The present invention is directed to a mechanical feed assembly for a radio frequency (RF) antenna, and more particularly to a mechanical scanning feed assembly for a dielectric spherical lens antenna.
Spherical dielectric lenses, also known as Luneberg lenses, have been widely used for antenna systems. A Luneberg lens is a spherical lens in which the dielectric constant varies as a function of the radius of the lens. The spherical lens shape has no intrinsic optical axis. Therefore, when a plane wave is incident on the Luneberg lens, the wave encounters an effective optical axis in the direction of the plane wave. The energy of the plane wave is then focused at a single focal point on the opposite side of the lens. This allows the lens to operate on multiple plane waves that are incident from different directions with little or no interference. Accordingly, the spherical lens is ideally suited for use in a multi-beam antenna system.
Conventional multi-beam antenna systems, which utilize a spherical lens, use a feed assembly that consists of a horn cluster and a switch tree made up of a number of switching circulators. Unfortunately, these conventional feed assemblies have several drawbacks. First, the conventional feed assemblies require a large number of active switching devices, which increases the complexity and the cost of the antenna system. Secondly, because the feed assemblies use horn clusters, the antennas can only provide hemispherical coverage due to blockage by the horn cluster. Finally, because the horn cluster fixes the beam pattern on a grid, these antennas experience losses due to scalloping.
Therefore, there is a continuing need for an inexpensive and low cost antenna feed for a beam scanning for a spherical dielectric lens antenna. In particular, there is a need for an inexpensive and low-loss antenna feed for a multi-beam RF spherical dielectric lens antenna that can provide spherical coverage.
The present invention meets the needs described above in a low-cost, low-loss mechanical feed that can be used to provide beam scanning for a spherical lens (Luneberg lens) antenna. Generally described, the invention includes a mechanical scanning feed for a spherical lens antenna. The mechanical feed includes a waveguide, which has a movable wall assembly that contains a guide slot. The moveable wall assembly also includes an end wall that is located proximate to the guide slot to prevent leakage of the energy propagating within the waveguide. The mechanical feed also includes a drive mechanism, which can move the moveable wall assembly along the waveguide so that the guide slot slides within the waveguide parallel to the direction of the propagating energy.
More particularly described, the moveable wall assembly may contain a single wall portion, which may contain a number of guide slots, which have a width dimension and a length dimension. The dimensions of each of the guide slots may be identical, or in some instances, the dimension of each guide slot, particularly the width dimension, may be different to provide beam forming capabilities.
Additionally, the moveable wall assembly may contain more than one moveable wall portion. In particular, the moveable wall assembly may contain a first moveable wall portion that has a single guide slot having a given width dimension and a second moveable wall portion located proximate to the first wall portion, which contains a number of additional guide slots. Each of the guide slots in the second moveable wall portion has a width dimension that is less than the width dimension of the guide slot in the first moveable wall portion. This allows the second movable wall portion and the first movable wall portion to be moved independently of one another so that at least one of the guide slots in the second moveable wall portion can be aligned with the guide slot of the first moveable wall portion, thereby altering the beam pattern of the antenna.
The invention may also be directed to an antenna system that includes a dielectric lens, a radio frequency source, and a feed assembly. The dielectric lens may be a spherical lens, also known as a Luneberg lens. The feed assembly contains a waveguide that includes a movable wall assembly with a guide slot, which allows a portion of the propagating energy to exit the waveguide. The feed assembly also includes a drive mechanism, which is capable of manipulating the movable wall assembly along the waveguide in a direction parallel to the propagation path of the energy within the waveguide. The motion of the moveable wall assembly by the drive mechanism changes an elevation angle of the guide slot. In addition, the waveguide may be curved, so that the curvature of the waveguide substantially approximates the curvature of the spherical dielectric lens.
The various aspects of the present invention may be more clearly understood and appreciated from a review of the following detailed description of the disclosed embodiments and by reference to the appended drawings and claims.
Turning now to the figures, in which like numerals refer to like elements through the several figures,
The antenna system 100 also contains a radio frequency (RF) power source 120, which may be located below the lens 110. The RF power source 120 feeds the waveguide 116 through a rotary joint 122, which is located just below the South Pole 114 of the spherical lens 110.
To prevent leakage of the energy along the bottom lip of the sidewall 128, 130 where the bottom wall 134 slides along the lip 132, choke joints 205 may be used. (See
The antenna system 100 also includes a drive mechanism for manipulating the position of the bottom wall 134 within the waveguide 116. The drive mechanism may include a pair of motors 124, 125. A first motor 124 is positioned at the North Pole 112 of the spherical lens 110, while the second motor 125 is positioned located at the South Pole 114 of the spherical lens 110. The first motor 124 can pull the bottom wall 134 up the waveguide 116 toward the North Pole 112, while the second motor 125 can pull the bottom wall 134 down the waveguide toward the South Pole 114 to position the guide slot 136 at any elevation angle between −90 degrees latitude (South Pole 114) and +90 degrees latitude (North Pole 112). Furthermore, by swinging the curved rectangular waveguide 116 around the spherical lens 110 from 0 degrees to 360 degrees in azimuth in combination with moving the bottom wall 134 vertically along the curved rectangular waveguide 116 so that the guide slot 136 may be positioned at any latitudinal position, a beam pattern may be formed at any elevation and azimuth position to provide approximately spherical coverage.
As shown in
For example, referring to
Although this invention has been describe for use with a spherical (Luneberg) lens 110 those skilled in the art will appreciate that the waveguide 116 may be made planar and used to move the guide slot 136 in the focal plane of a planar reflector or a planar lens to provide a mechanical scan of the beam.
The present invention provides several advantages over conventional systems. First, since the guide slot 136 may be positioned at any latitudinal position, a beam pattern may be formed at any elevation and azimuth position to provide approximately hemispherical coverage. Therefore, losses due to scalloping can be reduced. Second, since the present invention uses mechanical scanning, the number of active switching devices is eliminated, thereby greatly reducing the overall complexity of the antenna system and thus significantly reducing the cost of the antenna system. Although mechanical beam scanning is slower than electronic beam scanning, the scanning speed of the mechanical system for most applications, such as tracking a target from a moving platform, is acceptable. Thus, any decrease in scanning speed is outweighted by the improved performance and decreased cost associated with the present invention.
Other alternative embodiments will become apparent to those skilled in the art to which an exemplary embodiment pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description.
This application claims priority to U.S. Provisional Patent Application Ser. No. 60/587,889 filed on Jul. 14, 2004, which is incorporated herein.
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