US3701159A

US3701159A - Discone antenna

Info

Publication number: US3701159A
Application number: US196279A
Authority: US
Inventors: Peter Simonds
Original assignee: Minister of National Defence of Canada
Current assignee: Minister of National Defence of Canada
Priority date: 1970-12-18
Filing date: 1971-11-08
Publication date: 1972-10-24
Anticipated expiration: 1989-10-24
Also published as: CA896742A

Abstract

The antenna structure disclosed is of the discone type and comprises six support towers arranged at the vertices of a hexagon. Active element supporting cables extend between the towers along the sides of the hexagon. A plurality of active elements radiate outwardly from a feed point located centrally of the hexagon to terminate on the supporting cables. The supporting towers are guyed by a plurality of guys anchored at six anchor points located on lines of intersection of vertical planes through the supporting cables. The guys extend outwardly of the hexagon within these vertical planes. The supporting tower and guying arrangement is extremely simple compared to prior arrangements. Furthermore, the feed point is supported above a platform raised above actual ground level and a plurality of ground wires extend radially outward of the platform and downwardly therefrom with the major portion of their length being buried beneath the ground. This eliminates problems of high frequency noise adjacent actual ground level and also eliminates problems of wind blown refuse, snow, etc., interfering with proper operation of the antenna. The antenna may be tuned by adjusting the height of the feed point above the platform and by means of a variable capacitor in the feed line to the antenna.

Description

United States Patent Simonds [451 Oct. 24, 1972 DISCONE ANTENNA Peter Simonds, Ottawa, Ontario, Canada [73] Assignee: Her Majesty the Queen in right of Canada as represented by the Minister of the National Defence 22 Filed: Nov. 8, 1971 [21] Appl.No.: 196,279

[72] Inventor:

[30] Foreign Application Priority Data Primary Examiner-Eli Lieberman Att0rney-R. S. Sciascia et al.

[ ABSTRACT The antenna structure disclosed is of the discone type and comprises six support towers arranged at the vertices of a hexagon. Active element supporting cables extend between the towers along the sides of the hexagon. A plurality of active elements radiate outwardly from a feed point located centrally of the hexagon to terminate on the supporting cables. The supporting towers are guyed by a plurality of guys anchored at six anchor points located on lines of intersection of vertical planes through the supporting cables. The guys extend outwardly of the hexagon within these vertical planes. The supporting tower and guying arrangement is extremely simple compared to prior arrangements. Furthermore, the feed point is supported above a platform raised above actual ground level and a plurality of ground wires extend radially outward of the platform and downwardly therefrom with the major portion of their length being buried beneath the ground.

, This eliminates problems of high frequency noise adjacent actual ground level and also eliminates problems of wind blown refuse, snow, etc., interfering with proper operation of the antenna. The antenna may be tuned by adjusting the height of the feed point above the platform and by means of a variable capacitor in the feed line to the antenna.

11 Claims, 7 Drawing Figures 1 DISCONE ANTENNA STATEMENT OF GOVERNMENT INTEREST The invention described herein maybe manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION A. Field of the Invention This invention relates to an antenna structure and in particular to a large discone antenna structure having an omni-directional radiation pattern.

B. Description of Prior Art:

Prior to the present invention there existed a need for high frequency antennas not subject to excessive structural failures and maintenance costs and able to withstand a wide range of weather conditions (particularly temperature changes) such as encountered in Canada.

The initial costs and installationcosts of many prior antennas were very high and, in order to accommodate the wide range of frequencies dictated by changes in the sunspot cycle, some antennas had had to be greatly increased in numbers (particularly rhombics), while others (e. g. log periodic types) had had their gains partially sacrificed in order to cover very wide bandwidths.

Rotatable log periodic antennas have been used to enable a good gain to be obtained in any selected direction by pointing the antenna in that direction. However, these have proved disappointing because of varying degrees of mechanical trouble which render them useless for prolonged periods. One of the main mechanical faults has been solved by, introducing a slip clutch which points the antenna away from the direction where it will receive severe damage in a high wind. This is hardly a complete solution, however, as cases will arise, such as a search-and-rescue operation, where the antenna gets pointed away from the area of interest in order to protect its somewhat delicate rotating mechanism.

SUMMARY OF THE INVENTION The present invention comprises a discone antenna which overcomes the above difliculties and is relatively inexpensive.

The discone antenna as a class or family of antennas, is not too well documented in the literature, although variations of it have been used in the VHF, UHF and HF radio fields. In long range HF usage a discone antenna of triangular design (USAF) was a backbone of long range communications used by the Americans in the Pacific theatre during the second world war. The classic design, first employed in the VHF spectrum, consists of a cone (simulated by slanting rods) topped by a circular disc at right angles to the axis of the cone, also simulated by radiating rods. This design cannot easily be converted to the high frequency spectrum on account of the problems which occur in conjunction with supporting the disc and cone which have to be much larger for I-IF than for VHF operation. Therefore, in practice, the structure is inverted, making a radiating wire ground mat become the disc and pointing the cone, consisting of radiating wires suspended on poles made of a non-radiating material,

2 downwards. In this form the structure is really an inverted discone, but in the high frequency field it is nonetheless simply referred to as a discone.

Certain aspects of the discone antenna according to the invention make it electrically as well as mechanically superior to other designs of this class. It is preferably provided with certain unique electrical features which are not common to high frequency antennas, to wit, the introduction of two variable tuning means which enable the user:

a. to adjust the antenna for the most favorable voltage standing wave ratios (VSWRs) for a number of scattered (assigned) frequencies.

b. to favor a range of frequencies e.g. 3.0 to 15 MHz) to meet the long range variations in the Sunspot cycle.

These tuning means will be discussed later on in the ensuing description of the invention.

According to the present invention, there is provided an antenna structure comprising six support towers arranged at the vertices of a hexagon and having active element supporting cables extending between the towers along the sides of the hexagon. The structure has a plurality of active elements radiating outwardly from a feed point located centrally of the hexagon to terminate on the supporting cables. The support towers are guyed by a plurality of guys anchored at six anchor points located on lines of intersection of vertical planes through-the supporting cables, the guys extending outwardly of the hexagon within the vertical planes.

Two vertical planes pass through each supporting tower and a guy extends in each of these planes from the top of a supporting tower to an anchor point. Additional guys may be provided extending in each plane from points intermediate the top and bottom (e.g. middle) of a support tower to an anchor point.

Preferably, the feed point is supported above a platform raised above actual ground level and a plurality of ground wires extend radially outward of said platform and downwardly therefrom with the major portion of their length being buried beneath the ground. The ground wires may extend outward beyond the supporting cables, i.e. beyond the limits of the hexagon.

The distance of the feed point above the platform is, in the preferred embodiment, made adjustable so that the antenna may be tuned. A further tuning means comprises a tuning capacitor inserted between the feed line and antenna.

BRIEF DESCRIPTION OF DRAWINGS The invention will now be further described in conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of the antenna structure according to the invention;

FIG. 2 is a plan view of the antenna layout;

FIG. 3 is an elevational view showing in more detail the feed point of the antenna with the ground wires;

FIG. 4 is a plan view of part of the structure shown in FIG. 3;

FIG. 5 is a plan view showing in some detail the structure of the feed for the antenna;

FIG. 6 is an elevational view, in cross section, of the feed shown in FIG. 5; and

FIG. 7 is a plan view showing the layout of the ground wires in relation to the active elements of the antenna.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The simplicity of the antenna according to the invention will be readily appreciated upon consideration of FIGS. 1 and 2. The antenna comprises six support towers arranged at the vertices of a hexagon as clearly seen in FIG. 2. Active element supporting cables 12 extend between the towers along the sides of the hexagon. These are stretched taut but of course cannot be made perfectly straight when viewed from the side. The supporting cables inevitably sag to some extent along catenary curves. A plurality of active elements l3 radiate outwardly from a feed point 14 located centrally of the hexagon to terminate on the supporting cables 12. The support towers 10 are guyed by a plurality of guys 15 anchored at six anchor points 16 located on lines of intersection of vertical planes through the supporting cables, e.g. the

vertical planes

20 and 21 indicated in FIG.'2. The guys 15 extend outwardly of the hexagon within these vertical planes.

As can be seen in FIG. 2, two vertical planes pass through each supporting tower,

e.g. planes

20 and 22 each pass through the supporting tower 10 at the upper right vertex of the hexagon. A guy extends in each of these planes from the top of a supporting tower to an anchor point. For example, guys in

planes

20 and 22 pass to the

anchor points

16 and 16. Referring to FIG. 1, additional guys 17 may be provided if additional strength is required. These also extend in each vertical plane but from points intermediate the top and bottom of a support tower to an anchor point, e.g. the middle of a support tower or slightly thereabove.

Referring to FIG. 2, it can be seen that anchor points 16 and 16" and support towers 10 and 10' are all in a common plane. Thus the tensioning of the guys is easily adjusted without bending the support towers one way or the other. Thus the guying is extremely simple.

FIG. 3 shows in a little more detail the feed point of the antenna. The active elements 13 connect to a conductive feed member 25 supported on a platform 26 which, in turn, is supported on a column member 27.

As shown in FIG. 5, the feed member 25 is1also hexagonal in shape and has a plurality of holes 28 around its upper periphery for attachment of wires (active elements) 13. A non-conductive plate 30 (FIG. 6) fits within the feed member 25 and this has a central hole 31 through which fits a pin 32. This pin 32 is coupled to tensioning means, e.g. a turnbuckle arrangement, within column 27 for applying tension to the active elements 13. A simplified form of turnbuckle arrangement is shown at 48 in FIG. 3. Underneath the surrounding feed member 25 is a conductive ring 33 to which is attached the ground wires 34, these being led down off platform 26 and being then buried underground as indicated by dashed lines such as 35. The ring is more clearly seen in FIG. 4 wherein it is shown sitting on frame members 3639 which, in turn, are supported by outer frame 40 which may simply be constructed of wood. This outer frame 40 is supported on posts 27 having suitable footings not shown.

Obviously, the height of the feed member 25 above the platform 26 may be varied by adjusting the turnbuckle 48. These variations in height enable tuning of the antenna for reasons mentioned above. The fact that all modern radio circuits work on specific assigned frequencies makes the feature of being able to reinforce specific frequencies of particular importance.

Referring again to FIG. 3, lead 41 comprises a ground connection for the antenna while connection for the active elements may be made to post 42 having a lead 43 connected to the feed member 25. FIG. 3 also shows bracings 44 for frame member 26.

A feed line 51 is shown connected to the feed point through a variable capacitor 52 which enables further tuning of the antenna.

The relationship existing between the two tuning means is a complex one, being neither arithmetic or logarithmic in nature. While this relationship has not been worked out mathematically it has proven to be quite easy to tune the antenna empirically. Typically, the height of the feed member 25 above the platform 26 varies from 1.5 to 3.0 inches and the capacitor settings also vary considerably. This height is, of course, measured from the bottom (frustum) of the feed member 25.

Plates 45 may be buried in the ground through which ground wires 35 extend radially outward. FIG. 7 shows in plan view the arrangement of the ground wires 35, the tiny circles indicating where they enter the ground. The hexagonal outline of the active portion of the an tenna is also shown together with the support towers. The dotted line 50 indicates that the first ground wire should be offset slightly so as not to intersect one of the support towers l0. The ground wires 35 may extend for some distance beyond the outer limits of the active elements of the antenna, i.e. for some distance beyond the hexagon. Of course the ground mat may be a buried screen and the support for the feed means need not be as shown in FIGS. 3 and 4. The main thing is to have the feed member 25 raised above ground e.g. 6 feet, and a hole should be provided below the feed member for leaves or other wind-blown refuse to fall to the ground.

The size of the antenna depends on the frequencies to be used but it is pointed out that this antenna may be of considerable size. For a cut-off frequency between 2 and 3 IVE-I2 the sides of the hexagon may be feet and the supporting cables may be about 68 feet above the ground.

What is claimed is:

I. An antenna structure comprising six support towers arranged at the vertices of a hexagon and having active element supporting cables extending between said towers along the sides of the hexagon, said structure having a plurality of active elements radiating outwardly from a feed point located centrally of said hexagon to terminate on said supporting cables, said support towers being guyed by a plurality of guys anchored at six anchor points located on lines of intersection of vertical planes through said supporting cables, said guys extending outwardly of said hexagon within said vertical planes.

2. An antenna structure as claimed in claim 1 wherein two vertical planes pass through each support tower and a guy extends in each of these planes from the top of a support tower to an anchor point.

3. An antenna structure as claimed in claim 2 wherein additional guys extend in each plane from points intermediate the top and bottom of a support tower to an anchor point.

4. An antenna structure as claimed in claim 2 wherein said feed point is supported above a platform raised above actual ground level and a plurality of ground wires extend radially outward of said platform and downwardly therefrom with the major portion of their length being buried beneath the ground.

5. An antenna structure as claimed in claim 3 wherein said feed point is supported above a platform raised above actual ground level and a plurality of ground wires extend radially outward of said platform and downwardly therefrom with the major portion of their length being buried beneath the ground.

6. An antenna structure as claimed in claim 4 wherein said ground wires extend outwards beyond said supporting cables.

7. An antenna structure as claimed in claim 4 wherein means are provided for adjusting the height of r the feed point above said platform whereby the antenna may be tuned by adjusting said height.

8. An antenna structure as claimed in claim 5 wherein means are provided for adjusting the height of the feed point above said platform whereby the antenna may be tuned by adjusting said height.

9. An antenna structure as claimed in claim 1 including a feed line connected through a variable capacitor to said feed point whereby the antenna may be tuned by varying said capacitor.

10. An antenna structure as claimed in claim 4 including a feed line connected through a variable capacitor to said feed point whereby the antenna may be tuned by varying said capacitor.

11. An antenna structure as claimed in claim 8 including a feed line connected through a variable capacitor to said feed point whereby the antenna may be tuned by varying said capacitor.

Claims

1. An antenna structure comprising six support towers arranged at the vertices of a hexagon and having active element supporting cables extending between said towers along the sides of the hexagon, said structure having a plurality of active elements radiating outwardly from a feed point located centrally of said hexagon to terminate on said supporting cables, said support towers being guyed by a plurality of guys anchored at six anchor points located on lines of intersection of vertical planes through said supporting cables, said guys extending outwardly of said hexagon within said vertical planes.

7. An antenna structure as claimed in claim 4 wherein means are provided for adjusting the height of the feed point above said platform whereby the antenna may be tuned by adjusting said height.