EP1569297B1 - Ultra-wideband V-UHF antenna - Google Patents

Description

The invention relates to an antennal system with a very wide band operating in transmission as in reception without adaptation. It is intended for example for the frequency band varying from 30 to 512 MHz, VHF very high frequencies (in English Very High Frequencies) to UHF ultra high frequencies (Ultra High Frequencies).

This band encompasses in particular conventional bands: the usual VHF-FM band, or VHF frequency modulation of 30 to 88 MHz (or VHF-Frequency Modulation), the VHF-AM or VHF band amplitude modulation of 100 to 160 MHz (in English VHF - Amplitude Modulation) and the UHF-AM band of 225 to 400 MHz (UHF - Amplitude Modulation).

Modern transceiver (E / R) stations are likely to operate in all frequency bands from 30 to 512 MHz. On the other hand, the existing antenna systems associated with them, in particular those intended to be installed on mobile phones, ensure optimal operation only by sub-frequency bands, for example, the VHF-FM band (30-88 MHz). or the VHF-AM band (100-160 MHz) or the UHF-AM band (225-400 MHz). Therefore, the operation of these transceivers requires the implementation of several antennas and a switching device to select the most suitable antenna.

Wide-band antennas for seamless coverage of the entire 30 to 512 MHz band already exist for other radio-frequency systems, such as antennas for aircraft radiocommunication, antennal systems for listening and jamming in electronic warfare, etc. However, these antennas have drawbacks that make them unsuitable for use on a land mobile. Indeed, they have either an efficiency too low for the requested radio range for the ground-ground links, case antennas embedded on aircraft, or a footprint incompatible with the dimensions of the vehicle.

The antenna implementations covering a frequency band reaching the decade and having a small footprint are numerous. For example, patents US 4,443,803 , US 4 466 003 or US 4,958,164 describe such structures. However, these structures are all based on the contribution of resistive elements to artificially widen the bandwidth of the antenna. As a result, much of the RF radio frequency energy is not radiated by the antenna, but is transformed into heat inside the antenna. The output of these types of antenna is therefore very low. Another defect of the radiating structures described in the patents mentioned above is their poor radiation pattern in high frequencies.

Licences DE 3 826 777 or FR 2 758 012 propose so-called multi-band structures, which cover several frequency bands and which do not have the defects previously stated. However, the frequency bands covered by these types of antennas must be disjoined.

The patent US 6,177,911 discloses an antenna for use in a base station used for the mobile radio. The antenna consists of several elements operating in the same frequency ranges. The idea of the present invention is to propose a single antenna capable of operating without discontinuity at least in the entire frequency band of 30 to 512 MHz, ie in more than a decade, and having dimensions such that it can be installed in place of a conventional VHF-FM radiocommunication antenna, that is to say in the form of a whip while having a sufficient performance to ensure radio ranges at least equivalent to those of existing equipment. A representation of such an antenna is schematized on the figure 1 . The whip has a height for example of the order of 3 meters.

The invention relates to a broadband antenna system capable of radiating or receiving radio frequency signals in a given frequency band, comprising at least two substantially collinear radiating elements. It is characterized in that each of the two elements radiates in a frequency band, a first radiating element operating in the frequency band [Fhinf, Fhsup], a second radiating element operating in the band [Fminf, Fmsup], and in that that the first radiating element and the second radiating element are adapted so that, at the hinge frequencies, these two elements involved in the radiation, the system comprises a third radiating element operating in the frequency band [Fbinf, Fbsup], the frequency Fbsup is for example greater than or equal to the frequency Fminf, and the frequency Fmsup is for example greater than or equal to the frequency Fhinf, the radiating elements are connected to a power supply network comprising an input and three outputs respectively connected to the first, second and third elements by three transmission lines, the supply network comprises at least one band-pass filter, a duplexer whose duplex gap corresponds to the filter band and a hybrid 3dB power divider.

• ○ Elle présente un gain supérieur aux systèmes antennaires connus, de même encombrement et couvrant la même bande de fréquences.
• ○ Elle permet de disposer d'une antenne unique, à très large bande, couvrant sans discontinuité plus d'une décade, en particulier de 30 à 512 MHz, et ceci avec un rendement et un gain supérieur aux antennes connues ayant la même bande de fréquences de fonctionnement.

The antenna according to the invention has the following advantages:

• ○ It has a higher gain than the known antenna systems, with the same size and covering the same frequency band.
• ○ It allows to have a single antenna, very broad band, covering without discontinuity more than a decade, in particular from 30 to 512 MHz, and this with a yield and a gain higher than the known antennas having the same band of operating frequencies.

• ○ La figure 1 le schéma d'une antenne selon l'invention,
• ○ La figure 2 le schéma synoptique et le principe de fonctionnement d'une telle antenne,
• ○ Les figures 3a et 3b un exemple détaillé de réalisation d'antenne,
• ○ La figure 4 un détail de réalisation du dispositif d'alimentation et de sa liaison avec l'antenne.

Other features and advantages of the present invention will appear better on reading the following description of an annexed embodiment of the figures which represent:

• ○ The figure 1 the diagram of an antenna according to the invention,
• ○ The figure 2 the synoptic diagram and the principle of operation of such an antenna,
• ○ The Figures 3a and 3b a detailed example of antenna realization,
• ○ The figure 4 a detail of embodiment of the supply device and its connection with the antenna.

The figure 1 represents an example of antenna A installed on a vehicle V. This antenna consists for example of a radiating element 1 which is in the form of a whip, a base 2 which allows to fix the antenna on the carrier vehicle and which usually comprises a power supply network allowing maximum transfer of power from the transceiver to the radiator assembly 1. In order to protect the antenna accidental impacts against obstacles, a flexible element 3 is interposed at its base. This flexible element known to those skilled in the art will not be detailed for reasons of simplification.

• ○ Un ensemble rayonnant 1 constitué de deux dipôles colinéaires 11 et 12 et d'un monopôle 13,
• ○ Un réseau d'alimentation 14 ayant une entrée 15 et trois sorties 16, 17, 18 qui sont connectées respectivement aux dipôles 11, 12 et au monopôle 13 par trois lignes de transmission respectivement 21, 22, 23.

The figure 2 presents the synoptic diagram and the operating principle of an antenna according to the invention, operating in the band of 30 to 512 MHz. The values of this band are given for illustrative purposes and in no way limitative. The antenna A comprises for example:

• ○ A radiating assembly 1 consisting of two collinear dipoles 11 and 12 and a monopole 13,
• A power supply network 14 having an input 15 and three outputs 16, 17, 18 which are respectively connected to the dipoles 11, 12 and the monopole 13 by three transmission lines respectively 21, 22, 23.

The first dipole 11 placed at the top of the radiating assembly 1 is designed to operate in the upper part [Fhinf at Fhsup] of the useful band, for this example of 200 to 512 MHz. To facilitate understanding of the invention, the matching circuit and bandwidth widening devices known to those skilled in the art to grant this dipole in the band 200 to 512 MHz are not detailed.

The second dipole 12 placed below the first dipole 11, covers the adjacent band [Fminf to Fmsup] from 100 to 200 MHz. For the same reason, its adaptation circuit is not described.

The monopole 13 located in the lower part of the antenna (below the other two) ensures operation in the low band [Fbinf Fbsup] from 30 to 100 MHz. The choice of a monopole type structure can be replaced by a dipolar structure. Monopoly makes it possible to obtain a more limited antenna size.

• ○ les signaux Sbh de la bande haute [Fhinf à Fhsup] provenant de l'entrée 15 vers la sortie 16 qui alimente l'élément rayonnant 11,
• ○ les signaux Sbm de la bande moyenne [Fminf à Fmsup] provenant de l'entrée 15 vers la sortie 17 qui alimente l'élément rayonnant 12,
• ○ les signaux Sbb de la bande basse [Fbinf à Fbsup] provenant de l'entrée 15 vers la sortie 18 qui alimente l'élément rayonnant 13.

The power network 14 has the particular function of directing:

• ○ the signals Sbh of the high band [Fhinf to Fhsup] coming from the input 15 to the output 16 which supplies the radiating element 11,
• ○ the signals Sbm of the average band [Fminf to Fmsup] coming from the input 15 to the output 17 which supplies the radiating element 12,
• ○ the signals Sbb of the low band [Fbinf to Fbsup] coming from the input 15 to the output 18 which supplies the radiating element 13.

• ○ A la fréquence de recouvrement Fhinf, choisie égale ou sensiblement égale à Fmsup (pour l'exemple, fréquence de 200 MHz) entre la bande haute et la bande moyenne, le dipôle 11 présente un rayonnement de type demi onde alors que le dipôle 12 présente un rayonnement de type onde entière et en phase avec celui du dipôle 11. Cette mise en phase est obtenue par exemple dans l'exemple donné, en appariant radioélectriquement les longueurs des lignes de transmissions 21 et 22. La répartition de courant sur ces éléments rayonnants est représentée au schéma de la figure 2a.
• ○ A la fréquence de recouvrement Fminf choisie égale ou sensiblement égale à Fbsup (pour l'exemple, fréquence de 100 MHz) entre la bande moyenne et la bande basse, le dipôle 12 présente un rayonnement de type demi-onde alors que le monopôle 13 présente un rayonnement de type onde entière et en phase avec celui du dipôle 12. Cette mise en phase est obtenue dans l'exemple donné en appairant radioélectriquement les longueurs des lignes de transmission 22 et 23. La répartition de courant sur ces éléments rayonnants est représentée au schéma de la figure 2b.

The size of each radiating element 11, 12 and 13 is for example dimensioned so that:

• At the recovery frequency Fhinf, chosen equal to or substantially equal to Fmsup (for the example, frequency of 200 MHz) between the high band and the average band, the dipole 11 has a half-wave type of radiation while the dipole 12 has a radiation of the entire wave type and in phase with that of the dipole 11. This phasing is obtained for example in the example given, by radio-matching the lengths of the transmission lines 21 and 22. The current distribution on these elements radiating is represented in the diagram of the Figure 2a.
• ○ At the recovery frequency Fminf chosen equal to or substantially equal to Fbsup (for the example, frequency of 100 MHz) between the medium band and the low band, the dipole 12 has a half-wave type of radiation while the monopole 13 has a radiation of the entire wave type and in phase with that of the dipole 12. This phasing is obtained in the example given by radioelectrically matching the lengths of the transmission lines 22 and 23. The current distribution on these radiating elements is represented to the scheme of the figure 2b .

This arrangement thus allows the radiating assembly 1 to operate from the lowest frequency Fbinf (in the example given at 30 MHz) to the highest frequency Fhsup (in this example 512 MHz) without hinge frequencies (Fhinf, Fmsup) and (Fminf, Fbsup) the radiation is disturbed thus prohibiting the use of these frequencies as in antennas known from the prior art.

The figure 3a represents an embodiment of an antenna according to the invention and the figure 3b a corresponding sectional view. In order to better visualize the constitution of the antenna, openings are arranged expressly to the figure 3a in certain elements composing the antenna. In this example, the dipoles are skirt dipoles, the references 11, 12, 13 of the figure 2 having been kept for reasons of simplification.

The antenna comprises a first skirt 11 dipole located in its upper part, a second skirt 12 dipole collinear or substantially colinear to the first and a monopole 13 placed at the bottom of the antenna.

The skirted dipole 11 consists of a first radiating element 11a, which can be produced from a tubular section and a second radiating element 11b which is made from a hollow tubular element of length substantially identical to the length of the element 11a and wherein is fed the power cable 21 of the antenna. These two radiating elements are fed at point 11c by connecting the upper end of the core 21a ( Fig.3b ) of the coaxial supply cable 21 at the base of the element 11a and by connecting the shield 21b ( Fig.3b ) of this cable 21 at the periphery of the upper end 11bs of the element 11b to form what is usually referred to as a skirt. In order to optimize the operation of the antenna, an impedance matching quadrupole, not shown for the sake of clarity of figure, may be interposed at the point 11c.

The length of the radiating elements 11a and 11b is for example of the order of a quarter of the wavelength of the hinge frequency Fhinf = Fmsup so that the dipole can radiate half-wave at this frequency. For the given example, Fhinf = Fmsup = 200 MHz and the theoretical length of the quarter-wave in meters is given by the known relation 300 / 4F (Mhz) is 0.375 meters in this example, where F is the frequency expressed in MHz . In order to take into account the edge effect known to those skilled in the art, a shortening factor of 0.8 is taken here and the effective length of the elements 11a and 11b is 0.375 * 0.8 = 0.3 meter.

The colinear skirt dipole 12 is for example composed of a skirt or inverted skirt 12a and a skirt 12b, which together constitute the two radiating elements of the dipole. According to the invention, the length of these skirts is approximately double that of the dipole 11, in this example about 0.6 meters so that this dipole radiates in full wave at the hinge frequency Fhinf = Fmsup. To electrically isolate the skirt 12a of the coaxial cable 21 which passes therethrough, a skirt 12d having the role of an insulation device usually designated by the word "stub" is interposed between these two elements. The periphery of the upper end 12ds of the skirt 12d is connected to the shield 21b, while its other end 12di is connected to the lower part of the skirt 12a. The supply of this dipole is carried out at level 12c in connecting the upper end of the core 22a of the coaxial supply cable 22 to the lower edge of the isolation device 12d at point 12e and connecting the shield 22b of this cable 22 and the shield 21b of the cable 21 around the upper end 12bs of the skirt 12b. As mentioned above, it is possible to use an impedance matching quadrupole.

The monopole 13 is for example in the form of a counter skirt. Its lower end 13i is connected on its periphery to the shields 21b and 22b of the coaxial cables 21 and 22. According to the invention, the length of this counter skirt is approximately twice that of the skirts of the dipole 12, ie about 1.2 meters in this case. example, so that this monopole radiates in full wave at the hinge frequency Fminf = Fbsup = 100 MHz.

To radio-electrically isolate this monopole 13 of the ground plane M above which the antenna is installed, the cables 21 and 22 are wound around a core of known magnetic material 24, such as ferrite, powder iron, etc. This makes it possible to constitute a coil 25 whose impedance presented in the frequency band [Fbinf at Fbsup], is an impedance clearly greater than the own impedance of the monopole 13 in the same frequency band. The supply of this monopole is performed by connecting the upper end of the core 23a of the cable 23 to one of the turns of the winding 25 at the point 26 determined to obtain the best impedance matching in the frequency band [Fbinf at Fbsup ].

In the usual manner, in order to improve the decoupling between the radiating elements 11, 12, 13, insulation devices acting as a shock-inductor, such as devices based on ferrite beads, toroids or tubes of ferrite are interposed between these elements.

At the ground plane M, the shields 21b, 22b, 23b and the ground of the supply network 14, are connected thereto by the connection assembly 30. The lower ends of the cores of the coaxial cables 21, 22 and 23 are respectively connected to the outputs 16, 17 and 18 of the supply network 14, an exemplary embodiment of which is detailed in FIG. figure 4 . According to this figure, the radio frequency signal from the input 15 is divided in two by a hybrid 27 to the two channels 27a and 27b. The first channel 27a is filtered by a bandpass filter [Fminf - Fmsup] 28, for the exemplary embodiment [100MHz - 200MHz] and constitutes after filtering the output 17. The other channel 27b is separated by a duplexer 29 into two sub-bands, one low [Fbinf - Fbsup] or [30MHz - 100MHz] for the exemplary embodiment and the other high [Fhinf - Fhsup], ie [200MHz - 512MHz]. The low sub-band is connected to the output 18 and the high sub-band is connected to the output 16.

The example given to Figures 1 to 4 also applies to a broadband antenna capable of radiating or receiving radio frequency signals in a frequency band [Fminf, Fhsup], comprising two substantially collinear radiating elements (11, 12). The radiating element (11) operates in the frequency band [Fhinf, Fhsup], the radiating element (12) operates in the band [Fminf, Fmsup], and at the hinge frequencies between these two elements they both participate in the radiation.

The frequency Fmsup is greater than or equal to the frequency Fhinf.

Claims (6)

1. A wideband antenna system capable of radiating or receiving radio-frequency signals in a given frequency band, comprising at least two substantially collinear radiating elements (11, 12), characterised in that each of said two elements (11, 12) radiates in a frequency band, with said first radiating element (11) operating in the Fhinf to Fhsup frequency band, said second radiating element (12) operating in the Fminf to Fmsup band, and in that said first radiating element (11) and said second radiating element (12) are adapted so that at the hinge frequencies between two adjacent elements these two elements participate in the radiation, with said system comprising a third radiating element (13) operating in the Fbinf to Fbsup frequency band, with the frequency Fbsup being greater than or equal to the frequency Fminf, and the frequency Fmsup being greater than or equal to the frequency Fhinf, said radiating elements (11, 12, 13) being connected to a power supply network (14) comprising one input (15) and three outputs (16, 17, 18) respectively connected to said elements (11, 12, 13) by three transmission lines (21, 22, 23), said power supply network (14) comprising at least one band-pass filter (28), one duplexer (29), the duplex gap of which corresponds to the band of said filter (28), and a hybrid 3dB power splitter (27).
2. The antenna system according to claim 1, characterised in that the lengths of said transmission lines (21, 22, 23) are selected so that the RF signals at the Fhinf to Fmsup frequencies feed said first and second radiating elements (11, 12) in phase, and in that the RF signals at the Fminf to Fbsup frequencies feed said second and said third radiating elements (12, 13) in phase.
3. The antenna system according to claim 2, characterised in that at the Fhinf to Fmsup frequencies, said first radiating element (11) radiates in half waves.
4. The antenna system according to claim 2, characterised in that at the Fminf to Fbsup frequencies, said second radiating element (12) radiates in half waves.
5. The system according to claim 2, characterised in that said second element (12) radiates in full waves for Fhinf to Fmsup and said third element (13) radiates in full waves for Fminf to Fbsup.
6. The system according to claim 1, characterised in that said first and second radiating elements (11, 12) are dipoles and said third radiating element (13) is a monopole.

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