WO1997050146A1

WO1997050146A1 - Plastic coated axial antenna

Info

Publication number: WO1997050146A1
Application number: PCT/IL1997/000199
Authority: WO
Inventors: Kenneth E. Crowell
Original assignee: Galtronics Ltd.
Priority date: 1996-06-24
Filing date: 1997-06-18
Publication date: 1997-12-31
Also published as: AU3104997A; IL118721A0

Abstract

A plastic coated axial antenna (12) including a metal antenna element (22) surrounded by a foamed plastic material (24) is provided as well as a portable radio device (10), such as a cellular telephone comprising a transceiver and the plastic coated axial antenna (22). The foamed plastic is a thermosetting plastic, preferably polyurethane, or any other such plastic/polymer. Preferably, the foamed plastic material forms a relatively lower density core (26) and a relatively higher density exterior skin (28).

Description

PLASTIC COATED AXIAL ANTENNA

FIELD OF THE INVENTION

The present invention relates to antennas generally and more particularly to plastic coated axial antennas and to methods of manufacture thereof. BACKGROUND OF THE INVENTION

Various types of plastic coated axial antennas are known in the art and in the patent literature. The following U.S. Patents are believed to represent the state of the art:

5,446,469; 5,467,096; 5,469,177; 5,479,178; 5,341,149; 4,246,568; 4,435,713; 4,695,845;

4,725,395. The state of the art technique for manufacturing plastic coated axial antennas employs injection molding of a thermoplastic resin over a metal antenna element, which is often in the form of a coil. Often, the pressures encountered during injection molding cause deformation of the metal antenna element, which can cause degradation of antenna performance or antenna failure. SUMMARY OF THE INVENTION

The present invention seeks to provide an improved plastic coated axial antenna.

There is thus provided in accordance with a preferred embodiment of the present invention a plastic coated axial antenna comprising a metal antenna element surrounded by a foamed plastic material.

There is additionally provided in accordance with a preferred embodiment of the present invention a portable radio device, such as a cellular telephone comprising a transceiver and a plastic coated axial antenna comprising a metal antenna element surrounded by a foamed plastic material. It is noted that in the specification and claims, the term "portable radio device" refers to any communication device which communicates via an antenna.

In accordance with a preferred embodiment, the foamed plastic is a thermosetting plastic, preferably polyurethane, or any other such plastic/polymer. Preferably, the foamed plastic material forms a relatively lower density core and a relatively higher density exterior skin

In accordance with a preferred embodiment of the present invention, the relatively lower density core has an axial hollow core Alternatively, a dielectric hollow core defining element may be disposed in the relatively lower density core In accordance with a further preferred embodiment of the present invention, a wire may be axially disposed in the relatively lower density core

There is also provided in accordance with a preferred embodiment of the present invention a method of manufacture of a plastic coated antenna including the steps of providing a metal antenna element and molding a foamed plastic about the metal antenna element

In accordance with a preferred embodiment of the present invention, the step of molding includes centrifugal casting Preferably, the centrifugal casting is carried out about a non-vertical axis of rotation The present invention is characterized by the synergistic effects of improved antenna performance and greatly reduced manufacturing cost

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which

Fig 1 is a pictorial illustration of a portable radio including an antenna constructed and operative in accordance with a preferred embodiment of the present invention,

Figs 2A, 2B, 2C and 2D are sectional illustrations of three alternative embodiments of an antenna constructed and operative in accordance with a preferred embodiment of the present invention, Fig 3 is an exploded view illustration of a centrifugal casting technique used in manufacture of antennas in accordance with a preferred embodiment of the present invention, and

Fig 4 is a sectional illustration of a portion of a centrifugal casting technique as illustrated in Fig 3 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to Figs. 1 - 2D which illustrate a portable radio 10 including an antenna 12 constructed and operative in accordance with a preferred embodiment of the present invention and three alternative embodiments of that antenna. The portable radio 10 may be any suitable portable radio or cellular telephone, such as equipment manufactured, for example, by Motorola, Nokia, Ericsson and others.

In accordance with a preferred embodiment of the present invention, the antenna 12 is a plastic coated axial antenna comprising a metal antenna element surrounded by a foamed plastic material. Preferably, the foamed plastic is a thermosetting plastic, preferably polyurethane, and forms a relatively lower density core and a relatively higher density exterior skin.

Fig. 2 A shows one embodiment of the antenna of the present invention which includes a base 20, which is electrically connected to a metal antenna helical element 22 about which is cast a foamed plastic material 24 defining a relatively lower density core 26 and a relatively higher density exterior skin 28. A cap element 30 may be provided at the top of the antenna.

Fig. 2B illustrates an alternative embodiment of the antenna of Fig 2 A, which includes a base 40, which is electrically connected to a helical metal antenna element 42 about which is cast a foamed plastic material 44 defining a relatively lower density core 46 and a relatively higher density exterior skin 48. A cap element 50 may be provided at the top of the antenna. In this embodiment, as distinct from that of Fig. 2 A, a dielectric hollow core defining element 52, such as an elongate tube, is provided axially over the helical metal antenna element 42.

Fig. 2C illustrates a further alternative embodiment of the antennas of Figs. 2 A and 2B, which includes a base 60, which is electrically connected to a helical metal antenna element 62 about which is cast a foamed plastic material 64 defining a relatively lower density core 66 and a relatively higher density exterior skin 68. A cap element 70 may be provided at the top of the antenna. In this embodiment, as distinct from that of Fig. 2B, a dielectric hollow core defining element is not provided but nevertheless an axial hollow core 72 is present. Fig. 2D illustrates a further alternative embodiment of the antennas of Figs. 2A and 2B, which includes a base 73, which is electrically connected to a helical metal antenna element 74 about which is cast a foamed plastic material 75 defining a relatively lower density core 76 and a relatively higher density exterior skin 77. A cap element 78 may be provided at the top of the antenna. In this embodiment, as distinct from that of Fig. 2B, an axial wire 79 is disposed in the relatively lower density core 76.

Reference is now made to Figs. 3 and 4, which illustrate a method of manufacture of a plastic coated antenna including the steps of providing a metal antenna element and molding a foamed plastic about the metal antenna element. In accordance with a preferred embodiment of the present invention, the step of molding includes centrifugal casting. Preferably, the centrifugal casting is carried out about a non-vertical axis of rotation. Fig. 3 illustrates in a very general way a centrifugal casting machine 80 having an axis of rotation 82, which is tilted with respect to the vertical, represented by axis 84, typically by a 45 degree angle. Alternatively, axis of rotation 82 may be substantially vertical.

The centrifugal casting machine 80 typically includes a rotating plate 86 which is disposed in a plane substantially perpendicular to axis 82 for rotation thereabout. A plurality of radially directed cavities 88 are disposed in plate 86 and antenna base and coil assemblies 90 are disposed therein. As seen in Fig. 4, corresponding cavities 92 are formed in an upper plate 94 which is positioned in sealing engagement with plate 86 and plastic material, preferably thermosetting material, is supplied to the cavities via supply conduits 96 from a reservoir 98, as both plates 86 and 94 rotate together about non-vertical axis 82.

It is a particular feature of the present invention that molding of the antennas is carried out at very low pressures, approximating atmospheric pressure, thus avoiding defor- mation of and consequent damage to assemblies 90, which occurs often when injection molding techniques are employed to produce antennas of this type in accordance with the prior art.

It is also a particular feature of the present invention that the resulting foamed plastic antennas have enhanced electrical performance as compared with prior art antennas made by injection molding, inasmuch as the foamed plastic antennas have lower densities than the prior art antennas.

It is thus appreciated that the present invention realizes synergistic effects of improved antenna performance and greatly reduced manufacturing cost.

It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims which follow:

Claims

C L A I M S What is claimed is:

1. A plastic coated axial antenna comprising a metal antenna element surrounded by a foamed plastic material.

2. A plastic coated axial antenna according to claim 1 and wherein the foamed plastic is a thermosetting plastic.

3. A plastic coated axial antenna according to claim 2 and wherein said thermosetting plastic is polyurethane.

4. A plastic coated axial antenna according to any of claims 1 - 3 and wherein foamed plastic material forms a relatively lower density core and a relatively higher density exterior skin.

5. A plastic coated axial antenna according to any of claims 1 - 3 and wherein said relatively lower density core has an axial hollow core.

6. A plastic coated axial antenna according to any of claims 1 - 3 and wherein a dielectric hollow core defining element is disposed in said relatively lower density core.

7. A plastic coated axial antenna according to any of claims 1 - 3 and wherein a wire is axially disposed in said relatively lower density core.

8. A portable radio device including a transceiver and a plastic coated axial antenna comprising a metal antenna element surrounded by a foamed plastic material.

9. A portable radio device according to claim 8 and wherein the foamed plastic is a thermosetting plastic.

10. A portable radio device according to claim 9 and wherein said thermosetting plastic is polyurethane.

11. A portable radio device according to any of claims 8 - 10 and wherein foamed plastic material forms a relatively lower density core and a relatively higher density exterior skin.

12. A portable radio device according to any of claims 8 - 10 and comprising a cellular telephone.

13. A method of manufacture of a plastic coated antenna including the steps of providing a metal antenna element and molding a foamed plastic about the metal antenna element.

14. A method according to claim 13 and wherein the step of molding includes centrifugal casting.

15. A method according to claim 14 and wherein the centrifugal casting is carried out about a non- vertical axis of rotation.

16. A method according to either of claims 13 and 14 and wherein the foamed plastic is a thermosetting plastic.

17. A method according to claim 16 and wherein the thermosetting plastic is polyurethane.

18. A method according to either of claims 13 and 14 and wherein the foamed plastic material forms a relatively lower density core and a relatively higher density exterior skin.