US 3487413 A
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Description (OCR text may contain errors)
Dec. 30, 1969 M. w. sHoRl-:s 3,487,413
WIDE ANGLE ELECTRONIC SCAN LUNEBERG ANTENNA Filed DeG. QQ, 1966 2 Sheets-Sheet l TMve/Vree Dec. 30, 969 M, w, SHORES 3,487,413
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United States Patent O 3,487,413 WIDE ANGLE ELECTRONIC SCAN LUNEBERG ANTENNA Marvin W. Shores, Pomona, Calif., assignor to General Dynamics Corporation, a corporation of Delaware Filed Dec. 30, 1966, Ser. No. 606,116
Int. Cl. H01q .Z9/06 U.S. Cl. 343-754 Claims ABSTRACT OF THE DISCLOSURE This invention is directed to a scanning antenna characterized by a wide angle operational mode and minimum complexity. The illustrated embodiments 4of the `antenna comprise an array of spiral or the like antennae elements which are grouped in parallel-column fashion and firmly attached to a Luneberg lens over an arc which is approximately equal to one-half of the desired look angle, the individual antennae of the array being arranged to face the center of the Luneberg lens and being selectively energizable in accordance with a programmed sequence by way of appropriate pulse controlled gate-switch circuitry. The inventive antenna may be mechanically rotated by way of an axle extending axially through the Luneberg sphere in order to provide a full semi-spherical look angle.
BACKGROUND OF THE INVENTION This invention relates to electromagnetic energy scanning apparatus and more particularly to a wide angle antenna which utilizes an array of spiral antenna elements operatively positioned on a Luneberg lens.
A Luneberg lens, as known in the art, is a microwave lens which is spherical in shape and has the property of focusing parallel rays incident upon a side. of the spherical surface, to a point on the opposite surface where a diameter of the sphere, parallel to the incident rays, intersects the opposite surface.
The operation of spiral antennae is known in the art as exemplified by U.S. Patent 3,045,23 7. One explanation of their operation is that each spiral antenna element behaves as if it were a two wire transmission line which gradually, by virtue of its spiral geometry, transforms itself into a radiating structure or antenna.
SUMMARY OF THE INVENTION The present invention advances the state of the art relative to the design of search, surveillance and guidance receivers by providing a wide angle scan antenna which eliminates the intricate mechanism required by the prior art antenna systems to perform the same function.
Therefore, it is an object of this invention to provide a wide angle scan antenna.
A further object of the invention is to provide a wide angle scan antenna which eliminates intricate mechanism required by prior known antenna systems.
Another object of the invention is to provide a scan antenna which utilizes a Luneberg lens and a plurality of individually controlled spiral antenna units operatively positioned thereon.
Another object of the invention is to provide a wide angle electronic scan antenna which is capable of providing a full semi-spherical look angle.
Other objects of the invention will become readily ICC apparent from the following description and accompanying drawings wherein:
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a perspective View of an embodiment of the inventive antenna;
FIG. 2 is an enlarged view illustrating a portion of a three array embodiment of the inventive antenna;
FIG. 3 schematically illustrates a portion of the circuitry of the inventive antenna;
FIG. 4 is a view illustrating a full semi-spherical look capability of the invention with a narrow beam resolution;
FIG. 5 is a diagrammatc view illustrating the inventive antenna system for spherical look operation;
FIG. 6 is a view illustrating the tracking capability of the invention;
FIG. 7 illustrates an embodiment of the invention having multiple frequency capability; and] FIG. 8 illustrates an embodiment of the invention for applications requiring a narrow scan angle;
DESCRIPTION OF EMBODIMENTS Referring now to FIGS. 1-3, which broadly illustrate the inventive antenna, the FIG. 1 antenna consists of a Luneberg lens 10 and a scan array 11 firmly attached t0 the Luneberg lens 10 over an arc approximately equal to one half the desired look angle and over a width determined by the number of parallel arrays. To provide a full semispherical look angle the antenna can be mechanically rotated about the central axis 12 of the lens 10.
FIG. 2 illustrates a portion of a three array system comprising antennae elements 13, such as the spiral type, grouped in parallel-column fashion and firmly attached to the Luneberg lens 10 and arranged to face the center of the lens. The number of elements 13 depends upon the operating frequency, the look angle, and the number of arrays. The elements 13 are positioned with a cover member indicated at 14 and constructed of suitable material such as not to interfere with the operation thereof.
As seen in FIG. 3, the components of antenna elements 13 are shown schematically and each consists of a spiral antenna 15, an electric switch 16 operatively connected to a control indicated at 17 and to signal line indicated at 18. The reception angle of the antenna is determined by the spiral antenna 15 that is switched on to the signal line 18 by the pulse of the control 17 via switch 16. The pulses from control 17 may be. programmed as required to scan the look angle of the antenna system.
FIGS. 4 8 and the following description illustrate various applications and embodiments of the inventive antenna. In the following description the term receptor or antenna element designates that the antenna is usable on receivers as well as transmitters.
FIG. 4 illustrates a full semi-spherical look capability with a pencil beam resolution over the semi-spherical lield of view. A Luneberg lens 20 is provided with a single row of receptors or antenna elements 21-30 arranged on the circumference of the lens 20 over a 90 quadrant. With the receptor 21 on and the receptors 22-30 oli the receive or radiate pencil beam would appear as indicated at 21'. Next receptor 22 is switched on and 21 and 23 through 30 are olf producing a beam 22. The receptor or antenna elements 21-30 may be spaced such as to overlap beams 21'-30 at some arbritrary point, in the case illustrated at the one-half power points. The receptors 21-30 are switched on and off in sequence until a complete look through receptor 30 via beam 30 is completed, and the sequence is then repeated.
With the lens/receptor arrangement as illustrated in FIG. 4, the assembly is rotated about its axis 31 by suitable means, such as shown in FIG. 5 at 32, such that receptor 30 shifts an angle less than the beam width between the one-half power points in this case. The receptors 21 through 30 are again sequentially switched on and the rotation continued until the total area of the 180 semi-sphere has been sampled or radiated. In actual practice the assembly rotation would necessarily -he limited to some practical rate, for example, 60 or 120 revolutions per minute or one or two revolutions per second. The receptor or antenna element sample or radiate rate, being electronic, may, for example, be in the order of one megacycle per second. Thus, for one-r.p.s. rotation rate and receptor scan rate of one mc./s., each one of the elements 21-30 would be sampled 100,000 times per revolution of the antenna assembly.
It should be noted that the antenna field of View is not limited to a 180 semi-sphere. Beyond 180 some shadowing of the lens 20 aperture would occur because of further wrap around of the receptor or antenna assembly 13 as shown in FIG. 5. In certain applications this degradation may be negligible and a full hemispherical field of View is possible.
The invention antenna also -has the capability of beaming at any point in a hemispherical field of view. To point the antenna at a predetermined area in space, the FIG. 4 assembly, for example, is rotated to designated position and the appropriate receptor or antenna element 21-30 is enabled or turned on while all other of the receptors are offf This feature simulates a parabolic antenna, being pointed by mechanical linkage or gear drive systems.
FIG. 6 illustrates how radar target or object tracking capability can be performed by an embodiment of the inventive concept. This technique is referred to as lobing and consists of a Luneberg lens 40 with a double receptor array of elements 41-50 and 51-60 operably mounted thereon, lens 40 being rotatable about an axis or axle 52. If, for example, a tagret was located in the field of view relative to the convergent point x at the left, the antenna would Ibe switched as shown in FIG. 6 about this point.
If the convergent remains dead center of receptor elements 44, 54, 45 and l55, as shown, the signal power return from each element would appear relatively equal. When the target moves in the field of view the convergent point x would also move and the double array 41-50 and 51-60 would thereby cause an unbalance 50 in the signal power received in each of these four elements (44, 54, 45 and '55). The unbalance would be processed and corrective action generated to rotate the antenna to maintain proper tracking.
The inventive antenna concept is capable of multiple frequency band operation at a maximum eliiciency for a given diameter lens. For each frequency -band a separate array is provided as illustrated in FIG. 7 wherein the elements or spiral antenna for each of the frequency bands differ in dimension. For example, a Luneberg lens is provided with a C band 61-68, an X band 71-80, and a P band 6172', each of the frequency bands extending outwardly from an axis 81 over an arc approximately equal to one-half the look angle.
The inventive concept can also be readily utilized in applications where a narrow scan angle is accetpable and antenna gain degradation at extreme angles off the bore sight is acceptable, a half lens design may be used as shown in FIG. 8. As shown in FIG. 8, an antenna array 4 on the virtual image principle which is known in the art and, for example, is described in U.S. Patent 2,835,891. As illustrated in FIG. 8, with element 99 on an amount of aperture area is lost as indicated at 104, while with element 91 on maximum gain would be provided.
A spiral scan of the field of view is another capability of the inventive concept. For example, with the FIG. 4 embodiment, receptor or antenna element 21 would 4be left on for a full rotation of the lens 20, then element 22 is switched on during the second revolution and so forth, until the entire field has been examined by each of the receptors 21-30. The sequence would then be repeated.
While the receptors or antenna elements have been described as being of the spiral type, different types 0f antenna elements, both polarized and non-polarized, may be utilized depending on the application. For example, a radar-receiver application could utilize polarized slots or dipoles, while a surveillance receiver or a semi-active guidance system may have to be non-polarized.
It has thus been shown thatrthis invention provides an antenna system which substantially advances the state of the art and eliminates the intricate mechanism that is required by the prior known antenna systems to perform the same function. In addition, the scan rate of thls antenna can exceed the rate attainable by the known systems by several magnitudes.
Although particular embodiments of the invention have been illustrated and described, modifications and changes will become apparent to those skilled in the art, and it is intended to cover in the appended claims all such modifications and changes as come within the true spirit and scope of the invention.
What is claimed is:
1. An antenna system including a microwave spherical Luneberg lens for focusing electromagnetic energy, an array of spiral antenna elements positioned on the spherical surface of the lens over an arc at least approximately equal to one-half of the desired look angle, means for selectively energizing said antenna elements, and means for moving said lens about an axis through the sphere which lies in the plane of the spiral antenna arc.
2. The antenna system defined in claim 1, wherein said microwave lens is a Luneberg spherical type, and wherein said antenna elements are 0f the spiral type.
3. The antenna system defined in claim 1, wherein said array of antenna elements is grouped in a three columnparallel arrangement.
4. The antenna system defined in claim 1, wherein said array of antenna elements is grouped in a two column-parallel arrangement.
5. The antenna system defined in claim 1, wherein said means for selectively energizing said antenna eleme'nts includes electronic switch means for each of said antenna elements, and control means for directing control pulses to said switch means for operating sarne.
6. The antenna system defined in claim 1, wherein said microwave lens is of a Luneberg spherical type, and wherein said array of antenna elements comprises a single column of elements extending across about of said Luneberg lens.
7. The antenna system defined in claim 1, wherein said array of antenna elements is composed of a plurality of columns of antenna elements extending outwardly from said axis, at least certain of said columns being operable in different frequency bands.
8. The antenna system defined in claim 1, wherein said microwave lens is of the Luneberg type and is of a semi-spherical configuration, said lens being provided with a reflector means across the fiat surface thereof, the axis of movement of said lens extending in a direction substantially perpendicular to the flat surface of said lens, and wherein said array of antenna elements is a column on one side of said axis of movement.
9. The antenna system defined in claim 1, wherein said microwave lens is of a -Luneberg spherical type, wherein said antenna elements are of the spiral type, and wherein said means for selectively energizing said antenna elements includes electronic switch means lfor each of said antenna elements and control means for activating and deactivating said switch means, whereby said antenna elements may be programmed to sequentially scan the desired look angle of the antenna during movement of saidlens` References Cited UNITED STATES PATENTS 7/1962 Marston 343-895 12/1963 Johnson et al. 343-911 1/ 1966 `Cheston 343-754 11/1966 Atlas 343-911 5/1968 List et al. 343-911 11/1968 Young 343-754 10. The antenna system defined in claim 9, wherein 10 ELI LIEBERMAN Primary Examiner said array of antenna elements is congured in a single column and positioned so as to overlap adjacent beams at the one-half power points.
U.S. C1. X.R.