US3665479A

US3665479A - Omnidirectional tower supported antenna

Info

Publication number: US3665479A
Application number: US58975A
Authority: US
Inventors: Robert M Silliman
Original assignee: ELECTRONICS RESEARCH Inc
Current assignee: ELECTRONICS RESEARCH Inc
Priority date: 1970-07-28
Filing date: 1970-07-28
Publication date: 1972-05-23
Anticipated expiration: 1989-05-23

Abstract

A combined dipole-loop antenna for bipolarized radio frequency signals. A dipole-loop is mounted on each face of an electrically large multi-faceted tower such as a triangular tower with the plane of the loop being perpendicular to the axis of the tower and transverse to the face plane of the tower with the dipole portion extending above and below the loop and parallel to the vertical axis with the loop portion encircling the transmission line and the dipole portion facing the tower.

Description

United States Patent Silliman 5] May 23, 1972 54] ()MNIDIRECTIONAL TOWER 3,299,429 1/1967 McMullin ..343/803 SUPPORTED ANTENNA 3,413,644 11/1968 Laub et al ..343/890 3,474,452 10/1969 Bogner ..343/726 1 111mm" silliman, sllver 511mg, 3,555,552 1/1971 Alford ..343/726 :EtrniR hl.E 'll,ld. [73] Assignee lec 0 cs esearc nc vansvi e n Primary Examiner Eli Lie man [22] Filed: July 28, 1970 Attorney-Leonard H. King [21] Appl. No.: 58,975 [57] ABSTRACT A combined dipole-loop antenna for bipolarized radio [52] 11.8. CI ..343/726, 343/744, 35125383931, frequency Signals. A dipolfloop is mounted on each face of [51] Int Cl Holq 21/00 an electrically large multi-faceted tower such as a triangular [58] Fieid 730 744 tower with the plane of the loop being perpendicular to the 5 axis of the tower and transverse to the face plane of the tower with the dipole portion extending above and below the loop and parallel to the vertical axis with the loop portion encir- [56] Reerences cued cling the transmission line and the dipole portion facing the UNITED STATES PATENTS tower- 2,63l,237 3/1953 Sichak et al. ..343/800 9C1aims, 9 Drawing Figures PATENTEDMAY23 L972 3 665 479 sum 1 0r 2 (P2103 ART) FIG. 2

INVENTOR. ROBERT M JILL/MAN A Trail/v51 PATENTEDMAY 23 I972 3. 665 479 sum 2 OF 2 INVENTOR. ROBERT M JILL/MAN g m/wk ATTORNEY OMNIDIRECTIONAL TOWER SUPPORTED ANTENNA BACKGROUND OF THE INVENTION In broadcasting, it is often required to have a transmitting (or receiving) antenna which radiates approximately omnidirectionally, or equally in every horizontal direction, and which is also capable of transmitting both horizontally and vertically polarized electromagnetic waves. Such an antenna is described in the copending application of Richard D. Bogner, Ser. No. 616,541, now US. Pat. No. 3,474,452 and assigned to the assignee of this application. The prior art antenna employs a combined dipole and loop with the dipole exterior to the loop and a single feed point. The dipole extends from the ends of the open loop and is on the opposite side of the loop from a tower which comprises a small diameter structural support and serves as a transmission line feed support. The transmission line connects to the ground located transmitter. The tower is capable of supporting additional parts above and below each antenna bay. The antenna in the prior art application is shown to provide omnidirectional radiation in the horizontal plane, for both horizontal and vertical polarization. The percent of energy in each polarization occurs in controlled relative percentages depending on the length of the dipole in relation to the loop. However, this performance remains valid only when the combined major transverse dimension (that is, the dimension in the horizontal plane) of the feed line and supporting structure is less than about oneeighth wavelength.

It has been found that when this prior art Bogner dipoleloop combination is placed in front of a larger supporting structure, such as for example a multifaced or triangular metal tower having a transverse dimension greater than one-eighth wavelength and less than 1 wavelength, which range is commonly used for this purpose, the radiation pattern begins to depart considerably from omnidirectional because of the shadowing effect of the tower. It would appear to be an obvious solution to simply use more than one of the prior art Bogner dipole-loop combinations at each vertical level or bay level of the tower, for example, placing one opposite each face of the tower and feeding each with equal amplitude and phase voltages. It has been found, however, that when such a design is attempted, omnidirectional performance cannot be obtained in practice, when the tower face transverse dimension is in the range of one-eighth to l wavelength.

An unanticipated result is obtained when the transmission line extends outwardfrom the tower face and the circular loop with the dipole emanating from the end thereof doubles back" to the tower face, thereby encircling the transmission line, is placed at a proper distance in front of each tower face. The tower may now have a transverse dimension in the range of one-eighth to l wavelength without introducing a shadowing'effect to the radiation pattern.

It is an object of the present invention to provide an antenna which may be mounted on a medium sized multi-faceted tower and which will provide a bipolarized, omnidirectional radiation pattern.

Another object of the present invention is to utilize essentially the same type bipolarized antenna structure as has previously been employed with small towers, to achieve omnidirectional, bipolarized radiation of larger towers.

Still another object is to provide a tower mounted antenna array which provides a bipolarized omnidirectional radiation pattern.

A still further object is to provide a dipole-loop wherein the loop encircles the transmission line feeding the dipole-loop and the dipole extends orthogonally to the loop and the point of entry of the transmission line.

These and other objects, features and advantages of the invention will, in part, be pointed out with particularity and will,

in part, become obvious from the following more detailed description of the invention in conjunction with the accompanying drawing which forms an integral part thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows in perspective a prior art dipole-loop combination carried by a small tower as a support;

FIG. 2 shows in perspective the prior art dipole-loop combination mounted on a medium sized triangular tower;

FIG. 3 shows in perspective a medium sized triangular tower with a plurality of dipole loop antenna members mounted with the dipole portion positioned vertically and secured to the tower and the loop portion extending horizontally.

FIG. 4 shows a top view of the medium sized triangular tower with a single bay of the antennas of FIG. 3;

FIG. 5 shows in perspective a single dipole-loop element with another feed arrangement;

FIG. 6 is a perspective showing of a single dipole loop ele ment connected to a section of transmission line and a mounting plate for mounting the element to a tower (not shown).

FIGS. 7A, 7B and 7C are plan views of towers having mounted thereon arrays of dipole-loops of this invention in combination with parasitic elements.

Referring to FIG. 1, the transmission line and support structure 10' with vertical axis 30 and center conductor 26' support coaxial transmission line 12, which is connected to loop feed point 14 of the dipole-loop antenna P. The transmission line and support structure 10 feeds loop arms 16' and 18' and then feeds dipole arms 22' and 24' across gap 20. The

dipole arms

22 and 24 are arranged in a vertical direction and are parallel to axis 30, as is shown.

In FIG. 2 there is shown the prior art Bogner dipole-loop P mounted on a large tower (e.g., having a transverse dimension greater than one-eighth wavelength). It has been found that the large tower produces a shadow effect which destroys the desired omnidirectional pattern. It would appear that with a dipole-loop P on each face of the larger tower one would avoid the shadow effect of the tower. Surprisingly, in practice it has been found that this obvious application of the prior art dipole-loop to a larger triangular tower, does not produce a bipolarized omnidirectional signal. However, it has been found that interchanging the position of the

dipole

22 and 24 with the loop 16' and 18 of antenna P, a dipole-loop results which may be deployed in multiple around the tower and which overcomes the shadowing problem.

In FIGS. 3 and 4 there is shown the use of a plurality of the reversed dipole-loops arranged about a tower to avoid the shadow effect of the tower itself. It is to be understood that the tower may be constructed of many surfaces (multi-faceted) and that the triangular tower is one such embodiment. The an tenna arrays would be arranged to appear on each surface of the tower in the same horizontal plane. Each such horizontal bank is called a bay. For a circular tower in excess of a wavelength in transverse dimension, the dipole-loops would be spaced around the circumference at approximately wavelength intervals. For example, the shadow effect of a water tower used as an antenna support may be eliminated by proper placement of the antennas about the circumference, as will be described more fully hereinafter.

In the present embodiment the tower faces 32, 34 and 36 are open (or metal mesh-covered) and arranged about tower axis 30. Dipole-loops 21 are mounted on each of the faces. Dipole-loop feed line 10 is shown as representative of feed lines. Feed lines would be divided within the tower to place equal amplitude and phase voltages at each of the three dipole-loops 21 of a bay. The plane of the loops l6 and 18 is horizontal (transverse to the tower face) and perpendicular to the tower axis 30.

FIG. 4 shows a top view of a triangular

tower having faces

32, 34, 36 with a dipole-loop as shown in FIG. 3, attached to each one of the three faces. This group of antennas forms a single level or bay. In a vertical direction along the axis 30 of the tower there would be a number of such bays consistent with the gain desired.

Still another feed arrangement is shown in FIG. 5. A coaxial feed line 12 is coupled to vertical feed line 10. The outer conductor 1 1 of the horizontal feed line is mechanically and electrically connected to the loop 18. The inner conductor terminates in impedance matching strap 15. This feed arrangement differs from that disclosed in the earlier mentioned Bogner U.S. Pat. No. 3,474,452 in that the feed line passes between the

dipole elements

22 and 24. In order to compensate for the effect of the feed line on the interelectrode capacitance between the dipole elements, the spacing between the elements would have to be suitably adjusted. The proper spacing can be readily determined by empirical testing.

It has been found that the diameter of the loop formed by

arms

16 and 18 should be in the range of one-twelfth and onehalf wavelength (and generally between one-tenth and onefourth wavelength) and the total length of

arms

22 and 24 should be in the vicinity of one-third wavelength (generally between one-fourth and something slightly smaller than onehalf wavelength) for best performance.

The dipole-loop may be fed at feed point 14 by a feed line 12 which if rigid can provide mechanical support. In addition, dielectric supports 31 between the tower and the dipole elements may be used to provide mechanical rigidity. As shown in an alternative embodiment on face 36, a single feed line 12A may be coupled, through a splitter 128, to a pair of dipole-loop elements.

At feedpoint 14 a balun or other balance to unbalance transformer, may be employed to interconnect a coaxial transmission line with its two-wire input to dipole-loop 21. An impedance transformer may be combined with the balun for a proper impedance match. Capacitance plates may be used across gap 20 to provide additional capacity, or cause other impedance change at the gap. The dipole-loop may be made of any suitable metallic material. Brass and copper have been found suitable electrically and structurally for this application. The

loop arms

16 and 18 may be composed of a number of rings of 1 inch diameter copper tubing vertically arranged and interconnected electrically to effectively form a single, sheettype loop. The tower face may be covered with a metal mesh such that the openings are considerably less than one-eighth wavelength in dimension to form an effective closed ground screen. It has been found that thus enclosing the normally open work in the tower structure improves performance.

This invention has been found suitable with towers up to a wavelength in the transverse dimension and may be used on towers of triangular or square configuration provided a dipoleloop as described is mounted on each face. For multifaceted configurations which may be considered round in cross-section, approximately one dipole-loopwould be used for each wavelength of effective circumference. The antenna disclosed in this invention may also be utilized with towers having a transverse dimension of less than one-eighth wavelength.

The dipole-loop would be so located with reference to the tower that the vertical axis of the dipole portion is between one-eighth and one-half wavelength from the tower face.

A particularly rigid construction is obtained when the dipole-loop is mounted on metallic supports by its inner ends. As shown in FIG. 6 this is accomplished by extending the loop 50 back to the tower (not shown) by a metallic support 52, forming a resonant quarter wavelength balun like support bracket. The support bracket 52 has an opening and loop is hollow to permit the coaxial feed line 58 to reach the feed point C by running the inside of the supporting bracket through the hollow loop to a hole at point A through which the feed line 58 passes and at which point the outer conductor is grounded to the loop to form a feed loop. The outer conductor terminates at point B" and the inner conductor passes on to point C" where it connects to the loop completing the circuit of the coupling loop. Mounting plate 52 permits securing the device to the tower.

An unanticipated improvement in pattern circularity was obtained with the antenna system mounted on a sizeable (i.e. in excess of a wavelength in cross-section) triangular supporting tower as shown in FIG. 7A and FIG. 7B or circular supporting tower as shown in FIG. 7C. The improvement was obtained by mounting beam forming or parasitic radiating elements interspersed around the tower or supporting structure between the radiating elements 71 at critical distances out from the supporting structure between one-fourth wavelength and one-half wavelength. The parasitic elements contained a horizontal dipole member 73 and a vertical dipole member 75 each individually positioned and adjusted in length to produce the optimum pattern improvement. These elements are mounted on a dielectric support 77 extending from the tower or supporting structure.

This invention requires a minimum of two dipole-loops per bay as compared to the single dipole-loop employed in the aforesaid Bogner patent. However, the present invention permits the use of a large tower.

In the foregoing description and appended claims the term )t represents wavelengths of signals at the operating frequencies of interest.

There has been disclosed heretofore the best embodiment of the invention presently contemplated and it is to be understood that various changes and modifications may be made by those skilled in the art without departing from the spirit of the invention.

What I claim as new and desire to secure by Letters Patent is:

1. An omnidirectional bipolarized antenna system for signals of wavelength A, having a multi-faced vertical tower structure supporting a plurality of identical active antennas each opposite an individual face, wherein each of said antennas comprises: a transmission feed line extending perpendicularly outward from said face to feed the antenna with an equal amplitude and phase signal as the other antennas, a loop of approximately Va A diameter emanating from the end of said transmission line, said loop having two non-joining semi-circular sections folded back toward said face, encircling said transmission line but permitting it to pass between the unjoined ends, said loop and transmission line defining a plane transverse and perpendicular to the face, and two dipole arms each connected to a different end of said semi-circular sections and pointing in opposite directions, said arms each approximately A )t in length and being parallel to said transmission face, said dipole arms positioned about one-eighth A to about one-half A from each of said tower faces.

2. A system as in claim 1, wherein said tower is a large triangular tower having said antennas on each of its three faces in a lateral plane thereby forming a bay.

3. A system as in claim 2 wherein said tower compresses a plurality of bays, each spaced from the other in a vertical direction.

4. A system as in claim 1 further including a pair of capacitor plates each attached to an end of said semicircular sections, wherein said dipole arms are mechanically supported by said capacitor plates.

5. The system of claim 1 including a plurality of passive antenna elements operative at a wavelength A, said passive elements being interspersed between said active antennas.

6. A high frequency antenna array for radiation of an omnidirectional bipolarized signal of wavelength A comprising:

a. a metal tower extending vertically along a longitudinal axis and having a transverse dimension greater than I wavelength;

b. a plurality of dipole-loop radiators mounted on said tower and spaced therefrom, each said dipole-loop radiator comprising:

1. a conductor forming a peripherally incomplete loop having two ends spaced in opposed relationship, said loop being oriented in the horizontal plane and having a diameter suitable for radiating signals of wavelength A;

2. a first conductive member having one end joined to point.

one of said loop ends and a second vertical conductive 7. The array of claim 5 wherein at least two of said dipolemember having one end joined to the other of said loop loop radiators being positioned at points at the same tower ends, said vertical members extending in o it elevation separated from each other horizontally by at least a directions and of suitable length to act as a dipole 5 distance radiator for signals of wavelength X; and 8. The apparatus of claim 6 wherein said feedline means c. feedline means connected to said conductor at a point ap- Passes thl'ollgh the p f g in the Peripheral pproximately opposite the open point of said loop for car- The system of f" 6 mcludmg a P "Y P rying a signal from a transmission line to said dipole-loop tenna eleimeflis operatlve at a wavelength 531d Passive radiator said dipole loop radiator being Oriented with 10 ments bemg interspersed between said active antennas. said dipole radiator closer to the tower than said feed

Claims

1. An omnidirectional bipolarized antenna system for signals of wavelength lambda , having a multi-faced vertical tower structure supporting a plurality of identical active antennas each opposite an individual face, wherein each of said antennas comprises: a transmission feed line extending perpendicularly outward from said face to feed the antenna with an equal amplitude and phase signal as the other antennas, a loop of approximately 1/8 lambda diameter emanating from the end of said transmission line, said loop having two non-joining semicircular sections folded back toward said face, encircling said transmission line but permitting it to pass between the unjoined ends, said loop and transmission line defining a plane transverse and perpendicular to the face, and two dipole arms each connected to a different end of said semi-circular sections and pointing in opposite directions, said arms each approximately 1/3 lambda in lenGth and being parallel to said transmission face, said dipole arms positioned about one-eighth lambda to about onehalf lambda from each of said tower faces.

2. a first conductive member having one end joined to one of said loop ends and a second vertical conductive member having one end joined to the other of said loop ends, said vertical members extending in opposite directions and of suitable length to act as a dipole radiator for signals of wavelength lambda ; and c. feedline means connected to said conductor at a point approximately opposite the open point of said loop for carrying a signal from a transmission line to said dipole-loop radiator, said dipole-loop radiator being oriented with said dipole radiator closer to the tower than said feed point.

5. The system of claim 1 including a plurality of passive antenna elements operative at a wavelength lambda , said passive elements being interspersed between said active antennas.

6. A high frequency antenna array for radiation of an omnidirectional bipolarized signal of wavelength lambda comprising: a. a metal tower extending vertically along a longitudinal axis and having a transverse dimension greater than 1 wavelength; b. a plurality of dipole-loop radiators mounted on said tower and spaced therefrom, each said dipole-loop radiator comprising:

7. The array of claim 5 wherein at least two of said dipole-loop radiators being positioned at points at the same tower elevation separated from each other horizontally by at least a distance lambda .

8. The apparatus of claim 6 wherein said feedline means passes through the opening in the peripheral loop.

9. The system of claim 6 including a plurality of passive antenna elements operative at a wavelength lambda , said passive elements being interspersed between said active antennas.