Field of the Invention The present invention relates to antennas and antenna systems. In particular, the invention is directed to a gradient lens placed on a ground plane or ground enclosure.

Description of the Related Art Lenses are used to focus, direct, and/or shape electromagnetic radiation having a variety of wavelengths. A gradient lens is a type of lens that has a varying dielectric constant profile along various paths through the lens. The gradient of the lens (i. e., the varying dielectric constant profile) may be a stepped or a continuous function of distance along a particular path of travel through the lens.

A Luneberg lens is a particular type of gradient lens. Luneberg-type lenses were first proposed in the 1940's, and are discussed, for example, in the textbook "Mathematical Theory of Optics,"R. K. Luneberg, University of California Press, Berkeley and Los Angeles, 1964, Library of Congress Catalog #64-19010.

Conventionally, a Luneberg-type lens is in the form of a sphere of material having a dielectric constant (or index of refraction) that varies as a function of radius from the center of the sphere to an outer surface of the sphere, according to a particular mathematical relationship. An ideal Luneberg-type lens preferably has a continually varying dielectric constant as a function of radius (i. e., a continually varying gradient), but actual lenses often exhibit gradients that are a stepped function of radius due to manufacturing limitations. Luneberg-type lenses possess a unique focussing property; namely, plane waves of radiation incident upon the lens from a distant radiation source are imaged, or focussed, at a particular focal point. The incident planar waves are focussed on or near the lens surface at a focal point diametrically opposite the propagation direction of the incoming waves. Conversely, a radiation source located at a focal point on the outer surface of the lens and emitting radiation through the lens ultimately produces a plane wave of radiation propagating in a direction parallel to a diameter of the lens that includes the focal point.

The gradient for an ideal Luneberg-type lens generally is given by the equation: £r = 2- (r/R) 2 (1)

where Er is the dielectric constant at a given distance (r) from the sphere center, and R is the radius of the sphere. In some circumstances, it is desirable that the dielectric constant at the lens surface be equal to the surrounding medium to avoid reflections ; hence, as seen from Eq. (1), FR is equal to 1 when r = R. Additionally, it can also be seen from Eq.

(1) that the ratio of the dielectric constant ER at the center of the lens (i. e., r = 0) to that at the surface of the lens is 2 to 1.

Due to the inherent symmetry of conventional spherical Luneberg-type lenses, radiation that is transmitted through such lenses from one or more antenna feeds coupled to the lens generally has an essentially symmetric cross-sectional spatial profile as it propagates from the lens. In particular, with reference to an azimuth plane that is essentially parallel to the ground, and an elevation plane that is essentially perpendicular to the ground (and, hence, perpendicular to the azimuth plane), radiation transmitted through a conventional spherical Luneberg-type lens generally has a cross-sectional spatial profile, in a plane perpendicular to a direction of propagation, having essentially equal dimensions parallel to the azimuth and elevation planes, respectively. Similarly, radiation that is incident to a conventional spherical Luneberg-type lens and effectively focussed by the lens generally has an essentially symmetric cross-sectional spatial profile, as described above.

Summary of the Invention One embodiment of the invention is directed to an antenna system comprising a conductive ground element and a lens having at least one axis of rotation. The lens comprises an inner volume having at least one inner dielectric constant, and an outer surface that encloses the inner volume. The outer surface has an outer dielectric constant different from the at least one inner dielectric constant. Additionally, the outer surface has a contour essentially defined by a curve that connects a point on the at least one axis of rotation to a point on an orthogonal axis, wherein the curve is not a quarter circle.

The curve is rotated 360 degrees about the at least one axis of rotation such that the rotated curve forms the contour of the outer surface, and such that any cross section of the lens in a plane orthogonal to the at least one axis of rotation has an essentially circular shape and a center point on the at least one axis of rotation. The lens is mounted to the conductive ground element.

Another embodiment of the invention is directed to an antenna system comprising a conductive ground enclosure and a lens having at least one axis of rotation.

The lens comprises an inner volume having at least one inner dielectric constant, and an outer surface that encloses the inner volume. The outer surface has an outer dielectric constant different from the at least one inner dielectric constant. Additionally, the outer surface has a contour essentially defined by a curve that connects a point on the at least one axis of rotation to a point on an orthogonal axis, wherein the curve is not a quarter circle. The curve is rotated 360 degrees about the at least one axis of rotation such that the rotated curve forms the contour of the outer surface, and such that any cross section of the lens in a plane orthogonal to the at least one axis of rotation has an essentially circular shape and a center point on the at least one axis of rotation. The lens is mounted to the conductive ground enclosure. The conductive ground enclosure is constructed and arranged such that it reflects a radiation pattern from an antenna feed device radiating through the lens to shape a predetermined spatial profile that differs in at least one plane from a reference spatial profile associated with the antenna feed device radiating through a fully spheroidal lens in at least one plane.

Another embodiment of the invention is directed to an antenna system, comprising a conductive ground element and a lens having an azimuth plane and an elevation plane, wherein the lens coupled to the ground element. At least a portion of the conductive ground element projects out of the azimuth plane, such that for a radiation pattern radiated through the lens by an antenna feed device, a shape of the conductive ground enclosure reflects a predetermined modified image of the radiation pattern.

In another embodiment, an antenna system includes a hemispheroidally shaped dielectric lens with a varying radius mounted on a ground enclosure. By employing a hemispheroidally shaped lens, a cross-sectional spatial profile of a radiation pattern produced by the antenna system may be asymmetrical in an azimuth plane and an elevation plane. In one aspect, the hemispheroidally shaped dielectric lens may be a gradient lens.

In another embodiment, an antenna system includes a hemispheroidally shaped dielectric lens having a varying radius coupled to a conductive ground plane and one or more antennas feed devices coupled to the dielectric lens. In one aspect, the hemispheroidally shaped dielectric lens may be a gradient lens.

In another embodiment, an antenna system includes a hemispherically shaped or hemispheroidally shaped dielectric lens with at least one antenna feed device coupled to the lens. A conductive ground enclosure is coupled to the lens and at least a portion of the ground enclosure may project out of an azimuth plane. The antenna system of this embodiment may radiate a radiation pattern associated with the one or more antenna feed devices into a coverage area having an azimuth plane and an elevation plane. The azimuth plane is parallel to the conductive ground plane, and the elevation plane is orthogonal to the azimuth plane and passes through the dielectric lens. The conductive ground plane reflects an image of the radiation pattern, such that for a top hemispherical lens angle in the elevation plane, referenced to the azimuth plane, a spatial profile of the radiation pattern approximates that of a reference spatial profile associated with one or more similar antenna feed devices radiating through a fully spherical or spheroidal gradient lens.

In one aspect, the antenna system of this embodiment may also include a conductive enclosure located below the hemispherically shaped dielectric lens, in which the conductive ground plane forms a portion of the conductive enclosure. The shape of the conductive enclosure at least partially determines the spatial profile of the radiation pattern.

Another embodiment of the invention is directed to a lens assembly for a communications system comprising a conductive ground element and a lens having a center and a non-spherical outer surface defined by a smooth surface of revolution. A geometry of the lens is defined by a three-dimensional coordinate system having an origin at the center of the lens. The lens has a plurality of dielectric constant profiles, each dielectric constant profile being defined by a dielectric constant that varies as a function of a distance from the center to the outer surface of the lens at a particular azimuth angle and a particular elevation angle in the three-dimensional coordinate system. The lens comprises a substantially solid dielectric core having a core dielectric constant and at least one substantially solid dielectric enclosure enclosing the dielectric core, the at least one dielectric enclosure having an enclosure dielectric constant different from the core dielectric constant, wherein the smooth surface of revolution is one of a spheroid, an ellipsoid, a parabaloid, a hyperboloid, and an aspheroid. The lens is coupled to the conductive ground element.

Brief Description of the Drawings The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like reference character or numeral. For purposed of clarity, not every component may be labeled in every drawing.

FIG. 1A is a diagram showing a side view of an antenna system according to an illustrative embodiment of the present invention; FIG. 1B is a top view of the illustrative embodiment of FIG. 1A; FIG. 2 is a side view of another illustrative embodiment of the present invention; FIG. 3 is a side view of another illustrative embodiment of the present invention; FIG. 4A is a side view of an antenna according to an illustrative embodiment of the present invention; FIG. 4B is a top view of the illustrative embodiment of FIG. 4A; FIG. 5 is a side view of another illustrative embodiment of the present invention; FIG. 6 is a perspective view of an antenna system with multiple sectorization in the azimuth plane.

FIG. 7 is a perspective view of an antenna system with multiple sectorization in the elevation plane as well as the azimuth plane; and FIG. 8 is a top view of an antenna system showing coverage of a multibeam omnidirectional gradient antenna.

Detailed Description Gradient lenses as discussed above and, in particular, spherical Luneberg-type lenses, conventionally are used in a variety of scientific, military, and commercial applications. In particular, Applicants have appreciated that a conventional spherical Luneberg-type lens may be suitable for wireless communication applications.

Generally, wireless communication systems transport information on data carriers that are radiated by one or more antennas (or antenna systems) into open space throughout a coverage area. Applicants have recognized that in some types of wireless communication systems, a conventional spherical Luneberg-type lens may be used with one or more antenna feed devices to form an antenna system that transmits and/or receives radiation through the lens (for purposes of the present discussion, it should be appreciated that the term"feed device"refers to a device that can transmit and/or receive

radiation). Such an antenna system is capable of transmitting radiation throughout the coverage area, and also is capable of focussing radiation received by, or incident to, the antenna system (e. g., from transmitters located throughout the coverage area) to the one or more antenna feeds coupled to the lens.

In wireless communication systems, typically one or more data carriers transmitted to and/or received from some space within a coverage area constitute a wireless communication link. The geographic extent, or"range"of a given communication link in a wireless system generally may be defined by a spatial profile of the radiated data carriers.

At least one consideration in the design of a wireless communication system is the topological distribution of users; namely, the location, density, and overall distribution of users to which the wireless communication system provides communication services. In particular, throughout a given coverage area around an antenna or antenna system of a wireless communication system, a number of users may be dispersed in a variety of topological distributions. For example, in one portion of the coverage area, several users may be located together in close proximity, while in another portion of the coverage area other users may be more sparsely dispersed. Additionally, different users may be situated at different altitudes with respect to the antenna or antenna system, and at different distances along the ground from the antenna or antenna system.

The spatial profiles of radiation transmitted from an antenna or antenna system generally are based in part on the construction and arrangement of the antenna or antenna system. For example, as discussed above, an antenna system employing a conventional spherical Luneberg-type lens typically provides for transmission and reception of radiation having an essentially symmetrical radiation pattern, due to the spherical symmetry of the lens.

Applicants have recognized that while conventional spherical Luneberg-type lenses indeed may be useful for a wide variety of wireless communication system applications, the symmetrical geometry of the lens may provide for a limited range of possible spatial profiles for transmitted and received radiation in a wireless communication system. The essentially symmetrical spatial profile of radiation associated with such an antenna system in turn may limit the possible topological distributions of users throughout the coverage area to which the system can practically

and reliably provide communication services. Moreover, in situations were essentially symmetrical cross-sectional radiation spatial profiles are nonetheless desirable, Applicants have recognized that lenses having shapes other than spherical shapes may be employed with various other components to provide for essentially symmetrical spatial profiles.

In view of the foregoing, Applicants have recognized that a wireless communication system having an antenna or antenna system with the capability of radiating data carriers with a variety of diverse spatial profiles may be useful for accommodating a variety of topological distributions of users located at various heights and distances from the antenna or antenna system. In particular, Applicants have recognized that antenna systems that are constructed and arranged so as to transmit and receive radiation having unique or asymmetrical cross-sectional spatial profiles would facilitate the implementation of a wireless communication system capable of accommodating a wide variety of topological distributions of users. Additionally, Applicants have recognized that antenna systems including one or more lenses with other than spherical shapes may facilitate the implementation of a wireless communication system capable of accommodating a wide variety of topological distributions of users.

It should be appreciated that the foregoing discussion regarding wireless communication system applications for an antenna system is provided for purposes of illustration only, and that such antenna systems are not limited to this particular application. Additionally, it should be appreciated that the foregoing discussion is not intended to be limiting with respect to potential applications of various gradient lenses according to the invention, as discussed further below.

One embodiment of the present invention provides for a specific embodiment of a gradient lens antenna system. In an illustrated embodiment, an antenna system includes a gradient lens having a hemispheroidal shape. The hemispheroidal gradient lens may be mounted on a conductive ground plane, which, by reflection, produces an image of the source radiation radiated from the hemispheroidally shaped gradient lens, which image is superimposed on the source radiation.

A particular type of hemispheroid is a hemisphere that has a constant radius. It should be understood that the present descriptions of hemispheroidally shaped Luneberg- type lenses being mounted on conductive ground planes apply in the same manner to hemispherically shaped gradient lenses.

According to imaging principles of electromagnetic theory, source radiation emanated by an antenna or antenna system, and impinging upon a theoretically infinite ground plane made of conductive material and located below the antenna system, produces reflections from the ground plane. These reflections superimpose with the originally emanated source radiation. As a result of the superposition of source and image radiation, a spatial profile of the"composite"radiation, in an upper hemisphere of a coverage area around the hemispherically shaped gradient lens, is substantially similar to the spatial profile that would be associated with radiation emanated by an antenna system using a fully spherical gradient lens. In other words, the reflected radiation from the infinite ground plane below the hemispherically shaped lens substitutes for that portion of the source radiation that would have been emanated from the bottom hemisphere of a fully spherical lens.

It should be appreciated, however, that while in the top hemisphere of the coverage area above the infinite ground plane, the spatial profile of radiation from the hemispherically shaped lens would appear to be substantially identical to that associated with a fully spherical lens, in contrast, below the ground plane (i. e., in a bottom hemisphere of the coverage area), the radiation pattern would be null. In practice, since an infinite ground plane is not possible, the elevational spatial profile of the radiation emanated from the hemispherically shaped lens above a finite conductive ground plane does not exactly replicate that of radiation emanated from a fully spherical lens, but rather may be a close approximation thereof.

According to one embodiment of the invention, the use of a conductive ground plane allows the lens of an antenna system to be half the size of a full lens. In addition, according to one aspect, the area below the ground plane may be substantially shielded from the lens, thereby allowing the placement of additional feed devices which may be used as part of a multimode antenna system.

Following below are more detailed descriptions of various concepts related to, and embodiments of, lenses and antenna systems according to the present invention. It should be appreciated that various aspects of the invention as discussed above and outlined further below may be implemented in any of numerous ways, as the invention is not limited to any particular manner of implementation. Examples of specific implementations are provided for illustrative purposes only.

FIGS. 1 A and 1 B show an example of an antenna system 1 according to one embodiment of the invention employing a hemispherically shaped gradient lens 2 mounted on a ground plane 4. A hemisphere is a particular type of hemispheroid, and the antenna system 1 may employ a hemispherically shaped Luneberg-type lens 2. Such a system provides several advantages, as discussed further below. It should be appreciated, however, that the invention is not limited to the particular advantages discussed below, and that such advantages are presented merely for purposes of illustration.

For example, in the embodiments of Figs. 1A and 1B, below the conductive ground plane 4, radiation fields from the hemispherically shaped lens 2 are typically very small. This construction and arrangement allows for potentially reduced interference between the radiation patterns of a first antenna arrangement employing the hemispherical Luneberg-type lens 2, and other antenna arrangements. For example, second and third antenna arrangements utilizing planar type antenna arrangements, as shown in Figs. 6 and 7, may be located below the ground plane 4.

In FIGS. 1A and 1B, the hemispherically shaped Luneberg-type lens 2 is shown mounted above the ground plane 4. As discussed above, because a finite ground plane 4 is used in practice as opposed to a theoretically infinite ground plane, the spatial profile of radiation associated with the hemispherically-shaped Luneberg-type lens 2 approximates that of a fully spherical Luneberg-type lens, but may include slight differences, particularly in the elevation plane of the spatial profile.

As shown in FIGS. 1 A and 1 B, in one embodiment of a sectored antenna system according to the invention, one or more antenna feed devices 6 may be distributed about an equator 20 of the lens 2, proximate to the finite ground plane 4. In particular, the hemispherically shaped lens 2 may be coupled to the ground plane 4 at the equator 20 of the lens 2, and the antenna feed devices 6 may also be coupled to the ground plane 4 to improve the mechanical stability of the feed devices 6.

To compensate for differences in the spatial profile of the radiation pattern in the elevation plane due to a finite ground plane 4, according to one embodiment of the invention, the ground plane 4 may be extended to form a conductive enclosure 9 below the hemispherically shaped lens 2, as illustrated in FIG. 2. Generally, the shape of the conductive enclosure 9 and, in particular, the shape of a director line 10 along a perimeter of the conductive enclosure 9, at least partially determines the ultimate spatial

profile of the radiation pattern in the elevation plane due to a superposition of source and reflected radiation from the contour of the conductive enclosure 9.

Accordingly, as shown in FIG. 3, different shapes for the conductive enclosure 9, or different director lines 10 along the contour of the enclosure, may be chosen to compensate for any differences or aberrations in the spatial profile of the radiation field in the elevation plane resulting from a finite ground plane 4. An additional benefit of the conductive enclosure 9 may include isolation of any cables supplying signals to any of the antenna feed devices 6 coupled to the lens 2.

In some circumstances, it is desirable to radiate or receive an asymmetrical radiation pattern. One example of an antenna system capable of transmitting and/or receiving radiation having an asymmetric profile is given by a spherical Luneberg-type lens, to which is coupled one or more asymmetric feed devices. The symmetry of a spherical Luneberg-type lens results in an almost symmetrical radiation pattern in an azimuth plane and an elevation plane when the shape of a feed device coupled to the lens is symmetrical. However, altering an aspect ratio of the feed device changes the resultant radiation pattern. For example, increasing a dimension of the feed device along a direction perpendicular to the azimuth plane narrows the resultant radiation pattern in the elevation plane. Similarly, increasing a dimension of the feed device along a direction parallel to the azimuth plane narrows the resultant radiation pattern in the azimuth plane. In contrast, decreasing a dimension of the feed device in a direction parallel to a plane widens the resultant radiation pattern in that plane.

A typical relationship between antenna aperture size and a spatial profile (beamwidth) of a radiation pattern is given by: WB = -.(2) where WB is the beamwidth of the radiation pattern in a particular plane, A is the size of the antenna aperture (e. g., dimension of a feed device) in the plane, and X is the radiation wavelength (given by the speed of light c divided by a frequencyf of the radiation). The factor k is a constant associated with the radiation pattern. From the above relationship, it may be appreciated that increasing the aperture size A results in a smaller (or "narrower") beamwidth WB.

If the lens-based antenna system described above is used in an application that requires multi-directional coverage (e. g., some wireless communication systems), numerous feed devices may be coupled to and distributed around the lens. In such an antenna system, increasing one or more physical dimensions of one or more of the feed devices to achieve asymmetrical beam widths may not be possible due to size constraints of the lens.

In view of the foregoing, one embodiment of the present invention is directed to a lens having one or more of a particular shape, particular dimensions, and/or particular dielectric profiles, so as to facilitate the forming and/or focusing of asymmetrical radiation profiles. In one aspect of this embodiment, the lens is an axially symmetric gradient lens. In another embodiment, an antenna system including an axially symmetric gradient lens is provided, which antenna system has the capability of transmitting and/or receiving asymmetric radiation profiles. Such lenses and antenna systems are described in U. S. Non-Provisional Application filed on even date herewith (i. e., June 7,2000) and entitled"Axially Symmetric Gradient Lenses and Antenna Systems Employing Same." An axially symmetric gradient lens according to one embodiment of the invention has a dielectric constant that varies as a function of radial distance through the lens, in a manner similar to that of a conventional hemispherical Luneberg-type lens. In one aspect of this embodiment, however, the lens is not hemispherically shaped, unlike a conventional hemispherical Luneberg-type lens. Examples of different lens-shaped suitable for purposes of the invention according to various embodiments include, but are not limited to, a prolate hemispheroid shape, an oblate hemispheroid shape, a hemiellipsoid shape, and a hemiparabaloid shape.

According to one embodiment a lens is provided having a spheroidal or hemispheroidal shape. A spheroid is a surface of revolution obtained by rotating an ellipse around one of its axes. Rotating an ellipse around its minor axis results in an oblate spheroid, whereas rotating an ellipse around its major axis results in a prolate spheroid. If the ellipse to be rotated is a circle, the resulting spheroid is a sphere. The Cartesian equation for a spheroid is:

where a and c are constants. If a > c, the surface of revolution is an oblate spheroid. If a< c, the surface of revolution is a prolate spheroid.

A hemispheroidal lens according to one embodiment of the invention has an infinite number of focal points present within the circle of focal points on the outer surface. This characteristic allows one to place as many antenna feed devices as physically possible around the circle to obtain a corresponding number of radiation beams. According to one aspect, the use of a non-spherical lens to shape the radiation beams may allow the use of physically smaller antenna feed devices, and therefore permit the placement of a greater number of antenna feed devices than would be possible with a conventional spherical or hemispherical lens.

As discussed above, a conventional hemispherical Luneberg-type lens focuses plane waves of radiation incident upon the lens from a distant radiation source to a particular focal point. In particular, two perpendicular planar waves incident from any direction may be focused by a conventional hemispherical Luneberg-type lens; thus, such a lens has focal points over the entire outer surface of the lens. In contrast, an axially symmetric gradient lens, according to one embodiment of the invention, has focal points at particular locations around the lens or along a particular path circumscribing the lens. In particular, in one aspect, an axially symmetric gradient lens according to one embodiment of the invention has circular cross sections about one axis and has one circular circumscribed path of focal points on the outer surface of the lens. According to another aspect in a more generalized form, the focal points of the lens may be present on a path that circumscribes an imaginary surface that encompasses the lens.

A hemispheroidal lens according to one embodiment of the invention has an infinite number of focal points present within the circle of focal points on the outer surface. This characteristic allows one to place as many antennas feed devices as physically possible around the circle to obtain a corresponding number of radiation beams. According to one aspect, the use of a hemispheroidal lens to shape the radiation beams may allow the use of physically smaller antenna feed devices, and therefore permit the placement of a greater number of antenna feed devices than would be possible with a hemispherical lens.

FIGS. 4A and 4B illustrate one embodiment of the present invention wherein an antenna system 1 includes a prolate hemispheroid lens 2. In this embodiment, cross sections of the lens perpendicular to the X-Y plane of lens 2 are shaped as ellipses,

whereas cross sections of the lens 2 parallel to the X-Y plane are circles. It should be appreciated that the invention is not limited to the particular lens shape shown in FIGS.

4A and 4B, as the perimeter shape of a cross section of perpendicular to the X-Y plane may be any of variety of shapes.

In one embodiment, the lens 2 of FIGS. 4A and 4B is a gradient lens in that has a dielectric constant which varies as a function of a radial distance through of the lens according to a particular mathematical relationship. For example, in one aspect of this embodiment, the lens 2 may be a Luneberg-type lens wherein a ratio of the dielectric constant at an innermost portion of the lens 2 to a dielectric constant near the surface is approximately 2 to 1.

In the embodiment shown in FIGS. 4A and 4B, a plurality of feed devices 6 are provided along a focal point circle 7 that circumscribes an outer surface of the lens 2.

The feed devices 6 may be coupled to the lens 2 in a variety of manners, as the invention is not limited to any particular means of coupling. The focal point circle 7 includes an infinite number of focal points along a circle formed by the cross section of a plane parallel to the X-Y plane with the lens 2. As discussed above, the shape of lens 2 may be varied such that the focal point circle 7 is present at a different position and/or orientation with respect to the coordinate system shown in FIGS. 4A and 4B.

Additionally, the focal point circle 7 need not be present on the outer surface of the lens 2, but may be on a parallel"imaginary"surface (not shown in FIGS. 4A and 4B) spaced a certain distance from the outer surface of the lens 2.

In the exemplary antenna system shown in FIGS. 4A and 4B, the feed devices 6 may have symmetric apertures or asymmetric apertures depending on the desired spatial profile of radiation transmitted and/or received by the antenna system 1.

The feed devices 6 may be distributed around the lens 2 in a non-uniform manner to direct radiation into only certain sectors of a coverage area. Alternatively, the feed devices 6 may be distributed uniformly around the lens 2 to provide an omni-directional radiation pattern. In such an embodiment, the feed devices 6 may be positioned at essentially regular intervals around all or a portion of the focal point circle 7.

FIG. 5 shows a surface of revolution lens 2, which is not a hemispheroid, mounted to a conductive ground enclosure 9. Cross sections of the lens 2 in the azimuth planes are circular, but elevation cross sections may be of any shape. The conductive ground enclosure 9 reflects images of radiated wave beam patterns to project

predetermined electromagnetic radiation spatial profiles into a coverage area. The directional lines 10 of the ground enclosure 9 may be chosen to compensate for any differences or aberrations in the spatial profile of the radiation field in the elevation plane resulting from a finite ground plane 4. The directional lines 10 may also be chosen to form predetermined spatial profiles that are not similar to a reference radiation pattern formed by a lens that has a bottom half symmetric to the illustrated lens 2.

The invention is not limited by the particular construction and configuration of a support structure for the lens 2, an antenna, or an antenna system.

FIG. 6 illustrates a multimode sectored antenna system 12 according to one embodiment of the invention, in which a first antenna arrangement includes a Luneberg- type lens 2 and three antenna feed devices 6, each feed device 6 radiating a radiation beam having a beamwidth of approximately 13° in the azimuth plane of the coverage area, wherein the radiation beam is directed into, or propagates in, the azimuth plane.

The multimode sector antenna system of FIG. 6 also includes a second antenna arrangement that includes one or more planar radiating elements 17, each including one or more antenna feed devices. Each radiating element directs a radiation beam into the azimuth plane, wherein the radiation beam has a beamwidth of approximately 90° in the azimuth plane.

Additionally, FIG. 6 shows that a multimode sector antenna system 12 according to one embodiment of the invention may include a third antenna arrangement having at least one radiating element, for example a planar array of antenna feed devices 18. The third antenna arrangement may direct a respective radiation beam into the azimuth plane, wherein the radiation beam has a beamwidth of approximately 25° in the azimuth plane.

While FIG. 6 shows that the radiation beams associated with the first, second, and third antenna arrangements essentially are directed into the same portion or sector of a coverage area, the first, second, and third antenna arrangements, respectively, may be positioned so as to direct their respective radiation beams to different portions or sectors of the coverage area in the azimuth plane.

FIG. 7 shows another embodiment of the present invention similar to that of FIG.

6, in which one or more of the radiation beams associated with a particular antenna arrangement may be directed at an elevation angle in the elevation plane, referenced to the azimuth plane. In particular, FIG. 7 shows a first antenna arrangement employing a

Luneberg-type lens 2 and having two feed devices 6 for generating radiation beams directed at some elevation angle with respect to the azimuth plane.

Additionally, FIG. 7 shows a second antenna arrangement including a vertical planar array of antenna feed devices 19 that radiate a second asymmetrical radiation beam having a beamwidth of 90° in the azimuth plane and 30° in the elevation plane.

FIG. 7 also shows that the second antenna arrangement may direct the second radiation beam at some elevation angle with respect to the azimuth plane. Finally, FIG. 7 shows a third antenna arrangement including a planar array of antenna feed devices 18 constructed and arranged to radiate a third"symmetrical"radiation beam having a beamwidth of approximately 25° in both the azimuth and elevation planes.

From the foregoing, it should be appreciated that a wide variety of radiation beam profiles, elevations, and azimuthal coverages are possible using various sectored antenna systems in combination with a conductive ground plane or a conductive ground enclosure. For example, as shown in FIGS. 6 and 7, in a first antenna arrangement the antenna feed devices may be distributed non-uniformly around a Luneberg-type lens 2 to direct radiation into only certain sectors of a coverage area, depending on the location and distribution of users.

Alternatively, the first antenna arrangement employing the Luneberg-type lens 2 may include uniformly distributed feed devices 6 to provide an omnidirectional radiation pattern, as shown for example in FIG. 8, or a radiation pattern in one or more sectors comprised of a plurality of narrow radiation beams. In such embodiments, a number of feed devices 6 may be placed at essentially regular intervals around all or a portion of a Luneberg-type lens 2. Additionally, the feed devices 6 may be positioned to provide radiation at a variety of elevation angles; namely, feed devices 6 may or may not be placed around an equator 20 of the lens 2.

Having thus described at least one illustrative embodiment of the invention, various alterations, modifications and improvements will readily occur to those skilled in the art. Such alterations, modifications and improvements are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting.

What is claimed is: