Patent Grant
7075492
The present invention relates generally to antennae systems, and more particularly to reflector antenna systems and feed structures for use therewith.
What is needed is a reflector antenna system which exhibits low side lobe performance without the use of absorbing material.
The invention presents a reflector antenna system and corresponding reflector-feed assembly which provide a low f/D ratio, an extended angle of viewing, and low side lobe performance. The low f/D ratio allows the feed structure to be located below the rim of the reflector dish in order to more conveniently cover and protect the dish from environmental elements. Further, because the reflector-feed assembly is located below the rim of the reflector, no signal can reach the feed directly, and low side lobe performance can be obtained.
In a particular embodiment, the reflector-feed assembly includes a feeding waveguide and a reflector plate. The feeding waveguide is operable to support the propagation of a signal therethrough, the feeding waveguide having a major axis along which the signal is propagated, and one or more apertures operable to pass the propagating signal therethrough. The reflector plate is coupled to the feeding waveguide, and extends along a major axis which generally orthogonal to the major axis of the feeding waveguide. The reflector plate includes one or more reflecting surfaces which are positioned to reflect signals passing through the one or more apertures, the one or more reflecting surface extending at an acute angle relative to the feeding waveguide major axis.
These and other features of the present invention will be better understood when read in view of the following drawings and detailed description.
For clarity, previously identified features retain their reference indicia in subsequent drawings.
In an exemplary embodiment, the reflector dish 210 is defined by a diameter D, and focal distance f, at which the feeding waveguide 220 of the present invention is positioned. The ratio of f/D in an exemplary embodiment is less than 0.25, and in a particular embodiment is 0.22.
The feeding waveguide 222 further includes one or more apertures 222b through which the desired signal passes. In an exemplary embodiment, two laterally-opposed apertures are provided, although in alternative embodiments under the present invention, one aperture may be used, or three or more apertures employed. The dimensions of the apertures are determined by the desired frequency of operation, exemplary dimensions of which are provided below.
The reflector plate 224 is coupled to communicate signals to and from the feeding waveguide 222. In the particular embodiment shown, the reflector plate 224 is physically connected to the feeding waveguide 222. In such an embodiment, the feeding waveguide 222 and the reflector plate 224 may be individually manufactured and fastened together, or integrally formed. Alternatively, the feeding waveguide 222 and the reflector plate 224 are spaced apart and oriented relative to one another to couple the desired signal between the two structures.
The reflector plate 224 in an exemplary embodiment is constructed in generally a rectangular shape along a major axis 224a corresponding to the desired E field signal communicated, the reflector plate major axis being generally orthogonally to the major axis of the feeding waveguide 222a. In this particular embodiment, the rectangular-shaped reflector plate of the present invention presents a smaller cross-section to on-bore sight reception compared to a circular-shaped sub-reflector, and accordingly provides minimum feed blockage and higher antenna gain.
The reflector plate 224 further includes one or more reflecting surfaces 224b positioned to reflect signal exiting from, or entering into the one or more apertures 222b. The one or more reflecting surfaces 224b reflect signals exiting from the one or more apertures to the concave inner surface of the reflector dish, and accordingly to the far field during a transmission operation. During a receiving operation, received signals are reflected by the concave inner surface 212 of the reflector dish to the focal point where the reflector plate 224 is located. The one or more reflecting surfaces 224b reflect at least a portion of that signal through the one or more apertures 222b, into the feed guide 222, and onto connecting receiving circuitry.
As illustrated, the one or more reflecting surfaces 224b extend at an acute angle θ1 (i.e., less than 90 degrees) relative to the feed guide major axis 222a, and in the direction toward the inner surface of the reflector dish. Generally, the acute angle ranges between 30 degrees and 80 degrees, and in a particular embodiment is substantially 60 degrees. In the latter embodiment, the angular separation between the two laterally-opposed reflecting surfaces is substantially 120 degrees.
In the exemplary embodiment shown, the reflector plate 224 further includes an edge choke 224d which is formed between the reflecting surface structure 224c and a splash pate 224e. The edge choke 224d is operable to prevent surface currents present along the reflection surface 224b from migrating to the splash plate 224e, where these currents could create signal components propagating into the far field. In the particular embodiment shown, two edge choke portions are formed corresponding to the two reflecting surfaces. In an alternative embodiment in which fewer or a greater number of reflecting surfaces are provided, a corresponding fewer or greater number of edge chokes are also provided. Further, the reflecting surface structure 224c and splash plate 224e may be either separately formed and attached, or integrally formed. The edge choke depth is typically one quarter wavelength as defined by the frequency of operation, and an example embodiment of its dimensions is provided below.
In a particular embodiment, the sub-reflector splash plate 224e includes an impedance matching portion 224f. In one embodiment, this portion 224f comprises a raised taper which extends into the feed guide 222. Other embodiments of the impedance matching portion 224f include a stepped structure, or other impedance matching shapes known in the art. The combined features of the lateral edge-to-edge length of the reflecting surfaces 224b and length of splash plate 224e operate to provide a dish illumination angle θ2 greater than θ1.
The foregoing description has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the disclosed teaching. The described embodiments were chosen in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
This application claims the benefit of U.S. Provisional Application No. 60/594,552, filed Apr. 18, 2005, the contents of which are herein incorporated by reference in its entirety for all purposes.
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| Number | Date | Country | |
|---|---|---|---|
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