US3750184A

US3750184A - Super-balanced feed-through dipole antenna

Info

Publication number: US3750184A
Application number: US00217201A
Authority: US
Inventors: J Kuecken
Original assignee: Deutsche ITT Industries GmbH
Current assignee: TDK Micronas GmbH; ITT Inc
Priority date: 1972-01-12
Filing date: 1972-01-12
Publication date: 1973-07-31
Anticipated expiration: 1990-07-31

Abstract

The invention provides a novel LOS dipole antenna arrangement which permits substantial improvement in pattern characteristics by correspondingly reducing spurious coupling to adjacent structure, which may occur particularly where the antenna is situated closely adjacent to unrelated structure in a spacerestricted environment. Pattern improvement is based on the principle of the antenna''s symmetry being rigorously maintained, wherein a pair of adjacently arranged cylindrical radiators are fed by a double-ended balun structure created from the supporting and cable feed-through antenna mast. This balun feed assembly comprises a pair of oppositely arranged slots within the antenna cylindrical radiators, with each conductor of the coaxial feed cable running to the balun being coupled to either side of one of the slots proximate the center thereof. The excitation energy is transferred to the cylindrical radiators by way of symmetrically placed radial posts extending from either side of the energycoupled slot to the inside of the cylinders.

Description

will States Patent 1 Knecken [451 M sarsrs [75] Inventor: John A. Kuecken, Pittsford, N.Y.

[73] Assignee: international Telephone ahd Telegraph Corporation, N utley, N .J

[22] Filed: Jan. 12, 1972 [2]] Appl. No.: 217,201

[52] ILLS. Cll 343/792, 343/807, 343/821 [51] Int. Cl. H011 9/16 [58] Field of Search 343/791, 792, 807, 343/820, 821, 822

[56] References Cited UNITED STATES PATENTS 2,234,234 3/1941 Cork et al 343/791 3,030,622 4/1962 Leitner et al. 343/859 3,335,420 8/1967 Silliman 343/807 Primary Examiner-Eli Lieberman Attorney-CfCornell Remsen, Jr., Menotti J. Lombardi, Jr. et al.

[57] ABSTRACT The invention provides a novel LOS dipole antenna ar-.

rangement which permits substantial improvement in pattern characteristics by correspondingly reducing spurious coupling to adjacent structure, which may occur particularly where the antenna is situated closely adjacent to unrelated structure in a space-restricted environment. Pattern improvement is based on the principle of the antenna's symmetry being rigorously maintained, wherein a pair of adjacently arranged cylindrical radiators are fed by a double-ended balun structure created from the supporting and cable feed-through antenna mast. This balun feed assembly comprises a pair of oppositely arranged slots within the antenna cylindrical radiators, with each'conductor of the coaxial feed cable running to the balun being coupled to either side of one of the slots proximate the center thereof. The excitation energy is transferred to the cylindrical radiators by way of symmetrically placed radial posts extending from either side of the energy-coupled slot to the inside of the cylinders.

13 Claims, 7 Drawing Figures PATENTED 1 v 3.750.184

6261339. .1 (PR IOR AR 7) 53%? 16a 66 CABL INC" 7'0 UPPER ANTENNAS (PRIOR ART) LOWER POR T/O/V OF ANTENNAS MAST L SH/6L0 FARADA Y olsc 5/0540 SUPER-BALANCED FEED-THROUGH DIPOLE ANTENNA BACKGROUND OF THE INVENTION This invention relates to dipole antennas and more particularly to an LOS (line of sight) dipole antenna arrangement designed to be operative in the 225-400 MHz band in closely packed multiantenna type configurations.

Operation of conventional halfwave dipole antennas frequently is plagued with the problem that some of the exciting current will couple to an adjacent structure. This is particularly true in several notable military antenna applications, for example submarines, wherein available space is quite limited in that several antennas must be arranged on a single mast. At LOS frequencies particularly, spurious current levels and scalloping of the wave pattern are experienced as a result of this unwanted coupling. A 2 db scalloping of the pattern for example implies that the interference effect, which will add at some angles and subtract at others, is at a level of i 1 db referred to the undisturbed level of the dipole (i.e. the voltage goes to 1.12 and 0.89 times the undisturbed level). If the radiation pattern of the interferring or spurious excitation is assumed to demonstrate a gain as great as the dipole in the same direction, then the excitation would in all likelihood have to be suppressed say 'l8.4 db (0.12 X voltage) to achieve for instance a reduction in the spurious current levels to a desirable -l5 db level.

SUMMARY OF THE INVENTION It is an object of this invention to provide a novel dipole antenna configuration.

It is another object to provide a novel LOS dipole antenna configuration which has improved pattern characteristics and substantially reduces the effects of spurious coupling, particularly where space requirements call for a close packing of antennas and surrounding structure.

According to the broader aspects of this invention there is provided a dipole antenna arrangement comprising a radiating assembly disposed coaxially of a main axis, said radiation assembly including a pair of adjacent open-ended cylindrical radiators arranged about said axis and spaced apart a predetermined separation; and an energy feeding arrangement concentrically arranged about said axis and extending through said cylindrical radiators, and coupled to said radiating assembly, said energyfeeding arrangement including a balun assembly for providing a balanced impedance feed to said radiating assembly and a pair of energy transport means arranged within and associated in oneto-one correspondence with said pair of-cylindrical radiators, said energy transport means being disposed between said balun assembly and said radiators-to electrically couple to the latter the excitation energy from said balun assembly.

BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other objects of this inventionwill become more apparent and the invention itself best understood byreference to the following description takenin conjunction with the accompanying drawings, in which:

FIG. l-is a sectional-side view of an existing dipole antenna;

FIG. 2 is a diagrammatic illustration of the prior art antenna of FIG. 1 showing related decoupling apparatus;

FIG. 3A is a perspective representation of the feed balun assembly of the LOS dipole antenna arrangement according to the invention;

FIG. 3B is a cross-sectional view of the balun of FIG. 3A taken along the line IIIB IIIB of FIG. 3A;

FIGS. 4A and 4B are respectively perspective and partial sectional views illustrating the LOS dipole antenna arrangement according to the invention; and

FIG. 5 is a perspective representation illustrating an alternate energy coupling means for the balun assembly to the radiators according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An existing LOS antenna is arranged as shown in FIG. 1. The choking action which decouples the current from the cabling stems from the coaxial shorted choking action of the lower radiator 16a. The impedance of this choke (if assumed lossless) is given by where Z I38 log D/d. If it is assumed that D 5 inches and d 1 inch, then Z log m5 96.5.

Although the Z may be adequate to suppress the current at resonance, i.e. 2'rrl/ t it is a different matter above and below resonance. Nominally, the band is 225 to 400 MHz. Suppose that the choke is res onant at midband, i.e. 300 MHz. Then at 225 MHz the choke impedance becomes Z 96.5 tan 90 X 225/200 96.5 tan 67.5 +j 400,

and at 400 MHz, Z j 400.

If the end fed impedance of the dipole is on the order of 1000!), it may be seen that the choking action is relatively ineffectual at the band edges.

One possible solution involves the inclusion of a relatively large block of very high permeability (p/= 10,000) ferrite material. Such material has a very large loss at these frequencies and will present a very large choking effect. Specially fabricated ferrite blocks which can be clamped around the cables may be procured. In order to protect these blocks from overheating due to the extremely large fields generated by the circulating currents of the HF antenna, the inclusion of a Faraday shield about the blocks is probably advisable. See FIG. 2 in this regard.

The addition of the ferrite chokes is of course the least expensive and the simplest decoupling mechanism; however, it does little to helpthe direct capacitive coupling (stray capacitance) from the radiator end. It is perhaps possible toprovide a grounded shield disc positioned as shown in FIG. 2 in an attempt to control this form of coupling. The obvious particular difficulty here lies in the antenna space requirements wherein the very tight packing of several antennas is desired.

Another approach involves the development of a .novel, super-balanced feed-through dipole antenna which is the subject of this invention. A principle behind this antenna is that creation of a rigorously balanced (and geometrically symmetrical) antenna should considerably alleviate the decoupling problem. FIGS.

3-5 illustrate the proposed construction of the antenna.

Referring to FIGS. 3A-3B, there is shown respectively in perspective and cross-sectional views a through-feed pipe 1 having a pair of oppositely arranged elongated slots 2. Excitation of the slots is effected by way of connecting the outer conductor of the LOS dipole coaxial feed cable 3 to one side of the slot by any operably suitable means, for example at 4, and the center conductor thereof to the other side, for example at 5. Points 4 and 5 are preferably to be located substantially at the center of the longitudinal dimension of the slot. The slot now becomes a non-radiating double stub balun with parallel arc-shaped conductors, for transferring the unbalanced impedance of the line to a balanced impedance to feed the dipole. The minor dimension of the slots is optimized according to desired operating conditions. If the Z,, of the balun is held to be in the area of 1800, the susceptance of the balun will tend to broaden the bandwith of the dipole radiator formed by the two coaxial radiating

cylinders

6a and 6b (FIGS. 4A and 4B). The latter are fed by radially arranged posts 7 from opposite sides of the fed elongated slot 2, and in one-to-one correspondence, with the resulting dipole pattern being parallel to the feed balun l in a vertically polarized omni-directional excitation. The radiator posts 7 are less than lhin length and may be optimized according to space requirements and desired operating characteristics. The length of one of the posts plus the radius of the balun feed pipe physically define the radius of the cylinders.

The balun feed through section 1 is truely multifunctional, in that, in addition to performing a balun function, it permits the through-passing of unrelated cabling 8 running for example to other antennas mounted above the novel LOS dipole, in a closely packed arrangement on the same signal mast, of which the feed balun section 1 itself unitarily forms a part. This feed assembly, moreover, provides the entire structural support required for the radiating

cylinders

6a and 6b (see FIGS. 4A and 4B), via the feed posts 7. To this end dielectric washer-shaped wafers ll, slipped over the balun section 1 and within each

cylinder

6a and 6b, may be added as shown in FIG. 4B, to aid in supporting the structure in a secure manner. These dielectric wafers 11 are not shown in FIG. 4A for purposes of clarity.

The radiator feed posts 7 associated with each

cylinder

6a and 6b are symmetrically positioned in a predetermined distance s from the center of the gap G formed between the adjacent ends of the pair of mounted cylinders. Attachment of the feed posts 7 to the

cylinders

6a and 6b and the balun feed section 1 may be fixed or demountable by way of any suitable means, such as screws. The distance s is predicated on desired operating conditions, in that it controls the impedance tapoff. It is to be considered within the scope of this invention to have the arrangement provide for adjustability as to the distance s to provide optimum operability over a variable range. Performance may be further optimized by including in the center conductor connection of coaxial cable 3 running to the slot at 5 an adjustable trimmer capacitor 9.

While the longitudinal dimension of the slots 2 and the assembled pair of

cylinders

6a and 6b have been represented in FIGS. 3A and 4A as X and Y, experi- 6 ment has shown that for the operational frequency band above-mentioned the X and Y dimensions may typically be 19 inches and 23 inches (or less) respectively. In this regard I have found the inventive LOS dipole antenna to produce a clean pattern over the 225-400 MHz band while situated in a closely packed arrangement as hereinbefore described.

Since an open connection exists between points on the balun feed pipe 1 beneath opposite radiator cylinder ends 6a and 6b (FIG. 4A), one would expect that the undesirable coupled currents would flow principally within the radiated cylinders 60 and 6b and be shielded from radiation. Experimental results on similarly fed radiators indicate that the impedance may he held below 3:] VSWR over the entirety of the l400 MHz band.

Experiment has shown, moreover, that further improvement in performance of the inventive antenna ar rangement is realized by substituting for the radiator posts 7 light metallic (conductive) segments 10 of a cone. FIG. 5 illustrates such a segment, typically a /4 segment of cone. Satisfactory performance has been realized with varying sizes of elements 10 up to the largest tested size of a 36 segment of cone. Preferably the segment 10 associated with each radiating

cylinder

6a and 6b should be substantially of the same size. The segments 10 may be coupled to the balun feed pipe 1 and to the

cylinders

6a and 6b by any suitable means which will provide an operatively satisfactory conductive path. They also may provide, as a multifunctional consideration, structural stability and support as formally offered by the feed posts 7.

In the above there has been described a novel LOS dipole antenna arrangement which permits substantial improvement in pattern characteristics by correspondingly reducing spurious coupling to adjacent structure, which may occur particularly where the antenna is found closely adjacent to unrelated structure in a space-restricted environment. Pattern improvement is based on the principle of the antennas symmetry being rigorously maintained, wherein a pair of adjacently arranged cylindrical radiators are fed by a double-ended balun structure created from the supporting and cable feed-through antenna mast. This balun feed assembly comprises a pair of oppositely arranged slots within the cylindrical radiators, with each conductor of the coaxial feed cable running to the feed assembly being coupled to either side of one of the slots. The excitation energy is transferred to the cylindrical radiators by way of symmetrically placed radial posts extending from either side of the energy-coupled slot to the inside of the cylinders.

While the principles of this invention have been described with specific apparatus, it is to be understood that description is made only by way of example and not as a limitation on the scope of the invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

l. A dipole antenna arrangement comprising:

(a) a radiating assembly disposed coaxially of a main axis, said radiating assembly including a pair of adjacent open-ended cylindrical radiators arranged about said main axis and spaced apart a predetermined separation; and

(b) an energy feeding arrangement concentrically arranged about said main axis and extending through said cylindrical radiators to be coaxial therewith, and coupled to said radiating assembly, said energy feeding arrangement including a balun assembly for providing a balanced impedance feed to said radiating assembly, and a pair of energy transport means arranged within and associated in one-toone correspondence with said pair of cylindrical radiators, said pair of energy transport means being disposed between said balun assembly and the respective ones of said cylindrical radiators to electrically couple to the latter the excitation energy from said balun assembly.

2. The arrangement according to claim 1 wherein said balun assembly constitutes a portion of the hollow mast for supporting the antenna arrangement, said portion having a pair of oppositely arranged elongated slot apertures cut into the mast.

3. The arrangement according to claim 2 wherein the feed to said arrangement is coaxial, with the outer conductor being coupled to one side of one of said slots substantially in the center of the longitudinal dimension thereof and the inner conductor being coupled to the other side of said one slot also substantially in the center of the longitudinal dimension thereof.

4. The arrangement according to claim 3 wherein said pair of cylindrical radiators is oriented relative to said slots such that the coaxial feed coupling to said one slot is positioned substantially at the center of the gap G formed between said cylinders.

5. The arrangement according to claim 3 wherein each of said slots has a predetermined longitudinal dimension X, and wherein the total longitudinal dimension Y between the remote ends of said pair of radiated cylinders is predetermined, both said X and Y dimensions being selectable in accordance with desired optimum operating conditions.

6. The arrangement according to claim 4 wherein said pair of energy transport means constitutes a pair of radially arranged energy transport posts, each of which is arranged a predetermined distance s away from the center of the gap G between said radiated cylinders and on either side, and on opposite sides of said coaxially coupled slot.

7. The arrangement according to claim 6 wherein said distance s is variable to correspondingly change the tap-off impedance.

8. The arrangement according to claim 7 wherein said radially arranged posts are less than A long.

9. The arrangement according to claim 3 wherein said balun assembly permits the through passage of unrelated feed cabling running to other antennas positioned further along the antenna support mast.

10. The arrangement according to claim 4 wherein said pair of energy transport means constitutes a pair of electrically conductive segments of a cone.

11. The arrangement according to claim 10 wherein the operative size range of said segments of cone is at least V4 segment to 34 segment of cone.

12. The arrangement according to claim 4 wherein an adjustable trimmer capacitance is inserted in the center conductor feed line, with one side thereof being coupled directly to the one side of said coaxially coupled slot.

13. The arrangement according to claim 4 further including a pair of dielectric washer-shaped wafers each of which is transversely disposed about said balun assembly and within a corresponding one of said radiating cylinders near the end thereof remote from said energy transport means, said wafers providing additional structural stability to the antenna arrangement.

is m m m n

Claims

1. A dipole antenna arrangement comprising: (a) a radiating assembly disposed coaxially of a main axis, said radiating assembly including a pair of adjacent open-ended cylindrical radiators arranged about said main axis and spaced apart a predetermined separation; and (b) an energy feeding arrangement concentrically arranged about said main axis and extending through said cylindrical radiators to be coaxial therewith, and coupled to said radiating assembly, said energy feeding arrangement including a balun assembly for providing a balanced impedance feed to said radiating assembly, and a pair of energy transport means arranged within and associated in one-to-one correspondence with said pair of cylindrical radiators, said pair of energy transport means being disposed between said balun assembly and the respective ones of said cylindrical radiators to electrically couple to the latter the excitation energy from said balun assembly.

8. The arrangement according to claim 7 wherein said radially arranged posts are less than 1/8 lambda long.

11. The arrangement according to claim 10 wherein the operative size range of said segments of cone is at least 1/4 segment to 3/4 segment of cone.