COMPACT WIDE-ANGLE SCANNING ANTENNA SYSTEM
United States Patent 3833909
A compact, rapidly scannable, high frequency directional antenna system provides wide-angle space scanning in one or more dirctions by employing a moving feed for commutating energy flow through a wave guide array illuminating or receiving high frequency energy from a cylindrical or spherical energy collimator.
US Patent References:
Radio wave focusing device
Iams - September 1951 - 2566703
Rapid scanning radar antenna
Proctor - October 1955 - 2720589
Microwave scanning apparatus employing feed horn coupled to spaced lens by coaxial transmission lines
Ferrante et al. - January 1966 - 3230535
Luneberg lens with staggered waveguide feed
Young - October 1968 - 3404405
Radio wave focusing device
Iams - September 1951 - 2566703
Rapid scanning radar antenna
Proctor - October 1955 - 2720589
Microwave scanning apparatus employing feed horn coupled to spaced lens by coaxial transmission lines
Ferrante et al. - January 1966 - 3230535
Luneberg lens with staggered waveguide feed
Young - October 1968 - 3404405
Application Number:
05/358242
Publication Date:
09/03/1974
Filing Date:
05/07/1973
View Patent Images:
Export Citation:
Assignee:
Sperry Rand Corporation (New York, NY)
Primary Class:
Other Classes:
343/911L
International Classes:
H01Q3/14; H01Q3/24; H01Q3/00; H01Q19/06
Field of Search:
343/754,761,839,911L
Primary Examiner:
Lieberman, Eli
Attorney, Agent or Firm:
Terry, Howard P.
Claims:
I claim
1. Antenna apparatus comprising:
2. Apparatus as described in claim 1 wherein said array of wave guides has first and second opposed concave energy exchanging ends.
3. Apparatus as described in claim 2 wherein said array of wave guides is equipped with impedance matching means at said first and second opposed energy exchanging ends.
4. Apparatus as described in claim 2 wherein said delay means comprise dielectric phase delay means.
5. Apparatus as described in claim 2 wherein said electromagnetic wave distributor means comprises wave guide means journalled for movement about at least one axis.
6. Apparatus as described in claim 2 wherein said first and second opposed concave energy exchanging ends are each in the forms of segments of spherical surfaces.
7. Apparatus as described in claim 6 wherein said dielectric electromagnetic wave collimating means is a solid sphere of low loss dielectric material.
8. Apparatus as described in claim 7 wherein said solid sphere of low loss dielectric material has an effective index of refraction n which varies with the normalized sphere radius r as:
9. Apparatus as described in claim 7 wherein said electromagnetic wave distribution means comprises wave guide means journalled for movement about first and second mutually perpendicular axes.
1. Antenna apparatus comprising:
2. Apparatus as described in claim 1 wherein said array of wave guides has first and second opposed concave energy exchanging ends.
3. Apparatus as described in claim 2 wherein said array of wave guides is equipped with impedance matching means at said first and second opposed energy exchanging ends.
4. Apparatus as described in claim 2 wherein said delay means comprise dielectric phase delay means.
5. Apparatus as described in claim 2 wherein said electromagnetic wave distributor means comprises wave guide means journalled for movement about at least one axis.
6. Apparatus as described in claim 2 wherein said first and second opposed concave energy exchanging ends are each in the forms of segments of spherical surfaces.
7. Apparatus as described in claim 6 wherein said dielectric electromagnetic wave collimating means is a solid sphere of low loss dielectric material.
8. Apparatus as described in claim 7 wherein said solid sphere of low loss dielectric material has an effective index of refraction n which varies with the normalized sphere radius r as:
9. Apparatus as described in claim 7 wherein said electromagnetic wave distribution means comprises wave guide means journalled for movement about first and second mutually perpendicular axes.
Description:
The invention herein described was made in the course of or under a contract or a subcontract thereunder with the United States Air Force.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to scannable directional antennas for operation at high or microwave frequencies in such applications as radiometers and radar object detection systems and more particularly concerns an antenna system for rapid wide-angle scanning in one or in mutually perpendicular directions and having a configuration which is mechanically simple and electrically practical.
2. Description of the Prior Art
In the past, there have been many applications for directive antennas which permit the scanning of a radiation or receptivity pattern over an angular sector of space somewhat greater than one beam width. In some applications, it has been found convenient to move the entire antenna (both its feed and its collimation elements) in integral manner over the desired scan angle. When the latter method may not be used because of the relatively large size and inertia of an antenna, scanning has been achieved by moving the feed with respect to the collimator, as along a line including the focus of the collimator, or around a small circle centered at that focus, for example. Alternatively, a series of feeds may be located along the aforementioned line or circle, which feeds are successively connected to a transmitter or a receiver by a complex switching commutator Both alternatives require that the effective center of rotation of the feed element be at the vertex of the collimator, and both alternatives produce serious beam shape deterioration when approaching large scan angles. Even for scanning in a single plane, the mechanical difficulties encountered in attempting high-speed, wide angle scanning with such prior art devices are severe and excessive weight and size problems are encountered.
SUMMARY OF THE INVENTION
The present invention provides means for the rapid, wide-angle scanning with minimum distortion of a directive radiation or receptivity pattern in one or more planes in space by employing a moving feed for commutating energy flow with respect to repeatedly selectable portions of a wave guiding and scan direction reversing transmission line array cooperating with a cylindrical or spherical energy collimator.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view partly in cross section, of one embodiment of the invention.
FIG. 2 is a plan view, partially in cross section, of an alternative embodiment of the apparatus of FIG. 1.
FIG. 3 is an elevation view of a wave guide array for use in the embodiment of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The novel scanning antenna system, as seen in FIG. 1, may comprise as three major cooperating elements a scanning distributor element 1, a scan direction reversal or inversion element 2, and an energy collimating element 3. As will be explained, the apparatus may be constructed in the form of particular embodiments suited for scanning a radiation or reception pattern in a single plane or for scanning in mutually perpendicular or other planes. In general, the single plane scanning energy distribution element 1 will comprise a feed, such as a pyramidal horn 4, for propagating a plane electromagnetic wave front, with respect to an aperture cyclically and continuously movable along a sector of a circle or arc 5 in successive positions such as locations 6 and 7. Horn 4 is supported on a wave guide 8 with respect to a conventional transmission line rotary joint 9 in such a manner that the aperture of horn 4 may be rotated along arc 5 about the operational axis 10 of transmission line rotary joint 9.
The arc 5 is defined in the single plane scanning system by the ends of a plurality of wave guides which make up the body of the scan inversion element 2; element 2 has planar symmetry about the system plane of symmetry indicated by dot-dash line 15. Element 2 may consist of a stack of rectangular wave guides including a first pair of side by side central guides 16 contiguous with a successive wave guide pair 17 followed in a similar manner by guides 18, 19, 20, 21, and 22. The plurality of wave guide pairs 16 through 22 terminate in an arc shaped surface 23 at their ends opposite arc 5, the centers of arcs 5 and 23 both preferably falling in the system plane of symmetry 15. Each of the ends of wave guides 16 through 22 is provided with an impedance matching element such as elements 24 and 25 shown within the opposed ends of wave guides 22. In the drawing, these impedance matching transformers are illustrated by way of example as blocks of dielectric material, although other known types of impedance matching devices may be used. The guides preferably support waves whose electric vector E lies in the plane of the drawing as shown in connection with guide 22.
The objective of the scan inversion element 2 is to re-orient the direction of propagation of the plane wave propagated within horn feed 4. For example, when horn 4 is in the position shown in FIG. 1 for feeding the wave guides 21 and 22 at the extreme left side of scan inverter 2, the energy traversing the guides is to be redirected to flow as indicated by the dot-dash line 30 so as to form radiation or receptivity pattern 31. Pattern 32 is formed when the horn 4 is at location 6 on the system plane of symmetry 15. Pattern 33 is similarly to be formed when horn 4 is at location 7.
Redirection of energy flow is aided in the scan arc inversion system 2 by a system of pairs of wave guide delay elements 36 through 41 respectively associated with the wave guide pairs 16 through 21. The delay elements also assume that the scan inversion system is relatively short and permit the total system to be compact and simple in structure. With the exception of the outermost wave guide pair 22, the guides 16 through 21 are respectively loaded with dielectric delay elements 36 through 41 so that each electrical path length is equal to the electrical path length of the outermost guides 22. A relatively smaller delay is thus required for each of the delay lines in pair 21 than is required for each of the central delay lines 16.
Thus, the wave guide pair 21 requires relatively short delay elements which may be constructed of relatively low dielectric constant material. The same material may be used to form the progressively longer delay elements 39 and 40 respectively found in wave guide pairs 19 and 20. The same progression may continue to the central pair of guides 16, but it is alternatively found convenient to select a material having a greater dielectric constant for delay element pairs 36, 37, and 38, as seen in FIG. 1. The dielectric materials are selected from those readily found on the market which exhibit relatively low loss characteristics at high or microwave frequencies.
In the single plane scanning system of FIG. 1, the energy collimator 3 may in one embodiment be formed of a solid dielectric material, also of low loss characteristics, in the shape of a right circular cylinder. The curvature of the cylindric surface matches that of the arc 23 of the scan inversion element 2. In operation, therefore, the feed horn 4 cyclically traverses the arc 5. Because of the aforementioned equality of path lengths in the wave guides 16 through 23, the phases of the energy at the wave guide apertures on arcs 5 and 23 are not relatively shifted. Because of the physical geometry of the system, a phase front directed in the illustrated position of horn 4 away from the axis of rotation 10 is redirected at surface 23, as along dot-dashed line 30, through the center 42 of the circularly cylindric lens forming energy collimator 3 as is required for aberration free scanning, to form the desired undistorted radiation or reception pattern 31, for example. It will be understood that the travel of horn 4 may by cylically reversed at its extreme positions, or that horn 4 may travel continuously in a circle, being switched to an inactive status when the aperture of horn 4 is not on arc 5. It will also be understood by those skilled in the art that FIG. 1, as well as the other figures, is drawn in proportions intended to illustrate the invention with good clarity, and that the proportions shown do not necessarily represent proportions which would be selected for use by those skilled in the art.
As suggested in the foregoing, the novel scanning antenna system may comprise a feed horn 4 arranged as in FIG. 2 for solid angle scanning about two mutually perpendicular axes, such as azimuth and elevation axes. For this purpose, the scanning distributor element 1 may employ a conventional gimbal system including scan axes 10 and 45. Horn 4 may be supported with respect to a radar or radiometer receiver 46 gimballed for movement in a prescribed azimuth pattern about the shaft at axis 10 by motor 47 when the latter is excited in a conventional manner by azimuth scan voltages coupled to motor leads 48. The shaft associated with axis 10 may be journaled in a gimbal 58, in turn, mounted for rotation on a shaft at axis 45 within trunnions 40, 50 by operation of motor 51. Motor 51 may be operated according to a prescribed pattern by the application of appropriate elevation scan voltages applied to leads 53 of motor 51. Scanning about the axes 10 and 45 may be regular and in a cyclic synchronized manner according to methods well known in the art for achieving raster and related solid angle types of scan of a directive antenna.
In the solid angle scanning system of FIG. 2, the aperture of feed horn 4 is designed to move in two dimensions adjacent a spherical surface 55 made up of the multiplicity of apertures of a two dimensional stacked array using a plurality of planar arrays of guides 16 through 23 like the planar array shown in FIG. 1. The several wave guide delay elements employed are similarly arranged to provide equal propagation times for energy traversing scan inversion device 2 for any azimuth or elevation positional offset horn 4 with respect the axis 56 of the antenna system. The latter now has an axis of symmetry 56, replacing the plane of symmetry 15 of the FIG. 1 antenna scan system.
Each ed of the scan inversion element is in the form of a concave spherical surface, so that surface 55 has opposed to it a concave spherical end surface 57 which matches the curvature of the spherical dielectric lens forming energy collimator 3. It will be readily understood by those skilled in the art that the major elements 1, 2, and 3 of the solid-angle scanning system of FIG. 2 operate in a manner analogous to the components of the FIG. 1 system, but yield scanning of radiation or reception patterns such as patterns 31, 32, and 33 in elevation as well as in azimuth.
While the embodiment of FIG. 2 may be made to operate satisfactorily with a two dimensional array of rectangular wave guides, other guide shapes which represent minor variations of rectangular shapes may also be employed in the FIG. 2 system. For example, the two-dimensional array of generally hexagonal guides formed by a standard aluminum honeycomb panel may be employed, as in FIG. 3. In this instance, the hexagonal wave guide 60 may form the sole centrally located guide and is then equipped with a maximum delay element (not shown). Guides 61 immediately surrounding the central guide 60 require a slightly lesser delay element. Guides 62 immediately surrounding guides 61 require a lesser delay element than guides 61, and so on to the outermost circle of guides 64 which may be devoid of dielectric delay elements, if desired.
The energy collimator 3 employed in the single axis scanning system of FIG. 1 may take the form of a cylindrical lens which is a microwave analog of the conventional circularly cylindric Luneberg optical lens wherein the low loss dielectric medium has an effective index of refraction which varies radially outward from the axis of the cylinder. The index n therefore varies with the normalized radius r according to the relation:
n = √ 2 - r 2 (1)
such cylindric lenses have been fabricated in the prior art by forming a long, constant width ribbon of a material having progressively varying dielectric characteristics and then winding the ribbon into a spiral to form the desired cylinder. The ribbon may be composed of low loss artifical dielectric material consisting of a controlled-density array of randomly oriented metallic particles supported within a low density foam dielectric bead matrix. The particles may be insulated silver or aluminum needles having a length less than one eight of the operating wave length and supported in foamed polystyrene. Sperical lenses suitable for use as energy collimator 3 in FIG. 2 and having a radially varying index of refraction have been similarly made in the prior art by stacking a plurality of such short cylinders to approximate the desired spherical shape or by making an assembly of pyramidal sectors each having radially graded dielectric characteristics and each being assembled with an apex at the center of the sphere which they form in total. Such spherical lenses have the desired property of focusing a plane wave such as that produced by feed horn 4 accurately to a point on the sphere located diametrically opposite to the point of tangency of the plane phase front upon entering the sphere.
Accordingly, it is seen that the invention provides novel means for the rapid wide-angle scanning of space with minimum distortion of a directive radiation or receptivity pattern. Operation of the scanning feature may be in one or in two mutually perpendicular directions by employing a simple, light-weight feed chamber mechanism in an antenna system occupying a minimum of space and low in weight and cost.
While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than of limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to scannable directional antennas for operation at high or microwave frequencies in such applications as radiometers and radar object detection systems and more particularly concerns an antenna system for rapid wide-angle scanning in one or in mutually perpendicular directions and having a configuration which is mechanically simple and electrically practical.
2. Description of the Prior Art
In the past, there have been many applications for directive antennas which permit the scanning of a radiation or receptivity pattern over an angular sector of space somewhat greater than one beam width. In some applications, it has been found convenient to move the entire antenna (both its feed and its collimation elements) in integral manner over the desired scan angle. When the latter method may not be used because of the relatively large size and inertia of an antenna, scanning has been achieved by moving the feed with respect to the collimator, as along a line including the focus of the collimator, or around a small circle centered at that focus, for example. Alternatively, a series of feeds may be located along the aforementioned line or circle, which feeds are successively connected to a transmitter or a receiver by a complex switching commutator Both alternatives require that the effective center of rotation of the feed element be at the vertex of the collimator, and both alternatives produce serious beam shape deterioration when approaching large scan angles. Even for scanning in a single plane, the mechanical difficulties encountered in attempting high-speed, wide angle scanning with such prior art devices are severe and excessive weight and size problems are encountered.
SUMMARY OF THE INVENTION
The present invention provides means for the rapid, wide-angle scanning with minimum distortion of a directive radiation or receptivity pattern in one or more planes in space by employing a moving feed for commutating energy flow with respect to repeatedly selectable portions of a wave guiding and scan direction reversing transmission line array cooperating with a cylindrical or spherical energy collimator.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view partly in cross section, of one embodiment of the invention.
FIG. 2 is a plan view, partially in cross section, of an alternative embodiment of the apparatus of FIG. 1.
FIG. 3 is an elevation view of a wave guide array for use in the embodiment of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The novel scanning antenna system, as seen in FIG. 1, may comprise as three major cooperating elements a scanning distributor element 1, a scan direction reversal or inversion element 2, and an energy collimating element 3. As will be explained, the apparatus may be constructed in the form of particular embodiments suited for scanning a radiation or reception pattern in a single plane or for scanning in mutually perpendicular or other planes. In general, the single plane scanning energy distribution element 1 will comprise a feed, such as a pyramidal horn 4, for propagating a plane electromagnetic wave front, with respect to an aperture cyclically and continuously movable along a sector of a circle or arc 5 in successive positions such as locations 6 and 7. Horn 4 is supported on a wave guide 8 with respect to a conventional transmission line rotary joint 9 in such a manner that the aperture of horn 4 may be rotated along arc 5 about the operational axis 10 of transmission line rotary joint 9.
The arc 5 is defined in the single plane scanning system by the ends of a plurality of wave guides which make up the body of the scan inversion element 2; element 2 has planar symmetry about the system plane of symmetry indicated by dot-dash line 15. Element 2 may consist of a stack of rectangular wave guides including a first pair of side by side central guides 16 contiguous with a successive wave guide pair 17 followed in a similar manner by guides 18, 19, 20, 21, and 22. The plurality of wave guide pairs 16 through 22 terminate in an arc shaped surface 23 at their ends opposite arc 5, the centers of arcs 5 and 23 both preferably falling in the system plane of symmetry 15. Each of the ends of wave guides 16 through 22 is provided with an impedance matching element such as elements 24 and 25 shown within the opposed ends of wave guides 22. In the drawing, these impedance matching transformers are illustrated by way of example as blocks of dielectric material, although other known types of impedance matching devices may be used. The guides preferably support waves whose electric vector E lies in the plane of the drawing as shown in connection with guide 22.
The objective of the scan inversion element 2 is to re-orient the direction of propagation of the plane wave propagated within horn feed 4. For example, when horn 4 is in the position shown in FIG. 1 for feeding the wave guides 21 and 22 at the extreme left side of scan inverter 2, the energy traversing the guides is to be redirected to flow as indicated by the dot-dash line 30 so as to form radiation or receptivity pattern 31. Pattern 32 is formed when the horn 4 is at location 6 on the system plane of symmetry 15. Pattern 33 is similarly to be formed when horn 4 is at location 7.
Redirection of energy flow is aided in the scan arc inversion system 2 by a system of pairs of wave guide delay elements 36 through 41 respectively associated with the wave guide pairs 16 through 21. The delay elements also assume that the scan inversion system is relatively short and permit the total system to be compact and simple in structure. With the exception of the outermost wave guide pair 22, the guides 16 through 21 are respectively loaded with dielectric delay elements 36 through 41 so that each electrical path length is equal to the electrical path length of the outermost guides 22. A relatively smaller delay is thus required for each of the delay lines in pair 21 than is required for each of the central delay lines 16.
Thus, the wave guide pair 21 requires relatively short delay elements which may be constructed of relatively low dielectric constant material. The same material may be used to form the progressively longer delay elements 39 and 40 respectively found in wave guide pairs 19 and 20. The same progression may continue to the central pair of guides 16, but it is alternatively found convenient to select a material having a greater dielectric constant for delay element pairs 36, 37, and 38, as seen in FIG. 1. The dielectric materials are selected from those readily found on the market which exhibit relatively low loss characteristics at high or microwave frequencies.
In the single plane scanning system of FIG. 1, the energy collimator 3 may in one embodiment be formed of a solid dielectric material, also of low loss characteristics, in the shape of a right circular cylinder. The curvature of the cylindric surface matches that of the arc 23 of the scan inversion element 2. In operation, therefore, the feed horn 4 cyclically traverses the arc 5. Because of the aforementioned equality of path lengths in the wave guides 16 through 23, the phases of the energy at the wave guide apertures on arcs 5 and 23 are not relatively shifted. Because of the physical geometry of the system, a phase front directed in the illustrated position of horn 4 away from the axis of rotation 10 is redirected at surface 23, as along dot-dashed line 30, through the center 42 of the circularly cylindric lens forming energy collimator 3 as is required for aberration free scanning, to form the desired undistorted radiation or reception pattern 31, for example. It will be understood that the travel of horn 4 may by cylically reversed at its extreme positions, or that horn 4 may travel continuously in a circle, being switched to an inactive status when the aperture of horn 4 is not on arc 5. It will also be understood by those skilled in the art that FIG. 1, as well as the other figures, is drawn in proportions intended to illustrate the invention with good clarity, and that the proportions shown do not necessarily represent proportions which would be selected for use by those skilled in the art.
As suggested in the foregoing, the novel scanning antenna system may comprise a feed horn 4 arranged as in FIG. 2 for solid angle scanning about two mutually perpendicular axes, such as azimuth and elevation axes. For this purpose, the scanning distributor element 1 may employ a conventional gimbal system including scan axes 10 and 45. Horn 4 may be supported with respect to a radar or radiometer receiver 46 gimballed for movement in a prescribed azimuth pattern about the shaft at axis 10 by motor 47 when the latter is excited in a conventional manner by azimuth scan voltages coupled to motor leads 48. The shaft associated with axis 10 may be journaled in a gimbal 58, in turn, mounted for rotation on a shaft at axis 45 within trunnions 40, 50 by operation of motor 51. Motor 51 may be operated according to a prescribed pattern by the application of appropriate elevation scan voltages applied to leads 53 of motor 51. Scanning about the axes 10 and 45 may be regular and in a cyclic synchronized manner according to methods well known in the art for achieving raster and related solid angle types of scan of a directive antenna.
In the solid angle scanning system of FIG. 2, the aperture of feed horn 4 is designed to move in two dimensions adjacent a spherical surface 55 made up of the multiplicity of apertures of a two dimensional stacked array using a plurality of planar arrays of guides 16 through 23 like the planar array shown in FIG. 1. The several wave guide delay elements employed are similarly arranged to provide equal propagation times for energy traversing scan inversion device 2 for any azimuth or elevation positional offset horn 4 with respect the axis 56 of the antenna system. The latter now has an axis of symmetry 56, replacing the plane of symmetry 15 of the FIG. 1 antenna scan system.
Each ed of the scan inversion element is in the form of a concave spherical surface, so that surface 55 has opposed to it a concave spherical end surface 57 which matches the curvature of the spherical dielectric lens forming energy collimator 3. It will be readily understood by those skilled in the art that the major elements 1, 2, and 3 of the solid-angle scanning system of FIG. 2 operate in a manner analogous to the components of the FIG. 1 system, but yield scanning of radiation or reception patterns such as patterns 31, 32, and 33 in elevation as well as in azimuth.
While the embodiment of FIG. 2 may be made to operate satisfactorily with a two dimensional array of rectangular wave guides, other guide shapes which represent minor variations of rectangular shapes may also be employed in the FIG. 2 system. For example, the two-dimensional array of generally hexagonal guides formed by a standard aluminum honeycomb panel may be employed, as in FIG. 3. In this instance, the hexagonal wave guide 60 may form the sole centrally located guide and is then equipped with a maximum delay element (not shown). Guides 61 immediately surrounding the central guide 60 require a slightly lesser delay element. Guides 62 immediately surrounding guides 61 require a lesser delay element than guides 61, and so on to the outermost circle of guides 64 which may be devoid of dielectric delay elements, if desired.
The energy collimator 3 employed in the single axis scanning system of FIG. 1 may take the form of a cylindrical lens which is a microwave analog of the conventional circularly cylindric Luneberg optical lens wherein the low loss dielectric medium has an effective index of refraction which varies radially outward from the axis of the cylinder. The index n therefore varies with the normalized radius r according to the relation:
n = √ 2 - r 2 (1)
such cylindric lenses have been fabricated in the prior art by forming a long, constant width ribbon of a material having progressively varying dielectric characteristics and then winding the ribbon into a spiral to form the desired cylinder. The ribbon may be composed of low loss artifical dielectric material consisting of a controlled-density array of randomly oriented metallic particles supported within a low density foam dielectric bead matrix. The particles may be insulated silver or aluminum needles having a length less than one eight of the operating wave length and supported in foamed polystyrene. Sperical lenses suitable for use as energy collimator 3 in FIG. 2 and having a radially varying index of refraction have been similarly made in the prior art by stacking a plurality of such short cylinders to approximate the desired spherical shape or by making an assembly of pyramidal sectors each having radially graded dielectric characteristics and each being assembled with an apex at the center of the sphere which they form in total. Such spherical lenses have the desired property of focusing a plane wave such as that produced by feed horn 4 accurately to a point on the sphere located diametrically opposite to the point of tangency of the plane phase front upon entering the sphere.
Accordingly, it is seen that the invention provides novel means for the rapid wide-angle scanning of space with minimum distortion of a directive radiation or receptivity pattern. Operation of the scanning feature may be in one or in two mutually perpendicular directions by employing a simple, light-weight feed chamber mechanism in an antenna system occupying a minimum of space and low in weight and cost.
While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than of limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.