Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
2002-05-06
2004-04-06
Phan, Tho G. (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S785000, C333S02100R
Reexamination Certificate
active
06717553
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a primary radiator used in, for example, a satellite-television reflective antenna, and, more particularly, to a primary radiator for sending and receiving circularly polarized electrical waves.
2. Description of the Related Art
A related primary radiator of this type will be described based on
FIGS. 14 and 15
.
FIG. 14
is a sectional view of the related primary radiator, and
FIG. 15
is a front view of the primary radiator viewed from a horn section. As shown in
FIGS. 14 and 15
, the related primary radiator comprises a circular cross-section waveguide
210
having a horn section
210
a
at one end thereof and having the other end formed as an enclosed surface
210
b
, a pair of ridges
211
formed at the inside wall surface of the waveguide
210
so as to protrude therefrom, and a probe
212
disposed between the ridges
211
and the enclosed surface
210
b.
The waveguide
210
is molded out of a metallic material, such as zinc or aluminum, by die casting. Both of the ridges
211
are integrally formed with the waveguide
210
. These ridges
211
function as phase changing members (90-degree phase devices) for changing circularly polarized waves that have traveled into the waveguide
210
from the horn section
210
a
into linearly polarized waves. The ridges
211
have tapered portions at both ends thereof along the central axis of the waveguide
210
, and have predetermined heights, widths, and lengths. As shown in
FIG. 15
, when a plane including the central axis of the waveguide
210
and both ridges
211
is a reference plane, the probe
212
intersects the reference plane at an angle of approximately 45 degrees, and the distance between the probe
212
and the enclosed surface
210
b
is equal to about ¼ of a wavelength inside the waveguide. It is known that, instead of the ridges
211
, plate members, formed of dielectric materials, may also be used as phase converting members. The dielectric plates are inserted into/secured to the inside of the waveguide
210
. In that case, the probe
212
intersects at an angle of approximately 45 degrees a reference plane which is parallel to the surfaces of the dielectric plates and which passes the central axis of the waveguide
210
.
In the primary radiator having such a structure, when a clockwise or a counterclockwise circularly polarized wave sent from, for example, a satellite is received, the circularly polarized wave is guided from the horn section
210
a
to the inside of the waveguide
210
, and is converted into a linearly polarized wave when the circularly polarized wave passes the ridges
211
(or dielectric plates) inside the waveguide
210
. More specifically, since the circularly polarized wave is a wave in which a combined vector of two linearly polarized waves having the same amplitudes, being perpendicular to each other, and having phase differences of 90 degrees rotates, when the circularly polarized wave passes the ridges
211
(or dielectric plates), the wave portions which have been out of phase by 90 degrees are caused to be in phase, so that the circularly polarized wave is converted into a linearly polarized wave. Therefore, when the linearly polarized wave is received as a result of coupling at the probe
212
, it is possible to convert the received signal into an IF signal at a converter circuit (not shown), and to output the IF signal.
Conventionally, another known example of this type of primary radiator is a primary radiator comprising a waveguide having a horn section at one end thereof and having the other end formed as an enclosed surface, a phase converting member disposed inside the waveguide, and a probe installed between the phase converting member and the enclosed surface of the waveguide. The phase converting member converts a circularly polarized wave that has traveled into the waveguide into a linearly polarized wave. One example of the phase converting member is a dielectric plate having both longitudinal ends formed into a wedge shape. The probe intersects the phase changing member at an angle of approximately 45 degrees, and the distance between the probe and the enclosed surface of the waveguide is approximately ¼ of a wavelength inside the waveguide.
In the primary radiator having such a general structure, a clockwise or counterclockwise circularly polarized wave transmitted from a satellite is guided to the inside of the waveguide from the horn section and is converted into a linearly polarized wave at the phase converting member. More specifically, since the circularly polarized wave is a wave in which a combined vector of two linearly polarized waves having the same amplitude, being perpendicular to each other, and having phase differences of 90 degrees rotates, when the circularly polarized wave passes the phase converting member, the wave portions which have been out of phase by 90 degrees are caused to be in phase, so that the circularly polarized wave is converted into a linearly polarized wave. Therefore, when the linearly polarized wave is received as a result of coupling at the probe, the received signal is converted into an IF signal at a converter circuit (not shown), and the IF signal is output.
However, in each of the related primary radiators constructed as described above, the waveguide is molded out of a metallic material, such as zinc or aluminum, by die casting, so that an expensive molding die having a complicated structure is required, which is a big factor in increasing production costs of the primary radiator. In recent years, to overcome this problem, an attempt to form the waveguide by winding a metallic plate into a cylindrical shape has been made in order to eliminate the use of an expensive die-casting mold. However, such a waveguide gives rise to new problems with regard to the phase converting member or members.
More specifically, in the waveguide formed by winding a metallic plate into a cylindrical shape, it is difficult to form a large protrusion on a thin metallic plate by pressing, so that, even if the protrusion is successfully formed, the protrusion have low dimensional precision. Therefore, when a ridge is used as a phase converting member, it is difficult to process. On the other hand, when a dielectric plate is used as a phase converting member, since the inner peripheral surface of the waveguide formed by winding a metallic plate is circular, it is necessary to bond the phase converting member to a predetermined location inside the waveguide while the phase converting member inserted into the waveguide is positioned with a jig at the stage of assembling the primary radiator. Therefore, the assembly work becomes very complicated.
In each of the primary radiators of this type, since the probe and the phase converting member or members intersect at an angle of approximately 45 degrees inside the waveguide, it is necessary to secure the phase converting member or members inserted into the waveguide with proper means. In general, a bonding agent is used as such means for securing the phase converting member or members. However, in the securing method using a bonding agent, it is necessary to perform the complicated step of applying the bonding agent to a joining portion of the inside wall surface of the waveguide and the phase converting member or members while the phase converting member or members are positioned with a jig. Therefore, the problem that assembly workability is poor arises. A method of securing the phase converting member or members to the inside portion of the waveguide with a screw as another securing means has been proposed. In this case, the front end portion of the screw protrudes into the waveguide, thereby giving rise to the problem of reduced performance resulting from reflection of electrical waves at the front end portion of the screw.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the problems of the related art, and has as its first object the provision of a primary radiator which has
Dou Yuanzhu
Nakagawa Masashi
Sasaki Kazuhiro
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Phan Tho G.
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