EP1016165B1 - Radiating cable - Google Patents

Description

The present invention relates to a radiating cable used in particular in the field of cellular telephony or local wireless data transmission networks in the band from approximately 1 MHz to 3 GHz.
Radio coverage of large buildings often requires the installation of dedicated equipment. This coverage is carried out using antennas placed inside the buildings.
The use of radiating cables arranged in the corridors would be technically advantageous, but it often entails prohibitive costs. Indeed, the radiating cables currently installed in tunnels are coaxial cables with patterns of periodic slits. They are expensive, bulky, rigid and difficult to install.

Furthermore, Japanese patent application JP-60038902 discloses a radiating cable comprising two first insulated conductive wires having first ends connected to one of the terminals of an oscillator and two second insulated conductive wires having first ends connected to the other oscillator terminal.
The first wires and the second wires respectively constitute two pairs of wires twisted independently in a retaining sheath. In order to obtain a sufficiently low radiation frequency, the pairs have different helix pitches between them. This difference in pitch is obtained by twisting the two pairs of wires separately.

The objective of the present invention is to provide a radiating cable for the cover of buildings suitable for operating in a strip of high frequency up to around 3 GHz, more flexible, smaller and cheaper than cables known for tunnel applications. Compared to cable coaxial radiating slotted cable performance radiant of the invention are significantly reduced, especially with regard to weakening linear, the speed of propagation and weakening of reflection.

To this end, a high frequency radiating cable comprising first insulated conductive wires having first ends connected to each other, and second insulated conductive wires having first ends connected to each other, the first wires being equal in number to the second wires , and an external retaining sheath containing the first and second wires, is characterized in that the first and second wires are twisted together around a longitudinal axis of the cable, and of the second ends of the first insulated conducting wires and of the second ends of the second insulated conductor wires are connected respectively to the terminals of a load substantially equal to the characteristic impedance of the cable, or to the input terminals of an amplifier means. The output of the amplifier means is for example connected to one end of another radiating cable, or to an antenna.
The wires are thus in an even number, equal to or greater than 4 in the cable of the invention. For example, the cable comprises a quarter of conductive wires joined two by two and substantially symmetrical with respect to the longitudinal axis of the cable. According to another variant, the radiating cable of the invention comprises six insulated conductive wires equally distributed circularly, at the rate of three first wires on one side of a longitudinal diametral plane of the cable and three second wires on the other side of the plane diametral, or else at the rate of a first wire joined between two second wires and vice versa of a second wire joined between two first wires along a circle in cross section.
The connection of the second ends of the first and second conductive wires to a suitable load, that is to say substantially equal to the characteristic impedance of the cable, or to the input terminals of an amplifier means whose output can be connected to another radiating cable or to an antenna, ensures a better performance of the cable compared to the cable defined in application JP-60038902.

The wires are twisted together in a sheath external support, i.e. all wires have the same propeller pitch. Compared to cable according to application JP-60038902, a cable of the invention with first two sons and two second sons has a constant characteristic impedance along the cable and is more flexible and above all is easier to manufacture and therefore less expensive. The sons are twisted together at the same time as putting under holding sheath, or a set of envelopes including the retaining sheath, in a single operation continuously.

In practice, the first ends of the first insulated conductors and the first ends of the second insulated conductors are connected respectively to the external conductors and internal coaxial power cable that provides the link between the radiating cable and a station fixed transmitter / receiver, for example a radio station base of a cellular radio network. This connection can also be ensured by a cable power supply in twisted pairs or cable radiant can directly be connected to the system fixed transmitter / receiver. The first ends a pair of insulated conductors from the cable radiating and the first ends of each other pair of wires insulated from the radiating cable are then connected respectively to two conductors power cable or two system terminals fixed transmitter / receiver.

As will be seen below, although all the conductive wires are twisted simultaneously, the invention positively implements the harmful effects of the radiation of a conventional cable with two pairs of wires which generate crosstalk, and accentuates these effects mainly due to the imbalance of the pairs of wires.
In order to increase the radiation of the cable and the imbalance of the pairs of wires in it, a twist of wires is sometimes a succession of direct propellers, sometimes a succession of retrograde propellers. For example, the direction of the propellers changes every 8 to 12 propeller steps.
Preferably, a twisting section of direct helical wires is separated by a twisting section of retrograde helical wires by a section of cable in which the wires are substantially parallel to the axis of the cable.

For example, either the first conductive wires are arranged alternately with the second conductive wires around a longitudinal axis of the cable, or the set of first conductive wires is substantially symmetrical with the set of second conductive wires with respect to a longitudinal axis of the cable.
The helix pitch of the twisted wires can be between 10 and 50 times approximately the external diameter of the insulated conducting wires.
More generally, the radiation can be increased by causing imbalances between the various elements of the cable. These imbalances can be created by differences in dimensions between the different conductive wires or differences in linear capacities between the different conductive wires. These differences in linear capacitances can result either from different thicknesses of insulating sheaths of the insulated conductive wires, or by insulating materials with different dielectric constants of insulating sheaths of the insulated conductive wires. More generally, at least one of the first conductive wires and at least one of the second conductive wires can differ from one another by at least one of the following three parameters: diameter of conductive core of the wires, thickness of insulating sheath of the wires, and dielectric constant of the insulating sheaths.

According to another variant, the conducting wires isolated can have drowned conductive souls in a cylindrical dielectric sheath.

Linear attenuation of a radiating cable at high frequency very strongly depends on the losses by Joule effect in the conductors. At frequencies preferred cable usage, between 1 MHz and 3 GHz, current conduction takes place almost exclusively on the surface of the conductors. For limit these ohmic losses, the conductivity the periphery of the conductors must be as large as possible and the perimeter of the section conductors should be as large as possible. AT this end, in the radiating cable of the invention, each of the insulated conductors can include an electrically conductive core composed of a central part made of a first conductive material, and a coating surrounding the central part, said coating being of a second material conductive having electrical conductivity greater than that of the central part. The first one conductive material can be aluminum or low alloy aluminum and the second material conductive can be copper or silver, or low alloy copper or silver.

A dielectric tape can surround all of the insulated conductive wires and be surrounded by an external support sheath so as to avoid any sticking between the sheaths of the insulated conductive wires and the external support sheath. This dielectric tape may be made of a material giving the cable better fire resistance; for example the dielectric tape is a mineral tape made of mica or glass silk.
A metallic strip or one or more metallic wires can be wound helically around the insulated conductive wires and extend between the dielectric tape and the external support sheath, so as to improve the maintenance of a constant characteristic impedance along the cable. The metallic strip already removed can be replaced by a metallic screen with openings.
The external retaining sheath can be made of polyethylene, polyvinyl chloride, elastomer or halogen-free flame retardant material depending on the desired environmental properties for the cable.

• la figure 1 est une vue longitudinale en perspective schématique d'un câble rayonnant de l'invention, connecté à une tête de câble ;
• la figure 2 est une vue en coupe transversale schématique du câble rayonnant selon l'invention ;
• la figure 3 est une vue longitudinale en perspective d'une transition à fils conducteurs parallèles à l'axe d'un câble selon une deuxième réalisation de l'invention, située entre des hélices directes des fils et des hélices rétrogrades des fils selon une variante d'une deuxième réalisation de l'invention ;
• la figure 4 est une vue en coupe transversale d'un câble de l'invention avec un ruban diélectrique ; et
• la figure 5 est une vue en perspective longitudinale d'une extrémité d'un câble de l'invention avec un ruban diélectrique et un ruban métallique à déjoint.

Other characteristics and advantages of the present invention will appear more clearly on reading the following description of several preferred embodiments of the invention with reference to the corresponding appended drawings in which:

• Figure 1 is a schematic longitudinal perspective view of a radiating cable of the invention, connected to a cable head;
• Figure 2 is a schematic cross-sectional view of the radiating cable according to the invention;
• FIG. 3 is a longitudinal perspective view of a transition with conductive wires parallel to the axis of a cable according to a second embodiment of the invention, situated between direct helices of the wires and retrograde helices of the wires according to a variant of a second embodiment of the invention;
• Figure 4 is a cross-sectional view of a cable of the invention with a dielectric tape; and
• Figure 5 is a longitudinal perspective view of one end of a cable of the invention with a dielectric tape and a metal strip at a distance.

With reference to FIGS. 1 and 2, a radiating cable CR comprises four identical insulated conducting wires F1 to F4 arranged as in a twisted quarter star.
Each wire comprises a solid conductive core CF, or a strand of thin conductive wires to improve the flexibility of the cable, for example made of annealed copper, and an individual insulating sheath GF which isolates the conductive core from the conductive cores in the other three wires. As a variant, the core of each insulated conductor wire has a central portion of diameter less than a millimeter, made of low or low alloy aluminum, and a coating of thickness of a few tens of micrometres of copper, or low or low alloy silver, surrounding the central part, in order to increase the electrical conductivity at the periphery of the conductive core and thus reduce losses in the cable.
The GF insulating sheath is for example made of polyethylene, polypropylene, polyvinyl chloride, silicone or fluorinated, solid, cellular or double layer materials.
An external retaining sheath G surrounds the insulated conductive wires F1 to F4 and holds them together without being embedded in the retaining sheath G. The retaining sheath G is thin and is made of thermoplastic material, crosslinked or not, or elastomer and can be transparent so as to distinguish the different colors of the individual sheaths GF from the conducting wires F1 to F4.
In the retaining sheath G of tubular form, the wires F1 to F4 are substantially regularly twisted around the longitudinal axis XX of the cable so that in cross section the wires F1 to F4 are arranged at the vertices of a square. According to the illustrated embodiment, the wires F1 to F4 are numbered in ascending order of the numbers 1 to 4 by turning clockwise so that the first wires F1 and F3 are diagonally opposite and the second wires F2 and F4 are diagonally opposite. More generally, according to this configuration, the cable comprises N first wires and N second wires, which are twisted together with a predetermined helical pitch PH and simultaneously sheathed with the holding sheath G and which are, seen in cross section, circularly distributed around the longitudinal axis XX of the cable, each first wire being joined longitudinally to two second wires and vice versa, N being an integer equal to or greater than two.

According to the embodiment illustrated in FIG. 1, first ends E11 and E13 of first wires of the radiating cable CR, such as the diagonal wires F1 and F3 constituting a first pair of wires, have their conductive cores CF which are connected together and at a first end of an external tubular conductor CE of a coaxial supply cable CX, and of the first ends E12 and E14 of second wires of the radiating cable CR, such as the other two wires diagonally F2 and F4 constituting a second pair of wires, have their CF conductors connected to each other and to a first end of an internal conductor CI of the coaxial cable CX. These two sets of 2-to-1 connections are made in a first particular connector CN1 which minimizes any impedance mismatch between the radiating cable CR and the coaxial cable CX.
The other end of the coaxial cable CX is connected to a cable head TC to transmit through the radiating cable CR radiocommunication signals in the downward direction from one or more base stations included in the cable head to mobile radiotelephone terminals and for receiving radiocommunication signals in the uplink direction through the radiating cable CR from the mobile terminals to the base stations. For example, at least one coaxial cable CX is connected to the first ends of radiating cables to quarter CR of the invention arranged on the ceiling of central corridors on the floors of a building and is fixed in a vertical duct of the building up to a second end on the roof of the building where three base stations are installed for FRANCE TELECOM / GSM cellular radiotelephony networks for the band from 890 to 947.5 MHz, SFR / GSM for the band from 902.5 to 960 MHz and BOUYGUES TELECOM / DCS for the band from 1710 to 1880 MHz, as well as transceivers for emergency and paging services at frequencies below 470 MHz or access points for a local data transmission network without wire in the 2.4 GHz to 2.4835 GHz band. Each quadrant radiating cable radiates in the respective floor of the building within a radius of about 20 meters around the cable.
In a second particular connector CN2, second ends E21 and E23 of the first wires F1 and F3 of the radiating cable CR have their conductors CF connected to each other and to a first terminal B1 of a load CH, and of the second ends E22 and E24 of the second wires F2 and F4 have their conductors CF connected to each other and to a second terminal B2 of the load CH. Thus compared to a radiating coaxial cable according to the prior art, each of the external and internal conductors thereof is replaced by two respective wires of the fourth twisted in the radiating cable CR of the invention.

Alternatively, the first and second pairs of F1-F3 and F2-F4 wires connected to each other first and second ends are replaced by other first and second pairs of wires F1-F2 and F3-F4, or F1-F4 and F2-F3, the wires of each of these pairs being located in cross section at ends of one side of the square at the vertices of which insulated conducting wires F1 to F4 are arranged according to figure 2. More generally, seen in section cross, for a 2N twisted wire cable together, N first wires are arranged at the vertices a regular polygon with 2N vertices on one side of a cable diameter, and N second wires are arranged at the vertices of the polygon located on the other side with cable diameter, with N ≥ 2.

By analogy with a phantom circuit for a fourth star abandoned for several decades in telephony, the linear capacity of the radiating cable CR of the invention is deduced from that C _pair of a pair of conductive wires VS CR = 2.5 C pair .

The linear inductance L _CR of the radiating cable CR is equal to the linear inductance L _pair of two pairs of conductive wires placed in parallel: The CR = L pair / 2.

From the following formula of the characteristic impedance Z _CR of the high frequency radiating cable: Z CR = The CR / VS CR the relationship between the characteristic impedances Z _CR and Z _pair of the radiating cable CR and of the pair of wires is deduced: Z CR = Z pair / 2.2.

So, if it is possible to make a cable radiant consisting of a twisted pair of wires conductors usually insulated with GF sheaths made of polyethylene having a diameter approximately equal to double the diameter of the conductive core CF with a characteristic impedance of the order of 110 Ω, it is impossible to design a pair of wires with a characteristic impedance of 50 Ω with polyethylene insulating sheaths. A pair of wires to 50 Ω would be achievable with PVC insulation or another enough dielectric constant material high 4 to 5, but at the expense of others transmission characteristics such that weakening, speed of propagation.

The radiating cable CR of the invention thus reduces the characteristic impedance of a pair at 110 Ω to the characteristic impedance of 110 / 2.2 = 50 Ω. The load CH is thus equal to Z _CR = 50 Ω.
The linear loss α of the radiating cable is: α = R / 2Z CR where R is the linear resistance of the radiating cable and therefore R / 4 that of each conducting wire F1 to F4. At constant characteristic impedance, the linear loss α is chosen as a function of the diameter of the conductor CF of the wires and is all the smaller the larger the diameter of the conductor.

The diameter of the individual sheaths GF and the diameter of the conductive cores CF must be dimensioned in order to have a radiating cable of characteristic impedance 50 Ω and of correct linear loss.
The pairs of wires must not be too “balanced”, that is to say symmetrical, so as to favor the radiation of the cable. For a conductive core diameter CF of 1 to 2 mm and a diameter of insulated conductive wire F1 to F4 and therefore of sheath GF substantially equal to twice, i.e. 1.5 to 4 mm, the wiring pitch, that is that is to say the pitch of the helices PH of the wires, is between 10 and 50 times approximately the diameter of the sheath GF so as not to overly mechanically constrain the wires and maintain the flexibility of the radiating cable CR.

According to a preferred embodiment, a radiating cable CR comprises a twisted quarter with a pitch of propeller PH of approximately 50 mm, or approximately 2000 steps for a maximum length of cable of approximately 100 m. Each of the four wires F1 to F4 has a conductive core CF made of solid annealed copper with a diameter of 1.5 mm and an insulating sheath GF made of solid or cellular polyethylene with an external diameter of 2.8 mm. The external retaining sheath G is made of halogen-free flame retardant material defining the external diameter of the cable of 9.5 mm. For a characteristic impedance of the CR cable of 50 Ω, the linear loss of the cable is 8.5 dB / 100 m at 150 MHz, 15 dB / 100 m at 450 MHz, 21 dB / 100 m at 900 MHz, and from 30 dB / 100 m at 1800 MHz. The coupling losses at 2 m between 150 MHz and 1800 MHz are 70 to 80 dB. In particular, the length of the cable is of the order of approximately 80 m for useful frequencies reaching 2 GHz and approximately 120 m for useful frequencies limited to 1 GHz.
The flexibility of the cable is improved by replacing each solid conductive core CF with a strand of small copper conductive wires, for example a strand of 7 or 19 thin wires.

• le rayonnement est d'autant plus élevé que la symétrie des fils F1 à F4 dans le câble est déséquilibrée ; et
• plus le câble est déséquilibré, plus des désadaptations d'impédance sont rédhibitoires pour la transmission du signal.

   Selon une deuxième réalisation, le rayonnement est augmenté sans trop pénaliser la transmission en déséquilibrant périodiquement la répartition des quatre fils du câble CR. La désadaptation d'impédance engendrée n'est pas répartie sur tout le spectre mais localisée à une fréquence bien précise et aux harmoniques de celle-ci. En pratique, ces fréquences sont des fréquences d'utilisation interdites qui sont sélectionnées en dehors des bandes utiles de radiotéléphonie.
   Dans cette deuxième réalisation montrée à la figure 3, un câble CRa ayant les mêmes caractéristiques dimensionnelles et de matière que celui CR selon la première réalisation diffère de celui-ci par un changement de direction des torsades tous les 500 mm, c'est-à-dire pour un pas de torsade L de 50 mm, le câble comprenant dix hélices directes successives de longueur totale L, puis dix hélices rétrogrades successives de longueur totale L et ainsi de suite. L'inversion de la rotation des torsades crée une désadaptation d'impédance à la fréquence de 400 MHz et à ses multiples 400, 800, 1200, 1600, 2000 MHz. Ces fréquences constituent des fréquences d'utilisation interdites.
   Pour encore augmenter la puissance rayonnée, selon une variante de la deuxième réalisation montrée à la figure 3, l'inversion de l'enroulement hélicoïdal des fils conducteurs isolés F1 à F4 n'est pas effectuée immédiatement pour passer des hélices directes à des hélices rétrogrades et inversement, mais effectuée par l'intermédiaire d'un tronçon de câble de longueur LP dans lequel les fils conducteurs F1 à F4 sont sensiblement parallèles à l'axe XX du câble. La longueur LP peut atteindre environ le pas PH des hélices des fils F1 à F4.
   Selon une autre variante, le déséquilibre du câble est accentué par des différences de dimensions et/ou de diélectriques de gaine par exemple entre les quatre conducteurs CF des fils F1 à F4 ou entre les conducteurs des paires de fils F1-F3 et F2-F4. Plus généralement, au moins deux des 2N=4 fils conducteurs isolés F1-F4 diffèrent entre eux par au moins l'un des paramètres suivants : diamètre d'âme conductrice CF des fils, épaisseur de gaine isolante GF des fils, constante diélectrique des gaines isolantes GF, et matière ou conception de l'âme conductrice CF.To optimize the radiating cable, two contradictory phenomena must be considered:

• the radiation is all the higher as the symmetry of the wires F1 to F4 in the cable is unbalanced; and
• the more unbalanced the cable, the more unacceptable the impedance mismatches for signal transmission.

According to a second embodiment, the radiation is increased without penalizing the transmission too much by periodically unbalancing the distribution of the four wires of the CR cable. The resulting impedance mismatch is not distributed over the entire spectrum but localized at a very precise frequency and at its harmonics. In practice, these frequencies are prohibited use frequencies which are selected outside the useful radiotelephony bands.
In this second embodiment shown in FIG. 3, a CRa cable having the same dimensional and material characteristics as that CR according to the first embodiment differs from this by a change of direction of the twists every 500 mm, that is to say say for a twisting pitch L of 50 mm, the cable comprising ten successive direct propellers of total length L, then ten successive retrograde propellers of total length L and so on. The inversion of the rotation of the twists creates an impedance mismatch at the frequency of 400 MHz and its multiples 400, 800, 1200, 1600, 2000 MHz. These frequencies constitute prohibited use frequencies.
To further increase the radiated power, according to a variant of the second embodiment shown in FIG. 3, the inversion of the helical winding of the insulated conducting wires F1 to F4 is not carried out immediately to pass from direct propellers to retrograde propellers and vice versa, but carried out by means of a length of cable of length LP in which the conducting wires F1 to F4 are substantially parallel to the axis XX of the cable. The length LP can reach approximately the pitch PH of the helices of the wires F1 to F4.
According to another variant, the imbalance of the cable is accentuated by differences in dimensions and / or sheath dielectrics, for example between the four conductors CF of the wires F1 to F4 or between the conductors of the pairs of wires F1-F3 and F2-F4 . More generally, at least two of the 2N = 4 insulated conductive wires F1-F4 differ from one another by at least one of the following parameters: conductive core diameter CF of the wires, thickness of insulating sheath GF of the wires, dielectric constant of the sheaths insulating GF, and material or design of the conductive core CF.

According to other variants of the first and second embodiments, a dielectric separating tape RD shown in FIG. 4 surrounds all of the 2N = 4 insulated conducting wires F1 to F4 and is surrounded by the external retaining sheath G. The tape protects thermally the sheaths GF of the wires F1 to F4 during the extrusion of the holding sheath G and avoids sticking between the sheaths of wire GF and the external holding sheath G. For example, the ribbon RD is made of polyester, polypropylene or even in kraft paper. The RD dielectric tape can also be made of a material giving the cable better fire resistance; for example the RD ribbon is a mineral ribbon made of mica or glass silk.
As shown in FIG. 5, a metallic strip RM is wound helically around the set of 2N = 4 insulated conducting wires F1 to F4, and is preferably introduced over the dielectric strip RD under the external retaining sheath G. The RM ribbon is wound “already”, that is to say two turns of the helix of the metallic ribbon, or of several metallic ribbons, are separated by a helical gap, for example substantially equal to one to two widths of metallic ribbon. At high frequencies, of the order of a gigahertz, the metallic strip RM improves the maintenance of the characteristic impedance Z _CR of the radiating cable CR at a constant value, while allowing a release of radiant energy by the helical gap.
According to another variant, the metal strip already removed is replaced by one or more metallic wires wrapped around the 2N = 4 insulated conductive wires F1 to F4 or dielectric tape RD, leaving gaps, or by any other metallic screen comprising openings likely to let the radiated electromagnetic field pass.
To economically manufacture the cable of the invention, the twisting of the 2N insulated conductive wires, the possible laying of ribbons RD and / or RM, and the extrusion of the retaining sheath G are carried out in a single operation.

Claims (14)

1. A high-frequency radiating cable comprising first insulated conductive wires (F1,F3 ; or F1,F2) having first ends (E11,E13 ; or E11,E12) connected together, and second insulated conductive wires (F2,F4 ; or F3,F4) having first ends (E12,E14 ; or E13,E14) connected together, the number of the first wires equaling that of the second wires, and an outer retaining sheath (G) containing the first and second wires, characterized in that the first and second wires are twisted together about a longitudinal axis (XX) of the cable, and second ends (E21, E23) of the first insulated conductive wires (F1,F3) and second ends (E22, E24) of the second insulated conductive wires (F2, F4) are respectively connected either to the terminals (B1, B2) of a load (CH) substantially equal to the characteristic impedance of the cable, or to input terminals of amplifier means.
2. A radiating cable according to claim 1, wherein the first ends (E11, E13) of the first insulated conductive wires (F1, F3) and the first ends (E12, E14) of the second insulated conductive wires (F2, F4) are respectively connected to two conductors (CE, CI) of a feeder cable (CX), or to two terminals of a fixed emitter/receiver system (TC).
3. A radiating cable according to claim 1 or 2, wherein a twist of wires is sometimes a succession of forward helices and sometimes a succession of retrograde helices.
4. A radiating cable according to claim 3, wherein a wire twist section with a forward helix (L) is separated from a wire twist section with a retrograde helix (L) by a cable section (LP) in which the wires (F1-F4) are substantially parallel to the axis (XX) of the cable (CRa).
5. A radiating cable according to any one of claims 1 to 4, wherein the first conductive wires (F1, F3) are arranged in an alternate manner with the second conductive wires (F2, F4) about a longitudinal axis (XX) of the cable.
6. A radiating cable according to any one of claims 1 to 4, wherein the set of the first conductive wires (F1, F2) is substantially symmetrical to the set of the second conductive wires about a longitudinal axis (XX) of the cable.
7. A radiating cable according to any one of claims 1 to 6, wherein the helix pitch (PH) of the twisted wires lies between approximately 10 and 50 times the outside diameter of the insulated conductive wires (F1-F4).
8. A radiating cable according to any one of claims 1 to 7, wherein at least one of the first conductive wires (F1,F3 ; or F1,F2) and at least one of the second conductive wires (F2,F4 ; or F3,F4) differ from each other in terms of at least one of the following three parameters: diameter of conductive core (CF) of the wires, thickness of insulative sheath (GF) of the wires, and dielectric constant of the insulative sheaths (GF).
9. A radiating cable according to any one of claims 1 to 7, wherein the insulated conductive wires have conductive cores (CF) embedded in a cylindrical dielectric sheath.
10. A radiating cable according to claim 1 or 2, wherein each of the first and second insulated conductive wires (F1,F2,F3,F4) comprises an electrically conductive core made up of a central part and a covering surrounding the central part, said covering being made of a conductive material having an electrical conductivity greater than that of the central part.
11. A radiating cable according to any one of claims 1 to 10, including a dielectric tape (RD) surrounding the set of the insulated conductive wires (F1-F4) and surrounded by the outer retaining sheath (G).
12. A radiating cable according to any one of claims 1 to 11, including a metallic tape with non-contiguous turns (RM) which is wrapped helically around the set of the four insulated conductive wires (F1-F4).
13. A radiating cable according to claim 12 when she depends from claim 11, wherein the metallic tape (RM) extends between the dielectric tape (RD) and the outer retaining sheath (G).
14. A radiating cable according to claim 12 or 13, wherein said metallic tape with non-contiguous turns is replaced by one or several metallic wires or by a metallic shield incorporating openings.

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