Note: Descriptions are shown in the official language in which they were submitted.
CA 02921047 2016-02-16
DEPLOYABLE REFLECTARRAY ANTENNA
STRUCTURE
FIELD OF THE INVENTION
The invention relates to a deployable antenna structure and, more
specifically, to a deployable reflectarray antenna structure.
BACKGROUND OF THE INVENTION
In applications requiring a high-gain antenna, there are at least three
types of antennas that are typically employed, namely, a parabolic antenna,
phased-
array antenna, and a reflectarray antenna. The basic parabolic antenna
includes a
parabolic shaped reflector and a feed antenna located at the focus of the
paraboloid
and directed towards the reflector. The phased-array antenna includes multiple
antennas with a feed network that provides a common signal to each of the
antennas
but with the relative phase of the common signal being fed to each of the
antennas
established such that the collective radiation pattern produced by the array
of
antennas is reinforced in one direction and suppressed in other directions,
i.e., the
beam is highly directional. In many applications, the phased-array antenna is
preferred to the parabolic antenna because a phased-array antenna can be
realized
with a lower height profile relative to the parabolic antenna. However, the
phased-
array antenna typically requires a complicated and/or expensive feed network
and
amplifier structures. The basic reflectarray antenna includes a reflectarray
that is flat
or somewhat curved and a feed antenna directed towards the reflectarray. The
reflectarray includes an array of radiating elements that each receive a
signal from the
feed antenna and reradiate the signal. Each of the radiating elements has a
phase
delay such that the collective reradiated signal produced by the array of
radiating
elements is in a desired direction. Importantly, the radiating elements are
fed by the
feed antenna. As such, relative to the phased-arrayed antenna, the
reflectarray avoids
the need for a feed network to provide a signal to each of the radiating
elements.
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An application that frequently requires a high-gain antenna is a space-
related application in which the antenna is associated with a spacecraft,
e.g., a
communication satellite. Such space-related applications typically
impose an
additional requirement of deployability on the design of a high-gain antenna,
i.e., the
antenna needs to be able to transition from a stowed/undeployed state in which
the
antenna is inoperable or marginally operable to unstowed/deployed state in
which the
antenna is operable. As such, the high-gain antenna in these applications is
coupled
with a deployment mechanism that is used to transition the antenna from the
stowed/undeployed state to the unstowed/deployed state. Characteristic of many
space-related applications for such antennas is that the antenna and
deployment
mechanism occupy a small volume in the undeployed state relative to the volume
occupied by the antenna and deployment mechanism in the deployed state.
One approach for realizing a deployable high-gain antenna suitable for
use on a spacecraft is a parabolic antenna structure that includes a wire mesh
reflector, a feed antenna, and a deployment mechanism. The deployment
mechanism
operates to transition: (a) the wire mesh reflector from a stowed state in
which the
reflector is folded to an unstowed state in which the reflector is supported
in a
paraboloid-like shape by a frame associated with the deployment mechanism and
(b)
the wire mesh reflector and the feed antenna from an inoperable stowed state
in which
the wire mesh reflector and feed antenna are not operably positioned relative
to one
another to an unstowed state in which the wire mesh reflector and feed antenna
are
operatively positioned relative to one another. Characteristic of such
deployable
parabolic antenna structures is a high part count and the need for a
relatively large
volume to accommodate the stowed wire mesh reflector, feed antenna, and
deployment mechanism.
A second approach for realizing a deployable high-gain antenna
suitable for use on a spacecraft is a reflectarray antenna structure that
includes a two-
layer reflectarray membrane, a feed antenna, and an inflatable deployment
mechanism. The inflatable deployment mechanism operates to transition: (a) the
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reflectarray membrane from a stowed state in which the membrane is folded to
an
unstowed state in which the inflated deployment mechanism forms a frame that
is
used in tensioning the reflectarray membrane into a flat shape, similar to
trampoline
and (b) the reflectarray membrane and the feed antenna from an inoperable
stowed
state in which the reflectarray membrane and feed antenna are not operably
positioned with respect to one another to an unstowed state in which the
reflectarray
membrane and the feed antenna are operably positioned relative to one another.
Characteristic of such a deployable reflectarray are difficulties in
understanding the
deployment kinematics and reliability challenges, particularly in space-based
applications.
SUMMARY OF THE INVENTION
A deployable reflectarray antenna structure is provided that is suitable
for use in applications in which elements that are used to form the
reflectarray
antenna structure need to transition from an undeployed state in which the
elements
conform to a particular volume in which the elements are not situated so as to
function in a reflectarray antenna structure to a deployed state in which the
elements
are situated so as to function in a reflectarray antenna structure. One such
application
for a deployable reflectarray antenna structure is as part of a space vehicle,
(e.g., a
communication satellite) in which elements of the structure typically need to
conform
to a compact or dimensionally constrained volume for at least a portion of the
launch
of the space vehicle and then be deployed from the compact or dimensionally
constrained space so as to form a reflectarray antenna structure that
typically occupies
a considerably greater volume.
In one embodiment, the deployable reflectarray antenna structure
includes a pair of electrical elements and a deployment mechanism for
transitioning
the pair of electrical elements from an undeployed state in which the
electrical
elements are not positioned relative to one another to function in a
reflectarray
antenna towards a deployed state in which the electrical elements are
positioned
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relative to one another to function in a reflectarray antenna. To facilitate
the
transition of the electrical elements from the undeployed state towards the
deployed
state, a tape is employed in which one end of the tape is operatively
connected to one
of the electrical elements. In operation, the tape transitions from undeployed
state in
which the ends of the tape are relatively close to one another to a deployed
state in
which the ends of the tape are farther from one another than in the undeployed
state.
In performing this transition, the end of the tape that is operatively
connected to one
of the pair of electrical elements facilitates the positioning of the
electrical element
for use in a reflectarray antenna. To control the transition of the tape
between the
undeployed and deployed states, the deployment mechanism employs a damper. In
a
particular embodiment, one of the pair of electrical elements and the
deployment
mechanism cooperate to establish a reflectarray in a deployed
Cassegrain/Gregorian-
type reflectarray antenna structure. The other of the pair of electrical
elements and
the deployment mechanism cooperate to establish a subreflector in the deployed
Cassegrain/Gregorian-type reflectarray antenna structure.
In another embodiment, the deployable reflectarray antenna structure
includes a pair of electrical elements and a deployment mechanism that employs
multiple tapes in transitioning the two electrical elements from an undeployed
state
towards a deployed state. In the undeployed state, neither of the two
electrical
elements functions as an element of a reflectarray antenna system. In the
deployed
state, the two electrical elements and the deployment mechanism cooperate to
form
two elements of a reflectarray antenna structure. Further, the deployment
mechanism
functions in the deployed state to establish the necessary positional
relationships of
the two elements for functioning in a reflectarray antenna structure.
In one embodiment, multiple tapes in the deployed state cooperate
with one of the pair of electrical elements to form an element of a
reflectarray antenna
structure. In this regard, the multiple deployed tapes define a solid shape.
In a
particular embodiment, the first ends of four tapes define one base of a
frustum of a
pyramid-like structure, the second ends of the four tapes define the other
base of the
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frustum of a pyramid-like structure, and the substantial portions of the four
tapes that
are linearly disposed between the first and second ends define the edges of
the
frustum of a pyramid-like structure.
In another embodiment, multiple tapes in the deployed state form
support structures. In a particular embodiment, the first ends of three tapes
define one
base of a frustum of a tetrahedron-like structure (i.e., a particular type of
pyramid),
the second ends of the three tapes define the other base of the frustum of a
tetrahedron-like structure, and the substantial portions of the three tapes
that are
linearly disposed between the first and second ends define the edges of the
frustum of
the tetrahedron-like structure. In yet another embodiment, four tapes in the
deployed
state define a portion of a queen post like truss. In this regard, two of the
deployed
tapes form a substantial portion of the tie beam of the queen post like truss
and the
other two of the deployed tapes form the queen posts of the queen post like
truss.
Yet another embodiment of the deployable reflectarray antenna
structure includes a pair of flexible electrical elements, a feed antenna, and
a
deployment mechanism that includes a deployable frame structure. The
deployable
reflectarray antenna structure also includes a canister that defines an
enclosed space
for storing the flexible electrical elements, feed antenna, and deployment
mechanism,
when each such component of the structure is in an undeployed state. The
canister
includes a door or hatch that, when opened, allows the flexible electrical
elements,
feed antenna, and deployment mechanism to operate so that the deployable frame
structure and pair of flexible electrical elements cooperate to produce a
reflectarray
and a subreflector of a Cassegrain/Gregorian-type reflectarray antenna with
the
reflectarray and subreflector appropriately positioned relative to the feed
antenna for
a Cassegrain/Gregorian-type reflectarray antenna. When the
pair of flexible
elements, feed antenna, and deployment mechanism are undeployed and situated
within the canister, the deployable frame mechanism is located between the
pair of
flexible electrical elements.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates an embodiment of the deployable reflectarray
antenna structure in an undeployed state;
FIG. 2 is a cross-sectional view of the deployable reflectarray antenna
structure shown in FIG. 1 in the undeployed state;
FIG. 3 is an exploded view of the deployable reflectarray antenna
structure shown in FIG.1 in the undeployed state;
FIGS. 4A and 4B respectively are a perspective view and side view of
the reflectarray of the deployable reflectarray antenna shown in FIG. 1;
FIG. 5 is a perspective view of the subreflector of the deployable
reflectarray antenna shown in FIG. 1;
FIG. 6 is a perspective view of the primary tape dispenser for
transitioning a flexible membrane from an undeployed state towards a deployed
state
in which the flexible membrane is configured for use as the reflectarray
illustrated in
Figs. 4A and 4B;
FIG. 7 is a perspective view of the motor and transmission system
associated with the primary tape dispenser shown in FIG. 6;
FIG. 8 is a perspective view of the motor and drive train associated
with the primary tape dispenser shown in FIGS. 6 and 7;
FIG. 9 is a perspective view of the secondary tape dispenser for
transitioning a flexible membrane from an undeployed state towards a deployed
state
in which the flexible membrane is configured for use as the subreflector shown
in
FIG. 5;
FIG. 10 is a perspective view of the motor and transmission system
associated with the secondary tape dispenser shown in FIG. 9;
FIG. 11 is a perspective view of the motor and drive train associated
with the secondary tape dispenser shown in FIGS. 9 and 10;
FIG. 12 is a perspective view of a tape cartridge or dispenser used in
the secondary tape dispenser shown in FIGS. 9-11;
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FIG. 13 is an exploded view of the tape dispenser shown in FIG. 12;
FIG. 14 is a cross-sectional view of the tape dispenser shown in FIG.
12;
FIG. 15 illustrates the tape associated with the tape dispenser shown in
FIG.12 in its deployed state;
FIG. 16 illustrates the connection structure used to establish a
connection between a membrane, a pair of lanyards, and a tape;
FIGS. 17A-17C illustrate the method of folding the first flexible
electrical element to place in the element in an undeployed state; and
FIGS. 18A-18D illustrate the transition of the deployable reflectarray
antenna structure shown in the foregoing figures from the undeployed state to
the
deployed state.
DETAILED DESCRIPTION
With reference to Figs. 1-5 and 18A-18D, an embodiment of a
deployable reflectarray antenna structure 20 (hereinafter referred to as "the
deployable reflectarray 20") is described. The deployable reflectarray 20
conforms to
the CubeSat design specification. More specifically, the deployable
reflectarray 20
conforms to a 1U CubeSat design specification, which requires the deployable
reflectarray 20 be embodied within a cube that is 10 cm on a side and has a
mass of
no more than 1.33 kg. Although the deployable reflectarray 20 conforms to the
CubeSat 1U design specification, it should be appreciated that adaptation to
other
form factors and mass requirements is feasible.
The deployable reflectarray 20 includes a canister 22, a feed antenna
24, a first flexible electrical element 26, a second flexible electrical
element 28, and a
deployment mechanism 30. Generally, the canister 22 stores the feed antenna
24,
first and second flexible electrical elements 26, 28 and the deployment
mechanism 30
in an undeployed state and provides a base for supporting the feed antenna 24,
first
and second flexible elements 26, 28 and the deployment mechanism 30 in the
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deployed state. In the undeployed state, the feed antenna 24 is disposed
within a
particular volume within the canister 22. Additionally, the first and second
flexible
electrical elements 26, 28 are folded so as to conform to particular volumes
within the
canister 22. In the deployed state, the feed antenna 24 and the first and
second
flexible electrical elements 26, 28 are supported in a center-fed
Cassegrain/Gregorian-style reflectarray antenna configuration. More
specifically, the
deployment mechanism 30 respectively supports the first flexible electrical
element
26 so as to form a primary reflectarray 40 and the second flexible electrical
element
28 so as to form a secondary reflectarray 42 (reflectarray subreflector) in
the
configuration. Further, the deployment mechanism 30 positions the feed antenna
24,
primary reflectarray 40, and secondary reflectarray 42 relative to one another
to
realize the noted configuration. In this regard, the feed antenna 24, primary
reflectarray 40, and secondary reflectarray 42 are disposed along a center-
line 44.
With reference to Figs. 1 and 2, the canister 22 generally is comprised
of a tubular side surface 50, a bottom surface 52 that extends across one end
of the
tubular side surface 50, and door structure 54 that extends across the other
end of the
tubular side surface 50. The tubular side surface 50 includes four planar side
surfaces
56A-56D and four inside corner surfaces 58A-58D that each engages the lateral
edges
of two adjacent planar side surfaces.
Each of the inside corner surfaces
accommodates a square rod (not shown) that is part of the CubeSat design
specification. The bottom surface 52 is planar and defines at least one hole
or
passageway 60 that accommodates a coaxial cable (not shown) which allows
electrical signals to be communicated to and/or from the feed antenna 24. The
door
structure 54 includes a first hinged door 62 that is spring-biased towards an
open
position and a second hinged door 64 that is also spring-biased towards an
open
position. Associated with the door structure 54 is a latch mechanism 66 that
holds the
first and second hinged doors 62, 64 is a closed/undeployed state and can be
released
so as to allow the first and second hinged doors 62, 64 to each rotate towards
an open
or deployed position. In the illustrated embodiment, the latch mechanism 66
includes
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a meltable pin 68 that engages the second hinged door 64 to hold the doors in
the
closed/undeployed state. Associated with the canister 22 is a control board 70
that is
used to apply an electrical current to the meltable pin 68 via wires (not
shown) that
causes the pin to melt so that the first and second hinged doors 62, 64 can
each rotate
towards the open/deployed position.
The feed antenna 24 is an antenna that is capable of feeding the
secondary reflectarray 42 when the deployable reflectarray antenna structure
20 is in
the deployed state. In the illustrated embodiment, the feed antenna 24 is a
low-profile
phased array antenna. In other embodiments, a horn antenna is employed for the
feed
antenna.
With reference to Figs. 4A and 4B, the first flexible electrical element
26 is comprised of (a) a first flexible membrane 80 that supports an array of
reflectarray elements and (b) a second flexible membrane 82 that serves as a
ground
plane in the deployed state. A compressible and flexible dielectric structure
is located
between the first and second flexible membranes and operates to maintain a
desired
spacing between the first and second flexible membranes when the first
flexible
electrical element 26 is deployed as the primary reflectarray 40. Generally,
the first
flexible electrical element 26 has an outer edge 86 that defines a
substantially square
shape with catenary-shaped edges when the element is in the deployed state.
The
flexible element 26 also has an inner edge 88 that defines a hole which
accommodates
a portion of the deployment mechanism 30. The flexible characteristics of the
first
and second flexible membranes 80, 82 and the compressible and flexible nature
of the
dielectric structure allow the first flexible electrical element 26 to be
folded so as to
fit within a specified volume within the canister 22 when the element is in
the
undeployed state. When the first flexible electrical element 26 is in the
deployed
state, i.e., forming the primary reflectarray 40, the first flexible
electrical element 26
generally defines a frustum of a pyramid in which the outer edge 86 defines a
substantially square base of a pyramid-like structure and the inner edge
defines a
flattened apex of the pyramid-like structure. In other embodiments, the first
flexible
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electrical element in the deployed state is in the form of: a substantially
flat square. It
should be appreciated that the first flexible electrical element is not
limited to having
an outer edge that takes on a square shape when the element is in the deployed
state.
For example, other polygon shapes (e.g., triangles), curved shapes (e.g.,
circles), and
shapes comprised of curved and straight sections are feasible. In the case of
the
deployable reflectarray 20, the square characteristic of the outer edge 86 of
the first
flexible electrical element 26 substantially conforms to the square/cubic
nature of the
canister 22. Other applications may more naturally lend themselves to a first
flexible
electrical element having a different deployed shape. For instance, a
cylindrical
volume for storing a first flexible electrical element may suggest an element
with an
outer edge that is circular in the deployed state.
With reference to Fig. 5, the second flexible electrical element 28 is
comprised of (a) a first flexible membrane 90 that supports an array of
reflectarray
elements and (b) a second flexible membrane 92 that serves as a ground plane
in the
deployed state. A compressible and flexible dielectric structure is located
between
the first and second flexible membranes and operates to maintain a desired
spacing
between the first and second flexible membranes when the second flexible
electrical
element 28 is deployed as the secondary reflectarray 42. Generally, the second
flexible electrical element 28 has an outer edge 96 that defines a
substantially square
shape with catenary-shaped edges when the element is in the deployed state.
The
flexible element 28 also has an inner edge 98 that defines a hole. The
flexible
characteristics of the first and second flexible membranes 90, 92 and the
compressible
and flexible nature of the dielectric structure allow the second flexible
electrical
element 28 to be folded so as to fit within a specified volume of the canister
22 when
the element is in the undeployed state. When the second flexible electrical
element
28 is in the deployed state, i.e., forming the secondary reflectarray 42, the
second
flexible electrical element 28 is generally planar and the outer edge 96
generally
defines a square. It should be appreciated that the second flexible electrical
element
is not limited to having an outer edge that takes on a square shape when the
element
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is in the deployed state. For example, other polygon shapes (e.g., triangles),
curved
shapes (e.g., circles), and shapes comprised of curved and straight sections
are
feasible. Additionally, in other embodiments, the second flexible electrical
element
can be a reflector or polarizer, as opposed to a reflectarray subreflector.
With reference to Figs. 2 and 3, the deployment mechanism 30
operates to transition the deployable reflectarray 20 between an undeployed
state and
a deployed state. In the undeployed state, the feed antenna 24, first flexible
electrical
element 26, second flexible electrical element 28, and the deployment
mechanism 30
are disposed within the enclosed space defined by the canister 22 when the
first and
second hinged doors 62, 64 are closed. In the deployed state, the first and
second
flexible electrical elements 26, 28 are supported so as to respectively form
the
primary and secondary reflectarrays 40, 42 in a center-fed
Cassegrain/Gregorian-style
reflectarray antenna. Further, the feed antenna 24, primary reflectarray 40,
and
secondary reflectarray 42 are located with respect to one another so as to
implement a
center-fed Cassegrain/Gregorian-style reflectarray antenna.
The deployment mechanism 30 transitions the deployable reflectarray
between the undeployed and deployed states in two phases. In the first phase,
the
first and second flexible electrical elements 26, 28, which are in folded in
the
undeployed state, are positioned so that the elements can be unfolded and
deployed so
20 as to establish the primary and secondary reflectarrays 40, 42 and the
necessary
positional relationships with one another and the feed antenna 24 to establish
the
center-fed Cassegrain/Gregorian-style reflectarray antenna.
The second phase
involves the deployment of the first and second electrical elements 26, 28 so
as to
establish the primary and secondary reflectarrays 40, 42 and the positioning
of the
reflectarrays relative to the feed antenna 24 to establish the reflectarray
antenna.
Generally, the deployment mechanism 30 includes a guide tube
structure 110, a spring 112, a limit lanyard system 114, a primary housing
116, a base
plate 118, a tape dispenser 120, and a secondary housing 122.
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The guide tube structure 110 serves a number of purposes. To
elaborate, the guide tube structure 110 directs the displacement of the
primary
housing 116 with the undeployed first flexible electrical element 26 supported
by the
housing, the base plate 118, the tape dispenser 120, the feed antenna 24, the
secondary housing 122 with the undeployed second flexible electrical element
28
during the first phase of the transition of the deployable reflectarray 20
between the
undeployed and deployed states. The guide tube structure 110 also operates so
as to
prevent the base plate 118, tape dispenser 120, feed antenna 24, and secondary
housing 122 from rotating relative to the canister 122 during the transition
and
thereafter. Additionally, the guide tube structure 110 provides an axle about
which
the primary housing 116 can rotate during the second phase of the transition.
The
guide tube structure 110 also defines a portion of the passageway 60 that
accommodates the coaxial cable or other signal transmission structure that is
capable
of providing electrical signals to and/or from the feed antenna 24.
The guide tube structure 110 includes a ridged cylindrical guide tube
130 with a first end 132 fixedly attached to the bottom surface 52 of the
canister 22
and a free end 134. Additionally, the ridged cylindrical guide tube 130
defines a
longitudinally extending ridge 136.
The guide tube structure also includes a slotted cylindrical guide tube
140 with a first end 142 fixedly attached to the base plate 118, a free end
144, and a
slot 146 that is dimensioned to engage the ridge 136 associated with ridged
cylindrical guide tube 130. The inner diameter of the slotted guide tube 140
(excluding the ridge 146) is slightly greater than the outer diameter of the
ridged
cylindrical guide tube 130. As such, the slotted guide tube 140 is capable of
sliding
over the ridged guide tube 130 when the tubes are oriented so that the slot
146
engages the ridge 136. In the first phase of the transition between the
undeployed and
deployed states, the slotted guide tube 140 can be extended away from the
ridged
guide tube 130 to direct the primary housing 116 and other elements outside of
the
canister 22. The "keying" of the slot 146 and the ridge 136 prevents rotation
of the
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base plate 118 and other elements supported by the base plate during the
transition
and thereafter.
The spring 112 provides the energy for moving the primary housing
116 with the undeployed first flexible electrical element 26 supported by the
primary
housing, the base plate 118, the tape dispenser 120, the feed antenna 24, the
second
housing 122 with the undeployed second flexible electrical element 28 during
the first
phase of the transition of the deployable reflectarray 20 between the
undeployed and
deployed states. The spring 112 extends between the interior side of the
bottom
surface 52 of the canister and the primary housing 116. When the deployable
reflectarray 20 is in the undeployed state with the first and second doors 62,
64 of the
canister 22 closed, the spring 112 is compressed. After the first and second
doors 62,
64 are opened, the potential energy stored in the spring 112 is released and a
force is
applied to the primary housing 116 with the undeployed first flexible
electrical
element 26 supported by the housing, the base plate 118, the tape dispenser
120, the
feed antenna 24, the second housing 122 with the undeployed second flexible
electrical element 28 as directed by the guide tube structure 110 so that
these
elements are positioned for the second phase of the transition between the
undeployed
and deployed states. In the illustrated embodiment, the spring 112 provides
sufficient
energy so that the primary housing 116 and the first flexible electrical
element 26 and
the secondary housing 122 and the second flexible electrical element 28 are
sufficiently exposed for the second phase of the transition between the
undeployed
and deployed state. In this regard, the spring 112 provides sufficient energy
to
position the bottom of the primary housing 116 at or slightly above the edge
of the
canister 22 that is exposed following the opening of the first and second
doors 62, 64.
The limit lanyard system 114 operates to limit the extent to which the
spring 112 moves the primary housing 116 with the undeployed first flexible
electrical element 26 supported by the housing, the base plate 118, the tape
dispenser
120, the feed antenna 24, the second housing 122 with the undeployed second
flexible
electrical element 28 along the guide tube structure 110 during the first
phase of the
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transition between the undeployed and deployed states. To elaborate, the
spring 112
is designed to provide sufficient energy to move the noted elements to a
desired
position for the second phase of the transition. To ensure that the elements
reach the
desired position, the spring 112 is designed so as to be capable of providing
more
energy than is needed to position the elements at the desired position. As
such, the
spring 112 is potentially capable of moving the elements beyond the desired
position.
The limit lanyard system 114 prevents the spring 112 from moving the elements
beyond the desired position. The limit lanyard system includes lanyards 150A-
150D,
each with one end connected to the bottom surface 52 of the canister 22 and
the other
end connect to the base plate 118. The length of each of the lanyards 150A-
150D is
chosen so that when the lanyard is fully extended due to the force being
provided by
the spring 112, the elements are at the desired position for the second phase
of the
transition.
The primary housing 116 serves to define, in combination with a
portion of the canister 22, the space within which the first flexible
electrical element
26 resides when in the undeployed state. The primary housing 116 also operates
so as
to rotate about the slotted cylindrical guide tube 140 during the second phase
of the
transition of the first flexible electrical element 26 between the undeployed
and
deployed states. The need for the primary housing 116 and the first flexible
electrical
element 26 to rotate during the second phase of the transition is necessitated
by the
manner in which the first flexible electrical element 26 is folded when in the
undeployed state. The primary housing 116 also serves to provide a portion of
the
forces that are used to shape the first flexible electrical element 26 in the
manner
needed to realize the primary reflectarray 40.
The primary housing 116 includes a reel-like structure 160 that
includes a lower wall 162, an upper wall 164 that is substantially parallel to
the lower
wall 162, and a hollow cylindrical core 166 that extends between the lower
wall 162
and the upper wall 164. The upper wall 164 has an outer edge with four
scalloped
sections 168A-168D that are portions of channels that allow mechanical
connections
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to be established between the tapes associated with the tape dispenser 120 and
the
first flexible electrical element 26 and lanyards that extend between the
first and
second electrical elements 26, 28. The hollow cylindrical core 166 has an
inner
diameter sufficient to receive the slotted cylindrical guide tube 140. The
hollow
cylindrical core 166 also defines upper and lower bearing seats 170A, 170B
that
respectively support roller bearings 172A, 172B. The bearings 172A, 172B
extend
between the hollow cylindrical core 166 and the slotted cylindrical guide tube
140
and facilitate the rotation of the housing 116 about slotted cylindrical guide
tube 140
when the first flexible electrical element 26 is transitioned from the
deployed state
during the second phase of the transition. Clearance between the bearing 172A
and
the base plate 118 prevents the base plate 118 from inhibiting rotation of the
primary
housing 116. Also associated with the primary housing 116 are a series of
tapped
holes that are respectively engaged by screws 176A-176D that pass through
holes in
the first flexible electrical element 26 and are used to connect the primary
housing
116 to the first flexible electrical element 26.
The base plate 118 serves as a support for the tape dispenser 120, feed
antenna 24, secondary housing 122, and second flexible electrical element 28.
The
base plate 118 has an outer edge with four scalloped sections 180A-180D that
correspond with the four scalloped sections 168A-168D to provide pathways for
mechanical connections to be established between the tapes associated with the
tape
dispenser 120 and the first flexible electrical element 26 and lanyards that
extend
between the first and second electrical elements 26, 28. The base plate 118
also has
an inner edge that defines a hole 182 that forms a portion of the pathway that
accommodates a coaxial cable used to send electrical signals to and/or from
the feed
antenna 24.
The tape dispenser 120 provides a plurality of tapes (frequently
referred to as carpenter tapes) that are used to: (a) deploy the first
flexible electrical
element 26 so as to establish the primary reflectarray 40, (b) deploy the
second
flexible electrical element 28 so as to establish the secondary reflectarray
42, and (c)
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position the primary and secondary reflectarrays 40, 42 relative to one
another and to
the feed antenna 24 in a center-fed Cassegrain/Gregorian-style reflectarray
antenna
configuration.
The tape dispenser 120 is comprised of a primary tape dispenser 190
that is used to dispense tapes that are used to deploy the first flexible
electrical
element 26 and a secondary tape dispenser 192 that is used to dispense tapes
that are
used to deploy the second flexible electrical element 28.
With reference to Figs. 6-8, the primary tape dispenser 190 operates to
dispense four tapes that each engages the first flexible electrical element 26
at a point
adjacent to one of the corners of the outer edge 86 of the element. The four
tapes,
when dispensed or deployed, cooperate with the screws 176A-176D that each
engage
the element at a point adjacent to the inner edge 88 to hold the flexible
electrical
element 26 in the pyramid-like shape of the primary reflectarray 40.
The primary tape dispenser 190 includes: (a) four individual tape
dispensers 200A-200D that respectively have tape axles 202A-202D that are each
adapted to support a roll of tape with one end of the tape operatively
connected to the
axle and the other end operatively connected to the first flexible electrical
element 26,
(b) an electric motor 204 for providing the force needed to drive the axles
202A-202D
and thereby dispense the tapes from the dispensers, and (c) a transmission
system 206
for transmitting force from the motor 204 to each of the axles 202A-202D to
dispense
the tapes and to dispense the tapes at substantially the same time and at
substantially
the same rate.
The transmission system 206 includes a motor gear 210 that is
connected to the axle of the electric motor 204, a gearhead 212 with a first
gearhead
gear 214 that engages the motor gear 210 and a second gearhead gear 216 that
the
gearhead 212 causes to rotate at multiple times the rate at which first
gearhead gear
214 is caused to rotate by the electric motor 204, a drive train 218 that is
comprised of
a number of gears that transfer the force produced by the second gearhead gear
216 to
tape axle 202A, and a miter gear system that transfers the rotational force
imparted to
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tape axle 202A to axles 202B-202D. The miter gear system includes a first pair
of
miter gears 222A, 222B associated with the axle 202A; a second pair of miter
gears
224A, 224B associated with the axle 202B; a third pair of miter gears 226A,
226B
associated with axle 202C; and a fourth pair of miter gears 228A, 228B
associated
with the axle 202D.
With reference to Figs. 9-11, the secondary tape dispenser 192
operates to dispense four tapes that each engages the second flexible
electrical
element 28 at a point adjacent to one of the corners of the outer edge 96 of
the
element to hold the second flexible electrical element 28 in the flat shape of
the
secondary reflectarray 42.
The secondary tape dispenser 192 includes: (a) four individual tape
dispensers 240A-240D that respectively have tape axles 242A-242D that are each
adapted to support a roll of tape with one end of the tape operatively
connected to the
axle and the other end operatively connected to the second flexible electrical
element
28, (b) a motor 244 for providing the force needed to drive the axles 242A-
242D and
thereby dispense the tapes from the dispensers, and (c) a transmission system
246 for
transmitting force from the motor 244 to each of the axles 242A-242D to
dispense the
tapes and to dispense the tapes at substantially the same time and at
substantially the
same rate.
The transmission system 246 includes a motor gear 250 that is
connected to the axle of the electric motor 244, a gearhead 252 with a first
gearhead
gear 254 that engages the motor gear 250 and a second gearhead gear 256 that
the
gearhead 252 causes to rotate at many times the rate at which first gearhead
gear 254
is caused to rotate by the electric motor 244, a drive train 258 that is
comprised of a
number of gears that transfer the force produced by the second gearhead gear
256 to a
connecting rod system 260 that, in turn, transfers the rotational force to
axles 242A-
242D. The connecting rod system 260 includes connecting rods 262A-262D, a
first
pair of U-joints 264A, 264B associated with connecting rod 262A and
respectively
engaging axles 242A, 242B, a second pair of U-joints 266A, 266B associated
with
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connecting rod 262B and respectively engaging axles 242B, 242C, a third pair
of U-
joints 268A, 268B associated with connecting rod 262C and respectively
engaging
axles 242C, 242D, and a fourth pair of U-joints 270A, 270B associated with
connecting rod 262D and respectively engaging axles 242D, 242A. The connecting
rod system 260 operates to transfer the rotational force imparted by the drive
train
258 to the connecting rod 262A to each of the axles 242A-242D.
With reference to Figs. 12-15 tape cartridge or tape dispenser 240A of
the secondary tape dispenser 192 is described with the understanding that tape
dispensers 240B-240D are substantially identical. Further, the tape dispensers
200A-
200D of the primary tape dispenser 190 are also substantially identical to the
tape
dispenser 240A with two exceptions, namely, (a) the tape dispensers 200A-200D
dispense tape in a different direction than tape dispenser 240A and (b) the
tape
dispensers 200A-200D dispense a different length of tape than tape dispenser
240A.
The tape dispenser 240A includes a bi-stable composite tape 280, the tape axle
242A,
and housing 284. The bi-stable composite tape 280 has two stable states,
namely, (1)
a first state in which the tape has a coiled cylindrical shape and (2) a
second state in
which the tape extends in a linear fashion with a lateral cross-section that
has an arc.
The bi-stable composite tape 280 extends from a first end 286A to a second end
286B. The first end 286A defines a pair of holes 288A, 288B that are used to
engage
the tape to the tape axle 242A with a pair of screws 290A, 290B. The second
end
286B defines a hole 292 that is used to engage a fastener 294 which is used in
connecting the tape 280 to the second flexible electrical element 28. The
housing 284
includes a main housing 296 and side panels 298A, 298B that engage the main
housing. A substantial portion of the main housing 296 and the side panel
298A,
298B define a chamber 300 for holding, prior to deployment, the bulk of the
tape 280
in the first state, i.e., in the coiled cylindrical shape. The housing 284
also includes a
transition portion 302 that supports a short section of the tape 280 in a
manner that
transitions the short section of tape from the first state to the second
state. The side
panels 298A, 298B respectively define holes 304A, 304B that receive bearings
306A,
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306B. The bearings 306A, 306B facilitate the rotation of the tape axle 242A
within
the main housing 296. Each of the bearings 306A, 306B also engages one half of
a
U-j oint.
With reference to FIG. 18D, the primary tape dispenser 190 operates
to synchronously dispense four tapes 320A-320D and the secondary tape
dispenser
192 operates to synchronously dispense four tapes 322A-322D. Associated with
the
tapes 320A-320D and 322A-322D are lanyards 324A-324H with each lanyard
extending between an end of one of the tapes 320A-320D and an end of one of
the
tapes 322A-322D. Each of the lanyards 324A-324D cooperates with the two tapes
that it directly engages to facilitate the establishment of a truss structure
that supports
the primary and second reflectarrays 40, 42.
With reference to FIG. 16, a connection structure 330 is described that
interconnects the first flexible electrical element 26, tape 320A, and
lanyards 324A,
324B. The connection structure 330 is substantially identical to the
connection
structure associated with each of the tapes 320B-320D with the exception that
each of
these tapes engages a different pair of lanyards. Further, the connection
structure 330
is substantially identical to the connection structure associated with each of
the tapes
322A-322D with the exception that the connection structure associated with
each of
these tapes engages the second flexible electrical element 28, a different
pair of
lanyards, and does not include a spring. The connection structure 330 includes
a first
mount 332, second mount 334, and spring 336. The first mount 332 is
operatively
engaged to the first and second flexible membranes 80, 82 of the first
flexible
electrical element 26, one end of the lanyard 324A, one end of lanyard 324B,
and one
end of the spring 336. The second mount 334 operatively engages one end of the
tape
320A and the other end of the spring 336. In operation, the spring 336
operates to
keep forces applied to the first flexible electrical element 26 and the tape
320A
relatively constant and thereby prevent the application of forces that could
adversely
affect the functionality of one or both of the element and the tape.
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Before describing the operation of the deployable reflectarray 20, the
manner in which the first flexible electrical element 26 is folded so as to be
accommodated in the spaced defined by the primary housing 116 and a portion of
the
canister 22 when the deployable reflectarray 20 is in the undeployed state is
described. With reference to FIG. 17A, the first flexible electrical element
26 initially
is flat and the outer edge 96 substantially defines a square. Within the outer
edge 96
folding lines are defined with the solid folding lines representing "ridges"
and the
dashed folding lines representing "valleys." This particular pattern of
folding is
known as a "leaf-in" folding pattern. With reference to FIG. 17B, folding the
first
flexible electrical element 26 according to the leaf-in pattern produces a
four-branch
structure 340 with arms 342A-342D that each extend away from the inner edge 88
of
the first flexible electrical element 26. With reference to FIG. 17C, the
folding of the
first flexible electrical element 26 is completed by swirling the arms 342A-
342D
around the inner edge 88 so as to form a multi-arm spiral pattern that, as the
radius of
the spirals decreases, ultimately has the overall shape of a hollow cylinder.
With reference to FIGS. 18A-18D, the operation of the deployable
reflectarray 20 is described. Initially and as shown in FIG. 18A, the
deployable
reflectarray 20 is in an undeployed state with the door structure 54 of the
canister 22
closed and the meltable pin 68 intact. The feed antenna 24, first flexible
electrical
element 26, second flexible electrical element 28, and deployment mechanism 30
are
enclosed within the canister 22.
With reference to FIGS. 18B and 18C, the first phase of the
deployment commences with an electrical signal being applied to the meltable
pin 68
to cause the pin 68 to fail and the spring biased doors 62, 64 to open. Once
the doors
62, 64 are sufficiently open the spring 112 can apply a force to the overlying
components, namely, the feed antenna 24, first flexible electrical element 26,
second
flexible electrical element 28, primary housing 116, base plate 118, tape
dispenser
120, and secondary housing 122 to move these components to a location from
which
the first and second flexible electrical elements 26, 28 can be deployed to
realize the
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primary and secondary reflectarrays 40, 42 and to position the primary and
secondary
reflectarrays relative to one another and to the feed antenna 24 so as to
realize a
center-fed Cassegrain/Gregorian-style reflectarray antenna structure. In this
regard,
the spring 112 applies sufficient force to position the overlying components
outside of
the canister 22 and such that the lower wall 162 of the primary housing 116
extends
slightly above the upper edge of the canister 22. The limit lanyards 150A-150D
prevent the spring 112 from moving the overlying components beyond this point.
With reference to FIG. 18D, the second phase of the deployment of the
first and second electrical elements 26, 28 is accomplished by applying
electrical
power to the electric motor 204 of the primary tape dispenser 190 and to the
electric
motor 244 of the secondary tape dispenser 192. Electric power can be
simultaneously
applied to the electric motors 204, 244. Alternatively, electric power can be
sequentially applied to the electric motors 204, 244, i.e., electrical power
being
initially applied to electric motor 204 and subsequently applied to electric
motor 244
or being initially applied to electric motor 244 and subsequently applied to
electric
motor 204. The source of the electrical power for the motors is typically a
battery or
solar array that is located outside of the deployable reflectarray 20. The
electrical
power is conveyed to the electrical motors 204, 244 via conductors disposed
within
the passageway 60.
Regardless of the manner in which electrical power is applied to the
electrical motors 204, 244, the electric motor 204 and transmission 206
operate to
simultaneously deploy tapes 320A-320D from the primary tape dispensers 200A-
200D and in so doing establish the primary reflectarray 40. Due to the spiral
folding
of the first flexible electrical element 28, the dispensing of the primary
tapes 320A-
320D causes the primary housing 116 to rotate about the cylindrical guide tube
140.
The electric motor 244 and transmission 246 also operate to simultaneously
deploy
tapes 322A-322D from the secondary tape dispenser 240A-240D and in so doing
establish the secondary reflectarray 42. The deployment of the tapes 320A-320D
and
322A-322D also deploys the lanyards 324A-3241-I. It should be appreciated that
the
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electric motors 204, 244 are capable of being used so as to control the rate
at which
the tapes 320A-320D and 322A-322D are deployed. As such, the electric motors
204, 244 each function, at least in part, as dampers.
There are a number of features to note about the tapes 320A-320D and
322A-322D and/or the lanyards 324A-324H in the deployed state. First, each of
the
tapes is substantially located between the first flexible electrical element
26 and a
plane defined by the second flexible electrical element 28. However, because
the
tapes are made of a composite material (e.g., fiberglass and an epoxy), the
tapes act as
a dielectric and have little, if any, effect on the electromagnetic waves that
travel
between the primary and secondary reflectarrays 40, 42 during operation of the
antenna. Second, the deployed tapes 320A-320D apply sufficient force to the
first
flexible electrical element 26 so that a catenary is established between each
of the
corners of the outer edge 86. This, in turn, results in the first flexible
electrical
element 26 being deployed so as to have a relatively smooth surface that is
substantially free of wrinkles that could adversely affect the performance of
the
deployed element. Third, the deployed tapes 320A-320D cause the first flexible
electrical element 26 to have a shape that is pyramid-like and, more
specifically, a
frustum of a pyramid-like structure with the corners of the edge 86 of the
element
defining the base of the pyramid-like structure, the inner edge 88 of the
element
defining flattened apex of the pyramid-like structure, and the seams between
the
corners of the edge 86 and the inner edge 88 defining the edges of the pyramid-
like
structure. It is believed that the pyramid-like structure of the deployed
first flexible
electrical element 26 improves the bandwidth of the antenna. Fourth, the
deployed
tapes 320A-320D also define a pyramid-like shape with the outer ends 286B of
the
tapes defining the base of the pyramid-like structure, the inner ends 286A of
the tapes
defining the flattened apex of the pyramid-like structure, and the tapes
defining the
edges of the pyramid-like structure. However, in certain embodiments the
deployed
tapes 320A-320D lie substantially in a plane. Fifth, each of the deployed
tapes 320A-
320D is in compression due to the force applied to the first end 286A of the
tape by
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the tape axle to which the tape is connected and the force applied to the
second end
286B of the tape by one of the connection structure 330, two of the lanyards,
and the
first flexible electrical element 26. Sixth, the two lanyards and the first
flexible
electrical element 26 also cooperate to substantially limit any bending moment
being
applied to each of the deployed tapes 320A-320D. Seventh, the deployed tapes
322A-322D and the lanyards 324A-324H apply sufficient force to the second
flexible
electrical element 28 so that a catenary is established between each of the
corners of
the outer edge 96. This, in turn, results in the second flexible electrical
element 28
being deployed so as to have a relatively smooth surface that is substantially
free of
wrinkles that could adversely affect the performance of the deployed element.
Eighth, the deployed tapes 322A-322D and the lanyards 324A-324H also apply
sufficient force to the second flexible electrical element 28 so that the
element is
substantially planar. Ninth, the deployed tapes 322A-322D also define a
pyramid-
like shape with the outer ends 286B of the tapes defining the base of the
pyramid-like
structure, the inner ends 286A of the tapes defining the flattened apex of the
pyramid-
like structure, and the tapes defining the edges of the pyramid-like
structure. In
certain embodiment, the deployed tapes 322A-322D can be substantially parallel
to
one another. In this case, the deployed tapes 322A-322D define a column-like
structure with a polygonal cross-section. Tenth, four combinations of: (a) the
deployed tapes 320A-320D, (b) the deployed tapes 322A-322D, and (c) the
lanyards
324A-3241-1 each form a first tetrahedron truss structure. For example, the
combination of the deployed tape 320A, deployed tapes 322A and 322B, and
lanyards
324A and 3248 define one of the four first tetrahedron truss structures.
Eleventh,
four combinations of: (a) the deployed tapes 320A-320D, (b) the deployed tapes
322A-322D, and (c) the lanyards 324A-324H each form a second tetrahedron truss
structure. For example, the combination of the deployed tapes 320A and 320B,
deployed tape 322B, and lanyards 324B and 324C define one of the four second
tetrahedron truss structures. Twelfth, four combinations of: (a) the deployed
tapes
320A-320D, (b) the deployed tapes 322A-322D, and (c) the lanyards 324A-324H
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each substantially form a queens post-like truss structure. For example, the
deployed
tapes 320A and 320C with the base plate 118 define a tie beam of a queens post-
like
truss structure, deployed tapes 322B and 322C each define a queens post of a
queens
post-like truss structure, lanyards 324B and 324E each define a principle of a
queens
post-like truss structure, and the second flexible electrical element 28
defines the
strain beam of a queens post-like truss structure.
While the deployable reflectarray 20 operates to implement a center-
fed Cassegrain/Gregorian-like reflectarray antenna (i.e., a dual-reflector
configuration), it should be appreciated that a deployable single-reflector
configuration comprised of a reflectarray and a feed antenna is also feasible.
In such
a configuration, there would be no second flexible electrical element to
deploy.
Rather, the secondary tape dispenser would be adapted to deploy a feed antenna
at a
specific distance from a primary reflectarray (which, in such an embodiment,
is the
only reflectarray in the antenna). It should also be appreciated that tape
deployment
of one or more reflectarray antenna elements can be implemented for offset-fed
Cassegrain/Gregorian-like reflectarray antennas, i.e., dual-reflector
configurations in
which the feed antenna, reflectarray, and subreflector are not aligned.
Similarly, tape
deployment of one or more reflectarray antenna elements can be implemented for
an
offset single-reflector configuration in which the feed antenna and
reflectarray are not
aligned, i.e., a normal to the surface of the reflectarray or the boresight of
the
reflectarray is not aligned with the boresight of the feed antenna.
The foregoing description of the invention is intended to explain the
best mode known of practicing the invention and to enable others skilled in
the art to
utilize the invention in various embodiments and with the various
modifications
required by their particular applications or uses of the invention.
24
