US2973515A - Omnidirectional vertically polarized antenna - Google Patents

Description

Feb. 28, 1961 G. J. ADAMS OMNIDIRECTIONAL VERTICALLY POLARIZED ANTENNA Filed April 5. 1957 2 Sheets-Sheet 1 1 I I 1 I I 1 1 5 .1

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65mm Ao/ms m 4 4 P 0 z N N w w H u 8 5 3 OrwJ/ 2 2 53M, 0 3\ 4 5 3 m J ,,J v 4 3 M M a Q N w 5 M ow OMNIDIRECTIONAL VERTICALLY POLARIZED ANTENNA Filed April 5. 1957 2 Sheets-Sheet 2 5mm f 400m 2,973,515 6MNIDIRECTIONAL VERTICALLY POLARIZED ANTENNA Gerald J. Adams, Cambridge, Mass., assignor to Andrew Alford, Winchester, Mass.

Filed Apr. 5, 1957, Ser. No. 650,920 7 Claims. (Cl. 343-770) The present invention relates to an omnidirectional antenna.

It is an object of the present invention to provide a compact omnidirectional antenna having a low standing wave ratio, good impedance characteristics, and the ability to radiate large amounts of vertically polarized power in a selected frequency range of, for example, from 225 megacycles to 400 megacycles.

These and other objects of the present invention will be more clearly understood when considered in connection with the accompanying drawings in which:

Figure 1 illustrates a cross-sectional elevation of the antenna; H

Figure 2 is a schematic illustration of the antenna for the purpose of explaining its operation; and

Figures 3, 4 and 5 are typical, vertical plane radiation patterns of an antenna made in accordance with the present invention.

In the arrangement illustrated in Figure l, a center coaxial line 1 is formed of the inner conductor 2 and outer conductor 3 coaxial with one another. The inner conductor 2 is provided with a series of transformer sections for the purpose of providing a proper match to the transmission line. The inner conductor 2 is supported by suitable means along its length and is connected at its upper end to the conductive base 5 of the conductive cylinder 6. The connection is made by a slotted bullet 7 extending coaxially downwardly from the base 5. This bullet 7 fits, at its lower end, about the conductive projection 8, in turn secured by a screw 9, or other suitable means, to the member 10 which extends across the upper end of the inner conductor 2. A shoulder section may be formed in the element 8 to receive the dielectric spacing disc 11. A centering pin 12, suitably secured to the base 5 by a screw or other similar means, properly centers the element 8, the pin 12 fitting into a recess within the element 8. This arrangement prevents the fingers of the bullets from being damaged and also provides means for some differential expansion. A plurality of slots 14 are formed in the outer conductor 3 just above the disc 11 for purposes of providing a drainage through the outer conductor. The element or seal 11 is a pressure seal with low loss silicone O-rings 16 providing a tight and engaging seal.

The cylinder 6 and the base 5 of the cylinder are spaced by the gap 18 from the upper edge of the outer conductor 3 and thereby form a balun-like junction. A cylinder 29 is positioned above the cylinder 6 with the cylinder 29 of greater diameter than the cylinder 6. An inwardly extending flange connects the lower edge of the cylinder 20 and the upper edge of the cylinder 6, as is illustrated at 21. A sleeve 22 is coaxial with and equally spaced from the cylinder 6 and outer conductor 3 with the sleeve 22 being partially co-extensive with each of these elements. The sleeve 22 is also longitudinally aligned with and of the same diameter as the cylinder 26. A dielectric gap-23 is formed between the sleeve 22 and cylinder 20, with this gap being covered by the dielectric ring 24. This ring 24 may be suitably secured at its upper and lower annular edges to the cylinder 20 and sleeve 22, respectively, by suitable means such as a series of nuts and bolts. The sleeve 24 may be made of a suitable dielectric material as, for example, Teflon 2,973,515 Patented Feb. 28, 1961 of approximately one-sixteenth of an inch in thickness. A base sleeve 25 of conductive material of the same diameter of sleeve 22 is spaced from it by dielectric spacer 26, suitably covered with a dielectric sheath 27. The sheath or ring 27 may be made of the same material and may be secured in the same manner as sleeve 24. This base sleeve 25 is provided with an inwardly extending upper flange 28 with the flange. 28 having secured to it the outer conductor 3. The outer conductor 3 may be secured to the flange 28 by. suitable means as, for example, by the outwardly extending flange 29 which rests in face to face relation with flange 28 and is secured to it by such means as bolts 30; The base sleeve 25 is supported and secured to the conductive base member 32 by suitable means such as bolt arrangement 33. This base may comprise an outer vertical wall 34, inwardly extending transverse wall 35 and an inner downwardly extending wall 36 with the inner downwardly extending wall 36 being in face to face relation with a portion of the outer conductor 3. A pair of hollow toroids or toroidal elements 41 and 42 are formed of conductive sheet material and are positioned coaxial with the inner conductor 2. These members 41 and 42 are vertically located at the center transverse plane of the dielectric facing or slots 26 or 23, respectively. The outer walls 43 and 44 of these toroidal elements are longitudinally aligned with the wall 34 while the inner walls 45 and 46, respectively, are spaced outwardly from the slots 26 and 23. A pair of annular plates 48 and 49 spaced from one another and normal to the sleeve 22 cooperate respectively with the upper wall 50 and lower wall 51 of the toroidal elements 41 and 42 to form radiating slots 52 and 53. The annular conductive sheet interconnects the outer peripheral edges of plates 48 and 49, thereby forming a toroid or toroidal element 81. A third radiating slot 54 is formed between the lower wall 55 and the base 32 while a fourth radiating slot 56 is formed between the upper wall 57 of the toroidal element 42 and the conductive outwardly extending flange 58. The flange 58 is suitably secured to the cover member 59 which in turn is secured and forms a portion of the cylinder 2G. The radiating slots 52, 53, 54 and 56 are each covered with a thin dielectric supporting cover member suitably secured at its upper and lower edges to adjacent elements. These dielectric sheaths properly space and support the various mentioned elements in fixed relation to one another. An annular upwardly extending cylinder 68 is longitudinally aligned with the outer wall 44.

Extending upwardly from the cover member 59 and suitably secured to it is a lightning rod 62 which projects through the dielectric radome which may be made, for example, of fibre glass one-eighth of an inch thick. The lightning rod 62 protrudes through an O-ring seal comprising the clamping element illustrated at 63. .The lightning rod provides a DC. path to the inner conductor of the coaxial transmission line which in turn is grounded to an outer conductor at the bottom of a supporting mast by a high impedance stub. The lower peripheral edge of the radome may be secured to the base of the flange or wall 34 by suitable means as, for example, a series of nuts and bolts 64 which project through a lower peripheral flange of the radome into a coextensive flange formed atthe base of the wall 34.

In the operation of this invention, four radiating slots 56', 53, 52 and 54 are essentially connected in series with the coaxial transmission line 1 and in parallel with one another. Energy transmitted through the line 1 may be divided equally at the junction 7, half being transmitted upwardly in a TEM mode (the normal coaxial mode) between the wall of the cylinder 6 acting as the inner conductor and the sleeve 22 acting as the outer conductor. The other half of the energy is transmitted downwardly in a similar manner between the outer wall of the outer conductor 3 acting as the inner conductor and the sleeve 22 acting as the outer conductor. The relative directions of the electric field are shown by arrows in Figure 2. The energy propagated upward is similarly divided at the junction 23. Half of the energy from the junction 23 may be transmitted upwardly between the outer wall of the cylinder 2s and the inner wall 46 of the member 42 to the radiating slot 56. The other half of the energy is transmitted downwardly between the outer wall of the s eeve 6 and the wall 46 to the radiating slot 53. The energy transmitted from iunction 26 is also divided in half. One half is transmitted upwardly between the outer wall of the sleeve 6 and the wall 45 of the member 41 to radiating slot 52. The other half of the energy is transmitted downwardly between wall 25 and wall 45 to radiating slot 54.

As a result, the voltages across the radiating slots are equal in magnitude and are in the same phase since the paths from junction 7 to each slot are normally identical. This provides a relatively uniform illumination of the radiating aperture. The design of its structure is such that the supporting mast, partially formed by the coaxial conductor 1 and the lightning rod 62 do not become excited and thus have little effect on the radiation pattern.

Typical radiation patterns are illustrated in Figures 3. 4 and 5 where the vertical plane radiation of a typical antenna is illustrated for various frequencies. It will be noted that at each of the frequencies illustrated the radiation is kept relatively close to the horizon and vertical radiation is minimized. The radiation pattern in Figures'B, 4 and 5 show nulls at certain elevations. These may be at least partially fi led in, if desired, by adjusting the division of power at the various junctions 7, :23 and 26. This may be accomplished, for example. by makingthe diameter of cylinder 6 greater or smaller.

While the modification illustrated describes a symmetrical arrangement for maximum radiation at right angles to the antenna, the structure may readily be modified to send maximum radiation at angles other than right angles from the axis of the antenna. This may be accomplished by delaying the waves passing through one or more paths with respect to the other paths. This may be done by making one or several paths relatively longer than the others. Specifically, for example, the junction 7 may be lowered by making cylinder 6 longer and conductor 3 shorter. This would result in an uptilted radiation.

Having described my invention, I claim:

1. An omnidirectional antenna comprising four coaxial, inpart coextensive, conductors, the inner two conductors forming a first coaxial line, a junction in said first coaxial line for dividing energy transmitted therethrough into equal magnitudes with opposite electric fields,

"the outer of said inner two conductors and the next outwardly adjacent conductor forming a coaxial line means adapted to transmit in opposite directions said equal magnitudes of energy and having terminating junctions at either end thereof for dividing said equal magnitudes of energy transmitted therethrough into further equal magnitudes with opposite electric fields and means including in part said outermost coaxial conductor forming outer transmission lines terminating in a plurality of annular axially-spaced slots adapted to radiate energy passing therethrough in equal magnitude and phase, said outermost coaxial conductors being coupled to said terminating junction for receipt of energy therefrom.

2. An omnidirectional antenna for transmission of vertically polarized radio frequency energy comprising an inner and outer conductor forming a transmission line,

means forming a junction at the end thereof for equal division of energy passing therethrough, a cylindrical conductor longitudinally aligned with said outer conductor, a sleeve coaxially surrounding said outer conductor and said cylindrical conductor and forming therewith second ,4 and third transmission lines in series with each junction, means forming junctions at the end of each of said last mentioned lines for equal division of energy passing therethrough, means including a toroid partially coextensive and surrounding said sleeve and forming therewith additional transmission lines each in series with one of said last mentioned junctions, and means forming radiating slots at the end of each of said additional transmission lines, said slots being coaxial about and spaced along the axis of said coaxial lines.

3. An omnidirectional antenna for transmission of vertically polarized radio frequency energy comprising an inner conductor, and means forming three coaxial and at least partially coextensive sleeves about said inner conductor, means forming a plurality of electrical junctions interconnecting in series said inner conductor and sleeves as coaxial transmission lines for dividing and subdividing energy input between said inner conductor and next adjacent sleeve into four equal components, and means connected to the terminals of the outermost lines forming four axially spaced radiating slots concentric about the axis of said transmission lines, each of said slots being energized by a respective one of said four equal components.

4. An omnidirectional antenna for transmission of vertically polarized radio frequency energy comprising an inner conductor, and means forming three coaxial and at least partially coextensive sleeves about said inner conductor, means forming a plurality of electrical junctions for division of energy passing therethrough into two equal components, one of said junctions interconnecting the inner conductor and next adjacent sleeve as a transmission line with the outer wall of said next adjacent sleeve and the middlemost sleeve as a pair of transmission lines extending in opposite directions, a set of junctions interconnecting the ends of said last mentioned lines with the outer wall of said middlemost sleeve and outer sleeve as additional transmission lines extending in opposite directions, and means forming axially-spaced radiating slots at the ends of said last mentioned lines coaxial about the axis of said transmission lines.

5. A device as set forth in claim 4 wherein said radiating slots and junctions are covered by annular pieces of dielectric material, said pieces providing partial support for said sleeves.

6. An antenna comprising, a plurality of insulatedly separated annular conducting surfaces defining a plurality of annular radiating slots spaced along a common axis, an input waveguide terminating on said axis midway between the extreme slots, and means defining a plurality of channels symmetrical about a plane perpendicular to said axis and passing through the point midway between said extreme slots for coupling said input waveguide to said slots and defining respective wave transmission paths from said input waveguide to each of said slots, the elect-rical lengths of said paths being substantially equal.

7. An antenna in accordance with claim 6 wherein said coupling means includes means for delivering an equal amount of energy from said input Waveguide to each of said slots.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Antennas by J. D. Kraus, copyright 1950 by McGraw- Hill, page 353.

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