GB2077046A - Antenna - Google Patents

Abstract

A radio antenna comprises two components, one in the form of a tube (6) or flattened tube or plate which is constituted by, or the surface of which is covered by, conductors (1) extending generally parallel to the major axis of the tube and serially connected together to form a continuous conductive path, and the other of which is in the form of a winding (2) coaxial with the axis of and surrounding the tube, and the two components are connected together (8), (9) to form a closed loop. The tube may be of dielectric or ferrite material, the conductors consisting of a zig-zag trace deposited on the surface thereof. The antenna may be enclosed in a protective sheath. <IMAGE>

Description

SPECIFICATION Radio aerials This invention relates to radio antennae. Many known radio antennae include a length of conductive wire. In the case of an antenna for a radio receiver mounted in a motor car or other vehicle the wire is commonly between one and two metres in length and is mounted outside the vehicle body. This construction and method of mounting is inconvenient, and exposes the antenna to damage, either accidental or deliberate.

According to one aspect of the invention there is provided a radio antenna comprising a closed conductive loop having a first portion and a second portion, the first portion having parts thereof or associated therewith extending between two spaced guide paths and occupying the surface of a real or imaginary tube whose ends are defined by the guide paths, the second portion being formed as a winding around the tube with its axis parallel to or co-incident with that of the tube.

The tube may be a flattened cylinder so as to produce a more compact structure and may have an internal coating of ferrite material, or may contain or be lined with an insulating foil having such a coating.

According to another aspect of the invention the first portion may be formed as a printed circuit, or other similar structure having conductors on a flat substrate, the circuit being then folded concertina-wise with interleaved insulation between the folds on the conductor side, following which the second portion may be wound around the first and connected to it. Ferrite coated or metallised tape may be interleaved between the folds on the other side.

The invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagram showing the configuration of the first and second portions of an antenna according to the invention, Figure 2 shows one way of realising the first portion, Figure 3 shows a more compact form of the antenna of Fig. 1, Figure 4 shows a method of construction of an alternative form of antenna shown in Fig.

5, and Figure 6 shows alternative conductor patterns for the first portion of the antennae.

As shown in Fig. 1, the antenna comprises a first portion 1, and a second portion 2. The antenna can be connected to a radio receiver (not shown) by a lead 3.

The first portion 1 comprises an electrical, conductor, such as a wire, which starts at a point A and runs therefrom to and fro between lower and upper circular guide paths 4, 5. The two guide paths define the ends of a real or imaginary tube 6 whose outer surface is depicted by the lines 7. In running to and fro between the guide paths 4, 5, the first portion 1 occupies the outer surface 7 of the tube 6. Eventually the first portion 1 completes the surface of the guide paths 4, 5, and is terminated at the point B.

The second portion 2 comprises an electrical conductor, such as a wire, which is wound as a helix between two points C, D, The helix of the portion 2 is coaxial with and external to the tube 6, and is equidistant from the circular guide paths 4, 5.

A closed loop is formed by two strap connections 8, 9. The strap 8 connects the terminal points A, C, and the strap 9 connects the terminal points B, D. The lead 3 is connected to one, e.g. 8, of the straps as shown at E.

An antenna as just described may be realised in different ways. For example, the lead 3 and the antenna may comprise a single length of wire. This could be achieved by taking the lead 3 to the point A, then forming the first portion 1 until the point B is reached, the wire extending thence to the point D, whence it is wound as a helix until the point C is reached.

From the point C, the wire extends to the point E where it is joined to itself to establish a closed loop. Either or both of the first and second portions 1, 2, may be made of Litz wire.

In another construction, the first portion takes the form of a zig-zag trace of conductive material, deposited or otherwise provided, on the surface of a rod or tube of dielectric or ferrite material, the cylindrical surface serving as the outer surface of the tube 6. The second portion 2 comprises an insulated wire which is wound into a helix using the cylinder as a former. The strap connections 8, 9, are then provided, followed by the lead 3. The antenna - excluding the lead 3 - is finally encapsulated for physical protection. This encapsulation may be in the form of a close-fitting sheath made from non-ferrous material such as aluminium alloy without detriment to the antenna performance. The sheath may if desired be suitably shaped, for example for streamlining, if it is to be mounted on the outside of a vehicle, or for decoration.

It is possible to produce the first portion 1 by marking, with an etch resist, the trace of the first portion on one or both of the surfaces of a tuber faced with conductive material: the unmarked material is removed by etching, leaving the first portion 1. Alternatively, a printed circuit technique may be used to produce a conductor pattern on an insulating support, which may be flat and flexible so as to be formed, after printing, into a tube.

In the construction shown in Fig. 2, the first portion 1 comprises insulated wire which is wound toroidally around a tube 6 of nonconducting material. In each turn of the wire 1, one part 10 lies on the outer surface 7 of the tube 6, and another part 11 on the inner surface 1 2 of the tube.

In a further construction, the winding of the first portion can be replaced by a number of conductors situated parallel to the axis of the antenna between two spaced parallel circular guide paths and occupying the surface of a tube whose ends are defined by the guide paths. The conductors are conductively connected together at one end thereof by a circular conductor which occupies the guide path at the said one end of the conductors.

Another circular conductor which occupies the other guide path, conductively connects the other ends of the conductors together.

With this construction, the two circular conductors are respectively connected to the ends D and C of the helix portion 2 by means of the strap connections 8 and 9.

The antenna shown in Fig. 3 is constructed in the same manner as that described in connection with Fig. 1 except that the real or imaginary tube 1 6 is somewhat flattened in order to achieve a more compact construction.

The first portion 21 of the antenna may be laid on the outer surface of the tube, as shown in a zig zag form, or it may be wound as a flet toroid. The antenna is then completed by winding 22 wound around the outside of the winding 21, the ends of the winding 22 being connected as shown to the ends of the winding 21 and one of the junctions is used as the terminal to which the antenna lead 23 is connected.

A further form of the antenna is shown in Figs. 4 and 5 where a flexible substrate 36 carries a conductor winding 31 in the form of a wire or printed circuit conductor progressing in a series of more or less vertical spans across the substrate 36 from one side to the other. The substrate 36 is then folded concertina-fashion to form a compact, vertically elongated body. If the conductors 31 are not themselves insulated, suitable pieces of dielectric material may be interleaved between the folds, and these may be in the form of ferrite tape, or ferrite or metallised tape may be interleaved between the folds on the opposite side as shown at 38. As before, the antenna is completed by a shunt winding 32 which is wound around the longitudinal axis of the structure, as shown in Fig. 5.

Fig. 6 shows alternative conductor patterns that may be used in forming the first portion of the antenna, either forming a continuous winding, as in the construction of Fig. 1, or forming a kind of squirrel cage winding, as described in connection with Fig. 2. The tube may have an internal ferrite layer. The antennae according to the invention, if made symmetrically, are omnidirectional in a plane at right angles to their longitudinal axis, are as effective in transmission as they are in reception, and have minimal sensitivity to ignition interference.

A radio receiver in a motor vehicle has worked satisfactorily when connected to an antenna as described in relation to Fig. 1. The tube measured 2cm. in diameter, with a 4 cm. length between the two guide paths and was mounted inside the vehicle body.

Althouth the antenna has been described in connection with radio receivers in motor vehicles, it has been found that satisfactory television and F.M. audio reception is possible.

Claims (7)

1. A radio antenna comprising one component in the form of a somewhat elongated tube or flattened tube or plate formed of, or the surface of which is covered by conductors extending generally parallel to a major axis of the tube or plate and serially connected together to form a continuous conductive path, and a further component in the form of a winding coaxial with said axis and surrounding the tube or plate, the two components being connected together to form a closed loop.

2. A radio antenna according to claim 1, in which a low-loss ferromagnetic material is closely associated with the first portion.

3. A radio antenna according to claim 2, in which the ferromagnetic material is a thin ferrite layer on a flexible insulating tape.

4. A radio antenna according to any one of the preceding claims, which the first portion is in the form of a wire winding of zig-zag form.

5. A radio antenna according to claim 4, in which the first portion is in the form of a printed circuit.

6. A radio antenna according to claim 5, in which the first portion is in the form of a number of serially connected layers.

7. A radio antenna according to claim 6, in which the layers are formed on a flexible printed circuit in flat form which is subsequently folded concertina-wise into the final multilayer form.