US3568208A - Varying propagation constant waveguide - Google Patents

Abstract

A phased array waveguide antenna system having a rotatable member with a plurality of discontinuities to adjust for the electrical parameters disposed along the longitudinal axis of the waveguide feed line. The rotatable member may be rotated continuously at varying rates of speed of, for example, one scan per second and pulsed as well as continuous energy signals may be propagated.

Description

ilnited States Patent 7 2] Inventors Burrell R. Hatcher;

Troy E. Plunk, Bedford, Mass. I {21] Appl. No. 769,563 [22] Filed Oct. 22, 1968 {45] Patented Mar. 2, 1971 [73] Assignee Raytheon Company Lexington, Mass.

[54] VARYING PROPAGATION CONSTANT WAVEGUIDE 4 Claims, 9 Drawing Figs.

[52] U.S. Cl. 343/768, 343/771, 343/777, 343/785, 343/854 {51] Int. Cl ..H0lq 13/ i0, H01q 13/00, l-lOlq 3/21 [50] Field of Search 343/768, 771, 785, 854; 333/31 [56] References Cited UNITED STATES PATENTS 2,594,409 4/1952 Feldman 343/768X 2,596,492 5/1952 Lindenblad 343/768 2,604,594 7/1952 White 343/768 2,624,003 12/1952 Iams 343/785X 2,699,501 l/l955 Young 343/768 2,704,327 3/1955 Chandler 343/768 3,311,917 3/1967 Thourel 343/768X 3,348,227 10/1967 Rolfs 343/768 3,413,640 11/1968 Freeman 343/771 Primary Examiner-Herman Karl Saalbach Assistant Examiner-T. Vezeau Att0rneys--- Harold A. Murphy, Joseph D. Pannone and Edgar O. Rost ABSTRACT: A phased array waveguide antenna system having a rotatable member with a plurality of discontinuities to adjust for the electrical parameters disposed along the longitudinal axis of the waveguide feed line. The rotatable member may be rotated continuously at varying rates of speed of, for example, one scan per second and pulsed as well as continuous energy signals may be propagated.

PATENTED m 2|97l SHEET 2 [IF 3 F/G. 6A

FIG. 7

VARYING PROPAGATION CONSTANT WAVEGUIDE BACKGROUND OF THE INVENTION The present invention relates to phased array antenna systems which have the capability for scanning in one or more than one angular coordinate sometimes referred to as volumetric scanning. In such systems a considerable number of phase shifters are required coupled to each antenna element and the transmitter or receiver, depending on whether an active or passive system is provided. Another application involves antenna arrays where conformal mounting is desired directly to the outer wall of a vehicle such as a missile, aircraft or vessel. In such applications a specific fixed sector may be scanned by each antenna element for guidance or communication of other relevant information in what is referred to as quadrant scanning. Further, in other applications end fire patterns for the radiation or reception of electromagnetic energy are desired with antenna elements being controlled by individual phase shifters. In series fed antenna array alignment of the radiators, the energy may be transmitted from one end of the propagation line or it may be fed from the center out toward each end.

The slotted waveguide line having the transverse radiators represents an illustrative structure for series propagation and is commonly employed in the conformal mounting type of planar phased array antennas. The slots are of a predetermined dimension as well as the spacings therebetween and the antenna beam pattern radiates in a plane normal to the feed line axis. Commonly in such systems a rather narrow bandwidth is provided. For the series distributed system with discrete phase shifters for each element the resolution of the design is complicated by the losses encountered in each element of the array radiating the beam. This loss is additive in each section and therefore for the series array a loss of L in the first array element will effectively become 2L when the second antenna array element is encountered. This additive effect continues throughout the array so that new and improved means of the forming of the beam radiation pattern, particularly without individual phase shifters seems highly desirable.

In the prior art a means for the varying of the phase velocity of the waves propagating down a section of antenna waveguide has been effectively provided by rotatable rod members of a dielectric material distributed throughout the line length. A rather high dielectric constant material supported within a dielectric rod of substantial length has been utilized in certain antenna systems for the provision of a quadrant scanning beam pattern. Such a structure will reduce the number of components substantially; however, the utilization of dielectric materials within the waveguide has left a good deal to be desired due to inhomogeneous anisotropic materials. The high losses associated with the materials together with the relatively high cost creates a need for an improved structure for the formation of the antenna beam radiation pattern.

Further, utilization of a rotatable dielectric member has resulted in relatively small variations in the propagation constant in certain strip transmission line configurations.

SUMMARY OF THE INVENTION In accordance with the teachings of the present invention a slotted waveguide antenna is provided with a rotatable conductive member disposed along the longitudinal axis for varying the propagation constant characteristics of the line. The conductive member is provided with periodic discontinuities extending from opposing surfaces for varying the distributed capacitance and inductance characteristics of the propagation path. Control of the length and depth of such discontinuities will vary the distributed circuit in a reliable and reproducible manner for radiation of the desired antenna beam pattern. Rotation of the conductive member preferably embedded in a dielectric material for additional support will vary the effective parameters of the transmission line thereby varying the propagation constant. Both pulsed and continuous electromagnetic wave energy signals may be propagated and the rotatable member may be continuously rotated at any desired rate of speed. In one revolution a scanning pattern of two complete cycles may be realized, each intermediate angle being achieved four times. Control of the propagation characteristics in one coordinate of the antenna beam pattern coupled with phase shifting of the propagated energy in a sector pattern will result in a highly efficient phased array antenna system for many applications. Prior art difficulties with dielectric members in the applicable antenna systems for varying the propagation constant characteristics have been appreciably reduced, particularly in the series fed array antennas.

BRIEF DESCRIPTION OF THE DRAWINGS the invention partly in section;

FIG. 2 is a vertical cross-sectional view of the illustrative embodiment of the invention;

FIG. 3 is a schematic diagram of an exemplary rotatable conductive member of the invention;

FIG. 4 is a schematic drawing of the equivalent circuit of the rotatable member shown in FIG. 31;

FIG. 5 is a pictorial representation of a sector scanning beam pattern;

FIGS. 6 and 6A are diagrammatic representations illustrative of the conductive member in mutually perpendicular positions;

FIG. 7 is a pictorial representation illustrative of a variety of antenna radiator elements; 5

FIG. 8 is a diagrammatic representation of an embodiment of the invention for strip transmission line;

and FIG. 9 is a perspective view ofa portion of a phased array antenna system conformally mounted on an airborne vehicle.

7 DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the illustrative embodiment comprises an electromagnetic energy transmission line including a section of rectangular waveguide 10 having an array of slot radiators 11 in top wall 12. The slots may be filled with a dielectric material 13 to assist in matching of impedances between the propagated energy in air and within the waveguide. The antenna beam for this slot configuration radiates normal to the array antenna longitudinal axis. Waveguide 10 also defines narrow sidewalls 14 which along with the remaining broadwall 12 provides a closed end reflector. The slots 11 it will be noted may vary progressively in width along the longitudinal axis 15 with the result that radiator 11a is wider relative to radiator llb. In the illustration the narrower radiators will be disposed commencing at the transmitter end of an active system or in the case of a passive system the receiver end. By this means a tapered amplitude distribution along the array may be obtained. The orientation and dimensions of the slot radiators as well as the overall system and waveguide line parameters are all within the knowledge of skilled artisans and need not be elaborated on in the present description. The embodiment of the invention is shown as a planar conductive member 16 rotatably mounted along the waveguide longitudinal axis 15. The overall length of the embodiment is substantially longer than the width dimension. Member 16 is embedded in a low dielectric constant material 17. for support and rigidity in a composite circular configuration.

Referring now to FIGS. 2 and 3, therotatable conductive member 16 comprises a plurality of periodic discontinuities id teristics. Any highly conductive metal such as copper or brass is preferred for the member 16. The alternate discontinuities and remaining wall portions or paddlelike members 19 are thereby oriented along the overall length of the structure.

In accordance with the distributed circuit concept of the invention the propagation constant where L is the inductance and C the capacitance. The phase between any two points along the waveguide section separated by dimension X is then determined by X times ,8. In FIG. 3 the region denoted a or the paddle portion 19 will provide the capacitance parameter while the region b or the reduced portion determines the inductance characteristics to the first order effects. The discontinuities l8 and paddle members 19 have been shown as being of substantially equal dimension for a particular application in an exemplary embodiment. It is within the scope of the invention to have the discontinuities vary in dimension in accordance with any desired distributed inductance and capacitance characteristics along the length of the conductive member 16. In lieu of a separate planar conductive member defining the discontinuities the entire assembly may be fabricated by deposition of a layer of a metallic material on a dielectric substrate in the configuration desired and the covering of this layer by another layer of the dielectric material if desired for support. Further, the edges of the discontinuities extending towards the reduced portion 20 may be gradually tapered as shown by the dotted lines 21 to provide a smoother impedance transition where required. It may also be desired in specific applications to shorten some paddle members 19 with respect to others and thereby expose less conductive material in certain areas than in others. Additionally, the discontinuities 18 may be provided on only onehalf of the conductive member so as to be asymmetrical instead of extending from opposing edges to be symmetrically disposed with respect to the axis 15. Many variations and combinations therefore may be practiced within the purview of the invention.

In the exemplary embodiment schematically shown in FIG. 3 for a member having an overall length of 7.700 inches in an X-band array antenna system the dimension of each of the discontinuities 18 was .220 inches. This value results in dimension c for the paddle members 19 of a similar value of .220 inches. The height of the member 16 for dimension c was .230 inches and the resultant reduced portion 20 had a value for dimension b of .040 inches. The conductive member 16 was embedded in a dielectric material 17 such as that commercially available under the trade name Stycast in the configuration of a rod. The equivalent circuit for the conductive member 16 is shown in FIG. 4. The inductances 31 of the member 16 are connected in series and the capacitances 30 are connected in shunt. Upon rotation of these series inductances and shunt capacitances their values differ in each quadrant of a circle and thereby alter the propagation characteristics of the transmission line exciting the antenna radiators.

For the scanning operation rotation of member 16 will be provided by the mechanism illustrated in FIG. 2. A sprocketed actuator 22 driven by a belt or metallic band (not shown for the sake of clarity) is journaled within housing 23. The waveguide section 10 abuts the housing 23 with a hub portion 24 engaging actuator 22 by such structure as a spline and slot or other suitable mechanism. The opposing end of the conductive member 16 is provided with a shaft 25 rotating within bearing 26. A plurality of rotatable members may be driven in tandem and many such groupings may be actuated by a single motor source coupled by interconnecting belts or other drive means.

For a phased array antenna system a conventional phase shifter 27 is coupled to a suitable flange 28 at one end of waveguide section 10. A body of a ferrimagnetic material encircled by magnetic field producing means such as an electric current coil will provide the necessary phase shift characteristics, fixed or variable, of electromagnetic energy, illustratively, emanating from an oscillator 29. Such phase shifters may be employed for example in conformal mounted antenna systems to steer the radiated energy in a second or circumferential direction around the waveguide axis 15. In this manner a particular sector may be covered volumetrically by an individual antenna element over a substantial quadrant. Collectively phase shifting of energy sequentially with a pinrality of antennas each having a plurality of slot radiators will have the same omnidirectional effect as a single rotating dishtype antenna. The described phase shifters may also be desired for passive or receiving antenna systems for guiding or interrogation of an airborne vehicle. In certain applications the phase shifters may be dispensed with where a single command signal is sufficient to illuminate the antenna which is conformally mounted. In the prior art array antenna systems without the rotatable member 16 another set of phase shifters was required for each antenna section or radiator element to provide the beam pattern in another coordinate direction as for example an end fire radiation pattern. Such second sets of phase shifters have been eliminated therefore by the rotatable dielectric rod structures as well as the embodiment of the invention.

Referring next to FIG. 5, a sector scanning radiation pattern is illustrated for the described waveguide antenna. In this view similar structure has been similarly numbered as in FIGS. 1- 3. The sector may be delineated by bracket 32 for an end fire pattern for radiator slot 11. As the rotatable conductive member 16 is rotated through a complete revolution the aforementioned discontinuities will influence the propagated waves in a plurality of positions. In the drawing lobes 33, 34 and 35 represent a pattern with the member 16 illustratively at 0 or perpendicular to the narrow waveguide walls 14 and then at 45 and respectively. This latter position would be parallel to the walls 14 and the line 36 at one end of the bracket 32. In the illustrative embodiment propagating energy at a frequency of approximately 10.125 ,gigahertz and the TE mode the respective waveguide wavelengths resulting in these lobes was measured at 2.26, 2.60 and 3.24 centimeters. It will be evident that the rotatable member discontinuities may be empirically adjusted in actual working embodiments after initial theoretical calculations.

With the appended phase shifters for provision of the second radiating or receiving capability the radiation pattern shown may be provided at an angle 6 to a position indicated by dotted line 37. This scanning pattern then may be oriented circumferentially around the longitudinal axis 15 of the waveguide section 10.

FIGS. 6 and 6A diagrammatically illustrate displacement of the electric field of the propagated energy for varying the propagation constant of the waveguide. In FIG. 6 the electric field intensity is shown by arrows 38 with the direction of the field indicated by the arrow E. After 90 rotation to the position shown in FIG. 6A the electric field intensity distribution is represented by arrows 39. A complete-revolution will therefore result in two scan cycles or variations of the propagation constant.

FIG. 7 illustrates several embodiments of slotted waveguide array antennas which may be utilized with the present invention. Slot radiator 40 represents the transverse or series array hereinbefore discussed. Radiator 41 extends parallel with the rotatable member 16 and will yield a side viewing antenna radiation pattern. This configuration is referred to as the longitudinal or shunt type. Finally, the edge slot 42 in the narrow waveguide wall 14 provides still another variation of the shunt-type antenna radiator element to yield another beam pattern.

In FIG. 8 an embodiment of the invention is diagrammatically shown for strip transmission line. The outer conductors 43 and 44; are separated by a dielectric medium, for example air, in the space defined therebetween designated .5. The center conductor of the overall transmission line will be centrally located between the conductors as at 46. The propagation constant varying member 47 with the. longitudinal discontinuities as hereinbefore described is appended to the center conductor 46 and rotates about the axis of this conductor. In this configuration as in the previously discussed waveguide structure the rotatable member 47 may be supported by means of dielectric material to define a circular rod 48. Rotation of the rotatable member by any conventional means will yield propagation constant variations superior to those with dielectric rod members. The high lossesassociated with the prior art low and high dielectric constant materials will also be reduced.

FIG. 9 is illustrative of a conformally mounted phased array antenna embodiment 50 having a relatively. large number of antenna radiator elements disposed in a circular array to provide for an omnidirectional radiation or receiving pattern. The outer shell of the applicable vehicle is circumferentially provided with a plurality of radiator elements and phase shifters coupled to a transmitter which may be centrally located. Phase shifters 51 sequentially provide a varying degree of phase shift between the respective antenna radiator elements and the transmitter energy is coupled to the phase shifters through waveguide transducers 52. The rotatable conductive members are provided within each waveguide section 53 having a plurality of slot radiators 54. The actuating means are provided at the ends of the rods and are designated generally by the numeral 55. Such actuating means may comprise structure similar to that heretofore described and the driving means may be centrally located within the vehicle. It may be noted that each waveguide section 53 is provided with a tandem array of antenna radiator elements and similarly paired rotatable members. A single phase shifter also will suffice for each tandem pair of waveguide structures. This embodiment is an excellent demonstration of a working embodiment of the invention.

Many variations, modifications and alterations will be apparent to those skilled in the art. It is intended, therefore, that this description of an illustrative embodiment be considered as exemplary only without limiting in anyway the interpretation of the scope of the invention in its broadest aspects as set forth and defined in the appended claims.

We claim:

1. A transmission line element for propagation of electromagnetic energy comprising:

waveguiding conductive means defining an outer conductor having substantially flat walls and; a plurality of antenna radiating elements;

a substantially flat vane member of a-conductive material communicating with said antenna radiating elements and providing means for varying the propagation constant characteristics of said line to. influence excitation of individual antenna radiating elements;

said conducting member having a plurality of periodic discontinuities along the length thereof to define distributed shunt capacitances and series inductances; and

means for rotation of said conductive member about the axis of said waveguiding means.

2. In a phased array antenna system for propagation of electromagnetic energy:

a section of transmission line having substantially flat outer conductor boundary wall surfaces;

a plurality of antenna radiating elements arranged in at least one of said wall surfaces;

means for varying the propagation constant characteristics of said transmission line disposed along its longitudinal axis; 1

said means comprising a substantially flat conductive member defining periodic distributed capacitances in shunt and inductances in series throughout substantially its entire length; and.

means for rotation of said conductive member about its axis.

3. An antenna transmission device comprising:

asection of waveguide transmission line defined by substantially fiat outer wall conductors and-having a plurality of slot radiators in at least one wall;

rotatable center conductor means for varying the propagation constant characteristics of said waveguide line to influence propagation of electromagnetic energy therethrough disposed along its longitudinal axis;

said means comprising a substantially flat conductive vane member having a plurality of periodic discontinuities symmetrically disposed on opposing sides of said longitudinal axis;

said discontinuities defining distributed shunt capacitances and series inductances throughout the length of said member;

means for rotation of said conductive member about its axis.

4. An antenna transmission device according to claim 3 wherein said periodic discontinuities are defined asymmetrically with respect to said longitudinal axis.

Claims (4)

1. A transmission line element for propagation of electromagnetic energy comprising: waveguiding conductive means defIning an outer conductor having substantially flat walls and a plurality of antenna radiating elements; a substantially flat vane member of a conductive material communicating with said antenna radiating elements and providing means for varying the propagation constant characteristics of said line to influence excitation of individual antenna radiating elements; said conducting member having a plurality of periodic discontinuities along the length thereof to define distributed shunt capacitances and series inductances; and means for rotation of said conductive member about the axis of said waveguiding means.

2. In a phased array antenna system for propagation of electromagnetic energy: a section of transmission line having substantially flat outer conductor boundary wall surfaces; a plurality of antenna radiating elements arranged in at least one of said wall surfaces; means for varying the propagation constant characteristics of said transmission line disposed along its longitudinal axis; said means comprising a substantially flat conductive member defining periodic distributed capacitances in shunt and inductances in series throughout substantially its entire length; and means for rotation of said conductive member about its axis.

3. An antenna transmission device comprising: a section of waveguide transmission line defined by substantially flat outer wall conductors and having a plurality of slot radiators in at least one wall; rotatable center conductor means for varying the propagation constant characteristics of said waveguide line to influence propagation of electromagnetic energy therethrough disposed along its longitudinal axis; said means comprising a substantially flat conductive vane member having a plurality of periodic discontinuities symmetrically disposed on opposing sides of said longitudinal axis; said discontinuities defining distributed shunt capacitances and series inductances throughout the length of said member; means for rotation of said conductive member about its axis.

4. An antenna transmission device according to claim 3 wherein said periodic discontinuities are defined asymmetrically with respect to said longitudinal axis.

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