GB2242573A - Antenna assembly - Google Patents

Abstract

A two-piece antenna (1) assembly, especially for a portable cellular radio (2), comprises a housing (4) enclosing an impedance matching network (L, C1, C2; see Figure 2), and a separate antenna (3). The antenna (3) is screw-fitted onto the housing (4) and so can easily be replaced if it is broken without also having to replace the impedance matching network. The housing (4) is fitted to the radio (2) by means of a conventional SMA connector (14, 17, 21 22). <IMAGE>

Description

ANTENNA ASSEMBLY This invention relates to an antenna assembly comprising a radiating element, and means for matching the impedance of said radiating element.

Unitary antenna assemblies comprising integral radiating elements and impedance matching networks are commonly used for portable radio transceivers, for example cellular portable radio telephones when it is preferred not to include the impedance matching network within the body of the radio casing.

By their very nature, portable radio transceivers are susceptible to fairly harsh treatment and so tend to have a particularly rugged construction.

In the case of rod antennas, the elongate radiating element, (i.e. the antenna per se), generally has a flexible construction so that it simply bends if it is subject to any force. Nevertheless, the antenna remains relatively vulnerable and it is a common problem in portable cellular telephones for the antenna to break. This ordinarily necessitates replacing the whole antenna assembly including the (otherwise operative) impedance matching network, which can be relatively expensive.

According to the present invention there is provided an antenna assembly comprising a radiating element, and a dedicated housing enclosing means for matching the impedance of said radiating element, wherein the radiating element is removably attachable to the housing.

A two-piece antenna assembly in accordance with the invention has the advantage that the radiating element (antenna) can be replaced separately if it is broken, sparing the need and associated expense of also having to replace the impedance matching means.

Suitably the impedance matching means is automatically coupled to the radiating element when the radiating element is attached to the housing.

In a preferred embodiment the two parts of the assembly are attached by means of complementary threaded portions provided on each part respectively.

The threaded portions may be electrically conductive, thereby forming an electrical connection when the two parts are attached.

The impedance matching means may be connected to the threaded portion of the housing so that a direct electrical connection is made between the radiating element and the impedance matching means.

In a particular embodiment, a wall portion of the housing comprises a conductive member forming an electrical connection with the impedance matching means, and the wall portion may be capacitively coupled to the threaded portion of the housing, thus simplifying the electrical connections within the housing.

The radiating element itself may be elongate, or any other suitable form, for example helical.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a part cross-sectional view of an antenna assembly in accordance with the invention, and Figure 2 is a circuit diagram of the impedance matching network in the antenna assembly in Figure 1.

The antenna assembly 1 shown in Figure 1 is particularly intended for use with a portable cellular radio 2.

The antenna assembly 1 comprises an elongate rod antenna 3 (only part of which is shown in Figure 1) adapted to be removably connected to a housing 4 enclosing an impedance matching network; the housing itself being removably connected to a cellular radio 2.

The antenna 3 (only part of which is shown in Figure 1) comprises a flexible conductive core 5 surrounded by an insulating sheath 6. The length of the antenna will depend on the particular application, but may for example be a three-eighths, half, or five-eights wavelenth antenna.

The lower end of the conductive core 5 is fitted within a conductive ferrule 6 of a connector having an integral, electrically conductive, externally threaded member 7 at its base. The core 5 may be fixed to the connector 6, 7, for example, by compressing the ferrule 6 around the core 5.

The housing 4, which is preferably circular in section, comprises in its top face a centrally disposed electrically conductive internally threaded member 8 for receiving the complementary member 7 of the antenna 3. The housing 4 is dedicated to enclosing an impedance matching network, the circuit diagram of which is shown in Figure 2, and is discussed in more detail below.

The housing 4 comprises a generally cylindrical conductive member 9 forming part of the external wall of the housing. The member 9 includes an integral top flange 10 and a lower flange 11. The top flange 10 extends in the vicinity of the threaded member 8. The gap between the flange 10 and member 8 is plugged by an annular dielectric member 12 forming the capacitance C1 (see Figure 2).

A coating 20 of insulating material, suitably plastics is provided around the outside of conductive member 9 and on the top surface of flange 10.

The housing may have any suitable dimensions. For example, both the height and the circumference may be approximately 15mm.

A conductive coil 13, forming the inductance L (see Figure 2) has one end conductively fastened, e.g. by soldering, to the underside of threaded member 8. The opposite end of the coil 13 is electrically connected to a rigid conductive connector pin 14 disposed generally concentrically with the threaded member 8.

The pin 14 is provided integrally with a wider portion 15 at its upper end, in which is provided a depression (or so-called 'solder bucket') for accommodating the end of the coil 13 and to retain a drop of solder for connecting the coil to the pin 14.

The lower flange 11 abuts an upstanding conductive member 17 having an internal screw thread. An annular dielectric member 19 sits on a shoulder 18 at the upper portion of member 17, and surrounds the upper wider portion 15 on the pin 14. The conductive members 17, 18 and 15 and the interposed dielectric member 19 together form the capacitance C2 (see Figure 2).

The radio 2 comprises an upstanding member 21 extending through the external casing 24 thereof. Member 21 has an external screw thread and a concentric antenna connection socket 22 separated by an insulating block 23. The screw threaded member 21 and socket 22 extend above the outer casing 24 of the radio 2.

The antenna connection between the housing 6 and the radio 2 is suitably a conventional SMA connector.

When the housing 6 is screwed onto the radio casing the pin 14 docks in socket 22 to make the antenna connection therewith. The connection to earth is established via screw threaded member 21, the complementary screw threaded member 17 and also the cylindrical member 9 of housing 6 being electrically connected thereto to establish the pi coupling circuit shown in Figure 2.

The antenna 3 itself can readily be connected and disconnected by its screw-fitting attachment to the housing 6. Thus if the antenna becomes broken it is a very straightforward matter simply to unscrew the antenna from the housing 5 and to replace it with a new antenna, but retaining the original housing (and impedance matching network).

In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the present invention. For example the dimensions and physical configuration of the housing may be varied, and indeed so too may the actual electrical configuration of the impedance matching network to meet specific applications. Furthermore, any suitable form of RF connector other than an SMA type may be used for establishing the antenna connection between the housing and the radio. Likewise, the antenna may be attached to the housing by means other than a screw-fitting.

Also, the antenna need not be elongate. For example a helical antenna may be used.

Claims (13)

1. An antenna assembly comprising a radiating element, and a dedicated housing enclosing means for matching the impedance of said radiating element, wherein the radiating element is removably attachable to the housing.

2. An antenna assembly as claimed in claim 1, wherein the impedance matching means is automatically coupled to the radiating element when the radiating element is attached to the housing.

3. An antenna assembly as claimed in claim 1 or claim 2, wherein the housing includes means for removably connecting the housing to a radio frequency transmitter.

4. An antenna assembly as claimed in any preceding claims, wherein the radiating element and the housing are provided with complementary threaded portions enabling the radiating element to be attached to the housing.

5. An antenna assembly as claimed in claim 4, wherein the complementary threaded portions are electrically conductive.

6. An antenna assembly as claimed in claim 5, wherein the impedance matching means are connected electrically to the threaded portion of the housing.

7. An antenna assembly as claimed in claim 6, wherein the impedance matching means includes inductive means connected electrically to the threaded portion of the housing.

8. An antenna assembly as claimed in any of claims 5 to 7, wherein the impedance matching means includes capacitive means electrically coupled to the threaded portion of the housing.

9. An antenna assembly as claimed in any of the preceding claims, wherein a wall portion of the housing comprises a conductive member forming an electrical connection within the impedance matching means.

10. An antenna assembly as claimed in claim 9, wherein the wall portion is capacitively coupled to the threaded portion of the housing.

11. An antenna assembly as claimed in claim 9 or 10, wherein the housing comprises an outer layer of insulating material surrounding said conductive member.

12. An antenna assembly as claimed in any of the preceding claims, comprising an elongate radiating element-.

13. A two-piece antenna assembly substantially as herein described with reference to Figures 1 and 2 of the accompanying drawings.