GB2229319A

GB2229319A - Antenna

Info

Publication number: GB2229319A
Application number: GB9001236A
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: GB2229319B; GB9001236D0

Abstract

A radio antenna comprises a metal ground plate (10) and two metal radiator plates (14) mounted in parallel spaced relationship with respect to the ground plate (10) so that the antenna is of panel form and comprises two antenna units. One edge of each radiator plate (14) is grounded to the ground plate (10) and the opposite edge defines, with the ground plate (10), a slot (18) which serves as a radiating/receiving slot of the corresponding antenna unit. The two slots are parallel and spaced from one another by an odd number (preferring three) of quarter wavelengths at the operating frequency. The antenna is used in a diversity arrangement. <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 two electrically conducting radiator members mounted in parallel spaced relationship with respect to the ground member so that the antenna is of panel form and comprises two antenna units, one edge of each radiator member being grounded to the ground member and another edge defining, with the ground member, 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 ground member and the radiator members are preferably metal plates interconnected by earthing bars.

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.

The antenna was devised to form the antenna of a base station which is located in a fixed position in a public place such as a railway station, airport or garage filling station. The base station communicates by radio with portable handsets which are carried by subscribers to a cordless telephone system. The simplicity and robustness of the antenna, and the absence of any cash, considerably reduces the risk of the antenna being damaged by vandals.

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 dan 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 22 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 at any time 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 slot is a minimum.

The antenna is intended to be mounted in a vertical position, for example on 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 two electrically conducting radiator members mounted in parallel spaced relationship with respect to the ground member so that the antenna is of panel form and comprises two antenna units, one edge of each radiator member being grounded to the ground member and another edge defining, with the ground member, 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.

2. A radio antenna according to claim 1, wherein the ground member and the radiator members are metal plates interconnected by earthing bars.

3. A radio antenna according to claim 2, 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.

4. A radio antenna according to any of the preceding claims, wherein the slot spacing is three quarters of a wavelength which at an operating frequency of 866 Megahertz results in the spacing between the slots being 25.9cm.

5. A radio antenna according to any of the preceding claims, 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.

6. A radio antenna according to claim, 5 wherein the feed points are 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.

7. A radio antenna according to any of the preceding claims and forming the antenna of a base station located in a fixed position in a public place such as a railway station, airport or garage filling station, the base station communicating by radio with portable handsets which are carried by subscribers to a cordless telephone system.

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