US 1967881 A
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July 24, 19.314 E. GREEN 1,967,881
AERIAL AND AERIAL SYSTEM Filed sept. 7, 1929 Egg@ Ely. 2 ,Fg 5
INVENTOR N ERNEST GREEN ATTORN EY Patented July 24, 1934 AERIAL AND AERIAL SYSTEM Ernest Green, London, England, assigner t Radio Corporation of America, a corporation of Delaware Application September 7, 1929, Serial No. 390,963 In Great Britain September i9, 1928 l Claim.
This invention relates to aerials and aerial systems, and more particularly to aerial arrangements for use in .directive wireless signalling.
-In the specifications of British Patents Nos.
242,342 and 285,106 are described aerials adapted to be excited from one end, which are long in comparison with the wave length employed, and in which radiation is suppressed either wholly or in part from alternate half wave lengths of the aerials. The non-radiating portions or" such an aerial (which portions may be termed phasing elements) were formed in various ways; for example, by folding the aerial wire back upon itself so as to produce substantial cancellation of radiation, or by constituting the length of the aerial from which radiation was to be suppressed by inductance and/or capacity. The present invention has for its principal object to provide improved phasing elements for directive aerials.
According to this invention the phasing element or elements of a directive aerial or .aerial system is or are constituted by a transmission line or lines, i. e. a line or lines in which inductance and capacity are substantially uniformly distributed over the length thereof.
in one form of construction, an aerial comprises a plurality of radiating sections alternating with a plurality of phasing elements constituted each by a solenoid having a diameter small in comparison with its length. Alternatively a single solenoid separating a pair of radiating sections may be replaced by a plurality of solenoids in parallel.
The effect of the phasing elements depends upon their lengths, their positions in the aerial and the ratios of their surge impedances to that of the aerial itself; normally, however, the phasing elements should be arranged to suppress radiation from alternate half wave lengths. They 40 may be each greater than, equal to, or less than a half wave in electrical length.
If the radiating sections and the phasing elements are each a half wave length in electrical length, the phase of the current in the radiating 45 sections will be substantially the same for all values of the surge impedance of the phasing element. Such an aerial will give maximum radiation at right angles to its length.
If the radiating sections are longer than a half wave length and the phasing elements shorter, the relative phasing of the current in the radiating sections will depend upon the ratios of the surge impedances of the phasing elements to that of the aerial. If the surge impedance of -the phasing elements is equal to that of the aerial,
(Cl. Z50-33) f y the currents in the radiating sections will be in phase and the aerial will give its maximum radiation in directions at right angles to itself, whilst if the said surge impedance differs from that ofy the aerial, the currents in the radiating sections will differ in phase and the direction of maximum radiation will be deflected towards or away from the free end of the aerial, according as the surge impedance of the phasing elements is less or greater thanthat of the aerial.
If the radiating sections are shorter than a half wave length, and the'phasing elements longer, the direction of maximum radiation will be at right angles to the line of the aerial, or deiected I i towards or away from the free end of the aerial, m according as the surge impedance of the phasing elements is equal to, greater than or less than the surge impedance of the aerial.
There is also the case in which the terminal load of a radiating section is made to be that of a pure resistance. This may be effected either by locating the said load at a nodal point or by adding a suitable value of inductance and/or capacity. If to this point of the aerial there is connected a phasing element whose surge impedance is equal to the terminal resistance of the aerial, and if an E. M. F. be applied to the other end of the said phasing element, the phase of the current in the aerial will be controlled by the U length of the phasing element.
For example, suppose a half wave aerial giving a pure resistance load at its lower end to be connected at that end through a phasing element whose surge impedance is equal to the said resistance load to a lower and similar aerial. Then, if the length of the phasing element is a half wave, the phase of the current in the two aerials will be the same.
It will be seen that the phase of the current in the upper aerial may be made to lag or lead that in the lower to any desired extent by increasing or decreasing the electrical length of the said phasing element. The direction of maximum radiation can therefore be controlled by varying the length of the said phasing element.
Phasing elements of the type described provide a ready means of controlling the phase of the currents in the radiating sections, and therefore the direction of maximum radiation of aerials that are long in comparison with the Wave length. Such elements may be employed in a similar manner with single aerials or in aerial systems comprising a combination o-f aerials forming, for example, a so-called beam aerial system.
If desired, the phasing elements may be formed as transmission lines constituted by a section of aerial wire bent back upon itself one or more times so as to be substantially nonradiating. For example, Where the aerial consists of several wires in parallel, a phasing element may consist of a single Wire doubled back upon itself. The employment of such folded back aerial sections to secure suppressed or reduced radiation from alternate half wave lengths of an aerial is not per se part of the present invention, and it forms part of the subject matter of the British Patents Nos. 242,342 and 285,106 already referred to.
The invention is illustrated in the accompanying drawing, in which various embodiments in accordance therewith are shown diagrammatically.
Referring to Figure 1, this shows an aerial energized from the bottom as indicated, and comprising three radiating sections AB, CD, EF, each a half wave long and which alternate with phasing elements BC, DE. The phasing elements are constituted by solenoids whose diameter is small compared with the length. The current distribution in the aerial is represented by the dotted curved line.
Figure 2 shows a slight modification, differing from that of Figure 1 only in that radiating sections AB, CD, EF exceed a half wave in length.
In the arrangement shown in Figure 3, the phasing elements are constituted each by a plurality of similar relatively small diameter solenoids in parallel. It will be appreciated that this arrangement renders it a comparatively simple matter for the phasing elements to be designed to have any desired value of surge impedance.
Figure 4 shows an arrangement structurally resembling those of Figures 1 and 2, but in which the phasing element BC is designed to have a surge impedance equivalent to a pure resistance R1 equal to the load of the radiating section AB measured at B, the surge impedence of the phasing element DE being equivalent to a pure resistance R2 equal to the combined load of the two radiating sections AB, CD measured at D. The relative phases of the currents in the radiating sections AB, CD, EF are determined by the electrical lengths of the phasing elements BC, DE.
In the modification shown in Figure 5, the radiating sections GH, MN consist each of a plurality of wires in parallel (as shown three wires in parallel), and the phasingrelement consists of a single wire HIJKLM bent back and forth lupon itself and supported by means of insulators S.
Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim isz- A directive antenna comprising a plurality of equal length coaxial radiating sections which are electrically shorter than o-ne half wave length, and a plurality of phasing elements which are longer electrically than one half wave length connecting said radiating sections together.