US2195232A - Aerial and associated feeder system - Google Patents

Description

March 26, 1940 I N. WELLS ET AL 2,195,232

AERIAL AND ASSOCIATED FEEDER SYSTEM Filed Oct 8, 193a INVENTORS NORMAN WELLS ATTORNEY Patented Mar. 26, 1940 Y I m T D STATES PATENT OF I E T 1 AERIAL AND ASSOCIATED FEEDER SYSTEM Norman Wells, Epsom Downs, and Alan Wilfrid.

.Ladner, Danbury, England, assignors to Radio Corporation of America, a corporation of Dela- 7 Application October 8, 1938, SerialNo. 233,928 7 v In Great Britain October -28, 1937- 4Claims. (o1.250-s3)' I total electrical length of'conductor in the hori This invention relates .to aerial and associated feeder systems and more particularlyv to feeder elf systems for aerial systems of the type comprising aplurality of vertical aerials-commonly, though not necessarily, constituted by mastswhich are tion to directional aerial systems since, as will be apparent later the said invention can be applied to aerial systems which are non-directional or nearly so. The object of the present inventionis to provide improved feeder system ar rangements for aerial systems of the general type referred to. r

The aerials of a system of the type in question are usually energized by a branched feeder sys tem the branches of which are connected or coupled to the individual aerials at their bases. The directional qualities of such an. aerial system if it has directionalqualities at alldepend inter alia on the distances (in terms of the wave length) between the aerials of the system and on the phase and amplitude relationships of the currents in the individual aerials. Thus the horizontal polar diagram of a, system of the type referred to and comprising two vertical aerials separated by a distance equal to one quarter of the working wave length and fed by currents which are in phase and of equal amplitude, .is roughly elliptic with its major axis at right angles to the line joining the two aerials. If the distance between the aerialsis increased the polar diagram is changed, becoming, when the said distance has been increased to one half of the zontal feeder. branches each feeding one of the vertical aerials at its upper end.

The vertical feeder length of course consti- .tutes an additional (centrally placed) vertical aerial and since, in general, the separation between the other aerials willnot exceed one half the working wave length,.it is preferred where .maximum directivity is required, so to arrange matters that the radiationfrom the vertical feeder is reduced as far as possible in order to prevent its producing'a detrimental effect upon the desired directional diagram of the aerial system. To some extent the amount of directivity can be controlled either by adjusting the zontal feeder branches (as distinctfrom their overall lengths) or by loading, the main 1 vertical aerials or masts so as to vary the form of cur-i rent-distribution therein to that in the centrally placed vertical feeder length.

' Alternatively to they reduction :of radiation from the centrally placed vertical feeder length its vertical polar diagram may be made such."

that in conjunction with the vertical polar dia-i gram due to the main aerials, there. is provided a resultant vertical'polar 1 diagram having a re.-

ducedproportion of high angle rays (as com-. pared to. the result which would be obtained due to the vertical diagram of the mainaerial sys-.

tem alone) and-therefore of improved anti-fading ing properties.- -This is of particular advantage becauseit means that for a given allowable pro "portion of highangle rays, lower main aerials ormasts can be used than would'bepcssible were the central vertical feeder length not present- Another, and very important advantage of the present invention arises from the fact that the phasing andtuning of. the main aerials can be controlled by suitably disposing eithersymmetrh cally or otherwise, the'horizontal feeder branches and employing only a single tuning circuit at drawing injwhich Figure 1' shows one embodiment of the inventionwhile Figures 2,3, .4, 5 and 6. illustrate modifications thereof. In' Figure 1, there are employed two main vertical serials I 2, in the form of masts insulated from earth These 4 aerials are fed .by-mleans of a feeder systemcom-' prising a vertical feeder length 3 placedmid-way same height, this feederlength being terminated through asuitable input transformer represented by the coil 4 atits lower end; The upper end of this feeder length is connected to and supported from'the midpoint of an ordinary three wire triatic 5 suspendedbetween the masts and provided with cross wires as shown. The two ity of the central vertical feeder length to the two main aerial s. there, will be a coupling 'efi'ect tending to oppose the formation of current in lengthwill be, by virtue of the positionof the latter, appreciably greater than the effect *of the corresponding coupling of thesaid feeder length between'the two masts and of substantially the p Y the said:feeder length. This effect on the feeder and either main. aerial upon the other main aerial. Again the cross sections of the main aerials-especially if they be masts-,-and of the triatic arrangement will be normally considerably greater than the cross section of the vertical feeder length, which is made purposely small, and accordingly the wave impedance of the vertical feeder length will be high (e, g., of the order of 550 ohms) while the wave impedanceof each horizontal feeder branch and main aerial will be low (e. g., 200 to 300 ohms in the case of main aerials in the form of masts or towers). Hence for a given potential at the common junction of the two horizontal feeder branches and the vertical feeder length there will be appreciably less current in the said length than in either of the horizontal branches and main aerials.

Radiation from the horizontally disposed feeder branches is almost completely cancelled by reason of their symmetrical disposition.

There is a wide range of dimensions which can be adopted for a construction as shown in Figure 1 and Figures 2, 3, 4, and 5 show, in purely diagrammatic manner, various examples of dimensions which can be adopted. For example, as shown in Figure 2, the two. main aerials or masts could beta/8 high (A being the working wave length) and'spaced apart by a/Z; or, as

shown in Figure 3, theycould be we high and spaced apart by M2; or, as shown in Figure f,-

they could be 3V 16 high and spaced apart by M4;

- 01, as shown in Figure 5, they could be we high and spaced apart byX/ i. In order to achieve the desired space phase relationship between central feeder and main aerials, these latter may be earthed attheir respective bases either directly or through reactances. This is illustrated in Figure 3 where condensers 5 are shown, one being at the base of the member 3. The desired space phase relationship between central. feeder and I main aerials may also be achieved by suitably forming the horizontal feeder branches, forexample, by constituting them by wires folded back upon themselves. "This is illustrated in Figure 5 where in a system comprising two aerials each M4 1 h and spaced apart by M4 the'upper end of the centralvertical feeder length is connected to the middle of a horizontal wire 50 a little less than M4 longfland in the line of separation of the two main aerials the end of said wirenearer one main aerial being connected back to the other and the end of said :wire nearer said other main aerial being connected back to said one main aerial.

The invention is not limited to systems employing only two main aerials for systems employing more than two main aerials can be fed via a feeder system comprising a centrally dis posed vertical feeder length which branches out,

at the top via horizontal feeder branches to the tops of the main aerials. For example, as shown inFigure 6, which represents a practically non-- directional system, there could be three similar main aerials 10,, lb, 10 symmetrically arranged around a vertical feeder lengthfi at the centre, thetop of said length being connected to the tops ofthe main aerials through horizontal radially arranged branches 5d, 5e, 5

tom, with, however, an improvedvertical polar diagram.

In Figures 2, 3, '4 and 5 the current distributions are represented conventionally in broken line curves.

Such a system would constitute an omnidirectional sys- Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed we declare that what we claim is:

1. An aerial system comprising a plurality of vertical aerials each having a length less than half the length of the operating wave and means for cophasally energizing said aerials, said aerials being spaced apart, a distance not exceeding a half the length of-the operating wave whereby high angle radiation is reduced, said means comprising a vertical feeder which is branched outwards at its upper end into a plurality of hori-- whereby high angle radiation is reduced, said means comprising a vertical feeder which is branched outwards at itsupp'er end into a pluralityof horizontal feeder branches each feeding one of said verticalaerials at its upper end, said feeder being centrally disposed and so proportioned with respect to said aerials that radiation from saidfeeder produces no disturbingeffect on the radiation pattern of said system.

3. Ah aerial system comprising a plurality of vertical aerials having a length less than a quarter of the length of the operating wave and means for cophasally energizing said aerials, said aerials being spaced apart a distance equal to a quarter of the length of the operating wave whereby high angle radiation is reduced, said means comprising a vertical feeder which is branched outwards at its upper end into pluralityof horizontal feederbranches each feeding one of said vertical aerials at its upper end, said feeder being centrally disposed and so' proportioned with respect to said'aerials that radiation from said feeder produces no disturbing effect on the radiation pattern of said system, said vertical aerials being grounded at their lower ends.

4. An aerialsystem comprising a plurality of vertical aerials having a' length equal to a quarter of the length of the operating wave and means for cophasally energizing said aerials,

said aerialsbeing spaced apart a distance equal to a quarter of the length of the operating wave whereby high angle radiation is reduced, said means comprising a vertical feeder which is branched outwards at its upper end into a plurality of horizontal feeder branches each feeding one of said vertical aerials at its upper end, said feeder being centrallyfdisposed and so proportioned with respect 'to said aerials that radiation from said feeder produces no disturbing effect on the radiation pattern of said system, said horizontal feeder branches being folded back upon themselves whereby the current in said vertical feeder is in phase with the current in each of said vertical aerials.

NORMAN WELLS. I ALAN WILFRID LADNER.

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