1. Technical Field of the Invention
This invention relates generally to the field of ground-based satellite communications equipment. More specifically the present invention relates to lightweight, portable, ground satellite communications terminals and stowable antenna structures to be used therewith.
2. Background
Communication by satellite is essential in remote locations of the world where terrestrial communications networks do not exist. Moreover, when moving about remote locations, satellite communications equipment must be mobile. Smaller, lighter satellite communications equipment affords greater mobility. Satellite communications in the higher frequency bands such as X, K and Ku require a minimum transmit and receive directed gain that is much higher than the non-directional gain of handheld satellite transceivers in the L-band. Therefore, to achieve the necessary directional gain, mobile satellite transceivers in the X, K and Ku bands require directional antenna systems generally comprising parabolically shaped reflecting surfaces.
Generally speaking, while electronics have become smaller and more efficient over the years, minimum antenna size remains bounded by the physics of electromagnetic radiation and the need for larger physical antenna size (i.e., aperture) to achieve a higher directed gain. It is not uncommon for antenna systems to comprise the least transportable component of modern portable satellite transceivers.
Efforts have been made to achieve a higher degree of transportability of satellite communications antenna systems. Early efforts employed umbrella-like unfolding antennas comprising Mylar material stretched over lightweight metallic frameworks. Other efforts incorporated parabolic-shaped recesses into the satellite terminal enclosures themselves. Many others efforts involved assembling sections of flat or semi-flat panels into mosaics to achieve a larger reflecting surface. While some of these designs may indeed increase directed gain at low satellite frequencies such as in the L-band, they provide inherently unacceptable directive gain at X, K and Ku bands. The design constraint which prior attempts face at higher frequencies is their inability to provide true parabolic reflecting surfaces necessary for narrow, focused (i.e., directed) beamwidths required not only for gain, but also for discriminating among adjacent geostationary satellites position in equatorial orbits.
3. The Prior Art
U.S. Patent Application Publication 2005/0212715 A1 to Saunders (hereinafter, Saunders) attempts to overcome the effects of rain fade by increasing the physical reflecting surface of a fixed antenna reflector by adding extensions around its periphery. The invention in Saunders, however, provides no means for compacting the fixed portion of the antenna reflector. Therefore, the invention in Saunders would not solve portability issues in transportable satellite communications terminals.
U.S. Pat. No. 5,019,833 to Nonaka et al discloses a parabolic antenna for television signal reception that affords a degree of transportability by virtue of having its means for positioning incorporated into the rear of the parabolic antenna where both comprise a common assembly joined by hinges. The problem not solved by Nonaka is reducing the transportable size of the parabolic antenna reflector.
U.S. Pat. No. 4,862,190 to Palmer et al discloses a deployable parabolic dish antenna where alternating sections of triangular and rectangular reflector surfaces are connected about the periphery of a stationary main reflector surface by hinges. Upon deployment, the triangular and rectangular sections rotate outward to form a larger resultant parabolic reflecting surface centered about the main reflector. The problem with this approach is that the triangular and rectangular sections, when not deployed, are positioned perpendicularly to the main reflector, resulting in the overall displaced volume of the antenna structure to be as great when stowed as when deployed.
U.S. Pat. No. 3,618,101 to Emde et al discloses a collapsible parabolic antenna for use on-board satellites. The antenna in Emde employs at least one fixed semicircular segment and at least one movable semicircular segment which, when rotated into position, provide a 360 degree reflecting surface. Because this antenna is designed for automatic deployment, the movable segments remain connected to the primary axis of the antenna structure at all times. The result, therefore, is that the stowed volume of the antenna is less, but not significantly less, than the deployed volume of the antenna.
U.S. Pat. No. 5,554,999 to Gupta et al discloses a collapsible flat antenna that provides phasing so as to simulate the antenna radiation characteristics of a parabolic dish reflector antenna. Phasing is accomplished by a plurality of reactive elements responsive to different frequencies within the antenna's bandwidth. The antenna disclosed in Gupta is intended to be a flexible structure allowing stowage by collapsible folding. One limitation of this approach is that phased antennas yield optimum radiation patterns at the specific frequency their reactive elements are designed for, whereas parabolic reflecting antennas exhibit optimum radiation patterns across frequency bands. Another limitation of a flexible structure is the difficulty in physically supporting it and maintaining its orientation.
U.S. Patent Application Publication 2004/0196207 A1 to Schefter et al discloses a collapsible antenna for portable satellite terminals which employs a reflector assembly comprising a plurality of panels which may be connected to each other for deployment and disconnected for stowage. Connection of each panel to the other is by means of quarter turn quick release cam nuts. A separate boom arm is used to mount the feed assembly at a focused distance from the reflector assembly. Schefter discloses that the reflector is comprised of four (4) panels. However, the antenna design suffers from large overall size because, it is not a true parabolic structure and because it is a truncated structure, the feed focus is necessarily deep, as opposed to shallow feed focuses with non-truncated parabolic structures.
U.S. Pat. No. 5,061,945 to Hull et al discloses a lightweight, collapsible satellite communications dish antenna having a plurality of identical pre-shaped sectors joined at their apex which can be stowed by rotating all of the sectors about their apex so as to result in their lying substantially atop each other. The invention in Hull inherently requires that the sectors be made of a highly flexible material so as to be capable of being drawn into a curvature shape upon deployment while also capable of returning to a flat shape for stowage. Hull does not disclose any cognizable means for mounting a signal feed means at the dish focus.
What the prior art fails to provide and what is needed, therefore, is an antenna which (1.) is extremely compactable when stowed and (2.) still retains true parabolic reflector properties when deployed.
The present invention provides an apparatus for terrestrial-based satellite communications which provides improved transportability over the prior art.
It is therefore an object of the present invention to provide an antenna for a compact satellite terminal which exhibits characteristic parabolic radiation patterns at all angles.
It is a further object of the present invention to provide an antenna for a compact satellite terminal which utilizes a shallow, compact feed to reduce both its deployed and stowed volume.
It is still a further object of the present invention to provide an antenna for a compact satellite terminal which requires no tools for assembly, disassembly, and to change polarization.
It is yet still a further object of the present invention to provide an antenna meeting all of the above objectives yet being adaptable to a variety of satellite terminals operating at a variety of different frequencies.
An additional object of the present invention is to overcome a lack in the prior art of portable satellite antenna designs, some of which are compact but offer neither true parabolic characteristics nor ruggedness.
Briefly stated, the present invention achieves these and other objects by providing an antenna for a compact satellite terminal. The antenna is a rigid parabolic structure of metal matrix composite capable of disassembly into segments affording a high degree of portability such as for man-packable satellite terminals and the like. A shallow feed horn assembly is joined to an orthomode transducer by a common hub, the hub also serving as the attachment point for a plurality of antenna segments, where a quick release means joins the segments to the hub. The feed horn, hub, orthomode transducer and antenna segments are designed for extremely compact stowability in a variety of applications.
In a fundamental embodiment of the present invention, an antenna for a compact satellite terminal has a hub with a input side, an output side, and a plurality of slots equidistantly located on the periphery of the hub where a plurality of antenna segments being equal in number to said plurality of the slots are removably attached into and where a feed horn and an orthomode transducer are removably attached to the input and the output sides of the hub.
Still according to a fundamental embodiment of the present invention, an antenna for a compact satellite terminal, where each of the plurality of antenna segments are removably attached into each of the like plurality of said slots by means of a tab, one end of which forms an anchor being fastened to each antenna segment and the other end of which forms a tenon-like projection and also by detents located on at least one surface of each tenon-like projection into which spring actuated balls located inside at least one surface of said slot of said hub captively mate to secure each tab into its respective slot.
Still yet, according to a fundamental embodiment of the present invention, an antenna for a compact satellite terminal, where each of the plurality of antenna segments are conductive composite structures fabricated from a nickel nanostrand metal matrix composite material.
The above and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.
The present invention describes an antenna design that collapses into an optimally-dense package for stowage and carrying, and which can be easily set up and taken down. Such an antenna would find application in very compact and highly portable satellite communications terminals. The invention incorporates a number of unique features which collectively result in a very lightweight and compact system which can be configured to support full-duplex communications over satellites in earth orbit. These satellites are in most cases envisioned to be in geosynchronous orbit, with the satellite terminal antenna in a fixed orientation during the communications session. However, transportable terminal designs should be readily modifiable to provide for active tracking of the antenna for use on a moving platform, or with non geosynchronous satellites. Those skilled in the art would appreciate a practical implementation of the invention as readily applicable to a backpack transportable system weighing at 20 lbs or less and having rough stowed package dimensions of about one cubic foot or less (i.e., 12 inches by 12 inches by 12 inches). Such a terminal is depicted in
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To deploy an exemplary compact satellite terminal incorporating the antenna of the present invention, the elevation arms 90 are raised to an angle where the feed and hub assembly can be rotated (around feed pivot point) into a position perpendicular to the elevation arms. A spring-loaded pin is employed to hold the feed and hub assembly in this position. The antenna reflector segments 10 are then snapped into place and the deployed configuration take the exemplary form of that depicted in
Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.
This patent application claims the priority benefit of the filing date of provisional application Ser. No. 61/123,565, having been filed in the United States Patent and Trademark Office on Mar. 25, 2008 and now incorporated by reference herein.
The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalty thereon.
Number | Date | Country | |
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61123565 | Mar 2008 | US |