US3495250A

US3495250A - Expandable cavity-backed spiral antenna

Info

Publication number: US3495250A
Application number: US704880A
Authority: US
Inventors: Richard A Farran; John E R Bennett; George Yee
Original assignee: US Air Force
Current assignee: US Air Force
Priority date: 1968-02-12
Filing date: 1968-02-12
Publication date: 1970-02-10
Anticipated expiration: 1987-02-10

Description

Feb. 10, 19'50 R. A. FARRAN T EXPANDABLE CAVITY-BACKED SPIRAL ANTENNA Filed Feb. 12. 1968 'fFIE. 1

on T 5 mm H W M Na N A Wm m mw 5 r 2 p 2 H Z United States Patent O US. Cl. 343-834 6 Claims ABSTRACT OF THE DISCLOSURE An expandable fiat, cavity-backed spiral antenna designed to be light in weight, stored in a small volume and expanded to close tolerances with great reliability including a plurality of spring loaded folding arms mounted about a central shaft and flexible antenna surfaces attached to the center post and arms which fold completely and extend in near perfect parallel plane during operation.

BACKGROUND OF THE INVENTION This invention relates generally to expandable antennas and more specifically to a method and means for compactly storing and reliably displaying a close tolerance, flat, cavity-backed expandable spiral antenna.

A flat, cavity-backed spiral antenna is often desirable when communication is required over a Wide range of frequencies. This type of antenna consists generally of two flat, parallel surfaces; one surface is used as a structural support for one or more pairs of individual spirals, the other surface serves as a reflector to amplify the signals emitted and received by the spirals. The spirals emanate from the center of the surface, a coaxial cable is used to feed each spiral at this central point. This surface which supports the spirals is transparent to RF radiation.

In space applications, it is necessary during propulsion of a space vehicle into orbit to provide a regular shaped object in order to minimize drag and avoid complications in guiding the lifting vehicle. Once in orbit, outer coverings fall away on command and the essential parts are left exposed to perform their assigned tasks. The problem that arises, however, is to store large devices within this relatively small regular shaped nose cone. The storage volume constraint Within the spacecraft has necessitated the use of expandable antennas having expandable diameters of five to ten feet. In the case of deep space probes, antennas of even larger diameters may be needed.

In the past, antennas of various configurations and mechanical and chemical combinations have been proposed but fail to meet the rigid requirements of volume, weight, and reliability. Examples of prior art devices include an expandable flexible disk wherein a spiral surface is attached to a rigid thin-shell structure. The disadvantage of such a device is that for large antenna diameters the packaging within a restricted spacecraft volume is diflicult, if not imposible. Another mechanical antenna consists of a box-shape support frame which expands into an antenna configuration. This antenna likewise fails to meet the space requirement because of the many mechanical components needed to form this shape. Still another type of antenna is the internal or external flex rib antenna. The device utilizes the spring action of ribs wound around a center hub to display the antenna. When a band or similar device which restrains the ribs is released, the ribs are free to spring into their extended position. This antenna fails to meet the close tolerances needed to insure reliability.

3,495,250 Patented Feb. 10, 1970 A further example of the prior art consists of an elastic recovery foam antenna wherein an elastic recovery form or sponge-like material is used to display the antenna surfaces. The foam has a spoked-wheel shape over which the antenna surfaces are stretched. The antenna is compressed into a number of folds during packaging and, upon release, the foam assumes its original shape, thereby deploying the antenna. In this design, the antenna surfaces are fully supported by the foam. This antenna is particularly susceptible to failure in that foam or other sponge-like material fails to assume the contour to the accuracy required for this application. Similarly, since foam tends to lose some of its resiliency under prolonged compression, it has very limited shelf life and should be used almost immediately after manufacturing.

Other types of prior art antennas which have been proposed for use in space applications include yielded wire grid antennas and yielded foil antennas,, which show little or no advantage over the prior art described in detail herein.

SUMMARY OF THE INVENTION The instant invention utilizes a plurality of spring loaded arms for deploying and supporting antenna surfaces. The arms are folded against each other about a center post and are deployed by releasing a band or similar restraining device. The antenna surfaces are supported at the corners of a regularly shaped antenna or along the circumference of a circular shaped antenna and at the central support tube.

In the drawings:

DESCRIPTION OF THE DRAWINGS FIGURE 1 is a perspective view of the invention;

FIGURE 2 is a top view, partly in phantom, of a preferred embodiment of the invention;

FIGURE 3 is a side elevational view, partly in phantom, of the invention;

FIGURE 4 is an elevational drawing of the antennal tensioning mean shown along the lines '44 in FIG- URE 3; and

FIGURE 5 is a side elevational view of the spring loaded joints used in the antenna arms.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGURE 1, there is shown generally a flat cavity-backed antenna 10. The antenna consists of first and second

flat surfaces

12 and 14 respectively. The surfaces are formed of flexible material, preferably a fabric or film or a combination of these materials. A preferred material which shows superior results at an antenna is a film laminate of Kapton, aluminum and Komex fabric. The aluminum is etched or vapor-deposited to form the antenna spiral. This invention is, however, in no way meant to be limited to any particular fabric. The thickness of the spiral surface must be at least one electrical skin depth at the lowest frequency of operation.

Arms

16, 18, 20 and 22 extend outwardly from a center post 24. The fabric material of

surfaces

12 and 14 is securely mounted to the center post 24 and to the parallel extension of the arms at 26, 28, 30 and 32 and held by resilient means 34 (FIGURE 3) which insures the proper tension on the fabric at all times when in the extended position. A preadjustable tension means is provided at 38 and will be described hereinafter.

The surface 14 is a conducting surface and serves as a signal reflector while surface 12 contains the conducting spirals of the antenna. The spiral antenna surface 12 is attached near the end or top of each of the vertical members 26-32 while the reflector surface 14 is attached to 3 the vertical members at a point below the spiral surface, parallel to it, and at the desired distance from it. The connection of

surfaces

12 and 14 to the center post 24 is similarly adjustable in the vertical direction.

The center post 24 would be mounted at an appropriate location on the spacecraft or satellite. The lead-in Wires 40 from the antenna surfaces are located within the center post 24 and are suitably disposed for connection to mating wires located on its base (not shown).

A top view of the antenna is shown in FIGURE 2. Spiral surface 12 is completely parallel and symmetrical to reflecting surface 14. Likewise each antenna surface is equally disposed around the center post 24 and held tight by tension means such as an elastic cord 34.

In FIGURE 3 is shown a side elevation view of the invention with two phantom views indicating the position of the components in the closed or stored position, and the relative position of the various components during its opening operation.

In the closed position shown generally at 40 the arms and fabric are folded in such a manner that they are substantially parallel to and touching the center post. The joints in the arms are Spring loaded by spring 52 shown in FIGURE and are held in position by strap 42. In operation, the strap 42 is released by a signal from earth or a timer or other conventional means. Upon release, the arms and fabric move in the manner indicated generally at 44. The joint at the center post 46 is spring biased and drives the inner portion (22A) of the arm downward'and is locked in position by means of a spring loaded pin in 5-4 shown on joint 48 in FIGURE 5. At the same time the spring loaded joint 48 moves the outer portion of the arm (22B) upwardly where it is locked in position. Slightly before the movement of members 22A and 22B, the vertical member 30 is driven into position and locked by the spring biased joint 50. This occurs because of the manner in Which the arms are folded in the closed position, member 30 is in contact with strap 42 and is the first member to sense the release of the strap. This sequence of motion insures that the fabric will not become tangled while unfolding or due to a sudden strain caused by all joints locking at exactly the same. moment.

The means for applying tension and insuring the parallelism of the surfaces is shown in FIGURE 4. A collar 56 surrounds the member 30. Located in the collar is a set screw 58 which bears against the member 30 for securing the collar. The resilient means 34 is attached to and wound around a shaft 60. This shaft is locked in position by means of a ratchet (not shown) or alternatively by friction between the shaft and its mating hole. The shaft may therefore be turned and winds or unwinds the resilient means changing the tension on the antenna surface. The tensioning shaft is moved by hand or with and appropriate tool for the purpose.

Although the invention has been described with reference to a particular embodiment, it will be understood to those skilled in the art that the invention is capable of a variety of alternative embodiments within the spirit and scope of the appended claims.

We claim:

1. An expandable antenna comprising: a cylindrically shaped center post adaptable to be mounted on a space vehicle; collapsible arms mounted on the center post, said arms, when expanded, consisting of a plurality of hinged sections and extending transversely to the center post and further having a section hinged distally from the center post and parallel to it; flexible signal receiving means attached to the center post and to the said distally hinged section of the arm; flexible reflector means attached to the center post and to the said distally hinged section of the arm and parallel to the signal receiving means; and means for conducting a received signal from the antenna to a space vehicle.

2. An antenna according to claim 1 wherein the hinged sections of the arms are spring biased.

3. An antenna according to claim 2 wherein the hinged sections of the arms are locked in the expanded position.

4. An antenna according to claim 1 wherein the flexible signal receiving means comprises a laminate of aluminum and a fabric.

5. An antenna according to claim 1 wherein the signal receiving means and reflector means are attached to the distally hinged section of each arm by an adjustable tension means.

6. An antenna according to claim 1 including a removable restraining means for securing the arms and antenna and reflector surfaces in a collapsed condition.

References Cited UNITED STATES PATENTS 2,674,693 4/1954 Millett et a1 343-915 X 2,763,002 9/1956 Fitzgerald et a1. 343880 ELI LIEBERMAN, Primary Examiner MARVIN NUSSBAUM, Assistant Examiner US. Cl. X.R. 34388l, 897