EP2610965B1 - Compact broad-band antenna with double linear polarisation - Google Patents

Description

The invention relates to a compact antenna.

• deux dipôles orthogonaux, chaque dipôle comprenant deux éléments rayonnants,
• un plan réflecteur, et
• une surface absorbante.

More particularly, the invention relates to an antenna for transmitting / receiving electromagnetic waves, of the type comprising:

• two orthogonal dipoles, each dipole comprising two radiating elements,
• a reflective plane, and
• an absorbent surface.

The invention is in the field of antennas and antenna systems dedicated to applications for receiving and emitting electromagnetic waves in a very wide frequency band. For example, the compact antenna operates in the VHF and UHF bands, that is to say at frequencies between 30 MHz and 3 GHz, and more particularly at frequencies between 30 MHz and 500 MHz.

The document US 3,967,276 A describes an antenna having radiating elements, a reflective plane and an absorbing surface. The document JP 6 018650 A describes an antenna having two radiating elements.

Antennas as above are described in FR 2,736,212 and are used for various purposes, for example in the field of telecommunications, and are particularly intended to be carried on a craft, whether terrestrial, airborne or naval.

Therefore, these antennas are subject to a number of specific technical constraints.

Thus, these antennas must for example have a visual discretion or a SER, for Surface Equivalent Radar, low, have high radio performance such as a ROS, Stationary Wave Ratio, low, a strong gain, etc., all presenting small dimensions.

In some cases, they must also be adapted to receive, transmit and / or discriminate electromagnetic waves irrespective of their polarization.

In addition, they must have unidirectional radio coverage.

Finally, they must not degrade the aerodynamics or the road gauge of a vehicle to which they are integrated and present independent radio performances vis-à-vis it.

Antennas satisfying some of these constraints are known from the state of the art, for example in communication applications.

So, US 7,692,603 B1 describes an antenna whose radiating elements are spiraled. Such an antenna has small dimensions adapted to minimize coupling and electromagnetic interference with neighboring objects.

In addition, there are omnidirectional antennas of linear polarization monopole or dipole type, mainly vertical linear polarization, to cover the band between 30 MHz and 500 MHz.

However, these solutions are not entirely satisfactory.

Indeed, most antennas of the state of the art only have some of the characteristics described above.

• □ de discrétion visuelle,
• □ et/ou de réduction de la SER,
• □ et/ou d'optimisation de l'aérodynamisme de l'engin auquel elles sont intégrées,
• □ et/ou de respect du gabarit routier dudit engin.

Thus, most antennas known to those skilled in the art have a size incompatible with the criteria:

• □ visual discretion,
• □ and / or reduction of SER,
• □ and / or optimization of the aerodynamics of the gear in which they are integrated,
• □ and / or respect the road gauge of said machine.

In addition, the radio performance of dipole type omnidirectional antennas is substantially degraded when they are integrated with gear having metal parts located near said antennas.

Furthermore, omni-directional monopole antennas require a sufficiently large ground plane relative to the wavelength to obtain optimal radioelectric performance, these being moreover dependent on the surface of the machine on which they are arranged. . These antennas thus have radioelectric performances impacted by the surface on which they are arranged. Moreover, they do not make it possible to deal with the multi-polarization aspect of electromagnetic waves. Finally, although these antennas have reduced dimensions compared to dipole antennas, they sometimes remain incompatible with criteria of visual discretion, SER, aerodynamics and / or road gauge.

Similarly, the spiral antennas have a limitation of the low frequency of use located around 200 MHz in view of the congestion targeted by the subject of the present application. In addition, these antennas are for the most part right or left circular polarization and do not allow to treat the multi-polarization aspect of electromagnetic waves from a single antenna. In addition, these antennas generally have gain and ROS values and unidirectional radiation insufficient at low frequencies.

This last type of antenna finally has radio performance particularly degraded at low frequencies, that is to say below about 200 MHz, in the case where they must be placed in a metal cavity intended to improve the visual discretion. , the SER and / or the aerodynamics of the craft in which they are integrated. The level of performance degradation varies depending on the diameter of this cavity.

The object of the invention is therefore to obtain an antenna which makes it possible to improve the satisfaction of these criteria.

For this purpose, the invention relates to an antenna according to claim 1.

According to other aspects of the invention, the compact broadband antenna comprises one or more of the features defined in claims 2 to 10.

In addition, the invention relates to a land-based, airborne or naval machine according to claim 11.

According to other aspects of the invention, the machine may comprise the feature defined in claim 12.

• la figure 1 représente une vue du dessus d'un premier mode de réalisation d'une antenne selon l'invention,
• la figure 2 représente une vue d'une partie d'une bobine de liaison de l'antenne de la figure 1,
• la figue 3 représente une vue du dessus de la surface absorbante dans une antenne selon l'invention,
• la figure 4 représente une vue de côté du premier mode de réalisation d'une antenne selon l'invention,
• la figure 5 est un diagramme de représentation du rapport d'onde stationnaire en fonction de la fréquence pour une antenne selon le premier mode de réalisation de l'invention,
• la figure 6 est un diagramme de représentation du gain d'une antenne selon le premier mode de réalisation de l'invention en fonction de la fréquence,
• la figure 7 représente des diagrammes de rayonnement selon le plan azimutal d'une antenne selon le premier mode de réalisation de l'invention pour des fréquences valant 30 MHz, 50 MHz, 100 MHz, 300 MHz et 500 MHz,
• la figure 8 représente une vue du dessus d'un second mode de réalisation d'une antenne selon l'invention,
• la figure 9 est un diagramme de représentation du rapport d'onde stationnaire en fonction de la fréquence dans une antenne selon les premier et deuxième modes de réalisation de l'invention,
• la figure 10 est un diagramme de représentation du gain en fonction de la fréquence d'une antenne selon le premier et le second modes de réalisation de l'invention,
• la figure 11 représente des diagrammes de rayonnement selon le plan azimutal d'une antenne selon le second mode de réalisation pour des fréquences valant 30 MHz, 50 MHz, 100 MHz, 300 MHz et 500 MHz, et
• la figure 12 est une vue de côté de l'antenne de la figure 4 disposée dans une cavité.

The invention will be better understood with the aid of the description which follows, given solely by way of example and with reference to the appended drawings in which:

• the figure 1 represents a view from above of a first embodiment of an antenna according to the invention,
• the figure 2 represents a view of a part of a connecting coil of the antenna of the figure 1 ,
• FIG. 3 represents a view from above of the absorbent surface in an antenna according to the invention,
• the figure 4 represents a side view of the first embodiment of an antenna according to the invention,
• the figure 5 is a diagram of representation of the standing wave ratio as a function of the frequency for an antenna according to the first embodiment of the invention,
• the figure 6 is a representation diagram of the gain of an antenna according to the first embodiment of the invention as a function of frequency,
• the figure 7 represents radiation patterns in the azimuthal plane of an antenna according to the first embodiment of the invention for frequencies of 30 MHz, 50 MHz, 100 MHz, 300 MHz and 500 MHz,
• the figure 8 represents a view from above of a second embodiment of an antenna according to the invention,
• the figure 9 is a diagram of representation of the standing wave ratio as a function of the frequency in an antenna according to the first and second embodiments of the invention,
• the figure 10 is a representation diagram of the gain as a function of the frequency of an antenna according to the first and second embodiments of the invention,
• the figure 11 represents azimuthal plane radiation patterns of an antenna according to the second embodiment for frequencies of 30 MHz, 50 MHz, 100 MHz, 300 MHz and 500 MHz, and
• the figure 12 is a side view of the antenna of the figure 4 disposed in a cavity.

The antenna according to the invention 2 is intended to be fixed on a surface of a mobile machine, for example of an element or a structure of said machine. Advantageously, the antenna 2 is intended to be fixed in a metal cavity formed in the skin of said machine and provided for this purpose.

The antenna 2 is intended to emit and receive electromagnetic waves whose frequencies are in the entire frequency range 30 MHz - 500 MHz. Alternatively, it is intended to emit and receive electromagnetic waves whose frequencies are in the entire frequency range 30 MHz - 800 MHz.

With reference to the figure 1 and at the figure 4 , which respectively represent a view from above and a side view of an antenna 2 in a first embodiment of the invention, the antenna 2 comprises a plurality of radiating elements 4 and a wound wound coil 6 (c '). that is to say, it includes resistors, as will be seen later) associated with the radiating elements 4 of the antenna 2. In addition, it comprises means 8 for impedance matching and power supply radiating elements 4, an absorbent surface 10 and a reflector plane 12.

The radiating elements 4 are adapted to receive and emit electromagnetic waves.

For this purpose, the radiating elements 4 are made from an electrically conductive material.

In the embodiment of the figure 1 , the radiating elements 4 are made in printed technology known to those skilled in the art.

With reference to the figure 1 , the antenna according to the invention 2 comprises four radiating elements 4. These elements 4 are planar, coplanar and each have a generally triangular shape.

By "triangular general shape" is meant a triangle shape, a triangle of which one or more sides have a slight rounding, or a triangle of which one or more vertices are rounded, "chipped" or "blunted".

In the example shown on the Figure 1 each radiating element 4 has three vertices. In addition, each radiating element 4 comprises a slightly rounded free edge 14 and an opposite peak 16 to said rounded edge 14.

These radiating elements 4 are substantially in the same plane P. In addition, all have substantially the same dimensions.

In the example of the figure 1 , the radiating elements 4 also have an opening angle of about 40 ° to optimize the performance of impedance and gain of the antenna 2 over the bandwidth covered, while minimizing the clutter of the antenna. antenna, as will be seen later.

The radiating elements 4 are divided into two dipoles 18 each having two radiating elements 4.

Each dipole 18 is adapted to emit or receive electromagnetic waves having a vertical linear polarization for one and horizontal for the other. The emission and reception of any polarization wave (any linear polarization or circular polarization or elliptical polarization) are then obtained by combining the two linear polarizations in an analog manner by adding for example a coupling function or by digital processing, this being known to those skilled in the art.

For this purpose, the dipoles 18 are orthogonal. The two radiating elements 4 of a dipole 18 adapted for a given linear polarization are arranged between the two radiating elements 4 of the other dipole 18, two successive radiating elements 4 being connected by the charged wound corona 6, as will be seen by the following.

The two dipoles 18 are substantially inscribed in a circle K of center O, the rounded free edge 14 of each radiating element 4 belonging to this circle. In addition, the opposite vertex 16 of each radiating element 4 is oriented towards the center O of the circle K. The dipoles 18 are thus symmetrical with respect to the center O of the circle K.

The diameter of the circle K is equal to a fraction of the length of an electromagnetic wave, that is to say that the diameter is equal to ^λ / _n , where λ is the wavelength and n is a strictly positive.

For an ideal low-bandwidth antenna centered around a wavelength λ, n is typically chosen to be 2.

The dimensioning of the dipoles is then determined as a rule by the ^λ / ₂ ratio independently of the resulting bulk.

However, the congestion and bandwidth constraints to which the antenna 2 according to the invention responds result in a significant difference with this case.

Thus, in the embodiment considered, the diameter of the circle K is taken substantially equal to 330 mm, n therefore being approximately between 30 and 1.8 respectively for electromagnetic waves of frequency from 30 MHz to 500 MHz.

In some embodiments, the range of variation of n is adjustable depending on the desired frequency band and radio performance.

In known manner, an antenna whose radiating elements have small dimensions relative to the length of the electromagnetic waves they are intended to capture and / or transmit has degraded radioelectric properties at frequencies corresponding to these wavelengths.

Thus, the wound coil 6 is able to impart an inductive behavior to the antenna 2, which makes it possible to improve the gain values of the antenna 2 at low frequencies, particularly at frequencies below 300 MHz.

In addition, the wound coil 6 is adapted to optimize the impedance matching and the gain of the antenna 2 at low frequencies.

For this purpose, the wound coil 6 comprises a plurality of connecting coils 20 formed between the radiating elements 4.

In the embodiment of the figure 1 , the wound coil 6 thus comprises four connecting coils 20 each connected on each side to two adjacent radiating elements 4.

Each connecting coil 20 is formed between two radiating elements 4 so as to describe the arc of the circle K circumscribing the dipoles 18 between the two radiating elements 4 to which it is connected.

As illustrated on the figure 1 each coil 20 comprises a plurality of turns of constant diameter and pitch. Each of its turns comprises a point having a maximum distance at the point O. The connecting coils 20 are then arranged so that the circle K circumscribing the dipoles 18 is substantially circumscribed to all of these points for a given binding coil 20 , and this for each of the connection coils 20 that comprises the wound coil 6.

The wound coil 6 further comprises resistors 22 adapted to optimize the impedance matching of the antenna 2.

For this purpose, a resistor 22 is interposed between each end 24 that has a connecting coil 20 and the radiating element 4 to which it is connected.

In the example of the figure 1 , the value of each resistor 22 is for example substantially equal to 300 Ohms. The value of the resistor 22 is adjustable according to the desired frequency band and radio performance.

f ₀ étant en MHz, H la longueur de la bobine de liaison 20 (en m), D le diamètre de la bobine de liaison 20 (en m) et N le nombre de tours de fil bobiné de la bobine de liaison 20.In known manner and with reference to figure 2 which represents a view of a link coil 20, each link coil 20 generates a significant resonance around a frequency value f ₀ , this frequency f _0, referred to as the "resonant frequency of the connection coil 20" being defined by: $${\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">f</figure-callout>}}_0=\frac{29,85.<figure-callout\; id="1"\; label="\; H\; D"\; filenames="imgf0003.png,imgf0005.png"\; state="\{\{state\}\}">\; </figure-callout>{\left(\frac{H}{D}\right)}^{}{\left(\frac{}{}\right)}^{\left(\frac{1}{5}\right)}}{\mathrm{NOT}\mathrm{.}D},$$

f ₀ being in MHz, H the length of the connecting coil 20 (in m), D the diameter of the connecting coil 20 (in m) and N the number of turns of wound wire of the connecting coil 20.

In the embodiment of Figures 1 and 2 , the diameter D of a connecting coil 20 is equal to 20 mm, its pitch (the distance between two successive turns of the connecting coil 20) taken equal to 5 mm, and the number of turns N of each connection coil 20 is taken as 26, which gives a length H of about 150 mm.

Relation (1) then gives a resonance frequency of the connecting coil 20 at about 90 MHz.

This resonance then causes a degradation of the ROS performance of the antenna 2 for electromagnetic waves of frequency close to the resonance frequency of the connecting coils 20.

It is understood that it is advantageous to shift this resonance frequency by changing the dimensions of the connection coils 20 used, as will be seen later in a second embodiment of the invention.

In a manner known to those skilled in the art, the absorbent surface 10 is able to optimize the level of impedance matching, to increase the directivity of the antenna 2 and consequently to improve the gain of the antenna 2 at the low frequencies.

In addition, this absorbent surface 10 makes it possible to reduce the vertical bulk of the antenna 2 as well as the impact of the surface on which the antenna is fixed on the radio performance of the antenna according to the invention 2.

For this purpose, the absorbent surface 10 is made from a ferrite material and is located near the radiating elements 4.

The absorbent surface 10 thus absorbs a portion of the radiation emitted by the antenna 2 in the direction opposite to its preferred radiation direction.

With reference to Figures 3 and 4 , the figure 3 representing a top view of the absorbent surface 10, in the case in question, it has a generally octagonal shape and lies in a plane substantially parallel to the plane P of the radiating elements 4. The absorbent surface 10 is at a distance from the plane P radiating elements 4 substantially equal to 15 mm.

Absorbent surface 10 comprises a plurality of absorbent surface portions 26.

In the example of the figure 3 , the absorbent surface 10 comprises nine portions of absorbent surface 26 of generally square shape and edge with a length taken equal to 100 mm.

The absorbent surface 10 is thus included in a 300 mm square edge whose center C belongs to an axis AA 'perpendicular to the plane P and passing through O. The four absorbent surface portions 26 at the corners of this square have a bevel approximately 70 mm wide.

With regard to the Figure 4 the absorbent surface 10 has a thickness of about 7 mm.

In known manner, the reflective plane 12 of the antenna according to the invention 2 is able to provide a reference of mass and to reflect at the high frequencies of the band of the antenna 2, for example above about 350 MHz, a part of the electromagnetic radiation emitted by the antenna 2 in the direction opposite to its preferred radiation direction - the latter being along the axis AA 'and, with reference to the figure 4 , in the direction of the axis AA 'from the lower part of the figure to the upper part of the figure -, and thus increase the radio performance of the antenna 2 at high frequencies.

In addition, the reflector plane 12 contributes to minimizing the influence of the gear in which the antenna 2 is integrated on the radio performance thereof.

Thus, the reflective plane 12 is parallel to the plane P and remote from it by a distance equal to a fraction of the length of an electromagnetic wave, that is to say that the distance is equal to ^λ / _m , Where λ is the wavelength and m is a strictly positive number.

For an ideal low-bandwidth antenna centered around a wavelength λ, m is typically chosen to be equal to 4. The distance from the reflector plane to the dipoles is then determined by the ^λ / ₄ ratio independently of the resulting congestion. .

However, the congestion and bandwidth constraints to which the antenna 2 according to the invention responds result in a significant difference with this case.

Thus, in the embodiment considered, the distance from the reflective plane 12 to the plane P is taken substantially equal to 150 mm, m then being approximately between 67 and 4 respectively for electromagnetic waves of frequency ranging from 30 MHz to 500 MHz.

In some embodiments, the variation range of m is adjustable according to the desired frequency band and radio performance.

The reflector plane 12 has a generally circular shape of central axis A-A 'and diameter approximately 350 mm.

The radiating elements 4, the reflective plane 12 and the absorbing surface 10 are parallel to each other and are centered around the axis A-A '.

With reference to the figure 4 , the antenna according to the invention 2 thus has dimensions such that it is substantially comprised in a cylinder axis A-A ', diameter 350 mm and height 150 mm.

In addition, the arrangement of the reflective plane 12 and the absorbent surface 10 with respect to the dipoles 18 is able to minimize the interference between the main radiation of the antenna 2 and the portion of the radiation in the direction opposite to the preferred radiation direction of the antenna 2 which is reflected against the surrounding surfaces or objects and then interferes with the main radiation of the antenna 2.

The combination of the reflector plane 12 and the absorbing surface 10 is thus able to minimize the impact on the radio performance of the surface or cavity intended to receive the antenna 2.

More particularly, this combination makes it possible to minimize this impact when said surface or said cavity is made from a metallic material.

The impedance matching and power supply means 8 of the antenna 2 are adapted to ensure the impedance matching and the supply of the dipoles 18 of the antenna 2 as well as to symmetrize the currents in the elements radiating 4.

For this purpose, these means 8 comprise two connectors 28, two impedance transformers 30, electrical contacts 32 placed between the radiating elements 4 and the transformers 30. In addition, these means 8 comprise electrical contacts 34, 36 placed between the connectors 28 and transformers 30, the reference electrical contacts 36 being ground contacts.

The connectors 28 are adapted to provide the electrical interface between the antenna 2 and a device (not shown) for transmitting and / or receiving associated therewith.

In known manner, such connectors 28 are intended to be engaged with coaxial cables (not shown) for example, and then have a core 38 and a mass 40 complementary to those of the coaxial cables to which they are connected.

In the embodiment of the figure 4 , the core 38 of each connector 28 is connected to an asymmetrical channel 44 which comprises each impedance transformer 30 via an electrical contact 34, and the ground 40 of each connector 28 is connected to a ground path 46 of each transformer 30 via an electrical contact 36, the ground 40 of each connector 28 being in electrical continuity with the reflector plane 12 via an electrical contact 35.

Such electrical contacts 34, 35, 36 are well known to those skilled in the art and will not be described here.

In a known manner, an impedance transformer 30 is adapted to maximize the power transfer between the dipoles 18 of the antenna 2 and the transmitting and / or receiving device to which the antenna 2 is associated.

Each dipole 18 is associated with an impedance transformer 30.

As illustrated on the Figure 4 each impedance transformer 30 comprises two symmetrical channels 42 each connected to one of the radiating elements 4 of the corresponding dipole 18 via an electrical contact 32, as well as an asymmetrical channel 44 and a ground channel 46, as described hereinabove. above..

The reference electrical contacts 32 are well known to those skilled in the art and will not be described here.

With reference to the figure 5 , which is a representation curve of the ROS of the antenna 2 according to the first embodiment as a function of the frequency, the antenna 2 has lower standing wave ratio values or of the order of 3 for frequencies above 200 MHz, that is, it has good impedance matching qualities over a wide frequency band.

Moreover, with reference to the figure 6 , which is a representation curve of the gain of the antenna 2 according to this embodiment as a function of the frequency, the antenna 2 according to this embodiment of the invention has a gain substantially equal to -16 dBi at 100 MHz at -6 dBi at 200 MHz and becomes positive above 310 MHz.

The gain is further comprised between -38 dBi and -16 dBi between 30 MHz and 100 MHz.

The figure 7 provides the radiation patterns in the azimuth plane of an antenna 2 according to this first embodiment of the invention for frequencies of 30, 50, 100, 300 and 500 MHz.

It can be seen from these diagrams that such an antenna 2 has a main radiation lobe, that is to say radiation in its preferred direction, stable as a function of frequency and a good forward / backward ratio, and this even at frequencies less than or equal to 100 MHz. In addition, the reflector plane 12 and the absorbing surface 10 contribute to the optimization of the impedance, the directivity and therefore the gain on the utilization band of the antenna 2, as described above.

As described above and with reference to the figure 12 , which is a side view of an antenna 2 disposed in a cavity 43, the presence of the absorbent surface 10 and of the reflector plane 12 thus makes the antenna 2 suitable for being disposed both on a surface 41 and in a cavity 43 formed in the skin 45 of a terrestrial, naval or airborne machine 47, so that the radiating elements 4 are flush substantially opening the cavity 43.

• présente un faible encombrement par rapport aux longueurs d'onde d'utilisation,
• dispose d'une large bande passante,
• est discrète visuellement,
• présente de bonnes performances radioélectriques pour des fréquences comprises entre 30 et 500 MHz au regard des contraintes fixées,
• est propre à traiter des ondes électromagnétiques quelle que soit leur polarisation,
• présente un rayonnement permettant une couverture radioélectrique quasi-unidirectionnelle sur une large bande de fréquence,
• réduit la dépendance vis-à-vis de la surface de l'engin sur laquelle elle est agencée, et
• est avantageusement adaptée pour être installée dans une cavité métallique, comme illustré sur la Figure 12.

Thus, the antenna 2 according to this embodiment of the invention:

• has a small footprint compared to the wavelengths of use,
• has a wide bandwidth,
• is discreet visually,
• has good radio performance for frequencies between 30 and 500 MHz with regard to the constraints set,
• is capable of treating electromagnetic waves whatever their polarization,
• has a radiation allowing a quasi-unidirectional radio coverage over a wide frequency band,
• reduces the dependence on the surface of the machine on which it is arranged, and
• is advantageously adapted to be installed in a metal cavity, as illustrated in FIG. Figure 12 .

It is thus adapted to simultaneously satisfy many constraints to which antennas of the state of the art only partially respond.

In a variant, an antenna 2 according to a second embodiment is envisaged in which the radio performances are further improved.

Indeed, as illustrated on the figure 5 , the ROS value is greater than 3 for frequencies between 30 and 200 MHz and greater than 5 for frequencies between 50 and 150 MHz approximately.

This value of the ROS results from the presence of the connection coils 20 which degrade the impedance matching of the antenna 2 around their resonance frequency.

This variant of the invention is then advantageously used to improve the value of the standing wave ratio at low frequencies.

As illustrated on the figure 8 , which is a view from above of the antenna 2 according to the second embodiment, the wound ring 6 comprises four portions of wound crown 48.

Each wound coil portion 48 is disposed between two adjacent radiating elements 4 and has four adjacent connecting coils 50.

Between two adjacent connecting coils 50 is interposed a resistor 52. The value thereof is for example substantially equal to 300 Ohms. This value is adjustable according to the desired frequency band and radio performance.

The number of turns of each connecting coil 50 is decreased with respect to the first embodiment of the invention, as illustrated in FIG. figure 8 .

With reference to formula (1), the number of revolutions of each connecting coil 50 being brought back, for example, from 26 to 6. The connection coils 50 then have a resonance frequency around 300 MHz.

This shift of the resonant frequency of the connection coils 50 to the high frequencies is advantageous, since from this frequency of 300 MHz, the radiation of the antenna 2 is provided by the dipoles 18 only.

The performance of degraded ROS at the low frequencies of the antenna 2 according to the first embodiment of the invention due to the resonance of the connection coils can thus be improved.

With reference to figures 9 and 10 , which are curves respectively representing the ROS and the gain of an antenna 2 according to the two embodiments over the frequency range, it is then found that the dimensions of the connection coils 50 according to the second embodiment of the 2 antenna of the invention drop the value of the ROS from more than 9 to 100 MHz in the first embodiment of the antenna 2 according to the invention about 5.2 about 100 MHz in the second embodiment of the antenna 2 according to the invention.

In addition, the gain of the antenna 2 remains substantially identical as a function of the frequency regardless of the embodiment of the antenna 2 according to the invention, the value of the gain being substantially equal to -16 dBi at 100 MHz, at -6 dBi at 200 MHz and becoming positive beyond 330 MHz according to the second embodiment of the antenna 2 according to the invention.

The figure 11 provides the radiation patterns of the antenna 2 according to the second embodiment of the invention.

It can be seen that these radiation patterns are substantially similar to the radiation patterns of an antenna 2 according to the first embodiment, the antenna 2 according to the second embodiment of the invention thus having radio-directivity properties similar to those of the antenna 2 according to the first embodiment.

In a variant (not shown), the radiating elements 4 of the dipoles 18 of the antenna 2 according to the two embodiments of the invention are sized to be able to emit and / or receive electromagnetic waves of frequency between 30 MHz and 800 MHz .

Beyond 800 MHz, the radio performance of the antenna 2 is degraded because of the limitations related to the diameter and height dimensions of the antenna 2 vis-à-vis the wavelengths at high frequencies and the band pass of the impedance transformer 30 used.

In another variant (not shown), the antenna 2 according to the invention is protected by a radome whose shape and material are determined according to criteria known to those skilled in the art.

Claims (12)

1. An antenna (2) for emitting/receiving electromagnetic waves, of the type comprising:

   - two orthogonal dipoles (18), each dipole (18) comprising two radiating elements (4),

   - a reflective plane (12) and

   - an absorptive surface (10),

   where the radiating elements (4) are substantially planar and each have a general triangular shape, each radiating element (4) being laid out between both radiating elements (4) of the other dipole (18),
   characterized in that two successive radiating elements (4) are connected through a coiled crown (6).
2. The antenna (2) according to claim 1, characterized in that the radiating elements (4) are all substantially comprised in a same plane (P).
3. The antenna (2) according to claim 1 or 2, characterized in that each radiating element (4) has a slightly rounded free edge (14), the dipoles (18) being substantially included in a circle (K), the free edge (14) of each radiating element (4) belonging to said circle (K).
4. The antenna (2) according to claim 3, characterized in that each radiating element (4) comprises an apex (16) opposite to its rounded free edge (14), said apex (16) of each radiating element (14) being substantially oriented towards the center (O) of said circle (K).
5. The antenna (2) according to any one of the preceding claims, characterized in that the coiled crown (6) comprises connection coils (20), each connection coil (20) being connected to two successive radiating elements (4).
6. The antenna (2) according to claim 5, characterized in that a connection coil (20) has two ends (24), each connected via a resistor (22) to one of the radiating elements (4) to which the connection coil (20) is connected.
7. The antenna (2) according to any one of claims 1 or 4, characterized in that the coiled crown (6) comprises coiled crown portions (48), each coiled crown portion (48) connecting two successive radiating elements (4) and having several adjacent connection coils (50), a resistor (52) being positioned between two adjacent connection coils (50).
8. The antenna (2) according to any of the preceding claims, characterized in that it is entirely comprised in a cylinder with a diameter substantially equal to 350 mm and with a height substantially equal to 150 mm.
9. The antenna (2) according to any of the preceding claims, characterized in that it is suitable for emitting/receiving electromagnetic waves, the frequencies of which are comprised in the whole range of frequencies 30 MHz - 500 MHz, and advantageously in the whole range of frequencies 30 MHz - 800 MHz.
10. The antenna (2) according to any of the preceding claims, characterized in that it is able to emit and receive electromagnetic waves having a polarization from among any linear polarization, a circular polarization or an elliptical polarization, each dipole (18) being able to emit/receive electromagnetic waves having a horizontal linear polarization for one of the dipoles (18) and a vertical linear polarization for the other dipole (18), respectively.
11. A land, airborne or naval vehicle (47) of the type including:

    - a planar surface (41) and/or a cavity (43) arranged in the vehicle (47),

    - an antenna (2) according to any of the preceding claims laid out on the planar surface (41) and/or in the cavity (43).
12. The vehicle (47) according to claim 11, characterized in that the planar surface (41) and/or the cavity (43) are made from a metal material.

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