US2289856A - Broadcasting antenna system - Google Patents

Description

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l .Af ALFQRD; y Y i '2,289,856' BROADCASTING ANTENNA ss v v Filed sept. 25,

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3 Seets-Sheet llf' i' l 5v5- as INVENTOR Amway/raap July 14, 1942. A, ,M FQRDl 2,289,856"

` BROADCASTING ANTENNA SYSTEM y Filed sept. 25. 1940' l sheets-sheet 2 I L 4 @a 7S' INVENTOR manicura/w Patented July 14, 1942 naoancas'rmo ANTENNA srs'rml Andrew more. New "Ich, N.l Y.,

ternational Telephone algnorto Inlulio Manufacturing Corporation, a corporation of Delaware Application September 25, 1940, Serial No.358,214

1s claims. (ci. 25o-11) This invention relates to antenna systems and more particularly antenna units and arrays for broadcasting energy at high frequencies.

In high frequency broadcasting systems such as are used for television and frequency modulation transmission certain new problems arise.

`Since the high frequencies used have 'generally only a line of sight coverage it is desirable thatv the broadcasting antenna be mounted as high abovev the earth as possible. It is also desirable that the radiation pattern from the antenna be directed in a horizontal direction in order that the signal level be highat points distant from the transmitter. In order to obtain this concentration of energy it is necessary to provide an array of antennafunits ,or other means for con- Y centrating the energy. Since the antenna is to be supported at a high point and consists of an array of units, it is essential .for practical reasons that the units be relatively small and produce a high radiation characteristic so that a good signalstrength may be obtained without a huge structure or extensive array mounted high above the` ground.

Furthermore, since the antenna is usually mounted in a relatively inaccessible place, such' as a mast on the top of a high building, it is desirable that the units be made so as to require a minimum of maintenance.

` The broadcasting stations particularly for television and frequency modulation, are generally located in areas of dense population in order to reach the maximum number of people in the relatively limited coverage area. Accordingly, the antenna units may be located above the lheads of passers-by and the hazards accompanyv ing the accumulation of ice on the units would be quite high. Ice accumulated during a sleet storm may fall and causev considerable damage to people passing by as well as to inanimate objects. Furthermore, such ice accumulations may fall from' one unit to another unit of the antenna causing damage to parts thereof such as insulators.

be called upon to withstand considerable voltage.

stress. v

It is an object of my invention to provide a It is a further -abject of-my invention toprovide an antenna unit which may be supported on a metal mast or support` without the necessity of any insulation therefrom.`

It is a further object ofmy invention to provide a broadcast antenna system which'may be readily mounted in a relatively inaccessible place. will be relatively small for a given concentration of energy and will'need a minimum of attention.

It is `a still further object of my invention to provide a broadcast antenna system whichoperates to produce substantially pure horizontally polarized waves.

A better understanding of my invention, as

well as the objectsand features thereof, may be had from the followingdescription taken with radiation in the horizontal plane.

broadcast antenna system for use at high frequencies in which the antenna units are lsmall in dimensions and produce relatively great power output.

reference to the accompanying drawings, in which Fig. l illustrates a broadcast array in accordance with my invention;

Fig. 2 shows curves illustrating characteristics of an array in accordance with my invention;

Fig. 3 is a diagrammatic illustration of a preferred form of antenna unit in accordance with my invention; 1

Figs. 4 and 5 illustrate a preferred structural arrangement of an antenna in accordance withy Figs. ll and l2 show alternative forms of antenna units.

In Fig. l, I0 represents a supporting mast or structure upon which are mounted antenna units il, I2,HI3. 'Ihese' antenna units are such that 4 the radiation pattern from each unit produces a toroidal pattern with its minimum atv the center of the unit and having substantially circular Suitable antenna units for producing such radiation pattern are disclosed more fully in my previous application, Serial No. 270,173 filed Aprilv 26,I 1939.

It is known to produce a horizontal concentration of energy by arranging antenna units in a vertical array. However, if crossed dipoles are used it is evident that two units must be provided at each point in order to secure substantially uniform coverage. Thus, considering for example. two uniform radiating units spaced a distance s, such as II and I2 of Fig. 1, if a pair of crossed horizontal dipolesare used for each unit then only half of the energy fed to the two units is applied to those dipoles in the plane of the paper,` the other two dipoles at rightangles with those in the plane of the paper receiv-JV umts, such as I I,

I2 and Il, of Fig. l, arranged in a vertical array f with a separation s as shown therein. it is evident that al certain degree of concentration 'of y energy in the horizontal may be` achieved. When scribed above, the powergain in the horizontaly direction for` any number n unit, may be expressed by the following equation:

the characteristic of curve #2 of Fig. 2. It can y be seen that such an arrangement will give a power gain of substantially 4.6 at the maximum. For any other desired number of units. spacing 5 curves such as shown in Fig. 2 may be readily plotted from the equation and a suitable spacing chosen to secure the desired power gain, y. Curvesi and 2.of Fig. 2 are drawn for an arrangement wherein equal power is supplied' to l the various antennae. Such an arrangement will produce maximum gain in a horizontal direction for the desired number of units. It is known, v however, that with such an array wherein equal .power is fed to each of the units. a number of l5 minor lobes will be produced. Generally, these minor lobes willnot vbe bothersome since the angle of null between the first minor lobe and the groundrwill usually be such that the null point at the earths surface will be quite close to the transmitting antenna, Furthermore, in built up areas suillcient reflection from adjacent will be observed. However..if the null point and theminor lobes-are found to be objectionable `2`5 theyI may be obviated by a ,suitable division ofr i power in the antenna unit.V This contemplates energization of the center unit at a higher degree than the outer units in a manner known in the-art. If it is not desired to entirely eliminate the minor lobes but merely avoid the null so that there will be lsome radiation in the minimum direction between lobes, a small degree of n=number of antenna'units in array.

s=spacing expressed in radians= gx: (spacing in meters).

A=Wave1engthlinl meters. 'y l v Curves for satisfying the equation given above `are plotted for n=2 and n=4 in Fig. 2. From these curves the desired spacing between adiacent units .may be readily obtained for any desired power gain. yIt is preferable. in anycase, when a 'desired gain is to be provided. that the ascending portions ofthe curves up to the substantialmaximum thereof should be used. Thus,

inacurve i it is seen, .that the maximum occurs between 320 and 340 degrees. Consequently, a power sain 4of 2l is desired. twounits may be usedv and the units maybe spaced kbetween 260 and-340 degrees, one from another... For this particular set-up itis clear that thepower gain decreases very slowly for spacings above 320 degrees .and a'spacing up to 400 degrees; is entirely.

feasible.4 However, because of space limitations the .narrower spacing vis usually` desirable, and

for this reason the curve need not be used'byond the-maximum point.L

If,'ontheotl1er hand. a greater is desired, a four-unit array may be 'used having vpower vgain inequality of energization between the umts may be utilized. 1

In Flg.`3 is shown a new type of antenna unit in accordance with my invention particularly suitable for vertical broadcast arrays of the type shown iniFig. 1. This antenna comprises four radiating members 3D, 3l, 32, 33 arranged in the form of a square or other closed pattern.` Energy from high frequency source 34 is fed over a line 35 and branch conductors 36, 31 to radiating members 30,31. Lines 36, 31 are arranged so'as to energize the members 30, 3|, adjacent their midpoints in phase opposition. Accordingly, members 30 and 3| will operate to excite in the arms 32, 33 energy such that these members will be oppositely poled at their ends. Members 32 and 33 are preferably turned inwardly as indicated at 38 in order to increase the capacitive coupling of the system. It will be evident from the description given that each of the arms 30, 3|, 32 and 33 will have substantially a voltage node at its mid-point.' Accordingly, the members may be supported directly at their centers and need not be insulated at these points with respect to on'e another or to the ground, This antenna unit will produce substantially pure horizontally polarized energy thus avoiding reradiation or absorption of the energy by vertical objects in the ileld. Accordingly, guy wires for the support willnot interfere with the broadcast in any way. Furthermore, since the units are smallinv size and light in'weight they may be mounted on a mast or support above the guy wires supporting a tower or the like.

similar to 3,15 illustrated in Figs'. l4, 5 and 6. l'nFig. 4, antenna members 30, 3i, 32, 33 are buildings willA ordinarily occur so that no null` a practical constructional form l"of antennashown as formed ofv'hollow tubing. At the center of each of these elements are provided other supporting tubes 43, 4|, 42, 43 which may be of metal and may be connected at one end firmly by brazing or welding to the antenna element, and at the other end may'be nrmly fixed mechanically to a metallic supporting mast or pole 44. Since the antenna members to 33. inclusive, are each supported at voltage nodal points, it is unnecessary to provide any insulation for the radiating elements. The members 30, 3| may be energized by shielded leads contained inside the mast 44 and the tubular cross arms 40, 4| as indicated at 50. 5| of Fig. 5. The ends of the conductors inside the shielded lines may be spread apart as shown at 5|', 52 so as to secure the desired impedance match.

A better understanding of the detail of a cable suitable for use may be had by reference to Fig. 6. In this arrangement leads 5| are shown inside a metallic outer sheath 60. The conductors 5| may be brought out through an insulator 6|. The ends 52 thereof may be then spread apart for connection to the bar antenna conductor 3|. It can be seen that with such an arrangement the entire power supply wiring system and all of the insulators thereof are housed within the tubular metallic portions of the antenna and are thus protected from the weather and any mechanical stress.

The antenna units of the type shown in Figs. 4

and 5 may be readily formed in an array in a manner disclosed in Fig. 7. In this arrangement four radiator units are shown 10, 1|. 12 and 13 mounted on a common transmitter mast 14. A shielded conductor feed line 15, is connected to a branch transmission line 16, 11, the ends of which are connected to further branch lines 13, I8 which serve to supply energy respectively to antenna umts 12, 13 and 10, 1|. In order.- to match the impedance of the transmission line at the various junction points building-out elements may be bridged across as indicated at 8u. It is clear that the antenna array provided in Fig. 7 is of such a nature that the antenna elements may be readily installed in any desired tower since insulation between the various units and the mast, as well as between one another on the support, need not be provided. Furthermore, all of the insulation and wiring of the units may be contained wholly within the antenna structure itself, as shown in Fig. 5 and therefore the system is not subject to mechanical damage by objects falling on the unit for example.

The size of the loop used in the system, in accordance with my invention, is relatively small.

For example, if it is desiredrto operate the system at 46 magacycles, the antenna unit may be made to have an outside dimension of substantially three feet. The antennae themselves may be made of relatively rigid material such as aluminum channel about 3 or 4 inches wide and from 3 to 4 inches deep.. It is, therefore, evident that the unit may be rigidly iixed on a mast in a self -supporting fashion without danger of wind causing any substantial variation in the relative position of the parts of the antenna.

A further advantage of antenna units constructed in the manner shown in Figs. 4 to '1, resides in the fact that heating elements for removing sleet formations may be readily applied without in any way affecting the operation of the system for radio frequency. This may be accomplished easily, in the manner indicated in Fig. 8, which shows a fragmentary section of an antenna showing only two members such as 30, I3. In each of these members may be provided resistance elements 8|. 82 which mayI be connected directly to the grounded antenna members at the opposite ends and which may be connected to a supply of heating current, at their mid-points by conductors 83, 84 respectively, by way of a switch such as 35, if desired.

Antennae of the type shown in Figs. 3 to 8. inclusive, may be made in other forms, if desired. For example, in Fig. 9 the circular antenna form is shown comprising four antenna arms 90, 9|, 92, 33 provided with supporting elements 94. 95, 86, 91, so that they may be supported from a hollow post or mast 93. The ends of the radiating members are shown tuned in at 99 to provide the desired capacitive coupling therebetween.

In Fig. l0 still another form which the antena, in accordance with my invention, may take,

' is shown. In this arrangement each of the arms 30, 3|, 32, 33 is shown bent at right angles at the center point, the arms 32, 33 being provided with overlapping portions 36 which serve to produce the desired capacitive coupling. Supporting arms 40, 4|, 42, 43 connected to a supporting mast 44, are shown. It is clear in this connection that the energizing leads extending from arms 40 and 4| to elements 30, 3| may be brought out so as to contact the radiator at substantially 90.

Accordingly, adjustment of the spacing between lead 5| or lead 52 may be carried out without any subtsantial change in the length of these conductors. This design presents an advantage over that illustrated in Figs. 4 and 5 in that the adjustment of spacing between conductors 5| or conductors 52 does not necessitate so great a change in length and may be carried out Without having to actually cut the conductor to the desired length.

The examples so far considered have been directed to antenna units comprised of four members. However, the structure acording to my in vention is not limited to such a number of members. In fact any plural number .of elements may be used to produce useful results so long as the members are maintained at a length under a quarter of a wavelength and have their adjacent ends interconnected by a relatively large reactance. It is clear, however, that when an odd number of members is used, the vertically polarized components of the wave will not be eliminated in every direction about the antenna.

In Fig. 11 is shown one form of antenna unit comprised of six members to ||6, inclusive. Energy is fed from a source ||1 to each of members ||3 and |5 in such phase relation that the adjacent ends of the feed members are at opposite instantaneous potentials. Members ||2, ||4 and I|8 are thus parasitically energized so as to produce at their midpoints voltage nodes. The required capacitive reactance between the adjacent members may be obtained, as shown. by turning in the ends of members ||2, ||4 and H6;

It is evident that since the members of Fig. ll all have voltage nodes at their midpoints these members may be supported directly on a metal supporting pole or mast as in the systems of Figs. 3-8.

In 12 is shown an antenna unit made of three members, |2I, |22 and |23. Members |2|, |22 are directly fed from source |24 with energy such that their adjacent ends are at opposite instantaneous polarity and member |23 is parasitically energized therefrom so as to have a voltage node at its midpoint. The members are as in the other embodiments, and may be supported at their midpoints without requiringiurther insulation. However, the unit does not mede Snert witnre'speet te a han wavelength,

means4 for feeding energy to at least twooi said members adjacent their voltage nodal'points in such phase relation that the adjacentends of adjacent ones of said energy fed members are at have the symmetry possessed by units madeot 5 potentialsv of opposed polarity, at least one ot an even plurality of members and consequently ysaid members being parasitically energizedl by will not produce a uniform radiation ,in all dilsaid energy fed members. y n rections. This departure, however, may be -rela- 6. AnV antenna unit comprising an even plutively small and may in some-cases-be desired. ralityv of members ,each member being short with While I have described my inventionin conliirrespect to a half wave-length at thev operating nection with the accompanying drawings-, it frequency, means for supplying energy to altershould be distinctly understood that spenate ones of said members adjacent theirmidciiic embodiments thereof are incorporated to point to produce voltagenodal points thereat, in facilitate the understanding 'of the invention 'such phase relation that adiacentends of adjamerely by way of example, and are not toibe 15 cent ones vof `said energy supplied members arel construed as limitations on my invention. What 'at opposed potentials, and capacitive reactance` I consider to be my invention and upon which lmembers interconnecting adjacent ends of said I desire to secure protection is embodied inthe members. accompanying claims. i 7. Anantenna unit comprising four Amembers What I claim is: 20 arranged in the form oi a substantially closed 1. A broadcast antennaarray comprising at vpattern each of said members being short with least two antenna units, each= unit having a respect to half awavelength of the operating fretransmittlng characteristic for producing a pat- Aquency, means for energizing oppositely positern of substantially toroidal form having subtioned ones of said members at substantially their stantially uniform value'in a horizontal plane, 25 mid-points in opposite phase relationship, and said units each being spaced apart vertically means for capacitively coupling the other-two from the next adjacent uri-it a distance in the members, respectively, between the opposite ends order of 200 to 400 electrical' degrees at the opof said two members rst mentioned. erating frequency. y 8. An antenna unit according to claim '7, fur- 2. A broadcast antenna array according to 30 ther comprising metal supporting arms fixed subclaim 1, wherein said array comprises 1r.- number stantially to the mid-points of each of salu of units, the spacing between units being determembers. l mined for a desired power gain P bythe equation 9. An antenna unit according to claim 7, fur- P- 1 nl 1/31+2(n1)(8)+2(n-2)(28)+ 2l nl sl where l I ther comprising metal supporting arms fixed substantially at the midpoint of each of said mem- Ms) cos s+s in bers, and a metal supporting tower to which said s2 s3 i 40 members are fastened.

- 10. An antenna unit according to claim '7, fur- (2S)= cos 2s+sn 2s ther comprising a metal antenna supportingr (2s)2 (23) means, and means connected substantially at the midpoints of each of said members for y 45 mounting said unit on said supporting means. (n-l)= ---Z- l-lgi-s-u-Lbs-s! 11. An antenna unit according to claim 'I wherein said four members are each made of end s equals the Spacing between 'units ex hollow metallic material, further comprising Dressed in radnsheating means in said hollow, and connections 3- A broadcast antenna -er1`a5" aceoldmg t0 50 for energizing said heating means. Claim 1 wherein Seid umts each eemprise metal 12. An antenna structure comprising an even lie elements metallic-Supporting Ineens festened plurality of radiant acting members each memsubstantially at the center of each of said eleber being Short WthTespect to a half Wavelength ments. further COmDlSing means; -OI energizing at the operating frequency, said members being Certain 0f Said elements at the Operating fre- 55 hollow in form, capacitive reactive means interquency. a metallic tower and means'for fastenconnecting adjacent ends ef said members te ing Said metallic SUDDOIIIE means directly t0 provide in eiect a loop, hollow metal supports said tower. fastened to eachof said members at substantially 4. A broadcast antenna aCCOIding t0 Claim l. the center thereof, and a metallic antenna mast, wherein at least three antenna units are `pr0 60 said supports being fastened to said metallic vided, further comprising means for energizing f mast, respective ones of said units withpredetermined v13. An antenna structure according to claim different amounts of pov/en l A 12,` further comprising energy supply lines ar- 5. An antenna unitcom'prising a plurality oi ranged Vsubstantially within said-supports, and members each member being of theorder of one- 65 means cf connecting said supplyflines `to altertenth of a half wave-length at the operating f requency, capacitive reactance members vinterconnecting the adjacent ends o1 saidmmember's,l and nate ones of said members adjacent their midpoints to produce voltage'nodal points thereat. ANDREW AIFORD.

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