GB2242072A - Reflector antenna - Google Patents
Reflector antenna Download PDFInfo
- Publication number
- GB2242072A GB2242072A GB9005915A GB9005915A GB2242072A GB 2242072 A GB2242072 A GB 2242072A GB 9005915 A GB9005915 A GB 9005915A GB 9005915 A GB9005915 A GB 9005915A GB 2242072 A GB2242072 A GB 2242072A
- Authority
- GB
- United Kingdom
- Prior art keywords
- reflector
- feed unit
- axis
- central axis
- polarization
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/14—Reflecting surfaces; Equivalent structures
- H01Q15/22—Reflecting surfaces; Equivalent structures functioning also as polarisation filter
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/14—Reflecting surfaces; Equivalent structures
- H01Q15/16—Reflecting surfaces; Equivalent structures curved in two dimensions, e.g. paraboloidal
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
- H01Q19/10—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces
- H01Q19/12—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces wherein the surfaces are concave
- H01Q19/13—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces wherein the surfaces are concave the primary radiating source being a single radiating element, e.g. a dipole, a slot, a waveguide termination
- H01Q19/132—Horn reflector antennas; Off-set feeding
Landscapes
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Aerials With Secondary Devices (AREA)
- Variable-Direction Aerials And Aerial Arrays (AREA)
Abstract
To reduce the wind loading and weight of the antenna reflector (20), its surface is formed from a number of parallel spaced apart rods (24) joined by transverse link bars (26). A reflector mounting (28) permits rotation of the reflector (20) about a central axis (22) to align the nods (24) with the axis of polarization of a signal radiated by the offset antenna feed unit (32). The reflector surface, defined by a section of the surface of a sphere, is symmetrical about the central axis (22), such that the centre of gravity of the reflector lies on the axis (22) and the load on the reflector support structure (30) remains constant as the reflector is rotated. <IMAGE>
Description
REFLECTOR ANTENNA
The present invention relates to ref lector antennas and in particular to such antennas which are operable to radiate signals linearly polarised in either a vertical or a horizontal plane, the plane of polarization being defined by the direction of the electric (E) field.
The reflector surface may be a continuous dished surface, but for transportable operation where it is desired to use a lightweignt, easily erected supporting structure, this has the severe disadvantage of presenting an unacceptably large wind-loaded area. Wind loading may be reduced by making the ref lector surface in the form of a grid of rods.
In accordance with the present invention there is provided an antenna assembly including a feed unit, a reflector and a ref lector mounting, in which the reflector surface is substantially syrtirrietrical about a central axis and is formed fram a number of substantially parallel rods, and in which the mounting permits rotation of the ref lector about the central axis to align the rods with the axis of polarization of a signal radiated by the feed unit.
The use of bars extending in only one direction means that the reflector of the present invention has less total surface area and is thus lighter than grid surface reflectors.
The present invention has particular application to antennas having offset geometry, that is to say antennas in which the feed unit is positioned such that the radiation reflected by the reflector surface does not impinge on the feed unit. Such offset antennas thereby avoid the problems of scattering fran the feed unit and blockage of part of the main ref lector aperture.
The conventional form of offset antenna makes use of shape of reflector which represents part of the surface of a paraboloid, but this surface is not symmetrical about its centre. If operation in two planes of polarisation is required (even if not required simultaneously) the ref lector must be provided with rods in both the horizontal and vertical planes, increasing its wind-loaded area.
Since the reflector surface of the present invention is to be substantially symmetrical about a central axis and the reflector mounting permits rotation about that axis, the spatial relationship between the feed unit and reflector remains constant whether the rods of the reflector surface are aligned vertically or horizontally. Additionally, the centre of gravity of the reflector remains constant giving uniform loading on the support structure. A suitable shape for the reflector is a section of the surface of a sphere.
One particular preferred embodiment of the present invention, in the form of an offset antenna, will now be described with reference to the accompanying drawings, in which:
Figure 1 is a side sectional view of a known antenna structure illustrating the general principle of operation of an offset antenna;
Figure 2 shows an antenna assembly embodying the present invention arranged to radiate vertically polarized signals; and
Figure 3 is a schematic elevation showing the relative angular orientation of the reflector and feed unit.
Referring initially to Figure 1, an offset reflector is shown radiating a linearly polarized signal. The reflector surface 10 is in the form of a section of the surface of a sphere with the antenna feed 12 located at a predetermined position relative to the reflector 10. The signal 14 reflected from the reflector surface does not impinge on the feed unit 12. As can be seen, some distortion of the radiated signal 14 may occur at the upper edge of the reflector surface 10 where the angle subtended by the feed unit signal is greatest.
The reflector antenna assembly of the present invention is illustrated in Figure 2. The reflector 20 is in the form of a section of the surface of a sphere and is symmetrical about a central axis 22. The reflector surface is made up of a number of spaced apart parallel rods 24 joined together by transverse link bars 26. The reflector 20 is mounted on a rotatable support 28 with its central axis 22 at a predetermined angle e0 to the horizontal. The rotatable support 28 is in turn mounted on a suitable lightweight support structure 30.
The rotatable support 28 is positioned to allow rotation of the reflector 20 about its axis of symmetry 22, such that the positional relationship between the reflector 20 and the antenna offset feed unit 32 remains the sarre regardless of the degree of rotation of the reflector 20 about the axis 22.
The feed unit 32 is also rotatably mounted, allowing rotation about an axis 34 inclined at a predetermined angle fi to the horizontal. The feed unit 32 radiates a signal having a fixed polarization in relation thereto, the selection of vertical or horizontal polarization being achieved by rotation of the feed unit 32 about its axis.
In operation, when the antenna is set to radiate a vertically polarised signal as shown in Figure 2, the rods 24 making up the ref lector surface are positioned to extend in substantially vertical planes. The feed unit 32 is rotatably positioned such that the signal radiated towards the reflector 20 is vertically polarized.
To adjust the antenna to radiate a horizontally polarized signal, the feed unit 32 and ref lector 20 are rotated by 900 about their respective axes 34, 22, the rods 24 thus becang horizontally orientated.
Referring to figure 3, the reflector 10 has a width D and is defined by a section of the surface of a sphere of radius R centred on a point P. The reflectors' central axis 22 is inclined at an angle e0 to the horizontal. The antenna feed 12 is located between the reflector surface 10 and the point P, at a distance Zf from the point P. The feed axis 34 is inclined at an angle ss f to the horizontal. The maximum angle of elevation ef, with respect to the feed axis 34, of a signal radiated by the feed unit 12 occurs at the top edge of the reflector.
Suitable values for these distances and angles are:
R = 1300mm SO = 25.00
D = 1200mm Ef = 50.70
Zf = 805mm /3f = 38.40 The reflector 20 of the present invention has less wind loaded surface area and is lighter than known grid surface reflectors thereby requiring less strengthening of the support structure 30.
In addition, where the reflector 20 is symmetrical about its central axis 22, rotation of the reflector to a vertical orientation from a horizontal orientation or vice versa will not place stress on the support structure, due to the constant position of the centre of gravity of the reflector.
Claims (6)
1. An antenna assembly including a feed unit, a reflector and a reflector mounting, in which the reflector surface is substantially symmetrical about a central axis and is formed from a number of substantially parallel rods, and in which the mounting permits rotation of the reflector about the central axis to align the rods with the axis of polarization of a signal radiated by the feed unit.
2. Apparatus according to claim 1 in which the reflector surface is defined by a section of the surface of a sphere.
3. Apparatus according to claim 1 or claim 2 in which the feed unit is an offset feed unit.
4. An antenna assembly including a feed unit, a reflector and a reflector mounting, in which the reflector surface is defined by a section of the surface of a sphere, is substantially symmetrical about a central axis and is formed from a number of substantially parallel rods; in which the feed unit is an offset feed unit, and in which the mounting permits rotation of the reflector about the central axis to align the rods with the axis of polarization of a signal radiated by the feed unit.
5. Apparatus according to any preceding claim in which the signal radiated by the feed unit has a fixed polarization axis in relation thereto, and in which the feed unit is rotatably mounted to permit rotation of the said polarization axis.
6. An antenna assembly substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9005915A GB2242072B (en) | 1990-03-16 | 1990-03-16 | Reflector antenna |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9005915A GB2242072B (en) | 1990-03-16 | 1990-03-16 | Reflector antenna |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9005915D0 GB9005915D0 (en) | 1990-05-09 |
| GB2242072A true GB2242072A (en) | 1991-09-18 |
| GB2242072B GB2242072B (en) | 1993-12-08 |
Family
ID=10672709
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9005915A Expired - Fee Related GB2242072B (en) | 1990-03-16 | 1990-03-16 | Reflector antenna |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2242072B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009131177A1 (en) * | 2008-04-23 | 2009-10-29 | マスプロ電工株式会社 | Offset parabola antenna |
| CN102683855A (en) * | 2012-04-28 | 2012-09-19 | 深圳光启创新技术有限公司 | Portable satellite antenna |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2096398A (en) * | 1981-03-24 | 1982-10-13 | Era Patents Ltd | High performance radio antenna |
| GB2135132A (en) * | 1983-01-26 | 1984-08-22 | Anixter Bros | Grid parabolic antenna |
-
1990
- 1990-03-16 GB GB9005915A patent/GB2242072B/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2096398A (en) * | 1981-03-24 | 1982-10-13 | Era Patents Ltd | High performance radio antenna |
| GB2135132A (en) * | 1983-01-26 | 1984-08-22 | Anixter Bros | Grid parabolic antenna |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009131177A1 (en) * | 2008-04-23 | 2009-10-29 | マスプロ電工株式会社 | Offset parabola antenna |
| CN102683855A (en) * | 2012-04-28 | 2012-09-19 | 深圳光启创新技术有限公司 | Portable satellite antenna |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2242072B (en) | 1993-12-08 |
| GB9005915D0 (en) | 1990-05-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19940316 |