EP1192684B1 - Detachable whip antenna, with capacitive load, and method for making a radiating segment of such an antenna - Google Patents

Abstract

The invention concerns detachable whip antennae with capacitive load wherein the load does not need to contribute to the antenna mechanical strength. To achieve this, the entire load (3) is inserted in the conductor strand (2f-21-33-32-2n) of a radiating segment of the antenna, the mechanical strength being provided by a hollow plastic insulating tube (20) reinforced with glass fibres, which acts as support for the conductor strand and as housing for the load and said load consists of a metal enclosure (33) wherein penetrates the insulated part of an electric cable (32).The invention is particularly applicable to whip antennae designed for mobile stations.

Description

The invention relates to a demountable antenna for charging capacitive, whip type, whip antenna in English language; such a antenna, whether removable or not, presents a broad band of operating frequencies. It is known to expand this band further by associating with the antenna a box of agreement, Antenna Tuning Unit in language Anglo-Saxon; this chord box has the role of perfecting the adaptation impedance throughout the useful band.

It is known to produce a whip and load type antenna capacitive in different ways that will be illustrated using the figures 2a, 2b, 2c and the description therein.

But these achievements are not entirely satisfactory because either the antenna is relatively fragile at the level of the capacitive load, that is a mechanical reinforcement should be provided here, which makes the expensive manufacturing.

US Pat. No. 4,958,164 describes a demountable antenna which works in the broadband domain. It consists of several linear radiators arranged in series, one of which has a capacity.

In US Pat. No. 5,836,072 a process is described of an antenna assembly and more particularly the manner of embedding the elements of an antenna with a thermoplastic material.

The object of the present invention is to avoid or, at the very least, to reduce these disadvantages.

This is achieved thanks mainly to a capacitive load specially designed, and arranged not to weaken the antenna.

According to the invention, a demountable antenna is thus proposed. capacitive load, whip type, with several radiating segments distinct from each other and arranged one after the other, each segment with a conductive strand extending over the entire length of the segment, characterized in that at least one of the segments has a capacitive charge, all inserted into its conducting strand, and a tube hollow insulation forming a plastic protectice envelope reinforced with fiberglass which serves as a support for the conductor wire and inside which is accommodated the capacitive load, in that the capacitive load has a first frame constituted by a metal enclosure, a second reinforcement consisting of a section of a conductive wire covered with a sheath insulation, this section of wire being located in the enclosure and at least one of its ends is at the edge of the enclosure and extends out of the enclosure to constitute an access to the second frame.

According to the invention, it is also proposed a manufacturing method of a radiating segment of a demountable antenna, with a capacitive load, of whip type as described in claim 7.

• les figures 1a, 1b des schémas d'antennes fouets,
• les figures 2a, 2b, 2c des parties d'antennes fouets selon l'art antérieur,
• la figure 3, une antenne fouet démontable,
• les figures 4a, 4b, 4c des vues en coupe d'éléments d'antennes fouets selon l'invention,
• la figure 5a, une pièce détachée utilisée dans les antennes selon les figures 4a, 4b et 4c,
• la figure 5b, deux pièces détachées, dont celle selon la figure 5a, telles qu'elles sont associées dans les antennes selon les figures 4a, 4b, 4c,
• les figures 6a à 6d, des schémas qui illustrent différentes étapes du montage de l'élément d'antenne selon la figure 4a.

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

• FIGS. 1a and 1b of antenna patterns whips,
• FIGS. 2a, 2b, 2c of whip antenna parts according to the prior art,
• FIG. 3, a detachable whip antenna,
• FIGS. 4a, 4b, 4c are sectional views of whip antenna elements according to the invention,
• FIG. 5a, a spare part used in the antennas according to FIGS. 4a, 4b and 4c,
• FIG. 5b, two spare parts, including the one according to FIG. 5a, as they are associated in the antennas according to FIGS. 4a, 4b, 4c,
• Figures 6a to 6d, diagrams that illustrate different steps of mounting the antenna element according to Figure 4a.

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

For questions of understanding the drawing the proportions have not always been respected in particular in Figures 4 and 6.

By broadband antenna it will be necessary to understand, in the following, an antenna whose operating band covers more than one octave. To design a whip type antenna, for example for a vehicle and in the band 30 - 88 MHz, it is usual to adopt radiating structure a filiform monopole comprising at least one capacitive load, and to associate this monopole with a box of agreement designed to perfect impedance matching throughout the band useful ; the chord box is comparable to a bandpass filter.

FIG. 1 is a diagram of a broadband whip antenna, 1. This antenna has a vertical monopole consisting of the series of a first conductive strand 2a, a capacitive load 3 and a second conductor strand 2b. The antenna 1 also includes a box 5, arranged between the antenna port and the lower end of the conductor wire, 2a, from the bottom of the monopole.

For its use the antenna 1 is mounted on a plane of mass 4, also called counterweight, which is constituted for example by the metal roof of a vehicle.

Figure 1b is another diagram of a broadband whip antenna band, 1. This antenna with its vertical monopole and box agree, 5, is mounted on a ground plane, 4; it is different from the antenna according to Figure 1b by the constitution of its monopole which includes, in series from the box of agreement 5: a first strand conductor 2a, a first capacitive load 3a, a second strand conductor 2b, a second capacitive load 3b, a third strand conductor 2c, a third capacitive load 3c and a fourth strand driver 2d.

Different ways to realize these capacitive loads in whip antennas are known, they are illustrated by the figures 2a, 2b, 2c where two conductive strands 2a, 2b arranged in the extension of one another, are coupled by a capacitive load which is arranged where the two strands can be detached one of the other and which is constituted only when the two strands considered are assembled end to end.

In the case of Figure 2a the capacitive load requires a dielectric 30 and a metal sleeve 3d: the dielectric insulates the conductive strands 2a, 2b which it covers the ends facing each other while that the sleeve 3d surrounds the dielectric. Capacitive coupling between the strands 2a, 2b is partly carried out directly through the dielectric and in part via successively the dielectric, the metal sleeve and again the dielectric.

In the case of FIG. 2b, the conducting strand 2a is hollow and a dielectric hollow cylinder 30 is inserted into the strand 2a at the upper end of it. The conductive strand 2b has its section at level of its lower end which corresponds to the inner section hollow cylinder; so it can be threaded into this cylinder so that is realized a capacitive load between the ends of the two strands 2a, 2b separated by the dielectric of the cylinder 30. In Figure 2b the strand 2b is shown before depression in the hollow cylinder 30.

In the case of FIG. 2c, the capacitive load is obtained by coupling between two conductive wires 3e, 3f wound on a cylinder insulation 30; the cylinder 30 has its two ends which are solidary respectively strands 2a and 2b; the wires 3e, 3f are welded respectively, at one of their ends, on the strands 2a, 2b and have their other free end, moreover the wires 3e, 3f are isolated one of the other.

In practice the whips with capacitive loads of the kind of charges according to FIGS. 2a, 2b or 2c, show several disadvantages. Indeed the insulating element 30 must ensure, in these two roles: radio role by directly contributing, as a dielectric, to the value of capacitive charge and role mechanical by contributing to the mechanical strength of the whip. But for whips with a height of 2.5 to 3 meters the mechanical stresses can be very severe which requires reinforcements the capacitive loads and increases the price of returns from the antenna.

An overview of a detachable whip antenna is represented in FIG. 3 with a whip and a chord box 5 schematically installed on a ground plane 4 which may be the metallic body of a vehicle. In the example shown the whip can be dismantled into two distinct radiating segments from each other Sa, Sb; the disassembly is done thanks to a ferrule with 2n male thread, located at the upper end of the lower segment Sa and a ferrule to corresponding female thread 2g, located at the lower end of the segment Sb. The Sa segment has a female ferrule at its end lower. The electrical connection between the whip and the chord box is made through a connecting piece with 2m male thread and a spring damping 2r; in FIG. 3 the part 2m and the spring 2r are represented before the piece 2m was made integral with the spring 2r by interlocking in force; the piece 2m and the damping spring are usually an integral part of the chord box.

The antenna that has served as an example for Figure 3 is a Antenna according to the invention with an entire capacitive load arranged in the Sa segment and not, as in the examples according to FIGS. 2a, 2b, 2c, with a capacitive load arranged at where the strands 2a and 2b can be detached from each other.

Figures 4a, 4b, 4c are three views in longitudinal section of the segment Sa of FIG. 3 corresponding respectively to three different positioning heights of the capacitive load to the interior of the radiating segment Sa. In these figures, as elsewhere in Figures 5 and 6, the proportions were not respected for reasons for understanding the drawing; For example, conductive strands according to FIGS. 4 are 1.30 meters long, of which 1 meter long for their conical part, and are only 15 mm in their greatest width and that the ferrules 2n have a total length of 9 cm with a threaded portion on only 2 cm of this length.

The segments according to FIGS. 4a, 4b, 4c comprise a support consisting of a long hollow tube, insulating 20, terminated by two metallic ferrules 2f, 2n and the conducting strand is constituted by the two ferrules and an electrical connection with capacitive load, 3, between the two ferrules. In these embodiments according to FIGS. 4 it is the hollow tube, insulator 20 which ensures the mechanical strength of the segment; it is made up of plastic reinforced with fiberglass and the load 3 is housed at inside this hollow tube.

Figures 5a, 5b show how the load is carried out capacitive 3 in the examples shown in FIGS. This load comprises a metal block 33 represented alone and as if it were transparent, in Figure 5a; this block is constituted by a straight cylinder, with a large cylindrical hole, 3k, which opens into one of the bases of the right cylinder and two small cylindrical holes, 3g, 3h, which open in the other of the bases of the right cylinder; the three holes are parallel to the major axis, not shown, of the right cylinder and the small holes open into the big hole, roughly equal distance from the two bases of the right cylinder.

As shown in FIG. 5b, an electric cable 31 consisting of a conductive wire 32 and an insulating sheath 30, enters the hole 3g, makes a fold, C, inside the hole 3k and leaves the block in crossing the hole 3h. As in Figure 5a block 33 was drawn as if it were transparent; more a snatch in the wall block allows better to see the cable 31 at its fold. Thread 32 of the cable 31 is covered with its insulating sheath only in its part located in and adjacent to Block 33, beyond both bare wires are twisted with each other and the end of this twist is welded in the shell 2n as it appears in FIGS.

In the capacitive load example described, the block 33 is in brass, it has a length of 1 cm and a diameter of 5 mm; both 3g, 3h holes have a diameter of 1.5 mm and a length of 6 mm.

In this capacitive load block 33 constitutes one of the reinforcement while the wire 32, in its part located inside the block, is the other frame.

The 3k hole has a dual role: - it stabilizes the value of the capacity of the load by canceling the edge effect generated by the loop of fold - it facilitates the positioning of the block 33 in the radiating segment, as will be apparent from the description of FIGS. 6b, 6c, 6d. But, alternatively, the block 33 may not have a hole 3k, the holes 3g, 3h extending over the entire length of the block 33 and the fold outside the block.

In another variant the large hole 3k, according to FIGS. can be closed with a metal cap or lid; it results a small gain on the stabilization of the value of the capacity of the load and a slight increase in the cost of the charge.

Alternatively, also, the metal block 33 can take forms other than that of a straight cylinder, it being understood that it must constitute a metal enclosure in which penetrates the isolated part an electric cable; it is even possible that the cable has one of its ends in the metal enclosure and / or the cable is sheathed over almost its entire length.

In the embodiment according to FIG. 4a, the capacitive load 3, housed in the insulating hollow tube 20, is located in the vicinity of the ferrule 2n; it is connected to the ferrule 2f by a tubular metal braid 21 which is pressed against the inner wall of the hollow tube. Here the driver strand goes from ferrule 2f to ferrule 2n, passing successively through the braid metal 21, the capacitive load 3 and the stripped portion and twisted lead wire 3.

In the embodiment according to FIG. 4b, the capacitive load 3 is substantially lodged midway from the ends of the radiating segment and the electrical connection between the two ferrules comprises the same succession of elements than in the embodiment according to Figure 4a; through against the length of the metal braid 21 is half shorter than in the example according to Figure 4a and the length of the stripped portion and twisted output wire of the load 3 goes from ten to centimeters to about fifty centimeters.

In the embodiment according to FIG. 4c, the capacitive load 3 is in direct contact with the ferrule 2f in which it is embedded. Here the electrical connection between the two ferrules 2f, 2n is therefore reduced to two elements: the load 3 and the stripped and twisted part of the lead of load.

Figures 6 are diagrams that illustrate a way of make the conductive strand according to Figure 4a.

FIG. 6a shows a mandrel consisting of a length rod 6, symmetrical of revolution about an axis, with on one side a shoulder which forms a stop 61 and on the other side a post 62. This mandrel has a frustoconical portion whose smallest base is contiguous to the post 62 and whose total length is one meter; this length of the frustoconical portion, compared to the total length of the mandrel which is 1.3 m, shows that the proportions were not respected for the purpose, as indicated above, of making the design easier to understand.

A ferrule 2f is threaded onto the mandrel 6 and comes into contact with the fog 61. A capacitive load 3 of the kind of the load according to the Figure 5b is fitted on the tenon of the mandrel; block 33 of the load plays, with its big hole, the role of mortise in this nesting. Then a section of tubular braid made of tinned copper wire, 21, is fitted on the mandrel and welded at both ends, respectively on the ferrule 2f and on the block 33 of the load 3; this is this braid 21 which requires the presence of the mandrel to avoid being deformed during the coating operation which will be discussed more far.

The chuck equipped according to FIG. 6b is ready to receive a protective shell made of fiberglass-reinforced plastic, for form the insulating hollow tube 20 which was discussed during the Description of Figure 4a. This is a side coating that goes from the wire of output of the load 3 to the level of the stop 61 of the mandrel. For perform this coating different techniques can be put in for example the techniques that make use of coating, glass fibers or fiberglass fabric, these coating materials being pre-impregnated with a resin thermosetting; among the known techniques it is necessary to note: - the winding of glass fibers, - the operation of rolling with a fabric made of glass fibers, - continuous glass fiber removal technique with a machine commercially available under the registered trademark SPIRGLASS. The assembly thus covered with its tube 20 is shown in Figure 6c.

After thermosetting the mandrel can be removed; the element thus obtained is machined to be exact length desired and to allow the cap of a shell 2n which is stuck on the insulating tube 20. It then remains to weld the output wire of the load 3 on ferrule 2n to complete the manufacture of the radiating segment. The Figure 6d shows, in longitudinal section, this completed segment. Sure this figure, as elsewhere in FIGS. 4 and 6b and 6c, the tube 20 has been drawn slightly detached from the shells, the load capacitive, the output wire of the load and the braid when it exists; this representation was intended to better distinguish the elements constituting the conductor strand but, of course, in reality the tube 20 is perfectly plated on the elements it envelops.

Figures 6 deal with the process of manufacturing a segment radiating according to Figure 4a. These figures can be adapted to the making a segment according to FIGS. 4b and 4c respectively in using a shorter mandrel and not using a mandrel; indeed the role of the mandrel is to support the metallic braid when it exists, when depositing fiberglass reinforced plastic.

The present invention is not limited to the examples described or mentioned above, it is thus in particular that various means may be used to replace the ferrules to screws for the assembly of the radiating segments at the end of Other: smooth tubes interlocking into each other, bayonet, snap-in assembly ..., or even ferrules can be, for example, replaced by platelets and the link between two successive segments can be carried out by joining the platelets at the junction and attaching them to one another by means of means of the screw-nut type.

The present invention is particularly intended for antennas for mobile stations, whether these stations are mounted on a vehicle or be of the portable type.

Claims (7)

1. Dismantling-type antenna, with a capacitive load, of whip type, comprising several radiating segments (Sa, Sb) separate from one another and arranged end to end one after the other, each segment comprising a conducting stretch (2f-21-33-32-2n) which extends over the whole length of the segment, characterized in that at least one of the segments includes a capacitive load (3), inserted integrally into its conducting stretch, and a hollow insulating tube (20) forming a protective envelope made of glass-fibre reinforced plastic which serves as a support for the conducting stretch and within which the capacitive load is housed, in that the capacitive load (3) includes a first armature consisting of a metal enclosure (33), a second armature consisting of a length of a conducting wire (32) covered with an insulating sheath (30), this length of wire being located in the enclosure and at least one of its ends being situated at the limit of the enclosure and being extended out of the enclosure so as to constitute an access to the second armature.
2. Antenna according to Claim 1, characterized in that the metal enclosure (33) consists of a block of metal holed along a given path (3g, 3k, 3h), and in that the length of conducting wire (32) is arranged along the given path.
3. Antenna according to either of Claims 1 and 2, characterized in that the conducting wire is a twisted wire each of the ends of which is situated at the limit of the enclosure and is extended out of the enclosure in order to constitute an access to the second armature.
4. Antenna according to one of Claims 1 to 3, characterized in that the capacitive load (3) is arranged in the vicinity of the ferrule (2n) and linked to the ferrule (2f) by means of a tubular metal braid (21) pressed onto the wall of the hollow tube (20).
5. Antenna according to one of Claims 1 to 3, characterized in that the capacitive load (3) is housed substantially at mid-distance from the two ends of the radiating segment.
6. Antenna according to one of Claims 1 to 3, characterized in that the capacitive load (3) is in direct contact with the ferrule (2f).
7. Method for manufacturing a radiating segment (Sa) of a dismantling-type antenna, with a capacitive load (3), of whip type, characterized in that it includes at least the following stages:

   arranging a ferrule (2f) around a mandrel including a first and a second end,

   pushing in the capacitive load (3) including.a metal block (33) and a metal wire (32) covered by its insulting sheath in the immediate vicinity of the block (33), at a first end of the said mandrel,

   arranging a tubular metal braid (21) secured at its two ends, respectively to the ferrule (2f) and to the block (33), around the said mandrel,

   surrounding the assembly thus formed with a protective envelope made of glass-fibre reinforced plastic, the said protective envelope extending between the outlet wire from the load and the second end of the said mandrel,

   subjecting the assembly to a hardening stage,

   withdrawing the mandrel.

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