Omnidirectional antenna and associated naval platform

Abstract

Omnidirectional Antenna and Associated Naval Platform The present invention relates to an omnidirectional antenna (10) comprising: - a base structure (12) extending along a first axis (Z) and defining in each cross-section an N-sided polygon, the base structure (12) further defining N faces (16) arranged around the first axis (Z); - a unit antenna array (14) comprising N unit antennas (20), each unit antenna (20) being arranged on one of the N faces of the base structure (12); the unit antennas (14) defining the same radiation pattern. Figure for the abstract: Figure 1

Description

Title of the invention: Omnidirectional antenna and associated naval platform

[0001] The present invention relates to an omnidirectional antenna.

[0002] The present invention also relates to a naval platform comprising such an antenna.

[0003] The general problem of the invention is the design and integration of a communication system on board a naval platform for several actors (naval or aeronautical) in order to offer unicast, multicast and / or broadcast type services.

[0004] To perform these tasks, the antenna implementing such a communication system must meet several requirements.

[0005] According to a first requirement, the antenna must have radio coverage over the horizon (zero elevation angle) either over 360° also called broadcast-type link or multi-sector by selection of the desired spatial sector(s)

[0006] According to a second requirement, the antenna must provide a high-speed radio frequency link (typically > 2 GHz) (or conversely, consist of a high-gain antenna G > 8 dBi).

[0007] According to a third requirement, the antenna must provide left or right circular polarization.

[0008] According to a fourth requirement, the antenna must minimize the impacts on the mechanical stresses (mass, accelerations, shocks and vibrations) applied to the platform mast.

[0009] Finally, according to a fifth requirement, the antenna must ensure the ability to interface with an existing antenna for the mature integrated V / UHF communications system.

[0010] Other requirements may also be applied.

[0011] In the prior art, several solutions exist for ensuring omnidirectional coverage. These solutions can be grouped into several families.

[0012] A first family includes solutions implemented using a single antenna whose geometry of revolution ensures omnidirectionality. Wire antennas (half-wave for dipoles, quarter-wave for monopoles) or biconical antennas with low gain (2 to 5 dBi) are thus employed. Such an antenna exhibits little waviness in its radiation pattern in the azimuthal plane (ΔG < 3 dB). Polarization is exclusively vertical or horizontal.

[0013] A second family includes solutions featuring an antenna array in which each element is taken from the first family. The array geometry is circular, and a reflector (cylindrical or otherwise) is placed at its center. The antenna array provides omnidirectional radiation and moderate azimuth ripple (ΔG < 3 to 8 dB) if and only if the central element has small transverse dimensions (i.e., a diameter less than or equal to a fraction of the wavelength). In fact, these systems are primarily used at low frequencies (or long wavelengths). Polarization is either vertical or horizontal.

[0014] A third family includes solutions featuring a circular array antenna where each element is a directional antenna, without a central body or reflector. The antenna array thus offers high gain (> 6 dBi) and strong ripples in its radiation pattern (ΔG > 10 dB). These systems are often used to form radio direction finders. All polarizations are possible.

[0015] Some solutions based on the third family are used at high frequencies to obtain high-speed communications.

[0016] A solution of this type makes it possible to cover a sector in azimuth of predetermined value (for example 20°) in vertical polarization. According to this solution, the sector selection is carried out by switching.

[0017] Another solution networks small, low-gain directional antennas. Unlike the previous solution, this alternative solution allows for electronic control of beam orientation and addresses, depending on the modem type, for either point-to-point links (continuous tracking of the beam direction) or point-to-multipoint links (beam direction changing at each time interval). This solution relies on electronic components that do not cover all frequency bands.

[0018] While suitable for long-range, high-speed unicast links, these solutions cannot meet all the requirements stated above. In particular, these solutions cannot provide multicast and broadcast services because they cannot simultaneously cover multiple spatial sectors.

[0019] The present invention aims to solve these problems and therefore to provide an omnidirectional antenna meeting all of the aforementioned requirements.

[0020] To this end, the invention relates to an omnidirectional antenna comprising:

[0021] - a basic structure extending along a first axis and defining in each cross-section of an N-sided polygon, the basic structure further defining N faces arranged around the first axis;

[0022] - a unit antenna array comprising N unit antennas, each antenna unit being arranged on one of the N faces of the basic structure;

[0023] unit antennas defining the same radiation pattern.

[0024] According to other advantageous aspects of the invention, the antenna comprises one or more of the following features, taken individually or in all technically possible combinations:

[0025] - each polygon has a regular polygon;

[0026] - each polygon has axial symmetry with respect to the first axis;

[0027] - N is equal to 8;

[0028] - the basic structure has the shape of a truncated pyramid extending along the first axis;

[0029] - each unit antenna has a circular shape;

[0030] - each unit antenna has a metasurface;

[0031] - each unit antenna is configured to operate in C band;

[0032] - said radiation pattern as a function of an azimuth angle for an angle of elevation approximately equal to zero presents a hollow surrounded by two bumps;

[0033] - said radiation pattern has an elliptical shape as a function of a azimuth angle and an elevation angle; and

[0034] - the elliptical shape defines a maximum gain zone extending around the center of the ellipsis.

[0035] The invention also relates to a naval platform comprising the antenna as defined above.

[0036] The invention will become clearer upon reading the following description, given solely by way of non-limiting example and made with reference to the drawings in which: - [Fig.1] [Fig.1] is a perspective view of an antenna according to the invention; - [Fig.2] [Fig.2] is a top view of the antenna of [Fig.1]; - [Fig.3] [Fig.3] is a side view of the antenna of [Fig.1]; - [Fig.4] [Fig.5] Figures 4 and 5 present a radiation pattern of a unit antenna forming part of the antenna of [Fig.1]; - [Fig.6] [Fig.6] is a radiation pattern of the antenna of [Fig.1].

[0037] An omnidirectional antenna 10 according to the invention has indeed been illustrated in [Fig.1].

[0038] Such an antenna 10 is for example carried on a naval platform, such as a ship, in particular a military ship.

[0039] The antenna 10 is, for example, mounted on a mast forming part of this naval platform. The mast extends, for example, along a first axis Z visible in [Fig. 1]. The first axis Z is oriented towards the sky.

[0040] This Z axis also defines an azimuthal plane perpendicular to this Z axis and an elevation plane perpendicular to the azimuthal plane.

[0041] The antenna 10 is thus, for example, exposed at the horizon at 360°.

[0042] Antenna 10 is, for example, connected to a communication system of the naval platform. In particular, antenna 10 is configured to receive radio frequency signals intended for this communication system and to transmit radio frequency signals generated by this communication system. Such a communication system is, for example, well-known and will not be explained in detail hereafter.

[0043] With reference to figures 1 to 3, the antenna 10 comprises a basic structure 12 and a unit antenna array 14.

[0044] In particular, the basic structure 12 has, for example, a substantially circular structure extending around the first axis Z.

[0045] More specifically, in each cross-section taken with respect to this first Z-axis, the basic structure 12 forms an N-sided polygon. Advantageously, all the polygons are similar and differ from each other only in dimensions. In other words, all the polygons have the same shape.

[0046] Advantageously, each polygon has a regular polygon exhibiting axial symmetry with respect to the first Z axis.

[0047] In the example of the figures, it is an octagon. In other words, in the example of the figures, the number N of sides of each polygon is equal to 8.

[0048] Moreover, as can also be seen in the figures, the basic structure 12 has the shape of a truncated pyramid which extends along the first axis Z.

[0049] In particular, the basic structure 12 has a cross-section which narrows along the first axis Z. In other words, when the antenna 10 is mounted on the mast, its pyramidal shape is oriented towards the sky.

[0050] By way of example, the radius R of the basic structure 12 measured from the first axis varies between 400 and 500 mm.

[0051] Also by way of example, the height H of the basic structure 14, that is to say its dimension extending along the first axis Z, is advantageously between 300 and 400 mm and is for example substantially equal to 350 or 360 mm.

[0052] The polygons in the cross-sections of the basic structure 12 form a plurality of faces 16 of this structure. The number of faces is thus equal to the number N of sides of each polygon.

[0053] In the example of the figures, eight faces are illustrated.

[0054] Each face is for example substantially flat and is slightly inclined with respect to the first Z axis taking into account the pyramidal shape of the base structure 12. The angle of inclination with respect to the first Z axis is for example between 5° and 15°, and is advantageously equal to 10°.

[0055] Each face 16 thus presents a trapezoid, one of whose parallel sides forms the base of the pyramid and the other parallel side forms the truncated end of the pyramid of the base structure 12.

[0056] By way of example, the long side of each trapezoid has a length dl between 350 and 450 mm and advantageously equal to 390 mm. The length d2 of the opposite side is for example between 300 and 400 mm and for example substantially equal to 340 mm.

[0057] The basic structure 12 is made, for example, of a metallic or composite material. An example of such a material is a fiberglass composite material or an epoxy resin.

[0058] In its internal part, the basic structure 12 can receive any other component useful for the operation of the antenna 10 or any other mechanical component allowing the fixing of this antenna 10, for example on the mast.

[0059] The unit antenna array 14 consists of a plurality of unit antennas 20. The number of unit antennas 20 is thus equal to the number N of faces 16 formed by the basic structure 12.

[0060] Thus, each unit antenna 20 is arranged on one of the faces 16 of the basic structure 12.

[0061] Each unit antenna 20 has, for example, a circular shape with a radius r approximately between 100 and 200 mm. This radius r is, for example, equal to 160 mm.

[0062] Each unit antenna 20 is for example arranged in the center of the corresponding face 16.

[0063] Each unit antenna 20 has, for example, a metasurface.

[0064] The unit antennas 20 are, for example, all identical to each other and, in particular, exhibit the same radiation pattern. This radiation pattern is of the "gate" type known to those skilled in the art.

[0065] In addition, each unit antenna 20 is configured to operate in C band, for example in a frequency band between 4.4 and 5 GHz.

[0066] According to the invention, the radiation pattern of each unit antenna 20 has an elliptical shape as a function of an azimuth angle and an elevation angle of this antenna.

[0067] An example of such a radiation pattern is shown in [Fig.4] where the Az axis denotes the azimuth angle and the El axis denotes the elevation angle.

[0068] Thus, according to this example, the maximum gain Gmax is defined in an area extending around the center of the ellipse.

[0069] The gain G thus decreases towards the periphery of the ellipse as well as towards its center.

[0070] It should be noted that the minimum gain is defined at the periphery of the ellipse.

[0071] Figure 5 illustrates such a radiation pattern for an elevation angle approximately equal to 0°.

[0072] Thus, according to this example, the radiation pattern has a central part O (a hollow part) which is surrounded by two peaks exhibiting the maximum gain Gmax. From these peaks, the gain G decreases until it reaches negative values.

[0073] Figure 6 illustrates a radiation pattern resulting from the unit antenna array 14.

[0074] Thus, this diagram is composed of a plurality of ellipses, each ellipse corresponding to one of the unit antennas 20.

[0075] The ellipses overlap along their lateral sides, thus forming a slight gain spike. This radiation pattern then demonstrates the omnidirectional nature of the antenna 10.

[0076] It is therefore understood that the present invention has a number of advantages.

[0077] It is clear first of all that the antenna according to the invention allows the emission and reception of radio frequency signals in multicast and broadcast, and this in an omnidirectional manner.

[0078] Furthermore, the antenna meets all the requirements mentioned above.

[0079] Furthermore, the circular geometry of the antenna and its small thickness allow a installation as a covering for an existing metal structure or integrated into a composite sandwich.

[0080] The metasurface-based technology forming the antennas allows for isolation of the individual antennas, high unit gain, and good pattern combination. This reduces ripples in the azimuthal plane.

[0081] Finally, the metasurface-based technology does not require a strong field-sensitive electronic component and gives it a quality of robustness.

Claims

Demands

1. Omnidirectional antenna (10) comprising: - a base structure (12) extending along a first axis (Z) and defining in each cross-section an N-sided polygon, the base structure (12) further defining N faces (16) arranged around the first axis (Z); - a unit antenna array (14) comprising N unit antennas (20), each unit antenna (20) being arranged on one of the N faces of the base structure (12); the unit antennas (14) defining the same radiation pattern.

2. Antenna (10) according to claim 1, wherein each polygon has a regular polygon.

3. Antenna (10) according to claim 1 or 2, wherein each polygon has axial symmetry with respect to the first axis (Z).

4. Antenna (10) according to any one of the preceding claims, wherein N is equal to 8.

5. Antenna (10) according to any one of the preceding claims, wherein the basic structure (12) has the form of a truncated pyramid extending along the first axis (Z).

6. Antenna (10) according to any one of the preceding claims, wherein each unit antenna (20) has a circular shape.

7. Antenna (10) according to any one of the preceding claims, wherein each unit antenna (20) has a metasurface.

8. Antenna (10) according to any one of the preceding claims, wherein each unit antenna (20) is configured to operate in C-band.

9. Antenna (10) according to any one of the preceding claims, wherein said radiation pattern as a function of an azimuth angle for an elevation angle substantially equal to zero has a dip surrounded by two bumps.

10. Antenna (10) according to any one of the preceding claims, wherein said radiation pattern has an elliptical shape as a function of an azimuth angle and an elevation angle.

11. Antenna (10) according to claim 10, wherein the elliptical shape defines a maximum gain zone extending around the center of the ellipse.

12. Naval platform comprising antenna (10) according to any one of the preceding claims.

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