Wave transmission lines and networks – Wave mode converters
Reexamination Certificate
2000-05-02
2002-07-09
Lee, Benny T. (Department: 2817)
Wave transmission lines and networks
Wave mode converters
C333S157000, C333S126000, C333S135000
Reexamination Certificate
active
06417742
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a circular polarizer connected to a primary radiator of a parabolic antenna sharing two frequency bands, and particularly to a circular polarizer provided at an outer waveguide for a low frequency band in waveguides of the coaxial structure connected to a primary radiator.
Description of the Background Art
Recently, satellite broadcast receivers have become popular. In general, the polarized wave of a signal used in satellite broadcasting includes a circularly polarized wave in addition to a linearly polarized wave.
FIG. 1
shows an example of an appearance of a parabolic antenna employed by a satellite broadcast received using the conventional circularly polarized wave. Referring to
FIG. 1
, the parabolic antenna includes a dish
51
reflecting a circularly polarized wave, a primary radiator
52
receiving the circularly polarized wave collected by dish
51
, a circular polarizer
53
converting the circularly polarized wave received by primary radiator
52
into a linearly polarized wave, and a converter
54
converting the frequency of the linearly polarized wave output from circular polarizer
53
. A circular polarizer is a polarized wave converter converting a linearly polarized wave into a circularly polarized wave, or a circularly polarized wave into a linearly polarized wave.
FIGS. 2A
,
2
B,
2
C,
2
D schematically show structures of conventional circular polarizers. These circular polarizers
53
a,
53
b,
53
c
and
53
d,
respectively convert a circularly polarized wave into a linearly polarized wave. The operation mechanism will be briefly described hereinafter.
In the case where a circularly polarized wave is to be converted into a linearly polarized wave, it is assumed that the two linearly polarized waves orthogonal to each other constitute the circularly polarized wave and the phases of the two linearly polarized waves are displaced by 90°. A circularly polarized wave Ec is converted into a linearly polarized wave Er by retarding the phase of the linearly polarized wave that is advanced 90° to set the phase difference to 0°.
For example, a dielectric phase plate
61
in a circular polarizer
53
a
shown in
FIG. 2A
is provided to have an angle of approximately 45° with respect to a linearly polarized wave Er that is to be converted. An electric field E
1
parallel to dielectric phase plate
61
passes through dielectric phase plate
61
, whereby the wavelength is reduced. As a result, the phase of electric field E
1
is behind the phase of an electric field E
2
orthogonal to dielectric phase plate
61
. By setting this phase delay to 90°, the phase difference between electric fields E
1
and E
2
becomes 0°, whereby circularly polarized wave Ec can be converted into linearly polarized wave Er.
Circular polarizer
53
b
of
FIG. 2B
is provided with a plurality of cylindrical metal projections at the waveguide. By retarding the phase of electric field E
1
90° by the cylindrical metal projection, circularly polarized wave Ec is converted into linearly polarized wave Er. Circular polarizer
53
c
of
FIG. 2C
is provided with an arc shape metal bulk within the waveguide. By retarding the phase of electric field E
1
90° by the metal bulk, circularly polarized wave Ec is converted into linearly polarized wave Er. Circular polarizer
53
d
of
FIG. 2D
is provided with plate-like metal projections within the waveguide. By retarding the phase of electric field E
1
90° by the plate-like metal projection, circularly polarized wave Ec is converted into linearly polarized wave Er.
The method of receiving as many channels as possible with one antenna includes the method of receiving the signals of two frequency bands transmitted from one satellite through one antenna, and the method of receiving the signals of two frequency bands transmitted from two satellites located on the same orbit through one antenna. These two different frequency bands correspond to, for example, the C band in the vicinity of 4 GHz and the Ku band in the vicinity of 12 GHz, or an arbitrary combination of frequency bands such as the Ka band in the vicinity of 20 GHz. Two primary radiators are required in order to receive the signals of two frequency bands remote from each other with a parabolic antenna.
The antenna that receives signals of two frequency bands transmitted from the same direction must have directivity with respect to the two frequency bands. In order to provide the same directivity with respect to the signals of two different frequency bands for the parabolic antenna, two primary radiators for the frequency bands must be provided at the focal position of the dish. The same applies for an antenna that carries out transmission and reception at different frequency bands with respect to one satellite.
FIG. 3A
is a block diagram showing a schematic structure of a parabolic antenna for a linearly polarized wave where two primary radiators for the frequency bands are provided. This parabolic antenna includes a dish
51
reflecting a linearly polarized wave, a primary radiator
62
for a high frequency band (referred to as f
H
) receiving the linearly polarized wave collected by dish
51
, a primary radiator
63
for a low frequency band (referred to as f
L
) receiving a linearly polarized wave collected by dish
51
, a high frequency band (f
H
) waveguide
64
transmitting a signal of a high frequency band received by high frequency band (f
H
) primary radiator
62
, and a low frequency band (f
L
) waveguide
65
transmitting a signal of a low frequency band received by low frequency band (f
L
) primary radiator
63
. f
H
waveguide
64
and low frequency band (f
L
) waveguide
65
are formed of the coaxial structure.
FIGS. 3B and 3C
are diagrams to describe the electromagnetic mode of high frequency band (f
H
) waveguide
64
and low frequency band (f
L
) waveguide
65
. Since high frequency band (f
H
) waveguide
64
is a circular waveguide, the electromagnetic mode within the waveguide corresponds to the TE
11
mode of the general circular waveguide, as shown in FIG.
3
B. Low frequency band waveguide (f
L
)
65
is a coaxial waveguide having a conductor (high frequency band waveguide (f
H
) at the center, so that the electromagnetic mode within the waveguide corresponds to the TE
11
mode as shown in FIG.
3
C. In the case where a circular polarizer is to be provided at the inner high frequency band waveguide (f
H
)
64
with respect to a parabolic antenna for a circularly polarized wave, a circular polarizer of any of the structures shown in
FIGS. 2A-2D
is to be employed within high frequency band (f
H
) waveguide
64
.
FIGS. 4A and 4B
correspond to the case where a circular polarizer is provided at the outer f
L
waveguide
65
. A plurality of cylindrical metal projections
82
are provided to have an angle of approximately 45° with respect to the linearly polarized wave Er (linearly polarized wave Er to be converted) of the TE
11
mode of a coaxial waveguide. Electric field E
1
parallel to the plurality of cylindrical metal projections
82
passes cylindrical metal projections
82
, whereby the wavelength is reduced. As a result, the phase of electric field E
1
is behind the phase of electric field E
2
orthogonal to cylindrical metal projections
82
. By setting this phase lag to 90°, the phase difference between electric fields E
1
and E
2
becomes 0°. Thus, circularly polarized wave Ec can be converted into a linearly polarized wave Er.
Circular polarizer
81
provided with a plurality of cylindrical metal projections
82
shown in
FIGS. 4A and 4B
must have the phase and return loss optimized by altering the length of each cylindrical metal projection
82
. For this purpose, cylindrical metal projection
82
must be formed of a vis whose length is adjusted one by one in the low frequency band waveguide (f
L
).
FIG. 5
is a diagram to describe the method of adjusting the length of the, projection in the low frequency band waveguide (f
L
). As shown in
FIG. 5
, circular coaxial wav
Lee Benny T.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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