US2848715A - Conical scanning antenna - Google Patents

Description

Aug. 19, 1958 J. L. BUTLER 2,843,715

CONICAL SCANNING ANTENNA Filed May 19, 1954 2 Sheets-Sheet 1 Jesse L. Butler mwzzvroze At'torney Aug. 19, 1958 J. L. BUTLER 2,848,715

CONICAL SCANNING ANTENNA Filed May 18, 1954 2 She'ets-Sheet 2 DOWN v E k l8 UP LEFT E (c) LEFT RIGHT l8 DOWN E UP Fig. 4

Jesse L. Butler INVENTOR.

CONICAL SCANNING ANTENNA Jesse L. Butler, Nashua, N. H., assignor, by mesne assignments, to Sanders Associates, Incorporated, Nashua, N. H., a corporation of Delaware Application May 19, 1954, Serial No. 430,924

10 Claims. (Cl. 343763) The present invention relates to the art of radiating electromagnetic energy. More particularly, this invention relates to conical scanning antenna systems such as are used in certain systems of radar.

In the prior art various systems have been proposed for developing a conical beam of electromagnetic energy by causing the beam to rotate about the axis of the antenna system. This type of beam rotation is generally known as conical scanning in the art. It is to be distinguished from the azimuth and elevation scanning functions of the system as awhole.

Conical scanning systems as employed in the prior art are usually characterized by essentially unbalanced mechanical rotational systems. The speed which conical scanning requires in the most modern radar techniques has been unattainable by such systems.

In my copending application Serial Number 402,556, dated January 6, 1954, the illuminator as shown in the preferred embodiment herein is described.

It is, therefore, an object of the present invention to provide an improved, conical scanning, antenna system capable of ultra-high-speed, conical scanning.

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

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

In accordance with the invention, there is provided an antenna having an electrically non-conductive rod forming a dielectric radiator. Surface electromagnetic energy waves are propagated along the surface of the rod and sub-surface electromagnetic energy waves are propagated below the surface of the rod. A reflecting means is disposed at the end of the rod for causing the surface Waves and the sub-surface waves to be reflected in phase. An annular member having three radiating elements with their centers disposed substantially 120 apart is carried by the rod for radiating the waves.

In accordance with the invention, there is further provided a conical scanning antenna. The antenna includes a source of plane-polarized, electromagnetic energy having a path of propagation. An annular radiating member is disposed coaxial with the path and has three radiating elements circumferentially disposed at equal angles in a plane perpendicular to the path. Means are provided for effecting relative rotation between the direction of polarization of the energy and the member. Excitation of the radiating member by the energy develops an &- set beam of the energy which rotates about the path at a multiple of the frequency of rotation of the direction of polarization to produce a rotating beam of the energy and provide the conical scanning antenna.

In a particular embodiment there is provided an antenna comprising a source of electromagnetic energy for directive radiation and reception of electromagnetic waves. An electrically conductive reflecting means in the form 2,848,715 Patented Aug. 19, 1958 of a paraboloid provides directivity of radiation and reception. An illuminator for the paraboloid reflector is mounted axially and connected through its center. The illuminator comprises a nonconductive rod forming a dielectric radiator along the surface of which and through which are propagated the energy waves. An electrically conductive tube surrounds part of the rod adjacent one end thereof and provides a guide for the energy wave. Adjacent the opposite end of the rod and substantially at the focal point of the paraboloid, a reflector is provided having conductive surfaces perpendicular to and surrounding the rod. A cylindrical portion at the center of the perpendicular surface surrounds the end of the rod. An annular member is carried by the rod adjacent the perpendicular surface. The member comprises three radiating elements having their centers disposed substantially degrees apart. The novel antenna system disclosed in this specification is related to systems disclosed in concurrent applications Ser. Nos. 432,740 and 490,649 by the same inventor. The present application is directed, in general, to an antenna system utilizing a novel annular radiator. The application Ser. No. 490,649 is directed, in general, to an antenna system in which the electric vector of the electromagnetic energy is rotated with respect to a stationary annular radiator by means of a rotating antenna element. The application Ser. No. 432,740 is, in general, directed to the broad concept of obtaining high-speed scanning by utilizing a rotating electric vector in combination with a three element radiating member and, in particular, to the combination of an electromagnetic gyrator to effect rotation of the electric vector with respect to the annular radiator.

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 perspective view of a radiating member as used in the embodiment of Fig. 2; and

Fig. 4 is a series of diagrams illustrating the operation of the invention.

Referring now in more detail to the drawings and with particular reference to Fig. 1, an antenna system indicated at 1, is illustrated 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 illustrated. The rotating or circular motion of the beam axis 3 is indicated by the path 5. The extreme lower position of the beam is illustrated by the phantom 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 dielectric radiator 7 (for example, a polystyrene rod) developing a beam of electromagnetic energy for the system. A transmitter 8 is coupled to the radiator 7 through a cylindrical wave guide 9. The radiator 7 is divided into two sections, 7a and 7b, coupled together as shown. The section 7b is connected to a reflector 10 which reflects energy in the direction of a paraboloidal reflector 11. The paraboloid forms the energy into a beam that is radiated in the direction as shown at 12. A motor 13 mechanically coupled through a shaft 14 to the reflector 10 causes the section 7b and the members carried by it to rotate. A metallic annular member 15 having three slots formed therein is mounted on the radiator section 7b as shown. The member 15 is located substantially at the focal point of the paraboloid 11. The reflector 11 provides support for the motor assembly 13 through the support rods 16, connected as shown.

Referring now to Fig. 3 the radiating member 15 comprises three radiating elements'16,- a half-wave length long at the operating fi'equency, for example kilomegacycles, Theslots 17 are substantially a quarterwavelength deep at the operating frequency, as shown. The slotsfunction electrically like resonant quarter-wave length-transmission line sections and, therefore, present a very high impedance across the opening although they are apparently shorted at the opposite ends. It is to be noted that the centers of each of the elements 16 and of each of the slots 17 are respectively disposed substantially 120 degrees apart.

Theoperation of the system can be better understood with particular reference to Fig. 4. For purposes of analysis, electromagnetic energy incident upon the member may be assumed to be plane polarized such that its electric vector 18 or direction of polarization is veras described with respect tical as indicated. The energy radiated by the elements A, B and C of the member 15 maybe analyzed with respect to lines tangent thereto at their respective centers. A dipole (half-wave length element) radiates a maximum amount of energy when it is parallel to the direction of polarization or the electric vector, and a minimum or substantially zero when it is perpendicular to the electric vector. In particular, such an element radiates energy in accordance with the expression:

In the above expression, W equals the electromagnetic energy radiated by the dipole having a direction of polarization or electric vector parallel to the electric vector 18; k is a constant and 0 isthe angle between the dipole element and the electric vector 18. V

In this case the dipole elements are in the form of arcs of a circle and the angle 0 may be taken as the angle between the line tangentto its center and the electric vector. For the elements A, B and C the angles will be taken with respect to their tangent lines as shown.

Of particular significance in the present invention is the characteristic of the radiating member 15, whereby a single rotation of the member 15 through 360 degrees eifects three rotations of the resultant beam of energy as will be presently shown. In the diagrams a through c the tangent lines of the respective elements are disposed substantially in the form of an equilateral triangle as shown; hence, the elements are disposed substantially 120 degrees, apart. The effect of increasing the radiation of the dipole element is to cause the resultant beam to be radiated in the direction of the element exhibiting maximum radiation.

In'the diagram a the element A is positioned at zero degrees with respect to the electric vector 18 and therefore radiates k units of energy. The elements B and C radiate .25k units of energy in accordance with the expression for W above. Since the elements B and C are symmetrically disposed about the horizontal axis and the element A radiates the larger amount of energy to the right of the vertical axis, the resultant beam is directed to the right. a

In the diagram 12 the element A has been rotated 30 degrees. The element A then radiates .75k units of energy and in symmetry the element B also radiates .751: units of energy. The element C being perpendicular to the electric vector 18 radiates substantially zero energy. Since the radiation centers of the elements A and B are symmetrically disposed about the vertical axis and below the horizontal axis, the resultant beam is directed downward. v a p In the diagram 0 the element A has been rotated 60 degrees with respect to the electric vector 18. The elements A and C accordingly radiate .25k units of energy, while the element B, being parallel to the electric vector 18, radiates k units of energy. Since the element B is controlling, the main axis of the resultant beam will be directed to the left. I p

"-ln' th'e diagram d the'e'lement A is shown rotated'90 degrees with respect to the electric vector 18 and radiates substantially no energy. The elementsB and C radiate a total of 1.5k units of energy and since their radiation centers are displaced above the center 0, theresultant beam is displaced up as shown at 3 in Fig. 1. In the diagram 2 the element A is shown rotated 120 degrees with respect to. the electric vector 18. The element C is now positioned such that the operation of the system 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 radiating member 15 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 radiating member 15 mechanically rotates through 360 degrees one time.

' From the above description it is to be noted that the system as described is inherently electrically and mechanically balanced. Since the motor, shaft and annular radiating member 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.

While applicant does not intend to be limited to any particular parameters with respect to shape, size, speed or distances in the embodiment of the invention just described, the following relationships between the parts of the antenna system have been found to be particularly suitable. The shaft 7 has a diameter of .625 inch and the radiating member 15 is disposed such that the end facing the exposed surface of the reflector 10 is displaced .25 inch therefrom. The maximum outer diameter of the reflector 10 is 2 inches and the outer diam eter of the cylindrical wave guide 9 is .75 inch. The.

motor 13 is a synchronous motor and operates with a 400 cycle, 150 volt input at a typical speed of 6,000 R. P. M. to produce a conical scanning rate of 300 cycles per second. The paraboloid has the general form of y =4fx, where f is equal to the focal length. The ratio between the focal length and the diameter at maximum opening is chosen to be .3 inch. Thus, if the desired maximum aperture is 20 inches the focus point of the parabola will be displaced 6 inches from its center.

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 those changes and modifications as fall fairly within the scope of the present invention, as defined in the surface Waves to be reflected in phase; and an annular member carried by said rod for radiating said waves comprising three radiating elements having their centers disposed substantially degrees apart.

' 2. An antenna comprising an electrically nonconductive rod forming a dielectric radiator for propagating,

a o g he ?in???EF F P ,fi eetrem etiaea rsy. waves and below the surface thereof sub-surface electromagnetic energy waves; a reflecting means at the end of said rod for Causing said surface Waves and said subsurface waves to be reflected in phase; an annular membercarried by said rod for radiating said waves comprising three radiating elements having their centers disposed substantially 120 degrees apart; and a paraboloidal reflector adjacent said member for forming said radiated waves into a beam.

3. In a conical scanning antenna, the combination of a source of plane-polarized microwave energy; means for directing said energy along an axis; a rotatable annular radiating member disposed in a plane substantially perpendicular to and coaxially with said axis in the path of said energy and having three elements circumferentially disposed 120 apart varying in degree of radiation of said energy in accordance With their angular positions relative to the direction of polarization of said energy; and means for rotating said member about said axis to cause the resultant beam of said energy to rotate about said axis and effect said conical scanning at a frequency three times i that of the rotation of said member.

4. In a conical scanning antenna, the combination of a source of plane-polarized microwave energy; means for directing said energy along an axis; a rotatable annular radiating member disposed coaxially with said axis in the path of said energy and having formed therein three circumferential slots disposed 120 apart, the degree of radiation of said energy varying in accordance with the angular positions of said slots relative to the direction of polarization of said energy; and means for rotating said member about said axis to cause the resultant beam of said energy to rotate about said axis and eifect said conical scanning at a frequency three times that of the rotation of said member.

5. in a conical scanning antenna, the combination of a source of plane-polarized microwave energy; means for directing said energy along an axis; a rotatable annular radiating member disposed coaxially with said axis in the path of said energy and having formed therein three nonradiating circumferential slots disposed 120 apart and axially substantially one-quarter of a wavelength long at the operating frequency, the degree of radiation of said energy varying in accordance with their angular positions relative to the direction of polarization of said energy: and means for rotating said member about said axi to cause the resultant beam of said energy to rotate about said axis and effect said conical scanning at a frequency three times that of the rotation of said member.

6. In a conical scanning antenna, the combination of a source of plane-polarized microwave energy; means for directing said energy along an axis; an elongated, rotatable shaft disposed along said axis; a rotatable annular radiating member carried by said shaft and disposed coaxially with said axis, said member having three radiatin elements circumferentially disposed 120 apart and varying in degree of radiation of said energy in accordance with their angular positions relative to the direction of polarization of said energy; means for rotating said shaft about said axis; and a parabolic reflector adjacent said member, said shaft passing centrally therethrough, to form a beam of said energy whereby rotation of said shaft and member about said axis causes said beam to rotate about said axis and effect said conical scanning at a frequency three times that of the rotation of said member.

7. A conical scanning antenna comprising the combination of a source of plane-polarized microwave energy; an electrically non-conductive, rotatable, circular rod Cal - 6 forming a dielectric radiator along the surface of which are propagated sub-surface waves to direct said energy along an axis; a reflecting means at the end of said rod for causing said surface waves and said sub-surface waves to be radiated in phase; an angular member carried by said rod and disposed coaxially with said axis comprising three radiating elements transversely disposed apart and varying in degree of radiation of said energy in accordance with their angular positions relative to the direction of polarization of said energy; means for rotating said rod and member about said axis; and a parabolic reflector adjacent said member, said rod passing centrally therethrough, to form a beam of said energy whereby rotation of said rod and member about said axis causes said resultant beam to rotate about said axis and effect conical scanning at a frequency three times that of the rotation of said member.

8. In an antenna a radiating member comprising an annular metallic member; three like metallic radiating elements having the configuration of arcs less than 120 long extending axially from said member, said elements being circumferentially disposed 120 apart; and like slots substantially one-quarter wave length long at the operating frequency formed between the ends of said radiating elements and said member.

9. A conical scanning antenna comprising: a source of plane-polarized microwave energy; means of directing said energy along an axis including an elongated shaft having a rotatable section and a non-rotatable section coupled to said source; an annular radiating member encircling said rotatable section, said member having three radiating elements circumferentially disposed 120 apart and varying in degree of radiation of said energy in accordance with their angular positions relative to the direction of polarization of said energy; a parabolic reflector having said non-rotatable section forming centrally therethrough; and means for rotating said rotatable section including brackets mounted on the concave side of said reflector for supporting said rotatable section as an elongated extension of said non-rotatable section, whereby rotation of said rotatable section forms a beam in said reflector which rotates about said shaft to effect conical scanning at a multiple of the speed of said rotatable section.

10. A conical scanning antenna, comprising: a source of plane-polarized, electromagnetic energy having a path of propagation; an annular radiating member coaxial with said path and having three radiating elements circumferentially disposed at equal angles in a plane perpendicular to said path; and means for effecting relative rotation between the plane of polarization of said energy and said member, whereby excitation of said radiating member by said energy develops an off-set beam of said energy which rotates about said path at a multiple of the frequency of said rotation, thereby producing a rotating beam of said energy to provide said conical scanning antenna system.

References Cited in the file of this patent UNITED STATES PATENTS 2,423,508 Leek July 8, 1947 2,531,455 Barrow Nov. 28, 1950 2,539,657 Carter Jan. 30, 1951 OTHER REFERENCES Antennas (Kraus), published by McGraW-Hill (New York), 1950 (page 429 relied on).

Images