GB2229320A

GB2229320A - Antenna

Info

Publication number: GB2229320A
Application number: GB9001237A
Authority: GB
Inventors: Howard Frank Bottomley; Nicholas David Levin
Original assignee: Antenna Products Ltd
Current assignee: Antenna Products Ltd
Priority date: 1989-01-20
Filing date: 1990-01-19
Publication date: 1990-09-19
Anticipated expiration: 2010-01-19
Also published as: GB9001237D0; GB2229320B

Abstract

A radio antenna, intended to form a base station in a cordless telephone system, has an electrically conducting ground plate (10) carrying two metal radiator plates (14) which are spaced from the ground plate (10) to define radiating and receiving slots (18) of the antenna. The ground plate (10) and radiator plates (14) are covered by a plastics cover (22). To increase antenna visibility, the antenna has two flourescent lighting tubes (28) mounted behind elongated apertures (30) in the ground plate (10), so that the cover (22) and its identifying sign (26) are back lit. <IMAGE>

Description

Title: Antenna Field of the Invention This invention relates to antennas.

Summary of the Invention According to the invention a radio antenna comprises an electrically conducting ground member and a spaced electrically conducting radiator member, and lighting means for illuminating the antenna to increase antenna visibility.

The provision of lighting enables the antenna to be seen more easily, which is more important if the antenna is serving as the antenna of a base station in a cordless telephone system. Subscribers to such a system are equipped with portable handsets which establish a radio link with a base station mounted in a fixed position in a public place such as an airport, railway station or garage filling station.

The antenna preferably bears the logo or sign of the cordless telephone system, and the lighting means improve the visibility of this logo or sign, thereby helping subscribers to the system to locate and recognise a base station. The antenna may have a light transmitting cover which covers the ground member and radiator members and which bears the logo or sign, so that the latter is effectively back-lit by the illuminating means.

The provision of lighting also offers the possibility of incorporating advertising material on the antenna. For example, advertising material could be incorporated on the light transmitting cover.

The ground member is preferably a metal plate on the front face of which is mounted, in spaced parallel relationship, at least one metal radiator plate serving as a radiator member. The metal ground plate may be apertured, with the lighting means mounted behind the aperture or apertures to allow the passage of light to the front of the antenna without the lights interfering with radio operation. The lights may be electric fluorescent tubes or filament lamps, but in a preferred embodiment the ground plate is formed with two elongated apertures and the lighting means are two fluorescent tubes respectively mounted behind the two apertures. The apertures may be covered with lighttransmitting material which serve as a screen to radio frequency signals, to prevent operation of the lighting means impairing antenna reception or transmission.

A preferred embodiment of a radio antenna comprises two metal radiator plates mounted in parallel spaced relationship with respect to the ground plate so that the antenna is of panel form and comprises two antenna units, one edge of each radiator plate being grounded to the ground plate and another edge defining, with the ground plate, a slot which serves as a radiating/receiving slot of the corresponding antenna unit, the two slots being parallel and spaced from one another by an odd number of quarter wavelengths at the operating frequency.

The radiator plates may be any shape (e.g. circular) but are preferably rectangular or square and the adjacent edges of the radiator plates may be parallel and may be the grounded edges, the slots being at the remote edges of the radiator plates. Alternatively, the slots could face in the same direction, providing that they are spaced by the odd number of quarter wavelengths at the operating frequency.

The slot spacing is preferably three quarters of a wavelength which at an operating frequency of 866 Megahertz results in the spacing between the slots being 25.9cm. The slot spacing may alternatively be five quarters or seven quarters of a wavelength.

The feed point for each antenna unit is preferably taken through the ground plate and connected to the corresponding radiator plate at a position which imparts the required impedance, which is preferably 50 ohms.

In use, the feed points are preferably connected by coaxial cables to electronics which select one or other antenna unit as the radiating or receiving antenna unit depending on which slot is receiving the stronger signal.

Hence, the two slots are not provided to increase signal strength but are provided for what is called antenna diversity, ie the ability of the electronics to select the slot giving better radio reception and transmission.

A radio antenna according to the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view of the antenna with a cover shown removed, and Figure 2 is a sectional view on the line II-II of Figure 1.

Referrring to Figure 1, the antenna comprises a metal ground plate 10 which is rectangular in shape and connected along its longer edges to strengthening channels 12. Two rectangular metal radiator plates 14 are attached on the front face of the ground plate 10 by means of screws which pass through earthing bars 16. The earthing bars 16 position the radiator plates 14 in parallel spaced relationship to the ground plate 10 so that the assembly of ground plate and radiator plates is of flat, panel-like form.

It will be seen from Figure 1 that the adjacent edges of the two metal radiator plates 14 are grounded by the earthing bars 16. The remote edges of the radiator plates 14 define, with the ground plate 10, respective slots 18 which serve as the radiating and receiving slots of the antenna. It will be appreciated that the antenna can be regarded as being two antenna units arranged back to back, each comprising a corresponding radiator plate 14 and slot 18. The two slots 18 are spaced apart (in a direction parallel to the channels 12) by a distance which is three quarters of a wavelength at the operating frequency. The operating frequency is 866 Megahertz so the spacing of the slots is 25.9cm. The width of each radiator plate, ie the distance between each slot 18 and the corresponding earthing bar 16, is about a quarter of a wavelength, ie about 8.63cm.

As best shown in Figure 2, the feed for each antenna slot 18 is taken by a coaxial connector 20 through the ground plate 10 to a connection point on the corresponding radiator plate 14. The outer earth terminal of each coaxial connector 20 is connected to the ground plate 10 and the central terminal of each coaxial connector 20 is connected to the corresponding radiator plate 14. Each connector 20 (defining the feed point) is spaced from the corresponding earthing bar 16 by an amount which gives each antenna unit a 50 ohm impedance.

Reverting to Figure 1, the ground plate 10 and radiator plates 14 are covered by a plastics cover 22 which has a rim 24 attached by screws or rivets to the ground plate 10. A central area of the cover plate bears the trade mark, symbol or logo 26 designating the cordless telephone system with which the antenna is intended to be used. The antenna is mounted in a prominent position in a public place so that it can be readily seen by subscribers to the system who carry portable handsets for radio communication with the base station which comprises the described antenna and electronics (not shown) which processes the transmitted and received signals and selects the stronger of the two signals received by the two slots 18. Because the slots 18 are spaced by an uneven number-of quarter wavelengths, when the signal at one slot is a maximum the signal at the other sloc is a minimum.

To increase visibility, the antenna is provided with lighting means comprising two electrically powered 8 watt fluorescent tubes 28 respectively mounted behind elongated apertures 30 in the ground plate 10. Each aperture 30 is covered by a light-transmitting panel 32 which screens radio frequency signals and prevents operation of the tubes 28 impairing radio reception and transmission.

Light from the tubes 28 passes through the panels 32 and through the plastics cover 22 which is translucent. The logo 26 is therefore back lit.

The antenna is intended to be mounted in a vertical position, for example from a wall or depending from a support, but the antenna could be mounted horizontally, eg in a ceiling (where it may replace a ceiling tile or panel) or in a floor.

Claims

1. A radio antenna comprising an electrically conducting ground member and a spaced electrically conducting radiator member, and lighting means for illuminating the antenna to increase antenna visibility.

2. A radio antenna according to claim 1, wherein the antenna has a light transmitting cover which covers the ground member and radiator member and which bears a logo or sign, so that the latter is back-lit by the lighting means.

3. A radio antenna according to claim 1 or 2, wherein the ground member is a metal plate on the front face of which is mounted, in spaced parallel relationship, at least one metal radiator plate serving as the radiator member.

4. A radio antenna according to claim 3, wherein the metal ground plate is apertured, with the lighting means mounted behind the aperture to allow the passage of light to the front of the antenna without the lighting means interfering with radio operation.

5. A radio antenna according to claim 4, wherein the ground plate is formed with two elongated apertures and the lighting means are two fluorescent tubes respectively mounted behind the two apertures.

6. A radio antenna according to claim 5, wherein the apertures are covered with light-transmitting material which serves as a screen to radio frequency signals, to prevent operation of the lighting means impairing antenna reception or transmission.

7. A radio antenna according to any of claims 3 to 6, wherein the antenna comprises two metal radiator plates mounted in parallel spaced relationship with respect to the ground plate so that the antenna is of panel form and comprises two antenna units, one edge of each radiator plate being grounded to the ground plate and another edge defining, with the ground plate, a slot which serves as a radiating/receiving slot of the corresponding antenna unit, the two slots being parallel and spaced from one another by an odd number of quarter wavelengths at the operating frequency.

8. A radio antenna according to claim 7, wherein the radiator plates are rectangular or square and the adjacent edges of the radiator plates are parallel and are the grounded edges, the slots being at the remote edges of the radiator plates.

9. A radio antenna according to claim 7 or 8, wherein the slot spacing is three quarters of a wavelength which at an operating freqency of 866 Megahertz results in the spacing between the slots being 25.9cm.

10. A radio antenna according to any of claims 7 to 9, wherein a feed point for each antenna unit is taken through the ground plate and connected to the corresponding radiator plate at a position which imparts the required impedance of substantially 50 ohms.

11. A radio antenna constructed and arranged substantially as herein particularly described with reference to the accompanying drawings.