The coaxial access port 106 is delimited along the direction Z by the transmitting-receiving
surface 14 and the first interior surface 100. The coaxial access port 106 is cylindrical with
a circular base, having axis 2. The cylindrical access port 106 has a first diameter Dl.
15 The third interior wall 108 is positioned to face the transmitting-receiving surface
14. Along the direction Z, the third interior wall 108 is removed by a second distance H2
from the second interior wall 104.
The positioning cavity 110 is configured so as to receive the dielectric device 112
in an inserted position. In Figure 12, the positioning cavity 110 is cylindrical with a circular
20 base. The positioning cavity 110 has a second diameter D2. The positioning cavity 110
has a first depth PI.
The dielectric device 112 comprises a first end 120, a second end 122, a lateral
surface 124 and a receiving cavity 126 for receiving the elementary antenna 12.
The first rectilinear portion 114 extends along the direction Z while the second
25 rectilinear portion 116 extends along the direction Y.
The first rectilinear portion 114 presents a first length L1 along the direction Z. The
first rectilinear portion 114 is cylindrical, having axis Z. The first rectilinear portion 114 is
cylindrical with a circular base. The first rectilinear portion 114 has a third diameter 03.
The second rectilinear portion 116 presents a second length L2 along the direction
30 X. The second rectilinear portion 116 is cylindrical, having axis X. The second rectilinear
portion 116 has a fourth diameter D4. In Figure 13, the fourth diameter D4 is equal to the
third diameter D3.
The first length L1 is greater than the second length of L2. According to the
example in Figure 12, the first length L1 is greater than twice the second length L2.
35 The first end 120 is suitable to be inserted in the positioning cavity 110. The first
end 120 is planar. The first end 120 is perpendicular to the direction Z. The first end 120 is
12
cylindrical with a circular base, and has a fifth diameter D5. The fifth diameter D5 is
smaller than or equal to the second diameter D2.
The second end 122 is parallel to the first end 120. The second end 122 is planar.
The second end 122 is cylindrical with a circular base, and has a sixth diameter D6. The
5 sixth diameter D6 is greater than or equal to the fifth diameter 05. The sixth diameter D6
is smaller than or equal to the first diameter Dl.
The lateral surface 124 exhibits a symmetry of revolution around the Z axis. The
lateral surface 124 has a first end portion 128, a second end portion 130, and a middle
portion 132.
10 The receiving cavity 126 is configured so as to receive the rod 100. The receiving
cavity 126 is capable of maintaining the rod 100 in position in relation to the dielectric
device 112. The receiving cavity 126 is formed by the union of an axial cavity 134 and a
lateral cavity 136.
The first end portion 128 is located between the middle portion 132 of the lateral
15 surface 124 and the first end 120. The first end portion 128 includes a first shoulder 137, a
first portion 138 delimited along the direction Z by the shoulder 137 and the first end 120,
and a second portion 139 delimited along the direction Z by the shoulder 137 and the
middle portion 132.
The first shoulder 137 is located at a third distance H3 from the first end 120. The
20 third distance H3 is less than or equal to the depth PI. The first shoulder 137 is located at
a fourth distance H4 from the second end 122. In Figure 12, the fourth distance H4 is
equal to the second distance H2.
The first portion 138 is complementary to the positioning cavity 110. In Figure 12,
the first portion 138 is cylindrical having axis Z. The first portion 138 is cylindrical with a
25 circular base. The diameter of the first portion 138 is equal to the fifth diameter D5.
Preferably, the first portion 138 is capable of being tightly mounted into the positioning
cavity 110. For example, the fifth diameter D5 is equal to the second diameter D2.
The second portion 139 is cylindrical having axis Z. The second portion 139 is
cylindrical with a circular base. The diameter of the second portion 139 is equal to the
30 sixth diameter D6. The second end portion 130 is located between the middle portion 132
of the lateral surface 124 and the second end 122. The second end portion 120 is
cylindrical having axis Z. The second end portion 130 is cylindrical with a circular base.
The diameter of the second end portion 130 is equal to the sixth diameter D6.
The middle portion 132 is located between the first end portion 128 and the second
35 end portion 130. The middle portion 132 is delimited along the direction Z by a second
13
shoulder 140 and a third shoulder 142. In addition, the middle portion 132 includes a
crown ring 144.
The second shoulder 140 is comprised, along the direction Z, between the crown
ring 144 and the first end 120. The third shoulder 142 is comprised, along the direction Z,
5 between the crown ring 144 and the second end 122. Along the direction Z, the third
shoulder 142 is located at a fourth distance H4 from the second end 122. In Figure 12, the
fourth distance H4 is equal to the first distance HI.
The axial cavity 134 extends between the second end 122 and the first shoulder
142. The axial cavity 134 is able to receive the first rectilinear portion 114 by means of a
10 translational motion along the direction Y. For example, the axial cavity 134 is
parallelepiped shaped. In Figure 12, the three pairs of sides of the axial cavity 134 are
respectively perpendicular to the directions X, Y and Z. Along the direction X, the axial
cavity 134 presents a first width I1 that is greater or equal to the third diameter D3. In
Figure 12, the first width I1 is equal to the third diameter D3.
15 The axial cavity 134 is configured in a manner such that when the first rectilinear
portion 114 is inserted into the axial cavity 134, the axis of revolution of the first rectilinear
portion 114 is combined with the axis of revolution of the lateral surface 124. Along the
direction Y the axial cavity 134 presents a second depth P2 that is equal to half of the sum
of the sixth diameter D6 and the third diameter D3. In other words, this relationship is
20 represented mathematically as P2=(D6+D3)12.
The lateral cavity 136 is situated between the second shoulder 142 and the third
shoulder 144. The lateral cavity 136 is able to receive the second rectilinear portion 116
by means of a translational motion along the direction Y. For example, the lateral cavity
136 is parallelepiped shaped. In Figure 12, the three pairs of sides of the axial cavity 134
25 are respectively perpendicular to the directions X, Y and Z. Along the direction Z, the
lateral cavity 136 presents a second width 12 that is greater or equal to the fourth diameter
D4. In Figure 12, the second width 12 is equal to the fourth diameter D4.
The crown ring 144 is cylindrical with a circular base, having axis 2. The crown ring
144 has a seventh diameter 07. The seventh diameter D7 is greater than or equal to the
30 sixth diameter D6. In Figure 12, the seventh diameter D7 is smaller than the first diameter
Dl.
Along the direction Y, the lateral cavity 136 presents a third depth P3 that is equal
to half of the sum of the seventh diameter D7 and the third diameter D4. In other words,
this relationship is represented mathematically as P3=(D7+D4)12.
35 The crown ring 144 is delimited along the direction Z by the second shoulder 142
and the third shoulder 144.
14
Along the direction 2, the crown ring 144 has a third width L3. The third width L3 is
greater than the fourth diameter D4.
The operation of the antenna structure 10 according to the fourth embodiment is
similar to the operation of the antenna structure 10 according to the first embodiment.
5 Once inserted into the positioning cavity 110, the straightness of the dielectric
device 112 is secured by means of the construction of the radome 16 and the positioning
cavity 110. Therefore no specific tool is used to secure the straightness of the dielectric
device 112. When the dielectric device 112 is in its inserted position, the dielectric device
is fixed in relation to the radome 16, without there being any force exerted by the operator.
10 This means that, when the dielectric device 112 is in its inserted position, the positioning
cavity 110 exerts on the dielectric device a clamping force that is greater than the sum of
the weights of the dielectric device 112 and the elementary antenna 12.
In addition, it is possible to pre-assemble a plurality of elementary antennas 12
and dielectric devices 112 on to the radome 16 before attaching the radome 16 to the
15 housing 22. Each of the elementary antennas 12 can be removed or replaced easily. The
mounting of the antenna structure 10 is thus simplified. During installation of the antenna
structure 10, the elementary antenna 12 is inserted into the dielectric device 112.
Dielectric device 11 2 is subsequently inserted into the positioning cavity 110, and then the
radome 16 is attached to the housing 22. The dielectric device 112 then extends through
20 the coaxial access port 106 without being in contact with the transmitting-receiving
surface 14.
15

CLAIMS
I.A-n antenna structure (10) for telecommunications, in particular by satellite,
characterised in that the antenna structure (10) comprises at least one elementary
5 antenna (12) having a helical shape and dimensioned so as to transmit andlor receive at
least one electromagnetic wave having a frequency higher than 4 GHz, preferably
between 4 GHz and 50 GHz, in particular comprised within a spectral band selected from
among the X band and the Ku band.
2.-An antenna structure according to claim 1 including a transmitting-receiving
surface (14), with each elementary antenna (12) extending between a first near end (18)
that is adjacent to the transmitting-receiving surface (14) and a second distal end (20) that
is at a distance from the transmitting-receiving surface (14).
3.- An antenna structure according to claim 2, in which the antenna structure (lo),
in addition, includes a housing (22) the base surface of which is the transmitting-receiving
surface (14) which delimits an electromagnetic wave feed cavity for feeding
electromagnetic waves to the elementary antennas (12), arranged to be in contact with
the transmitting-receiving surface (14).
4.-An antenna structure according to claim 3, in which the elementary antennas
(12) are devoid of an insertion loop for inserting the magnetic field and include moreover
an insertion element for inserting the electric field (100).
25 5.- An antenna structure according to claim 4, in which the insertion element (100)
is a metal rod and the elementary antennas (12) include, in addition, a dielectric insulation
device (112) inserted between the rod (100) and the housing (22).
6.- An antenna structure according to claim 5, including, in addition, a radome (16)
30 capable of being attached to the housing (22) and comprising a positioning cavity (110)
that is able to receive the dielectric device (1 12) in an inserted position.
7.- An antenna structure according to claim 5 or 6, in which the housing (22)
includes an first interior wall (102) that is parallel to the transmitting-receiving surface (14),
35 the transmitting-receiving surface (14) being comprised between the first interior wall
(102) and the radome (16), with the dielectric device (112) being supported against the
16
first interior wall (102) when the radome (16) is attached to the housing (22) and the
dielectric device (1 12) is in the inserted position
8.- An antenna structure according to any one of claims 5 to 7, in which the
5 dielectric device (1 12) includes a receiving cavity (126) for receiving the rod (100).
9.- An antenna structure according to claim 8, in which the rod (100) includes a
first rectilinear cylindrical portion (114) with a circular base, the dielectric device (1 12)
includes a first end portion (128) and.second cylindrical end portion (130) with a circular
10 base, and the receiving cavity (126) comprises an axial cavity (134) capable of receiving
first rectilinear portion (1 14),
the first rectilinear portion (114), having a fourth diameter (D4), the second end
portion (130) having a sixth diameter (D6) and the axial cavity (134) having a second
depth (P2) that is equal to half of the sum of the fourth diameter (D4) and the sixth
15 diameter (D6).
10.-An antenna structure according to any one of claims 5 to 9, in which the
dielectric device (112) includes a cylindrical crown ring (144) having a circular base
presenting a seventh diameter (D7), the transmitting-receiving surface (14) comprises a
20 coaxial access port (106) capable of receiving the dielectric device (1 12), with the coaxial
access port (106) being cylindrical with a circular base and presenting a first diameter
(Dl), the first diameter (Dl) being greater than the seventh diameter (D7).
11.- An antenna structure according to any one of claims 2 to 10, in which the
25 transmitting-receiving surface (14) has a generally circular form and the antenna structure
(10) includes at least two assemblies of a plurality of elementary antennas (12), the
elementary antennas (12) of each assembly (30, 32, 34, 36) being arranged along a circle
having a given radius (RI, R2, R3, R4) that is specific to this particular assembly (30 32,
34, 36), with all the said circles being concentric.
30
12.-An antenna structure according to any one of claims 2 to 10, in which the
transmitting-receiving surface (14) has a generally rectangular form.
13.- An antenna structure according to claim 12, including power supply sources
35 (52) and at least two assemblies (50) of a plurality of elementary antennas (12), the
elementary antennas (12) of each assembly (50) being arranged along a supply line
17
specific to this particular assembly (50), with each line being parallel to the other specific
supply lines and being powered by a respective power supply source (52).
14.-A platform, in particular an aerial platform, comprising at least one antenna
5 structure (10) according to any one of claims 1 to 13.
15.- A method for telecommunications, in particular by satellite, between two
stations comprising a transmission or reception step for transmitting or receiving
electromagnetic waves having a frequency higher than 4 GHz, preferably between 4 GHz
10 and 50 GHz, in particular comprised within a spectral band selected from among the X
band and the Ku band, by an antenna structure (10) according to any one of claims 1 to
13.