U.S. patent number 3,763,493 [Application Number 05/186,911] was granted by the patent office on 1973-10-02 for antenna device applicable for two different frequency bands.
This patent grant is currently assigned to Nippon Telegraph and Telephone Public Corporation. Invention is credited to Masahiro Karikomi, Masaki Koyama, Hiroyuki Kumazawa, Sadakuni Shimada.
United States Patent |
3,763,493 |
Shimada , et al. |
October 2, 1973 |
ANTENNA DEVICE APPLICABLE FOR TWO DIFFERENT FREQUENCY BANDS
Abstract
A branching filter using dielectric elements is disposed on the
side of one of a pair of reflectors for reflecting emitted or
incident waves, the branching filter being capable of reflecting
one of the two frequency group components and of transmitting the
other frequency group component to branch and converge the two
components at different points.
Inventors: |
Shimada; Sadakuni (Koganei-shi,
Tokyo, JA), Koyama; Masaki (Sayama-shi,
JA), Kumazawa; Hiroyuki (Saitama-ken, Tokorozawa-shi,
JA), Karikomi; Masahiro (Suginami-ku, Tokyo,
JA) |
Assignee: |
Nippon Telegraph and Telephone
Public Corporation (Tokyo, JA)
|
Family
ID: |
14025921 |
Appl.
No.: |
05/186,911 |
Filed: |
October 6, 1971 |
Foreign Application Priority Data
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Oct 17, 1970 [JA] |
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45/91422 |
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Current U.S.
Class: |
343/755; 343/837;
343/781R; 343/911R |
Current CPC
Class: |
H01Q
5/45 (20150115); H01Q 15/0033 (20130101); H01Q
19/104 (20130101) |
Current International
Class: |
H01Q
15/00 (20060101); H01Q 19/10 (20060101); H01Q
5/00 (20060101); H01q 019/14 () |
Field of
Search: |
;343/840,909,755,781,837,911 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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335,425 |
|
Feb 1959 |
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CH |
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562,602 |
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Sep 1958 |
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CA |
|
Primary Examiner: Lieberman; Eli
Claims
What is claimed is:
1. An antenna for reflecting emitted and incident wave components
of first and second frequency groups, comprising first and second
reflectors positioned in opposed relation to sequentially reflect
wave components, and a third reflector positioned adjacent one of
said first and second reflectors, said third reflector being
comprised of a branching filter having a plurality of dielectric
layers positioned to reflect wave components of said second group
and transmit wave components of said first group, said first and
second reflectors being positioned to converge wave components of
said first group at a first point, and said third and otherof said
first and second reflectors being positioned to converge wave
components of said second group at a second position spaced from
said first position, said branching filter being comprised of a
plurality of alternate layers of materials of two different
dielectric con-stants with thickness substantially equal to
one-quarter of the wave length of the center frequency of the
second group.
2. The antenna of claim 1 wherein said one reflector is said second
reflector, said first and second reflectors are paraboloidal with a
common focal point, and said third reflector is positioned between
said first and second reflectors and is hyperboloidal with a focus
at said common point.
3. The antenna of claim 1 further comprising a horn for said second
group at the conjugate focal point of said common focal point, and
a second horn for said group positioned at the center of said first
reflector.
4. The antenna of claim 3 wherein said first group is in the
microwave frequency band and said second group is in the
quasimillimeter band.
5. The antenna of claim 1 wherein said one reflector is said second
reflector, said second and third reflectors are hyperboloidal, said
first reflector is paraboloidal with a focus common with one focus
of said second reflector a horn at the other focus of said second
reflector with the axis of the two focal points of the second
reflector at an angle to the axis of said first reflector, one
focus of the third reflector coinciding with the one focus point of
said second reflector, and a horn at the other focus point of said
third reflector, the axis of the focal points of said third
reflector being at a different angle to the axis of the first
reflector.
6. The antenna of claim 1 wherein said one reflector is said first
reflector, said first and third reflectors are paraboloidal, and
said second reflector is a plane reflector at an angle to the axis
of the first reflector, the axes of said first and third reflectors
being spaced apart.
7. The antenna of claim 1 wherein said one reflector is said second
reflector, said first reflector is paraboloidal and said second and
third reflectors are plane reflectors at different angles to the
axis of said first reflector.
Description
BACKGROUND OF THE DISCLOSURE
The present invention relates to an antenna device comprising a
pair of reflectors and more particularly an antenna device in which
a branching filter using dielectric elements is disposed adjacent
to one of a pair of reflectors so that the waves of two different
frequency groups may be directly branched or composed in the
antenna section.
In the telecommunication systems utilizing the telecommunication
satellites as the relay stations, there has been proposed the use
of two or more frequency bands such as the microwave frequency band
of 4 - 6 GHz and the quasi-millimeter frequency band of 17 - 30
GHz. The antenna devices used in such telecommunication system must
have the capability of simultaneously composing or branching the
frequency groups in the microwave and quasi-millimeter frequency
bands. This is accomplished by use of the frequency group branching
filters connected to the Cassegrain antennas which are widely used
in the microwave communication systems. In antenna devices of the
type described, two wave guides are coupled through many slots that
are equidistantly spaced apart to constitute a wave-guide type
frequency group branching filter which in turn is coupled to the
feeder section of the antenna device. In case of transmission the
frequency group branching filter composes the two signal components
of the microwave and quasi-millimeter frequency bands which are
transmitted by the two different wave guides respectively, and the
composed signals are transmitted to a primary horn through a feeder
section, reflected by a subreflector and a main reflector and
emitted into the space. In case of reception, the incident waves
are reflected first by the main reflector and then by the
subreflector to be transmitted into the feeder section through the
primary horn, and are branched into the microwave and millimeter
frequency group signal components by the frequency group branching
filter to be fed into the two different wave guides
respectively.
However, the number of slots in the frequency group branching
filter must be increased as the frequency of the signals
transmitted is increased. Furthermore since the signals of the
quasi-millimeter frequency band which is four to five times higher
than the microwave frequency band are transmitted or received
simultaneously with the signals of the microwave frequency band,
the feeder section coupled to the primary horn of the antenna
device tends to become oversized relative to the signals in the
quasi-millimeter band. Therefore the undesired high order mode of
the quasi-millimeter band tends to be excited in the frequency
group branching filter and the feeder section and so the quality of
the transmitted signals is much deteriorated. The undersired high
order mode produced causes tracking error when the antenna device
is steered to track a communication satellite. Furthermore, there
is heat loss in the walls of the wave guides of the frequency group
branching filter when the signal current flows. This heat loss is a
cause of the deterioration of the gain-noise temperature ratio
(G/T) of the antenna device. Therefore it is not preferable to use
a frequency group branching filter of the type comprising wave
guides in order to branch or compose the wide band signal waves
extending from a relatively lower frequency group to a relatively
higher frequency group which is several times higher than the lower
frequency group in frequency.
One of the objects of the present invention is therefore to provide
an antenna device in which the frequency group branching and
composition may be carried out directly in the antenna section
without using the wave-guide type frequency group filter.
Another object of the present invention is to provide an antenna
device incorporating a branching filter using dielectric elements
which is capable of reflecting a high frequency beam of the two
different frequency group components and of transmitting
therethrough the other frequency group component so that the
frequency group branching and composition of the beam may be
effected.
According to one embodiment of the present invention, first and
second reflectors are disposed in opposing relation, and a third
reflector or a branching filter using dielectric elements capable
of reflecting the waves in the higher frequency group and of
transmitting therethrough the waves in the lower frequency group is
disposed adjacent to one of the first and second reflectors, for
example the second reflector. In reception the incident waves in
the low frequency group are first reflected by the first reflector,
transmitted through the third reflector and reflected again by the
second reflector to converge toward a primary horn for low
frequency group. The waves in the high frequency group are first
reflected by the first reflector and then by the third reflector or
branching filter to converge toward a primary horn for high
frequency group. In case of transmission the direction of the
propagation or transmission of the waves in the high and low
frequency groups are reversed.
In the antenna device of the present invention, at least one of the
first, second and third reflectors is a paraboloidal reflector
while the other two reflectors are hyperboloidal reflectors.
Alternatively one of the three reflectors is a plane reflector
which is disposed at an angle relative to the axes of the
paraboloidal or hyperboloidal reflectors. The former type antenna
device in accordance with the present invention is especially
adapted for use in an earth station in the satellite
telecommunication system using two or more frequency bands, while
the latter type antenna device is adapted to be mounted on a
telecommunication satellite.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG.1 is a schematic sectional view of a prior art Cassegrain
antenna device incorporating therein a wave-guide type frequency
group filter;
FIG.2 is a fragmentary longitudinal sectional view, on enlarged
scale, of the frequency group filter thereof;
FIG.3 is a sectional view taken along the line 3--3 of FIG.2;
FIG.4 is a schematic sectional view illustrating one embodiment of
an antenna device in accordance with the present invention;
FIG.5-(a) is a perspective view of a branching filter using
dielectric elements used in the antenna device in accordance with
the present invention;
FIG.5-(b) is a diagram for explanation of the principle of
operation thereof;
FIG.6 is a graph illustrating the frequency characteristic curves
of the branching filter shown in FIG.5;
FIGS.7-9 are schematic sectional views of some variations of the
antenna device in accordance with the present invention;
FIG.10 is a sectional view of the antenna device of the present
invention used as an antenna for an earth station;
FIG.11 is a schematic sectional view illustrating the antenna
device in accordance with the present invention used as a satellite
antenna;
FIG.12 is a view for explanation of the mode of operation thereof;
and
FIG. 13 is a cross sectional view of a reflector which may be
employed in the antenna device of FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Prior Art
Referring to FIG.1, a prior art Cassegrain antenna device generally
designated by 10 comprises a main reflector 11, a subreflector 12,
a primary horn 13 located at the center of the main reflector 11, a
feeder section 14, and a frequency group branching filter 15
including a pair of wave guides 16 and 17. In case of transmission,
two signal components of different frequency bands such as
quasi-millimeter frequency band and the microwave frequency band
which are respectively transmitted through the wave guides 16 and
17 are composed by the frequency group branching filter 15 and led
to feeder section 14 and transmitted from the primary horn 13. The
electromagnetic waves emitted from the primary horn 13 are
reflected by the subreflector 12 and the main reflector 11 in the
order named and transmitted into space. In case of reception, the
incident waves are reflected by the main reflector 11 to the
subreflector 12 from which they are led into the primary horn 13,
the feeder section 14 and the frequency group branching filter 15
where they are branched into the signal components of the
quasi-millimeter frequency band and of the microwave frequency band
respectively. The branched signals are transmitted through the wave
guides 16 and 17 respectively to a reception apparatus (not
shown).
Next referring to FIGS.2 and 3 illustrating the enlarged sectional
views of the frequency group branching filter 15, the two wave
guides 16 and 17 are coupled to each other through a plurality of
slots 18 which are substantially equidistantly spaced apart from
each other, and the transmitted wave frequency band characteristic
of the coupler is so selected as to comply with the
quasi-millimeter frequency band. Therefore in case of the
reception, the incident waves fed from the feeder section 14 in the
direction indicated by the arrow 19 into the frequency band
branching filter 15 are so branched that the signal components in
the quasi-millimeter frequency band are transmitted through the
slots 18 into the wave guide 16 while the signal components in the
microwave frequency band are transmitted through the wave guide 17.
In case of transmission, the propagation of these signal components
is of course reversed, and the signal components in the
quasi-millimeter and microwave frequency bands which are composed
by the group frequency branching filter 15 are led toward the
primary feeder 14.
However, as stated previously, it is not preferable to couple the
frequency group branching filter of the type described comprising a
pair of wave guides 16 and 17 to the feeder section of the
Cassegrain antenna in order to branch and compose the waves widely
extending in frequency from the microwave frequency to the
quasi-millimeter frequency band, because of many associated
problems.
THE INVENTION
FIG.4 is a schematic sectional view of an antenna device in
accordance with the present invention for explanation of the
underlying principle thereof. A main reflector 101 is a
paraboloidal reflector with the focal point indicated by 102, and a
first subreflector 103 that is a paraboloidal reflector with the
focal point indicated by 102 and a second subreflector 104 which is
a hyperboloidal reflector are disposed in opposing relation with
the main reflector 101. The second subreflector 104 comprises a
branching filter using dielectric elements to be described in more
detail hereinafter, so that the electromagnetic waves in higher
frequency bands such as the quasi-millimeter frequency band may be
reflected while the waves in the lower frequency bands such as the
microwave frequency band may be transmitted therethrough. A primary
horn 106 for high frequency band is located at the conjugate focal
point 105 of the focal point 102 of the hyperboloidal subreflector
104, and another primary horn reflector 107 for lower frequency
band is located at the center of the main reflector 101.
Now it is assumed that the waves in the low frequency band
indicated by the solid lines 108 and the waves in the higher
frequency band indicated by the dashed lines 109 arrive at the same
time at the antenna device 100. The waves 108 in the lower
frequency band are reflected by the main reflector 101, transmitted
through the second subreflector 104 or the branching filter using
the dielectric elements and then reflected again by the
subreflector 103 to be made incident onto the primary horn 107 as
plane waves. The incident waves are converged at the focal point
110 of the primary horn reflector 107 and derived in the direction
indicated by the arrow 111. The waves in the higher frequency band
109 are first reflected by the main reflector 101 and then by the
second hyperboloidal subreflector 104 or branching filter using
dielectric elements, converged at the focal point 105 and made
incident onto the primary horn 106, from which the waves are
derived in the direction indicated by the arrow 112. It is of
course understood readily that in case of transmission the
propagation paths of the waves are reversed.
As described above according to the present invention the waves in
the higher and lower frequency bands are branched or composed
directly at the antenna section so that oversized wave guides
coupled to the primary horns 106 and 107 are not required.
Furthermore the branching and composition of the waves over the
wide frequency band may be effected with a negligible loss and the
minimum of undesired higher order mode.
FIG.5 illustrates a branching filter using dielectric elements for
branching two waves in the two frequency bands. For the simplicity
of explanation, the frequency bands used are the quasi-millimeter
frequency bands of 18 GHz and 26 GHz and the microwave frequency
bands of 4 GHz and 6 GHz. Referring to FIG.5-(a), the branching
filter 200 is shown as comprising a plurality of sheet-shaped
dielectric elements 201-205 of two types having different
dielectric constants. The thickness of the elements 201-205 is
substantially equal to,for example, one fourth of the wave length
of the center frequency (23.5 GHz), of the two quasi-millimeter
frequency bands of 18 and 26 GHz. The filter 200 is inclined as
shown in FIG.5-(b), and the composed waves 206 in the above stated
quasi-millimeter and microwave frequency bands are made incident to
the filter 200. The substantial components in the quasi-millimeter
frequency bands are reflected by the first dielectric element 201
as indicated by 211, and the remaining components are transmitted
through the element 201 as indicated by 207. The transmitted waves
207 are then reflected by the second dielectric element 202 so that
the substantial components in the quasi-millimeter frequency bands
included in the transmitted waves 207 are reflected as shown by
212. The remaining components are transmitted through the second
dielectric element 202 as indicated by 208. In a manner similar to
that described the waves are successively reflected by and
transmitted through the successive dielectric elements 203-205. As
a consequence the substantial components in the quasi-millimeter
frequency bands are derived as the reflected waves 211, 212 and 213
while the substantial components in the microwave frequency bands
are derived as the transmitted waves 210. FIG. 13 is a cross
sectional view of the combination of the first subreflector 103 and
second subreflector 104 of FIG. 4 employing the branching filter as
illustrated in FIG. 5(b).
The frequency characteristic curves of the filter 200 shown in
FIG.5 are illustrated in FIG.6. The solid curves indicate the
theoretical values while the dotted line curves, those marked with
"measured," indicate the measured values. The frequency is plotted
against the abscissa while the transmission loss (T) and reflection
loss (R) against the ordinate. From FIG.6, it is seen that the
filter shown in FIG.5 has the excellent capability of branching the
waves in the quasi-millimeter frequency band of 18-26 GHz from
those in the microwave frequency band of 4-6 GHz.
The present invention is not limited to the arrangement shown in
FIG.4, and various variations and modifications can be effected as
will be described hereinafter by reference to FIGS.7-9 without
departing from the scope of the invention.
In a variation illustrated in FIG.7, both of the first and second
subreflectors for reflecting the waves in the lower and higher
frequency bands are hyperboloidal reflectors at one focus or focal
points of which are located the primary horns respectively. More
specifically, one of the focal points of the first hyperboloidal
subreflector 303 is located to be coincident with the focal point
302 of the paraboloidal main reflector 301. The other focal point
or focus of the hyperboloidal subreflector 303 is indicated by 308.
The axis connecting the points or focal points 302 and 308 of
course makes an angle with respect to that of the paraboloidal main
reflector 301. The primary horn 310 for reception of the lower
frequency bands is located at the focal point 308 of the first
subreflector 303 in opposed relation therewith. One focal point of
the second hyperboloidal subreflector or branching filter 304
similar in construction to the filter shown in FIG.5 coincides with
the focal point of the main reflector 301. The other focal point is
indicated by 309. The axis of the second hyperboloidal subreflector
304 is also inclined at an angle relative to the axis of the main
reflector 301, but on the opposite side relative to the axis of the
first subreflector 303. The primary horn 311 for reception or
transmission of the higher frequency band is located at the focal
point 309 of the second subreflector 304 in opposed relation
therewith and is aligned with the axis thereof.
The incident waves in the lower frequency band indicated by the
solid lines 314 are first reflected by the main reflector 301 to
converge toward the focal point 302 and then transmitted through
the second subreflector or branching filter 304 and again reflected
by the first subreflector 303 to converge toward the focal point
308. Consequently the waves in the lower frequency band are made
incident into the primary horn 310 and derived in the direction
indicated by the arrow 313. The incident waves in the higher
frequency band indicated by the dashed lines 315 are first
reflected by the main reflector 301 and then by the second
subreflector or filter 304 to converge toward the focal point 309
at which the primary horn 311 is located so that the waves may be
derived in the direction indicated by the arrow 314.
An antenna device generally designated by 400 in FIG.8 comprises a
plane reflector 401 which is disposed at about 45.degree. relative
to the axes of a first and a second paraboloidal reflectors 402 and
403. The second paraboloidal reflector 403 comprises a branching
filter using dielectric elements. The incident waves in the lower
frequency band indicated by 410 are first reflected by the plane
reflector 401, transmitted through the second paraboloidal
reflector 403 and then reflected again by the first paraboloidal
reflector 402 to converge toward the focal point 404, at which is
located a primary horn 408 so that the waves in the lower frequency
band may be derived in the direction indicated by the arrow 406.
The incident waves 411 in the higher frequency band are first
reflected by the plane reflector 401 and then by the second
paraboloidal reflector 403 to converge toward the focal point 405,
at which is located a primary horn 409 so that the incident waves
may be derived i the direction indicated by the arrow 407.
A still further variation of an antenna device in accordance with
the present invention illustrated in FIG.9 is similar in
construction to that shown in FIG.8 except that a branching filter
502 is flat and is disposed on the side of a first plane reflector
501 in spaced apart relation therewith. A paraboloidal reflector
503 is disposed in opposed relation with the first plane reflector
501 and the second plane reflector or the branching filter 502. As
in the case of the antenna devices described hereinbefore, the
antenna device 400 is provided with a primary horn 504 for
reception and transmission of the lower frequency band and another
primary horn 505 for the reception and transmission of the higher
frequency band. The waves in the lower frequency band are
propagated as indicated by 506 while the waves in the higher
frequency band are propagated as indicated by 507. The mode of
operation is similar to that of the antenna device shown in FIG.8
so that no description will be made.
As described above, the antenna devices of the present invention
may have various arrangements, and those shown in FIGS.4 and 7 are
especially adapted for use in the earth stations of the satellite
communication systems, while those shown in FIGS.8 and 9 are
adapted for use as the satellite antennas.
An antenna for an earth station in accordance with the present
invention is schematically illustrated in FIG.10. The antenna
device comprises a main paraboloidal reflector 601 with a focal
point indicated by 623, a first paraboloidal subreflector 602 made
of metal with its focal point indicated by 623 and a second
hyperboloidal subreflector 603 or filter of the type described
comprising a plurality of dielectric elements. One of the foci or
focal points of the second subreflector 603 coincides with that of
the first subreflector 602. The first and second subreflectors 602
and 603 are supported by stays 604. The antenna device is provided
with a horn reflector 605 for reception of the lower frequency band
and a primary horn 624 for reception of the higher frequency band
which is located at the other focus 606 of the hyderboloidal
reflector 603. Lower and higher frequency band reception apparatus
607 and 608 are coupled through rotary joints 609 and 610 to the
primary horns 605 and 624 respectively. Since the antenna device is
elevated about the axis 616, the transmission and reception
apparatus 607 and 608 which are fixed, are coupled to the primary
horns 605 and 624 through the rotary joints 609 and 610 coaxial
with the axis 616.
When the waves in the higher and lower frequency groups arrive
simultaneously, the waves in the lower frequency group are
reflected by the main reflector 601, transmitted through the second
subreflector 603 and reflected by the first subreflector 602 to
form the plane waves which are converged by the horn reflector 605
and transmitted to the transmission and reception apparatus 607.
The waves in the higher frequency group are reflected by the main
reflector 601 and then by the second hyperboloidal reflector or
dielectric filter 603 to converge toward the focal point 606 at
which is located the primary horn 624. The waves are then
transmitted to the transmission and reception apparatus 608. In
case of transmission, the wave propagation paths are reversed.
The main reflector 601 is supported by the stays 617 and 618
securely fixed to the main reflector and an altitude-azimuth mount
619 respectively, and is adapted to rotate about the altitude axis
616 as described previously by a motor 614 through a gear 613 which
is carried by a motor drive shaft 615 and is in mesh with a gear
612 carried by the altitude shaft 616. The motor 614 is securely
fixed to the mount 619 which in turn rides on a rail 620 on a
foundation 621 to rotate about the axis 622. Therefore the
elevation or altitude and azimuth of the antenna device may be
selected to track a communication satellite.
FIG.11 is a schematic view illustrating a mechanical despun antenna
of a satellite. In general, the geostationary satellite is spun in
order to stablize its hovering and then the satellite antenna must
be rotated in the direction opposite to the direction of spin of
the satellite in order to direct the antenna beam toward the earth.
In case of the satellite antenna in accordance with the present
invention which is not symmetrical about the axis of spin, both of
the primary horns and transponders must be rotated as the antenna
device is rotated. The antenna device of this type is called a
platform despun antenna.
The satellite antenna illustrated in FIG.11 comprises a metal
paraboloidal reflector 701 with an axis 703 and a focus or focal
point 706, another paraboloidal reflector 702 comprising a filter
using dielectric elements with an axis 704 and a focus or focal
point 705, a lower frequency group primary horn 708 located at the
focal point 706, a higher frequency group primary horn 707 located
at the focus or focal point 705, a plane reflector 709 disposed at
about 45.degree. relative to the axes 703 and 704 and supported by
stays 711 and an arm 710 or supporting the reflectors 701 and 702.
The satellite 712 carries a solar cell 713, a despun motor 714
whose rotary shaft 715 is securely fixed to the reflectors 701 and
702, the primary horns 707 and 708 and a platform 718, high and low
frequency group transponders 716 and 717 and an apogee motor
719.
In case of reception, the waves in the lower frequency group are
reflected by the plane reflector 709, transmitted through the
reflector 702 and reflected again by the reflector 701 to converge
toward the focal point 706. The converged waves are fed to the
transponder 717 through the primary horn 708 which is located at
the focal point 706. In like manner waves in the higher frequency
group are reflected first by the plane reflector 709 and then by
the reflector 702 to converge toward the primary horn 707 which is
located at the focal point 705, and are transmitted toward the
transponder 716.
The rotation of the antenna device is effected by the stator 714
fixed to the satellite proper and the rotary shaft 715 fixed to the
platform 718 and the primary horns of the antenna device, the
stator and the rotary shaft constituting a despun motor. Therefore,
the antenna elements, the primary horns and the transponders may
rotate in unison in the direction opposite to the direction of spin
of the satellite proper so that the beam may be always directed
toward the earth.
The following advantages may be accrued from the satellite antenna
shown in FIG.11. First there is no blocking because the primary
horns and their stays are not disposed in the propagation paths.
Secondly the reflector shaping of the two reflectors may be
effected relative to each other so that the high antenna efficiency
and the easy beam shaping may be attained.
FIG.12 schematically illustrates a geostationary satellite 804
having an antenna device comprising a reflector assembly 801
including a pair of paraboloidal reflectors one of which is a
dielectric filter of the type described, and a plane reflector 802
which is disposed at an angle relative to the axis 803 of the
reflector assembly 801. The geostationary satellite 804 spins about
the axis 803 which is perpendicular to a plane including the
equator of the earth 805 so that when the plane reflector 802 is
inclined at 45.degree. relative to the axis 803, the antenna beam
is directed toward the equator as indicated by 806. In order to
direct the beam to, for example, Japan as indicated by 806', the
plane reflector 802 is inclined as indicated by the dashed line
802'. In such a simple manner as described above, the beam may be
directed to any desired direction without adversely affecting the
antenna characteristics.
Although the dielectric filter has been described as being capable
of transmitting the waves in the lower frequency group and of
reflecting the waves in the higher frequency group, it may be
designed to reflect the waves in the lower frequency group and to
transmit the waves in the higher frequency group.
* * * * *