EP0851532B1 - Double antenna, in particular for vehicle - Google Patents

Description

The present invention relates to dual antennas, for fixed stations or vehicles and, in particular, but not exclusively, the antennas intended for vehicles on wheels and whose frequencies work fall in the VHF / UHF band commonly called VHF and UHF bands according to their acronym in the literature Anglo-Saxon.

By double antenna is meant an antenna made of several radiating elements and arranged to operate in transmission and / or reception in a first frequency band with a first arrangement of the radiating elements and in a second frequency band with a second arrangement; some of these antennas can be used simultaneously in both bands frequencies.

It is known to make a double antenna with an element radiating unipolar type, for low frequencies, overcome, for high frequencies, a dipole type radiating element fed through the radiating element of unipolar type. Antennas known, of this type, operate in a frequency band which is insufficient for some applications.

The object of the present invention is to avoid or, at the very least, to reduce this drawback in dual two-port antennas.

The study of known double antennas with unipolar antenna surmounted by a dipole, like that described in the DE patent 3826777, shows a mass return from the high frequency channel which is not direct but which passes through a filter located in the low channel frequency; this means that, for proper functioning, the bands frequencies corresponding to the two channels must be strongly distant from each other and that the antenna is therefore not a broadband.

To achieve the desired goal, it is proposed, in particular, in the antenna according to the invention to supply the unipolar antenna with a secondary transformer connected in series with the radiating element of the unipolar antenna.

According to the invention, a double antenna is thus proposed, in particular for a vehicle, characterized in that it comprises: a plane of mass pierced by an orifice, with on one side of the ground plane the space outside the vehicle and on the other side a protected space; a cable coaxial which crosses the orifice, with a first end in space outside the vehicle and a second end in the protected space, the cable forming turns between the orifice and its second end; a connection between the external conductor of the cable and the ground plane at second end level; a radiating element of the dipole type, connected, to be powered, at the second end of the cable; a transformer whose secondary includes the external conductor of turns; an impedance of value equal to the characteristic impedance of the cable ; a power cable; and switching means for, either connect the power cable to the second end of the cable coaxial or couple the power cable to the transformer primary and simultaneously connect the second end of the impedance to the internal conductor of the second end of the coaxial cable.

According to the invention a double antenna is also proposed, in particular for a vehicle, characterized in that it comprises: a ground plane pierced with an orifice, with one side of the ground plane the space outside the vehicle and on the other side a protected space; a coaxial cable passing through the orifice, with a first end in space outside the vehicle and a second end in space protected, the cable forming turns between the orifice and its second end; a connection between the external conductor of the cable and the plane of mass at the second end; a radiant element of dipole type, connected, to be powered, at the second end of the cable ; a transformer whose secondary includes the conductor external of the turns; an impedance of value equal to the impedance cable characteristic; a first and a second cable food; and connection means to authorize a coupling between the first cable and the transformer primary, between the second cable and the second end of the coaxial cable and between the second end of the impedance and the internal conductor of the second end of the coaxial cable.

• la figure 1, une vue simplifiée d'une antenne à monopôle surmonté d'un dipôle,
• les figures 2 et 3, des schémas électriques de l'antenne selon la figure 1, dans chacun de ses deux modes de fonctionnement,
• les figures 4 et 5, des schémas de deux variantes à l'antenne selon la figure 1.

The present invention will be better understood with the aid of the description below and of the figures relating thereto which represent:

• FIG. 1, a simplified view of a monopole antenna surmounted by a dipole,
• FIGS. 2 and 3, electrical diagrams of the antenna according to FIG. 1, in each of its two operating modes,
• Figures 4 and 5, diagrams of two variants of the antenna according to Figure 1.

In the various figures, the corresponding elements are designated by the same references.

The following description considers transmitting antennas but, of course, because of the reversibility of the waves electromagnetic, these antennas can also operate in reception.

Figure 1 shows an antenna with switchable elements. For a better understanding of the drawing, the relationships between dimensions have not been observed in this figure.

The antenna which served as an example for the description which follows track is an antenna intended to operate in the 30-400 band MHz.

The antenna is shown as it is mounted on the roof metallic, M, seen in section, of a vehicle. It includes, under the roof M, a metal case B, seen in section and the content of which will be described more far ; on the roof M, the antenna has radiating elements protected by a radome 3. The radiating elements include a skirted dipole, 1, and a conductive cylindrical section, 20, consisting of the outer conductor of the top of a flexible coaxial cable 2; this coaxial cable passes through the roof M and the lower part is contained in the housing B; cable 2 passes through the roof through a hole circular, with an insulating ring 30 between the cable and the edges of the hole.

The radome, made of dielectric material transparent to waves electromagnetic, keeps the radiating elements in position vertical and makes them integral with the housing B.

In this assembly, the roof M and the housing B constitute a counterweight for the antenna, i.e. a set of conductors which provides the antenna, isolated from the ground, with a mass reference.

The skirted dipole 1 has a vertical conductive bar 11 for its upper part and a skirt 12, formed by a conductive tube with a bottom pierced with a hole, for its lower part. This dipole is fed in its center by the coaxial cable 2; for that the driver internal 21 of the cable is connected, at its upper end, to the end bottom of the vertical bar 11 and the metal braid which constitutes the outer conductor of the cable is connected to the edges of the hole drilled in the bottom of the skirt 12. In FIG. 1, the skirt 12 has only been shown by its traces in the drawing plane, so that you can see how the coaxial cable 2 is connected, at its upper end, to the dipole 1.

Cable 2, after having crossed the roof M to enter the case B, wraps around a ferromagnetic core 5 forming a coil 22 then, towards its lower end, has its external conductor connected to box B and its internal conductor connected to the fourth access of a switch, 7, with five ports and two positions.

Switch 7 is a mechanical switch whose electric control is shown by a broken dashed line 70. The first access of switch 7 is connected to the internal conductor of a coaxial power cable 8 which, coming from outside the housing B, leads to a hole drilled in this housing; the metallic braid of external conductor of the cable 8 is welded to the walls of this hole. The second access of switch 7 is connected, through a resistor 6, to the housing B. The third access is connected, at a point P of the coil 22, to the external conductor of cable 2 and the fifth access is not logged. In its high position, as shown in Figure 1, the switch 7 connects its first access to its third access and its second access to its fourth access while in its position low, it connects its first access to its fourth access and its second access to his fifth access.

Thus, with switch 7, in the low position, the cable 8 and cable 2 are connected end to end inside the case B and everything happens as if the supply of dipole 1 was done by a simple coaxial cable which would have the same origin as cable 8 and which would end, like cable 20, at the center of dipole 1.

With switch 7 in the high position the conductors cables 2 and 8 are always interconnected by through the housing B which serves as a mass reference; however the internal conductor of cable 8 is connected at a point P of the conductor external of the coil 22. The external conductor of the coil 22, with the core 5, constitutes an autotransformer with: a common point connected to ground, a primary located between ground and point P and a secondary located between the mass and the section 20 which was discussed further during the designation of the radiating elements of the antenna. Thus, in the high position of the switch 7, the signal supplied by the cable 8 is applied to the outer conductor of cable 2.

The value of resistance 6 is chosen, purposely, equal to the characteristic impedance of the transmission line constituted by the coaxial cable 2; and when the switch 7 connects this resistor to the lower end of cable 2, line theory shows that everything is electrically as if the resistor were connected between the upper ends of the inner and outer conductors of the cable 2.

In the case where the switch 7 is in the high position, which corresponds to the use of the antenna in the low band, 30-108 MHz, its operating frequencies, the pattern radio antenna can be drawn as shown on the figure 2. In this figure the influence of the skirt 12 of the dipole 1 has been represented by an impedance, 12 ', placed at the end bottom of the skirt. At the frequencies of use considered this impedance is selfic and of negligible value. The influence of resistor 6 discussed above is represented by a resistance 6 'equal to resistance 6 and placed between elements 11 and 12.

The antenna, in its configuration according to FIG. 2, is a unipolar antenna charged by a 12 'inductor which has only one role negligible, and by a 6 'resistor which helps to reduce the overvoltage of this unipolar antenna and therefore to broaden its bandwidth. This unipolar antenna has, at the level of its foot, a ground plane M constituted by the roof of the vehicle, and is powered at its foot thanks to the autotransformer 22-5 on the primary of which the cable is connected supply 8.

In the case where the switch 7 according to FIG. 1 is in low position, which corresponds to the use of the antenna in the high band, 108-400 MHz, its operating frequencies, the antenna radio diagram can be drawn as shown in figure 3.

The antenna, in its configuration according to FIG. 3, is a dipole 11-12 fed in its center by cables 8, 2 placed end to end.

Curves A2 and A1 represent the current distribution which circulates respectively in the unipolar antenna 20, 12, 11 according to the figure 2 and in dipole 11-12 according to figure 3.

• - une longueur totale de chacun des éléments 11, 12 égale aux 5/8èmes de la longueur d'onde à 400 MHz soit sensiblement 45 cm,
• une hauteur totale au-dessus du toit M égale aux 5/8èmes de la longueur d'onde à 108 MHz soit sensiblement 170 cm,
• un diamètre de radôme de 20 mm pour conserver une certaine discrétion à l'antenne,
• une impédance caractéristique de travail de 93 ohms ce qui nécessite d'intercaler un transformateur d'impédance entre le commutateur 7 et le câble 8 pour rendre l'antenne compatible avec les postes standardisés sur une valeur d'impédance caractéristique de 50 ohms ; pour ne garder que les éléments nécessaires à la compréhension de l'invention ce transformateur d'impédance n'a pas été dessiné sur les figures.

The antenna which served as an example for the above description has:

• a total length of each of the elements 11, 12 equal to 5 / 8ths of the wavelength at 400 MHz, ie approximately 45 cm,
• a total height above the roof M equal to 5 / 8ths of the wavelength at 108 MHz, ie approximately 170 cm,
• a radome diameter of 20 mm to maintain a certain discretion on the antenna,
• a characteristic working impedance of 93 ohms which necessitates the insertion of an impedance transformer between the switch 7 and the cable 8 in order to make the antenna compatible with the standardized stations on a characteristic impedance value of 50 ohms; to keep only the elements necessary for understanding the invention, this impedance transformer has not been drawn in the figures.

Figure 4 is the diagram of a first variant on the antenna according to Figure 1. It is a two-port antenna on which two transmitters and / or receivers can be connected respectively but only one of these two transmitters and / or receivers can operate at that time.

The antenna according to FIG. 4 is not distinguished from that according to the Figure 1 only by a 7 'switch whose wiring is different from that of switch 7, and by the presence of two coaxial cables supply 8a, 8b instead of one.

The 7 'switch is a mechanical switch with two positions and five accesses in service; its electric control is figured by a broken arrows 70 '. Cables 8a, 8b, like cable 8 according to Figure 1, come from outside the housing B, terminate respectively in two holes drilled in this case and have the braid metallic of their external conductor which is welded to the wall of the housing; their internal conductors extend respectively up to the second and fourth access of the switch 7 '.

In the high position, as shown in Figure 4, the switch 7 'leaves cable 8a without connection to the antenna, but via its third and fourth access, ensures a connection of the internal conductor of cable 8b with the lower end of the conductor internal of cable 2, that is to say with the high frequency dipole antenna.

In the low position, the switch leaves the cable 8b without connection with the antenna but, via its first and second access, ensures connection of cable 8a with point P, that is to say with the primary of the unipolar antenna power supply autotransformer low frequency. In addition, in the low position, the switch 7 ', via its third and fifth access, connect resistor 6 to the end bottom of the cable's internal conductor 2.

Figure 5 is the diagram of a second variant on the antenna according to Figure 1. It is a two-port antenna on which two transmitters and / or receivers can be connected respectively with, this time, possibility of simultaneous operation of the two transmitters and / or receivers.

The antenna according to FIG. 5 is not distinguished from that according to the Figure 1 that by the absence of the switch, replaced by a duplexer 9, by the presence of two coaxial supply cables 8a, 8b and by specific wiring at the cables and duplexer level. Compared on the antenna according to FIG. 4 where the switching was a switching in space using the 7 'switch, this is a switching in frequencies using the duplexer 9.

The cables 8a, 8b come from outside the housing B, lead respectively into two holes drilled in this housing and have the metallic braid of their external conductor which is soldered to the housing wall while their internal conductors extend respectively to point P by a direct link 90 and to the first input of a duplexer 9, the other input of which is connected to the resistance 6; the output of the duplexer 9 is connected to the lower end of the internal conductor of cable 2 and the earth of the duplexer is connected to the housing B.

Thanks to the duplexer 9 everything happens as if it were the resistor 6 which was connected for low frequencies, i.e. for the unipolar antenna, whereas for the high frequencies, that is to say for the operating frequencies of the dipole antenna, everything is goes on as if cable 8b was connected. It should be noted that the operation of the duplexer requires that the frequency band high and low frequencies are separated from each other by the duplex difference specific to the duplexer used.

• le câble coaxial 2 peut être un câble relativement rigide, afin de ne pas avoir à utiliser de radôme ou du moins de radôme rigide et cela sous réserve de rendre suffisamment rigide l'ensemble 1-2 selon la figure 1,
• à la place de l'autotransformateur 22-5, il est possible d'employer un transformateur dont le secondaire serait constitué, par exemple, par la bobine 22 ; le primaire pourrait être constitué par une autre bobine enroulée autour du noyau 5 au-dessus de la bobine 22 avec une première extrémité reliée à la masse, par exemple en contact avec l'extrémité inférieure du conducteur externe du câble 2 ; la seconde extrémité du primaire du transformateur serait reliée au conducteur qui, sur les figures 1, 4 et 5, aboutissait au point P et qui maintenant n'y aboutirait plus, le point P n'ayant, d'ailleurs, plus de rôle à jouer,
• le barreau vertical 11 peut être de plus ou moins grand diamètre et, par exemple, avoir le même diamètre que la jupe ; il peut également être remplacé par un conducteur filaire chargé par des condensateurs c'est-à-dire par un alignement fait de tronçons conducteurs séparés par des condensateurs avec, par exemple, trois tronçons conducteurs et deux condensateurs,
• le dipôle à jupe 1 peut même être remplacé par toute autre antenne de type dipôle, susceptible d'être employée aux fréquences de travail considérées,
• deux filtres peuvent être introduits pour améliorer l'adaptation de l'antenne au poste auquel elle est destinée : un filtre passe-bas pour le fonctionnement dans la bande des fréquences basses et un filtre passe-haut pour le fonctionnement dans la bande des fréquences hautes,
• les fréquences de travail peuvent, surtout en ce qui concerne les antennes pour stations fixes, se situer dans la bande des ondes décamétriques, couramment dite bande HF selon son sigle dans la littérature anglo-saxonne,
• les commutateurs 7 et 7' peuvent être des commutateurs électroniques.

The invention is not limited to the examples described and drawn; this is how :

• the coaxial cable 2 can be a relatively rigid cable, so as not to have to use a radome or at least a rigid radome, and this subject to making the assembly 1-2 sufficiently rigid according to FIG. 1,
• instead of the autotransformer 22-5, it is possible to use a transformer whose secondary would be, for example, by the coil 22; the primary could be constituted by another coil wound around the core 5 above the coil 22 with a first end connected to ground, for example in contact with the lower end of the external conductor of the cable 2; the second end of the transformer primary would be connected to the conductor which, in Figures 1, 4 and 5, ended at point P and which now would not end there, point P having no more role to play. to play,
• the vertical bar 11 can be of greater or lesser diameter and, for example, have the same diameter as the skirt; it can also be replaced by a wired conductor charged by capacitors, that is to say by an alignment made of conductive sections separated by capacitors with, for example, three conductive sections and two capacitors,
• the dipole with skirt 1 can even be replaced by any other antenna of the dipole type, capable of being used at the working frequencies considered,
• two filters can be introduced to improve the adaptation of the antenna to the station for which it is intended: a low-pass filter for operation in the low frequency band and a high-pass filter for operation in the high frequency band ,
• the working frequencies can, especially with regard to antennas for fixed stations, be situated in the HF band, commonly known as the HF band according to its acronym in Anglo-Saxon literature,
• switches 7 and 7 'can be electronic switches.

Claims (8)

1. Double antenna, in particular for vehicle, wherein it comprises: a ground plane (M) drilled with an orifice, with on one side of the ground plane the space outside the vehicle and on the other side a protected space; a coaxial cable (2) which passes through the orifice, with a first end in the space outside the vehicle and a second end in the protected space, the cable forming turns (22) between the orifice and its second end; a link between the external conductor of the cable and the ground plane at the level of the second end; a dipole type radiating element (1) connected, so as to be fed, to the first end of the cable; a transformer (5, 22) whose secondary comprises the external conductor of the turns; an impedance (6) of equal value to the characteristic impedance of the cable; a feeder cable (8); and switching means for, either coupling the feeder cable to the second end of the coaxial cable or coupling the feeder cable to the primary of the transformer and, simultaneously, linking the second end of the impedance to the internal conductor of the second end of the coaxial cable.
2. Double antenna, in particular for vehicle, wherein it comprises: a ground plane (M) drilled with an orifice, with on one side of the ground plane the space outside the vehicle and on the other side a protected space; a coaxial cable (2) which passes through the orifice, with a first end in the space outside the vehicle and a second end in the protected space, the cable forming turns (22) between the orifices and it second end; a link between the external conductor of the cable and the ground plane at the level of the second end; a dipole type radiating element (1) connected, so as to be fed, to the first end of the cable; a transformer (5, 22) whose secondary comprises the external conductor of the turns; an impedance (6) of equal value to the characteristic impedance of the cable; a first (8a) and a second (8b) feeder cable; and hook-up means (7'; 9, 90) for permitting coupling between the first cable (8a) and the primary of the transformer, between the second cable (8b) and the second end of the coaxial cable (2) and between the second end of the impedance (6) and the internal conductor of the second end of the coaxial cable (2).
3. Antenna according to Claim 2, wherein it comprises the hook-up means comprise a switching device (7') for effecting, under the control of a control signal (70') , either the coupling between the first cable (8a) and the primary of the transformer and the coupling between the impedance (6) and the second end of the coaxial cable (2), or the coupling between the second cable (8b) and the second end of the coaxial cable (2).
4. Antenna according to Claim 2, wherein it comprises the hook-up means comprise a direct link (90) between the first cable (8a) and the primary of the transformer and a frequency switching device (9) for, in a first frequency band, effecting the coupling between the impedance (6) and the second end of the coaxial cable (2) and, in a second frequency band, effecting the coupling between the second cable (8b) and the second end of the coaxial cable (2).
5. Antenna according to one of Claims 1 to 4, wherein it comprises the coaxial cable (2) is a flexible cable and in that it comprises a rigid radome (3), integral with the ground plane (M) and which surrounds the dipole type radiating element (1) as well as that part of the coaxial cable (2) situated in the space outside the vehicle.
6. Antenna according to one of Claims 1 to 4, wherein it comprises the dipole type radiating element (1) is a skirted dipole.
7. Antenna according to one of Claims 1 to 4, wherein it comprises the transformer (5, 22) is an autotransformer whose primary consists of a part of the outside conductor of the turns (22).
8. Antenna according to one of Claims 1 to 4, wherein it comprises the transformer (5, 22) comprises a ferromagnetic core (5) around which the turns (22) are wound.

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