US 3871000 A
A wide-band vertically polarized omnidirectional antenna consists of an outer first cylindrically-shaped metal surface with a second cylindrically-shaped metal surface coaxial with and located within the first metal surface and concentrically disposed about a third cylindrically-shaped metal surface. The first metal surface is formed of individual antenna elements each having a ring of circumferentially extending slots spaced axially from the ends of the elements with adjacent elements spaced apart by a circumferential ring slot. Alternatively, the first metal surface can be a continuous tubular member divided in the axial direction by a number of axially spaced rings of circumferentially extending slots. Each ring of slots consists of a number of uniformly circumferentially spaced rectangularly-shaped slots. A three-wire line is associated with each ring of slots with two of the wires extending circumferentially while the third or inner wire extends radially inwardly from the first metal surface through the second metal surface in contact-free relationship and then into contact with the third metal surface.
Description (OCR text may contain errors)
United States Patent [1 1 Tymann [111 3,871,000 [451 Mar. 11, 1975 WIDE-BAND VERTICALLY POLARIZED OMNIDIRECTIONAL ANTENNA  Inventor: Gerhard Tymann, Unterhaching,
Germany  Assignee: Messerschmitt-Bolkow-Blohm Gesellschaft Mit Beschrankter Hoftung, Munich, Qermany  Filed: Nov. 30, 1973  Appl. N0.: 420,581
 Foreign Application Priority Data Dec. 2. 1972 Germany 2259082  U.S. Cl. 343/771, 343/791  Int. Cl. H0lq 13/10  Field of Search 343/769, 770, 771, 791-  References Cited UNITED STATES PATENTS 2,973,515 2/1961 Adams 343/790 3,417,400 12/1968 Black 343/771 Primary E.\'aminerEli Lieberman Attorney, Agent, or Firm-Toren, McGeady and Stanger "Ill  ABSTRACT A wide-band vertically polarized omnidirectional antenna consists of an outer first cylindrically-shaped metal surface with a second cylindrically-shaped metal surface coaxial with and located within the first metal surface and concentrically disposed about a third cylindrically-shaped metal surface. The first metal surface is formed of individual antenna elements each having a ring of circumferentially extending slots spaced axially from the ends of the elements with adjacent elements spaced apart by a circumferential ring slot. Alternatively, the first metal surface can be a continuous tubular member divided in the axial direction by a number of axially spaced rings of circumferentially extending slots. Each ring of slots consists of a number of uniformly circumferentially spaced rectangularly-shaped slots. A three-wire line is associated with each ring of slots with two of the wires extending circumferentially while the third or inner wire extends radially inwardly from the first metal surface through the second metal surface in contact-free relationship and then into contact with the third metal surface.
12 Claims, 6 Drawing Figures HJ'EHTEUHARI LISTS 3,871,000 sum 1 pg 3 PATENTEU I 3,871,000
SHEET 2 [IF 3 PATENTEDHARI 1 I 3.071.000
snmaurs Fig. 30
WIDE-BAND VERTICALLY POLARIZED OMNIDIRECTIONAL ANTENNA SUMMARY OF THE INVENTION The present invention is directed to a wideband, vertically polarized omnidirectional antenna and, more particularly, it concerns the arrangement of such antenna and especially its outer surface which is formed of a hollow cylindrical metal surface divided by circumferentially extending rings of slots located in planes extending perpendicular to the axis of the metal surface. The rings of slots are arranged to divide the first surface into hollow cylinders having a height or axial length of about A to A of the wavelengths. A three-wire line feeds each of the ring slots and a second hollow cylindrically-shaped metal surface disposed inwardly of and coaxially with the first metal surface serves as a meter frame or support.
For certain uses, for example, in space travel, antennas with a good circular radiation pattern or characteristic are required in a plane with medium gain. In addition to high mechanical stability, the ability to withstand extremely high temperature stresses from about 80C to +200C is required in many space probes, for example, in solar probes. Frequently the antenna dimensions, particularly the diameter, are given. In many satellites, several antennas must be superposed with a magnetometer arranged at the end of the antenna arm. The necessary feed lines for the upper antennas and for the magnetometer must be arranged within the interior of the lower antennas.
To meet these requirements it has been known to use slot radiators which consist of two coaxial hollow cylindrical metal surfaces where the outer metal surface contains a circumferentially extending ringslot located in a plane disposed perpendicularly to the axis of the metal surface. In such an arrangement the inner metal surface serves as a meter frame or support. Two hollow cylindrical rings separated by a ring slot form a slot radiator element. For focusing the radiation in a plane perpendicular to the axis of the elements, several of the elements are superposed coaxially to form a collinear system, with the inner continuous hollow cylindrical metal surface serving as a common supporting tube (see DOS, 1,441,614; Jasik Antenna Engineering Handbook, McGraw-I-Iill Book Company, New York, 1961, pages 26-2 to 26-4, and Silvers Microwave Antenna Theory and Design, McGraw-Hill Book Company, New York, 1949, page 309). In the wide-band omnidirectional antenna with vertical polarization describedv in the above patent, the distance between two slot radiator elements is about one wavelength, and the distance between the inner and outer hollow cylindrical metal surfaces is 0.2-0.12 wavelengths. The outer hollow cylindrical surface is secured over narrow stirrups on the inner hollow cylindrical metal surface. The omnidirectional antennas mentioned in the two publications use the two outer conductors of the three-wire symmetrization to maintainthe distance of the outer hollow cylinders. These known omnidirectional antennas do not meet, however, the mechanical stability requirements for air and space travel. Reinforcement of the supports is not possible without, at the same time, impairing the electrical properties of the omnidirectional antenna.
The installation of a toriodal dielectric to increase the mechanical strength also has disadvantages. For
space probes, for example, for a solar probe, a low-loss dielectric must be found which can withstand at least 200C. Further, it is very difficult, particularly with regard to thermal and mechanical stresses, to obtain good contact'between the dielectric and the metal surface. When large temperature fluctuations occur, an air gap develops due to the different coefficients of expansion of the metal and dielectric. Since the electrical field strength in the air gap is higher than in the dielectric, a breakdown may occur. Moreover, the antenna becomes highly frequency-sensitive, particularly in the form of a coaxial line radiator (note the Silver publication mentioned above).
The mounting of the hollow cylindrically-shaped rings with a constant slot width over the entire slot ring presents certain difficulties. Any change of the generally very narrow slot or eccentricity of the hollow cylindrically-shaped ring results in considerable differences in the radiation and impedance diagrams.
The omnidirectional antenna described in the abovementioned patent is fed over two-wire lines arranged within hollow cylindrically-shaped rings. With many feeding points and several ring slots, such a system becomes very complicated and unwieldy, particularly since impedance converters and concentrated blind elements must be inserted into the feeding line system.
In the omnidirectional antennas described in the two publications, the space within the second hollow cylindrically-shaped metal surfaces is designed as a tubular or coaxial conductor. The high-frequency energy is uncoupled over probes and is fed to the ring slots. To assure that a wave can be excited at a given frequency, the tubular conductor must have a corresponding diameter. In the design of the coaxial conductor, a certain diameter ratio of the outer to the inner conductor must be maintained in view of wave resistance. If the diameter of the inner conductor is selected at a dimension such that a foreign cable can be laid within its interior, the diameter of the antennais frequently too great in respect to the wavelengths. In any case, it is not possible to arrange thicker supply lines for components arranged above the omnidirectional antenna inside the hollow cylindrically-shaped metal surfaces in the proximity of the antenna axis.
If the diameter of the omnidirectional antenna is great compared to its wavelength, the use of ring slots with discrete feeding results in a lack of symmetry in the radiation diagram. With ring slots, the radiation diagram can be influenced in the azimuth only by the number of coupling points and the diameter of the omnidirectional signal. Further, wide-band coupling of the ring slots is hardly possible.
Therefore, the primary object of the present invention is to provide an antenna with a good circular radiation characteristic in a plane and of great band width, where the quality of the circular radiation is, for all practical purposes, independent of the diameter of the antenna and where the antenna has both high mechanical and thermal strength with easy mountability and a simple and insensitive feeding system. Further, the arrangement of the antenna permits the placement of additional supply cables inside the antenna structure particularly in the proximity of its axis.
Accordingly, the problems experienced in the past are solved in the present invention by dividing the ring slot in a uniform manner into individual or separate circumferentially extending slots spaced apart in the circumferential direction. Further, the individual slots can have a rectangular form or they can be widened conically or in steps, or they can be arranged as dumbbellshaped slots and each individual slot is fed over a threewire line from one or more coaxial conductors, and, if necessary, a third hollow cylindrically-shaped metal surface is provided inwardly of the first and second such surfaces. The second and third hollow cylindrically-shaped surfaces are designed as a feeding system for the antenna arrangement and the inner wires or conductors of the three-wire line pass inwardly from the first metal surface in contact-free relationship through bores in the second metal surface and are coupled capacitatively or galvanically with the third metal surface.
Concentration of the radiation in a plane through the system axis is achieved by providing a ring of individual slots in an omnidirectional radiator element so that two hollow cylinder rings are formed and by arranging several such omnidirectional radiator elements, whose height is about equal to half the mean operating wavelength, in a superposed coaxially arranged group with the individual radiator elements spaced apart in the axial direction by a circumferential ring slot.
In another arrangement of the first or outer hollow cylindrically-shaped metal surface, the omnidirectional radiator elements are joined together in the form of a continuous tubular member provided with the individual interrupted ring slots but without the separating circumferential ring slots.
The feeding or supply, which is not limited to the antenna according to the present invention, is effected in the wide-band model in such a way that at least one coaxial conductor is positioned within the third hollow cylindrically-shaped metal surface and acts as a coaxial feed conductor with the outer wire of the feed conductor conductively connected to the third metal surface and with its inner conductor conductively connected to the second metal surface.
To be able to mount the feed or supply in an assembled antenna in a simple manner from the exterior of the antenna, and to obtain other advantages, the feed arrangement is laid out so that the coaxial connection to the feed is arranged in the center of the antenna structure with the outer wire of the coaxial feed conductor conductively connected to the third hollow cylindrically-shaped metal surface over a hollow cylinder extension extended through an opening in the third metal surface and attached to it by a through connection and with the inner wire of the coaxial feed conductor passing outwardly through the hollow cylinder extension within another cylindrically-shaped member and attached to the exterior of the second metal surface. Further, an adjustable and fixable short-circuit plane is provided at the free end of the coaxial feed conductor at a distance of about $41 of the mean operating wavelength for adjusting the amplitude and phase conditions in the coaxial feed conductor.
By virtue of the present invention, it is possible to obtain a good circular radiation characteristic in a plane which is, to a great extent, independent of the ratio of the antenna diameter to the wavelength. By using individual spaced slots in the interrupted ring of slots and by using different geometric forms for the slots, it is possible to obtain optimum wide-band matching. Furthermore, the symmetry of the arrangement can be improved, if necessary, by varying the lengths of the single or individual slots, or a designed asymmetry can be produced in the radiation pattern. By virtue of the single slots and the use of larger antenna diameters, which is possible because of the independence of the quality of the circular radiation characteristic from the antenna diameter/wavelength ratio, a very high mechanical strength is obtained, particularly in the design which does not use separating ring slots between individual radiator elements. By employing the continuous outer hollow cylindrically-shaped metal surface a further stiffening effect is obtained. Due to the feeding arrangement provided in the present invention, additional cables for other uses can be positioned within the antenna structure close to its axis and at the same time, a wide-band cabling can be effected which is accessible from the exterior even after the final mounting of the antenna. Interference impedances producedby probes or other connecting pieces can be compensated partly by short-circuit planes at both ends of the omnidirectional antenna between the second and third hollow cylindrically-shaped metal surfaces. Since no dielectric is used, the antenna has a high thermal strength. Further, all atmospheric charges are positively led off, since all parts of the antenna are grounded. It is also possible to feed the omnidirectional antenna without the use of the third hollow cylindrically-shaped surface by using a tubular conductor arrangement. Further, the third metal surface could be used as an outer wire of a coaxial feed line. However, the advantages of wideband cabling and of incorporating other cables close to the axis of the antenna would not be available.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:
FIG. 1a is a partial view, partly in section, of an omnidirectional antenna embodying the present invention, and incorporating radiator elements having a length of about one-half the wavelength;
FIG. lb is a view similar to FIG. la, embodying the present invention with a continuous outer hollow cylindrically-shaped metal surface in place of the individual radiator elements;
FIG. 2 is an enlarged sectional view showing the feeding arrangement for the antenna; and
FIG. 3a to 30 show possible forms of the individual slots.
DETAILED DESCRIPTION OF THE INVENTION In FIG. la an omnidirectional antenna is illustrated with its outer surface formed of a plurality of collinear radiator elements 12 each having a height or axial length of about 5% the wavelength. The individual radiator elements 12 are spaced apart in the axial direction of the antenna by circumferentially extending slots 3 formed between adjacent ends of the elements. Intermediate the ends of each element in a plane extending perpendicularly of the axis of the antenna, an interrupted ring of rectangularly shaped individual slots 4 extend in the circumferential direction of the elements.
Each individual slot 4 is fed over a three-wire line 5, 8, 9. The outer wires 8, 9 of the three-wire line serve to maintain the distance of the elements 12 from a radially inner hollow cylindrically-shaped metal surface which is arranged coaxially with the radiator elements. Further, a third hollow cylindrically-shaped metal surface 14 is located coaxially within the second metal surface 10. Each inner wire 5 of the three-wire line is connected at its radially outer end to a nose 7 which protrudes in the axial direction from the surface of the radiator element 12 into the slot 4. Bores are formed in the second hollow metal surface 10 so that each of the inner wires 5 passes inwardly through the bore in contact-free relationship from the second metal surface 10 and is conductively connected'to the third metal surface 14.
In FIG.'lb another embodiment of the omnidirectional antenna is illustrated which has the same design as shown in FIG. 1a. However, instead of the individual radiator elements 12 of FIG. la, in FIG. 1b the radiator elements 12 are formed in a continuous tubular metal surface 2 in which the rows of individual slots 4 extending circumferentially about the tubular member 2 are spaced apart at about the mean operating wavelength.
In FIG. 2 a feeding arrangement for the invention is illustrated. As shown, the coaxial conductor 16 opens into an outer cylinder 20 which forms'a coaxial conductor together with an inner conductor member 21 which is connected to the conductor 16. The outer wire of the coaxial conductor 16 is conductively connected with the hollow cylinder 20- and its inner wire is conductively connected with the inner conductor member 21. The hollow cylinder is disposed tangentially to the inner surface of the third hollow metal surface 14. A hollow cylindrical extension 23 extends normally to the axis of the hollow cylinder and outwardly from it passing through an opening in the third metal surface 14 and it is secured by a screw conductor 24 to the outside surface of the third metal surface 14. Spaced inwardly from the hollow cylindrical extension 23 is another extension 26 provided with a female thread into which a screw connector 31 is fitted for providing contact with the inner conductor member 21. The screw connector is mounted within a stepped hollow cylinder 27 having a narrow portion which extends through the extension 23 and a wider hollow cylindrical portion 28 which extends through the. second metal surfacev 10 and has a flange 29'extending laterally over the outer surface of the metal surface 10 so that the flange can be connected by screw members to the metal surface 10. Accordingly, the outer conductor provided by the hollow cylinder 20 is connected to the third metal surface 14 while the inner conductor 21 is connected to the second metal surface 10 with the surfaces of the connection disposed in spaced relationship. At a distance of about'% of the mean operating wavelength, an adjustable and fixable short-circuit plane is arranged in the innermost coaxial conductor to compensate or adjust the amplitude and phase conditions within the feed arrangement.
The outermost hollow cylindrically-shaped metal surface 2, that is the radiator elements 12, contains the slot radiators which radiate a vertically polarized electromagnetic wave. The next inner hollow cylindrical metal surface 10 serves as a meter frame or support as well as an outer wire for the coaxial feed system of the antenna arrangement and as a reflector. The inner wire of the coaxial feed conductor is in contact with this second metal surface 10. The innermost hollow cylindrically-shaped metal surface 14 forms the inner wire for the coaxial feed system and it is connected with the outer wire of the coaxial feed conductor.
Coaxial cable 15 shown in FIG. la-is provided to feed an external load mounted above the antenna.
FIG. 3a shows an individual slot, which widens conically and FIG. 3b an individual slot, which widens in steps. FIG. 3c shows an individual slot with dumbbelllike shape. In the middle of the axial length of this dumbbell-like shaped slot 4" a projection extends into the slot.
Without departing from the concept of the invention, the omnidirectional antenna according to the invention can also be designed for horizontal polarization.
The feeding device disclosed above is not limited to antennas of the type described herein, it also applies generally to individual radiator elements or radiator groups.
Preferred applications of the omnidirectional antenna according to the invention are for air and space travel, as well as in mobile and stationary telemetry stations. The omnidirectional antenna described is particularly suitable for the superposition of several antennas. Another advantageous application of the antenna of the present invention is as a primary radiator for reflection antennas, particularly for cylindrical-parabolic antennas.
The wide-band vertically polarized omnidirectional antenna has a wavelength of about 5,5 inches. Typical diameter dimensions of the first, second and third hollow cylindrically-shaped metal surfaces would be as follows: 3, 1,5 inches and 1 inch. Based on the above wavelengths, the axial lengths of the antenna elements 12 would be 0,45 wavelengths. Similary, based on the above wavelengths, the spacing between the interrupted rings of slots 4 in FIG. 1b would be of the wavelength.
1. A wide-band vertically polarized omnidirectional antenna comprisinga first hollow cylindrically-shaped metal surface divided transversely of its axis by a circumferentially extending slot into at least two hollow cylindrically-shaped rings having an axial length of $41 or k of thewavelength, three-wire lines distributed uniformly over the circumference of said first metal surface for feeding said slots, and a second hollow cylindrically-shaped metal surface arranged within and coaxially with said first metal surface as a support, wherein the improvement comprises that said slot is formed of a plurality of circumferentially extending individual slots uniformly spaced apart in thecircumferential direction and forming a circumferentially extending interrupted ring slot, one said three-wire line for feeding each said individual slot, at least one coaxial conductor positioned within said second metal surface, said second metal surface and said coaxial conductor arranged as a coaxial feeder system, said three-wire line comprising inner wires extending radially inwardly from said first metal surface, said second metal surface having bores therethrough aligned with said inner wires so that said inner wires pass contact-free through said second metal surface and are coupled capacitatively or galvanically with said coaxial conductor.
2. A wide-band vertically polarized omnidirectional antenna, as set forth in claim 1, wherein a third hollow cylindrically shaped, metal surface is positioned within said second metal surface, said third metal surface comprising one or several coaxial conductors in order to feed the antenna system and, if necessary, comprising also other conductors and feed lines not used for feeding the antenna system, said second metal surface and said third metal surface arranged as a coaxial feeder system of the antenna, said three-wive line comprising inner wires extending radially inwardly from said first metal surface, said second metal surface having bores therethrough aligned with said inner wives so that said inner wives pass contact-free through said second metal surface and are coupled capacitatively or galvanically with said third metal surface.
3. A wide-band vertically polarized omnidirectional antenna, as set forth in claim 1, wherein said individual slots are rectangular in form.
4. A wide-band vertically polarized omnidirectional antenna, as set forth in claim 3, wherein a projection on said first hollow cylindrically-shaped metal surface extends into said rectangularly shaped slot from one side thereof and is spaced from the other side thereof, and one said inner wire of said three-wire line being coupled with said projection into said slot.
5. A wide-band vertically polarized omnidirectional antenna, as set forth in claim 1, wherein said individual slots have conically widening configuration.
6. A wide-band vertically polarized omnidirectional antenna, as set forth in claim 1, wherein said individual slots widen in a step-wise manner.
7. A wide-band vertically polarized omnidirectional antenna, as set forth in claim 1, wherein said individual slots have a dumbbell-like shape.
8. A wide-band vertically polarized omnidirectional antenna, as set forth in claim 7, wherein a projection on said first hollow cylindrically-shyped metal surface extends into said dumbbell-like shaped slot from one side thereof and is spaced from the other side thereof, and one said inner wire of said three-wire line being coupled with said projection into said slot.
9. A. wide-band vertically polarized omnidirectional antenna, as set forth in claim 1, wherein said first metal surface comprises a plurality of cylindrically-shaped omnidirectional antenna elements arranged in surface alignment, each said antenna element having an axial length about equal to half the mean operating wavelength, said antenna elements being spaced apart in the axial direction and forming a continuous circumferentially extending slot therebetween, and each said antenna element having said interrupted ring slot therein positioned axially from and intermediate its opposite ends.
10. A wide-band vertically polarized omnidirectional antenna, as set forth in claim 1, wherein said first metal surface comprises a continuous axially elongated tubular member having a plurality of axially spaced said interrupted ring slots therein dividing said tubular member into a plurality of interconnected omnidirectional antenna elements.
11. A wide-band vertically polarized omnidirectional antenna, as set forth in claim 2, wherein at least a part of oneof said coaxial conductors comprises an axially elongated hollow cylinder forming an outer conductor and an axially elongated inner conductor positioned coaxially within and spaced inwardly from said hollow cylinder, said hollow cylinder connected conductively to said third metal surface and said inner conductor connected conductively to said second metal surface.
12. A- wide-band vertically polarized omnidirectional antenna, as set forth in claim 11, wherein said hollow cylinder forming the outer conductor is in surface contact with the surface of said third metal surface and said third metal surface having an opening therethrough, said hollow cylinder having a tubular-shaped extension secured thereto and extending laterally outwardly therefrom transversely of the axial direction of said hollow cylinder through the opening in said third metal surface, a threaded connector member in screwed engagement with the outer surface of said extension for fixing said hollow cylinder to said third metal surface, said second metal surface having an opening therethrough aligned with the opening in said third metal surface, a hollow cylindrically-shaped member secured to the outer surface of said second metal surface and extending through the opening in said second metal surface and through said tubularshaped extension secured to said hollow cylinder and in spaced relationship to said tubular-shaped extension, and a connector member displaceably mounted in said hollow cylindrically-shaped member and connected to and phase conditions in said coaxialconductor.