Dipole antenna array having equally spaced dipoles of decreasing lengths

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Filed Oct. 6, 1966 ^DIF°^LES· °^{F DECREASIN(}} LENGTHS

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Dec. 2, 1969 w s maner 8 482 2ςη

DIPOLE ANTENNA ARRAY HAVING EQUALLY SPACED

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Filed Oct. 6, 1966

LENGTHS

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INVENTOR

WSLIMM S.

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ATTORNEY ^DeC' ²· ¹⁹⁶⁹ DIPOLE ΑΚ,ΒΕΕΑ SPACED ^²⁵⁰

Filed Oct. 6, 1966 ^DIP°^LES °^{P DECREASING} LENGTHS

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ATTORNEY

United States Patent Office

3,482,250

Patented Dec. 2, 1969

3,482,250

DIPOLE ANTENNA ARRAY HAVING EQUALLY SPACED DIPOLES OF DECREASING LENGTHS

William S. Maner, Anniston, Ala., assignor to Viewall

Television Products Corp., Oxford, Ala., a corporation of Alabama ⁰

Filed Oct. 6,1966, Ser. No. 584,902

Int. Cl. HOlq 3/00, 11/04, 11/10

U.S. Cl. 343—766 10 Claims

ABSTRACT OF THE DISCLOSURE

This invention relates to the art of antennas, more particularly of the unidirectional type, to receive television signals, said antenna comprising a pair of elongated vertically aligned parallel bars with a plurality of pairs of receiving elements extending outwardly from the sides of said bars and equally spaced along the length thereof.

As conducive to an understanding of the invention it is noted that as a television receiving point is progressively moved away from the signal source, the power of such signal materially decreases.

To counteract this decrease in power, so-called “high gain” antennas have been employed, positioned at a relatively great height above the ground by the use of masts or the like.

When the receiving point is relatively close to the transmitter, say a distance of twenty-five miles, the use of an elevated antenna is generally satisfactory since the strength of the transmitted signal at such moderate distance is normally sufficient to suppress undesired signals. However, beyond the twenty-five mile range, for example, the present so-called “high gain” antennas do not operate satisfactorily. This is due to the unwarranted “noise” of undertermined and composite origin which is picked up by the antenna in an omni-directional manner. When this noise is presented along with the desired signal to the television antena, the overall effect is to sharply degrade the quality of the picture appearing on the television tube.

Further, when the receiving point is between two stations transmitting on the same frequency, if the antenna is not able to exclude the unwanted station, the resultant picture will be distorted.

Furthermore, since television antennas are generally inaccessible for maintenance, it is an important criteria in their design that they be able to withstand relatively high wind velocities and inclement weather.

The design criteria of an efficient television antenna would therefore have to satisfy a number of problems. For example:

(a) The antenna must withstand wind velocities of fifty miles per hour under an ice load of one-half inch;

(b) The material from which the antenna is fabricated must have a minimum life of approximately five years;

(c) The overall length of the antenna should not exceed twelve feet;

(d) The boom and elements of the antenna mounted thereon must have sufficient inherent strength so as to minimize bracing;

(e) The antenna design must be such as to facilitate manufacture, shipping and installation.

(f) The antenna should possess a flat frequency response over the frequency range of 54 me. to 216 me. which cover the major existing television channels;

(g) The antenna should have a uniform flat gain of + or — .5 db;

(h) The antenna should have a variable standing wave ratio of 1.2 to 1, as measured at the output terminals;

(i) The antenna should possess high front to back and front to side ratios of at least 25 db down;

(j) The overall antenna gain should be a minimum of 12 db;

(k) The antenna should possess a very narrow front radiation lobe, thus yielding sharp directivity to the desired signal source.

The use of conventional antennas, such as the yagi type, the multiple dipole and log periodic type, failed to solve the existing problem due to the fact that none of these antennas possessed all of the desired qualities.

It is, accordingly, among the objects of the invention to provide a television receiving antenna that may readily be fabricated by mass production methods from relatively inexpensive materials that are strong and durable, which antenna may readily be shipped in disassembled form in a relatively compact container and which may readily be assembled with simple tools, and when installed will be capable of withstanding high winds and inclement weather with a minimum of bracing, and which will be capable of receiving the desired signal, while at the same time rejecting unwanted noise and co-channel transmissions, thereby providing a picture of extreme clarity.

In view of the fact that the antenna per se is highly directional, it is important that such capability be utilized to the best advantage.

Where the antenna is mounted on a mast and a motor is employed to rotate the antenna in steps, exact directional positioning of the antenna with respect to a particular signal source is not possible.

Where the transmission line from the antenna is fed to an amplifier located adjacent the television receiver, due to the length of the transmission line, stray signals could be picked up by the line of strength often greater than the relatively weak signals picked up by the antenna, with the result that the picture will be unsatisfactory.

It is accordingly another object of the invention to provide an antenna system employing an antenna of the above type in which the antenna is capable of being oriented so that it can be directly aimed as desired toward the signal source to be received and in which the signal transmitted from the antenna to the television receiver is immediately electronically amplified at the physical location of the antenna, thus yielding a signal strength far in excess of any undesired signal picked up by the transmission line from the antenna to the television receiver.

According to the invention, these objects are accomplished by the arrangement and combination of elements hereinafter described and more particularly recited in the claims.

In the accompanying drawings in which are shown one of various possible embodiments of the several features of the invention,

FIG. 1 is a diagrammatic view of an antenna system according to the invention.

FIG. 2 is a perspective view of the antenna.

FIG. 3 is a side elevational view of the antenna.

FIG. 4 is a top plan view of the antenna.

FIG. 5 is a sectional view taken along line 5—5 of FIG. 4.

FIG. 6 is a detail view of an enlarged scale of the rear end of the antenna.

FIG. 7 is a view similar to FIG. 6 of the front end of the antenna.

FIG. 8 is a sectional view taken along line 8—8 of FIG. 3 showing the mounting bracket, and

FIG. 9 is a schematic view of the antenna.

Referring now to the drawing, the antenna 10 comprises a pair of hollow elongated bars 11, 12, desirably of extruded aluminum, each preferably rectangular in cross section and illustratively of one inch square aluminum tubing having a wall thickness of Vs inch.

The bars 11 and 12 are maintained in spaced parallel

3,482,250 vertically aligned relation by means of a plurality of insulating straps 13 spaced along the length thereof to define the antenna boom which mounts the receiving elements R.

In order to neutralize the effect of the boom on the receiving elements R for optimum performance of the antenna, the boom length is selected to be one wave length of a frequency that falls in the frequency spectrum above the FM band (108 me.) and below the frequency of channel 7 (174 me.). The frequency selected is preferably 123 me. which is not one of the television transmitting frequencies so that in the preferred embodiment shown the boom length is 96 inches. As a result, standing waves reflections and harmonics that could interefere with the reception of the desired signals are eliminated.

The ends 14, 15 of the bars 11, 12 are connected by means of a U-shaped bracked 16 of conducting material, the legs 17 of which extend into the open ends 14, 15 of the bars and are secured thereto as by screws 18, thereby shorting such bars. The short will occur exactly one wavelength from the front of the boom defined by the ends 19, 20 of the bars. As a result, the back of the antenna defined by the end 14, 15 of the bars, will be at zero potential which maintains the front to back ratio and also maintains the side lobe suppression characteristics of the antenna.

A plurality of pairs of rods R, illustratively nine in number and of varying lengths and designated Rl, R'l, R2, . . . R9, R'9, which define the receiving elements of the antenna, are secured to the bars 11 and 12 along the length thereof and extend outwardly therefrom at right angles thereto. Each of the rods R preferably is an extruded aluminum tube, desirably circular in cross section, and illustratively having a diameter of Ά inch and a wall thickness of .035 inch.

As shown in FIG. 2, the rods R of each pair are alternately secured to bars 11 and 12 and extend outwardly from one side thereof and the rods R' are alternatively secured to bars 12 and 11 and extend outwardly from the other side thereof. The rods of each pair extend in different plans and are transversely aligned.

Thus, the elements R of the antenna are staggered so that each half of a pair of elements is 180 degrees out of phase with the other. The signal which strikes the elements in a perpendicular fashion will maintain a correct phase relationship and will be additive at the feed point. Signals which arrive on the sides or at an angle to the front will induce a phase shift between the corresponding elements. This in turn will cause a cancellation at the feed point.

More particularly, to mount the rods R, each of the bars 11, 12, has transversely aligned pairs of openings 21, 21', through which the end of an associated rod R extends, being secured in position as by set screw 22.

The pairs of rods R form dipoles, which are equally spaced along the length of the bars with the longer rods R9 related to the lowest frequency to be received (illustratively 54 me.) being adjacent the rear ends 14, 15 of the bars and the shorter rods Rl related to the highest frequency to be received (illustratively 216 me.) being adjacent the front ends 19, 20 of the bars.

Each of the pairs of rods R at the front and rear of the boom is of length substantially equal to one-half wavelength of the associated frequency, i.e.,. 54 me. and 21.6 me.

In determining the lengths of the intervening pairs of rods, experimentation clearly indicated that the rods should, first of all be equally spaced along the boom from front to back.

The length of the rods was determined by cutting them to a size equal to the distance between an imaginary line connecting the ends of the first and last element and a point perpendicular to the boom at the location on the boom where the specific element was to be located.

Following the above described procedure, the proper number of elements was determined by experimentation to yield maximum efficiency on all the desired television channels.

To provide an output from the antenna, as shown in FIG. 7, a co-axial fitting 31 is mounted on the end 20 of bar 12. The outer shield conductor 32 is electrically connected to bar 12 and the inner conductor 33 extends through the bar 12 and is connected as at 34 to the end of the bar 11.

Thus, referring to FIG. 9, the outer conductor 32 will be connected to rods R'9, R8, R'7, R6, R'5, R4, R'3, R2, R'l, secured to bar 12 and the inner conductor 33 will be connected to rods R9, R'8, R7, R'6, R5, R'4, R3, R'2, Rl secured to bar 11.

The antenna above described is thus designed on a linear concept basis with the elements equally spaced along the length of the bar.

The antenna is preferably mounted on a vertical mast 36 which has a mounting pad 37 at its upper end. Secured to said pad is a housing 38 which contains a wide band amplifier 39 and a motor 41. The shaft 42 of the motor 41 is secured to the antenna by means of U-bolts 43 which extend through a mounting plate 44 bolted to the bars 11, 12 to support the antenna at right angles to the shaft 42. A feed cable 45 is connected at one end to fitting 31 on bar 12 and at its other end to the amplifier 39 and a transmission line 46 which illustratively carries a power cable for the motor, and an RF transmission line for the signal, extends down the mast 36 to a control box 47 which may be positioned on top of the television receiver 48. The control box 47 has a junction 49 whereby the signal input of the television receiver 48 may be connected to the RF transmission line and the rheostat (not shown) controlled by the dial 51 is provided to energize the motor 41 to turn the antenna to the desired position.

Thus, if a particular station is to be received, the dial 51 is turned to rotate the antenna so that its ends 19, 20 are aimed toward such station. The proper setting will be determined when the received picture is of optimum clarity. By reason of the fact that the received signal is amplified closely adjacent the antenna, the strength of the signal travelling down the transmission line will be much greater than any noise or unwanted signals picked up by such line.

As the rear end 14, 15 of the antenna is shorted, signals impinging on the antenna from the rear will have substantially no effect on the desired signal received from the station desired toward which the front of the antenna is aimed.

The antenna above described will have the physical strength and life required and since all of the components thereof are readily assembled, shipping of the disassembled parts is facilitated.

The antenna arrangement above described provides all of the electrical characteristics required for optimum performance of the television receiver at relatively great distances from the transmission point of the desired signal.

As many changes could be made in the above equipment, and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.