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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to antennas and more particularly to an improved
deployable log periodic VEE antenna especially adaptable for space craft
where compactness, reliability and resistance to thermal distortion is
important.
Deployable antennas are well known in the art. Typical examples thereof are
shown in the U.S. patents to Mirrione et al. U.S. Pat. No. 3,950,758, to
Carr U.S. Pat. No. 3,213,415, to Barbano, et al. U.S. Pat. No. 3,500,424,
and to Esposito, et al. U.S. Pat. No. 3,715,759.
The Mirrione et al. antenna uses self locking hinges intermediate the ends
the mast and the antenna elements for folding of the antenna primarily for
the purpose of convenient boxing. This antenna is heavy being directed to
the home and commercial market.
The Carr antenna has its antenna elements connected at the ends by pins for
collapsing and expanding the antenna in a zigzag fashion. This antenna is
utilizable in commercial television, and like the Mirrione et al. antenna,
is generally unsuitable for space craft.
The Barbano et al. antenna is formed of a flexible sheet to permit folding
for storage and the Eposito et al. antenna is similar but uses an
inflatable spherical enclosure to unfurl the antenna elements.
Also, there are numerous patents teaching log periodic principles in a
design of antennas, one such patent for example, is the U.S. patent to
Cory et al. U.S. Pat. No. 3,697,999. However, none of the foregoing have
the concept of utilizing low expansion material in a log periodic antenna
whereby dimensional stability is obtained over a large temperature range
so as to be useful in space craft, nor do they show an antenna capable of
being easily collapsed into a small configuration for transportation
purposes and yet reliably deployed when desired, by a means which also
gives rigidity to the deployed antenna.
Accordingly, it is a primary object of this invention to provide a log
periodic antenna configuration utilizing low expansion material so that
dimensional stability is obtained over a large temperature range so as to
be particularly useful in space craft and which can be collapsed into a
small compact configuration and reliably deployed.
SUMMARY AND ADDITIONAL OBJECT OF THIS INVENTION
The antenna which accomplishes the foregoing object comprises a central
mast having a plurality of antenna elements connected thereto and
constructed of a light weight low expansion material. The antenna elements
themselves, in one embodiment, are made of semi-cylindrical light weight
easily bendable material so as to be collapsed into a relatively small
compact configuration and containable in a shell which acts as a
confinement means. Upon removal from the shell, the antenna elements are
suitably deployed into a log periodic VEE antenna configuration by the
bendable material returning to its original state in a spring-like
fashion. The shell serves to position and confine the antenna elements in
their collapsed bent position and the semi-cylindrical bendable material
gives an overall stiffness to antenna structure upon deployment. In
another embodiment of the invention, the semi-cylindrical material is
formed to act as a hinge which is easily bent and provides a spring action
by returning to its original state for deployment of the antenna elements
upon release of the confinement means.
Thus, still another object of this invention is to provide a log periodic
VEE antenna utilizing semi-cylindrical material in spring-like fashion to
enable confinement of the antenna and to deploy the antenna elements upon
release from a confining means.
Additional objects of this invention will become apparent to those skilled
in the art from the following description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows one embodiment of the antenna constructed in accordance with
the teachings of this invention with some of the antenna elements shown
deployed;
FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1 and
looking into the direction of the arrows to show the center support mast
and a portion of the deployed antenna elements;
FIG. 3 is an enlarged fragmentary cross-sectional view of a portion of the
mast to show the coaxial feed for the antenna elements;
FIG. 4 is a perspective view, partially broken away, to show the means for
attaching the antenna elements to the mast;
FIG. 5 is a elevational cross-sectional view of the antenna encased in a
container shell;
FIG. 6 is a cross-sectional view of the antenna and mast to show the
container shell in more detail than shown in FIG. 5;
FIG. 7 is another embodiment of the antenna shown in a deployed condition;
FIG. 8 is an enlarged view, partly in section to show the semi-cylinder
deployment springs of the antenna of the embodiment of FIG. 7; and
FIG. 9 is a elevational view of the antenna of FIG. 7 shown with the
antenna elements in a collapsed position and with some of the antenna
elements shown in phantom to show their deployed position.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning first to FIGS. 1 through 6 which discloses the first embodiment of
the invention, it can be seen that there is provided an antenna, indicated
in its entirety as 10, comprising a central mast 12 and a plurality of
antenna elements 14. The antenna in the embodiment disclosed is a log
periodic VEE type antenna and, typically the dipole elements are longest
at the lower end of the antenna gradually decreasing in length to a short
element near the top. The length of the elements and their spacing from
one another is according to conventional criteria for forming a log
periodic antenna. As such, the length and spacing of the elements do not
form a part of this invention and need not be discussed further herein
except to point out that they are alternately spaced on the central mast
and thus do not interfere with one another in their collapsed position.
The mast 12 is a slightly tapered cone with the narrowest portion at the
top and is formed of four relatively thin flat sidewalls 16 each having a
pair of outwardly extending flanges disposed in abutting relationship to
form the mast of generally rectangular configuration, the cross section of
which is shown in FIG. 2. The flanges 18 are connected together in a
suitable manner, as by brazing or soldering, and give rigidity to the
mast.
As shown in FIG. 4, the antenna elements are semi-cylindrical and are
connected on each side of the flanges 18 by a flexible conductive hinge 20
one leg of which is fixed to the flanges and the other positioned in the
direction coextensive with the desired angle of the deployed dipole
elements. Further, as shown in FIG. 3, suitable transmission lines 22 are
plated or bonded to the flanges 18 and a plurality of U-shaped straps 24
are riveted to the flanges at several places throughout their length to
secure a suitable transmission line in the form of a coaxial cable 26
located coextensively with the center line of each of the joints between
the flanges.
With the antenna elements themselves being formed of semi-cylindrical
material, which material is determined by two requirements; the material
must be suitable for the electrical antenna properties and must be
sufficiently rigid yet flexible enough to bend in spring-like fashion.
Thus, formed they are capable of being bent upwardly, that is, toward the
small end of the tapered central mast 12 to form the collapsed position of
the antenna for confinement in a shell-like container 28.
In the collapsed position, the antenna may be confined within the container
28 which is shown more particularly in FIGS. 5 and 6. The container is
formed of relatively thin sidewalls 30, slightly longer than the mast and
antenna in its collapsed position. The sidewalls 30, being relatively
thin, are reinforced with spaced apart reinforcing members 32 shown as
rectangular in cross-section, except for those reinforcing members 34
forming the corners of the container and are spaced apart a distance
sufficient to allow the antenna elements to be positioned therebetween in
their proper alternating relationship within the container. The spaces for
the antenna elements are indicated at 36, and the spaces to accommodate
the cables 26 and clamps 24 are shown at 38. In this container shell, the
antenna may be confined in its collapsed position for transportation
purposes and at the appropriate time the four sidewalls of the shell,
being held together by any suitable means such as wire straps (not shown)
are separated and the confined antenna members will then spring apart ie.,
be deployed to form the antenna by virtue of the operation of the bent
semi-cylindrical material. This position is shown in FIGS. 1 and partially
in 2.
Thus described in the first embodiment is log periodic VEE antenna which is
first confined in a container then deployed, when removed from the
container, by the spring-like action of the antenna element. The material
used in forming the mast 12 and the antenna elements as well as the
sidewalls of the container shell is resistant to thermal distortion being
a low expansion material such as PRD49 Kevlar. Too, when the antenna
elements, being semi-cylindrical, are rigid when deployed adding to the
overall stiffness of the antenna structure.
From the foregoing description of the first embodiment it can be seen that
the principle of utilizing semi-cylindrical bendable means which is forced
into a bent position has a tendency to return to its original state to
collapse and deploy an antenna. This concept is incorporated in the
antenna elements themselves so that the spring-like action of this
semi-cylindrical means is utilized in the deployment of the antenna
elements. This principle is carried forward in another embodiment of the
invention which will now be described.
Turning now to FIGS. 7, 8, and 9, the antenna 40 of this embodiment
comprises a long central hollow rod forming a mast 42 with a plurality of
wire antenna elements 44 radiating therefrom and configured into trusses
46 (four shown), to form a cone shaped antenna when deployed. This mast is
formed with a flange 48 on the bottom serving to support the antenna and
to which is hinged a plurality of spines 50 which, in the deployed
position, extend outwardly in the general direction of the antenna
elements and form the first elements of the trusses 46. The mast is also
provided with a top flange 52 to which is also hinged as at 54 a second
set of spines 56 which form the second elements of the trusses 46. Each
spine of this second set is hingedly connected at 58 to the first
mentioned spines 50, at their ends apart from the mast, and thus form
deployable trusses for the wire antenna elements 44. These spines are
rigid and shown as hollow rods, circular in cross-section, to adequately
support the antenna elements in a deployed position.
Each of the first spines 50 is provided substantially midway with a short
section of semi-circular material which forms the flexible means 60 ie, in
this embodiment a hinge, and shown in FIG. 8, partially in section for
clarity, which may be bent so as to collapse the antenna as shown in FIG.
9. In this embodiment, the antenna elements are of a length which
determined by the criteria for log periodic antennas, and as such are
attached at their inner end to the mast 42 and at their outer end to the
spines 56. Being of wire they do not interfere with the collapsing of the
trusses 46 in collapsed position.
To collapse the antenna, the flexible hinge means 60 is bent so that the
outer spines 56 move inwardly towards the center mast about their top
hinge means 60 into two legs which fold back on one another generally in
the direction of the arrow 62 as shown in FIG. 9. In this position a clamp
64 of any suitable type is placed around the mast and spines holding them
parallel to the central mast. The antenna in this position is readily
transportable. However, when deployment is desired, the clamp 62 is
removed and the spring-like action of the semi-circular hinge means 60
with its tendency to return to its original position, straightens the
lower spines 50 causing the outer spines 56 to assume a cone position thus
deploying the antenna elements.
In this embodiment like the previous embodiment the center mast is provided
with suitable cables and transmission lines for the antenna elements.
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