US3541570A

US3541570A - Circularly polarized antenna

Info

Publication number: US3541570A
Application number: US747949A
Authority: US
Inventors: Peter K Onnigian
Original assignee: Computer Equipment Corp
Current assignee: JAMPRO ANTENNAS INC A CORP OF; Computer Equipment Corp
Priority date: 1968-07-26
Filing date: 1968-07-26
Publication date: 1970-11-17
Anticipated expiration: 1987-11-17

Description

Nov. 17, 1970 P. K. 0NN|GlAN CIRCULARLY POLARIZED ANTENNA 2 Sheets-Sheet 1 Filed Jul 26, 1968 INVENTOR. PETER K. ONN IGIAN ATTORNEYS Nov. 17, 1 970 P. K. ONNIGIAN 3,541,570

CIRCULARLY POLARIZED ANTENNA Filed July 26, 1968 2 Sheets-Sheet 2 FIG/T3 ofizy zw ATTORNEYS United States Patent Olhce Patented Nov. 17, 1970 US. Cl. 343704 9 Claims ABSTRACT OF THE DISCLOSURE A substantially horizontal support tube mounted on an antenna tower carries at each end a V-shaped element, each element including a part of arms each onefourth wavelength in length. Together, the two V-shaped elements form a substantially square-shaped configuration with the support tube as a diagonal. Electrical signal conducting means connect the center of one of the arms on each of the V-shaped elements to a terminal on the support tube. By providing an appropriate electrical signal at the terminal, the elements serve as radiators of a circularly polarized signal. The elements can also be used as receivers. By angularly inclining the planes formed by the two V-shaped elements, the respective horizontal and vertical field strengths can be selectively regulated.

The invention relates to improvements in antennas for radiating or receiving circularly polarized electromagnetic radiation.

In connection with radio broadcasting it is well known that the polarization of a receiving antenna varies between pure vertical and pure horizontal. Exemplary of the vertical type is the automobile whip; of the horizontal, the outdoor yagi type mounted on a rooftop. The former responds efliciently only to vertically polarized radiation; the latter, only to horizontally polarized radiation.

T o afford satisfactory reception to both kinds of radiation, separate transmitting antennas have heretofore been constructed and operated so as to radiate signals having dual polarization, i.e., one radiator to afford vertical linear polarization and another to provide horizontal linear polarization.

A disadvantage of the dual polarization system of transmitting, however, is that the use of two antennas has been costly and complicated as well as being difficult to mount. Excessive weight and increased wind resistance has also been a problem.

It is therefore an object of the invention to provide an eflicient and relatively inexpensive antenna which produces both vertically polarized as well as horizontally polarized radiation.

It is a further object of the invention to provide a circularly polarized antenna wherein the ratio of horizontally polarized to vertically polarized radiation can be regulated with a nice degree of control.

It is yet a further object of the invention to provide a radiating element which has a useful VSWR (Vertical Standing Wave Ratio) bandwidth, thereby being exceptionally useful in connection with TV broadcasting transmitters.

It is still a further object of the invention to provide a radiating device which is omnidirectional, i.e., one which radiates in all degrees of azimuth, even when side mounted, for example, on a steel supporting structure.

It is another object of the invention to provide an antenna which produces circularly polarized radiation with but one single feed point.

It is still another object of the invention to provide a radiating element which can be efficiently utilized in vertically stacked arrays so as to provide additional power gain ratios over that obtained by using one such element.

It is yet another object of the invention to provide a radiation element which, when arrayed with other such elements, can be arranged so as to tilt the main resulting beam below the horizontal in a controlled manner.

It is an additional object of the invention to provide an antenna system in which circularly polarized radiating elements can be used to afford electrical null fill-in at appropriate vertical angles of radiation in all azimuth directions.

It is also an object of the invention to provide an antenna radiating element which can readily be de-iced.

It is another object of the invention to provide a generally improved circularly polarized antenna.

Other objects, together with the foregoing, are attained in the embodiment described in the following description and shown in the accompanying drawings in which:

FIG. 1 is a perspective view showing a circularly polarized antenna mounted on a typical, elevated supporting structure the de-icing elements being shown diagrammatically and in phantom;

FIG. 2 is a fragmentary side elevational view, to an enlarged scale, of the support tube, portions being broken away to reveal interior details of construction;

FIG. 3 is a fragmentary, front elevational view, to a diiferent scale, showing the planes of the two V-shaped radiating elements arranged in approximately a 45 relationship.

While the circularly polarized antenna of the invention is susceptible of numerous physical embodiments, depending upon the environment and requirements of use, and can also efi'iciently be utilized as a receiving antenna, it has found its greatest utility in connection with commercial TV transmitters.

In the latter environment, the antenna of the invention, generally designated by the reference numeral 12, is customarily mounted, by suitable hardware 13, on an elevated supporting structure 14, such as a tower. In order to achieve higher gain a plurality of substantially identical antennas are usually arrayed vertically on the tower in suitably spaced relation, such as a wave-length apart. The mounting hardward 13 includes a mounting plate 16 affixed by U-clamps 17 to the tower pole 14. The mounting plate 16 carries an upwardly and outwardly extending post 18 terminating in a clamping bracket 19 secured by fastenings 21 to a horizontal main support arm 22 constructed of strong brass tubing.

. Either a simple shunt fed system or a power divider with individual feed lines going to each bay can be utilized for the feed system connecting the signal source to the respective' radiating elements. Included in the feed system is the customary coaxial cable 31 and attendant fittings 32 which are all of conventional construction. Since the feed system forms no direct part of the present invention it is neither shown not described in detail.

At the base end of the main support tube 22 is a collar 36 having mounted thereon a V-shaped, radiating element 37. The V-shaped element 37 is defined by a pair of oppositely located

inclined sleeves

38 and 39 carrying a live arm 41 and a parasitic arm 42, respectively. Threadably mounted on the end of the parasitic arm 42 is a trimmer cap 43 enabling the horizontal radiator 37 to be trimmed, i.e., to be adjusted so as to obtain the desired electrical characteristics.

Each of the arms 41 and 42 is equal in length to onefourth the wave-length of the transmitter frequency and the arms are made of brass tubing, brass also being the preferred material from which the other radiator components are fabricated.

Arranged in opposed symmetry with respect to the V- shaped radiator 37 is a V-shaped radiating element 47.

The radiator 47 includes a collar 51 mounted on the free end of the support tube 22. The collar 51 carries, on opposite sides, a pair of support sleeves '52 and 53, within which sleeves are disposed

arms

56 and 57, respectively. The arm 57 is a live arm in the sense that it is electrically connected to the signal source. The arm 56 on the other hand, is parasitically excited. An adjustable trimmer cap 58 on the end of the arm 56 is utilized to achieve for the radiator 47 the desired electrical characteristics.

The signal from the coaxial cable 31, as previously explained, is conducted through the conventional fitting 32, thence along an axially disposed rod 61 (see FIG. 2) and into a vertical stub rod 62 extending upwardly into a terminal housing 63 located intermediate the ends of the main support arm 22. Preferably, the terminal 63 is located midway on the arm 22, consistent with the symmetrical arrangement of the radiator components. The axial rod 61 is suitably supported by insulating spacers 66 from the tubing 67, and the vertical stub rod conductor 62 passes upwardly through the housing 63, projecting upwardly through the top 68 of a cap 69 of insulating material. The upper projecting end 71 of the stub conducting rod 62 is threaded so as to receive a nut 72 holding down the flattened central portion 73, or hub, of a pair of oppositely extending tubular conductors 76 and 77, or feed arms. In the usual case, the feed arms 76 and 77 extend outwardly at an angle of about 12 above horizontal (see FIG. 2).

The first feed arm 76 extends to a clamp 78 located midway between the ends of the live arm 57 and the second feed arm 77 extends to a clamp 79 located midway between the ends of the live arm 41, as appears most clearly in FIG. 3.

In the embodiment shown and described herein, each of the

sleeves

38 and 39 projects away from the collar 36 at a 45 angle, thus together forming a 90 corner. The

sleeves

38 and 39, furthermore, and thus the radiator arms 41 and 42, lie in a common plane. The resultant radiator 37, in other words, is a V-shaped structure wherein the arms intersect in effect, at 90, and the arms diverge in a direction away from the proximal end of the main support arm 22.

In comparable fashion, but with the

arms

56 and 57 diverging in a direction extending away from the nether end of the main support tube, and toward the opposite end, the radiator 47 is formed into a V-shaped configuration, with the arms intersecting, as it were, at an angle of 90".

For purposes of explanation it will first be assumed that both radiator 37 and radiator 47 are substantially horizontal, varying therefrom only because of the outer diameters of the touching tubular arms, i.e., with arm 41 touching arm 56, and with arm 42 touching arm '57.

In this configuration, the four arms define, in essence, a square, with the main support tube 22 forming a diagonal of the square.

With the

radiators

37 and 47 in this substantially horizontal posture a signal emanating from the antenna will, for the most part, be horizontally polarized.

However, by rotating the collar 36 in one direction and the collar 51 in the other direction so that the

respective radiators

37 and 47 assume the angular relationship shown most clearly in FIG. 3, a circularly polarized wave form is generated and transmitted in an omnidirectional fashion.

It has been found, furthermore, that this construction, comprising in a sense two dipoles bent to form a generally square in plan configuration, affords an extremely low VSWR. There is no capacity loading and thus the Q is low. The length to diameter ratio of the four 4 wavelength arms is approximately 15, thereby also improving the VSWR. There are no matching transformers inside the elements, and this recognized limitation to effective VSWR is also removed. The resulting VSWR on normal size towers is under 1.1 to 1.0 for bandwidth of carrier frequency i200 kilocycles. At carrier i500 kc., the VSWR is under 1.15 to 1.00.

Although neither shown nor described in detail it is also believed to be of great practical importance, under certain installations, that de-icing can readily be effected with the apparatus herein. The antenna can, in fact, withstand a slight coating of an inch) of ice without deterimental effects, either mechanically or electrically. If heavier icing occurs, electrical de-icers can readily be installed. Each antenna is preferably fitted with five deicing members 1, 2, 6 and 7, respectively one in each of the /4

wavelength radiating arms

41, 42, 56 and 57 and one 5, in the main support feed arm 22. A separate two wire system 8 drawing 500 watts at 220 volts has been found to serve in a very satisfactory manner.

The adjustability of the two radiating

elements

37 and 47 has been found to provide a high degree of flexibility and control over the relative amounts of power gain in the two planes (i.e. horizontal and vertical). For example, ratios from 50% horizontally polarized and 50% vertically polarized power gains, to 80% horizontal and 20% vertical can readily be achieved by appropriate angulation of the two support collars 36 and 51.

In many instances, for example, it has been found that owing to transmitter power limitations, costs, and other factors, it may not be desirable to have 50/ 50 horizontal to vertically polarized gain ratios. With the construction illustrated and described herein it becomes readily possible to vary the ratio. Thus, while space phasing from the common feed point provides the phase quadrature necessary for true circular polarization, such as is obtained by twisting the square to the 45 relationship shown in FIG. 3, it is also to be noted that by shifting the collars 36 and 51 to other angular positions, elliptical polarization is attained, thereby achieving other ratios than 50/50, as is sometimes desired.

It can therefore be seen that I have provided a versatile, readily adjustable antenna which affords numerous desirable mechanical and electrical properties under a Wide range of circumstances.

What is claimed is:

1. A circularly polarized antenna comprising:

(a) a support tube arranged for mounting in horizontal attitude at an elevated location;

(b) a first pair of V-shaped arms mounted on one end of said tube;

(c) a second pair of V-shaped arms mounted on the other end of said tube; and,

(d) means for conducting an electrical signal between a first location intermediate said ends of said support tube and a second location intermediate the ends of one of said first pair of arms, and between said first location and a third location intermediate the ends of one of said second pair of arms.

2. An antenna as in claim 1 wherein said first pair of arms lies in a first plane and said second pair of arms lies in a second plane, and wherein said first pair of arms and second pair of arms are mounted on said support tube to afford selective angular positioning between said first plane and said second plane.

3. An antenna as in claim 1 wherein said signal conducting means conducts an electrical signal from said first location to said second location and from said first location to said third location in the case of a transmitting antenna and in a reverse direction in the case of a receiving antenna.

4. An antenna as in claim 1 wherein said first pair of arms and said second pair of arms together form a substantially square-shaped configuration, and wherein said support tube substantially forms a diagonal element of said square-shaped configuration.

5. An antenna as in claim 4 wherein each of said arms has a length equal to one fourth the wavelength of the electrical signal; and wherein said first location is substantially midway between said ends of said support tube;

and wherein said second and said third locations are substantially midway between the ends of the respective ones of said first pair of arms and said second pair of arms.

6. An antenna as in claim 5 wherein the others of said first and said second pair of arms are parasitically excited.

7. An antenna as in claim 6 further characterized by trimming means on each of said pair of arms for selectively adjusting the electrical characteristics thereof.

8. An antenna as in claim 1 including a coaxial conducting member connected to said electrical signal conducting means.

UNITED STATES PATENTS 3,213,456 10/1965 Korvin 343-797 ELI LIEBERMAN, Primary Examiner US. Cl. XJR.