GB2226186A - An offset reflector antenna - Google Patents
An offset reflector antenna Download PDFInfo
- Publication number
- GB2226186A GB2226186A GB8924447A GB8924447A GB2226186A GB 2226186 A GB2226186 A GB 2226186A GB 8924447 A GB8924447 A GB 8924447A GB 8924447 A GB8924447 A GB 8924447A GB 2226186 A GB2226186 A GB 2226186A
- Authority
- GB
- United Kingdom
- Prior art keywords
- feed horn
- offset
- horn
- reflector
- reflector antenna
- 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.)
- Withdrawn
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
- H01Q13/02—Waveguide horns
-
- 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
- H01Q19/02—Details
- H01Q19/021—Means for reducing undesirable effects
- H01Q19/028—Means for reducing undesirable effects for reducing the cross polarisation
-
- 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
- Aerials With Secondary Devices (AREA)
- Waveguide Aerials (AREA)
Abstract
A cross polarisation component of electric field on an aperture plane of a reflector 1 in an offset reflector antenna is prevented by purposely generating a cross polarisation component on an opening plane 4 of a feed horn 2, so as to reduce the cross polarisation component of electric field on the aperture plane of the reflector. The structure for providing the cross polarisation component on the aperture of a feed horn 2 may be, for instance, an oblique structure, figure 4a, with a slant angle theta A-between normal axis direction of an aperture of a feed horn and an axis of the feed horn; an asymmetrical flange (6), figure 4C, attached on an aperture plane of the feed horn (2); asymmetrical chokes (8a-8n), figure 5a, on a symmetrical flange on an aperture plane of the feed horn; or an asymmetrical corrugated structure (9), figure 5b, attached on an inner wall of the feed horn. <IMAGE>
Description
An Offset Reflector Antenna
The present invention relates to an offset reflector
antenna.
An offset reflector antenna, for instance an offset
parabolic antenna has the structure that a primary horn
and other structures do not block the electromagnetic wave reflected by a reflector. Therefore, it has the
advantages of high gain and low side lobe
characteristics, and so, an offset reflector antenna has
been utilized in a radar antenna, an earth station
antenna for satellite communication, a terrestrial radio
communication antenna, a satellite antenna, a direct satellite broadcast reception antenna, et al.
However, a prior offset reflector antenna has the foilowing disadvantages.
The first disadvantage is a mechanical problem, in
which the structure ofthereflection mirror is less simple
to manufacture because of an offset configuration ofthe reflection mirror. The mechanical problem is being solved
by the latest development in precision machine tooling.
The second disadvantage is electrical problem. The
most significant electrical problem is the undesired generation of a cross polarization component because of the asymmetrical structure of a reflection mirror.
Some methods for solving said cross polarization in an offset parabolic antenna have been proposed as follows.
a) A cross polarization component generated by a main offset parabolic reflector is compensated by introducing a sub-reflector which is an offset hyperbolic reflector or an elliptic reflector (The Institute of
Electronics, Information, and Communication Engineers in
Japan, vol. 58-B, No.12, page 643 December 1975).
b) A plurality of primary horns (cluster horns) are used, and the excitation coefficient of each horn is adjusted so that the cross polarization component is reduced (1987 National Convention record of The Institute of Electronics, Information and Communication Engineers in Japan, No.641, page 3-83, March 1987).
c) A grid reflector plate which has a polarization selection property is used in a mirror element of a reflector, and the cross polarization component is suppressed by restricting direction of the current on the mirror (C.C.Chen and C.F.Franklin, "Ku-Banå Multiple Beam Antenna", NASA CONTRACT REPORT 154364,
December, 1980).
d) A grid plate which has the polarization selection property is put on an aperture plane of a reflector so that only desired polarization is radiated, and undesired cross polarization is blocked (R.W.Gruner and
W.J.English, "Antenna Design Studies for a U.S.domestic
Satellite", Comsat Technical Review, vol.4, No.2, page 413, 1974).
e) A grid plate which has the polarization selection property is put between a primary horn and a reflector so that the polarization direction of an input wave of a reflector is adjusted to reduce cross polarization of the reflected wave from a reflector. (1986 National
Convention record of The Institute of Electronics,
Information and Communication Engineers in Japan, No.59, page 1-59, September 1986).
f) The UK patent No. 1,525,514 shows uncontinuous elements, like a pin and/or an iris, on a mode conversion portion of a feed horn to generate asymmetrical high order mode (TEo2 mode in case of a conical horn), resulting the reduction of the cross polarization of an offset reflector antenna.
However, the above methods have disadvantages as follows.
The first prior art (a) has the disadvantage that an additional sub-reflector must be used.
The second prior art (b) has the disadvantage that the structure of a feed circuit is complicated.
Therefore, it would only suit a multi-shaping beam antenna for a satellite with cluster feed.
The third prior art (c) has the disadvantage that the manufacturing process ofthereflector is complicated.
The prior art (d) and (e) has the disadvantage that an additional polarization grid plate must be used.
Further, the prior art (c), (d) and (e) have the disadvantages that a dual polarization antenna (and a circular polarization antenna) is impossible, that a side lobe level is high due to undesired scatter wave by a grid plate, and that a grid plate having excellent characteristics in a wide frequency band is difficult.
The prior art (f) has the disadvantages that the manufacturing process of a feed horn is complicated, and that the frequency band is narrow since it is difficult to impose a higher mode on a main mode with predetermined ratio over a wide frequency band.
It is an object, therefore, of the present invention to provide a new and improved offset reflector antenna by overcoming the disadvantages and limitations of prior offset reflector antennas.
In accordance with the present invention, an offset reflector antenna comprises a reflector and a feed horn for feeding the reflector at a non-zero offset angle C so that aperture blockage by the feed horn is eliminated, wherein an asymmetrical structure is provided at an opening portion of the feed horn, so that a slant angle OA is provided between the axis of the feed horn, and the normal direction of an opening plane of the feed horn.
The invention provides an offset reflector antenna which has excellent cross polarisation characteristics with a simple structure.
Some examples of antennae according to the invention will now be described and contrasted with a known antenna with reference to the accompanying drawings, in which:
Figure 1 shows a cross section of a known offset reflector antenna;
Figures 2A and 2B show field distribution on aperture planes of a known feed horn and main reflector, respectively;;
Figs.3A and 3B show field distribution on aperture planes of a feed horn, and a main reflector, respectively, according to the present invention,
Figs.4A through 4C show structures of a first embodiment of an offset reflector antenna according to the present invention,
Figs.5A through SD show structures of a second embodiment of an offset reflector antenna according to the present invention,
Fig.6 shows the experimental curves of the present offset reflector antenna with those of a prior art,
Fig.7 shows the other experimental curve of the improvement of cross polarization component according to the present invention.
The basic idea of the present invention is the relations of the electric field on an aperture plane of a main reflector and structure of an opening portion of a feed horn.
Fig.l shows a cross section of an offset refelctor antenna, in which the numeral 1 is a main reflector mirror plane, 1' is an aperture plane of the main reflector 1, 2 is a feed horn, and 4 is an opening plane oftnefeed horn 2. It should be noted thatthereflecting surface of the main reflector is a portion of a paraboloid which is not symmetrical with respect to its beam axis RB, and does not include the vertex V of said paraboloid, so-called parent paraboloid, so that aperture blockage by the feed horn is eliminated.
Conventionally, the electric field on the aperture plane of the feed horn 2 is symmetrical as shown in
Fig.2A. However, the field on the aperture plane of the main reflector 1 is not symmetrical in spite of the symmetrical field of Fig.2A because of the asymmetrical structure of the main reflector, and the undesired horizontal component A which causes the cross polarization component is generated as shown in Fig.2B.
The undesired horizontal component A is perpendicular to the desired component B. Here, in Fig.2, the definition of the symmetricity of electric field on the aperture is whether the electric field on the circular aperture is expressed by the following form or not.
E#α sin # E#α cos # where Ep and E are -component and -component of the electric field in cylindrical coordinates, respectively.
The basic idea of the present invention is shown in Figs.3A and 3B. In those figures, the field on the aperture plane of the feed horn 2 is asymmetrical as shown in Fig.3A so that the field on the aperture plane of the main reflector 1 has no horizontal component, as shown in Fig.3B. In other words, the direction of polarization of the output of the feed horn 2 is adjusted so that the direction of the polarization of the output beam of the main reflector 1 is only in one direction.
The undesired component A in Fig.2B is cancelled out by the cross polarization component in the field on an aperture plane of a feed horn of Fig.3B.
Figs.4A through 4C show the structure of the first embodiment of the present invention. In those figures, the feed horn 2 illuminates the offset reflector 1 with offset angle 60.
It should be noted that the physical axis 3 (propagation direction) of the feed horn 2 does not coincide with the normal direction 5 of the opening plane 4 of the feed horn 2. The angle e is the slant angle between said physical axis 3 and the normal direction 5.
The normal direction 5 is of course perpendicular to the aperture plane 4.
In the embodiment of Fig.4A, the opening plane 4 of the feed horn 2 is not perpendicular to the axis 3 of the feed horn 2. Therefore, the normal direction 5 of the opening plane 4 of the feed horn 2 is slanted in view of the opening plane 4 of the feed horn 2.
When the feed horn 2 is a conical horn antenna, the non-zero slant angle EA forms the shape of an oblique cone whose base 4 is not perpendicular to its principle axis 3.
It should be noted in Fig.4A that the angle eA is chosen so that the normal direction 5 of the opening plane 4 is directed to the neibourhood of the vertex V of the parent paraboloid.
The slant angle eA is preferably equal to the offset angle e0. In that case, the normal direction 5 of the opening plane 4 of the feed horn 2 is directed exactly to the vertex V of the parent paraboloid and the undesired cross polarization compoment becomes minimum.
In the prior art, since the opening plane 4 is perpendicular to the axis 3 of the feed horn 2, the slant angle eA is zero.
Fig.4B shows the embodimentwhere the feed horn 2 is the combination of a plurality of horns (for instance 2 horns) which are connected in series with one another so that the horn axis is offset in view of that of the adjacent horn.
Fig.4C shows the embodiment in which the aperture plane 4 of the feed horn 2 is perpendicular to the physical axis of the feed horn 2, but the horn 2 has an asymmetrical flange 6 on the aperture plane 4 of the feed horn 2. The aperture plane 4 and the asymmetrical flange 6 constitutes an opening portion 7.
As explained above, the embodiment of Figs.4A through 4C has the feature that the axis 3 of the feed horn 2 is slanted to the normal direction 5 of the opening plane 4 or the opening portion 7 of the feed horn 2.
Figs.5A through SB show the second embodiment of the present invention. The feature of the second embodiment is that the normal direction of the aperture plane coincides physically with the axis of the feed line, but said normal direction is electrically slanted to the axis of the feed horn.
In the embodiment of Fig.5A, the opening plane 4 and the opening portion 7 of the feed horn 2are perpendicular to the axis 3 of the feed horn 2. However, the flange 6 arranged on the opening portion 7 has asymmetrical chokes 8a through 8n so that the normal line 5 slants electrically to the axis 3 of the horn 2. Fig.5A shows the embodimentwnere the depth of each choke 8a through 8n is designed so that the normal line slants electrically to the axis of the horn. In one modification, the chokes with a uniform depth can also electrically slant the normal line to the axis by changing the spacing between two adjacent chokes from one another.
Fig.5B is the embodiment of a corrugated horn, in which the corrugated structure 9 of the horn 2 is asymmetrical between the upper portion and the bottom portion, as shown in the drawing. The asymmetrical structure of the corrugated structure 9 changes the propagation constant of the feed horn 2 between the upper portion and the bottom portion of the horn 2, and therefore, the phase difference is obtained between the upper portion and the bottom portion of the horn.
Therefore, the normal line 5 is electrically slanted to the axis 3 of the horn 2.
Fig.6 shows the curves which show the improvement of cross polarization level according to the present invention. In Fig.6, the horizontal axis shows the azimuth angle (degrees) of the antenna, and the vertical axis shows the relative gain (dB) of the antenna. The curve A shows a radiation pattern of the reference polarization component, the curve B is a prior radiation pattern of the cross polarization (yea=0), and the curve C is the present radiation pattern of the cross polarization in which eA is 40 and e;=.e0. It is clear in Fig.6 that the cross polarization characteristics of the present invention are improved by about 20 dB as compared with those of a prior art.There is no difference in the radiation pattern of the reference polarization component between a prior art and the present invention.
Fig.7 shows the experimental curve of the improvement of the cross polarization characteristics according to the present invention. In the figure, the abscissa shows the angle e (see Fig.3A), and the ordinate shows the ratio of the peak level of the cross polarization level to the peak level of the reference polarization level. It should be appreciated in Fig.7 that when 8 =8 , the cross polarization level is the lowest. The present invention is useful in the region that #A##0/2 is satisfied.
Some modifications are of course possible.
For instance, although a conical horn is described in the embodiments, a pyramid horn, and/or a diagonal horn is possible in the present invention.
As described above in detail, the present invention improves the cross polarization characteristics of an offset reflector antenna by controlling the field on an aperture plane of a feed horn so that the cross polarization field on an aperture plane of a main reflector is cancelled out or at least reduced by the cross polarisation component on the opening plane of a feed horn.
Claims (8)
1. An offset reflector antenna having a reflector and a feed horn for feeding the reflector at a non-zero offset angle 60, so that aperture blockage by the feed horn is eliminated, wherein an asymmetrical structure is provided at an opening portion of the feed horn, so that a slant angle OA is provided between the axis of the feed horn, and the normal direction of an opening plane of the feed horn.
2. An offset reflector antenna according to claim 1, wherein the asymmetrical structure comprises an obliaue opening of the feed horn.
3. An offset reflector antenna according to claim 1, wherein the asymmetical structure is an asymmetrical flange attached to the opening portion of the feed horn.
4. An offset reflector antenna according to claim 1, wherein the asymmetrical structure is a symmetrical flange having a plurality of chokes arranged asymmetrically and attached to an opening portion of the feed horn.
5. An offset reflector antenna according to claim 1, wherein the asymmetrical structure is a corrugated horn which has an asymmetrical corrugated structure on an inner wall of the horn.
6. An offset reflector antenna according to any of the preceding claims, wherein OA= > O 0/2 is satisfied.
7. An offset reflector antenna according te any of claims 1 to 5, wherein the slant angle GA is substantially equal to the offset angle 60.
8. An offset reflector antenna substantially as hereinbefore described with reference to any of the examples shown in Figures 3 to 7 of the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP28689688A JPH02134001A (en) | 1988-11-15 | 1988-11-15 | Offset reflection mirror antenna |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8924447D0 GB8924447D0 (en) | 1989-12-20 |
| GB2226186A true GB2226186A (en) | 1990-06-20 |
Family
ID=17710401
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8924447A Withdrawn GB2226186A (en) | 1988-11-15 | 1989-10-31 | An offset reflector antenna |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPH02134001A (en) |
| GB (1) | GB2226186A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0921590A2 (en) * | 1997-12-04 | 1999-06-09 | Nec Corporation | Antenna for communicating with low earth orbit satellite |
| WO2000079649A1 (en) * | 1999-06-21 | 2000-12-28 | Thomson Licensing S.A | Device for transmitting and/or receiving signals |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1057441A (en) * | 1963-08-09 | 1967-02-01 | Cossor Ltd A C | Asymmetrical horn |
| EP0079533A1 (en) * | 1981-11-07 | 1983-05-25 | Messerschmitt-Bölkow-Blohm Gesellschaft mit beschränkter Haftung | Horn antenna |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS544049A (en) * | 1977-06-13 | 1979-01-12 | Nippon Telegr & Teleph Corp <Ntt> | Offset antenna |
| JPH0744381B2 (en) * | 1987-08-20 | 1995-05-15 | 三菱電機株式会社 | Antenna device |
-
1988
- 1988-11-15 JP JP28689688A patent/JPH02134001A/en active Pending
-
1989
- 1989-10-31 GB GB8924447A patent/GB2226186A/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1057441A (en) * | 1963-08-09 | 1967-02-01 | Cossor Ltd A C | Asymmetrical horn |
| EP0079533A1 (en) * | 1981-11-07 | 1983-05-25 | Messerschmitt-Bölkow-Blohm Gesellschaft mit beschränkter Haftung | Horn antenna |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0921590A2 (en) * | 1997-12-04 | 1999-06-09 | Nec Corporation | Antenna for communicating with low earth orbit satellite |
| EP0921590A3 (en) * | 1997-12-04 | 1999-09-15 | Nec Corporation | Antenna for communicating with low earth orbit satellite |
| WO2000079649A1 (en) * | 1999-06-21 | 2000-12-28 | Thomson Licensing S.A | Device for transmitting and/or receiving signals |
| US6618012B1 (en) | 1999-06-21 | 2003-09-09 | Thomson Licensing S.A. | Device for transmitting and/or receiving signals |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8924447D0 (en) | 1989-12-20 |
| JPH02134001A (en) | 1990-05-23 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |