Half-loop antenna for land vehicle

(54) Half-loop antenna for land vehicle.

(© The antenna 20 is of the half-loop type, that is to say comprising a radiating element in the form of a monopole folded in a plane, loaded at the end by a capacitive element 24. According to the invention, this antenna is arranged above the level of the body of a land vehicle 11 at least of which lateral body elements are made of a conductive material; it is supported by a superstructure element 30 of the vehicle - for example an aerodynamic deflector 32 - substantially planar and disposed above the level of the vehicle body. The monopole is folded in the plane of this superstructure elem ent, and the end I near the supply point 27 as well as the capacitive element 24 are both arranged in the lower part of the superstructure element and electrically connected 31 to the metallic elements, forming an electromagnetic counterweight, of the vehicle body.

FR 2,553,584

Applicants): TECHNICAL COMPANY FOR APPLICATION OF ELECTRONIC RESEARCH. - FR.

\ © Inventeurfs): Jean Choquer and Pierre Weinberg.

(73) Holderfs)

Agents); Cabinet Regimbeau, Corre. Martin, Schrimpf, Warcoin and Ahner.

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Sale of forms to IMPRIMERIE NATIONALE, 27. rue de la Convention - 75732 PARIS CEDEX 15

The present invention relates to an antenna of the so-called half-loop type, that is to say comprising a radiating element in the form of a monopoly folded in a plane, supplied at a coupling point in the vicinity of one of its ends and loaded at its other end by a capacitive element.

The invention provides a means for adapting such antennas - which are already used on board aircraft to a land vehicle, to allow short and long distance links, preferably by using the band 3-25 MHz, for example on a single band 6-7 MHz. Land vehicles generally use vertical whip antennas for transmissions in this band.

The invention is particularly applicable to long-distance road transport vehicles with a high value charge. For these transportations, it appeared recently necessary to develop remote monitoring systems allowing the emission of distress messages or remote control signals of the vehicle, in particular in the event of theft of the latter in isolated regions.

To this end, it seemed necessary to get rid of the conventional whip antenna, which was too easy to spot and neutralize. To find a stolen vehicle, it is indeed necessary that the emission of remote sensing signals go unnoticed by the thief, which supposes an antenna as discreet and undetectable as possible. The invention precisely makes it possible to produce such an antenna.

Another object of the invention, still with a view to this particular application, is to propose an antenna which allows a link without discontinuity for distances varying between a few kilometers and more than a thousand kilometers.

It turns out that whip antennas are not likely to provide such coverage. Their radiation pattern only allows them to ensure direct propagation by ground wave (up to approximately 60 km for the frequency band indicated above), or else indirect propagation by long ionospheric reflection (from 150 km); this latter mode of propagation corresponds to radiation in a direction having a low elevation angle, that is to say a direction which is slightly inclined with respect to the horizon. On the other hand, since the whip antenna practically does not radiate in its axis, the weak radiation for the high elevation angles (that is to say in directions close to the zenithal direction) prevents any link by short ionospheric reflection, corresponding to distances between approximately 60 and 150 km.

The antenna of the invention precisely makes it possible to cover this hole and to ensure a transmission without discontinuity at any distance by simultaneously using all the possible propagation modes (ground wave, short ionospheric reflection, long ionospheric reflection).

Finally, a whip antenna generally needs a reflective plane, at least if one wishes to use it with maximum efficiency, in particular a good radiation diagram. This condition is not fulfilled if the whip is mounted on a vehicle roof of an electrically insulating material, which is more and more often the case with road transport vehicles, the roof of which is often made of a composite material. based on resin and glass fibers.

The antenna according to the invention on the contrary makes it possible to overcome this drawback; its performance and its radiation pattern are in fact little affected by the conductive or insulating nature of the roof of the vehicle.

For this purpose, the antenna is arranged above the level of the bodywork of a land vehicle of which at least the lateral bodywork elements are made of a conductive material, and supported by a substantially flat and arranged vehicle superstructure element. above the level of the bodywork thereof; the monopoly is folded in the plane of this superstructure element, and the end near the coupling point as well as the capacitive element are both arranged in the lower part of the superstructure element and electrically connected to the metallic elements, forming a counterweight electromagnetic, of the vehicle body.

Preferably, the monopole forming a radiating element is folded so as to substantially follow the peripheral rim of the superstructure element. This makes it possible in particular to optimize the performance of the antenna, for an equal surface.

Advantageously, the superstructure element comprises a solid insulating surface, coplanar with the antenna; it is arranged at the front of the vehicle and inclined relative to the horizontal so as to form aerodynamic deflector means.

The dimensions (for the frequency range indicated above) and the shape of the antenna are in particular compatible with the dimensions and shape of the deflectors which are commonly used to reduce the resistance to travel and turbulence, on tractors. towing tall semi-trailers.

Thus, in addition to the fact that the same element makes it possible to ensure at the same time two different functions, the antenna will not be distinguished externally from the deflector, which meets the need for discretion mentioned above, in particular if the coaxial cable of power supply and transmitter are carefully concealed.

The monopole can be formed by a metal frame supporting the deflector; it can also be formed of a conductive track attached to one of the faces of the deflector, or molded with it at the time of manufacture.

In another embodiment, the monopole is folded in a substantially horizontal plane, the superstructure element being made of an insulating material and forming a raised roof of the vehicle. This arrangement is particularly suited to the case of raised vehicles, the folded monopole can also have, in addition to its role as a radiating element, a mechanical role of support or reinforcement of the roof. It will be noted that, as regards the radiation diagram, the fact that it is practically omnidirectional makes it possible to arrange the loop horizontally without significant loss of performance.

Other characteristics and advantages of the invention will appear on reading the detailed description below, made with reference to the appended drawings, in which:

. FIG. 1 is a side view of the antenna according to the invention, in the embodiment where it also forms an aerodynamic deflector,. FIG. 2 is a plan view of the antenna, explaining its structure and its electrical operation,. FIG. 3 is a detail view, in rear perspective, of the deflector of FIG. 1,. FIG. 4 represents a second embodiment, in which the antenna is arranged in a substantially horizontal plane,. FIG. 5 represents a third embodiment, in which the antenna forms a metal support frame, arranged on the roof of the vehicle.

In FIG. 1, the vehicle 10, for example a tractor-trailer, carries the antenna 20, which is integrated into a superstructure element 30, here an aerodynamic deflector.

The antenna is arranged above the roof 11 of the vehicle, in a plane forming an angle Θ with the horizontal. Due to the practically omnidirectional radiation pattern, the angle Θ is not critical, which makes it possible to adjust the position of the superstructure element 30 as a function of the particular mechanical or aerodynamic constraints. Furthermore, the roof 11 is not necessarily made of a conductive material, insofar as it is the metal bodywork elements which form the electromagnetic counterweight to the antenna. A conductive roof, if there is one, however makes it possible to further improve the performance of the antenna by forming a reflective plane for the latter.

FIG. 2 specifies the structure of the antenna 20: this is, conventionally, a half-loop antenna comprising a folded monopole, for example in three segments 21, 22, 23 at the periphery of the deflector. At one of its ends 29, the monopoly is charged at the end by a tunable capacitor 24, the other end of which is connected to ground, for example by means of a metal bar 31 on which the deflector is articulated. The other end 28 is also connected to the earth in the same way, while a supply is provided at a coupling point 25 in the vicinity of the end 28 and at a distance therefrom; the location of the coupling point 25 on the segment 21 is chosen so as to ensure the impedance matching between the supply line and the antenna. The conductive element comprised between the coupling point 25 and the supply point 27 where the coaxial cable 26 opens out thus forms an auxiliary loop for excitation of the main loop constituted by the folded monopoly.

FIG. 3 shows more precisely how this antenna is arranged mechanically on the superstructure element 30. The monopoly has been shown folded in the form of a conductive track attached to the inner face of the deflector 32, but it is also possible to provide a track overmolded with the deflector at the time of manufacture of the latter, or in the form of a mechanical support for the deflector, as will be seen later.

The deflector 32 is articulated around a transverse bar 31 further forming a mass connection by means of the supports 33 and 34 ensuring the mechanical connection and the electrical connection to the lateral bodywork elements of the vehicle. The elements 35 and 36 ensure the positioning of the deflector at the desired angle.

The coaxial power cable 26 leaves the feed point 27 of the antenna, chosen as close as possible to the crossbar 31 for the sake of discretion. In the same vein, the coaxial cable is fixed along this same bar and the support 34, in the vicinity of which it crosses the roof 11 of the vehicle to go towards the transmitter.

FIG. 4 represents another embodiment, in which the monopoly 20 is folded in a substantially horizontal plane, parallel to the ceiling 11 of the vehicle and above it. The assembly is enclosed in a roof made of insulating material 40 corresponding to an elevation of the vehicle. The monopoly can be attached to this raised roof for example by means of insulators 41, but it is also possible to envisage using the antenna to provide a mechanical function for supporting the raised roof; in the latter case, the elements of the folded monopoly are suitably sized and stiffened.

In FIG. 5 is shown another embodiment, in which the superstructure element 50 is merged with the radiating element of the antenna, the three segments 51, 52, 53 of a frame forming the antenna.

This frame is fixed to the bodywork by two fasteners 54 and 55 and held in place by two stiffening elements 56 and 57. At the end of the upright 53 is the tuning capacitor 24.

This antenna-forming frame can serve as a mechanical support for a deflector (whereas previously it was the deflector which supported the antenna), or for any other element placed at the front of the vehicle.

In the figure, these are the three uprights 51, 52, 53 which form the antenna; one could also, as a variant, replace the insulating stiffeners 56 and 57 with conductive stiffeners, the antenna then being formed by the segments 56, 52 and 57 (in this case, the uprights 51 and 53 are insulating or insulated).