Patent Grant
7450079
This invention relates to antennas, and more particularly to a gimbaled reflector antenna.
Gimbaled reflector antennas provide a high gain signal path over a wide field of regard extending beyond the beam width of a fixed antenna of equivalent design. This high gain signal path is provided by mechanically steering the beam to a desired location through appropriate actuation of the associated gimbals. In this fashion, a gimbaled reflector antenna may be used to track moving targets regardless of whether the antenna position itself is also changing. Gimbaled reflector antennas may also perform sequential acquisition of multiple targets at multiple positions or be used to move a fixed set of multiple beams to different locations. Thus, gimbaled reflector antennas have numerous applications in both wireless communication systems and sensor systems.
As illustrated in
To eliminate the complications associated with a fixed feed/reflector design, one current approach is to use what is called a “beam waveguide” that eliminates “hard” electrical connections (connection made with cables, waveguide, or other physical media such as flexible electrical connection 120) through the gimbals of a reflector system. A beam waveguide is a multiple reflector system that produces an image of the feed that is displaced from where the feed is located. This feed image orientation can be changed by rotation of one or more of the beam waveguide reflectors. This image of the feed is then used to feed a focused reflector system, producing the high gain spot pattern. Conventional beam waveguide systems require four or five reflectors in addition to two reflectors for the final focused main reflector. This large number of reflectors requires complicated design, assembly, and alignment procedures. For electrically small antenna systems, this may be impractical.
Another approach to providing large field of regard is to use a phased array antenna. Phased array antennas require small element spacing for large scan angles, resulting in a large number of elements for a given gain requirement. In addition, it difficult and expensive to produce an array that looks over a spherical field of regard of pi steradians. Moreover, the number of active electronic devices such as amplifiers and phase shifters typically make the cost prohibitive.
Accordingly, there is a need in the art for improved gimbaled reflector antenna systems that provide a large field of regard.
In an exemplary embodiment, a gimbaled reflector antenna is provided that includes: a Gregorian antenna having a sub-reflector and a main reflector; a feed; a first reflector; a second reflector, wherein the first reflector is adapted to reflect a beam from the feed to the second reflector, the second reflector is adapted to reflect the beam to the sub-reflector, and the sub-reflector is adapted to reflect the beam to the main reflector; an elevation gimbal adapted to rotate both the second reflector and the Gregorian reflector with respect to the first reflector; and an azimuth gimbal adapted to rotate the first reflector with respect to the feed.
In another exemplary embodiment, a gimbaled antenna system is provided that includes: a Gregorian antenna having a sub-reflector and a main reflector; a feed; a first reflector; a second reflector, wherein the first reflector is adapted to reflect a beam from the feed to the second reflector, the second reflector is adapted to reflect the beam to the sub-reflector, and the sub-reflector is adapted to reflect the beam to the main reflector; an azimuth gimbal adapted to rotate the first reflector, the second reflector, and the Gregorian antenna with respect to the feed; and an elevation gimbal adapted to rotate both the second reflector and the Gregorian reflector with respect to the first reflector.
A better understanding of the above and many other features and advantages of the present invention may be obtained from a consideration of the detailed description of the exemplary embodiments thereof below, particularly if such consideration is made in conjunction with the appended drawings, wherein like reference numerals are used to identify like elements illustrated in one or more of the figures therein.
Reference will now be made in detail to one or more embodiments of the invention. While the invention will be described with respect to these embodiments, it should be understood that the invention is not limited to any particular embodiment. On the contrary, the invention includes alternatives, modifications, and equivalents as may come within the spirit and scope of the appended claims. Furthermore, in the following description, numerous specific details are set forth to provide a thorough understanding of the invention. The invention may be practiced without some or all of these specific details. In other instances, well-known structures and principles of operation have not been described in detail to avoid obscuring the invention.
To avoid the aforementioned problems in the prior art, a beam waveguide gimbaled reflector antenna is provided that includes as few as four mirror elements. Turning now to
Because antenna 200 is a beam wave guide antenna in which feed horn 240 is fixed with respect to the remaining antenna components, feed horn 240 mounts on a substrate 270 that forms the mounting reference for antenna 200. For example, in a space-based application, substrate 270 would comprise the spacecraft that incorporates antenna 200. First flat plate reflector 230 also mounts on substrate 270 through an elevation gimbal 275. Thus, as elevation gimbal 275 is actuated, first flate plate 230, azimuth gimbal 235, second flat plate 250, and Gregorian sub-system 215 rotate about an elevation axis such that projected beam 255 is scanned in the elevation direction. Advantageously, the image of the feed in main reflector 210 does not change with regard to azimuth or elevation scan angle changes provided that the feed radiation from feed horn 240 is symmetrical about its axis. Thus, the antenna performance is unperturbed as antenna 200 is scanned to a desired azimuth and elevation location, provided that surrounding structure comprising substrate 270 does not electrically interfere with projected beam 255. In this fashion, hemispherical fields of regard may be achieved with no degradation in antenna performance with just four reflectors. In addition, because the gimbaled mass is reduced through the use of just four reflectors, light weight gimbals may be used, further decreasing the overall mass.
Turning now to
A comparison of antennas 200 and 300 shows that elevation axis 280 is closer to main reflector 210 in antenna 300 as compared to antenna 200. To better reflect this feature, cutaway side views showing only the reflectors (for better illustration clarity) for antennas 300 and 400 are shown in
By now, those of skill in this art will appreciate that many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations of the present invention without departing from its spirit and scope. Accordingly, the scope of the present invention should not be limited to the particular embodiments illustrated and described herein, as they are merely exemplary in nature, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.
This invention was made with Government support under contract number FA8808-04-C-0022 awarded by the U.S. Air Force. The Government has certain rights in this invention.
| Number | Name | Date | Kind |
|---|---|---|---|
| 6061033 | Hulderman et al. | May 2000 | A |
| 7015867 | Miller et al. | Mar 2006 | B1 |
