CA1296422C - Multibeam antenna - Google Patents
Multibeam antennaInfo
- Publication number
- CA1296422C CA1296422C CA000556203A CA556203A CA1296422C CA 1296422 C CA1296422 C CA 1296422C CA 000556203 A CA000556203 A CA 000556203A CA 556203 A CA556203 A CA 556203A CA 1296422 C CA1296422 C CA 1296422C
- Authority
- CA
- Canada
- Prior art keywords
- reflector
- antenna
- partial
- multibeam antenna
- partial reflector
- 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.)
- Expired - Fee Related
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Classifications
-
- 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
- H01Q19/18—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 having two or more spaced reflecting surfaces
- H01Q19/19—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 having two or more spaced reflecting surfaces comprising one main concave reflecting surface associated with an auxiliary reflecting surface
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q25/00—Antennas or antenna systems providing at least two radiating patterns
- H01Q25/007—Antennas or antenna systems providing at least two radiating patterns using two or more primary active elements in the focal region of a focusing device
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- Aerials With Secondary Devices (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A multibeam antenna capable of communicating with a plurality of satellites on stationary orbits at the same time includes a single main reflector, and a plurality of primary radiators for radiating electromagnetic waves toward the main reflector. The main reflector is constituted by the same number of partial reflectors as the primary radiators, the partial reflectors being joined to each other. Each of the partial reflectors is defined by a part of a different one of paraboloids which are different in the position of focus from each other.
The primary reflectors are located at the positions of individual focuses. A subreflector is disposed between the main reflector and the positions of focuses and made up of a plurality of curved portions and a single flat portion.
A multibeam antenna capable of communicating with a plurality of satellites on stationary orbits at the same time includes a single main reflector, and a plurality of primary radiators for radiating electromagnetic waves toward the main reflector. The main reflector is constituted by the same number of partial reflectors as the primary radiators, the partial reflectors being joined to each other. Each of the partial reflectors is defined by a part of a different one of paraboloids which are different in the position of focus from each other.
The primary reflectors are located at the positions of individual focuses. A subreflector is disposed between the main reflector and the positions of focuses and made up of a plurality of curved portions and a single flat portion.
Description
MULTIBEAM ANT}~:NNA
BACKGROUND OF THE INVENTION
The present invention relates to a multibeam antenna capable of communicating with a plurality of satellites which are positioned on stationary orbits at the same time.
A prior art multibeam antenna is constituted by a plurality of primary radiators and a single parabolic reflector for reflecting an electromagnetic wave radiating from each primary radiator in a different direction. The primary radiators are located in the vicinity of the focus of the parabolic reflector, or paraboloid, at a suitable distance from each other. A feeder section and a low-noise amplifier are associated with each of the primary radiators in such a manner as to extend along the axis of the antenna.
In the above-described prior art antenna, the deviation of ~; 15 the beams radiating from the parabolic reflector cannot be increased without increasing the distance between the primary radiators. However, an increase in the distance between the nearby primary radiators necessarilY results in th~ shift of the primary radiators awaY from the focus of the parabolic - 2 0 reflector, whereby the wavefront in the aperture plane of the , ~:
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parabolic reflector is disturbed to lower antenna gain. Another problem with the prior art antenna is that the feeder section and amplifier section directly connected to each of the primarY
reflectors increase the len~th of antenna axis because they are 5 arranged along the antenna axis.
For details of such a prior art multibeam antenna, a reference may be made to U. S. Patent 3, 852, 763 bY waY of example.
SUMMARY OF THE INVENTION
It is an obiect of thè present invention to provide a multibeam antenna having improved antenna efficiency.
It is another obiect of the present invention to provide a multibeam antenna which eliminates the disturbance to the 15 wavefront in an aperture plane to thereby allow the deviation of beams radiating to be increased.
It is another obiect of the present invention to provide a multibeam antenna which allows the length of an antenna axis reduced.
2 0 I$ is another obiect of the present invention to provide a multibeam antenna which suppresses the decrease in the phase performance in an aperture plane.
It is another obiect of the present invention to provide a multibeam antenna which allows the lateral dimension of a main reflector to be reduced.
.
~296422 It is another object of the present invention to provide a generally improved multibeam antenna.
A m~lltibeam antenna of the present inYention comprises a main reflector constituted by at least a first and a second partial reflector, the first partial reflector being defined by a part of a first paraboloid which has a first focus and a first axis of rotation, the second partial reflector being defined by a part of a second paraboloid which has a second focus and a second axis of rotation, the first and second partial reflectors being joined to each other with the first and second axes oriented in different directions from each other, a first primary radiator radiating an electromagnetic wave toward the main reflector to irradiate the first partial reflector and a part of the second reflector, and a second primary radiator for radiating an electromagnetic wave toward the main reflector to irradiate the second partial reflector and a part of the first partial reflector.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other obiects, features and advantages o~ the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which:
Fig. l is a shcmeatic YieW showing a prior art multibeam antenna;
Figs. 2A and 2B are views showing a first embodiment of , .
~2~i422 the multibeam antenna in accordance with the present invention;
Figs. 3A and 3B are views showing a second embodiment of the present invention;
Figs. 4A and 4B are views showing a third embodiment of 5 the present invention i Figs. 5A and 5B are views showing a fourth embodiment of the present invention;
Fig. 6 is a view showing a fifth embodiment of the present invention;
Fig. 7 is an external view of a subreflector of the multibeam antenna as shown in Fig. 6; and Figs. 8 and 9 are schematic diagrams showing how the curved configuration of the subreflector shown in Fig. 6 is designed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
To facilitate an understanding of the present invention, a brief reference will be made to a prior art multibeam antenna, shown in Fig. 1. As shown, an exemplary multibeam antenna 20 10 includes a plurality of, three for example, primarY radiators 12, 14 and 16, and a single parabolic reflector 18 which reflects each of electromagneSic waves radiated from the primary radiators in a different direction. The primary radiators 12, 14 and 16 are located in the vicinity of the focus F of the parabolic 2 5 reflector 18 at a suita~le distance from each other. A feeder ' ' :
.
~2~fi4~2 soction 1 2a and a low-noise amplifier 1 2b are associated with each of the primarY radiators, as represented by the radiator 12 in the figure, and so arranged as to extend along the axis of the antenna.
As previouslY discussed, a problem with the prior art antenna 10 is that an increase in the distance between the Primary radiators 12, 14 and 16 causes them to be shifted away from the focus F, disturbing the wavefront in the aperture plane or the parabolic reflector 18 and, thereby, lowering antenna 8ain. Further, the feeder section and low-noise amplifier directly connected to each of the primary radiators extend in the axial direction of the antenna, increasing the overall length of thc antenna axis.
Referring to Figs. 2A and 2B, a multibeam antenna embodying the present invention is shown and generallY
dosignated by the reference numeral 20. In this particular embodiment~ the antenna 20 comprises two-beam antenna which is made up of a main reflector 22 and two main radiators 24 and 2 6 . The main reflector 2 2 is constituted by two partial roflectors 22A and 22B which are defined by, respectivelY, a Part of a paraboloid A and a part of a paraboloid. The partial roflectors 22A and 22B are joined to each other along a boundary line 3 2 such that the axis of rotation 2 8 of the Paraboloid A and the axis of rotation 3 0 of the paraboloid B
25 illtorsect each other. Each of the axes of rotation 28 and 30 is inclined by an angle of ~/2 relative to the center axis 34 of the antenna. The foci Fa and Fb of the paraboloids A and B, respectively, which are located on the individual axes are spaced apart by a distance of 2d from each other.
The primary radiator 24 is positioned at the focus Fa on the axis 28 while the primary radiator 26 is positioned at the focus Fb on the axis 30~ In this configuration, the primary radiator 26 mainly irradiates a region 22b of the partial reflector 22A, and the primary reflector 26 mainly irradiates a region 22b of the partial reflector 22B. As shown, the regions 22a and 22b overlap each other as at 22c along the boundary line 22.
Specifically, the region 22a is constituted bY the partial reflector 22A and a part of the partial reflector 22B while the region 22b is constituted by the partial reflector 22B and a part of the partial reflector 22A. The surface curve of the region 22a and that of the region 22 b can be approximately equalized to the paraboloids A and B, respectively, by adequately selecting the ` ~ distance 2d between the primary radiators 24 and 26.
In the abo~e arrangement, rays radiating from the focus Fa are reflected by the region 22a of the main reflector 22 to become rays which are substantially parallel to the center axis 28 of the paraboloid A (radiation direction of beam A) .
Likewise, rays radiating from the focus Fb are reflected by the ~; region 22b of the main reflector 22 to become rays which are substantially parallel to the center axis 30 of the paraboloid B
: ~
~2~6422 (radiation direction of beam B). Specifically, electromagnetic waves coming out of the primary radiators 24 and 26 are radiated in different directions from each other, i. e., in the direction of the axis 28 and that of the axis 30.
The construction described above constitutes a two-beam antenna.
Referring to Figs. 3A and 3B, a second embodiment of the multibeam antenna in accordance with the present invention is shown. While in the first embodiment the primary radiators 24 1~ and 26 and their associated partial reflectors 22A and 22B are located on the same side with respect to the center axis 34 of the antenna 20, in the second embodiment the radiators 24 and 26 and their associated partial reflectors 22A and 22B are located at the opposite sides. Specifically, as shown in Fi8s. 3A and 3B, the partial reflector 22A associated with the primarY reflector 24 is constituted by a part of the paraboloid B while the partial reflector 2 2B associated with thc primarY radiator 2 6 is constituted by a part of the paraboloid A. The rest of the second embodiment is identical in construction as the first embodiment.
~eferring to Figs. 4A nd 4B, a third embodiment of the ; ~ multibeam antenna in accordance with the present invention is shown. As shown, the multibeam antenna 5 0 includes a flat reflector 52 which is located between the main reflector 22 and the two foci Fa and Fb. The primary radiators 24 and 26 are , .
.
~2~642Z
located at, respectively, the inYervted image points fa and fb of the foci Fa and Fb as defined by the flat reflector 52, the radiators 24 and 26 each facing the flat reflector 52. In this construction, electromagnetic waves radiating from the primary radiators 24 and 26 are individually reflected by the flat reflector 52 and, then, by the main reflector 22 to be radiated in two different directions. The flat reflector 52 simply serves to bend the paths of electromagnetic waves and, therefore, the antenna 50 per se shares the same principle of operation as the antenna 20 of the first embodiment. An advantage attainable with the flat reflector 52 is the reduction of the axial length of the antenna.
Referring to Figs. 5A and 5B, a fourth embodiment of the multibeam antenna in accordance with the present invention is shown. In the figures, a multibeam antenna 60 is constructed to function as a three-beam antenna. As shown, the main reflector 22 includes three partial reflectors 22A, 22B and 22C.
The partial reflectors 22A and 22B join each other along the boundary line 32, and the partial relectors 22B and 22C ioin each other along a boundary line 62. The reMectors 22A, 22B
and 22C are constituted by, respecti~ely, a part of the paraboloid A, a part of the paraboloid B, and a part of a parabolic plane C. The parabolic planes A, B and C have, respectively, foci Fa, Fb and Fc which are different from each other and axes of rotation 28, 30 and 64 which are different in ~2~6422 g direction from each other. The primary radiators 24 and 26 and a primary radiator 66 are located at, respectiYely, the foci Fa, Fb and Fc of the axes 28, 30 and 64. The principle of operation of the antenna 6 0 is the same as that of the first 5 embodiment and, therefore, will not be described to avoid redundancy.
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129fi422 The overlapping portion 22c of the radiation regions on the main reflector in any of the first to fourth embodiments will be described in more detail. As preYiously stated, the regions 22a and 22b can be aligned with the paraboloids A and B, 5 respectively, by adequately selecting the distance 2 d between, for example, the primary radiators 24 and 26 of Figs. 3A and 3B. However, the alignment is onlY approximate and not precise. Specifically, that part of the region 22b which lies in the ovelapping portion 22c has a surface curve which is defined 10 by the paraboloid B, and that part of the region 22a which lies in the overlapping portion 22c has a surface curve which is defined by ths paraboloid A. In this condition, since the focus Fa is not coincident with the focus of the partial reflector 2 2B
(paraboloid B), that part of rays radiating from the focus Fa 15 which are incident to the partial reflector 22B in the overlapping portion 22c become substantially and not precisely parallel to the center axis 28 after being reflected by the reflector 22B. It follows that the optical path which interconnects the focus Fa, the reflector 22B and a plane which is perpendicular to the axis 2~ 28 in this order is not constant in length and has some error, i. e., phase error.
No doubt, such a phase error does not affect ths usefulness of the first to fourth embodiments at all because the phase error is not noticeable, because the curve of the major part of the 25 region 22b is defined by the paraboloid A, and because the curve .
~''' .
i2~6422 of the region 2~a is defined by the paraboloid B. Specifica~lY, for such reasons, the decrease in the phase efficiency in the aperture plane which is ascribable to the phase error is lower than that ascribable to a phase error which would be caused if any of the primary radiators of the prior art multibeam antenna shown in Fig. 1 were deviated from the focus.
In order to allow a minimum of decrèase to occur in the phase efficiency in the aperture plane, it is a prèrequisite that the regio~s 22b and 22a mainlY use the partial reflectors 22A
and 22B, respectively, i. e., the overlapping portion 22c be reduced. This, however, brings about another drawback that the lateral dimension of the main reflector 22 is increased.
Referring to Fig. 6, a fifth embodiment of the present invention is shown which solves the above dilemmatic situation.
As shown, a multibeam antenna 70 of Fig. 6 includes the main reflector 2 2, two primary radiators 2 4 and 2 6, and a single subreflector 7 2 . The main reflector 2 2 is constituted by the partial reflectors 22A and 22B which constitute, respectivelY, a part of the paraboloid A and a part of the paraboloid B~ The partial reflectors 22A and 22B are joined to each other along the - ~ boundary line 32 such that their center axes 28 and 30 intersect each other. The subreflector 72 is located between the focus Fa of the paraboloid A which is positioned on the axis 28 and the focus Fb of the paraboloid B which is located on the axis 30.
As shown in Fig. 7, the subreflector 72 is made up of three , .
12~6422 portions, i. e., a cur~ed portion 72A close to the partial reflector 22A, a cur~led portion 72~ close to the partial reflector 22B, and a flat intermediate portion 72C which interconnect the two curved portions 72A and 72B. The surface curves of the curved portions 72A and B are individually determined as will be describe later.
The primary reflectors 24 and 26 are located at, respectively, inYerted image points F'a and F'b which are symmetrical to the foci Fa and Fb with respect to the subreflector 72, each radiating an electromagnetic wave toward the subreflector 72.
How the curves of the subreflector 72 are determined will be explained with reference to Figs. 8 an 9. In Fig. 8, assuming that the subreflector 72 is absent, those of the numerous rays radiating from the focus Fa which are incident to the partial reflector (paraboloid A) 22A are reflected by the paraboloid A
without exception to become rays which are parallel to the center ;~ ~ axis 28; the distances measured from the focus Fa to a plane ~; which is perpendicular to the axis 28 by way of the paraboloid A
are equal to each other. It follows that if that portion of subreflector 72 which is associated with the paraboloid A, i. e., the intermediate portion 72c is flat, those of the rays radiating , from the point F'a which are incident to the intermediate portion 72C are reflected by the portion 72C and, then, by the ;~:
~ ~ ~ 25 paraboloid A to be therebY turned into rays which are parallel to ~2~fi422 the axis 28.
On the other hand, when the subreflector 7 2 is absent, among rays radiating from the focus Fa, those which are incident to the partial reflector (paraboloid B) 22B are reflected 5 by the paraboloid B to become generally parallel to the axis 28.
However, the distances measured from the foc~ls Fa to the plane which is parallel to the axis 28 by way of the paraboloid B are not the same as each other and involve some error. In light of this, that part (curved portion 72A) of the subreflector 72 10 which is associated with the paraboloid is provided with a predetermined curve which is slightlY deviated from a plane. In this condition, the lengths of the optical paths along which rays are radiated from F'a, then reflected by the curved portion 72A, and then incident to the plane which is perpendicular to the axis 15 2 8 become equal to each other. This reduces the decrease in efficiency due to phase errors which are ascribable to the paraboloid B.
Fig. 9 is a view similar to Fig. 8, showing rays which are radiating from the other point F~ toward the axis 30. Details of 20 Fig. 9 will be understood by analogy from Fig. 8.
The gist is that the surface curves of the curved portions 7 2A and 7 2B of the subreflector 7 2 are so selected as to compensate for or reduce the phase error in the event when electromagnetic waves reflected by the curved portions are 25 radiated by their associated partial reflectors.
It will be seen from the above that the size of the curved portion 7 2A and that of the curved portion 7 2B are dependent upon the sizes and focuses of their associated partial reflectors and the location of the subreflector 72. While the intermediate portion 72c is shown as being sized substantially the same size as the curved portions 72A and 72B, its size is variæble depending upon, for example, the difference in focal length ~etween the two paraboloids. By comparing Figs. 8 and 9, it will be understood that that area of the subreflector 72 to which 10 the rays radiating from the point F'a and those radiating from the point F'b are incident is included in the intermediate portion 72C. This, coupled with the fact that the intermediate portion 72C is flat, allows the intermediate portion 72C to be shared by those two different groups of rays without entrailing any phase 15 error. In this manner, the subreflector 24 is capable of simultaneously compensating for phase errors which-occur on the main reflector 22 with respect to the two different directions of radiations. ConsequentlY9 since that part of an electromagnetic wave radiating from the primary radiator 24 which is incident to 20 the partial reflector 22B is compensated for in phase error, the limitation that, for example, the wave from the radiator 24 should mainly use the partial reflector 22A is eliminated. Hence, as shown in Figs. 8 and 9, the same region of the main reflector 2 2 can be shared by two different beams, promoting the 25 decrease in the lateral dimension of the main reflector 22.
~ .
While the present inYention has been shown and described in relation to a two-beam and a three-beam antenna, it will be apparent that it is similarly applicable to an antenna of the type using four or more beams.
Further, although the foregoing description has concentrated on a situation wherein a plurality of focuses and the axes of rotation of a plurality of paraboloids are positioned in the same plane, such is only illustrative and may be replaced with a situation wherein, for example, the axes 2 8 and 3 0 of the paraboloids A and 8, respectively, are in a distorted relationship. Specifically, the axes 2 8 and ~ 0 may each be extended in any desired direction other than the same plane.
It is not necessary that angles between the individual axes of rotation and the associated primary reflectors be equal to each 1 5 other.
In addition, the focal lengths of the paraboloids may not be equal to each other, and the contour of the main reflector is open to choice.
In summary, it will be seen that the present invention proYides a highly efficient multibeam antenna despite that nearby ., ones of a plurality of radiation regions which are defined on a single main reflector overlap each other. This is because the :~ cur~e of each radiation region is provided with substantiallY the same paraboloid as the surface curve of a radiation region which 2 5 is defined on a single main reflector and, hence, each of the : : ;
~296422 radiation regions can be regarded as a parabolic reflector which is independent of the others. Another advantage attainable with the present invention is that the length of antenna axis can be reduced ~y transmitting electromagnetic radiations from a 5 plurality of primary radiators indirectly to a main reflector by way of a single flat reflector.
Further, in accordance with the present invention, a subreflector capable of compensating for phase errors particular to the radiation of electromagnetic waves by a main reflector is 10 interposed between the main reflector and primary radiators, whereby the decrease in the phase efficiency in the aperture plane is suppressed. Since phase errors are compensated for by the subreflector as stated, it is not necessary to accurately match the primary reflectors with partial reflectors which constitute the 15 main reflector and, therefore, the lateral dimension of the main reflector can be reduced.
Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without deParting from the scope thereof.
, .
BACKGROUND OF THE INVENTION
The present invention relates to a multibeam antenna capable of communicating with a plurality of satellites which are positioned on stationary orbits at the same time.
A prior art multibeam antenna is constituted by a plurality of primary radiators and a single parabolic reflector for reflecting an electromagnetic wave radiating from each primary radiator in a different direction. The primary radiators are located in the vicinity of the focus of the parabolic reflector, or paraboloid, at a suitable distance from each other. A feeder section and a low-noise amplifier are associated with each of the primary radiators in such a manner as to extend along the axis of the antenna.
In the above-described prior art antenna, the deviation of ~; 15 the beams radiating from the parabolic reflector cannot be increased without increasing the distance between the primary radiators. However, an increase in the distance between the nearby primary radiators necessarilY results in th~ shift of the primary radiators awaY from the focus of the parabolic - 2 0 reflector, whereby the wavefront in the aperture plane of the , ~:
' :.~
parabolic reflector is disturbed to lower antenna gain. Another problem with the prior art antenna is that the feeder section and amplifier section directly connected to each of the primarY
reflectors increase the len~th of antenna axis because they are 5 arranged along the antenna axis.
For details of such a prior art multibeam antenna, a reference may be made to U. S. Patent 3, 852, 763 bY waY of example.
SUMMARY OF THE INVENTION
It is an obiect of thè present invention to provide a multibeam antenna having improved antenna efficiency.
It is another obiect of the present invention to provide a multibeam antenna which eliminates the disturbance to the 15 wavefront in an aperture plane to thereby allow the deviation of beams radiating to be increased.
It is another obiect of the present invention to provide a multibeam antenna which allows the length of an antenna axis reduced.
2 0 I$ is another obiect of the present invention to provide a multibeam antenna which suppresses the decrease in the phase performance in an aperture plane.
It is another obiect of the present invention to provide a multibeam antenna which allows the lateral dimension of a main reflector to be reduced.
.
~296422 It is another object of the present invention to provide a generally improved multibeam antenna.
A m~lltibeam antenna of the present inYention comprises a main reflector constituted by at least a first and a second partial reflector, the first partial reflector being defined by a part of a first paraboloid which has a first focus and a first axis of rotation, the second partial reflector being defined by a part of a second paraboloid which has a second focus and a second axis of rotation, the first and second partial reflectors being joined to each other with the first and second axes oriented in different directions from each other, a first primary radiator radiating an electromagnetic wave toward the main reflector to irradiate the first partial reflector and a part of the second reflector, and a second primary radiator for radiating an electromagnetic wave toward the main reflector to irradiate the second partial reflector and a part of the first partial reflector.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other obiects, features and advantages o~ the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which:
Fig. l is a shcmeatic YieW showing a prior art multibeam antenna;
Figs. 2A and 2B are views showing a first embodiment of , .
~2~i422 the multibeam antenna in accordance with the present invention;
Figs. 3A and 3B are views showing a second embodiment of the present invention;
Figs. 4A and 4B are views showing a third embodiment of 5 the present invention i Figs. 5A and 5B are views showing a fourth embodiment of the present invention;
Fig. 6 is a view showing a fifth embodiment of the present invention;
Fig. 7 is an external view of a subreflector of the multibeam antenna as shown in Fig. 6; and Figs. 8 and 9 are schematic diagrams showing how the curved configuration of the subreflector shown in Fig. 6 is designed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
To facilitate an understanding of the present invention, a brief reference will be made to a prior art multibeam antenna, shown in Fig. 1. As shown, an exemplary multibeam antenna 20 10 includes a plurality of, three for example, primarY radiators 12, 14 and 16, and a single parabolic reflector 18 which reflects each of electromagneSic waves radiated from the primary radiators in a different direction. The primary radiators 12, 14 and 16 are located in the vicinity of the focus F of the parabolic 2 5 reflector 18 at a suita~le distance from each other. A feeder ' ' :
.
~2~fi4~2 soction 1 2a and a low-noise amplifier 1 2b are associated with each of the primarY radiators, as represented by the radiator 12 in the figure, and so arranged as to extend along the axis of the antenna.
As previouslY discussed, a problem with the prior art antenna 10 is that an increase in the distance between the Primary radiators 12, 14 and 16 causes them to be shifted away from the focus F, disturbing the wavefront in the aperture plane or the parabolic reflector 18 and, thereby, lowering antenna 8ain. Further, the feeder section and low-noise amplifier directly connected to each of the primary radiators extend in the axial direction of the antenna, increasing the overall length of thc antenna axis.
Referring to Figs. 2A and 2B, a multibeam antenna embodying the present invention is shown and generallY
dosignated by the reference numeral 20. In this particular embodiment~ the antenna 20 comprises two-beam antenna which is made up of a main reflector 22 and two main radiators 24 and 2 6 . The main reflector 2 2 is constituted by two partial roflectors 22A and 22B which are defined by, respectivelY, a Part of a paraboloid A and a part of a paraboloid. The partial roflectors 22A and 22B are joined to each other along a boundary line 3 2 such that the axis of rotation 2 8 of the Paraboloid A and the axis of rotation 3 0 of the paraboloid B
25 illtorsect each other. Each of the axes of rotation 28 and 30 is inclined by an angle of ~/2 relative to the center axis 34 of the antenna. The foci Fa and Fb of the paraboloids A and B, respectively, which are located on the individual axes are spaced apart by a distance of 2d from each other.
The primary radiator 24 is positioned at the focus Fa on the axis 28 while the primary radiator 26 is positioned at the focus Fb on the axis 30~ In this configuration, the primary radiator 26 mainly irradiates a region 22b of the partial reflector 22A, and the primary reflector 26 mainly irradiates a region 22b of the partial reflector 22B. As shown, the regions 22a and 22b overlap each other as at 22c along the boundary line 22.
Specifically, the region 22a is constituted bY the partial reflector 22A and a part of the partial reflector 22B while the region 22b is constituted by the partial reflector 22B and a part of the partial reflector 22A. The surface curve of the region 22a and that of the region 22 b can be approximately equalized to the paraboloids A and B, respectively, by adequately selecting the ` ~ distance 2d between the primary radiators 24 and 26.
In the abo~e arrangement, rays radiating from the focus Fa are reflected by the region 22a of the main reflector 22 to become rays which are substantially parallel to the center axis 28 of the paraboloid A (radiation direction of beam A) .
Likewise, rays radiating from the focus Fb are reflected by the ~; region 22b of the main reflector 22 to become rays which are substantially parallel to the center axis 30 of the paraboloid B
: ~
~2~6422 (radiation direction of beam B). Specifically, electromagnetic waves coming out of the primary radiators 24 and 26 are radiated in different directions from each other, i. e., in the direction of the axis 28 and that of the axis 30.
The construction described above constitutes a two-beam antenna.
Referring to Figs. 3A and 3B, a second embodiment of the multibeam antenna in accordance with the present invention is shown. While in the first embodiment the primary radiators 24 1~ and 26 and their associated partial reflectors 22A and 22B are located on the same side with respect to the center axis 34 of the antenna 20, in the second embodiment the radiators 24 and 26 and their associated partial reflectors 22A and 22B are located at the opposite sides. Specifically, as shown in Fi8s. 3A and 3B, the partial reflector 22A associated with the primarY reflector 24 is constituted by a part of the paraboloid B while the partial reflector 2 2B associated with thc primarY radiator 2 6 is constituted by a part of the paraboloid A. The rest of the second embodiment is identical in construction as the first embodiment.
~eferring to Figs. 4A nd 4B, a third embodiment of the ; ~ multibeam antenna in accordance with the present invention is shown. As shown, the multibeam antenna 5 0 includes a flat reflector 52 which is located between the main reflector 22 and the two foci Fa and Fb. The primary radiators 24 and 26 are , .
.
~2~642Z
located at, respectively, the inYervted image points fa and fb of the foci Fa and Fb as defined by the flat reflector 52, the radiators 24 and 26 each facing the flat reflector 52. In this construction, electromagnetic waves radiating from the primary radiators 24 and 26 are individually reflected by the flat reflector 52 and, then, by the main reflector 22 to be radiated in two different directions. The flat reflector 52 simply serves to bend the paths of electromagnetic waves and, therefore, the antenna 50 per se shares the same principle of operation as the antenna 20 of the first embodiment. An advantage attainable with the flat reflector 52 is the reduction of the axial length of the antenna.
Referring to Figs. 5A and 5B, a fourth embodiment of the multibeam antenna in accordance with the present invention is shown. In the figures, a multibeam antenna 60 is constructed to function as a three-beam antenna. As shown, the main reflector 22 includes three partial reflectors 22A, 22B and 22C.
The partial reflectors 22A and 22B join each other along the boundary line 32, and the partial relectors 22B and 22C ioin each other along a boundary line 62. The reMectors 22A, 22B
and 22C are constituted by, respecti~ely, a part of the paraboloid A, a part of the paraboloid B, and a part of a parabolic plane C. The parabolic planes A, B and C have, respectively, foci Fa, Fb and Fc which are different from each other and axes of rotation 28, 30 and 64 which are different in ~2~6422 g direction from each other. The primary radiators 24 and 26 and a primary radiator 66 are located at, respectiYely, the foci Fa, Fb and Fc of the axes 28, 30 and 64. The principle of operation of the antenna 6 0 is the same as that of the first 5 embodiment and, therefore, will not be described to avoid redundancy.
~ ~ /
, ~ /
~ ~ /
:`
, ~
129fi422 The overlapping portion 22c of the radiation regions on the main reflector in any of the first to fourth embodiments will be described in more detail. As preYiously stated, the regions 22a and 22b can be aligned with the paraboloids A and B, 5 respectively, by adequately selecting the distance 2 d between, for example, the primary radiators 24 and 26 of Figs. 3A and 3B. However, the alignment is onlY approximate and not precise. Specifically, that part of the region 22b which lies in the ovelapping portion 22c has a surface curve which is defined 10 by the paraboloid B, and that part of the region 22a which lies in the overlapping portion 22c has a surface curve which is defined by ths paraboloid A. In this condition, since the focus Fa is not coincident with the focus of the partial reflector 2 2B
(paraboloid B), that part of rays radiating from the focus Fa 15 which are incident to the partial reflector 22B in the overlapping portion 22c become substantially and not precisely parallel to the center axis 28 after being reflected by the reflector 22B. It follows that the optical path which interconnects the focus Fa, the reflector 22B and a plane which is perpendicular to the axis 2~ 28 in this order is not constant in length and has some error, i. e., phase error.
No doubt, such a phase error does not affect ths usefulness of the first to fourth embodiments at all because the phase error is not noticeable, because the curve of the major part of the 25 region 22b is defined by the paraboloid A, and because the curve .
~''' .
i2~6422 of the region 2~a is defined by the paraboloid B. Specifica~lY, for such reasons, the decrease in the phase efficiency in the aperture plane which is ascribable to the phase error is lower than that ascribable to a phase error which would be caused if any of the primary radiators of the prior art multibeam antenna shown in Fig. 1 were deviated from the focus.
In order to allow a minimum of decrèase to occur in the phase efficiency in the aperture plane, it is a prèrequisite that the regio~s 22b and 22a mainlY use the partial reflectors 22A
and 22B, respectively, i. e., the overlapping portion 22c be reduced. This, however, brings about another drawback that the lateral dimension of the main reflector 22 is increased.
Referring to Fig. 6, a fifth embodiment of the present invention is shown which solves the above dilemmatic situation.
As shown, a multibeam antenna 70 of Fig. 6 includes the main reflector 2 2, two primary radiators 2 4 and 2 6, and a single subreflector 7 2 . The main reflector 2 2 is constituted by the partial reflectors 22A and 22B which constitute, respectivelY, a part of the paraboloid A and a part of the paraboloid B~ The partial reflectors 22A and 22B are joined to each other along the - ~ boundary line 32 such that their center axes 28 and 30 intersect each other. The subreflector 72 is located between the focus Fa of the paraboloid A which is positioned on the axis 28 and the focus Fb of the paraboloid B which is located on the axis 30.
As shown in Fig. 7, the subreflector 72 is made up of three , .
12~6422 portions, i. e., a cur~ed portion 72A close to the partial reflector 22A, a cur~led portion 72~ close to the partial reflector 22B, and a flat intermediate portion 72C which interconnect the two curved portions 72A and 72B. The surface curves of the curved portions 72A and B are individually determined as will be describe later.
The primary reflectors 24 and 26 are located at, respectively, inYerted image points F'a and F'b which are symmetrical to the foci Fa and Fb with respect to the subreflector 72, each radiating an electromagnetic wave toward the subreflector 72.
How the curves of the subreflector 72 are determined will be explained with reference to Figs. 8 an 9. In Fig. 8, assuming that the subreflector 72 is absent, those of the numerous rays radiating from the focus Fa which are incident to the partial reflector (paraboloid A) 22A are reflected by the paraboloid A
without exception to become rays which are parallel to the center ;~ ~ axis 28; the distances measured from the focus Fa to a plane ~; which is perpendicular to the axis 28 by way of the paraboloid A
are equal to each other. It follows that if that portion of subreflector 72 which is associated with the paraboloid A, i. e., the intermediate portion 72c is flat, those of the rays radiating , from the point F'a which are incident to the intermediate portion 72C are reflected by the portion 72C and, then, by the ;~:
~ ~ ~ 25 paraboloid A to be therebY turned into rays which are parallel to ~2~fi422 the axis 28.
On the other hand, when the subreflector 7 2 is absent, among rays radiating from the focus Fa, those which are incident to the partial reflector (paraboloid B) 22B are reflected 5 by the paraboloid B to become generally parallel to the axis 28.
However, the distances measured from the foc~ls Fa to the plane which is parallel to the axis 28 by way of the paraboloid B are not the same as each other and involve some error. In light of this, that part (curved portion 72A) of the subreflector 72 10 which is associated with the paraboloid is provided with a predetermined curve which is slightlY deviated from a plane. In this condition, the lengths of the optical paths along which rays are radiated from F'a, then reflected by the curved portion 72A, and then incident to the plane which is perpendicular to the axis 15 2 8 become equal to each other. This reduces the decrease in efficiency due to phase errors which are ascribable to the paraboloid B.
Fig. 9 is a view similar to Fig. 8, showing rays which are radiating from the other point F~ toward the axis 30. Details of 20 Fig. 9 will be understood by analogy from Fig. 8.
The gist is that the surface curves of the curved portions 7 2A and 7 2B of the subreflector 7 2 are so selected as to compensate for or reduce the phase error in the event when electromagnetic waves reflected by the curved portions are 25 radiated by their associated partial reflectors.
It will be seen from the above that the size of the curved portion 7 2A and that of the curved portion 7 2B are dependent upon the sizes and focuses of their associated partial reflectors and the location of the subreflector 72. While the intermediate portion 72c is shown as being sized substantially the same size as the curved portions 72A and 72B, its size is variæble depending upon, for example, the difference in focal length ~etween the two paraboloids. By comparing Figs. 8 and 9, it will be understood that that area of the subreflector 72 to which 10 the rays radiating from the point F'a and those radiating from the point F'b are incident is included in the intermediate portion 72C. This, coupled with the fact that the intermediate portion 72C is flat, allows the intermediate portion 72C to be shared by those two different groups of rays without entrailing any phase 15 error. In this manner, the subreflector 24 is capable of simultaneously compensating for phase errors which-occur on the main reflector 22 with respect to the two different directions of radiations. ConsequentlY9 since that part of an electromagnetic wave radiating from the primary radiator 24 which is incident to 20 the partial reflector 22B is compensated for in phase error, the limitation that, for example, the wave from the radiator 24 should mainly use the partial reflector 22A is eliminated. Hence, as shown in Figs. 8 and 9, the same region of the main reflector 2 2 can be shared by two different beams, promoting the 25 decrease in the lateral dimension of the main reflector 22.
~ .
While the present inYention has been shown and described in relation to a two-beam and a three-beam antenna, it will be apparent that it is similarly applicable to an antenna of the type using four or more beams.
Further, although the foregoing description has concentrated on a situation wherein a plurality of focuses and the axes of rotation of a plurality of paraboloids are positioned in the same plane, such is only illustrative and may be replaced with a situation wherein, for example, the axes 2 8 and 3 0 of the paraboloids A and 8, respectively, are in a distorted relationship. Specifically, the axes 2 8 and ~ 0 may each be extended in any desired direction other than the same plane.
It is not necessary that angles between the individual axes of rotation and the associated primary reflectors be equal to each 1 5 other.
In addition, the focal lengths of the paraboloids may not be equal to each other, and the contour of the main reflector is open to choice.
In summary, it will be seen that the present invention proYides a highly efficient multibeam antenna despite that nearby ., ones of a plurality of radiation regions which are defined on a single main reflector overlap each other. This is because the :~ cur~e of each radiation region is provided with substantiallY the same paraboloid as the surface curve of a radiation region which 2 5 is defined on a single main reflector and, hence, each of the : : ;
~296422 radiation regions can be regarded as a parabolic reflector which is independent of the others. Another advantage attainable with the present invention is that the length of antenna axis can be reduced ~y transmitting electromagnetic radiations from a 5 plurality of primary radiators indirectly to a main reflector by way of a single flat reflector.
Further, in accordance with the present invention, a subreflector capable of compensating for phase errors particular to the radiation of electromagnetic waves by a main reflector is 10 interposed between the main reflector and primary radiators, whereby the decrease in the phase efficiency in the aperture plane is suppressed. Since phase errors are compensated for by the subreflector as stated, it is not necessary to accurately match the primary reflectors with partial reflectors which constitute the 15 main reflector and, therefore, the lateral dimension of the main reflector can be reduced.
Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without deParting from the scope thereof.
, .
Claims (11)
1. A multibeam antenna comprising:
a main reflector constituted by at least a first and a second partial reflector, said first partial reflector being defined by a part of a first paraboloid which has a first focus and a first axis of rotation, said second partial reflector being defined by a part of a second paraboloid which has a second focus and a second axis of rotation, said first and second partial reflectors being joined to each other with said first and second axes oriented in different directions from each other;
a first primary radiator radiating an electromagnetic wave toward said main reflector to irradiate said first partial reflector and a part of said second reflector; and a second primary radiator for radiating an electromagnetic wave toward said main reflector to irradiate said second partial reflector and a part of said first partial reflector.
a main reflector constituted by at least a first and a second partial reflector, said first partial reflector being defined by a part of a first paraboloid which has a first focus and a first axis of rotation, said second partial reflector being defined by a part of a second paraboloid which has a second focus and a second axis of rotation, said first and second partial reflectors being joined to each other with said first and second axes oriented in different directions from each other;
a first primary radiator radiating an electromagnetic wave toward said main reflector to irradiate said first partial reflector and a part of said second reflector; and a second primary radiator for radiating an electromagnetic wave toward said main reflector to irradiate said second partial reflector and a part of said first partial reflector.
2. A multibeam antenna as claimed in claim 1, wherein said first and second focuses are different in position from each other.
3. A multibeam antenna as claimed in claim 1, wherein said first and second primary reflectors are located at said first focus and said said second focus, respectively.
4. A multibeam antenna as claimed in claim 1, wherein said first primary radiator and said first partial reflector are located on one side with respect to a center axis of said antenna, and said second primary radiator and said second partial reflector are located on the other side with respect to said center axis.
5. A multibeam antenna as claimed in claim 1, wherein said first primary radiator and said second partial reflector are located on one side with respect to a center axis of said antenna, and said second primary radiator and said first partial reflector are located on the other side with respect to said center axis.
6. A multibeam antenna as claimed in claim 1, further comprising a subreflector located between said main reflector and said first and second focuses.
7. A multibeam antenna as claimed in claim 6, wherein said first and second primary radiators are located at, respectively, a first and a second inverted image point which are symmetrical to, respectively, said first and second focuses with respect to said subreflector, said first and second primary reflectors each radiating an electromagnetic wave indirectly toward said main reflector through said subreflector.
8. A multibeam antenna as claimed in claim 7, wherein said subreflector comprises a flat reflector.
9. A multibeam antenna as claimed in claim 7, wherein said subreflector comprises a first curved portion located on the same side as said first partial reflector which is located on one side with respect to a center axis of said antenna, a second curved portion located on the same side as said second partial reflector which is located on the other side with respect to said center axis, and an intermediate portion interconnecting said first and second curved portions.
10. A multibeam antenna as claimed in claim 9, wherein said intermediate portion has a flat surface.
11. A multibeam antenna as claimed in claim 10, wherein said first and second curved portions have surface curves each being so selected as to compensate for a phase error which occurs when an electromagnetic wave reflected by said first or second curved portion is radiated via said first or second partial reflector.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP453587A JPS63173404A (en) | 1987-01-12 | 1987-01-12 | Multi-beam antenna |
| JP62-4535 | 1987-01-12 | ||
| JP975387A JPH0612853B2 (en) | 1987-01-19 | 1987-01-19 | Multi-beam antenna |
| JP62-9753 | 1987-01-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1296422C true CA1296422C (en) | 1992-02-25 |
Family
ID=26338338
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000556203A Expired - Fee Related CA1296422C (en) | 1987-01-12 | 1988-01-11 | Multibeam antenna |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0275062B1 (en) |
| AU (1) | AU605227B2 (en) |
| CA (1) | CA1296422C (en) |
| DE (1) | DE3885308D1 (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2227609A (en) * | 1989-01-30 | 1990-08-01 | David James George Martin | Double aerial [daerial] |
| ES1008936Y (en) * | 1989-01-31 | 1989-12-16 | Televes S.A. | SUPPORT FOR MULTISATELLITE PARABOLIC ANTENNA FEEDERS. |
| US5258767A (en) * | 1989-03-14 | 1993-11-02 | Kokusai Denshin Denwa Co., Ltd. | Antenna system for shaped beam |
| FR2674377B1 (en) * | 1991-03-22 | 1993-06-04 | Alcatel Espace | RADIOELECTRIC ANTENNA WITH MULTIFOCAL REFLECTOR. |
| FR2677815B1 (en) * | 1991-06-14 | 1994-03-18 | Claude Chapu | RECEPTION OF 3 SATELLITES ON A FIXED PARABLE. |
| FR2684809B1 (en) * | 1991-12-09 | 1994-01-21 | Alcatel Espace | MULTI-BEAM PASSIVE ANTENNA WITH CONFORMITY REFLECTOR (S). |
| US6258895B1 (en) * | 1992-06-26 | 2001-07-10 | The Procter & Gamble Company | Polymers having spiro orthoester groups, process of manufacturing and using |
| IT1271871B (en) * | 1994-03-03 | 1997-06-09 | Space Eng Srl | MULTI-BAND ANTENNA ABLE TO RECEIVE / TRANSMIT SIGNALS AT THE SAME FREQUENCY, FROM / TOWARDS MULTIPLE DIRECTIONS, SIMULTANEOUSLY. |
| US5945960A (en) * | 1996-12-02 | 1999-08-31 | Space Systems/Loral, Inc. | Method and apparatus for reconfiguring antenna radiation patterns |
| RU2694813C1 (en) * | 2018-10-10 | 2019-07-17 | Федеральное государственное бюджетное учреждение наук Институт проблем машиноведения Российской академии наук (ИПМаш РАН) | Method of reflecting mirror surfaces formation of space radio telescope antenna |
| WO2024044956A1 (en) * | 2022-08-30 | 2024-03-07 | 华为技术有限公司 | Antenna and communication device |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3852763A (en) * | 1970-06-08 | 1974-12-03 | Communications Satellite Corp | Torus-type antenna having a conical scan capability |
| JPS5357727A (en) * | 1976-11-04 | 1978-05-25 | Nec Corp | Multiple shaped beam antenna |
| US4259674A (en) * | 1979-10-24 | 1981-03-31 | Bell Laboratories | Phased array antenna arrangement with filtering to reduce grating lobes |
| US4482897A (en) * | 1982-06-28 | 1984-11-13 | At&T Bell Laboratories | Multibeam segmented reflector antennas |
| JPS6094508A (en) * | 1983-10-28 | 1985-05-27 | Nec Corp | Shaped beam antenna |
-
1988
- 1988-01-11 CA CA000556203A patent/CA1296422C/en not_active Expired - Fee Related
- 1988-01-11 AU AU10169/88A patent/AU605227B2/en not_active Ceased
- 1988-01-11 EP EP19880100249 patent/EP0275062B1/en not_active Expired - Lifetime
- 1988-01-11 DE DE88100249T patent/DE3885308D1/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0275062B1 (en) | 1993-11-03 |
| EP0275062A3 (en) | 1989-10-11 |
| DE3885308D1 (en) | 1993-12-09 |
| EP0275062A2 (en) | 1988-07-20 |
| AU1016988A (en) | 1988-07-14 |
| AU605227B2 (en) | 1991-01-10 |
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| MKLA | Lapsed |