US2818564A

US2818564A - Refractive antenna system

Info

Publication number: US2818564A
Application number: US430477A
Authority: US
Inventors: Jesse L Butler
Original assignee: Sanders Associates Inc
Current assignee: Lockheed Corp
Priority date: 1954-05-18
Filing date: 1954-05-18
Publication date: 1957-12-31
Anticipated expiration: 1974-12-31

Description

SERGE? RGSM Dec.'31; 1957 J. L. BUTLER REFRACTIVE ANTENNA SYSTEM 3 Sheets-Sheet 1 Filed May l8, 1954 Jesse L. Butler INVENTOR.

AHor ney Dec. 31, 1957- J. L. BUTLER 2,818,564

REFRACTIVE ANTENNA SYSTEM Filed May 18, 1954 v f s Sheets-Sheet 2 DOWN Jesse L.Bu1ler' uvmvroze.

Attorney Dec.31, 1957 J. L. BUTLER 2,318,564

' REFRACTIVE ANTENNA SYSTEM Filed May 18, 1954 3 Sheets-Sheet 3 Fig.6

JesseL. Butler INVENTOR.

United States REFRACTIVE ANTENNA SYSTEM Jesse L. Butler, Nashua, N. H., assignor, by mesne assignments, to Sanders Associates, 1nc., Nashua, N. l-L, a corporation of Delaware Application May 18, 1954, Serial No. 430,477

4 Claims. (Cl. 343756) The present invention relates to the art of radiating electromagnetic energy. More particularly, this invention relates to conical scanning antenna systems as used in radar.

ln the prior art many systems have been proposed for developing a conical beam of electromagnetic energy by causing beam rotation about the axis of the antenna system. This beam rotation is familiarly termed conical scanning in the art, and is to be distinguished from the azimuth and elevation scanning functions of the system as a whole.

Conical scanning systems as developed in the prior art are characterized by an essentially unbalanced mechanical rotational system. The speed of conical scanning required by modern radar techniques is unattainable by such systems.

it is therefore an object of the present invention to provide an improved antenna system providing high speed conical scanning.

It is a further object of the present invention to provide a conical scanning antenna system that is electrically and mechanically balanced.

A still further object of the present invention is to provide an improved conical scanning antenna system that is reliable.

Other and further objects of the invention will be apparent from the following description of typical embodiments thereof, taken in connection with the accompanying drawings.

in my copending application, Serial No. 427,146, dated May 3, 1954, there IS described another invention embodying a somewhat similar device to obtain desired conical scanning.

in accordance with the invention there is provided a refractive antenna system. The system comprises the combination of a source of plane-polarized electromagnetic energy characterized by an electric vector having a predetermined direction of polarization and a reflector for directing the energy in the form of a beam. A lens is disposed between the source and the reflector. The lens has a plurality of elements for effecting predetermined refractions of the energy in accordance with the relative positions of the elements and the direction of polarization of the polarized energy. The elements of the lens are disposed in adjacent 120 sectors for eflecting the rotation of the center of radiation about an axis. Means are provided for directing the energy through the lens with the plane of polarization parallel to the plane of the elements. Means are further provided for rotating the lens to effect a resultant conical scanning beam at three times the frequency of rotation of the lens.

In the accompanying drawings:

Fig. 1 is a schematic diagram illustrating conical scanning as provided by the present invention;

Fig. 2 is a side view, partly in section, of a preferred embodiment of the present invention;

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Fig. 3 is an enlarged, detailed end view of a radio frequency lens as used in the embodiment of Fig. 2;

big. 4 is an enlarged, detailed end view of a modification of the lens in big. 3;

big. 5 is a series of schematic diagrams illustrating the operation of this invention employing the lens of Fig. 3; and

big. 6 is a series of schematic diagrams illustrating the operation of this invention employing the lens of big. 4.

keterring now in detail to the drawings and with particular reterence to Fig. 1, an antenna system indicated at 1 is depicted as radiating a beam 2 of electromagnetic energy as shown. The main axis 3 or center of radiation of the beam is caused to rotate about the antenna system axis or boresight 4, as shown. The rotating or circular motion of the beam axis 3 is illustrated by the path 5. The extreme lower position of the beam is illustrated by the phantom lines 6. This rotation of the center of radiation of the beam about an axis thus provides what is known as "conical scanning.

Referring now to Fig. 2, the antenna of the present invention comprises a primary radiator 7 (for example, a rectangular wave guide) developing a beam of electromagnetic energy for the system. A transmitter 16, coupled to the primary radiator 7, provides a source of electromagnetic energy. The energy radiated by radiator 7 is plane-polarized and directed through the lens 8. It is then reflected in the form of a beam by the paraboloidal reflector 11, in the direction as indicated at 12. A shaft 9 is mechanically coupled to the lens 8 and is rotated by a motor 10, as shown. The reflector 11 is attached to and supported by the wave guide 7 and support rod 17.

Referring now to Fig. 3 the lens 8 is shown in detail. A web structure comprising three metallic members 13 are connected together and to a metallic ring member 14, as shown. The metallic elements 18 are disposed greater than a half-wave length apart at the operating frequency, for example, 10 kilo-megacycles. The members 13 define three equal sectors of the ring 14, comprising a grating of stacked wave guides. The central radii of the adjacent sectors are disposed substantially degrees apart.

It is to be noted that the elements 18 are connected parallel to the central radii of their respective sectors. Each pair of parallel elements 18 defines a wave guide element.

In the lens as shown in Fig. 4 the construction is similar to the embodiment of Fig. 3, with the exception that the elements 19 are perpendicular to the central radii of their respective sectors.

The operation of the system employing the lens of Fig. 3 can be better understood with particular reference to Fig. 5. Electromagnetic energy, plane polarized such that its electric vector 15 is vertical as shown, is directed through the lens. A wave guide element effects a maximum phase change in the energy that passes through it when the elements bounding the frequency sensitive di mension are parallel to the electric vector and a minimum, substantially zero, when the elements are perpendicular to the electric vector. In particular, such a Wave guide element effects a change in phase angle ofthe energy passing through it in accordance with the expression:

In the above expression, o equals the change in phase angle in degrees of the electromagnetic energy passing through the wave guide element having an electric vector parallel to the electric vector 15. The factor n equals the maximum phase displacement in degrees that may take place and is a function of the spacing of the boundary elements and the length of the lens. The angle 0 gamma equals the angle between the wave guide boundary elements and the electric vector 15.

Of particular significance in the present invention is the characteristic of the lens as described, whereby a single rotation through the 360 degrees effects three rotations of the resultant beam of energy as will be presently shown. The rotation of the lens thus effects rotation of the center of radiation about an axis. In the diagrams (a) through (e), the lens of Fig. 3 is schematically illustrated by the central wave guide elements A, B and C abstracted from their respective sectors and disposed such that the angles AOB, ECG and COA equal 120 degrees, as shown. The effect of increasing the phase velocity within each element is to cause the resultant beam to be refracted in the direction of the energy having least phase change. The diameter of the lens 8 may be small relative to the diameter of the paraboloidal reflector 11 to avoid excessive shadowing and retransmission of the electromagnetic energy through the lens after the energy has been reflected.

Thus, in the diagram (at) the element A is positioned at degrees with respect to the electric vector 15 and etfects a phase change (p,; of n degrees in the energy that passes through it. In accordance with the expression for 90 above, the elements B and C effect a phase change of 0 and w equal to .25n degrees, respectively. Since the elements B and C are symmetrically disposed about the vertical axis, there exists no tendency for the axis of the resultant beam to be directed to the right or left. Since the centers of radiation B and C' of the elements B and C are disposed below the common center 0, the principal axis of the resultant beam is directed down as at 6 in Fig. 1. In particular, the main axis of the resultant beam is directed at an angle with respect to the boresight axis (see 4, Fig. l) in proportion to the differences (PA-(PB and (DA p,- which euual .75n degrees.

Tn the diagram (b), the element A is shown rotated 30 degrees. The element C is then precisely perpendicular to the electric vector and effects zero degrees phase change. The elements A and B each effect .75n phase change, and are symmetrically disposed about the horizontal axis. Here again, -o equals D which equal .7511 degrees. In this case the main axis of the resultant beam is directed to the left.

In the diagram (0) the element A is shown rotated 60 de rees with respect to the electric vector 15. The element B is precisely parallel to the electric vector 15 and accordingly eflects n degrees of phase change in the energy that passes through it. The elements B and C each effect .25n degrees of phase change and p (p equals (PB-(PC, which equals .75n degrees. The main axis of the resultant beam is directed up.

In the diagram (d) the element A is shown rotated 90 de rees with respect to the electric vector 15 and accordingly eflects zero degrees of phase change. The elements B and C each eflect .7511 degrees of phase change to direct the main axis of the resultant beam to the right. in the diagram (2) the element A is shown rotated 120 de rees with respect to the electric vector 15. The element C is now positioned such that the operation of the system as described with respect to the element A above is repeated.

In the diagram (1) the locus of the main axis of the resultant beam due to the rotation of the lens through an an le of 120 de rees is illustrated. The points W, X, Y and Z relate to the positions as illustrated by the diagrams (a). (b). (c) and (d). respectively. By this analysis, it is clear that the main axis of the beam rotates throu h 360 degrees three times while the lens mechanicallv rotates through 360 degrees once.

The operation of the system employing the lens of Fig. 4 can be better understood with particular reference to Fig. 6. In the diagrams (a) through (2) the lents of Fig. 4 is schematically illustrated by the central wave guide elements A, B and C (perpendicular to their re-= spective central radii) abstracted from their respective sectors and disposed substantially in the form of an equilateral triangle as shown.

In the diagram (a) the element A is positioned at 0 degrees with respect to the electric vector 15 and effects a phase change p of n degrees of the energy that passes through it. Since the elements B and C are symmetrically disposed about the horizontal axis there exists no tendency for the main axis of the resultant beam to be deflected up or down. The elements B and C effect phase changes a and (p equal to .2511 degrees, respectively. Then (p --(p equals a which equals .75n degrees. Thus, the main axis of the resultant beam is directed to the left.

In the diagram (b) the element A is shown rotated 30 degrees and accordingly elfects a phase change of the energy passing through it of .75n degrees. The element C is precisely perpendicular to the electric vector 15 and effects zero degrees phase change; thus, p 0 equals go go which equals .7511 degrees. Since the elements A and B are symmetrically disposed about the vertical axis, the main axis of the resultant beam is directed up.

In the diagram (0) the element A is shown rotated 60 degrees with respect to the electric vector 15 and, accordingly, the element B effects n degrees phase change. The elements A and C eflect .25n degrees phase change, respectively, and the main axis of the resultant beam is directed to the right.

In the diagram (d) the element A is shown rotated degrees with respect to the electric vector 15 and eifects zero degrees phase change. The elements B and C effect .7511 degrees of phase change; hence, the resultant beam is directed down. In the diagram (2) the element A is shown rotated degrees with respect to the electric vector 15. The element C is positioned such that the operation of the system as described with respect to the element A above is repeated.

In the diagram the locus of the main axis of the resultant beam due to the rotation of the lens through an angle of 120 degrees is illustrated. The points W, X, Y and Z relate to the positions as illustrated by the diagrams (a), (b), (c) and (d), respectively. By this analysis, it is clear that the main axis of the beam rotates through 360 degrees three times while the lens mechanically rotates through 360 degrees once.

From the above descriptions it is to be noted that the systems as described are inherently electrically and mechanically balanced. Since the motor, shaft and lenses may be very light and are mechanically balanced, the physical speed of rotation may be so increased that conical scanning rates may be increased from a typical value of 50 cycles per second to as high as 1,000 cycles or more per second.

The present invention greatly enhances the effectiveness of modern radar techniques as used in the detection and control of supersonic aircraft.

While there has been hereinbefore described What is at present considered preferred embodiments of the invention, it will be apparent that many and various changes and modifications may be made with respect to the embodiments illustrated, without departing from the spirit of the invention. It will be understood, therefore, that all such changes and modifications as fall fairly within the scope of the present invention, as defined in the appended claims, are to be considered as a part of the present Invention.

What is claimed is:

1. An antenna system comprising the combination of a source of plane-polarized electromagnetic energy characterized by an electric vector having a predetermined direction of polarization; a parabolic reflector for directing said energy in the form of a beam; a lens in the form of a grating disk, disposed between said source and said parabolic reflector, having a plurality of wave guide elements disposed in three adjacent 120 sectors with their boundary conductors parallel to the central radius of their respective centers providing gratings effecting predetermined refractions of said energy in accordance with the relative positions of said elements and said plane of polarization of said polarized energy to efiect the rotation of the center of radiation about an axis; means directing said energy through said lens with said plane of polarization parallel to the plane of said elements; and means for rotating said lens, elfecting a resultant conical scanning beam at three times the frequency of rotation of said lens.

2. An antenna system comprising the combination of a source of plane-polarized electromagnetic energy characterized by an electric vector having a predetermined direction of polarization; a parabolic reflector for directing said energy in the form of a beam; a lens in the form of a grating disk, disposed between said source and said parabolic reflector, having a plurality of wave guide elements disposed in three adjacent 120' sectors with their boundary conductors perpendicular to the central radius of their respective centers providing gratings effecting predetermined refractions of said energy in accordance with the relative positions of said elements and said plane of polarization of said polarized energy to effect the rotation of the center of radiation about an axis; means directing said energy through said lens with said plane of polarization perpendicular to the plane of said elements; and means for rotating said lens, effecting a resultant conical scanning beam at three times the frequency of rotation of said lens.

3. A refractive antenna system, comprising the combination of: a source of plane-polarized, electromagnetic energy characterized by an electric vector having a predetermined direction of polarization; a reflector for directing said energy in the form of a beam; a lens, disposed between said source and said reflector, having a plurality of elements for efiecting predetermined refractions of said energy in accordance with the relative positions of said elements and said direction of polarization of said polarized energy, said elements being disposed in adjacent sectors for efiecting the rotation of the center of radiation about an axis; means for directing said energy through said lens with said plane of polarization parallel to the plane of said elements; and means for rotating said lens to eifect a resultant conically scanning beam at three times the frequency of rotation of said lens.

4. A refractive antenna system, comprising the combination of: a source of plane-polarized electromagnetic energy characterized by an electric vector having a predetermined direction of polarization; a parabolic reflector for directing said energy in the form of a beam; a lens, in the form of a grating disk, disposed between said source and said parabolic reflector, having a plurality of wave guide elements disposed in adjacent 120 sectors, each sector effecting a different predetermined refraction of said energy in accordance with the relative positions of said elements and said plane of polarization of said energy, for effecting the rotation of the center of radiation about an axis; means for directing said energy through said lens with said plane of polarization parallel to the plane of said elements; and means for rotating said lens to eifect a resultant conically scanning beam at three times the frequency of rotation of said lens.

References Cited in the file of this patent UNITED STATES PATENTS