EP0643876B1

EP0643876B1 - Antenna

Info

Publication number: EP0643876B1
Application number: EP93924766A
Authority: EP
Inventors: Martin Allan Mclaren; David Blyth Mcgregor; James Thomas Michael Armstrong
Original assignee: STIK (INTERNATIONAL) Ltd; STIK INTERNATIONAL Ltd
Current assignee: STIK (INTERNATIONAL) Ltd
Priority date: 1992-11-13
Filing date: 1993-11-15
Publication date: 1999-04-14
Anticipated expiration: 2013-11-15
Also published as: ES2133419T3; GB2272578A; DE69324488D1; WO1994011921A1; GB9223889D0; DE69324488T2; DK0643876T3; EP0643876A1

Abstract

There is disclosed an em-wave antenna, particularly suitable for reception of DBS television signals. Known antennae are of the "dish" type and suffer from a number of problems such as size, wind-loading, lack of eye-appeal, expense of manufacture and difficulty of installation. The present invention, therefore, provides: a satellite antenna (5, 5d) comprising an elongate member in the form of a rod (10, 10d) and a horn (15, 15d), a first end (60, 60d) of the rod (10, 10d) being rigidly retained at or near a narrow end (61, 61d) of the horn (15, 15d), which end also provides connection means (65, 65d) for connecting the antenna (5, 5d) to receiving means, a second end (70, 70d) of the rod (10, 10d) extending outwardly of a wide end (75, 75d) of the horn (15, 15d), and wherein, in use, the second end (70, 70d) of the rod (10, 10d) is pointed substantially in the direction of the DBS satellite.

Description

This invention relates to electromagnetic wave antennae, and in particular to an antenna for receiving electromagnetic signals from a satellite orbiting the earth.
There has been an upsurge in the past few years in the availability of satellite television channels. This is due to the launching of a number of DBS (Direct Broadcast Satellites). These are a breed of high-powered satellites which are specifically designed to beam television signals direct to domestic and/or business customers equipped with relatively small satellite antennae - otherwise known as satellite dishes. These DBS are positioned within the Clarke belt in a geostationary orbit, i.e. they are positioned approximately 36000km above the equator and travel in the same direction as the earth's rotation in designated positions around the equator. The result of this is that the satellite effectively remains above the same point on the earth's surface.
A number of types of satellite dish antennae presently exist, e.g. the prime-focus type, the offset type and the flat plate type.
Although most local authorities allow a householder to erect one such dish up to 90cms in diameter without planning permission, they are aesthetically displeasing to the environment. Many householders are, therefore, unhappy regarding installing such a dish, but have no option if they wish to receive satellite television.
The dishes are also awkward to install and expensive to manufacture and consequently to purchase, and have in some cases become a danger due to high wind-loading.
EP-A-0330303 relates to an end fire aerial which comprises a solid block of dielectric foam material which extends outwardly of a horn. The gain allegedly obtained from this type of aerial is in the range of about 26.6B which results from increasing the effective area of the aperture of the horn by mounting the dielectric block in the open end of the horn.
WO87/06066 describes a wideband horn antenna which comprises a dielectric rod which is seated in the narrow end of a circular section horn. The free end of the rod terminates adjacent the open end of the horn. The object of this antenna is to produce a fixed beamwidth substantially independent of frequency over a wideband.
US-A-2727233 describes a dielectric rod antenna which comprises a horn into which is mounted a hollow elongate member which is formed from four dielectric rods, one mounted at each corner of the horn. Each rod is connected to the two adjacent rods by a sheet of dielectric material. It is an object of this antenna to provide an antenna array of dielectric rods which are excited directly by an electromagnetic horn.
A further antenna is proposed in an article entitled Engineering Approach to the design of Tapered Dielectric Rod and Horn Antennas (The Radio and Electronic Engineer Vol 42 No 6, June 1972).
It is an object of the present invention to obviate or mitigate at least some of the aforementioned problems in the prior art.
According to a first aspect of the present invention there is provided a satellite antenna comprising an elongate member and a horn, a first end of the elongate member being rigidly retained at or near a narrow end of the horn, which end of the horn also provides connection means for connecting the antenna to receiving means, a second end of the elongate member extending outwardly of a wide end of the horn, characterised in that the antenna further comprises a plurality of elongate rods surrounding the elongate member, and an elongate sheath capable of being received on the elongate member, the sheath having a plurality of channels at or near an outer surface thereof, each channel receiving one of the plurality of elongate rods, the arrangement being such that in use, the second end of the elongate member is pointed substantially in the direction of the satellite.
The antenna may be adapted to operate in the Ku-band, and particularly between 10.7GHz and 11.96GHz or between 12.2GHz and 12.7GHz.
The elongate member may be a rod, which may be solid or hollow.
The rod may be made from a suitable dielectric material, for example a plastic such as solid polypropylene, PVC, polystyrene or the like.
The horn preferably comprises a frusto-conical portion having a first end of a base portion connected to a narrow end of the frusto-conical portion.
The base portion may be in the form of a cylindrical portion or alternatively may be in the form of a plurality of integrally connected cylindrical portions, each adjacent cylindrical portion being of reduced diameter with increasing distance from the narrow end of the frusto-conical portion.
The connection means may comprise a threaded or flanged portion provided at or near a second end of the base portion, the threaded or flanged portion allowing connection of the horn to a low noise block converter (LNB) or the like.
The horn may be made from aluminium or from any dicast metal with magnetic reflectability.
The sheath may provide a first open end suitably shaped so as to be snugly received within the wide end of the horn.
A main elongate portion of the sheath may be of any suitable shape in cross-section, for example circular, square or elliptical.
Further, the sheath may have a narrowing second closing end.
The sheath may be made from an expanded plastics material.
The rods may be made from a plastic such as solid polypropylene, PVC, polystyrene or the like.
A weather-proof covering may be provided on at least part of the outer surface of the sheath, for example, a thin film plastic covering or a layer of suitable paint or the like.
According to a second aspect of the present invention there is provided a method of receiving electromagnetic signals from a satellite comprising employing a satellite antenna, the antenna comprising an elongate member and a horn, a first end of the elongate member being rigidly retained at or near a narrow end of the horn, which end of the horn also provides connection means for connecting the antenna to receiving means, a second end of the elongate member extending outwardly of a wide end of the horn, a plurality of elongate rods surrounding the elongate member, and an elongate sheath capable of being received on the elongate member, the sheath having a plurality of channels at or near an outer surface thereof, each channel receiving one of the plurality of elongate rods, and pointing the second end of the elongate member substantially in the direction of the satellite.
Various embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings, which are:

Fig 1: a schematic side view of an antenna;
Fig 2: an end view along direction 'A' of the antenna of Fig 1;
Fig 3: a graph of experimental results showing output power versus frequency of a low noise block converter (LNB) fed by the antenna;
Figs 4 (a), (b), (c): various designs of horns for use in the antenna;
Fig 5: a focusing element for use in the antenna;
Fig 6: a schematic cross-sectional side view of an antenna according to the present invention;
Fig 7: an end view along direction 'B' of the antenna of Fig 6;
Figs 8 (a)-(e): end views of various modifications to the antenna of Fig 7; and
Figs 9 (a)-(b): further designs of horns for use in an antenna according to the present invention.

Referring to Figs 1 and 2, there is illustrated a satellite antenna, generally designated 5. The antenna 5 comprises an elongate member in the form of a hollow rod 10, and a horn 15. The horn 15 comprises a frontmost frusto-conical portion 20 and a rearmost portion 25 integrally connected thereto. In this embodiment the rearmost portion 25 comprises first, second and third cylindrical portions 30, 35, 40 of decreasing diameter, the first portion 30 being integrally connected to the frusto-conical portion 20 by a first annular lip 45.
The first and second cylindrical portions 30, 35 are likewise integrally connected by a second annular lip portion 50, and the second and third cylindrical portions 35, 40 by a third annular lip portion 55.
A first end 60 of the rod 10 is rigidly retained within a narrow end 61 of the horn 15 provided by the third cylindrical portion 40 the internal diameter of which is a close fit with the outer diameter of the rod 10.
Further, provided on an outer surface 62 of the third cylindrical portion 40 are connection means comprising a threaded portion 65, the threaded portion 65 allowing connection of the antenna 5 to a conventional low noise block converter (LNB) (not shown), as is known in the art.
As can be seen best from Fig 1, a second end 70 of the rod 10 extends outwardly of a frontmost wide end 75 of the horn 15.
Typically, for an antenna 5 operating between 10GHz and 13GHz the dimensions of the antenna are as follows:- for the rod 10: length = 1000mm, outer diameter = 20mm, inner diameter = 17.5mm; for the horn 15: length = 215mm, diameter of wide end = 100mm, half angle of imaginary apex of frusto-conical portion 20 = 20°, outer diameter of first cylindrical portion 30 = 50mm, outer diameter of second cylindrical portion 35 = 40mm, outer diameter of third cylindrical portion 40 = 17.5mm.
The rod 10 may be made from any suitable dielectric material, for example, solid PVC having a dielectric constant, ε_r = 3.0 to 3.5 or solid polystyrene having ε_r = 2.2 to 2.6.
In use, the antenna 5 may be suitably mounted on a building by means of brackets or the like, the threaded portion 65 connected to an LNB and the orientation of the antenna 5 adjusted until the second end 70 of the rod 10 points substantially in the direction of the satellite. The precise direction of orientation of the rod 10 may then be finely adjusted until a suitable level of signal is received by the antenna 5 and converted by the LNB.
Using such an antenna 5 it has been found that a gain of 29 dB or even higher may be achieved.
Referring now to Fig 3, there is illustrated the output from an LNB connected to an antenna 5 receiving signals from the Astra Satellite as viewed on a spectrum analyser. The LNB output range of 1.1GHz to 1.8GHz corresponds approximately to a detection bandwidth of the antenna 5 of 10.7GHz to 11.9GHz, Each peak in Fig 3 corresponds to a separate satellite television channel.
The centre detection frequency of the antenna 5, and the bandwidth thereof, may be chosen by suitable design of the rod 10 and horn 15. Therefore, the centre frequency and bandwidth may be influenced by any or all of: the length, outer diameter and inner diameter of the rod 10 and the design of the horn 15.
The centre frequency may be chosen by suitable design of the rod 10, and the bandwidth by suitable design of the horn 15.
Referring to Figs 4(a), (b) and (c) there are illustrated various horn designs. Each of the horns 15a, 15b, 15c illustrated comprise a frust- conical portion 20a, 20b, 20c and a substantially cylindrical portion 25a, 25b, 25c. The design of these horns 15a, 15b, 15c are as follows:

Horn Diameter of Wide End (mm) length of frustoconical portion (mm) length of cylindrical portion (mm)

15a 100 130 100

15b 100 270 200

15c 100 210 140
It should also be appreciated that suitable choice and control of the chemical properties of the materials used to make the antenna 5, and particularly the rod 10, may aid in obtaining desired operation of the antenna 5.
Referring to Fig 5 there is illustrated a focusing element 80 which is intended to be inserted within the first end 60 of the rod 10. The element 80 comprises a cylindrical portion 85 having first and second ends 90, 95. Within the cylindrical portion 85 there is provided a conical aperture 100, the base of which is substantially co-incident with the first end of the cylindrical portion 80. Integrally connected to the second end of the cylindrical portion 85 is the base of a conical portion 105. An apex 110 of the conical portion 105 is intended to be substantially level with the first end 60 of the rod 10, in use.
Referring to Figs 6 and 7, there is illustrated an embodiment of a satellite antenna according to the present invention, generally designated 5d. Parts of the antenna 5d are identified with the same integers as like parts of the antenna of Fig 1 but postscripted 'd'.
The horn 15d of this antenna 5d is substantially the same as that of the antenna 5 excepting that there is no first annular lip portion 45 and further that the second and third annular lip portions 50d, 55d are frusto-conic rather than annular.
The antenna 5d further comprises an elongate sheath 115d having an elongate space 120d, such that the sheath 115d is capable of being received on the solid elongate member 10d.
The sheath 115d provides a first open end 125d suitably shaped so as to snugly fit within the frusto-conical portion 20d of the horn 15d. As can be seen from Fig 7, in the embodiment, a main elongate portion 130d of the sheath 115d is substantially elliptical in cross-section. Further, the sheath 115d has a closed tapering second end 135d.
The sheath 115d is provided with two opposing elongate channels 140d at or near an outer surface thereof. Each channel 140d contains an elongate rod 145d. On the outermost surface of the sheath 115d there is provided a waterproof (weatherproof) cover 150d.
Further the antenna 5d is mounted on an X-Y-Z mount 155d such that the orientation of the antenna 5d ("stick") can be adjusted.
Regarding the various parts of the antenna 5d:
The shape of the horn 15d determines the overall signal gain. It also defines the signal frequency. The horn 15d can be made from stamped, spun or dicast metal as long as the internal dimensions are accurate and the surface is relatively smooth.
The rod 10d is the main collector of the electro magnetic signal and utilises its surface wave properties. Signal strength and frequency is controlled by rod diameter, rod wall thickness, type of plastic rod used and rod length.
The elongate rods 145d are used to excite the rod 10d and increase the signal strength in the horn 15d prior to it entering the chosen LNB. Again rod length, the diameter, rod wall thickness, type of plastic rod used and spacing from the rod 10d all have an effect on the signal strength available to the LNB.
The sheath 115d is basically there to position the rods 10d, 145d and keep them straight but it is found that the type of material used to make the sheath 115d is critical in over-all signal gain.
While the rods 10d, 145d may be made from a solid plastic, the sheath may be made from an expanded (foamed) plastic.
The cover 150d has to be a minimum distance from the rod 10d otherwise inclement weather will severely degrade the electromagnetic signal. Again the type of plastic used is critical. For example, the material is preferably UV resistant and may be silicon coated.
Referring to Figs 8(a) to (e) there are illustrated various alternative embodiments of antenna 5e to 5i having a variety of cross-sections of sheath 115e to 115i and a variety of number of elongate rods 145e to 145i.
In each of the disclosed embodiments 5, 5d, the basic TE11 mode is introduced at the LNB end of the feedhorn 15, 15d and the TE11/TM11 mode is produced at the outer rim. This agitates the propagated waves travelling along the transmission line which in this case is the centre rod 10, 10d and creates a transition between the centre plastic rod 10, 10d and the feedhorn 15, 15d thereby producing gain, radiation pattern and impedance matching. Typical figures are as follows:

Gain 29.6 dB

Carrier/Noise (C/N) - 12.2

Sidelobe Suppression 14.0 dB

Gain 32.0 dB minimum

C/N 14.0

Sidelobe Suppression - 24.0 dB
Referring to Figs 9(a) and 9(b) there are illustrated further embodiments of horns 5j, 5k suitable for use in an antenna according to the present invention.
It should be appreciated that although in the preferred embodiments disclosed herein the LNB is connected to the horn externally thereof, it may be envisaged that the LNB may well be suitably located within the horn.
Further, increased signal gain can be obtained by using a longer rod but becomes impractical if too long a length is used.
Additional signal can also be achieved by providing a plurality of shorter rods inserted in a specially designed horn for this purpose.
The antenna can also be motorised to enable other satellites of suitable power and frequencies to be received.

Claims

A satellite antenna (5) comprising an elongate member (10) and a horn (15), a first end (60) of the elongate member being rigidly retained at or near a narrow end of the horn, which end of the horn also provides connection means for connecting the antenna to receiving means, a second end (70) of the elongate member extending outwardly of a wide end of the horn, characterised in that the antenna further comprises a plurality of elongate rods (145) surrounding the elongate member, and an elongate sheath (115) capable of being received on the elongate member, the sheath having a plurality of channels (140) at or near an outer surface thereof, each channel receiving one of the plurality of elongate rods, the arrangement being such that in use, the second end of the elongate member is pointed substantially in the direction of the satellite.
A satellite antenna as claimed in claim 1, wherein the antenna is adapted to operate in the Ku-band, and particularly between 10.7GHz and 11.96GHz or between 12.2GHz and 12.7GHz.
A satellite antenna as claimed in any preceding claim, wherein, the elongate member is a rod.
A satellite antenna as claimed in claim 3, wherein the rod is solid.
A satellite antenna as claimed in any of claims 3 or 4, wherein, the rod is made from a suitable dielectric material.
A satellite antenna as claimed in claim 5, wherein the rod is made from a plastic such as solid polypropylene, PVC, polystyrene or the like.
A satellite antenna as claimed in any preceding claim, wherein the horn comprises a frusto-conical portion (20) having a first end of a base portion (25) connected to a narrow end of the frusto-conical portion.
A satellite antenna as claimed in claim 7, wherein the base portion (25) is in the form of a cylindrical portion(s).
A satellite antenna as claimed in claim 7, wherein the base portion is in the form of a plurality of integrally connected cylindrical portions (30, 35, 40), each adjacent cylindrical portion being of reduced diameter with increasing distance from the narrow end of the frusto-conical portion.
A satellite antenna as claimed in any preceding claim, wherein the connection means comprise a threaded or flanged portion (65) provided at or near a second end of the base portion, the threaded or flanged portion allowing connection of the horn to a low noise block converter (LNB) or the like.
A satellite antenna as claimed in any preceding claim, wherein the horn is made from aluminium or from a dicast metal with magnetic reflectability.
A satellite antenna as claimed in any preceding claim, wherein the sheath provides a first open end (125) suitably shaped so as to be snugly received within the wide end of the horn.
A satellite antenna as claimed in any preceding claim, wherein a main elongate portion (130) of the sheath is circular, square or elliptical in cross-section.
A satellite antenna as claimed in either of claims 13 or 14, wherein the sheath has a narrowing second end (135).
A satellite antenna as claimed in any preceding claim, wherein the sheath is made from an expanded plastics material.
A satellite antenna as claimed in any preceding claim, wherein the elongate rods are made from a plastic such as solid polypropylene, PVC, polystyrene or the like.
A satellite antenna as claimed in any preceding claim, wherein a weatherproof covering (150) is provided on at least part of an outer surface of the sheath.
A method of receiving electromagnetic signals from a satellite comprising employing a satellite antenna (5), the antenna comprising an elongate member (10) and a horn (15), a first end (60) of the elongate member being rigidly retained at or near a narrow end of the horn, which end of the horn also provides connection means for connecting the antenna to receiving means, a second end (70) of the elongate member extending outwardly of a wide end of the horn, a plurality of elongate rods (145) surrounding the elongate member, and an elongate sheath (115) capable of being received on the elongate member, the sheath having a plurality of channels (140) at or near an outer surface thereof, each channel receiving one of the plurality of elongate rods, and pointing the second end of the elongate member substantially in the direction of the satellite.