US2507225A - Wide band antenna structure - Google Patents

Description

y y 19'50 M. w. SCHE'LDORF 2,562,225"

WIDE BAND ANTENNA STRUCTURE Filed April 11, 1946 2 Sheets-Sheet l Trans/711T fer- I nvencor: Marvel W. Soheldorfi H is Attorney.

FREQUENCY y 1950 M. w. SCHELDORF 2,507,225

WIDE BAND ANTENNA STRUCTURE Filed April 11, 1946 2 Sheets-Sheet 2 Ff .5. Pi .4. 2 E 2 Q t S 2/ g Q g E W E s U /HZ Q 22 t E $51.1 V)

FREQUENCY FREQUENCY FEB. 5.

Inventor: Mar-vel W. Scheldorfi His Attorney.

Patented May 9, 1956 WIDE'BAND ANTENNA STRUCTUEE Marvel W. Scheldorf, Syracuse, .Y,, :assignot .to :.General Electric icompamz, ainorporation 20f New York Application Aprilifl 1946,"'SerialNo."66132;14

21 pclaim. 1

*My invention relates to antennas for -operation over -a widebandof radio frequenciesandit has for its object to provide a new =and improved antenna suitable for use for television and other purposes requiring wide band operation.

A'general characteristic of antennas having a narrow band of satisfactory -'operation -is one of rapid variation -in-reactance relative to the rescnan-t resistance. The slope of this reactance maybe eitherpositive or negative, the only-mag or difference *being that antennas with a negative reactanceslope may be compensated more easily by associated terminal transmission line units. I have found that the band width of the usual antenna "is limited primarily by the cross-sectional dimensionofthe-radiators-empioyedwhich dimension, in turn, determines the antenna reactance. Furthermore, a serious limiting factor is the limitation placed upon band width by the terminal end of the radiating structures. In the past, attempts have been made :to improve the r-eaotance characteristics of antennas -by enlarging the outer endsof the radiator, while the ter minal en'd-s were'con-fined to the size of asma'll transmission line conductor, thus to reduce the reactance to a low value. It is :an obiect of :my invention to provide a new and improved wide band antenna in which the radiators thereof .are of uniform dimensions throughout their lengths and are so related spatially "that they have the eif ec't of a large radiating sheet.

":It isanothercbjectnf my inrention'to provide new and improved methods and :means of :coupling radiators in an antenna having a plurality of radiators.

'It' is a turtheriobject oimyinnention toapl ovide a now and improved wide band antenna sharing improved impedance characteristics.

'Itisastili further object .ofsmy imcentionzto provide .a new and improved WideLband antenna in which theradiators thereof are sospacedthad; their mutual inductance is a minimum.

One of the features of my invention :consi-sts in emp'loying spaced -radiators which I are .uniform throughout their lengths and so connected that they .areded in phase to operate .efiect-ively as a large radiating-sheet. In one .of -its aspents my invention contemplates the use f a plurality of radiating elements so connected ::by transmission lines sth-a't impedance matching :hetween vsets M elements and-the immediatezfeed iines'isachieyed ao erall connection between :resistance radiators and a low resistance feed :line .is achieved without :the use :of impedance elements \Mhichtend to restrict :the :hand width of anaantenna.

Theaeaturesoi my :invention which I beliave to be novel are set fonth with particularity in the appended claims. invention itself, however, both :as to-its organization and method of .operation, :together with f-urth'er objects :and advantages thereof may best I-be understood by :ree1= ence to the followingidescription taken in connection with the accompanying drawings which Fig. 1 illustrates diagrammatically a :wide band antenna suitably embodying my :invention; Fig. '2 -illustratescertainrcharacteristicsof anon ventional v-antenna; Figs. 3-46 are curr es rillus tr-atingicertaincoperational characteristics of the antenna of Fig. 1-; and Figfifl 51s adiagvammatic illustration Gi a modification of the an'tennazot Fig. 1.

1h 1 --there is illustmted an antenna :comtprising four yertiea lly spaced arrays of iv-aele ments. Each of :the --arnays :comprises two :tu-bm lar radiators formed of a suitable conductiveniw ter ial ihaving t-heir adjacent tends aelatively close- 1y spaced and angularlyirelated, themnper amay comprising the :radiators I, Disposed wmtie caily be'low the radiators :1, :2 are :the mazdiators t, I. which are =copla'nar and coextensive, mespecth ong-With esradiatmszl, 2. llhirdand fourth pairs of re." ators 5, 15 and :1, 58 Kare located belpw ithezradiators rl :2 and rare snhstan tiaily coplanar and coextensire therewith. 'ilhe radiators 3, :4 are spaced equal :distanc'es. respew t'ivel-y, tram the radiators 1,5 and 2, 6, :Sinnlamly, the radiators 5, 5 iaresspaced iequal distances, erespectively, from the radiators3,'s'|samdd,28, Each of s mediators ;l-.-+:8 dimensions throughout its length and R ms length detersmined .loyithe ifrequency at which wijhe antenna topper-ate.

'In accordance -.n;1-y invention, it qmoxzide means fonsupplying current to :the radiating isle, merits vso :that rthe excitation :of :allzthe relements is in .phasaand iea'ch nf thersets :of :elements 11;, 3, *5, and :2, at, .5, :3, =rcrnae'ctively, sonar-ates effectively as ashee't of high :Erequency means .comnrises :an ionen wire transmission dine comprisingicondmtors :9, in which :are zconnecteii respectively to the endssofradiators :and 2, Similarly, adjacent :endsrnf radiators :5, 1 and 5, 2B :are connected respectively to the ends fiat conductors cm or which ieomprise :a amen wire transmission line. Connected to the mid points of itheil-inesia, It are the upper ends, mespectively, of :a pair @033 inner conductors J3, .M of :a pair of .-,conc,entric :tramsmission lines haying tubular iouter conductors ":l 5 15.. who flower ends of the inner s-conductors ti, :l 4 :are similarly 500D?" nected, mesnectively, itoahe mid points of :the conductors ll, l2. Inner conductors l3, M, in turn, are connected at their mid points to a respective one of the conductors of an input transmission line H. The transmission line I! may supply high frequency currents to be radiated to the respective elements from any suitable source, such as the transmitter I8; 1

Preferably,- the impedances of the lines 9, I and H, l2 are matched respectively to the impedance of the radiating elements connected therewith. Thus, for example, the radiators I, 2 may have an impedance of 260 ohms. If so,'the open wire transmission line 9, l0 should have a surge impedance equal to 260 ohms. The upper and lower sections of the transmission line 9, ID are in parallel at their mid points. Hence, the line 9, may be connected to coaxial transmission line arrangement having a surge impedance which is one-half the surge impedance of the line 9, I U, i; e.;. 130. ohms. In a similar manner, since the line H is connected to the mid points of the coaxial lines l3, I5 and l4, IS, the impedance at this mid point is equal to one-half the surge impedance of each of the coaxial line arrangements. Thus, the conductors of the transmission line I! may be connected to a standard 65-ohm line, utilizing some conventional form of line balance converter at that point.

, In Fig. 2, I have illustrated the terminal impedance characteristics of a one-layer V-antenna, for example, the antenna comprising the radiators l, 2. The resistance curve [9 has a gradual increase across the band of operation. The reactance curve has a positive slope and varies rapidly as the frequency is varied from a mid frequency. At the mid frequency at which the reactance is zero, the radiating elements I, 2 are of. course approximately one-quarter wave in length.

The input impedance characteristic of the antenna structure of Fig. -1 is illustrated in Fig. 3. In contrast with the characteristic of a single V-antenna, the resistance characteristic 2] of Fig. ,3 is flatter than that of the characteristic IQ of. Fig. 2.. A greater change, however, is noticeable inthe reactancecharacteristic 22, the slope of. which is considerably .smallerthan' the slope of the reactance curve 200]? a single -V- antenna In'Fig. 3, the reactance curve, 22 has anegative slope so that it may be compensated more easily by associated terminal transmission line units for well-known reasons.

'In Fig. 4, there is illustrated the standing wave ratio of a single V-antenna .and the antenna illustrated in Fig. 1. .Thus,'curve 23 shows how standing waves are established on the single V antenna as the frequency is varied from the resonant frequency, and curve 24 illustrates the same characteristic for the antenna of Fig. 1. Of particular interest is the change in frequency which is permitted without establishing a standingwave ratio greater than 1.1., Thus, comparison of curves 23 and 24 illustrates that the band 4 mid band frequency, and curve 21 illustrates the horizontal field pattern when the impressed frequency is .95 times the mid band frequency.

According to one theory of operation in the antenna structure of Fig. 1, by splitting the current path of the high frequency currents to be radiated into four distinct circuits which extend in a transverse dimension over the entire length of the radiating conductors between the ends of those conductors, the radiators I, 3, 5, 1 and 2, 4, 6, 8, respectively, as a group operate in effect as a single conductive sheet and the currents flow in phase from the inner edges of each of these sheets to the outer edges thereof. Best operation is obtained by proper adjustment of the spacing between adjacent radiators in each of the perpendicular planes so that the mutual reactive coupling or effective mutual inductance between adjacent conductors is a minimum. In this way, I have found that there is a minimum change of the reactance component of the antenna impedance and a multiplication or increase of the resistance component. Thus, my improved antenna achieves the basis for a band width improvement in any system, namely, a reduction in the relative values of reactance to resistance.

Generally speaking, the antenna structure of my invention proceeds on the theory that, when the number of conductors is doubled, the resistance of the individual conductors is approximately doubled and the reactance of the individual conductors is essentially unchanged. The manner in which this is made possible can best be understood from a study of the mutual impedance of layers of simple dipole antennas. For such structures, there is available information generally accepted as accurate and a portion of which is illustrated in the curves of Fig. 6. In-

; formation on V-antennas elements would show of frequencies over which the operating frequency '1' Curve 26 illustrates the horizontal field pattern '1."-

when the impressed frequency is 1.05 times the characteristics similar to those shown in Fig. 6. In Fig. 6, there is shown the variation of both mutual resistance and mutual reactance with the spacing between adjacent dipole antennas. The abscissa values are noted as the ratio of d/x, where d is the distance between the respective dipole antennas and A the wavelength. It will be noted from Fig. 6 that for a spacing of d such that d/ \=.l4, the mutual reactance is zero, while the mutual resistance has a value which is substantially equal to the resistance of the single dipole. Of course, the resistances of the individual dipoles are denoted by the values given when d/ \=0. This distance d/ \=.14 may be called the critical spacing distance and it is this particular spacing which provides most desirable operation of arrays of elements. This characteristic, therefore, leads to certain improvements in coupling of feeding transmission lines to the antenna structure and results in a structure in which open wire transmission lines may be connected between adjacent arrays and concentric transmission lines having low impedance characteristics may be employed for supporting and connecting the open wire lines.

In order for the improvements described above to be most effective, it is desirable that every raditing conductor be spaced approximately the critical wavelength distance from each of the other I conductors which form the antenna structure.

When the spacing of each radiating element from the other radiating elements deviates much from the critical wavelength distance, the mutual reactance of that radiating element is not zero. Thus, although the final composite resistance increases as the number of radiating conductors,

the reactance also increases undesirably above a minimum value which is usually reached at the center of the frequency band. It is apparent, therefore, that, while the antenna arrangement of Fig. 1 provides marked improvement in impedance characteristics of antennas so that the antenna is extremely suitable for wide band operation, yet optimum spacing is not provided. One radiator arrangement which approaches the requirement of critical spacing between all the component radiators is that in which the radiators are arranged on the surface of a cylinder, rather than in vertical planes as shown in Fig. 1.

In the structure of Fig. 7, therefore, I have illustrated a modification of my antenna structure which both embodies the principles underlying the structure of Fig. 1 and incorporates a conductor arrangement which approaches a cylindrical configuration. The antenna structure there illustrated comprises two integral structures 28, 29. The structure 28 comprises a first pair of coplanar radiators 30, 3! and a second pair of coplanar radiators 32, The radiators 39, 3| and 32, 33, respectively, are each arranged in the same vertical pane and the sets of radiators 34, and 353, 3'1 are similarly each supported in the same vertical plane. The radiators 39, 34 are arranged in the same horizontal plane and have their adjacent ends so spaced that they form, in effect, a single V-antenna. Similarly, the pair of radiators 3!, 35 is arranged in the same horizontal plane. Likewise, the radiators 32, 39 and the radiators 33, 3'! are arranged respectively, in the same horizontal plane and each set of radiators constitutes a single V-antenna. Thus, the sets of elements 3il33 and 39-4! are each arranged along the four edges of a rectangular prism. Adjacent ends of the radiators 39, 34 are connected by means of an open wire transmission line comprising conductors 33, 39 to the upper end of an input transmission line having conductors 4!. Similarly, the open wire line 42, 43

connects the radiators Si, 35 to the point of connection of line 39 with line 40, M. In this structure, conductors 33, 39, i2, 43 connect diagonally opposite sets of the radiators. In structure, therefore, each of the single V-antennas is connected over an open wire line with the input line d9, 4!. The four open wire lines which are connected to the four V-antennas may have their surge impedance matched to equal the impedance of the antenna and at their input points these lines are connected to an input line whose surge impedance is equal to only one-quarter that of the feed lines individually. The lines 40, 4| may be the inner conductors respective y of a pair of coaxial transmission lines having outer conductors 42, 95 and may be adapted to supply high frequency currents to the radiators 303! from any suitable source, such as the transmitter !8 shown in Fig. 1.

In the antenna structure of Fig. 7, therefore, there are employed four equal radiators of uniform physical characteristics which are fed with currents in phase over four short transmission lines so that all the high frequency currents seem to emanate from two conductive surfaces of large diameters increasing considerably the band width characteristics of the resultant antenna.

An important feature of my invention consists in feeding a pair of input terminals of a radiating conductor system and permitting the current to flow on the conductors over a uniform and large area from the input terminals to the end thereof. In such a construction, of course, it is essential that the effective cross sectional dimensions of the radiating conductor be large enough so that the antenna has an effectively low reactance with a consequent increase in band width.

While, in the foregoing, I have described my invention as being applied to V-antennas, it will be obvious that other types of antennas may be used. Thus, my invention is not restricted to V-antennas but may be employed with equal advantage to radiating loops, dipoles, or rhombic antennas. In such alternative arrangements, of course, appropriate consideration should be given to the separation of the component radiators so that zero mutual reactance is obtained at the center frequency of the band over which the antenna is to operate.

While I have shown and described a particular embodiment of my invention, it will of course be understood that various changes and modifiryations may be made without departing from the invention and I therefore aim in the appended claim to cover all such changes and modifications as fal within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

In an antenna for operation over a relatively wide band of frequencies, a first group of four parallel linear radiating elements lying along the edges of a rectangular prism, adjacent elements being closely spaced from each other by a distance substantially equal to .14 times wavelength at the mean operating frequency so as to approximate a continuous radiating sheet, a second identical group of radiating elements arranged at an ang e with respect to said first elements, upper and lower pairs of elements in both groups lying in the same plane and having their inner ends closely spaced to form four V-radiators, each of said elements having an effective electrical length substantially equal to .25 times wavelength at said mean operatin frequency,

- and means to energize all the elements in each group cophasally, whereby the mutual reactance between adjacent eements in each group has a minimum value and their mutual resistance has a substantial value at said mean operating frequency.

MARVEL W. SCHELDORF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,922,115 Stone Aug. 15, 1933 Re. 20,922 Lindenblad (3) Nov. 22, 1938 2,212,625 Thomas Aug. 27, 1940 2,217,911 Lindenblad (2) Oct. 15, 1940 2,254,697 Godet Sept. 27, 1941 2,267,550 Brown Dec. 23, 1941 2,286,179 Lindenblad (1) June 9, 1942 2,350,916 Morrison June 6, 1944 OTHER REFERENCES "Directional Antennas, by G. H. Brown, Proc. I. R. E. vol. 25, pages 78-145, January 1937. (Copy in Division 10.)

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