US2821707A

US2821707A - Directional antenna

Info

Publication number: US2821707A
Application number: US428933A
Authority: US
Inventors: Jesse L Butler
Original assignee: Sanders Associates Inc
Current assignee: Lockheed Corp
Priority date: 1954-05-11
Filing date: 1954-05-11
Publication date: 1958-01-28
Anticipated expiration: 1975-01-28

Description

SEARC siesi we Jan. 28, 1958 J. L. BUTLER DIRECTIONAL ANTENNA 3 Sheets-Sheet l Fi1ed.May 11, 1.954

Fig.4

' Jesse L. Butler 7 INVENTOR.

- Attorney Jam'zs, 1958 J. L. BUTLEF? 2,821,707

DIRECTIONAL ANTENNA Filed May 11, 1954 s Sheets-Sheet 2 Jesse L Butler mmvron.

Jam. 28, 1958 J. L. BUTLER 2,821,707

DIRECTIONAL ANTENNA,

Filed May 11, 1954 5 Sheets-Sheet 5 RIGHT DOWN Fig. 6

Jesse L. Butler INVENTOR.

Attorney United States Patent DIRECTIONAL ANTENNA Jesse L. Butler, Nashua, N. H., assignor, by mesne assignments, to Sanders Associates, Inc., Nashua, N. H., a corporation of Delaware Application May 11, 1954, Serial No. 428,933

6 Claims. (Cl. 343-756) 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.

In 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 therefor 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 having variable transparency to electromagnetic energy.

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 accordance with the invention, there is provided a directional antenna system. The system includes a source of plane-polarized mircrowave energy. Means are provided for direction of the energy along an axis. A lens is disposed in the path of the energy in a plane substantially perpendicular to the axis and has three elements varying in transparency to the energy in accordance with their angular positions in the plane. Means are also provided for rotating the lens about the axis. The elements are so disposed as to cause the resultant beam of energy to rotate about the axis at a frequency three times that of the 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;

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

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

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

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

Referring now in more detail to the drawings and with particular reference 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 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 plantom lines 6. This rotation of the beam 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 directed through the lens 8 and is 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 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 a metallic member 13 has wave guide slots 14 formed therein. The slots 14, as shown, are less than a half-Wave length wide at the operating frequency, for example, 10 kilomegacycles, and much greater than a half-Wave length long. The wave guide slots are disposed substantially degrees apart as shown.

In the lens as shown in Fig. 4 the construction is similar to the embodiment of Fig. 3 with the exception that the wave guide slots 18 are disposed susbtantially in the form of an equilateral triangle, as shown.

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 slot is completely opaque to the energy that would pass through it if the slot is parallel to the electric vector 15, and is completely transparent when the slot is perpendicular to the electric vector 15. In particular, the degree to which such a wave guide slot is transparent to the energy tending to pass through it may be expressed:

W=k sin 0 In the above expression, W equals the electromagnetic energy passing through the wave guide slot having an electric vector parallel to the electric vector 15. The factor k is a constant and the angle 6 equals the angle between the Wave guide slot 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 360 degrees effects three rotations of the resultant beam of energy as will be presently shown. In the diagrams (a) through (e), the lens of Fig. 3 is schematically illustrated by the central wave guide slots A, B and C disposed such that the angles AOB, BOC and COA equal 120 degrees, as shown. The effect of decreasing the transparency of each slot is to cause the resultant beam to be refracted in the direction of the slots exhibiting maximum transparency.

Thus, in the diagram (a) the slot A is positioned at 0 degree with respect to the electric vector and permits zero units of energy pass through it. In accordance with the expression for W above, the slots B and C each permit .75k unit of energy to pass, or a total of 1.5k units. Since the slots 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 slots B and C are disposed below the common center 0, the principal 3 axis of the resultant beam will be directed down as at 6 in Fig. 1.

In the diagram (b) the slot A has been rotated 30 degrees. The slot C is then precisely perpendicular to the electric vector and permits it units of energy to pass. The slots A and B each permit .25k unit of energy to pass and are symmetrically disposed about the horizontal axis. In this case, the main axis of the resultant beam will be directed to the left.

In the diagram (c) the slot A has been rotated 60 degrees with respect to the electric vector 15. The slot B is precisely parallel to the electric vector 15 and accordingly permits unit of energy to pass through it. The slots B and C each permit .75]: unit of energy to pass and consequently the main axis of the resultant beam is directed up.

In the diagram (d) the slot A is shown rotated 90 degrees with respect to the electric vector and accordingly permits k units of energy to pass through it. The slots B and C each permit .25k unit of energy to pass; thus, the main axis of the resultant beam is to the right. In the diagram (e) the slot A is shown rotated 120 degrees with respect to the electric vector 15. The slot 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 (f) 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.

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 (e) the lens of Fig. 4 is schematically illustrated by the wave guide slots A, B and C disposed substantially in the form of an equilateral triangle, as shown. A

In the diagram (at) the slot A is positioned at 0 degree with respect to the electric vector 15 and is opaque to electromagnetic energy tending to pass through it. In accordance with the expression for W above, the slots B and C each permit the passage through them of .75k unit of energy. The slots B and C, being symmetrically disposed about the horizontal axis, exhibit no tendency to direct the main axis of the resultant beam up or down. Since the centers of the slots B and C are disposed to the left of the vertical axis, the main axis of the resultant beam is directed to the left.

In the diagram (1)) the slot A has been rotated degrees and accordingly permits .25k unit of energy to pass through it. The slot C is precisely perpendicular to the electric vector 15 and is therefore completely transparent to the energy. The slot B also permits .25k unit of energy to pass through it. Since the slots A and B are symmetrically disposed about the vertical axis and the energy passing through the slot C is controlling, the main axis of the resultant beam is directed up.

In the diagram (C) the slot A has been rotated 60 degrees with respect to the electric vector and accordingly permits .75k unit of energy to pass through. By symmetry, the slot C also permits .75k unit of energy to pass through it. The slot B is precisely parallel to the electric vector 15 and is therefore opaque to the energy. Since the centers of the slots A and C are disposed to the right of the vertical axis, the main axis of the resultant beam is directed to the right.

In the diagram (d) the slot A has been rotated 90 degrees with respect to the electric vector and permits K units of energy to pass through it. The slots B and C each permit .25k unit of energy to pass through them. Since the slot A is controlling, the main axis of the resultant beam is directly down.

In the diagram (e) the slot A has been rotated degrees with respect to the electric vector 15. The slot C is positioned such that the operation of the system as de scribed with respect to the slot A above is repeated.

In the diagram (f) 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 lensmechanically rotates through 360 degrees once.

From the above descriptions it is to be noted that the systems as described are inherently electrically and mechanically symmetrical. 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 1,0000 cycles or more per second.

Although the invention as described is related to the propagation of radio frequency electromagnetic energy, it is clear that the principles of the invention are readily applicable to other electromagnetic radiations. For example, the construction of an analogous system employing a polarized light source and polarized lenses is obvious.

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. In a directional antenna system the combination of a source of plane-polarized microwave energy; means for directing said energy along an axis; a lens disposed in the path of said energy in a plane substantially perpendicular to said axis and having three elements varying in transparency to said energy in accordance with their angular positions in said plane; and means for rotating said lens about said axis, said elements being so disposed as to cause the resultant beam of said energy to rotate about said axis at a frequency three times that of the rotation of said lens.

2. In a directional antenna system the combination of a source of plane-polarized microwave energy; means for directing said energy along an axis; a metallic lens disposed in the path of said energy in a plane substantially perpendicular to said axis and having three elongated slots formed therein with one dimension in said plane less than one-half of one wavelength long at the highest operating frequency of said antenna, said slots varying in transparency to said energy in accordance with their angular positions in said plane; and means for rotating said lens about said axis, said slots being so disposed as to cause the resultant beam of said energy to rotate about said axis at a frequency three times that of the rotation of said lens.

3. In a directional antenna system the combination of a source of plane-polarized microwave energy; means directing said energy along an axis; a lens disposed in the path of said energy in a plane substantially perpendicular to said axis and having three elongated waveguide elements with one dimension in said plane less than one-half of one wavelength long at the highest operating frequency of said antenna, said elements varying in transparency to said energy in accordance with their angular positions in said plane; and means for rotating said lens about said axis, said elements being so disposed as to cause the resultant beam of said energy to rotate about said axis at a frequency three times that of the rotation of said lens.

4. In a directional antenna system the combination of a source of plane-polarized microwave energy; means directing said energy along an axis; a circular metallic lens disposed in the path of said energy in a plane substantially perpendicular to said axis and having three elongated slots formed therein with one dimension in said plane less than one-half of one wavelength long at the highest operating frequency of said antenna, said slots being radially disposed at substantially equal angles and varying in transparency to said energy in accordance with their angular positions in said plane; and means for rotating said lens about said axis to cause the resultant beam of said energy to rotate about said axis at a frequency three times that of the rotation of said lens.

5. In a directional antenna system the combination of a source of plane-polarized microwave energy; means directing said energy along an axis; a metallic lens disposed in the path of said energy in a plane substantially perpendicular to said axis and having three elongated slots formed therein with one dimension in said plane of each slot less than one-half of one wavelength long at the highest operating frequency of said antenna, said slots being disposed substantially in the configuration of an equilateral triangle coaxial with said axis and varying in transparency to said energy in accordance with their angular positions in said plane; and means for rotating said lens about said axis to cause the resultant beam of said energy to rotate about said axis at a frequency three times that of the rotation of said lens.

6. In a directional antenna system the combination of a source of plane-polarized microwave energy; means directing said energy along an axis; a metallic lens disposed in the path of said energy in a plane substantially perpendicular to said axis and having three elongated slots formed therein with one dimension in said plane of each slot less than one-half of one wavelength long at the highest operating frequency of said antenna, said slots varying in transparency to said energy in accordance with their angular positions in said plane; a parabolic reflector adapted to form said energy in a beam; and means for rotating said lens about said axis, said slots being so disposed as to cause the resultant beam of said energy to rotate about said axis at a frequency three times that of the rotation of said lens.

References Cited in the file of this patent UNITED STATES PATENTS