CA1185364A - Antenna system for different frequency bands - Google Patents
Antenna system for different frequency bandsInfo
- Publication number
- CA1185364A CA1185364A CA000451811A CA451811A CA1185364A CA 1185364 A CA1185364 A CA 1185364A CA 000451811 A CA000451811 A CA 000451811A CA 451811 A CA451811 A CA 451811A CA 1185364 A CA1185364 A CA 1185364A
- Authority
- CA
- Canada
- Prior art keywords
- reflector
- antenna system
- horns
- focusing
- frequency bands
- 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.)
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Abstract
ABSTRACT OF THE DISCLOSURE
An antenna system having a main reflector, a sub-reflector, and a plurality of horns for radiating different frequencies includes a beam waveguide system which cancels cross polarization otherwise inherent in the system. The beam waveguide system can be used with a rotationally symmetric and stationary sub-reflector by being positioned to reflect said beam on the axis of the main reflector.
Either the horns or the focusing reflectors may be rotat-ably switched, the other group being stationary.
An antenna system having a main reflector, a sub-reflector, and a plurality of horns for radiating different frequencies includes a beam waveguide system which cancels cross polarization otherwise inherent in the system. The beam waveguide system can be used with a rotationally symmetric and stationary sub-reflector by being positioned to reflect said beam on the axis of the main reflector.
Either the horns or the focusing reflectors may be rotat-ably switched, the other group being stationary.
Description
;3 6~
1 This applica-tion is a division of co-pending application serial number 384,673 filed Aug~lst 26, 1981.
This invention relates to a large antenna sys-tem for transmit-ting and receiving radio waves in a plurality of frequency bands, in which -the primary radiators are switched to transmit and receive such radio waves, BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an explanatory diagram showing a conventional focused beam type antenna system.
Figure 2 is an explanatory diagram showing a conventional horn switching type antenna switch.
Figure 3 is an explanatory diagram showing one example of an antenna system according to the invention.
Figure ~ is an explanatory diagram showing anotherexample of the antenna system according to the invention.
Figure 5 is an explanatory diagram showing one example of a Gregorian antenna to which the technical con-cept of the invention is applied.
Figure 6 is an explanatory diagram showing a further example of the antenna system accordiny to the invention.
Conven-tional antenna systems employed as satel-lite communication antennas or large radio telescopes are as shown in Figures 1 and 2.
Figure 1 shows an antenna system in which a beam waveguide system is employed as a primary radiation system .
~L~8~3~
1 and a plurali-ty of horns for many frequency bands are pro-vided. In Figure 1, reference characters la, lb, lc and ld designate horns Eor radiating radio waves having frequency bands fa, fb, fc and fd, respectively; 2, a sub-reflector;
3, a main reflector; 4a, 4b, 4c and 4d, feeding units pro-vided for the frequency bands, respectivelyj 6 and 7, rad-iated beams provided by reflecting the radio wave from sub-reflector 2 and main reflector 3; 8 (indicated as 8a or 8b~, 9, 10, 11, L2, 13, 14 and 15, focusing reflecto.rs which are curved mirrors or plane mirrors as shown; and 16, -the axis of the main reflector 3.
In case of frequency band fa, the focusing re-flector 8 is retracted so that the radio wave from horn la is directed to the focusing reflector 12. The radio wave reflected from the focusing reflector 12 is directed to the focusing reflector 13, where it is reflected~ The radio wave thus reflected is further reflected by the focusing reflectors 14 and 15, the sub-reflector 2 and the main reflector 3, and is finally radiated in the form of beam 7.
1 This applica-tion is a division of co-pending application serial number 384,673 filed Aug~lst 26, 1981.
This invention relates to a large antenna sys-tem for transmit-ting and receiving radio waves in a plurality of frequency bands, in which -the primary radiators are switched to transmit and receive such radio waves, BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an explanatory diagram showing a conventional focused beam type antenna system.
Figure 2 is an explanatory diagram showing a conventional horn switching type antenna switch.
Figure 3 is an explanatory diagram showing one example of an antenna system according to the invention.
Figure ~ is an explanatory diagram showing anotherexample of the antenna system according to the invention.
Figure 5 is an explanatory diagram showing one example of a Gregorian antenna to which the technical con-cept of the invention is applied.
Figure 6 is an explanatory diagram showing a further example of the antenna system accordiny to the invention.
Conven-tional antenna systems employed as satel-lite communication antennas or large radio telescopes are as shown in Figures 1 and 2.
Figure 1 shows an antenna system in which a beam waveguide system is employed as a primary radiation system .
~L~8~3~
1 and a plurali-ty of horns for many frequency bands are pro-vided. In Figure 1, reference characters la, lb, lc and ld designate horns Eor radiating radio waves having frequency bands fa, fb, fc and fd, respectively; 2, a sub-reflector;
3, a main reflector; 4a, 4b, 4c and 4d, feeding units pro-vided for the frequency bands, respectivelyj 6 and 7, rad-iated beams provided by reflecting the radio wave from sub-reflector 2 and main reflector 3; 8 (indicated as 8a or 8b~, 9, 10, 11, L2, 13, 14 and 15, focusing reflecto.rs which are curved mirrors or plane mirrors as shown; and 16, -the axis of the main reflector 3.
In case of frequency band fa, the focusing re-flector 8 is retracted so that the radio wave from horn la is directed to the focusing reflector 12. The radio wave reflected from the focusing reflector 12 is directed to the focusing reflector 13, where it is reflected~ The radio wave thus reflected is further reflected by the focusing reflectors 14 and 15, the sub-reflector 2 and the main reflector 3, and is finally radiated in the form of beam 7.
2~ A received radio wave is trans~itted to the horn la, re-trac-ing the above-described path.
In the case of frequency band fb, the focusing reflector 8 is set as indicated at 8a, so that the radio wave from the horn lb ls direc-ted to the focusing reflector 12 after being reflected by the focusing reflector 9 and 8a.
Then, similarly as in the case of the frequency fa the radio wave is reflected by the sub-reflector 2 and the main re-i3~i~
1 flector 3 and is finally radia-ted in the form of a beam 7 from the main reflec-tor 3.
In the case of the frequency band fc, the focus-ing reflector 8 is set as indicated at 8a, and the focusing reflector 9 is retracted, so that the radio wave of the frequency band fc from the horn lc i5 directed to the focusing reflector 10, thus reaching the main reflector 3 through the same path as that in the case of the frequency band fb. Finally, the radio wave is radiated in the form of a beam 7 from the main reflec-tor 3.
In the case of the frequency band fd, the focus-ing reflector 8 is set as indicated at 8b. The radio wave of the frequency band fd from the horn ld is directed to ~he focusing reflector 11, where it is reflected towards the focusing reflector 8b. Then, the radio wave reaches the maln reflector 3 through the same path as that in the case of the frequency band fb or fc, and is finally radiated in the form of a beam 7 from the main reflector 3.
In the above described antenna system, while the antenna rotates around an elevation angle Ee; -the horns la through ld and the feeding units 4a through 4d are sta-tionary. As a result inspection and maintenance are facilitated. However, the antenna system has certain dis-advantages. Since a plurality of focusing reflec-tors are arranged in association with mechanical means for controlling azimuth and elevation angles, the antenna system is intri~
cate and bulky.
~8~36~
1 In ano-ther type of conventional antenna system, as shown in Figure 2, a beam waveyuide system is no-t used.
Instead, different primary radiators (or horns) are selected for different frequency bands.
In figure 2, reference characters la and lb designate horns; 2a or 2b, sub-reflectors; 3, a main re-flector; 4a and 4b, feeding units; 5a, 5b, 6a, 6b and 7, the paths of radio waves radiated by the horns la and lb;
16, the axis of the main reflector 3; and 17, the axis of the horn.
In the case of frequency band fa, the sub reflector is turned towards horn la as indicated at 2a.
Therefore, the radio wave from horn la is reflec-ted by the sub-reflector (2a~ and the main reflector 3, i.e., it is radiated through the path 5a, 6a and 7. A received radio wave reaches the horn la retracing the above-described path.
In the case of frequency band fb, the sub-reflector ïs se-t as indicated at 2b so as to face the horn lb.
In the above-described antenna system, the horn axis 17 is offset from -the axis 16 of the main reflector
In the case of frequency band fb, the focusing reflector 8 is set as indicated at 8a, so that the radio wave from the horn lb ls direc-ted to the focusing reflector 12 after being reflected by the focusing reflector 9 and 8a.
Then, similarly as in the case of the frequency fa the radio wave is reflected by the sub-reflector 2 and the main re-i3~i~
1 flector 3 and is finally radia-ted in the form of a beam 7 from the main reflec-tor 3.
In the case of the frequency band fc, the focus-ing reflector 8 is set as indicated at 8a, and the focusing reflector 9 is retracted, so that the radio wave of the frequency band fc from the horn lc i5 directed to the focusing reflector 10, thus reaching the main reflector 3 through the same path as that in the case of the frequency band fb. Finally, the radio wave is radiated in the form of a beam 7 from the main reflec-tor 3.
In the case of the frequency band fd, the focus-ing reflector 8 is set as indicated at 8b. The radio wave of the frequency band fd from the horn ld is directed to ~he focusing reflector 11, where it is reflected towards the focusing reflector 8b. Then, the radio wave reaches the maln reflector 3 through the same path as that in the case of the frequency band fb or fc, and is finally radiated in the form of a beam 7 from the main reflector 3.
In the above described antenna system, while the antenna rotates around an elevation angle Ee; -the horns la through ld and the feeding units 4a through 4d are sta-tionary. As a result inspection and maintenance are facilitated. However, the antenna system has certain dis-advantages. Since a plurality of focusing reflec-tors are arranged in association with mechanical means for controlling azimuth and elevation angles, the antenna system is intri~
cate and bulky.
~8~36~
1 In ano-ther type of conventional antenna system, as shown in Figure 2, a beam waveyuide system is no-t used.
Instead, different primary radiators (or horns) are selected for different frequency bands.
In figure 2, reference characters la and lb designate horns; 2a or 2b, sub-reflectors; 3, a main re-flector; 4a and 4b, feeding units; 5a, 5b, 6a, 6b and 7, the paths of radio waves radiated by the horns la and lb;
16, the axis of the main reflector 3; and 17, the axis of the horn.
In the case of frequency band fa, the sub reflector is turned towards horn la as indicated at 2a.
Therefore, the radio wave from horn la is reflec-ted by the sub-reflector (2a~ and the main reflector 3, i.e., it is radiated through the path 5a, 6a and 7. A received radio wave reaches the horn la retracing the above-described path.
In the case of frequency band fb, the sub-reflector ïs se-t as indicated at 2b so as to face the horn lb.
In the above-described antenna system, the horn axis 17 is offset from -the axis 16 of the main reflector
3. That is, the antenna system is a so-called offset type antenna system. The sub-reflector is in the form of a non-rotationally-symmetric (not axially symmetric) mirror sur-face (even if the main reflector is of an axially symmetric mirror surface). Therefore, a cross polarization is pro-duced by the non-rotationally-symme-tric mirror surface.
369~
1 Accordinyly, in the use of a circularly polarized wave, the beams of the clockwise and counterclockwise polarized waves which are orthogonal with each other are tilted in the opposite directions, as a result of which so-called "beam separation" is caused. This lowers the accuracy in directivity of the antenna and the gain; that is it de-grades the characteristics of the antenna. Fur-thermore, in the use of a linearly polarized wave, -the cross polar-ization characteristic of the antenna is lowered.
SU~`lAR~ OF THE INVENTION
In view of -the foregoing, an objec-t of this invention is to provide a relatively small antenna system in which the cross polariza-tion attributed to the offset type antenna system is cancelled, and the primary radiators are switche~ for transmitting and receiving radio waves in a plurality of frequency bands.
These and other object of the invention are obtained by the inven-tion, wherein in an antenna system oE
the type which is used for a plurality of frequency bands by switchiny primary radiator sys-tems and has a rotationally symmetric sub-reflector, the improvement comprising: means, including a beam waveguide system having -two focusing re-flectors for cancelling the cross polarization attributed to said focusing reflectors.
In the case where a rotationally symmetric auxi~-iary reflector is employed in the antenna system~ the beam waveguide system each comprise at least two focusing re-~:~8536~
1 flectors and meet -the concli-tions for cancelling -the cross polarization. Therefore, the antenna system according to the inven-tion is relatively simple in arrangement and small in size.
DETAILED DESCRIPTIO~ OF THE INVENTION
One example of an antenna system according to this invention will be described wi-th reference to Figure 3.
The an-tenna system is used for two frequencies. In Figure 3, reference characters la and lb designa-te primary radia-tors (or horns); 2 (indicated as 2a or 2b), a sub-reflector; 3, a main reflector; 4a and 4b, feeding uni-ts; 6a, 6b and 7, the paths oE radio waves radiated by the horns la and lb;
9a, 9b, 12a and 12b, focusing reflectors; 16, axis of the main reflector; and 18a and 18b, the central axes of beams.
If, in Figure 3, angles between radio waves in-cident to focusing reflectors 9a and 12a and the sub reflector set at 2a and those reflected thereby are repre-sented by ~ 2 and a3, the beam radii of these reflectors are represented by ~ 2 and l~3, and the focal distances of these reElectors are fl~ f2 and f3, respectively, then 3~
1 a cross polariza-tion level C provided by this non-rotation-ally-symme-tric mirror system can be represented by -the following e~pression:
S C = 1 { 1 tan 1 + 2 tan 2 + 3 tan 3 } (1) 2e fl 2 f2 2 f3 2 where ~ = Di .~ 8.69 i = 1, 2, 3 (2) Ri Ri in ~hich Di is the diameter of each reflector (for instance, Dl, D2 and D3 being the diameters of the sub-reflector, the focusing reflector 9a and the focusing reflector 12a, respectively) L is the edge level of each reflector Ri is the curvature of a radio wave front incident to each reflector, Ri' is the curvature of a radio wave front re-flected by each reflector; and e = 2.71828.
If DI~ fi' ~i and ~1 are suitably selected with the frequency fa, then the mirror system can be converted in-to one in which C = 0, i.e., no cross polarization componen-ts are produced. This means that the cross polarization attributed to the offset type antenna system shown in Figure 2 is cancelled out by that which is produced by the beam wave 353~
1 guide system (which is the combina-tion of -the horn (1) and the focusing reflectors (9 and 12) in this example).
In the mirror system in which, with the frequency 1' 2' f3' ~ 2 and ~3 are defined to have C = 0, it is possible that, wi-th the frequency fb, C = 0 or C _ 0 can be obtained by changing the dimensions of the horn.
The mirror system thus defined for the frequency fa is constituted by the horn la, focusing reflectors 9a and 12al sub-reflectors 2a and main reflector 3. The focusing reflectors 9a and 12a, the sub-reflector 2a and the main reflector 3 are commonly employed in the mirror system for the frequency fb. Therefore, if the horn for radiating the frequency fb is set on the circumference ! 15 which is scribed by the axis 17a of the horn la when the axis 17a is turned around the axis 16 of the main reflector 3 (in -the example shown in Figure 3, the horns la and lb being positioned symmetrical with each o-ther~ and the focus-ing reflectors 9a and 12a and sub-reflector 2a are set at 9b, 12b and 2b by turning them through 1~0 abou-t the axis 16, then the mirror system for the frequency fb with the as indicated by the broken lines.
In the above-described system, the horns are set stationary, and the reElec-tors 9a, 12a and 2a are turned;
however, it is obvious that the system may be so modified that the reflectors are set stationary, and the horns are turned about the axis 16.
~3S36~
1 Fi~ure 4 shows one example of the arrangement of horns for four frequencies. Four horns la, lb, lc and ld are arranged so that the antenna system can be used for four frequency bands. In the example, four horns are provided; however, the invention is not limited thereto.
That is, more than four horns may be arranged if they are set mechanically correctly.
Figure 5 shows one example of a Gregorian antenna to which the technical concept of the invention is applied.
Similarly as in the above-described examples, a plurality of horns and a plurality of feeding units are provided ~although only one horn 1 and one feeding unit 4 are shown~.
In one particular example of the antenna system of the invention as shown in Figure 6 in which the ~3 is equal to zero, the axis 16 of the main reflector coincides with the beam reflected by the focusing reflector 9a. In this case~ the sub-reflector 2 is set stationary, and only the focusing reflec-tors 9a and 12a are turned about the axis 16 so as to be set at 9b and 12b, respectively.
The same effect is obtained by turning the horn lb about the axis 16 with the focusing reflectors 9a and 12a, similarly as in the above-described case. In this case, the condition for cancelling the cross polarization is met only by the beam wavegu~de system which is the primary radiator.
_9~
369~
1 Accordinyly, in the use of a circularly polarized wave, the beams of the clockwise and counterclockwise polarized waves which are orthogonal with each other are tilted in the opposite directions, as a result of which so-called "beam separation" is caused. This lowers the accuracy in directivity of the antenna and the gain; that is it de-grades the characteristics of the antenna. Fur-thermore, in the use of a linearly polarized wave, -the cross polar-ization characteristic of the antenna is lowered.
SU~`lAR~ OF THE INVENTION
In view of -the foregoing, an objec-t of this invention is to provide a relatively small antenna system in which the cross polariza-tion attributed to the offset type antenna system is cancelled, and the primary radiators are switche~ for transmitting and receiving radio waves in a plurality of frequency bands.
These and other object of the invention are obtained by the inven-tion, wherein in an antenna system oE
the type which is used for a plurality of frequency bands by switchiny primary radiator sys-tems and has a rotationally symmetric sub-reflector, the improvement comprising: means, including a beam waveguide system having -two focusing re-flectors for cancelling the cross polarization attributed to said focusing reflectors.
In the case where a rotationally symmetric auxi~-iary reflector is employed in the antenna system~ the beam waveguide system each comprise at least two focusing re-~:~8536~
1 flectors and meet -the concli-tions for cancelling -the cross polarization. Therefore, the antenna system according to the inven-tion is relatively simple in arrangement and small in size.
DETAILED DESCRIPTIO~ OF THE INVENTION
One example of an antenna system according to this invention will be described wi-th reference to Figure 3.
The an-tenna system is used for two frequencies. In Figure 3, reference characters la and lb designa-te primary radia-tors (or horns); 2 (indicated as 2a or 2b), a sub-reflector; 3, a main reflector; 4a and 4b, feeding uni-ts; 6a, 6b and 7, the paths oE radio waves radiated by the horns la and lb;
9a, 9b, 12a and 12b, focusing reflectors; 16, axis of the main reflector; and 18a and 18b, the central axes of beams.
If, in Figure 3, angles between radio waves in-cident to focusing reflectors 9a and 12a and the sub reflector set at 2a and those reflected thereby are repre-sented by ~ 2 and a3, the beam radii of these reflectors are represented by ~ 2 and l~3, and the focal distances of these reElectors are fl~ f2 and f3, respectively, then 3~
1 a cross polariza-tion level C provided by this non-rotation-ally-symme-tric mirror system can be represented by -the following e~pression:
S C = 1 { 1 tan 1 + 2 tan 2 + 3 tan 3 } (1) 2e fl 2 f2 2 f3 2 where ~ = Di .~ 8.69 i = 1, 2, 3 (2) Ri Ri in ~hich Di is the diameter of each reflector (for instance, Dl, D2 and D3 being the diameters of the sub-reflector, the focusing reflector 9a and the focusing reflector 12a, respectively) L is the edge level of each reflector Ri is the curvature of a radio wave front incident to each reflector, Ri' is the curvature of a radio wave front re-flected by each reflector; and e = 2.71828.
If DI~ fi' ~i and ~1 are suitably selected with the frequency fa, then the mirror system can be converted in-to one in which C = 0, i.e., no cross polarization componen-ts are produced. This means that the cross polarization attributed to the offset type antenna system shown in Figure 2 is cancelled out by that which is produced by the beam wave 353~
1 guide system (which is the combina-tion of -the horn (1) and the focusing reflectors (9 and 12) in this example).
In the mirror system in which, with the frequency 1' 2' f3' ~ 2 and ~3 are defined to have C = 0, it is possible that, wi-th the frequency fb, C = 0 or C _ 0 can be obtained by changing the dimensions of the horn.
The mirror system thus defined for the frequency fa is constituted by the horn la, focusing reflectors 9a and 12al sub-reflectors 2a and main reflector 3. The focusing reflectors 9a and 12a, the sub-reflector 2a and the main reflector 3 are commonly employed in the mirror system for the frequency fb. Therefore, if the horn for radiating the frequency fb is set on the circumference ! 15 which is scribed by the axis 17a of the horn la when the axis 17a is turned around the axis 16 of the main reflector 3 (in -the example shown in Figure 3, the horns la and lb being positioned symmetrical with each o-ther~ and the focus-ing reflectors 9a and 12a and sub-reflector 2a are set at 9b, 12b and 2b by turning them through 1~0 abou-t the axis 16, then the mirror system for the frequency fb with the as indicated by the broken lines.
In the above-described system, the horns are set stationary, and the reElec-tors 9a, 12a and 2a are turned;
however, it is obvious that the system may be so modified that the reflectors are set stationary, and the horns are turned about the axis 16.
~3S36~
1 Fi~ure 4 shows one example of the arrangement of horns for four frequencies. Four horns la, lb, lc and ld are arranged so that the antenna system can be used for four frequency bands. In the example, four horns are provided; however, the invention is not limited thereto.
That is, more than four horns may be arranged if they are set mechanically correctly.
Figure 5 shows one example of a Gregorian antenna to which the technical concept of the invention is applied.
Similarly as in the above-described examples, a plurality of horns and a plurality of feeding units are provided ~although only one horn 1 and one feeding unit 4 are shown~.
In one particular example of the antenna system of the invention as shown in Figure 6 in which the ~3 is equal to zero, the axis 16 of the main reflector coincides with the beam reflected by the focusing reflector 9a. In this case~ the sub-reflector 2 is set stationary, and only the focusing reflec-tors 9a and 12a are turned about the axis 16 so as to be set at 9b and 12b, respectively.
The same effect is obtained by turning the horn lb about the axis 16 with the focusing reflectors 9a and 12a, similarly as in the above-described case. In this case, the condition for cancelling the cross polarization is met only by the beam wavegu~de system which is the primary radiator.
_9~
Claims (3)
1. In an antenna system of the type which is used for a plurality of frequency bands by switching primary radiator systems and has a rotationally symmetric sub-reflector, the improvement comprising:
means, including a beam waveguide system having two focusing reflectors for cancelling the cross polarization attributed to said focusing reflectors.
means, including a beam waveguide system having two focusing reflectors for cancelling the cross polarization attributed to said focusing reflectors.
2. An antenna system as claimed in claim 1, wherein said focusing reflectors of said beam waveguide system are set stationary, and a group of horns for plurality of frequency bands are switched so as to turn towards said focusing reflectors.
3. An antenna system as claimed in claim 1, wherein a group of horns for a plurality of frequency bands are set stationary, and said focusing reflectors of said beam wave-guide system are turned so as to turn towards a selected one of said group of horns.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP55119988A JPS5744302A (en) | 1980-08-28 | 1980-08-28 | Antenna device |
| JP119988/80 | 1980-08-28 | ||
| CA000384673A CA1184651A (en) | 1980-08-28 | 1981-08-26 | Antenna system for different frequency bands |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000384673A Division CA1184651A (en) | 1980-08-28 | 1981-08-26 | Antenna system for different frequency bands |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1185364A true CA1185364A (en) | 1985-04-09 |
Family
ID=25669417
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000451811A Expired CA1185364A (en) | 1980-08-28 | 1984-04-11 | Antenna system for different frequency bands |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1185364A (en) |
-
1984
- 1984-04-11 CA CA000451811A patent/CA1185364A/en not_active Expired
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