GB2302990A - Dipole antenna - Google Patents

Abstract

Each pole 41, 42 of a centre-fed HF biconical dipole antenna comprises a respective regular tetrahedral spaceframe of metal tubes 411-416; 421-426, an insulating spacer being arranged between the adjoining apices. Mechanical geometry is maintained by insulated halyards 401-406. The antenna is self-supporting and is suitable for deployment at ground level without requiring a mast, insulating spacers 427-429 providing galvanic isolation between the lower pole 42 and the ground. The configuration facilitates transportation, erection and dismantling. Polyhedra other than tetrahedra may be used. Rigid struts may be used instead of halyards.

Description

DIPOLE ANTENNA This invention relates to a dipole antenna, in particular to an antenna of the biconical type.

Antennas of the biconical type are well known to those skilled in the art. A biconical antenna consists essentially of a pair of conical members arranged with their apices adjacent and whose axis of symmetry are substantially co-linear. The conductors of the antenna feeder are connected to the respective apices of the cones.

The present invention arose from an attempt to provide an improved antenna.

In accordance with the invention a self-supporting biconical dipole antenna comprises first and second radiating elements, the elements comprising respective first and second skeletal pyramids of which at least the inclined edges comprise electrically conductive members, and stay means to maintain the first and second radiating elements in predetermined spatial relationship with each other.

This allows the solid conical members of prior art biconical antenna to be implemented as a "spaceframe", the inclined edges of the skeletal pyramids providing electrical perforrnance similar to that of a true cone. Such a construction is particularly advantageous at HF frequencies (3-30 MHz).

An antenna in accordance with the invention is light, easily transportable, and offers minimal wind resistance.

All edges of a pyramid may comprise electrically conductive members. This produces an improved electrical performance, the effective height of the antenna being increased thereby.

Each pyramid may be a regular pyramid. This allows the sloping edges to be of identical construction. All edges of each respective pyramid may be of equal length. This can facilitate transportation and assembly where the antenna has to be erected in the field.

Both pyramids may be substantially identical. Each pyramid may be a tetrahedron. This is particularly advantageous as it allows all edges to be of substantially the same length.

The triangular configuration results in an inherently stable configuration. However, other configurations of pyramid are also possible.

At least the inclined edges of each pyramid may comprise tubular metal members. This results in a relatively lightweight construction. At least one corner of each pyramid may comprise coupler means, each coupler means comprising means to secure the end of a tubular member thereto. This is advantageous where an antenna needs to be rapidly erected, especially in relatively inaccessible terrain where the vehicular access is difficult. The coupler means may comprise a socket arranged to receive the end of a tubular member therein. The members may also be attached together by bolting together via holes drilled in their end, which ends may be flattened. The pyramids may be coupled together at their apices via a dielectric spacer. The stays may comprise rigid dielectric rods extending between the inclined edges of the respective pyramids and rigidly attached thereto.The stays may comprise halyards. Each halyard may extend between a corner of one pyramid and a corner of the other pyramid. While anchoring the halyards at the corners is particularly advantageous, halyards may also be anchored at intermediate positions along the inclined edges. Arranging the halyards to be in tension ensures that the two pyramids maintain their positions with respect to one another. The halyards may comprise a substantially inextensible dielectric rope or ropelike material.

Each pyramid may be arranged to be erected and dismantled into its constituent elements. Alternatively the constituent elements may be permanently attached to each other e.g. by welding or rivetting.

The first and second pyramids may be arranged such that their bases are aligned with each other. This provides a symmetrical arrangement. The first and second pyramids may be arranged such that the apices of one are aligned with the centres of the sides of the other.

The self-supporting design of antennas in accordance with the invention makes such antennas particularly suitable for deployment at ground level. However they may also be mounted above ground using a mast. Ground level deployment offers the advantages that no mast or guy ropes are required, thereby facilitating deployment in confined spaces and on ground in which it is difficult to obtain a good anchorage for guy ropes.

The antenna can just be placed on the ground, or if weather conditions dictate, can be pegged down if the ground is suitable or else simply weighted down. Preferably the lower pyramid is electrically insulated from ground. The insulation may consist of discrete insulators on which the antenna simply rests, or the insulators may be physically attached to the lower pyramid. Alternatively the members constituting the base of the lower and/or upper pyramid may comprise dielectric material. These members may consist entirely of dielectric material or may comprise conductive material having a dielectric coating.

The lightweight and easily transportable nature of the antenna, as well as its suitability for deployment at ground level without the need for mast or towers, makes it particularly suitable for use as an element in an antenna array. It is particularly useful in HF radar applications.

Embodiments of the invention will now be described by way of non-limiting example only with reference to the drawings in which: Figure 1 shows an oblique view of a first embodiment of the invention; Figure 2 shows a plan view of Figure 1; Figure 3 shows a partly sectioned elevation of a portion of Figure 2 on an enlarged scale; Figure 4 shows an oblique view of a second embodiment of the invention; Figure 5 shows an oblique view of a third embodiment of the invention; and Figure 6 shows a plan view of Figure 5.

Referring now to Figures 1 to 3, the antenna has first and second radiating elements 1, 2, comprising first and second skeletal pyramids, each pyramid comprising a regular tetrahedron. The first and second tetrahedra are constructed from tubular members 11, 12, 13, 14, 15, 16 and 21, 22, 23, 24, 25, 26 respectively. All members are of substantially the same length. The tetrahedra 1, 2 are arranged apex to apex such that the base of the first 1 defined by members 14, 15, 16 is aligned with the base of the second 2 defined by members 24, 25, 26. The tetrahedra are held in fixed mutual relationship by insulating spacing members 101, 102, 103 and by insulating spacer 110 disposed intermediate the apices. The upper and lower ends of member 101 are rigidly coupled to respective intermediate portions of members 11 and 21 by fastening means which have not been shown for clarity. In the present embodiment the fastening means comprises a base-clip type clamp which urges the ends of member 101 into engagement with members 11, 21. Any suitable fastener or clamp may however be employed such as a conventional nut and bolt passing through holes in the respective members.

Similarly members 102, 103 are arranged between members 12, 22, and 13, 23 respectively.

As can be seen from Figure 3 the apices of the first and second tetrahedra are somewhat truncated and terminate at respective metal plates 18, 28. Plates 18, 28 are spaced apart by a electrically insulating spacer 110. The inner end of member 11 terminates in a flattened portion and is attached to plate 18 by a countersunk screw 160, washer 161 and nut 162. The inner ends of members 12, 13, 21, 22 and 23 are attached to their associated plates 18, 28 in like manner. Lower plate 28 carries a connector 150 which in the present embodiment is a type N male coupling, the outer conductor of which is galvanically coupled to plate 28. The centre conductor of the connector 150 is galvanically coupled to plate 18 via a conductor 115 via countersunk screw 163, nut 164, solder tag 165 and washer 166.Plates 18, 28 and spacer 110 are secured together by insulated fasteners comprising nylon bolts 121 and nuts 131.

Connection to the antenna is made via cable 140 which extends from coupling 150, through and under the edges of tetrahedron 2 so as not to obscure the field of view of the antenna.

The lower tetrahedron 2 is electrically isolated from the ground on which the antenna rests by insulating members 27, 28, 29.

The total height of the antenna is approximately equal to a quarter wavelength of the frequency at which the antenna is resonant. It thus combines the advantages of a monopole (small height) with a dipole (no ground wires). Its bandwidth is in the order of 20%. Its inherently rigid construction limits wind-induced displacement thus making it particularly suitable for HF radar applications.

It can be seen that the assembled antenna is self-supporting and requires no auxiliary stays or supports to maintain its shape.

A second embodiment, Figure 4, has first and second radiating elements 41, 42 each comprising a regular tetrahedron constructed from six tubular metal members 411-416 and 421426 respectively, arranged in a similar manner to the first embodiment. In this embodiment elements 41, 42 are maintained in alignment by halyards 401-406 comprising substantially inextensible electrically insulating rope-like material. The halyards are arranged to be in tension in the assembled antenna The antenna provides a self-supporting triangulated three-dimensional structure of good mechanical stability.

The lower element 42 rests on insulating members 427, 428, 429 which provides electrical insulation between the antenna and ground. The cable by which connection is made to the antenna has been omitted for clarity.

A third embodiment, shown in Figures 5 and 6, has first and second radiating elements 51, 52 each comprising a regular tetrahedron. As in the previously-described embodiment, each tetrahedron is constructed from six tubular metal members 511-516 and 521-526 respectively. As can be seen from Figure 6, the tetrahedra are arranged with their bases out of alignment such that the apex of one is aligned with the middle of the side of the other. Elements 51, 52 are maintained in alignment by halyards 501-506.

A number of modifications are possible within the scope of the invention. The members constituting the edges may be secured together at the outer corners by any convenient means. For example they may be flattened and drilled to allow them to be bolted together. Alternatively comer pieces may be provided each having a plurality of sockets and/or spigots into or onto which the ends of the tubular members may be fitted. Similar sockets or spigots may be provided where the members meet at the adjacent apices of the tetrahedra. The sockets and/or spigots may be provided with any convenient clamping or securing arrangement such as screw clamps or latching detents to facilitate assembly and dismantling.

By employing one or more discrete insulators in series with the halyards, halyards having relatively poor electrical insulation properties may be employed, the insulators providing the required galvanic insulation between the two halves of the dipole.

Insulators may be provided at the apices of the pyramids, the halyards being attached via the insulators, and/or at one or more intermediate positions along the length of each halyard.

The halyards need not be attached to the apices of the pyramids. One or both ends of the halyards may be attached to intermediate positions along the edges. The halyards may be replaced by rigid dielectric members such as plastics tubing.

While the preferred embodiment utilises regular tetrahedra, any type of pyramid may be employed and the members need not all be the same length.

Claims (23)

1. A self-supporting dipole antenna comprising first and second radiating elements, the elements comprising respective first and second skeletal pyramids of which at least the inclined edges comprise electrically conductive members, and stay means to maintain the first and second radiating elements in predetermined spatial relationship with each other.

2. An antenna as claimed in Claim 1 in which each pyramid is a regular pyramid.

3. An antenna as claimed in Claim 2 in which all edges of each respective pyramid are of equal length.

4. An antenna as claimed in any preceding claim in which the pyramids are substantially identical.

5. An antenna as claimed in any preceding claim in which each pyramid is a tetrahedron.

6. An antenna as claimed in any preceding claim in which at least the inclined edges of each pyramid comprise metal members.

7. An antenna as claimed in Claim 6 in which the metal members are tubular.

8. An antenna as claimed in Claim 6 or 7 in which at least one corner of at least one pyramid comprises coupler means, the coupler means comprising means to secure the end of a member thereto.

9. An antenna as claimed in Claim 8 in which the coupler means comprises a socket arranged to receive the end of a member therein.

10. An antenna as claimed in any preceding claim in which the stay means comprises a plurality of dielectric members, one end of each member being attached to an edge of the first element, the other end being coupled to a corresponding edge of the second element.

11. An antenna as claimed in any one of Claims 1 to 9 in which the stay means comprises a plurality of dielectric members, each member being arranged between an apex of the first pyramid and an apex of the second pyramid.

12. An antenna as claimed in Claim 10 or 11 in which the dielectric members are arranged to be operated in tension.

13. An antenna as claimed in Claim 12 in which the dielectric members comprise a substantially inextensible rope-like material.

14. An antenna as claimed in Claim 13 in which the dielectric members comprise insulator means disposed in series with the rope-like material.

15. An antenna as claimed in any preceding claim in which the first and second pyramids are arranged such that their bases are aligned with each other.

16. An antenna as claimed in any one of Claims 1-14 in which the bases are arranged such that the apices of one are aligned with the centres of the sides of the other.

17. An antenna as claimed in any preceding claim for deployment at ground level in which the second pyramid comprises insulating means arranged to provide electrical insulation between the antenna and the ground on which it rests.

18. An antenna as claimed in Claim 17 in which the insulating means comprises a plurality of insulators coupled to the second pyramid.

19. An antenna as claimed in Claim 17 in which at least those members of the second pyramid constituting its base comprise electrically insulating material, said members constituting the insulating means.

20. An antenna substantially as described with reference to Figure 1, Figure 4 or Figure 5 of the drawings.

21. An antenna according to Claim 1 substantially as described.

22. An antenna as claimed in any preceding claim for use at frequencies in the HF frequency band.

23. An antenna array comprising a plurality of antennas according to any preceding claim.