EP0888648B1 - Helical antenna with built-in duplexing means, and manufacturing methods therefore - Google Patents

Description

The field of the invention is that of wide bandwidth antennas and hemispherical or quasi-hemispherical radiation pattern. More precisely, the invention relates to resonant helical antennas operating in two bands of neighboring frequencies corresponding to transmission and reception, and in particular the decoupling of these two channels, and therefore the duplexer function.

The antenna of the invention finds applications in particular in the context of mobile satellite communications between fixed users and all types of mobiles, for example aeronautical, maritime or terrestrial. Several systems in this area communication systems are implemented, or are currently being development (e.g. INMARSAT, INMARSAT-M systems, Globalstar ...). These antennas are also of interest in the deployment personal communication systems (PCS) by geostationary satellites.

For all these systems, which provide for links with satellites geostationary, the very different incidences of the signals received or emitted impose on the antennas to possess a hemispherical coverage radiation pattern. Moreover the polarization must be circular with an ellipticity ratio better than 5 dB in the useful band.

More generally, the invention can find applications in all systems requiring the use of a wide band, a cover diagram hemispherical, circular polarization and a good ellipticity ratio.

In the fields of application mentioned above, the antennas must indeed have the above characteristics either in a very wide bandwidth, around 10%, ie in two neighboring sub-bands corresponding respectively to the reception and broadcast.

We already know, by patent FR-89 14952 in the name of the same applicant, a type antenna particularly suitable for such applications.

This antenna, called the resonant quadrifilar helix antenna (HQR), has characteristics very close to the criteria set out in a frequency band limited by generally at 5% by impedance matching problems. Two out of two bands is possible using dual-layer HQR antennas. These antennas are formed by the concentric "nesting" of two coaxial resonant quadrifilar propellers, electromagnetically coupled.

A quadrifilar antenna is formed by four radiating strands. An example of realization is described in detail in the document "Analysis of quadrifilar resonant helical antenna for mobile communications "(analysis of the resonant quadrifilar helix antenna for communications with mobiles), by A. Sharaiha and C. Terret (IEEE - Proceedings H, vol. 140, no.4, August 1993).

According to this embodiment, the radiating strands are printed on a substrate thin dielectric, then wound on a transparent cylindrical support of the radio point of view. The four strands of the propeller are open or short-circuited one end and electrically connected at the other end with segments conductors arranged on the base of the lower part of the support cylinder. The fourth strands of the helix are therefore excited through these conductive segments.

This antenna conventionally requires a supply circuit, which ensures the excitation of the different antenna strands by signals of the same amplitude in phase quadrature. Several techniques are known for making such circuits Power.

In the document "Analysis of quadrifilar resonant helical antenna for mobile communications "cited above, this function is performed from the structure of couplers (3 dB, -90 °) and a hybrid ring. This set is located on a circuit printed which is placed at the base of the antenna.

This technique has the advantage of being relatively simple to carry out and to put in action. On the other hand, it leads to a not insignificant bulk, compared to the size of the antenna (which can for example have a size of the order of ten centimeters). This drawback makes this solution incompatible with many applications, especially when maximum miniaturization is required.

According to a second technique, described in the document "UHF satellite array nulls adjacent signais "by J. L. Wong and H. E. King (Microwaves & RF, March 1984), each two-wire propeller can be powered by a coaxial balun of the so-called "balun" type folded ". The two two-wire are then excited in phase quadrature using a hybrid coupler.

The advantage of this method is that it only requires the use of one external hybrid element. However, the balun / adapter assembly used for this type of antennas (made for example from a coaxial section, the core and sheath form dipole) is complex and bulky.

Furthermore, this type of assembly has the disadvantage of forming a kind of band pass filter still too narrow.

A third, more complex technique is described in the document "resonant quadrifilar helix "(resonant quadrifilar propeller) by C.C. Kilgus (Microwave Journal, December 1970) The coaxial supply line is split at its end to constitute a balun. Phase quadrature is ensured by adjusting the length of the strands.

This technique eliminates hybrid couplers. It presents in however the disadvantage of requiring a delicate adjustment of the length of the strands. Moreover, the antenna is no longer symmetrical, and production will be more complex. Furthermore, this method remains specifically reserved for systems using a band of close operation.

In the case of bidirectional antennas, which must ensure the transmission and reception of signals, it is of course necessary to decouple as far as possible the transmit frequency band and receive frequency band, which are generally neighboring.

This is the role of the duplexer, usually placed at the power point of the antenna. Several types of duplexers are known. The document "RF filters and Diplexers for Cellular Applications ", by Gord Neilson and John Mchory (Antem'90) thus present various types of duplexers used in the field of radiocommunication.

In general, these known devices have the disadvantage of being in the form of an independent and complementary element to the antenna. So they train significant footprint, especially in cases where the antennas are large very small.

Furthermore, these are complex elements to be produced and implemented. In consequently, their cost price is high, compared to the cost of the antenna proper.

Finally, these duplexers act as filters, and can therefore introduce loss of useful signal parts.

The invention particularly aims to overcome these various disadvantages of the state of technique.

More specifically, an objective of the invention is to provide an antenna and its power system (thereafter, the term "antenna" includes the antenna itself and its power system) which has two sub-bands which are sufficiently decoupled so as not to require the presence of a conventional additional duplexer.

In other words, the invention aims to provide an antenna bidirectional ensuring simple and efficient duplexing function, without call to known duplexers.

Another objective of the invention is to provide such an antenna, which is of a cost cost of little importance, and easily achievable industrially. In particular, the invention aims to provide such an antenna, which can be manufactured in a very small number of successive operations.

Another object of the invention is also to provide such an antenna, which does not requires specific and complex adjustments.

Yet another objective of the invention is to provide such an antenna (and including its power system), which is compact, compared to to known devices.

The invention also aims to provide such an antenna, which provides a excitation equiamplitude of the four strands and a law in exact phase quadrature, and therefore a good quality of circular polarization, in the two sub-bands.

These objectives, as well as others that will appear later, are achieved according to the invention using a helical antenna with integrated duplexing means, comprising two decoupled coaxial propellers, each formed of radiating strands printed on a substrate, each of said helices being associated with a structure independent and miniaturized broadband feed of said radiating strands, said supply structures being printed on said corresponding substrate and comprising at least one hybrid coupler made from semi-localized elements, so as to reduce the dimensions.

Realization of antenna strands and supply of printed elements allows the antenna, its power supply and the duplexer to be produced in a single operation, without specific connection means, and in a particularly reduced format.

The use of hybrid couplers made from semi-localized elements allows to obtain all the desired qualities, and in particular to reduce the overall size of the assembly, compared to the conventionally used lines.

The two layers forming each of said coaxial helices being perfectly decoupled, this structure directly plays the role of duplexer, without any element additional. The feed points of each of the propellers correspond respectively and directly to the transmit signal and the receive signal.

This gives a very simple, low-cost bidirectional antenna. come back.

Advantageously, said propellers have, when they are laid flat, strands having directions symmetrical with respect to the axis of said antenna, and are wound in opposite winding directions, so that said strands are substantially parallel.

This technique allows the printed side of the internal propeller to face inside, and that of the external propeller towards the outside.

Preferably, in order to increase the decoupling, the excitation points of each of said quadrifilar propellers are offset with respect to each other, in a plane perpendicular to the axis of said propellers. According to an advantageous embodiment, they are offset by 135 °.

The invention can be applied to all types of helical antennas. According to a preferred embodiment, said propeller is a quadrifilar propeller, formed of four radiating strands supplied by a supply structure comprising three couplers hybrids.

Advantageously, in the latter case, said supply structure includes a first 180 ° hybrid coupler combining an input and / or output supplying said antenna with two phase-shifted outputs and / or intermediate inputs of 180 °, and two 90 ° hybrid couplers each associating one of said outputs and / or intermediate inputs of said first hybrid coupler at one end of two said radiating strands.

According to an advantageous embodiment of the invention, said antenna is mounted on a support having first and second separate parts having different permittivities, said first part carrying said radiating strands and said second part carrying said supply structure.

Preferably, said first part carrying the antenna strands has a permittivity greater than 1.

Thus, it is possible to further reduce the size of the antenna.

An antenna as described above can be used alone, or in a network antennas.

The invention also relates to the manufacture of such antennas, which turns out particularly simplified, compared to known techniques.

• impression sur un substrat plan d'au moins deux brins rayonnants, destinés à former une hélice, et d'une structure indépendante d'alimentation miniaturisée large bande desdits brins rayonnants comprenant au moins un coupleur hybride réalisé à partir d'éléments semi-localisés, de façon à en réduire les dimensions ;
• enroulement dudit substrat autour d'un support cylindrique.

According to a first method of manufacturing a resonant helical antenna, the following steps are provided:

• printing on a flat substrate of at least two radiating strands, intended to form a helix, and of an independent broadband miniaturized power supply of said radiating strands comprising at least one hybrid coupler produced from semi-localized elements, so as to reduce its dimensions;
• winding said substrate around a cylindrical support.

• obtention d'un support cylindrique portant un substrat ;
• impression sur ledit substrat d'au moins deux brins rayonnants, destinés à former une hélice, et d'une structure indépendante d'alimentation miniaturisée large bande desdits brins rayonnants comprenant au moins un coupleur hybride réalisé à partir d'éléments serai-localisés, de façon à en réduire les dimensions.

According to a second method of manufacturing a resonant helical antenna, which is even simpler to implement, the following steps are carried out:

• obtaining a cylindrical support carrying a substrate;
• printing on said substrate of at least two radiating strands, intended to form a helix, and of an independent miniaturized broadband power supply structure of said radiating strands comprising at least one hybrid coupler produced from serai-localized elements, so as to reduce the dimensions.

• la figure 1 illustre un exemple d'hélice quadrifilaire à alimentation intégrée selon l'invention, formant la couche externe de l'antenne, développée à plat;
• la figure 2 présente l'hélice de la figure 1, enroulée cylindriquement, de façon à former une première hélice opérationnelle ;
• la figure 3 illustre une seconde hélice quadrifilaire à alimentation intégrée selon l'invention formant la couche interne de l'antenne, développée à plat;
• la figure 4 présente l'hélice de la figure 3, enroulée cylindriquement, de façon à former une seconde hélice opérationnelle ;
• la figure 5 présente une vue en coupe de l'antenne montée, comprenant les hélices des figures 2 et 4, montées en décalage ;
• la figure 6 présente de façon plus détaillée la structure d'alimentation des figures 1 et 3 ;
• les figures 7A à 7C illustrent la conception d'un coupleur -3 dB 90° selon l'invention :
  • figure 7A : coupleur classique en éléments distribués ;
  • figure 7B : représentation correspondante à l'aide de cellules en π ;
  • figure 7C : coupleur en lignes microrubans correspondant ;
  • les figures 8A et 8B illustrent la conception d'un coupleur -3 dB 180°;
  • figure 8A : représentation d'un anneau hybride 180° ;
  • figure 8B : coupleur en lignes microrubans correspondant.
• la figure 9 illustre le rapport d'onde stationnaire (ROS) d'un mode de réalisation particulier de l'antenne des figures 1 et 2 ;
• les figures 10 et 11 présentent des diagrammes de rayonnement mesurés en polarisation circulaire droite et gauche du même mode de réalisation, respectivement aux fréquences 1,98 GHz et 2,2 GHz ;
• la figure 12 montre le découplage (S₂₁) entre les deux hélices.

Other characteristics and advantages of the invention will appear on reading the following description of a preferred embodiment of the invention, given by way of simple illustrative and nonlimiting example, and of the appended drawings among which:

• FIG. 1 illustrates an example of a quadrifilar propeller with integrated feed according to the invention, forming the outer layer of the antenna, developed flat;
• Figure 2 shows the propeller of Figure 1, wound cylindrically, so as to form a first operational propeller;
• FIG. 3 illustrates a second quadrifilar helix with integrated feed according to the invention forming the internal layer of the antenna, developed flat;
• FIG. 4 shows the propeller of FIG. 3, wound cylindrically, so as to form a second operational propeller;
• Figure 5 shows a sectional view of the mounted antenna, comprising the propellers of Figures 2 and 4, mounted offset;
• Figure 6 shows in more detail the supply structure of Figures 1 and 3;
• FIGS. 7A to 7C illustrate the design of a -3 dB 90 ° coupler according to the invention:
  • FIG. 7A: conventional coupler in distributed elements;
  • FIG. 7B: corresponding representation using cells in π;
  • FIG. 7C: corresponding microstrip line coupler;
  • Figures 8A and 8B illustrate the design of a -3 dB 180 ° coupler;
  • FIG. 8A: representation of a 180 ° hybrid ring;
  • FIG. 8B: corresponding microstrip line coupler.
• FIG. 9 illustrates the standing wave ratio (ROS) of a particular embodiment of the antenna of FIGS. 1 and 2;
• FIGS. 10 and 11 present radiation diagrams measured in right and left circular polarization of the same embodiment, respectively at the frequencies 1.98 GHz and 2.2 GHz;
• Figure 12 shows the decoupling (S ₂₁ ) between the two propellers.

The invention therefore relates to an antenna with a broadband feed system and integrated duplexer, produced using a simple manufacturing technique and presenting a low cost.

As indicated above, the invention can be applied to any type of antenna in propellers. The preferred embodiment described above relates to an antenna with quadrifilar propellers.

According to the invention, the antenna therefore has two coaxial propellers ensuring transmission and reception respectively. Each of these propellers is made up of four strands printed on a substrate, on which a structure is jointly printed Power.

Thus, in a single operation, the antenna functions are implemented, feeder and duplexer. This makes it possible to obtain a very compact antenna, and at cost very low cost.

The first helix forming the layer will now be described in detail.

Figure 1 illustrates the printed elements, when developed flat.

First of all, it includes four radiating antenna strands 11 ₁ to 11 ₄ .

A method of determining the characteristics of these strands is for example given in patent FR-89 14952 already cited.

• longueur : 90 mm ;
• largeur : 2 mm ;
• épaisseur : 35 µm ;
• angle d'inclinaison : 54,5°.

The antenna dimensions vary depending on the frequency band and the coverage required. By way of example, the dimensions of these strands can be as follows:

• length: 90 mm;
• width: 2 mm;
• thickness: 35 µm;
• tilt angle: 54.5 °.

They are for example made of copper, on a thin dielectric substrate, such as kapton (ε _r ≈ 3.8).

The four strands 11 ₁ to 11 ₄ are preferably open at their upper end 15 ₁ to 15 ₄ . They can also be short-circuited. However, the system of the invention is particularly suitable for the excitation of antennas with more open strands which, for equal performance, have smaller dimensions than the antennas with short-circuited strands.

The other end 16 ₁ to 16 ₄ of the strands is connected to the feed lines of the supply circuit.

The supply system is produced on the same substrate, as an extension of the antenna. It is made up of three hybrid couplers 12, 13 and 14 designed in elements semi-localized.

The first hybrid coupler 12 is connected on the one hand to the input (respectively output depending on use) 17 signal from the antenna, and the other at the two inputs (respectively outputs) 18 and 19 of the two other couplers 13 and 14. It is a 180 ° hybrid coupler.

The hybrid couplers 13 and 14 are two identical 90 ° couplers. They are connected on the one hand to the input 18 (respectively 19) and on the other hand to the end of the strands 16 ₁ and 16 ₂ (respectively 16 ₃ and 16 ₄ ).

Thus, the four strands are supplied in perfect phase quadrature, on a broadband.

The assembly thus obtained is then wound on a cylindrical support in the counterclockwise, outward (the printed elements being outside the cylinder), to obtain the external propeller, shown in front view in Figure 2.

The cylindrical support is a transparent support from the radioelectric point of view, that is to say having a permittivity close to 1.

It should be noted that it is easy to further reduce the height of the assembly, by using a support of permittivity greater than 1, for the part corresponding to the strands antenna.

FIG. 3 illustrates the elements forming the internal layer of the antenna, shown flat. These elements are quite similar to those described in connection with FIG. 1, except that the antenna strands 51 ₁ to 51 ₄ are inclined in the opposite direction, the winding direction 52 being opposite to the winding direction 17 of the first propeller.

In this example, the dielectric substrate is identical to the first. The system power supply 53 is also in the extension of the antenna strands 511 and 514 and is made of semi-localized elements.

The assembly is then wound inwards (arrow 52) on a support radio-transparent, to provide the internal helix of Figure 4.

The two layers thus obtained are finally mounted concentrically one in the other, as illustrated by the sectional view in FIG. 5.

The outer layer (formed of the outer conductors 61) and the outer layer (formed of internal conductors 62) are offset by an angle α = 135 ° relative to their excitement points.

• des lignes de faible largeur, présentant une caractéristique inductive ;
• des lignes plus larges, présentant une caractéristique capacitive.

FIG. 6 illustrates in a more precise manner the structure for supplying localized elements according to the invention, magnified substantially by a factor of 3 compared to reality. It includes two types of printed lines:

• lines of small width, having an inductive characteristic;
• wider lines, having a capacitive characteristic.

Thus, the 90 ° couplers 13 and 14 each consist of 4 wide elements 31 ₁ and 31 ₄ , connected 2 to 2 by 4 lines of small width 32 ₁ to 32 ₄ . The 190 ° coupler includes 6 wide elements 331 to 336 connected by 6 narrow lines 34 ₁ to 34 ₆ .

Figures 7A and 7C illustrate the design of a -3 dB 90 ° coupler.

Further information can be found, if necessary, in the thesis from M. Coupez, University of Western Brittany, "Study of phase shifter structures potentially integrable at 900 MHz ", May 1988.

FIG. 7A presents a conventional diagram of a -3 dB 90 ° coupler in elements distributed. It includes two sections of line 81, 82 of length λg / 4 and of impedance characteristic Zc, and two sections of line 83, 84 of length λg / 4, and of impedance Z c / √2.

We can replace each of these line sections by cells in π of localized elements, formed of capacitances C and of inductances L and L ', such as illustrated in Figure 7B.

Using the inductive (lines of small width 85) and capacitive properties (wider lines 86) microstrip lines, we can then transform the coupler in distributed elements, as illustrated in FIG. 7C.

We do the same to transform the classic structure of a hybrid ring -3 dB, 180 illustrated in FIG. 8A, in a coupler in semi-localized elements, illustrated in Figure 8B.

• elle est à brins ouverts, donc l'impédance de chaque brin est aisément adaptable à 50 Ω pour une antenne ayant les propriétés souhaitées (couverture hémisphérique et polarisation inverse faible) ;
• la structure d'alimentation utilisant des hybrides est large bande, et parfaitement équilibrée :
  • en amplitude (identique pour chaque brin) ; et
  • en phase (0° ; ± 90° ; ± 180° ; ± 270°) ;
• les dimensions du dispositif d'alimentation sont plus faibles que celles des systèmes connus (un gain de l'ordre de 50 % peut être obtenu). En effet, on constate aisément que chaque élément semi-localisé est de taille très inférieure à la ligne qu'il remplace (qui est généralement d'une taille multiple de λ/4) ;
• l'antenne présente une forte isolation brin à brin.

Such a propeller has the following advantages in particular:

• it is open stranded, so the impedance of each strand is easily adaptable to 50 Ω for an antenna having the desired properties (hemispherical coverage and weak reverse polarization);
• the feed structure using hybrids is broadband, and perfectly balanced:
  • in amplitude (identical for each strand); and
  • in phase (0 °; ± 90 °; ± 180 °; ± 270 °);
• the dimensions of the supply device are smaller than those of known systems (a gain of the order of 50% can be obtained). Indeed, we can easily see that each semi-localized element is very much smaller than the line it replaces (which is generally of a size multiple of λ / 4);
• the antenna has strong strand-by-strand insulation.

As an indication, we now present the measurement results obtained from of a particular embodiment, intended for communications with the materials and for proximity communications.

• diamètre :   26 mm ;
• hauteur :   130 mm;
• poids total :   70 g.

The dimensions of the assembly formed by the antenna and the integrated power supply are as follows:

• diameter: 26 mm;
• height: 130 mm;
• total weight: 70 g.

• émission :   2.17 - 2.2 GHz
• réception :   1.98 - 2.01 GHz
• polarisation : circulaire droite
• couverture : 180°
• ellipticité :   < 5 dB pour  < 90°
     < 2 dB pour  < 75°
• défaut d'omnidirectionnalité : ± 0,6 dB à l'horizon.

The radio characteristics noted are:

• transmission: 2.17 - 2.2 GHz
• reception: 1.98 - 2.01 GHz
• polarization: right circular
• coverage: 180 °
• ellipticity: <5 dB for  <90 °
  <2 dB for  <75 °
• omnidirectionality fault: ± 0.6 dB on the horizon.

In Figure 9 we present the standing wave ratio (ROS) at the input of each antenna, as a function of the frequency of each of the propellers. We see that we obtains a ROS lower than 2 for each antenna, in a band of 400 MHz.

Figures 10 and 11 relate to the radiation patterns measured in right circular polarization (a) and left circular polarization (6), with a dipole operating respectively at 1.98 GHz (Figure 10) and 2.2 GHz (Figure 11) frequencies.

• une ouverture moyenne à -3 dB quasi-hémisphérique supérieure à 180° ;
• une réjection de la polarisation inverse supérieure à -15 dB dans toute la couverture.

We can observe that we obtain:

• an average aperture at -3 dB quasi-hemispherical greater than 180 °;
• rejection of reverse polarization greater than -15 dB throughout the coverage.

Figure 12 shows that the decoupling between the two propellers is greater than 20 dB.

An antenna according to the invention can be produced in several ways.

Thus, according to a first embodiment, the propellers can be printed at flat, as illustrated in FIGS. 1 and 3. They are then rolled up on a support for form the antenna (figures 2 and 4).

According to another, even faster embodiment, the substrate intended for receive the printed elements can be made directly in its cylindrical shape final. In this case, the printing of the strands and the feeding structure is carried out directly on the cylinder.

In addition, it should be noted that, although it can be used individually, the antenna the invention advantageously lends itself to the production of antenna arrays.

Claims (10)

1. Helical antenna operating in two neighbouring frequency bands corresponding respectively to transmission and reception, of the type having two coaxial helices each formed by radiating strands (11₁ to 11₄; 51₁ to 51₄) printed on a substrate,
   characterised in that each of the said helices is associated with an independent feed and duplex structure, also printed on the said substrate and comprising at least one hybrid coupler (12, 13, 14) made from semi-localised elements which are obtained in the following way:

   designing a coupler comprising distributed elements, each section having a length at least equal to _g/4, _g being the maximum operating wavelength of the said antenna;

   determining a corresponding structure comprising localised elements, each of the said sections being replaced with a n cell formed by a capacitor C and two inductors L and L';

   determining a structure comprising semi-localised elements, in which structure each of the said capacitors C is replaced with a broad line (86) and each of the said inductors L and L' is replaced with a narrower line (85),

   so that the said feed and duplex structure has a size smaller than _g/4, sufficient decoupling of the transmission and reception channels and a broad band.
2. Antenna according to Claim 1, characterised in that the said helixes have, when they are placed flat, strands (11₁ to 11₄; 51₁ to 51₄) having symmetrical directions with respect to the axis of the said antenna, and are wound according to opposite winding directions so that the said strands are substantially parallel.
3. Antenna according to either one of Claims 1 and 2, characterised in that the excitation points (61, 62) of each of the said quadrifilar helices are offset with respect to one another in a plane perpendicular to the axis of the said helices.
4. Antenna according to Claim 3, characterised in that the said excitation points (61, 62) are offset by 135°.
5. Antenna according to any one of Claims 1 to 4, characterised in that the said helices are quadrifilar helices, each formed by four radiating strands (11₁ to 11₄; 51₁ to 51₄) fed by a feed structure comprising three hybrid couplers.
6. Antenna according to Claim 5, characterised in that each of the said feed structures comprises a first 180° hybrid coupler (12) associating a feed input and/or output of the said antenna with two intermediate outputs and/or inputs which are 180° out of phase, and two 90° hybrid couplers (13, 14) each associating one of the said intermediate outputs and/or inputs of the first hybrid coupler with one of the ends of two of the said radiating strands.
7. Antenna according to one of Claims 1 to 6, characterised in that at least one of the said helices is mounted on a support having a first and a second separate part with different permittivities, the said first part carrying the said radiating strands (11₁ to 11₄; 51₁ to 51₄) and the said second part carrying the said feed structure.
8. Antenna according to Claim 7, characterised in that the said first part carrying the said radiating strands (11₁ to 11₄; 51₁ to 51₄) has a permittivity which is greater than the permittivity of the said second part.
9. Method of manufacturing a resonant helical antenna with integrated miniaturised duplex and feed means comprising two decoupled coaxial helices, characterised in that it comprises the following steps:

   printing, on a plane substrate, at least two radiating strands (11₁ to 11₄; 51₁ to 51₄) which are intended to form a helix, and an independent miniaturised broadband feed structure for the said radiating strands, comprising at least one hybrid coupler (12, 13, 14) made from semi-localised elements which are obtained in the following way:

   designing a coupler comprising distributed elements, each section having a length at least equal to _g/4, _g being the maximum operating wavelength of the said antenna;

   determining a corresponding structure comprising localised elements, each of the said sections being replaced with a n cell formed by a capacitor C and two inductors L and L';

   determining a structure comprising semi-localised elements, in which structure each of the said capacitors C is replaced with a broad line (86) and each of the said inductors L and L' is replaced with a narrower line (85),

   so that the said feed and duplex structure has a size smaller than _g/4, sufficient decoupling of the transmission and reception channels and a broad band,

   winding the said substrate around a cylindrical support.
10. Method of manufacturing a resonant helical antenna with integrated miniaturised duplex and feed means comprising two decoupled coaxial helices, characterised in that it comprises the following steps:

    obtaining a cylindrical support carrying a substrate;

    printing, on the said substrate, at least two radiating strands (11₁ to 11₄; 51₁ to 51₄) which are intended to form a helix, and an independent miniaturised broadband feed structure for the said radiating strands, comprising at least one hybrid coupler (12, 13, 14) made from semi-localised elements which are obtained in the following way:

    designing a coupler comprising distributed elements, each section having a length at least equal to _g/4, _g being the maximum operating wavelength of the said antenna ;

    determining a corresponding structure comprising localised elements, each of the said sections being replaced with a n cell formed by a capacitor C and two inductors L and L';

    determining a structure comprising semi-localised elements, in which structure each of the said capacitors C is replaced with a broad line (86) and each of the said inductors L and L' is replaced with a narrower line (85),

    so that the said feed and duplex structure has a size smaller than _g/4, sufficient decoupling of the transmission and reception channels and a broad band.

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