EP2422403B9 - Multiple wide band antenna with low profile - Google Patents

Description

The object of the invention relates to multiple antennas, used in particular, for radio communication equipment.

The antennas according to the invention apply, for example, to equip vehicles and for a frequency band varying from 225 to 400 MHz. They can be spatial diversity, all antenna elements constituting the antenna then operating in the same frequency range. The antennas may also consist of several antenna elements operating in different frequency bands from each other. The position of the different antenna elements forming the antenna, relative to each other, depends on the application.

An antenna according to the invention may be in the form of whip, better known by the English expression "low profile", provide at least two independent inputs or power supply, maintain an omnidirectional coverage and be predisposed to signal processing of space diversity type.

In the remainder of the description, the expression "low profile" corresponds to the transverse dimensions of the antenna itself, that is to say its section.

avec Zc = 60 In (D / d), D étant le diamètre du stub, d le diamètre apparent des câbles qui le traversent, L la longueur du stub et λ la longueur d'ondeIt is known to provide a dual antenna comprising a power supply means. For example Figures 1A and 1B (respectively perspective view and sectional view) represent an antenna system consisting of a first dipole 1 composed of an upper radiating element 1s and a lower radiating element 1b having the shape of a skirt, a second dipole 2, placed collinearly at the dipole 1 and composed of an upper radiating element 2s in the form of a counter skirt (upside-down skirt) and a lower element 2b also having the skirt-like shape, of a first coaxial cable 3 passing through the assembly 2b, 2s, 1b and feeding the dipole 1 by the electrical connections of its core 5 with the element 1s and its sheath 6 with the element 1b, a second coaxial cable 4 feeding the dipole 2 by the electrical connections of its soul 7 to a quarter wave trap 9, usually designated by its English terminology "stub" level point A and its sheath 8 with the element 2b. The disadvantages of this type of structure come from the use of the stub. Indeed, it is known that the effectiveness of the "stub" is governed by the relationship giving its apparent impedance $$\mathrm{Z\; stub}\mathrm{=}\mathrm{<figure-callout\; id="2"\; label="Zc\; tg"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">Zc\; tg</figure-callout>}\left(\mathrm{2}\mathrm{\pi L}\mathrm{/}\mathrm{\lambda }\right)$$

with Zc = 60 In (D / d), where D is the diameter of the stub, d is the apparent diameter of the cables passing through it, L is the length of the stub and λ is the wavelength

As the efficiency of the stub is all the higher as the apparent impedance Zstub is large, it follows that the wider the bandwidth to be covered, the greater the value of D must be, which goes against looking for a weak profile for an antenna while maintaining a high bandwidth on the air.

Another dual antennal structure is described in the patent FR 2,300,429 and represented at figure 2 . This antenna system consists of a first dipole 1 composed of an upper radiating element 1s connected to the core 11 of a multiaxial line 12 and a lower radiating element 1b connected to the sheath 12 ₁ of the multiaxial line. , a second dipole 2 composed of an upper radiating element 2s connected to the sheath 12 ₁ at the point 10 and a lower radiating element 2b connected to the sheath 12 ₂ of the multiaxial line 12. Such a system, s' it is effective, but has the disadvantage of having to implement, to cover a wide frequency band, thick radiating elements, for example, cone sections, discs, etc. which lead to an increase in the size of the antenna, which goes against one of the desired objectives, namely, to minimize the size of the antenna while maintaining a desired bandwidth.
The chapter 5.7.3 in E. da Silva's book (London 2001) "High Frequency Engineering", Elsevier, pp. 233-235 (ISBN 07065646) ) discloses autotransformers for impedance matching.

One of the objectives of the invention is to provide an antenna system capable of covering a wide frequency band from thin radiating elements and therefore of low profile. In order to achieve these objectives, the structure of said present antenna makes it possible to feed dipoles in collinear arrangement without resorting to "stubs" whose transverse dimensions are important when one wants to cover a broad band of frequencies.

A dual antenna, produced according to the invention and operating in the UHF band of 225 to 400 MHz, is, for example, in the form of a whip of 2.5 m high and about 25 mm in diameter, while the equipment similar art market designed according to the prior art, have a diameter greater than 100mm.

• un dipôle D₁ (k=1) disposé dans la partie supérieure de ladite antenne, ledit dipôle D₁ comportant au moins un premier élément antennaire haut D_1s connecté à l'âme dudit câble multiaxial comprenant n gaines et dont l'élément antennaire bas D_1b est connecté à la première gaine adjacente à l'âme,
• un dispositif de connexion positionné entre un élément haut D_ks d'un dipôle D_k (k>1) et l'élément antennaire bas D_kb dudit dipôle D_k, l'élément antennaire haut D_ks est connecté en un point à la gaine d'indice (k-1) du câble multiaxial après que l'ensemble de l'âme et des gaines d'indice (1 à k-1) s'enroulent en Q spires autour d'un noyau magnétique et l'élément antennaire bas D_kb du dipôle D_k est connecté à la gaine d'indice k en un point, et en ce que [ledit dispositif de connexion comprend au moins un enroulement secondaire monofilaire de P spires disposé sur le même noyau magnétique relie un point bas dudit élément antennaire bas D_kb dudit dipôle D_k à la gaine d'indice (k-1) au point correspondant au début de l'enroulement afin de réaliser l'adaptation d'impédance large bande et l'alimentation du dipôle D_k.

The object of the invention relates to a low profile broadband multiple antenna corresponding to the transverse dimensions of the antenna (support in the description on page 1 lines 18-20) comprising at least two dipoles each dipole k designated D _k consisting of a high antennal element D _ks and a low antenna element D _kb , said antenna being fed by a coaxial cable comprising a core and n sheaths arranged concentrically around the core with k varying from 1 to n, characterized in that it comprises at least the following elements arranged as indicated below:

• a dipole D ₁ (k = 1) disposed in the upper part of said antenna, said dipole D ₁ comprising at least a first high antenna element D _1s connected to the core of said multiaxial cable comprising n sheaths and whose low antennal element D _1b is connected to the first sheath adjacent to the core,
• a connection device positioned between a high element D _ks of a dipole D _k (k> 1) and the low antenna element D _{kb of} said dipole D _k , the high antenna element D _ks is connected at a point to the sheath of index (k-1) of the multiaxial cable after the entire core and index sheaths (1 to k-1) wind in Q turns around a magnetic core and the antennal element low D _kb of the dipole D _k is connected to the cladding of index k at a point, and in that [said connection device comprises at least one monofilar secondary winding of P turns disposed on the same magnetic core connects a low point of said low antenna element D _{kb of} said dipole D _k to the index cladding (k-1) at the point corresponding to the beginning of the winding in order to achieve broadband impedance matching and feeding of the dipole D _k .

The magnetic element is, for example, a torus or a tube.

All dipoles D _k constituting said antenna can operate in the same frequency range.

The dipoles D _k constituting the antenna can also be powered with different powers.

The invention also relates to an antenna system comprising at least one antenna comprising two dipoles, a dipole k designated D _k consisting of a high antenna element D _ks and a low antenna element D _kb , said antenna being fed by a cable coaxial device comprising a core and two sheaths arranged concentrically around the core, with k equal to 1 or 2, characterized in that it comprises two separate coaxial cables and allowing the connection of said antenna to two disjointed radio channels, and that the soul of the first cable corresponds to the extension in the vehicle of the soul of the invention and in that the sheath of this cable corresponds to the extension of a first sheath, a second sheath when it does not extend into the space Int that of sufficient length to be connected to the core of the second cable at a point F, said sheaths of the first and second cables are in contact with each other and are connected to a counter-skirt at a point M to form a quarter-wave balun system.

The dipoles are, for example, adapted to operate in the frequency range [225-400 MHz].

• Les figures 1A et 1B, un premier exemple d'antenne utilisant un « stub » selon l'art antérieur,
• La figure 2, un deuxième exemple de structure antennaire selon l'art antérieur,
• Les figures 3A, 3B, un exemple de structure antennaire selon l'invention,
• La figure 4, le détail d'un exemple de réalisation pour le système d'alimentation,
• Les figures 5A et 5B, d'autres exemples de réalisation pour le système d'alimentation,
• La figure 6, une antenne incorporant un moyen permettant de limiter, voir annuler les courants de fuite,
• Les figures 7A et 7B, un exemple de réalisation du dispositif de raccordement de la structure antennaire aux postes radio, et
• La figure 8, une représentation schématique de l'application de l'invention à une structure antennaire comprenant n dipôles, et
• La figure 9, le détail du système d'alimentation pour l'exemple d'antenne de la figure 8.

Other features and advantages of the device according to the invention will appear better on reading the description which follows of an example of embodiment given by way of illustration and in no way limiting attached to the figures which represent:

• The Figures 1A and 1B , a first example of an antenna using a "stub" according to the prior art,
• The figure 2 a second example of antenna structure according to the prior art,
• The Figures 3A, 3B , an example of antenna structure according to the invention,
• The figure 4 , the detail of an exemplary embodiment for the power system,
• The Figures 5A and 5B , other embodiments for the power system,
• The figure 6 an antenna incorporating a means for limiting or even canceling the leakage currents,
• The Figures 7A and 7B an embodiment of the device for connecting the antenna structure to the radio stations, and
• The figure 8 a schematic representation of the application of the invention to an antenna structure comprising n dipoles, and
• The figure 9 , the detail of the power system for the antenna example of the figure 8 .

In order to better understand the object of the present invention, the description will be given by way of non-limiting example in the context of a low profile double antenna used for radio communication equipment, in particular in the UHF band ( Ultra High Frequency) 225-400MHz intended to be installed and used on vehicles that are stationary or in motion. The antenna can thus be used in a context of spatial diversity, that is to say that each antenna element operates in the same frequency range. The antenna can operate in transmission, reception or transmission / reception.

More generally, the antenna structure can also be composed of a number of dipoles n with n greater than or equal to 2. Each dipole can be adapted to operate in the same frequency range, or in different frequency ranges.

The Figures 3A and 3B (respectively perspective view and cross-sectional view) show an exemplary embodiment of a dual antenna according to the invention.

The antenna consists of a first dipole 1 composed of an upper radiating element 1s and a lower radiating element 1b forming a skirt ( figure 3B ), the cylindrical shape for the elements radiating is taken in the example for ease of understanding the text, a second dipole 2, placed collinearly to the dipole 1 and composed of an upper radiating element 2s forming a counter skirt (skirt returned) and a lower element 2b also forming a skirt, a triaxial cable 14 consisting of a core ₁₄₀ , a first concentric sheath 14 ₁ and a second concentric sheath 14 ₂ . For the mechanical strength of the core and sheaths, the space between them can in practice be filled by a dielectric material such as polyethylene or Teflon brand material (registered trademark), not shown here for reasons of clarity.

The asymmetrical type of supply (known by the term "unbalanced") of the dipole 1 is achieved by the connection of the core 14 ₀ to the upper element 1s and by the connection of the first sheath 14 ₁ to the lower element 1b. , the system may comprise a broadband impedance matching circuit known to those skilled in the art and interposed between the core 14 ₀ and the element 1s which, for the sake of facilitating the understanding of the invention, n ' is not represented.

The supply of the dipole 2 is also of asymmetrical type produced by the connection of the second sheath 14 ₂ to the lower element 2b at point 27 and by the device 20 detailed in FIG. figure 4 which is placed between the two elements 2s and 2b. The device 20 is, for example, composed of a winding 21 of the cable section in the form of Q turns, consisting of the portion of the core ₁₄₀ and the sheath portion 14 ₁ located between these two elements 2s and 2b, around a magnetic element or core 22, a secondary winding (P turns) formed by a monofilar cable 23, one end of which is electrically connected to the element 2b at point 24 and the other end is connected to the sheath 14 ₁ at the beginning of the winding 21 (considered starting from the antenna element 2b below the dipole) at point 25, and a connection 26 between the sheath 14 ₁ and the upper radiating element 2s at the end of the winding 21. The monofilar cable 23 is itself wound around the magnetic core.

Similarly, to facilitate understanding of the invention, any additional circuits known to those skilled in the art to improve the broadband adaptation of the impedance are not represented; for example, there may be mentioned the use of a LC plug circuit connecting the elements 2s and 2b, and / or an LC resonant circuit placed in series with the secondary winding 23. The element 20 has the particular function of providing a excitation by magnetic coupling and thus allow to expand the frequency band in which the antenna can operate, without having to use so-called antenna elements "thick" and in fact, without increasing the size of the antenna.

The Figure 5A represents a first embodiment for which the magnetic element or magnetic core 22 is a torus 28. This form advantageously makes it possible to obtain a "tighter" magnetic coupling and, in this way, facilitates the transfer of RF (radio frequency) power to radiating elements of the dipole.

The Figure 5B represents another alternative embodiment for which the magnetic element or magnetic core 22 is a tube 29. This form allows the use of a cable 14 of rigid type which is not arranged to be wound.

The figure 6 represents an alternative embodiment which makes it possible, in particular, to improve the decoupling between the two elementary antennas 1 and 2. For example, this type of arrangement is more particularly suitable in the case of use in a multi-channel system. To obtain this improvement, the idea is to add ferrite sleeves 13 by placing them around the sheath 14 ₁ located between the antennas 1 and 2. The effect of inductance thus produced limits or cancels the leakage currents or return on the surface of the sheath, and thus increases the decoupling between the two elementary antennas.

The embodiment of the dual antenna given to better understand the invention uses two dipoles. The Figures 7A and 7B (respectively perspective view and sectional view) are an example of asymmetrical-asymmetrical type connection device for connecting the antenna to two transceiver stations with 2 separate coaxial cables.

Ext denotes the space corresponding to the outside of the carrier vehicle where a low profile is requested and Int inside the vehicle.

A preferred embodiment is to position only the antenna part according to the invention in the space Ext and to install the supply device 30 allowing the connection of two radio stations in the space Int where no drastic constraint of dimension n is imposed.

The device 30 comprises two separate coaxial cables 15 and 16 which allow the connection of the antenna according to the invention to two disjointed radio channels. A preferred embodiment is that the core 15 ₀ of the cable 15 corresponds to the extension in the vehicle of the core ₁₄₀ of the invention and that the sheath 15 ₁ of the cable 15 corresponds to the extension of the sheath 14 ₁ . Sheath 14 ₂ While in it extends into the Int space of sufficient length to be connected to the core 16 of the cable 16 ₀ at point F. The sheaths 15 ₁ and 16 ₁ for cables 15 and 16 are in contact with each other and are connected to a counter-skirt 31 at the point M to form a system usually designated by the one skilled in the quarter-wave balancing machine. The effectiveness of this type of balun is all the higher as the relative diameter of the counter-skirt with respect to the diameter of the sheaths is large. Given the position of this equipment inside the vehicle, there is no drastic dimensional constraint in the design of the antenna.

The figure 8 schematically represents the case where the antenna has n dipoles fed by a multiaxial cable composed of a core and n concentric ducts in this example, the antenna is n access broadband. The broadband, low profile, n access antenna is composed of a collinear stack of n dipoles fed by a multiaxial cable consisting of a core 14 ₀ and n concentric sheaths 14 _k with k = 1 to n.
The connections between the antennal elements and the sheath or the core are as described below. A dipole k designated D _k on the figure 8 consists of a low element D _kb and a high element D _ks , as indicated for example by elements 2b and 2s of the preceding figures. The antenna comprises a dipole D ₁ at the top of the antenna whose antenna top _1w D element is connected to the core 14 ₀ a multiaxial cable comprising n concentric ducts to each other and therefore not fed this last, and whose low antennal element D _1b is connected to the first sheath 14 ₁ adjacent to the core ₁₄₀ . The first sheath is the sheath that is disposed closest to the core, the second sheath 14 ₂ of the multiaxial cable is the sheath disposed between the first and the third sheath 14 ₃ and so on. This provision is only a convention used for the example of the description.

The device 40 ( figure 9 ) corresponding to the device 20 described above is used to connect the other dipoles. This device 40 is positioned between the high element D _ks of the dipole k or D _k and the low element D _kb of the dipole D _k . The high element D _ks is connected at point 46 to the index cladding (k-1) of the multiaxial cable after the set of sheaths of index (1 to k-1) and of the core wind up. in Q turns 41 around a magnetic core 42 and that the low element D _kb of the dipole D _k is connected to the cladding of index k at point 47 and that a monofilar winding of P turns, 43, on the same magnetic core 42 connects at point 44 this low element D _kb to the index cladding (k-1) at point 45 beginning of the winding 41 to achieve broadband impedance matching and the power supply of the dipole k or D _k .

A double antenna consists of 2 elementary antennas of collinear dipole type with skirt, placed one above the other; each elemental antenna having its own input.

• soit le branchement de 2 postes radio pouvant fonctionner en Evasion de Fréquence ou EVF sans faire appel à un coupleur large bande donc à pertes,
• soit l'association des deux entrées pour constituer un ensemble rayonnant unique avec un gain de directivité, soit la connexion à 2 voies de réception pour réaliser la fonction de diversité dans l'espace,
• soit la connexion d'un récepteur et d'un émetteur dans le cadre d'un système full duplex, c'est-à-dire, en émission réception simultanées.

When the broadband antenna is a two-input antenna, this will, for example:

• the connection of 2 radio sets that can operate in Evasion Frequency or EVF without using a broadband coupler so losses,
• either the combination of the two inputs to form a single radiating unit with a directivity gain, or the connection to two reception channels to realize the diversity function in space,
• or the connection of a receiver and a transmitter in the context of a full duplex system, that is to say, in simultaneous transmission reception.

• la réalisation des éléments rayonnants à partir de tubes (plein ou tressé),
• la protection des éléments rayonnants sous un radôme, par exemple, en plastique renforcé de fibres de verre (robustesse, souplesse bien adaptée aux chocs répétés sur des obstacles),
• la réalisation du système de raccordement qui sera placé à la base de l'antenne et n'aura pas d'influence notoire sur le profil et la taille de l'antenne.

The antenna can be implemented using the usual realization techniques broadband antennas for mobiles, particularly the antennas of the VHF-FM band, an English translation of (Very High Frequency -Frequency modulation), namely:

• the production of the radiating elements from tubes (solid or braided),
• the protection of the radiating elements under a radome, for example, made of glass-fiber reinforced plastic (robustness, flexibility well adapted to repeated impacts on obstacles),
• the realization of the connection system which will be placed at the base of the antenna and will have no noticeable influence on the profile and the size of the antenna.

The antenna or radiating structure according to the invention is a multiple structure of fine collinear dipole type. It implements elements of small transverse dimensions, so low profile, able to operate in a wide frequency band. It has a lower profile than broadband antennas known by implementation of thin dipole structure and an adaptation circuit instead of so-called "thick" structure. It offers an optimization of the physical dimensions of the multiaxial cable and magnetic coupling system instead of a stub feeding. It also offers the possibility of adding complementary circuits to improve impedance matching. Its structure is adapted for use on moving vehicles, for tactical multi-use. It also offers the possibility of coupling to the emission: + 3dB directivity, a possibility of spatial diversity at the reception: fight against fainting, a phenomenon better known by the abbreviation Anglo-Saxon "fading".

Claims (6)

1. A multiple broadband antenna with a low profile that corresponds to the transverse dimensions of the antenna comprising at least two dipoles (1, 2, D_k), each dipole k designated D_k being constituted by an upper antenna element D_ks and a lower antenna element D_kb, said antenna being fed via a coaxial cable comprising a core (14₀) and n sheaths disposed in a concentric manner around said core (14₀), with k varying from 1 to n, said antenna comprising at least the following elements disposed as indicated hereafter:

   • one dipole D₁, with k = 1, disposed in the upper part of said antenna, said dipole D₁ comprising at least one first upper antenna element D_1s connected to said core (14₀) of said multi-axial cable comprising n sheaths, and the lower antenna element D_1b of which is connected to the first sheath (14₁) adjacent to said core (14₀), said antenna being characterised in that it comprises at least:

   • one connection device (20, 40) positioned between an upper element D_ks of a dipole D_k, with k > 1, and the lower antenna element D_kb of said dipole D_k, said upper antenna element D_ks being connected at a point (46) to the sheath of index (k-1) of the multi-axial cable once the assembly of the core (14₀) and of the sheaths of index (1 to k-1) has been wound into Q turns (41) around a magnetic core (42) and said lower antenna element D_kb of said dipole D_k being connected to the sheath of index k at a point (47), and in that said connection device (20, 40) comprises at least one secondary single wire winding of P turns (43) disposed on the same magnetic core (42) connecting at a lower point (44) said lower antenna element D_kb of said dipole D_k to the sheath of index k-1 at the point (45) that corresponds to the start of the winding of the Q turns (41).
2. The antenna according to claim 1, characterised in that the magnetic core (42) is a torus (28) or a tube (29).
3. The antenna according to claim 1, characterised in that all of the dipoles D_k that constitute said antenna operate over the same frequency range and are supplied with the same power value.
4. The antenna according to clam 1, charaterised in that the dipoles D_k that constitute the antenna are supplied with different powers.
5. An antenna system, comprising at least one antenna according to claim 1, comprising two dipoles, one dipole k, designated D_k, being constituted by an upper antenna element D_ks and a lower antenna element D_kb, said antenna being fed via a coaxial cable comprising a core and two sheaths disposed in a concentric manner around said core, with k being equal to I or 2, characterised in that it comprises two separate coaxial cables (15 and 16) allowing the connection of said antenna to two separate radio channels, and in that the core (15₀) of the first cable (15) corresponds to an extension in a vehicle of the core (14₀) and that the sheath (15₁) of said first cable (15) corresponds to an extension of a first sheath (14₁), with a second sheath (14₂) extending into a space (Int) only with sufficient length so as to be corresponds to the core (16₀) of the second cable (16) at a point F, said sheaths (151 and 161) of said first cable (15) and of said second cable (16) being in contact with each other and being connected to a counter-skirt (31) at a point M so as to constitute a quarter-wave balun system.
6. The antenna and antenna system according to any one of claims 1 to 5, characterised in that the dipoles are designed to operate in a frequency range of 225-400 MHz.

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