Information
-
Patent Grant
-
6239763
-
Patent Number
6,239,763
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Date Filed
Tuesday, June 29, 199925 years ago
-
Date Issued
Tuesday, May 29, 200123 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
- Swidler Berlin Shereff Friedman, LLP
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CPC
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US Classifications
Field of Search
US
- 343 781 P
- 343 781 CA
- 343 781 R
- 343 837
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International Classifications
-
Abstract
A configurable antenna includes a main reflector and at least two subreflectors. Each of the subreflectors is configurably disposed relative to the main reflector to provide an active subreflector for reflecting radiation between the main reflector and a point off of the main reflector in a desired beam pattern. Each subreflector typically has a different shape and may be moved into the active subreflector position to produce a desired beam pattern during operation of the antenna. The antenna further includes a horn disposed at a point off of the main reflector for feeding signals to the reflectors and for receiving signals from the reflectors. The configurable antenna is typically mounted on a satellite system which itself, or in response to instructions or commands from a ground station, reconfigures the antenna to provide the desired beam shape.
Description
FIELD OF THE INVENTION
The present invention relates generally to antennas and beam forming and more particularly to techniques for dynamically reconfiguring antenna contoured beams by switching between shaped-surface subreflectors.
BACKGROUND OF THE INVENTION
Antennas are designed to project beams of a certain shape for both transmitting and receiving radio waves. For example, geo-stationary satellite mounted antennas may be configured to project a beam that is roughly the shape of a geographic region, such as a state within the United States. Thus, the satellite antenna is configured to transmit radio waves to and receive radio waves from the geographic region on the earth's surface defined by the beam.
From time to time it may be desirable to change the shape of the beam that a given antenna transmits and receives in. The change may be necessitated by a change in the geographic distribution of demand for a communications service provided via the antenna, by a need to transfer the satellite to a different orbital location, or by a need to respond to an emergency. When the antenna is mounted on a satellite, there is no economically feasible way to retrieve and reconfigure the antenna. Therefore, it would be desirable to provide dynamically configurable antennas that are capable of being reconfigured to form beams of different shapes from a remote location.
There are at least two conventional techniques for reconfiguring the shape of a beam produced by an antenna. In the first technique, an array of horns is configured to transmit/receive via a reflector. In the case of transmission, for example, by varying the amplitude and phase excitation of each horn in the array of horns, the beam shape may be changed to a desired shape.
In the second technique a single or multiple horns are configured to transmit and receive via a reflector. The reflector is either shaped or unshaped. In its unshaped configuration, the reflector is a paraboloid. In its shaped configuration, the reflector may be shaped to reflect radio waves to produce the desired shape. To make the antenna configurable, the reflector is made deformable and includes motors or servos coupled to its non-reflective side. The motors or servos may be commanded to urge the reflector into different shapes thus producing a corresponding change in shape of the transmitted and received beams.
Each of these conventional techniques has disadvantages. In the case of the array of horns, the array is heavy which may add substantially to launch costs in the case of a satellite based antenna. The array of horns also takes up a substantial amount of space compared to other antenna configurations, particularly where 100 or more horns are required for the array. Available space on a satellite for mounting apparati is scarce, particularly as a goal of satellite design is miniaturization. Therefore, this conventional technique may not be practical for many if not most satellite communication applications.
In the case of using motors or servos to urge a reflector into different shapes to produce a corresponding change in beam shape, this technique is clumsy. Moreover, it may be expensive, inaccurate, heavy by comparison to other antenna configurations and prone to failure.
It would be desirable to provide a new technique for remotely reconfiguring an antenna to form beams of different shapes. It would further be desirable for the new technique to be inexpensive, light weight and take up correspondingly less space on a satellite than conventional techniques.
SUMMARY OF THE INVENTION
According to the present invention, a method and apparatus provide an antenna that is remotely configurable to change the shape of a beam associated with the antenna.
The configurable antenna includes a main reflector and at least two subreflectors. Each of the subreflectors is configurably disposed relative to the main reflector to provide an active subreflector for reflecting radiation between the main reflector and a point off of the main reflector in a desired beam pattern. Each subreflector typically has a different shape and may be moved into the active subreflector position to produce a desired beam pattern during operation of the antenna.
The antenna further includes a feed element such as a horn, helix, dipole, microstrip or a small array of similar feed elements disposed at a point off of the main reflector for feeding signals to the reflectors and for receiving signals from the reflectors. The configurable antenna is typically mounted on a satellite system which itself, or in response to instructions or commands from a ground station, reconfigures the antenna to provide the desired beam shape.
BRIEF DESCRIPTION OF THE FIGURES
The above described objects, features and advantages will be more fully understood with reference to the detailed description and appended figures, where:
FIG. 1
depicts a configurable antenna using an array of feed horns according to the prior art.
FIG. 2
depicts a configurable antenna using a deformable reflector according to the prior art.
FIG. 3
depicts an unconfigurable, dual-reflector antenna according to the prior art.
FIG. 4
depicts a configurable, dual-reflector antenna having multiple subreflectors movably disposed relative to the main reflector according to an embodiment of the present invention.
FIG. 5
depicts positioning of the active subreflector in a Gregorian configuration according to the present invention.
FIG. 6
depicts positioning of the active subreflector in a Cassegrain configuration according to the present invention.
FIG. 7
depicts an antenna configuration having multiple feed elements according to an embodiment of the present invention.
FIG. 8
depicts a functional view of an embodiment of a satellite system including the present invention.
FIG. 9
illustratively depicts a technique for mounting a configurable antenna onto a satellite according to an embodiment of the present invention.
FIG. 10
depicts an alternative mounting technique in which the satellite includes a recess for receiving the configurable antenna.
FIG. 11
depicts an embodiment of the configurable antenna as a single assembly according to the present invention.
DETAILED DESCRIPTION
FIG. 1
depicts an arrangement of an antenna
10
according to the prior art for generating a configurable beam. The antenna
10
includes a main reflector
12
, an array of horns
14
, a feed network
18
and a transponder
20
. The transponder
20
generates signals for transmission via the antenna
10
and also receives signals from the antenna
10
. The transponder is coupled to the feed network
18
. The feed network
18
in turn is coupled to an array of horns
14
which are generally arranged along a feed plane
16
. The horns
14
are waveguides that project signals received from the feed network
18
onto the main reflector
12
. The feed network
18
is configurable and may be configured to change the amplitude and phase excitation of individual horns
14
within the array of horns. By changing the amplitude and phase excitation of each horn
14
in delivering signals from the transponder
20
, the shape of a beam carrying the transmitted signals also is changed. The beam issuing forth from the array of horns
14
then reflects off of the main reflector
12
toward a target. The beam is thus projected at the target and may be changed by changing the amplitude and phase excitation of the feed network.
Although configurable, the antenna
10
has several disadvantages. Most notably, the array of feed horns
14
is heavy and takes up a substantial amount of space on the satellite as compared to other antenna configurations. This is particularly problematic where the array must include more than 50 to 100 horns
14
. A reconfigurable feed network is complex, expensive, and may have to include redundant elements to ensure reliable operation.
FIG. 2
depicts an alternate scheme for shaping beams issuing from an antenna
10
. According to this scheme, the main reflector
12
is deformable under urging by motors or servos (not shown). The deformation is, in theory, controlled to produce different desired beam shapes. The main reflector may be used with a single horn
14
and transponder
20
, without the need for an elaborate feed network to excite an array. This technique may be clumsy and inaccurate for several reasons. First, the surface deformation of the main reflector must be elastic (fully recoverable to initial state). Therefore, the range and rate of surface modification is severely limited. Second, a mesh material may have to be used, which restricts polarization and/or frequency of the signal. Third, the motors or servos require a sturdy mounting structure and a control network which may require a lot of space.
FIG. 3
depicts a fixed beam shape, dual reflector antenna
10
according to the prior art. The antenna
10
includes a main reflector, a subreflector
30
, a horn
14
and a transponder
20
. During a transmit operation, the transponder
20
transmits a signal via the horn
14
to the subreflector
30
. The subreflector reflects the signal from the horn to the main reflector where the signal emanates as a transmitted beam toward a target. During a receive operation, the main reflector
12
receives incident radiation from a field of view. Only incident radiation that is within a receive beam shape will then be reflected from the main reflector
12
, off of the subreflector
30
toward a communicating end of the horn
14
. The transponder in turn receives the signal from another communicating end of the horn
14
. The subreflector
30
is an ellipsoid for Gregorian optics and a hyperboloid for Cassegrain optics.
FIG. 4
depicts a configurable beam antenna according to the present invention. The antenna
100
includes a main reflector
102
, a plurality of subreflectors
104
and a feed element
110
. The main reflector
102
may be an unshaped parabolic mirror in which case it has the appearance of a dish in three dimensions. Alternatively, the main reflector may be a shaped mirror, such as a spherical, hyperbolic, ellipsoid or irregular shape where irregularities are introduced in order to provide a particular beam shape. The main reflector
102
has a reflective surface oriented toward a field of view and the subreflector. The inner surface of the main reflector
102
may be convex or concave.
The plurality of subreflectors
104
are movably disposed relative to the main reflector
102
. Each of the plurality of subreflectors
104
may have the same or a different shape in order to produce a different shaped beam. During use of the antenna, at least one of the plurality of subreflectors is an active subreflector
106
and therefore communicates radiation between the main reflector
102
and the feed element
110
. Each of the subreflectors
104
may have any convenient shape, including ellipsoid, hyperboloid, paraboloid or irregularly shaped where irregularities are chosen to create a desired beam shape.
In order to configure or re-configure the antenna
100
, the active subreflector
106
is moved relative to the main reflector so that it no longer communicates radiation between the main reflector
102
and the feed element
110
. Subsequently, a different subreflector
104
is moved relative to the main reflector
102
so that it becomes the active subreflector
106
that communicates radiation between the main reflector
102
and the feed element
110
. In a preferred embodiment of the invention each of the subreflectors
104
has a different shape that is chosen, along with the size, shape and distance from the main reflector
102
to produce different beam shapes.
Any technique for movably disposing the subreflectors
104
relative to the main reflector
102
is contemplated. For example, in one embodiment of the invention, three subreflectors
104
are mounted around a common axis of rotation
112
as shown in
FIG. 4. A
single-axis gimbal may be used as the common-axis of rotation
112
as shown. The gimbal may be driven by a motor coupled thereto which rotates the gimbal in order to change the active subreflector
106
. Alternatively, the common axis of rotation
112
may be a shaft of a motor to which the subreflectors
104
are coupled. The coupling may be direct or through a gearing arrangement. Many other techniques may be used. For example, one or more movable arms may be configured to move an appropriate one of a set of subreflectors
104
into the active subreflector
106
position. In this embodiment, one or more subreflectors may be rigidly attached to one or more arms. Alternatively, one or more arms may be configured to release and attach subreflectors in response to commands. In still another embodiment, a track having a movable portion such as a belt, strip or chain to which subreflectors
104
are attached may be used to move appropriate ones of the subreflectors
104
into the active subreflector
106
position.
In any of these embodiments, once the desired subreflector
104
is moved into the active subreflector
106
position, the active subreflector may be locked into position to ensure alignment stability. This may be done in any convenient manner including using a gimbal holding torque which is a well known technique. Alternatives may include spring loaded mechanisms or the resistance to rotation of the motor shaft and gears while in a stationary position.
In a preferred embodiment of the invention, positioning of the active subreflector
106
is done to so that one focus of the active subreflector
106
coincides with the focus of the main reflector
12
and so that the other focus of the active reflector
106
coincides with a communicating end of the feed element
110
. This is shown in
FIG. 5
for the case of Gregorian optics and in
FIG. 6
for the case of Cassegrain optics.
FIG. 7
depicts an alternate embodiment of the invention in which multiple feed elements
110
, or a single movable feed element
110
, are/is positioned relative to a plurality of configurable subreflectors
104
. Each of the plurality of positions for the feed element(s)
110
are chosen so that a communicating end of the desired feed element
110
is at the focus of an active subreflector
106
within the plurality of subreflectors
104
. This embodiment may be preferred in order to minimize the motion required to move each subreflector
104
into an active position relative to the main reflector
102
and each feed element
110
. The feed element
110
is typically a feed horn. However, the feed element
110
may also be a helix, dipole or microstrip or an array of horns, helices, dipoles or microstrips.
FIG. 8
depicts a functional view of an embodiment of a satellite system
200
incorporating the present invention. The satellite system
200
includes a command and control unit
202
coupled to a transponder
204
and a power system
206
and a telemetry unit
208
. The transponder unit
204
is in turn coupled to the configurable antenna
100
.
The power system
206
, which may include solar arrays, batteries and/or a nuclear power generator, generates, stores and distributes power to all of the units of the satellite. The telemetry unit
208
stabilizes and keeps the satellite
208
and its configurable antenna
210
properly aligned. Stabilization may be accomplished in a well known manner using spin stabilization, three axis stabilization or other techniques including magnetic torque rods.
The command and control unit
202
is essentially a computer and communications system which runs program instructions to carry out the mission of the satellite. The command and control unit
202
may receive and upload instructions to run or commands to execute from a ground station. For example, the command and control unit
202
may receive a command from a ground station to reconfigure the configurable antenna
100
to bring a different subreflector
104
into the active position. In response, the command and control unit
202
may command or control the motor
114
of the antenna
100
to move a desired one of the subreflectors
104
into the active position
106
. The result is a change in the shape of the beam transmitted to and received from the field of view of the antenna
100
. The motor
114
typically includes a motor control system, well known in the art, that includes a feed back loop with position, velocity, and/or acceleration sensors. The control system receives the commanded position and controls movement of the motor shaft to reach the desired position.
The transponder receives signals for transmission from the command and control unit
202
, amplifies the signals and outputs the signals to a communicating end of the feed element
110
for transmission via the reflectors
106
and
102
to the field of view of the antenna
100
in the desired beam pattern. The transponder
204
also may receive signals from the desired beam pattern emanating from the field of view and output those signals to the command and control unit
202
for signal processing or other applications as pursuant to the mission configuration of the satellite system
200
.
There are numerous ways of mounting the antenna
100
for use in communications. Any convenient mounting technique may be used. For example the antenna
100
may be a single assembly that is fixedly or configurably mounted to a structure for use in communications. Alternatively, the antenna
100
may be mounted as separate parts to a structure for use in communications, where each of the separate parts may be movably disposed relative to each other or the structure. The structure itself may be disposed on land or may be part of a vehicle such as a satellite, airplane or automobile.
FIG. 9
illustratively depicts a technique for mounting a configurable antenna
100
onto a satellite
120
. The satellite
120
has a deck
121
that, during orbit, is oriented generally facing a target, such as the earth. On the deck
121
, individual parts of the configurable antenna
100
are mounted. Referring to
FIG. 9
, the main reflector
102
is mounted to the deck
121
via a support structure
122
. The support structure
122
may mount the reflector
102
in a fixed position relative to the deck
121
when the support structure is a rigid member. Alternatively, the support structure may mount the reflector
102
in a movable position relative to the deck
121
, such as when the support structure is a single or multiple axis gimbal.
The motor
114
may be mounted to the deck
121
and may include a rotating shaft
115
coupled to a bar
124
at ends of which subreflectors
104
are disposed. The motor
114
may be part of a multiple axis gimbal in which case the shaft
115
may also be movable relative to the deck
121
off of the axis of rotation of the shaft
115
.
The feed element
110
is mounted to the deck
121
by the arm
126
. The arm may be fixed or movably disposed relative to the deck
121
. Each of the parts that participate in the mounting, such as the motor
114
, shaft
115
, bar
124
, support structure
122
and arm
126
are positioned on the deck
121
and relative to each other and to the subreflectors
104
, main reflector
102
and the feed element
110
to preserve the geometry of the antenna
100
as described with reference to
FIGS. 4-7
. Moreover, each of the parts may be secured to each other or the deck
121
(or other part of the satellite
120
) in any convenient way, including by welding, bolting, riveting, using adhesives or by being integrally formed.
FIG. 10
depicts an alternative mounting technique in which the satellite
120
includes a recess
150
. In the recess
150
, all or parts of the antenna
100
may be mounted in any convenient manner. The recess
150
permits the antenna
100
to be mounted in a way that minimizes the volume of the satellite
120
to facilitate launching the satellite
120
on a launch vehicle. When the antenna
100
is mounted in separate parts, the main reflector
102
may be movably mounted, for example, to a face of the satellite
120
as shown such that it may be unfurled for use as depicted in FIG.
10
. The mounting of the main reflector to permit unfurling may be accomplished in any convenient manner, including using a gimbal or hinge.
FIG. 11
depicts an embodiment of the antenna
100
as a single assembly. In this embodiment, the main reflector
102
, the motor
114
and the feed element
110
are each mounted to an arm
155
. In this arrangement the arm
155
and attachments thereto may be configured in any desired manner consistent with the geometry of the antenna
100
as described with reference to
FIGS. 4-7
.
Although specific embodiments of the present invention have been disclosed, it will be understood by those having ordinary skill in the art that changes may be made to those embodiments without departing from the spirit and scope of the invention. For example, while embodiments have been described in which the subreflectors are moved and the main reflector remains fixed, the main reflector may be moved, instead or in addition to the movement of the subreflectors, to bring different subreflectors into the active position. The language “moving (configuring or re-configuring) the subreflectors relative to the main reflector . . . ” is intended to encompass these variations.
Claims
- 1. A configurable antenna, comprising:a main reflector; a feed element; and at least two subreflectors, each of the subreflectors being configurably disposed relative to the main reflector to provide a selected active subreflector, among the at least two subreflectors, for reflecting radiation between the main reflector and the feed element in a desired beam; wherein the selected active subreflector changes based on a configuration of the antenna.
- 2. The antenna according to claim 1, wherein the feed element is a horn.
- 3. The antenna according to claim 1, wherein the feed element is a helix.
- 4. The antenna according to claim 1, wherein each of the subreflectors has a different shape.
- 5. The antenna according to claim 1, further comprising:a single axis gimbal for mounting the subreflectors to a satellite; and a motor, coupled to the gimbal and a satellite, for rotating the subreflectors about the single axis to change the configuration of the antenna.
- 6. The antenna according to claim 1, wherein the main reflector is shaped to provide a desired beam.
- 7. The antenna according to claim 1, further comprising a motor rigidly disposed relative to the main reflector, the motor including a rotatable shaft coupled to the at least two subreflectors, the motor rotating the shaft to urge the at least two subreflectors into desired configurations.
- 8. A method of providing a configurable beam antenna, comprising the steps of:providing a main reflector; providing a feed element; providing at least two subreflectors, each of the subreflectors being configurably disposed relative to the main reflector to provide a selected active subreflector, among the at least two subreflectors, for reflecting radiation between the main reflector and the feed element; wherein the selected active subreflector changes based on a configuration of the antenna.
- 9. The method according to claim 8, wherein the feed element is a horn.
- 10. The method according to claim 8, wherein the feed element is a helix.
- 11. The method according to claim 8, further comprising the step of:mounting the main reflector to a satellite system.
- 12. A configurable, satellite-based communications system comprising:a main reflector disposed on a satellite; a feed element; and at least two subreflectors, each of the subreflectors being configurably disposed relative to the main reflector to provide a selected active subreflector, among the at least two subreflectors, for reflecting radiation between the main reflector and the feed element; wherein the selected active subreflector changes based on a configuration of the antenna.
- 13. The configurable communications system according to claim 12, further comprising:a transponder for transmitting signals to and receiving signals from a second communicating end of the feed element.
- 14. The configurable communications system according to claim 12, wherein the feed element is a horn.
- 15. The configurable communications system according to claim 12, wherein the feed element is a helix.
- 16. The configurable communications system according to claim 12, further comprising a motor rigidly disposed relative to the main reflector, the motor including a rotatable shaft coupled to the at least two subreflectors, the motor rotating the shaft to urge the at least two subreflectors into desired configurations.
- 17. The configurable communications system according to claim 12, further comprising:a transponder for transmitting signals to and receiving signals from a second communicating end of the feed element; a motor rigidly disposed relative to the main reflector, the motor including a rotatable shaft coupled to the at least two subreflectors, the motor rotating the shaft to urge the at least two subreflectors into desired configurations; and a command and control unit, coupled to the transponder and the motor, for commanding the motor to change the desired configurations and for controlling the transponder.
US Referenced Citations (5)