U.S. patent number 3,680,141 [Application Number 05/093,795] was granted by the patent office on 1972-07-25 for antenna device.
This patent grant is currently assigned to Nippon Telegraph and Telephone Public Corporation. Invention is credited to Mashahiro Karikomi.
United States Patent |
3,680,141 |
Karikomi |
July 25, 1972 |
ANTENNA DEVICE
Abstract
An antenna device comprising a main spherical reflector; a
sub-reflector for reflecting electromagnetic waves to said main
reflector so as to compensate for the spherical aberration of said
main reflector, a primary radiator, plane reflectors and a
parabolic reflector wherein the sub-reflector and plane reflectors
are interlocked with each other so as to cause plane waves to be
brought from the primary radiator to the sub-reflector through the
plane reflectors and parabolic reflector.
Inventors: |
Karikomi; Mashahiro (Tokyo,
JA) |
Assignee: |
Nippon Telegraph and Telephone
Public Corporation (Tokyo, JA)
|
Family
ID: |
14124537 |
Appl.
No.: |
05/093,795 |
Filed: |
November 30, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Nov 28, 1969 [JA] |
|
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44/94962 |
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Current U.S.
Class: |
343/758;
343/781R; 343/914; 343/761; 343/839 |
Current CPC
Class: |
H01Q
19/191 (20130101); H01Q 3/16 (20130101) |
Current International
Class: |
H01Q
19/10 (20060101); H01Q 3/16 (20060101); H01Q
19/19 (20060101); H01Q 3/00 (20060101); H01q
019/14 () |
Field of
Search: |
;343/781,837,839,840,758,761,914 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Electronics; Oct. 30, 1967 Vol. 40, No. 22, pp. 169, 170.
|
Primary Examiner: Lieberman; Eli
Claims
What is claimed is:
1. An antenna device comprising:
a main spherical reflector for reflecting electromagnetic
waves;
a sub-reflector disposed between the curvature center and
reflecting surface of the main reflector so as to reflect
electromagnetic waves to said surface and having a mirror surface
which is arranged to compensate for the spherical aberration of
said main spherical reflector;
a parabolic reflector whose focal point is coincident with said
curvature center so as to reflect electromagnetic waves to said
sub-reflector;
a primary radiator for radiating plane electromagnetic waves;
a plane reflector for reflecting said electromagnetic waves to said
parabolic reflector;
means for rotating said sub-reflector around an axial line passing
through said curvature center of said main spherical reflector,
with the central axis of said sub-reflector directed to said
curvature center; and
means for moving said plane reflector in interlocking relationship
with the rotation of said sub-reflector so as to cause the plane
electromagnetic waves to be conducted from said primary radiator to
said sub-reflector through said parabolic reflector.
2. An antenna device according to claim 1 wherein said primary
radiator, plane reflector, parabolic reflector, sub-reflector,
means for rotating said sub-reflector and means for moving said
plane reflector are respectively provided in a sufficient number to
constitute a plurality of wave radiating and conducting systems and
are so as to reflect a plurality of electromagnetic waves to said
main reflector in such a manner that the deflections of said
electromagnetic waves are separately controllable.
3. An antenna device according to claim 1 wherein a wave radiating
and conducting system comprising said primary radiator, plane
reflector, parabolic reflector, sub-reflector, means for rotating
said sub-reflector and means for moving said plane reflector is
positioned outside of the path of electromagnetic waves reflected
from said main spherical reflector.
4. An antenna device according to claim 1 wherein said means for
moving said plane reflector in interlocking relationship with the
rotation of said sub-reflector comprises:
a detector for detecting deflection errors in radiated waves and
for generating error signals corresponding to vertical plane errors
and horizontal plane errors; and
means responsive to said error signals for selectively rotating
said plane reflector so as to reduce said deflection errors.
5. An antenna device according to claim 4 wherein said means
responsive to said error signals includes means for generating
respective control signals corresponding to said vertical plane and
horizontal plane error signals, said plane reflector being
selectively rotated in response to said control signals.
6. An antenna device according to claim 5 wherein said means
responsive to said error signals further includes motor means
responsive to said control signals and coupled to said plane
reflector for selectively rotating said plane reflector to reduce
said deflection errors.
Description
The present invention relates to an antenna device comprising a
main spherical reflector and a sub-reflector for compensating the
spherical aberration of the main reflector, and more particularly
to an antenna device capable of deflecting electromagnetic waves
without moving the main spherical reflector.
Where telecommunication is conducted through a space satellite
using signals in a superhigh frequency band (SHF band), the
conventional antenna device of a ground station has been so
designed as to track an object space satellite by turning the main
reflector upward or downward or rotating it in accordance with the
movement of said satellite. Even in the case of a stationary
satellite, for example, which travels only through an extremely
limited angle with respect to the ground station, it has been
necessary to operate the whole of an antenna device in tracking
such stationary satellite.
Since the main reflector has a considerably large diameter there
must be built a gigantic antenna mount with the resulting
complicated construction in order to firmly support and drive the
main reflector against a certain magnitude of wind force.
Obviously, the structure and weight of said main reflector is
subject to limitation from the standpoint of constructing said
antenna mount.
The aforesaid stationary satellite travels through an extremely
minute angle with respect to a ground station, so that beams for
tracking the satellite have only to be deflected through a small
angle. If, therefore, the antenna device is so designed as to
permit the tracking of the stationary satellite simply by
deflecting radiated beams within the range of angles through which
the satellite travels, with the greater part of the antenna device
including the main reflector fixed in place, then the construction
of the antenna device will obviously be considerably simplified.
Further, if the antenna device is so arranged as to include a
single main reflector and separately control the deflections of a
plurality of radiated beams without moving said reflector, then it
will enable the antenna device to display a more effective action
and also offer economic advantage.
A ground station antenna device for satellite telecommunication has
heretofore consisted of a Cassegrain type in many cases. There has
also been employed a parabola antenna. The Cassegrain antenna
device is known to be capable of deflecting radiated beams by
inclining a sub-reflector (not intended to compensate spherical
aberration) with respect to the main reflector. It is also known
that both Cassegrain and parabola antenna devices can radiate a
plurality of beams by providing a plurality of primary radiators,
using a single main reflector. In either case, however, the
opto-geometrical conditions demanded of an antenna device are
obstructed with the resulting loss of gain expected therefrom.
Therefore, such a process has not yet been practically applied in
an antenna device.
It is accordingly an object of the present invention to provide an
antenna device capable of deflecting beams within a prescribed
range of angles satisfying the opto-geometrical conditions without
moving a main reflector.
Another object of the present invention is to provide an antenna
device capable of radiating a plurality of beams whose deflection
can be controlled independently, using a single main reflector.
SUMMARY OF THE INVENTION
The antenna device of the present invention comprises a main
spherical reflector for reflecting electromagnetic waves; a
sub-reflector disposed between the curvature center and reflecting
surface of the main reflector so as to compensate for the spherical
aberration of the main reflector; a parabolic reflector whose focal
point is coincident with the curvature center of the main spherical
reflector so as to reflect electromagnetic waves to the
sub-reflector; a plane reflector for reflecting electromagnetic
waves to the parabolic reflector; a primary radiator conducting
plane waves to the plane reflector; means for rotating said
sub-reflector around an axial line passing through said curvature
center of said main spherical reflector, with the central axis of
said sub-reflector directed to said curvature center; and means for
moving said plane reflector in interlocking relationship with the
rotation of said sub-reflector so as to cause the plane
electromagnetic waves to be conducted from said primary radiator to
said sub-reflector through said parabolic reflector.
The reflecting surface of the main spherical reflector is faced to
its center side. When there are brought to said effective surface
plane waves parallel with a main axial line connecting the center
of the reflecting surface and the curvature center, then the
resulting reflected waves are not converged exactly at a focal
point due to the spherical aberration of the main reflector. If,
however, the path of electromagnetic waves is made to have a fixed
length and there is provided a sub-reflector having its mirror
curve so calculated as to satisfy the opto-geometrical law of
reflection, then compensation of the aforesaid spherical aberration
will be accomplished. Said compensation is conducted in such a
manner that electromagnetic waves reflected by the sub-reflector
may be deemed as spherical waves from the curvature center. The
aforementioned compensatory means is based on opto-geometrical
considerations, so that, strictly speaking, there may be required
some correction by taking into consideration the concept of wave
mechanics. With an antenna device whose main spherical reflector
has a much longer diameter than the wavelength of electromagnetic
waves brought thereto, the above-mentioned opto-geometrical
consideration will fully serve the practical purpose.
The present invention will be more fully understood from the
following description taken by reference to the appended drawings,
in which:
FIG. 1 is an elevation of an antenna device according to an
embodiment of the present invention, showing the schematic
arrangement of its major parts;
FIG. 2 is an elevation of the antenna device of FIG. 1, indicating
the relationship of the reflector system and the direction in which
there are reflected electromagnetic waves;
FIG. 3 is a plan view showing the positional relationship of the
primary radiator and the plane reflector used in FIG. 2;
FIG. 4 is an elevation of a mechanism for rotating the
sub-reflector of FIG. 1 in a vertical plane;
FIG. 5 is an elevation of a mechanism for causing the pane
reflectors of FIG. 1 to move parallel with their respective
original positions;
FIG. 6 is a block diagram of a beam deflection control system for
causing the mechanisms of FIGS. 4 and 5 to be electrically driven
in interlocking relationship by signals for detecting errors in
defining the deflection of electromagnetic waves;
FIG. 7 illustrates the arrangement of a Cassegrain antenna device
using a parabola reflector and a primary radiator;
FIG. 8 represents the directional characteristics of
electromagnetic waves in the horizontal plane of the antenna device
using the reflector system of FIG. 7;
FIGS. 9 and 10 respectively are elevations of the reflector systems
of the present antenna device and the conventional Cassegrain
antenna device using a parabola reflector;
FIG. 11 is a diagram comprising the gains of the antenna devices of
FIGS. 9 and 10 for a frequency of 4 GHz;
FIG. 12 is a diagram comparing the gains of the antenna devices of
FIGS. 9 and 10 for a frequency of 18 GHz;
FIG. 13 illustrates the arrangement of reflectors in an antenna
device according to another embodiment of the invention; and
FIG. 14 shows the arrangement of reflectors in an antenna device
according to still another embodiment of the invention.
Referring to FIGS. 1 and 2, a main spherical reflector 1 having a
prescribed curvature radius is fixed on a mount 3 by a support 2.
Between the curvature center 5 and the reflecting surface of the
main reflector 1 is disposed a sub-reflector 4 for compensating the
spherical aberration of the reflecting surface. Means 6 for driving
the sub-reflector 4 is held by supports 7 fixed to the main
reflector 1 so as to rotate the sub-reflector 4 in the later
described direction. At the center of the main reflector 1 is
positioned part 8 of a parabolic reflector whose focal point is
constituted by the curvature center 5 of the main spherical
reflector 1. Numerals 9 and 10 are plane reflectors each so
designed as to move parallel with its original position. Numeral 12
is the conical horn reflector of the primary radiator fixed at a
prescribed point. This horn reflector 12 is connected to a
stationary transmission and reception apparatus and radiates plane
waves. The horizontal positional relationship of the horn reflector
12, and the plane reflectors 9 and 10 of FIG. 2 is presented in
FIG. 3. Referring to FIG. 2, numeral 14 denotes a central axial
line connecting the center of the reflecting surface of the main
spherical reflector 1 and its curvature center 5, 15 the central
axial line of the parabolic reflectors 8 and 16 the central axial
line of the conical horn reflector 12.
In the above-mentioned antenna device, the central axial line 17
(shown in a solid line) of the sub-reflector 4 assumes a position
rotated about the curvature center 5 in a vertical plane (that is,
a plane parallel with the surface of the drawing sheet) through an
angle .theta. with respect to the first mentioned central axial
line 14. Said sub-reflector 4 is so designed as to compensate the
spherical aberration of the main spherical reflector 1, with
respect to, for example, electromagnetic waves introduced in the
direction of the central axial line 17. On the other hand, plane
waves from the conical horn reflector 12 are reflected, as
indicated in solid lines, by the plane reflectors 10 and 9 in turn.
The plane waves thus reflected are conducted to the parabolic
reflector 8 in parallel with a line 15' which is also parallel with
the central axial line 15. The parabolic reflector 8 has a focal
point 5 on said central axial line 15, so that electromagnetical
beams brought to said reflector 8 are so reflected as to be
focussed at said focal point 15. The beams are further reflected by
the sub-reflector 4 and main reflector 1, rearranged in phase in
the direction of the central axial line 17, and emitted in the form
of beams having a sharp directivity in said direction.
There will now be described the case where radiated waves are
deflected without moving the main reflector 1. When, there are
emitted beams in the direction 17' in a vertical plane, the central
axial line 17 is made to rotate about point 5 so as to be aligned
with the line 17'. In this case, the sub-reflector 4 is inclined to
a position indicated by 4'. At the same time the plane reflector 9
is moved up to point 9' parallel with its original position along
the axial line 16. In this case, electromagnetic waves are
conducted through a route indicated by dotted lines, that is, plane
waves from the conical horn reflector 12 are reflected by the plane
reflector at point 9' and parabolic reflector 8, and advance to the
focal point 5 or the curvature center of the main reflector 1,
again reflected by the sub-reflector at point 4' and main reflector
1 and emitted in the form of waves fully rearranged in phase in the
direction of the central axial line 17'.
Next where radiated waves are deflected in a horizontal plane (that
is, a plane perpendicular to the surface of the drawing sheet),
then the plane reflector 10 is brought, as shown in FIG. 3, to
point 10' parallel with its original position along the axial line
18, a direction in which there are conducted plane waves from the
horn reflector 12, and the sub-reflector 4 is made to rotate about
the focal point 5 in a plane perpendicular to the surface of the
drawing sheet.
There have been described the cases where radiated waves are
deflected in vertical and horizontal planes. If, in this case, the
plane reflectors 9 and 10 and sub-reflector 4 are made to move in
interlocking relationship according to the direction in which
electromagnetic waves are to be deflected, such deflection can be
effected in a state fully meeting the opto-geometrical conditions
involved with respect to any direction in which said
electromagnetical beams pass through a conical region having a half
vertical angle .theta. which is disposed about the central axial
line 14. Accordingly, the antenna device of the present invention
can track a stationary satellite without moving the main reflector
and reducing the radiation property.
There will now be described means for causing the sub-reflector 4
and plane reflectors 9 and 10 to interlock with each other. The
sub-reflector 4 has, as shown in FIG. 4, a rotary shaft 19
extending in the direction of the axial line 17 and engaged with a
gear 20, which in turn is rotated by a motor 22. For the
sub-reflector 4 there is also provided a movable guide member 25
comprising a toothed section 23 engaged with said gear 20 which
jointly act as a sort of rack-pinion mechanism, and a groove 24
through which there are guided two rollers rotatably fitted to two
supports respectively which are fixed to the back of the
sub-reflector 4. As seen from FIG. 4, rotation of the motor 22
causes the sub-reflector 4 to be inclined in a vertical plane. In
this case, the axial line 17 of the sub-reflector 4 is so designed
as to be deflected through an angle .theta. at maximum with respect
to the central axial line 14. To incline the sub-reflector 4 in a
horizontal plane, it is only required to deflect the entire
assembly 26 of FIG. 4 in a horizontal plane through an angle
.theta. at maximum about point 5 of FIG. 2. A drive mechanism used
in such case may consist of a horizontally disposed guide member
25', a gear 20' engaged with the toothed section 23' of said guide
member 25' and a motor 27 (FIG. 6) for driving said gear 20' (20',
23', 25', are not shown). In this case the guide member 25' is
fixed to the support member 7 of FIG. 1.
There will now be described a mechanism (FIG. 5) whereby one plane
reflector 9 is made to move parallel with its original position
along the axial line 16 of FIG. 2. In this case, there are provided
two guide members 28 disposed at a prescribed position with respect
to the main reflector 1, each of said guide members 28 having a
guide groove 30 through which there slides one of the two rollers
29 rotatably fitted to the plane reflector 9 so as to cause it to
move parallel along the axial line 16 of FIG. 2. The plane
reflector 9 is fitted with a gear 33 driven by a motor 32 and
engaged with a toothed guide member 34 fixed at a prescribed
position, said gear 33 and toothed member 34 jointly acting as a
sort of rack-pinion mechanism. Accordingly, rotation of the motor
32 enables the plane reflector 9 to move parallel along the axial
line 16.
When the other plane reflector 10 is made to move parallel along
the axial line 18, there is used the same drive arrangement as that
of FIG. 5 though it is fitted in a different direction. The gear
33' (not shown) of the drive arrangement for the plane reflector 10
is driven by a motor 35 (FIG. 6).
There will now be described means for causing the sub-reflector 4
and the plane reflectors 9 and 10 to be moved in interlocking
relationship. As shown in FIG. 6, there is provided a detector 36
for finding errors in deflecting radiated beams or waves. As used
herein, the term "errors" means those degrees of an angle through
which the radiated beam should be deflected in order to properly
track a space satellite which has happened to shift its position.
Error signals are supplied to a generator or an analyzer 37 for
generating signals indicating errors occurring in a vertical plane
(EL plane) and also to another generator 38 for producing signals
representing errors in a horizontal plane (AZ plane), thereby
obtaining control signals 39 and 40 respectively. These control
signals 39 and 40 are conducted to a circuit 42 for controlling the
rotation of motors 22 and 32, namely, a circuit for driving said
motors 22 and 32 so as to eliminate errors in the EL plane and also
to a circuit 43 for controlling the rotation of motors 27 and 35,
namely, a circuit for driving said motors 22 and 32 so as to
eliminate errors in the AZ plane so as to actuate the servo motors
of these circuits. Now the motors 22, 32, 27 and 35 are driven by
outputs from said circuits 42 and 43. Thus detection signals from
the detector 36 can vary the angle at which there are radiated
electromagnetical beams in the EL plane and such angle in the AZ
plane separately, so that electromagnetical beams can be
collectively deflected in an arbitrary direction passing through
the previously mentioned conical region having a half vertical
angle .theta. which is disposed about the central axial line
14.
There will now be described the deflection characteristics of
electromagnetic waves radiated by the antenna device of the present
invention in comparison with those obtained with the conventional
Cassegrain antenna device using a parabola reflector. FIG. 7
represents a Cassegrain antenna device comprising a parabola
reflector 1a 100 cm in outer diameter, sub-reflector 4a 12 cm in
outer diameter and a conical horn reflector 12a having a beam hole
9.84 cm in diameter. The sub-reflector 4a is so designed as to be
deflected through an angle .phi. with respect to its original axis
about point 41. FIG. 8 indicates the directional characteristics
and gain loss of electromagnetic waves having a frequency of 50 GHz
which were radiated by said prior art antenna device. The abscissa
denotes the actual inclination (in a horizontal plane) of
electromagnetic waves with respect to the direction of the beams
which were radiated when the sub-reflector 4a was inclined at angle
.phi. = 0. The ordinate indicates gain loss by -dB as against a
gain of 51.2 dB in the case of the aforesaid inclination at angle
.phi. = 0 of the sub-reflector 4a. Curves 44a to 44h represent the
directional characteristics of electromagnetic wave radiated when
the inclination of the sub-reflector 4a assumed angles of 0, - 8, +
8, - 16, +16, - 20 and +20. As seen from FIG. 8, a 1.degree. to
2.degree. inclination in either way of the radiated beams from the
standard direction causes an appreciable decline in their
directional characteristics.
FIG. 9 shows the reflector system of the present invention used in
an antenna device and FIG. 10 that of the conventional Cassegrain
antenna device using a parabola reflector. The experimentally
determined directional characteristics of radiated beams when the
main reflectors of both antenna devices were alike 125 cm in center
diameter are compared in both FIGS. 11 and 12. FIG. 11 represents
the case where there were used beams having a frequency of 4 GHz
and FIG. 12 18 GHz. Throughout these figures, the abscissa denotes
the deflection of radiated beams in a horizontal plane with respect
to the axis of the main reflector, and the ordinate the antenna
gain as measured on a comparative basis. The curves 46a and 46b
show the directional characteristics of electromagnetic waves
radiated from the conventional antenna device of FIG. 10 and the
curves 47a and 47b those obtained with the present antenna device.
Here it should be noted that all these curves were drawn by joining
the peaks of curves representing the directional characteristics of
radiated beams, that is, the points of highest gain. As apparent
from FIGS. 11 and 12, the antenna device of the present invention
displays a substantially fixed gain when radiated beams are
deflected through an angle falling within a range of .+-.2.degree.,
and, what describes particular notice, presents a prominently
increased gain as radiated beams have a higher frequency. The
aforementioned favorable characteristics of radiated beams prove
that the antenna device of the present invention is well adapted
for space satellite telecommunication.
FIG. 13 illustrates another embodiment of the present invention
capable of generating a plurality of beams in such a manner that
their deflections can be separately controlled using a single
spherical reflector. There are provided a pair of parabolic
reflectors 8b and 8'b in symmetrical relationship with respect to
the axis 14 of the main spherical reflector 1, the focal point of
said paired parabolic reflectors being constituted by the curvature
center 5 of the main reflector 1. For these paired parabolic
reflectors 8b and 8'b there are provided, as illustrated, the
corresponding sub-reflectors 4b and 4'b, two groups of plane
reflectors 9b-9'b and 10b-10'b and conical horn reflectors 12b and
12'b. That is, there are used two primary radiator systems each
including from the conical horn reflector to the sub-reflector. The
arrangement of each primary radiator system and its optical
position with respect to the main spherical reflector 1 are the
same as in the embodiment of FIG. 2. Accordingly, when the axis of
the sub-reflector 4b is deflected from the central axial line 14b
and the plane reflectors 9b and 10b are moved in interlocking
relationship with said deflection by the same means as used in the
embodiment of FIG. 2, then radiated beams 17b can be deflected.
Similarly when the axis of the sub-reflector 4'b is deflected from
the central axial line 14'b and the plane reflectors 9'b and 10'b
are moved in interlocking relationship with said deflection, then
radiated beams 17'b can be deflected independently of the first
mentioned beams 17b. Though the embodiment of FIG. 13 includes two
primary radiator system the present invention is obviously not
limited to said number.
FIG. 14 represents still another embodiment of the present
invention wherein there is positioned a primary radiator system in
front of a main spherical reflector 1. Namely, outside of the
passage of electromagnetic waves radiated from the main reflector
1, is disposed a primary radiator system including a sub-reflector
4. Under this arrangement, it is possible to provide a space
satellite tracking antenna device capable of eliminating blocking
and radiating a plurality of electromagnetic waves in such a manner
that even when there are juxtaposed a plurality of primary radiator
systems like that illustrated in FIG. 14, there does not occur
mutual interference.
As mentioned above, the present invention can deflect radiated
beams through a specified range of angles without moving the main
spherical reflector simply by operating the movable constituent
units of the primary radiator system in interlocking relationship,
and further can deflect a plurality of electromagnetic waves
separately, without degrading the directional characteristics of
said waves or beams, so that the antenna device of the present
invention is particularly adapted for use in a ground station
tracking a stationary space satellite.
* * * * *