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(11) | EP 0 433 092 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Polarization converter having two converting devices therein |
| (57) Disclosed is a polarization converter (9) allowing one down converter to receive
four types of polarizations of a horizontal polarization, a vertical polarization,
a right-handed circular polarization and a left-handed circular polarization without
deteriorating a pass loss characteristic and a return loss characteristic (VSWR characteristic)
of an antenna apparatus as a whole. The polarization converter (9) includes a circular
waveguide (20) having dielectric plate (8) for converting a circular polarization
to a linear polarization, a ferrite pole (10) for changing the direction of the electric
field of the linear polarization and a coil (11), all of which are integrally provided
therein. As a result, the design is easily obtained which optimizes the return loss
characteristic (VSWR characteristic) of the entire antenna apparatus, which allows
one converter to receive said four types of polarizations without deteriorating the
pass loss characteristic and the return loss characteristic (VSWR characteristic)
of the entire antenna apparatus. |
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates generally to polarization converters, and more particularly, to polarization converters of antenna apparatuses receiving radio wave transmitted from broadcasting satellites and communication satellites.
Description of the Background Art
[0002] In recent years, improvements in satellite communication have been rapidly changing the broadcast industry. In particular, the start of the DBS (Direct Broadcasting Satellite) has reduced prices of receiving apparatuses to enable people to receive television broadcasting at home by means of satellites. This is followed by developments of receiving antenna apparatuses.
[0003] Fig. 4 is a view of an arrangement of a conventional receiving antenna apparatus. With reference to Fig. 4, the conventional receiving antenna apparatus comprises a reflecting mirror 1 for reflecting radio wave transmitted from broadcasting satellites and communication satellites, a horn 2 through which the radio wave reflected by reflecting mirror 1 enters, and a down converter 3 for receiving the incident radio wave through horn 2.
[0004] The radio wave transmitted from satellites includes four types of polarizations of different electric field directions, that is, a right-handed circular polarization, a left-handed circular polarization, a horizontal polarization and a vertical polarization. The right-handed circular polarization is a circular polarization turning right-handed circularly and the left-handed circular polarization is a circular polarization turning left-handed circularly. The horizontal polarization is a linear polarization changing in a horizontal direction and the vertical polarization is a linear polarization changing in a vertical direction.
[0005] In an operation of the antenna apparatus, the above-described polarization is reflected by reflecting mirror 1, which reflected wave enters horn 2. Then, the radio wave passed through horn 2 enters down converter 3.
[0006] Fig. 5 is a sectional view of the part of the down converter 3 shown in Fig. 4. With reference to Fig. 5, down converter 3 comprises a waveguide 4 and a conductor pole 5 attached to waveguide 4 for receiving radio wave. Herein, the radio wave which can be received by down converter 3 is limited to a polarization component of a parallel direction to conductor pole 5. Thus, when receiving both horizontal and vertical linear polarizations, for example, such manners as follows are conventionally required. That is, one is to use two converters each having a conductor pole 5 faced to each polarization. The following manner is proposed as a method of receiving both the linear polarizations by one converter. Fig. 6 is a schematic view showing a main part of a conventional antenna apparatus for receiving both horizontal and vertical linear polarizations. With reference to Fig. 6, the antenna apparatus is provided with a polarization converter 6 in front of (at the entrance of the radio wave) of down converter 3. The polarization converter 6 is capable of inclining by 90° the direction of the polarization from a horizontal direction to a vertical direction or from a vertical direction to a horizontal direction, for which converter, a polar rotor and a polarizer, for example, can be used. The provision of polarization converter 6 in front of down converter 3, which converter 6 is capable of inclining the direction of the polarization by 90° from horizontal to vertical directions or vertical to horizontal directions, allows one converter to receive both the linear polarizations. In Fig. 6, horn 2 is illustrated in section and polarization converter 6 and down converter 3 are illustrated seen from the side.
[0007] The following is a method of receiving a circular polarization. Fig. 7 is a schematic view showing a main part of a conventional antenna apparatus for receiving a circular polarization. With reference to Fig. 7, the antenna apparatus is provided with a dielectric plate 8 in a waveguide 7 in front (at the entrance of the radio wave) of down converter 3. Dielectric plate 8 functions to convert a circular polarization to a linear polarization. In Fig. 7, horn 2 and waveguide 7 are illustrated in section and down converter 3 is illustrated seen from the side.
[0008] The antenna apparatus of such an arrangement, however, has the following drawbacks. That is, the direction of the linear polarization after a conversion by dielectric plate 8 differs by 90° depending on whether the incident circular polarization through horn 2 is of right-handed or left-handed turning. As a result, receiving antenna apparatuses are conventionally required one for a right-handed circular polarization and the other for a left-handed circular polarization.
[0009] As the foregoing, it is conventionally possible to receive both horizontal and vertical linear polarizations by one down converter by providing a polarization converter such as a polar rotor or a polarizer. It is however difficult to receive a circular polarization by one down converter even with a provision of dielectric plate 8 in waveguide 7 as shown in Fig. 7 because the direction of the linear polarization after conversion differs by 90°. In addition, such an antenna apparatus is not capable of receiving a circular polarization as is provided with a polarization converter such as a polar rotor or a polarizer. Therefore, in a conventional antenna apparatus, it is difficult to receive four types of polarizations of a horizontal polarization, a vertical polarization, a right-handed circular polarization and a left-handed circular polarization by one down converter.
[0010] An antenna apparatus is therefore proposed which is capable of receiving the above-described four types of polarizations by converting the same to one type of polarization by one down converter, which is disclosed in "Wide Band LNB for Europe" in Sharp Technical Journal, No. 43, November 1989. The disclosed antenna apparatus comprises separate down converter (LNB: Low Noise Block), polar rotor which is a polarization converter, and polarization converter primary radiator with a phase plate (dielectric plate) attached thereto. The combination of these devices enables a reception of four types of polarizations which are converted to one type of polarization.
[0011] The conventionally proposed antenna apparatus having such an arrangement however has the following problems. That is, a geometrical angle between the phase plate (dielectric plate) and the down converter (LNB) is of importance for the reception of the four types of polarizations. The conventionally proposed antenna apparatus however comprises the polar rotor between the phase plate and the LNB. In this case, it is difficult to precisely adjust the geometrical angle between the phase plate and the LNB when these parts are connected. An erroneous angle between the phase plate (dielectric plate) and the LNB (down converter) increases a pass loss and a return loss of the entire antenna apparatus.
[0012] An erroneous connection between the phase plate (dielectric plate) and the polar rotor might deteriorate the entire performance because electric characteristics of the same affect to each other. That is, the respective return losses of the phase plate and the polar rotor adversely affect to each other to deteriorate the return loss characteristic (VSWR: Voltage Standing Wave Ratio characteristic) of the antenna apparatus as a whole.
[0013] In other words, it is difficult to receive a horizontal polarization, a vertical polarization, a right-handed circular polarization and a left-handed circular polarization by one down converter without deteriorating a pass loss characteristic and a return loss characteristic (VSWR characteristic) of the antenna apparatus as a whole.
SUMMARY OF THE INVENTION
[0014] One object of the present invention is to allow one down converter to receive a horizontal polarization, a vertical polarization, a right-handed circular polarization and a left-handed circular polarization by using a polarization converter without deteriorating a pass loss characteristic and a return loss characteristic (VSWR characteristic) of an antenna apparatus as a whole.
[0015] Another object of the present invention is to receive a horizontal polarization, a vertical polarization, right-handed circular polarization and a left-handed circular polarization by using one converter without complicating an arrangement of the entire antenna apparatus.
[0016] A further object of the present invention is to reduce an error in an attachment of a polarization converter when an antenna apparatus is assembled.
[0017] The polarization converter according to the present invention includes a circular waveguide, a phase plate and an electric field direction changing device. The circular waveguide is for transmitting radio wave. The phase plate is for converting a circular polarization to a linear polarization and provided at a horn side in the circular waveguide. The electric field direction changing device is for changing the direction of the electric field of the linear polarization and provided at a converter side in the circular waveguide.
[0018] Since the circular waveguide is provided with the phase plate for converting a circular polarization to a linear polarization and the electric field direction changing device for changing the direction of the electric filed of the linear polarization, in operation, the four types of polarizations of a horizontal polarization, a vertical polarization, a right-handed circular polarization and a left-handed circular polarization are converted to one type of polarization by the combination of the phase plate and the electric field direction changing device. In addition, the phase plate and the electric field direction changing device integrally provided in the circular waveguide prevent the combination of a phase plate and a polar rotor (electric field direction changing device) from adversely affecting a pass loss characteristic and a return loss characteristic (VSWR characteristic) of the entire antenna apparatus, which is a conventional problem.
[0019] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Fig. 1 is a schematic view showing a main part of a receiving antenna apparatus using a polarization converter according to one embodiment of the present invention.
[0021] Fig. 2 is a table showing conversions of a direction of a radio wave electric field at each part of the polarization converter shown in Fig. 1.
[0022] Fig. 3 is a sectional view of a polarization converter according to another embodiment of the present invention.
[0025] Fig. 6 is a schematic view showing a main part of a conventional antenna apparatus for receiving both horizontal and vertical linear polarizations.
[0026] Fig. 7 is a schematic view showing a main part of a conventional antenna apparatus for receiving a circular polarization.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The embodiments of the present invention will be described in the following with reference to the drawings. With reference to Fig. 1, the antenna apparatus according to the present embodiment comprises a horn 2 through which the radio wave reflected by a reflecting mirror (not shown) enters, a polarization converter 9 for converting the incident radio wave through horn 2 to a horizontal polarization and a down converter 3 receiving the horizontal polarization converted by polarization converter 9. Polarization converter 9 is attached between horn 2 and down converter 3. A dielectric plate 8 is vertically provided at the horn 2 side in a circular waveguide 20 constituting polarization converter 9. Provided at the down converter 3 side in circular waveguide 20 is a ferrite pole 10 with its center axis coincident with the center axis of circular waveguide 20. Ferrite pole 10 is fixedly provided by a formed resin 12. A coil 11 is wound around the outer periphery of circular waveguide 20. The coil is arranged to apply a magnetic field to ferrite pole 10 in a parallel direction with the center axis of the same.
[0028] Operations of the antenna apparatus according to the present embodiment will be described with reference to Figs. 1 and 2. First, the radio wave transmitted from a satellite is reflected by a reflecting mirror (not shown). The radio wave reflected by the reflecting mirror (not shown) enters horn 2. The incident radio wave through horn 2 enters polarization converter 9. After passing through polarization converter 9, the direction of the electric field is changed depending on a type of the input polarization, as shown in Fig. 2. As a result, every output polarization from polarization converter 9 is converted to a horizontal polarization which is input to down converter 3.
[0029] In other words, when the input polarization to polarization converter 9 is a right-handed circular polarization, after passing through dielectric plate 8, the polarization is converted to a linear polarization with the electric field direction inclined right-handed at 45° with respect to the vertical direction. When the incident polarization is a left-handed circular polarization, it is converted to a linear polarization inclined left-handed at 45°. On the other hand, when both horizontal and vertical linear polarizations are input polarizations, the directions of the electric fields of the same are not changed even after passing through dielectric plate 8.
[0030] After the above-described conversions by dielectric plate 8, ferrite pole 10 carries out the following conversions. That is, when passing through ferrite pole 10, an electric field direction is changed based on a direction and a strength of the magnetic field applied to ferrite pole 10 as described above. The direction and the magnitude of the current (direct current) flowing in coil 11 are therefore adequately settled according to a type of an incident polarization. By properly changing the direction and the strength of the electric field applied to ferrite pole 10 based on this setting, the output polarization from polarization converter 9 can be converted to a horizontal polarization as shown in Fig. 2. More specifically, when the input polarization is a right-handed turning polarization or a vertical polarization, the magnetic field is applied to ferrite pole 10 in the same direction as the forward direction of the radio wave. Then, an adequate selection of the magnetic field strength changes the direction of the electric field of the radio wave rightward by 45° or 90°. As a result, every output polarization can be converted to a horizontal polarization. When the incident polarization is a left-handed circular polarization, the magnetic field is applied in the opposite direction to the forward direction of the radio wave. Then, an adequate selection of the magnetic field strength changes the direction of the electric field leftward by 45°. As a result, every output polarization can be converted to a horizontal polarization. When the input polarization is a horizontal polarization, no magnetic field is applied to ferrite pole 10 because the direction of the electric field should not be changed.
[0031] Through the above-described operations, the radio wave entering through horn 2, which any wave may be out of right-handed turning or left-handed turning circular polarization, or horizontal or vertical linear polarization, is converted to a horizontal polarization to enter the down converter at any time by settting the direction and the magnitude of the current flowing through coil 11 according to a type of the incident polarization. As a result, on down converter allows a selective reception of four types of polarization.
[0032] The antenna apparatus according to the present invention having dielectric plate 8, ferrite pole 10 and coil 11 integrally provided in circular waveguide 20 as described above, does not cause such problems as of the conventionally proposed antenna apparatus. That is, the present embodiment requires only the adjustment of a relative angle between polarization converter 9 with dielectric plate 8 provided therein and down converter 3 when in assembling the same, so that the angle between dielectric plate 8 and down converter 3 can be easily adjusted. As a result, it is possible to effectively prevent a conventional increase of a pass loss and a return loss of the entire antenna apparatus caused due to an angle gap between dielectric plate 8 and down converter 3.
[0033] Furthermore, with dielectric plate 8, ferrite pole 10 and coil 11 in circular waveguide 10 provided integrally, the present embodiment allows prevention of an adverse effect to a characteristic of an antenna apparatus produced by a combination of dielectric plate 8 (phase plate) and a polar rotor, which is the problem of the conventionally proposed antenna apparatus. That is, the present embodiment enables a design in which the best pass loss characteristic and return loss characteristic can be obtained by integrating dielectric plate 8, ferrite pole 10 and coil 11 (equivalent to a polar rotor).
[0034] With reference to Fig. 3, anther embodiment of the present invention will be described. In the present embodiment, coil 11 for applying a magnetic field to ferrite pole 10 is provided in the circular waveguide. With such an arrangement, the same effect as by the embodiment shown in Fig. 1 can be obtained.
[0035] While in the embodiments shown in Figs. 1 and 3, dielectric plate 8 is vertically provided at the horn 2 side of circular waveguide 20, the present invention is not limited thereto and any arrangement is possible as long as the surface of dielectric plate 8 is parallel with the center axis (the forward direction of the radio wave) of circular waveguide 20. In this case, however, the current flowing through coil 11 should be changed according to the direction of the provision of dielectric plate 8. In the embodiments shown in Figs. 1 and 3 in which dielectric plate 8, ferrite pole 10 and coil 11 are integrally attached in circular waveguide 20, one converter allows a selective reception of the above-described four types of polarizations without complicating the arrangement of the entire antenna apparatus.
[0036] As the foregoing, the polarization converter according to the present invention including a circular waveguide provided with a phase plate for converting a circularly polarization to a linear polarization and an electric filed direction changing device for changing the direction of the electric field of the linear polarization, allows conversion of four type polarizations of a horizontal polarization, a vertical polarization, a right-handed circular polarization and a left-handed circular polarization to one type of polarization by the combination of the phase plate and the electric field direction changing device. In addition, the phase plate and the electric field direction changing device integrally provided in the circular waveguide effectively reduces an adverse effect on a pass loss characteristic and a return loss characteristic of the entire antenna apparatus exerted by a combination of a phase plate and a polar rotor (electric field direction changing device) which is a conventional problem. As a result, one converter allows receptions of not only both horizontal and vertical linear polarizations but also both right-handed turning and left-handed turning circular polarizations without deteriorating the pass loss characteristic and the return loss characteristic (VSWR characteristic) of the entire antenna apparatus.
[0037] Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.
1. A polarization converter provided between a horn (2) and a down converter (3) of an
antenna apparatus receiving radio wave transmitted from broadcasting satellites and
communication satellites, said polarization converter (9) comprising:
a circular waveguide (20) for transmitting said radio wave,
phase plate (8) provided at said horn side in said circular waveguide for converting a circular polarization to a linear polarization, and
electric field direction changing means provided at said converter side in said circular waveguide for changing the direction of the electric field of said linear polarization.
2. The polarization converter according to claim 1, wherein said phase plate includes
a dielectric plate (8).
3. The polarization converter according to claim 2, wherein said dielectric plate (8)
is vertically provided at said horn side in said circular waveguide.
4. The polarization converter according to claim 1, wherein said electric field direction
changing means includes a ferrite pole (10) for changing the direction of the electric
field of said linear polarization and a coil (11) for applying magnetic field to said
ferrite pole.
5. The polarization converter according to claim 4, wherein said ferrite pole (10) is
provided on the center axis of said circular waveguide.
6. The polarization converter according to claim 4, wherein said coil (11) is provided
externally to said circular waveguide.
7. The polarization converter according to claim 4, wherein said coil (11) is provided
in said circular waveguide.
8. The polarization converter according to claim 5, wherein said ferrite pole (10) is
fixed in said circular waveguide by a resin member.
9. A polarisation converter for an antenna apparatus comprising:
means for converting circularly polarised signals to linearly polarised signals; and
means for aligning the direction of the electric field of the linearly polarised signal with a predetermined direction.
10. A polarisation converter according to claim 9 wherein the means for converting comprises
a phase plate.
11. A method for converting a circularly or linearly polarised signal into a linearly
polarised signal with a direction of polarisation aligned in a predetermined direction
comprising the steps:
converting a circularly polarised signal to linearly polarised signal; and
aligning the direction of the electric field of the linearly polarised signal with the predetermined direction.