US3482250A

US3482250A - Dipole antenna array having equally spaced dipoles of decreasing lengths

Info

Publication number: US3482250A
Application number: US584902A
Authority: US
Inventors: William S Maner
Original assignee: Viewall Television Products Corp
Current assignee: Viewall Television Products Corp
Priority date: 1966-10-06
Filing date: 1966-10-06
Publication date: 1969-12-02
Anticipated expiration: 1986-12-02

Description

Dec. 2. 1969 w. s. MANER 3,482,250

DIPOLE ANTENNA ARRAY HAVING EQUALLY SPACED DIPOLES OF DECREASING LENGTHS 3 Sheets-Sheet 1 Filed Oct. 6, 1966 4 FIG.

INVENTOR W/LL/AM s. M/u/ee ATTORNEY Dec. 2. 1969 W. S. DIPOLE ANTENNA ARRAY HAVING EQUALLY SPACED DIPOLES 0F DECREASING LENGTHS Filed Oct. 6, 1966 MANER 3 Sheets-Sheet 2 W/l 1 64M MJ/VEK ATTORNEY Dec.2,1969 s MAQER 3,482,250

DIPOLE ANTENNA ARRAY HAVING EQUALLY SPACED DIPOLES OF DECREASING LENGTHS Filed Oct. 6, 1966 3 Sheets-Sheet (5 INVENTOR F/ 9 M4 1/4/11 5. AMA Fe ATTORNEY United States Patent O U.S. Cl. 343-766 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 antennain 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 eflicient 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 mc. to 216 mc. 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 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. a

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 88 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 inch.

The

bars

11 and 12 are maintained in spaced parallel 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 mc.). 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 R1, Rl, 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 /2 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 R1 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 216 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 R9, R8, R7, R6, R'S, R4, R3, R2, R'l, secured to bar 12 and the inner conductor 33 will be connected to rods R9, R'S, R7, R6, R5, R'4, R3, R'2, R1 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.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. A television antenna comprising a pair of elongated bars defining a boom, means maintaining said bars in spaced parallel, vertically aligned relation, a plurality of pairs of receiving elements extending outward, respectively, from the sides of said bars at right angles thereto, said pairs of receiving elements being equally spaced along the length of the boom, the elements on each side of said bars being alternately secured thereto, the length of the receiving elements at one end of the boom being greater than the length of the receiving elements at the other end of the boom, the lengths of the receiving elements between the ends of the boom progressively decreasing from the longer elements to the shorter elements, means to short circuit the ends of the bars associated with the longer receiving elements and means to connect an output lead to the other ends of the bars.

2. The combination set forth in claim 1, in which said antenna is designed to receive signals in a given frequency range from a plurality of transmission sources, each having a given transmission frequency falling in such range and said boom is of length related to one wavelength of a frequency within said range and distinct from any of said transmission frequencies.

3. The combination set forth in claim 2 in which said frequency to which the length of the boom is related is approximately 123 me.

4. The combination set forth in claim 1, in which the pairs of elements adjacent the ends of the boom are of length related, respectively, to one-half wavelenth of the lowest and highest frequencies to be received and each of the intervening pairs of elements, starting with the pair adjacent the pair related to the lowest frequency, is successively of length equal to the distance from the boom to an imaginary line connecting the ends of the first and last elements.

5. The combination set forth in claim 1 in which each of said bars is an aluminum tube and is rectangular in cross section and each of said receiving elements is an aluminum tube circular in cross section.

6. The combination set forth in claim 5 in which said bars have a plurality of pairs of vertically aligned openings spaced along the length of the boom along each side thereof, each pair of openings on one side being transversely aligned with a pair of openings on the other side and one end of each of the elements of each pair of elements is positioned in each of the transverse pairs of openings so that said elements extend from opposed sides of said bars with one of the elements of each pair being secured to one bar and the other to the other bar.

7. The combination set forth in claim 1, in which a conductive member is secured to the adjacent ends of said bars to short circuit said bars.

8. The combination set forth in claim 1, in which a plurality of insulating straps are provided, secured to said bars along the length thereof to retain the bars in spaced parallel relation.

9. The combination set forth in claim 1, in which a mounting plate is secured to said bars, substantially midway between the ends thereof and in a plane perpendicular to the plane of said elements, an upright mast is provided, a motor and amplifier unit secured to the upper end of said mast, said motor having a shaft, means securing said shaft to said mounting plate, a transmission cable having a power lead connected to said motor and a radio frequency lead connected at one end to the output of said amplifier, and a lead connecting the input of said amplifier tothe connecting means at the other ends of said bars.

10. The combination set forth in claim 9 in which means are provided to connect said radio frequency lead to said television receiver.

References Cited UNITED STATES PATENTS 3,221,332 11/1965 Krauis et al 343-792.5 3,259,904 7/1966 Blonder et al 343792.5

ELI LIEBERMAN, Primary Examiner US. Cl. X.R.