Patent Application
20090109108
The present invention relates in general to reflective antennas, and more particularly to a reflective antenna assembly including a reflective antenna configured to provide beam scanning in the elevation plane.
Conventional reflective antennas have been used for many applications including communications, radar, scanning, tracking, etc. Typical reflective antennas employ parabolic reflectors to focus electromagnetic energy to a particular focal point. Conventionally, reflective antenna structures are limited by restrictions imposed by parabolic reflectors. For example, parabolic reflectors are severely limited for use in high wind applications as parabolic reflectors exhibit high resistance to air flow. Conventional structures have suggested the use of enclosures for such reflective antennas. However, the parabolic curvature for such structures requires a deep curve in the reflector, limiting mobility the parabolic reflector within such structures.
Further, it has been suggested to electromagnetically emulate curved reflective surfaces of any geometry using a substantially planar microwave reflector antenna configuration. U.S. Pat. No. 4,905,014 issued to Gonzalez et al., Feb. 27, 1990, the contents of which are fully incorporated herein by reference, teaches a phasing structure emulating desired reflective surfaces regardless of the geometry of the physical surfaces to which the microwave phasing structure is made to conform, wherein the structure may be fabricated as a fraction of the wavelength of the operating frequency of the phasing surface. The aforementioned technology, marketed as Flat Parabolic Surface (FLAPS™) technology accomplishes the aforementioned function using a dipole antenna placed in front of a ground plane. However, such planar structures require large reflective surfaces at operating frequencies and may be susceptible to scan degradation.
While conventional antenna structures teach phasing structures of multiple geometries and different surfaces, such structures struggle to provide multiple high gain beams.
Disclosed and claimed herein is a reflective antenna assembly according to one or more embodiments of the invention. In one embodiment, the reflective antenna assembly includes a radome having a fixed orientation within the elevation plane and a reflective antenna positioned within the radome. The reflective antenna includes a feedhorn configured to provide electromagnetic energy at an operation frequency and a reflective surface having a plurality of electromagnetically loading structures. The reflective surface may be curved in the azimuth plane and configured to reflect the electromagnetic energy relative to at least one focal point. The reflective antenna further includes a support structure configured to position the feedhorn and the reflective surface within the radome in order to angularly steer the electromagnetic energy with respect to the elevation plane.
Other aspects, features, and techniques of the invention will be apparent to one skilled in the relevant art in view of the following detailed description of the invention.
One aspect of the invention is to provide a reflective antenna assembly having a reflective antenna positioned within a radome. In one embodiment, the reflective antenna may include a reflective surface, a feedhorn arrangement and a support structure. The reflective surface may include a plurality of electromagnetic loading structures and a ground plane. According to another embodiment, the reflective surface geometry may be characterized as curved in the azimuth plane. Further, the reflective surface may be configured to reflect the electromagnetic energy relative to at least one focal point. For example, the reflective surface may reflect electromagnetic energy associated with a feedhorn. Similarly, it may be appreciated that electromagnetic energy incident on the reflective surface may be reflected to a focal point. In certain embodiments, the curved reflective surface may be characterized as having a non-parabolic geometry.
According to another embodiment, the reflective antenna feedhorn may include a single feedhorn and/or a feedhorn array. The feedhorn may be configured to provide electromagnetic energy at an operation frequency. In another embodiment, the support structure may be configured to position the feedhorn and the reflective surface within the radome in order to angularly steer the electromagnetic energy with respect to the elevation plane. In yet another embodiment, the radome may be arranged in a fixed orientation with respect to the elevation plane.
According to another embodiment, a reflective antenna assembly may be provided including a sub-reflector having a plurality of electromagnetically loading structures configured to reflect the electromagnetic energy. The support structure may be configured to position the feedhorn, sub-reflector and reflective surface within a radome in order to angularly steer the electromagnetic energy with respect to the elevation plane. In that fashion, the feedhorn, reflective surface and sub-reflector may be arranged in a cassegrain configuration.
In one embodiment, the reflective antenna may include a mechanical actuator configured to position the reflective antenna in the elevation plane. The mechanical actuator may be integrated with the support structure. According to another embodiment, the geometry of the reflective surface may allow for angular positioning in the elevation plane within the radome. As such, the reflective antenna may be positioned a predefined degree in relation to a reference angle. To that end, the reflective antenna may be employed for scanning, tracking and telemetry applications. For example, a reflective antenna may be provided for telemetering data between a manned airborne vehicle and one at least one of a Unmanned Aerial Vehicle (UAV) and a terrestrial communications system.
As used herein, the terms “a” or “an” mean one or more than one. The term “plurality” mean two or more than two. The term “another” is defined as a second or more. The terms “including” and/or “having” are open ended (e.g., comprising). The term “or” as used herein is to be interpreted as inclusive or meaning any one or any combination. Therefore, “A, B or C” means any of the following: A; B; C; A and B; A and C; B and C; A, B and C. An exception to this definition will occur only when a combination of elements, functions, steps or acts are in some way inherently mutually exclusive.
Reference throughout this document to “one embodiment”, “certain embodiments”, “an embodiment” or similar term means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of such phrases or in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner on one or more embodiments without limitation.
Referring now to
According to another embodiment of the invention, the reflective surface 115 of reflective antenna 100 may include an arrangement of electromagnetic loading structures. In one embodiment, the arrangement of electromagnetically-loading structures may be disposed on the reflective surface 115 to emulate a desired reflective geometry. Such electromagnetically-loading structures may vary in dimension, having an orientation and interspacing from each other. In certain embodiments, such electromagnetically-loading structures may correspond to the electromagnetically-loading structures disclosed in the previously-incorporated U.S. Pat. No. 4,905,014, the details of which are fully disclosed therein. By way of example, the arrangement of electromagnetically-loading structures may comprise an array of metallic patterns, where each metallic pattern having a cross (i.e., X) configuration with dimensions, orientation, and interspacing such that the desired reflective surface of selected geometry is obtained. Each metallic pattern may constitute a shorted crossed dipole. In that fashion, reflective surface 115 may conform to a plurality of geometries including at least one of a planar surface, curved surface and any other surface geometry in general. As shown in
According to another embodiment, reflective surface 115 may be an electrically thin surface. For example, an electrically thin phasing surface may provide electromagnetically emulating of a desired reflective surfaces regardless of the geometry of the physical surfaces to which the electrically thin microwave phasing structure is made to conform. As used hereinafter, the term “electrically thin” shall mean on the order of a fraction of the wavelength of the operating frequency of the microwave phasing structure.
In certain embodiments, reflective antenna 100 may include a sub-reflector 125. Similar to reflective surface 115, sub-reflector 125 may include an arrangement of electromagnetic loading structures. As such, sub-reflector 125 may be configured to reflect electromagnetic energy relative to at least one of reflective surface 115 and feed horn 105. As shown in
According to another embodiment, reflective surface 115 may be configured to reflect incident electromagnetic energy relative to one of feedhorn 105 and sub-reflector 125. Similarly, it may be appreciated that electromagnetic energy incident on reflective surface 115 may be reflected to one of feedhorn 105 and sub-reflector 125. In yet another embodiment, reflective surface 115 may include a ground plane. The ground plane may be place a distance from electromagnetic loading structures supported by reflective surface 110. Similarly, sub-reflector 125 may be configured to reflect incident electromagnetic energy relative to one of feedhorn 105 and reflective surface 115. Additionally, sub-reflector 125 may include a ground plane.
Continuing to refer to
According to another embodiment, support structure 110 may include sub-structure 120 configured to support reflective surface 115. According to another embodiment, support structure 110 may include base 130 configured to arrange reflective antenna 100. Base 130 may be coupled to support structure 110 by mechanical actuator 135 such that feedhorn arrangement 105 may be adjusted angularly and/or repositioned as discussed in more detail below with respect to
Referring now to
According to another embodiment, reflective antenna 200 may be configured to produce a beam of electromagnetic energy characterized by scan pattern 220a. As shown in
As shown in
As shown in
Referring now to
Referring now to
Referring now to
According to another embodiment of the invention, radome 310 may be manufactured of an electrically transmissive material. In one embodiment, radome 310 may be configured to be electrically transmissive to operation frequencies of a reflective antenna (e.g., reflective antenna 100). As such, radome 310 may be constructed of one of fiberglass, Kevlarm and Spectracloth™. According to another embodiment, radome 310 may be a sealed enclosure configured to provide a protective enclosure for reflective antenna 305.
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art. Trademarks and copyrights referred to herein are the property of their respective owners.
