US2576748A - Antenna structure - Google Patents

Description

N0V- 27, 1951 G. N. cARMlcHAEL 2,576,748

ANTENNA STRUCTURE Filed May l5, 1948 Patented Nov. 27, 1951 UNITED STATES PATENT OFFICE'TV ANTENNA STRUCTURE Gershom N. Carmichael, Griggsville, Ill.

Application May 15, 1948, Serial No. 27,202

14 Claims. (Cl. Z50-33) This invention relates to an antenna structure, and more particularly to improvements in a high gain antenna.

Beam antennae including a di-pole and relatively closely spaced parasitic elements are considerably more efcient than other types of antennae, as a long line or a conventional di-pole, but have heretofore proved to have certain disadvantages which is many cases offset their advantages. A conventional high gain beam antenna of the type here under discussion, for example, including a di-pole and two parasitic elemen/ts, has been extremely frequency sensitive, its efficiency both for transmission and reception falling ofi very rapidly with change of frequency. While the eiliciency of such an antenna is very much better than that of a conventional di-pole at the precise frequency for which if, is designed and adjusted, the eilciency of such a high gain antenna falls on so rapidly that it is down to or below the efficiency of a conventional di-pole when about 3% off frequency. This made its preferred frequency operating band so narrow that such an antenna could not properly cover a single amateur band, as the 20 meter band, and would be completely out of 'consideration for the broad band of frequencies required in connection with frequency modulation or television signals, for example. o

Another disadvantage of such a high gain beam antenna with parasitic elements, one which it had in common with a conventional di-pole, was the need of relatively complicated and critical impedance matching networks if such an antenna, with its relatively low radiation resistance, was to be connected into a lead-in of the highly efficient spaced transmission line type.

Moreover, when such antennae were stacked in a structure comprising a pair of similar portions spaced half a wave length vertically, there was a further need for a coupling network providing proper phasing of the currents so that the transmission line would be operating at maximum efficiency in relation to both the upper and lower portions of the antenna structure.

I have devised and am here disclosing and claiming an antenna structure which overcomes these and other disadvantages of high gain antennae previously known, which may be directly connected in simple manner to a spaced line leadin with proper matching of radiation resistance and current phases, and which has extremely high efticiency, both on transmission and reception, over almost-l unbelievable frequency band widths. invention will be apparent from the following specification and the drawings, in which:

Figure 1 is a side elevational view of a presently preferred embodiment of my antenna inventions, comprising upper and lower stacked portions each Other features and advantages of my consisting kof an active section and a pair of parasitic elements; Figure 2 is a view at right angles to that of Figure 1, along the line 2-2 of that figure; Figure 3 is a plan view of the upper` portion of the antenna; Figure 4 is an enlarged end view of one of the active sections as shown in Figure 1; Figure 5 is an end elevational view of another form of active section; and Figure A6 is a similar view of still another modification.

While my improved antenna is very eilicient for transmission, and has been used for that pur; pose with great success, it realizes its advantages to the fullest in the reception of wide band signals such as those of television or frequency mod-'- ulation, particularly at points beyond what is con.- sidered the satisfactory service area for such sig; nals. While such signals are normally considered as serving only a line of sight area, there appears to be some diffraction of these waves orsome other phenomenon which makes weak signals available at points definitely under the horizon of the service area of such a station, as 60 to 100 miles away. My antenna provides unexpectedly efficient reception of such signals and fully satis,- factory service all bui, a very few per centv of the time under conditions heretofore considered so adverse as not even to warrant any attempt'to provide television or F. M. service. Moreovenit does this with such wide band characteristics that a single antenna will provide very satisfactory opgeration on all the channels of one television band, for example, and where conditions are not too ad.- verse will extend this satisfactory coverage also through the frequency modulation band and possibly even on down into the lower television band, rather than requiring a multiplicity of antennae for satisfactory coverage of various channels and bands. A lead-in of the spaced parallel line type provides a very efficient energy transmission medium between an antenna and the radio apparatus, but it must normally work into a resistance, at the antenna end, of the order of 300-400 ohmsto achieve its efficiency. Present television receivers, for example, have adopted a 300 ohm input as a standard, so that a similar resistance would have to exist at the antenna end of the transmission line. I have found that by making my active or center section of the high gain antenna, the one to which the lead-in connection is made, cagelike in character, with the di-pole an interior element in a cage including surrounding rod-like elements connected at their ends to the di-pole, an unexpectedly high radiation resistance and operating efficiency are obtained which are very much greater than theory would indicate from mere multiplication of a folded doublet, for ex' ample. An antenna having two parasitic elements and a cage-like active element comprising a central di-pole and live rod-like elements sym' metrically spaced therearound and connected thereto at the ends, with all of said elements `be` 2,576,748 if i?? ing parallel and having a length slightly less than that of a half wave of a frequency at the center of the band in which the antenna is designed tbo'perate'; provides not' onlythe extremely high gain operational eihciency- I have mentioned, but also a radiation resistance of about 300 ohms,

so that a spaced parallel line transmission li'ne':v

may be used to directly connect such activesec tion to the input of the television receiver,`for example. cageelements very greatly increases `the tradiation resistance, the addition of one more exterior element, in a high gain antenna havingftwo-parasitic elements in addition to the cage-like active section increasing the radiationresistance from the order of! 300` ohmstoupver-y nearly to 500 ohms.

When Ispeak oi"` radiationgresistance. throughout thisrrspecification-,r/it is to be understood that I- aml speaking of` the eiectiveresistance oft-the antenna, whether it beused for transmission or reception. While the term radiation .resistance isV normally associated w-itha characteristeofthev antenna during transmissionI am hereusingthe term asa measurecf thefeieetive or working resistance of the antenna,A whether it s-beingf used for transmission Y or reception.

L have*- also' found that, where. identica-luantennastructuresare stacked a half ,wavef length apartf a simpleY spaced line connection' may'xbe usedtherebetween', and: as a lead-ingrif ther con'- Vnectionbetween' ther two portions" of theI stacked antenna is` rever-"sedY or crossed near" one ofi the portions;A as thelow'er portion. and the lead-in connection' isV made tothe' itu-,ormedia't'eV connection'a't ay point above thi's'c'ro'ss-over and' where the' currl'e'nts'` haveth'eir maximumfadditive effect: that is, are in' phase. Wave propagation o'f thekindf of which I' anr speaking, in` a transmission' line" ribbon with'a plastic dielectric, as used television and.' F. has a speedofthe order of 82% of*V the velocity of radio waves' in free space, and I have found that ata pointl half wayv between the 82% point and the' closer" an"- tena portion (that is, about.9% of the'distance from" such antenna portion), the maximum additive effect may be obtained. While other factors' provide some slight variations whichk may reduire very minor adjustment of the spacing Vo'f this point, having the lead-in connection: half of the distance from one portion. of a' stacked antenna', as the lower portion, vand `.the point which is the same percentage ofA distance-from rangement with a simple parallel. line connection therebetween and with a parallel line lead-in or transmission line Awith'notv only proper impedr-v ance lmatching but also with complete elimination` of :any necessity for phasing networks.v v

Referring now to the particular embodiment ofmy invention illustrated in Figures 1 to` i of the drawings, the antenna structure is-shown ascomprising identical upper and` lower stacked portions having Ythe centers of their conductive antenna elements spaced half a wave length. The `two portions are shown as supported by; a post l0, which may be rotatable about its'axis andA controlled in anyV conventional manner vto vary thedirectionof vthe axis of best propaga--` tion- ,andf 4reception (hereinafter termed theY beam axisllif desired: Since the upper and lowerpor-,f '1Q tions are identical only the upper portion will be described in detail.

The post lll carries at the top thereof a crossbai" I lf carryihgtwo supporting Aor, frame members illustrated' as pipes l2 and I3,` extending parallel to the beam axis. At the front and back of the antenna, speaking in terms of the beam axisare.a pair of continuous or unbroken rodlike elements I4 and I5 supported at an appro- The addition of furtherfexterion or? 10i .priateb'distance-above the supporting frame-work by pairs of insulators, as for example rods I6 and' Il' of Lucite. The two rod-like elements lll-.and 'I5 are conductive, as for example being copper rods or tubes 5/8' of an inch in diameter (althoughV wire is satisfactory,- andi-intended to beincludedalso-by the term frod-like," element-s. and comprise the parasitic elementsofya@4 high gain antenna withftwosuchelements; Theffor- WardI element 1.4-, normally termed Ythe director in. transmission! andA collector ,in reception, should. be slightly less thancha-lf.' a wave length in IengthVas for Vexample V.96. of; a halff'wavc length., spaced.. ay small. fraction of. `awave-'length from` the activeI section of. the. antenna. .being spaced ofA awaVe-length in the antenna illus.- trated.;y The other. elementzl5 comprises a Vsirnilar. continuous conductiveiod. nor tube, and should have a length slightlygreater. than ahalf wavel length, as for exam-ple,4 1.05.- times, a-fhalf wave length,v and'A ist preferably ,spaced slightly farther than. the otherI element as 'fort-example .l5r wave length-from' the center of the active section It willlbetunderstocd that when a-wave length is spoken of, ity is-.thewai/er leng th-.of.r a frequency at or near themiddleoiirthe-.band of frequencies 'which the antenna iszdesigned'l@ cover., vSince the-fantennafhasvery wideband characteristicsfthelengths are. not critical;-but best: results areobtained for a givenwavelength at, or preferably 'slightly below thevcenter'frequency. of theband' -to 'be-covered-.; fact,.;the lack offrequency `sensitivity` is suchnthatcthe parts may be cut to length by formula, withu absolutely 1 noneedof -themechanicalfadjustments of elementy length now considered'necessary-A in connection .with `high gain antennae of 'conventional type. -i

The: intermediate or-vactive section of vtheauten-na,l in the sense that-it iszthe section toV which currents are conductively delivered during transmission and from whicn'they areconductively led during reception,v isa cage-like device; identiied in general ras A. Itis? shown as comprising.V a central di-poleconsisting of the symmetricalrod-likefparts- I8at and Ib, separated at. the center by a smallf'spacing, as for example two inches. WhileA thisy space. isshownf openin the drawings; forclarity' of illustrationfit woulcixin practice normallybemechanically closed by insulating material, as ashort rodi of Luciter.to provide a single mechanical entity; The entire cage-like actieve section is preferably supported from the supporting frame, as bya transverse member I9: and insulating. rods#y Zik-2t, 22 and 23; with the center ofthe diepole element in the same plane asA the-elements I4 and'l;

Surrounding the di-'pole areI aplurality of symmetrically spaced. continuous .rod-like elements forming the exterior elements ofthe cagelike section, 'thesebeinghere identified as 24; E5', 2B, 2, 28.a'nda29; They 'are connected tothe Vdi-pole-at each end conductively,iasfby the transspaced more than the diameter of either, but 4I prefer to have the di-pole somewhat larger than the exterior elements. Moreover, the spacing between the interior and exterior elements, while it should be greater than the diameter of either, is preferably only a very small fraction of the wave length for which the antenna is being designed, as for example 21/2 to 5%. 'Ihe length of the cage-like element (that is, of all of the parallel components thereof) should preferably be equal to a half wave length less twice the diameter of the cage.

While the exterior elements of the cage shown in Figures 1 to 4 are six in number, this results in a slightly higher radiation resistance than described for best reception of television, for example, where such resistance should be of the order of 300 ohms. In Ian antenna of the character described I find that this value of radiation resistance can be achieved by using ve symmetrically spaced exterior elements, and in such case I may provide an end structure for the cage of the character shown in Figure 5. Here the central element or di-pole 50 has at each end thereof a ve-armed metal plate 5| carrying the exterior rod-like elements 52, 53, 54, 55 and 56. By having the interior element a di-pole and the exterior elements continuous, with connections at the ends of the cage-like device, some phenomenon occurs which I cannot at present fully explain in theory, but which results in an unexpectedly high radiation resistance of an antenna including this section when there are sufficient exterior elements, in more than one plane, to provide a cage effect, and which results in more efficient transmission and reception of energy than would be the case from merely increasing the effective surface. The conductive and inductive currents set up in the various elements of the cage bear such phase relationships that the radiation resistance rises as the square of the total number of elements (including the interior element) in this section. That is, instead of the radiation resistance of a cage-like section with six exterior elements being only about 18%% greater than one with five exterior elements, as would be indicated by conventional folded doublet theory, such an arrangement actually provides in the order of 45% higher radiation resistance. In addition, the radiation and reception efficiency is not only very much greater at the wave length for which the antenna is designed, but is still greater, at as much as an octave higher frequency, than that of the conventional oli-pole designed for such higher frequency. j The spacing between the two sections of the dipole at the center, shown somewhatlarger than actual in the drawings for purposes of clarity, is very satisfactoryv when in the neighborhood of two inches, the inner ends of the di-pole sections then connecting directly to the leads of a spaced parallel line transmissiontape of the kind found so satisfactory for television, these Y leads being here identified as 33 and34. Referring particularly to Figure 2, it will be noted that these's'ame leads 33 and 34connected to the inner ends of the two sections ofthe di-pole of the lower portion of the stacked antenna structure, but in reversed relationship, crossing quite close to the lower antenna. With a propagation velocity in the lead-in of the order of 82% of that in free space, as mentioned heretofore, the lead-in transmission line comprising the two par- ' allelspaced conductors 35 and 36 is preferably' connected at a point about 9% ofthe distance between the antenna portions, speaking of the center line of the conductors. At or ,very close to this point the maximum additive effectsof the currents from the upper and lower antenna portions are obtained, with maximum energy through the lead-in to the receiver, speaking in terms of reception, Moreover, this point provides, during transmission, the optimum arrangement such that allphasing networks are eliminated. It will thus be noted that I have designed an antenna structure which not only has high gain and extremely advantageous Wide band characteristics, but which also completely eliminates any necessity for impedance matching or phasing networks in the connection to the radio apparatus.

It will be understood that, where high radiation resistance is desirable, additional numbers of exterior cage elements may be used. Moreover, the connections between the elements at the end of the cage-like device do not appear to be critical so long as the elements are all connected to each other. For example, in the form shown in Figure 6, one di-pole section 66 has at one end thereof a conductive rod 6I carrying a circular end connector 62 on which are mounted the exterior cage elements 63, 64, 65, 66, 61 and 63. My inventions have been embodied in experimental antennae with cage-like sections having up to as many as ten exterior elements, and in antenna arrangements including three parasitic .elements instead of the two illustrated, proving advantageous in all such cases. It is also to be understood that the advantages of a cagelike active section may be obtained in connection with any type of antenna where increase in radiation resistance, for example, is desired, as a long line antenna with the cage-like section as the active or driving section.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and ar- I rangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

l. A radio antenna having a single cage-like active section comprising an interior rod-like electrically active antenna element and a plurality of exterior rod-like elements disposed to encase said interior element and lying in more than one plane and connected at their ends to said interior element.

2. A radio antenna having a cage-like active section comprising an interior rod-like electrically active antenna element and a plurality of exterior rod-like elements lying in more than one plane and connected lat their ends to said interior element, said exterior elements being parallel and symmetrically encasing said interior element and being mechanically and electrically continuous over the whole length of the antenna.

3. A radio antenna having a cage-like active section comprising an interior rod-like electrically active antenna element having electrically spaced portions, and a plurality of exterior rodlike elements disposed to surround said interior element and lying in more than one plane and connected at their ends to said interior element, all of said elements having a length slightly less than half the wave length of a frequency near the center of the band `for which said antenna is designed. A f ,i

7 4. PAfradio 'gantennaliaving a cage-likeactive sectionjcomprisingyan interior di-pole'and a plu- Vrality'"orig-:xterior rod-like elements lying'in'mcre Vthan nne planenandrconnectedat their ends to having electrically spaced portions, yand at least five'electrically andmechanically continuous exterior rod-like elements lying in more than one planev and connected atthe'ir ends to opposite ends said di-pole.

6..A Afradioantennahaving a cage-like active section comprising an interior rod-like electrically active antenna element adapted to be connectedto an external circuit intermediate its ends andaplurality of exterior rod-like elements lying in incre than one plane land connected at their ends ,to said interior element, .said 'exterior ,elements symmetrically lsurrounding s-aid interior element. and all of said,el ements being parallel and .having a length slightly less than half the .wave length of a frequency near the centerof the band forwhich said antenna is designed.

' '75A radio antenna having .a cage-like active section comprising an interior di-pole and a plum ralitypf exterior rod-lik'eelements lying in incre than one` plane and connected at their endsto said di-pole, said Vexterior elements symmetrically surrounding said dij-pole. and said di-pole and elements being vparallelanl having a lengthslightly less than half the wave length ,of a frequency near the. center of the band for which said antenna is designed,.said exterior elements being continuous throughout the entire length of said cli-pole.

8. A radio antenna having a cage-like active section comprising an interior krod-like element having electrically spacedportions, and a plurality of exterior rod-like elements lying in more than one plane and connected at their ends to said interior element, said exterior elements being spaced thr'oughout their length from said interior element more than the diameter of said interior element and being mechanically and electrically continuous over the whole length of both spaced portions of said interior element and being dis'- posed to encase said interior element.

9. A-radio antennahaving a cage-like active section comprising an interior rod-like dipole element having electrically spaced portions and being adapted to be connected to an external circuit intermediate its ends, and a plurality of exterior rod-like elements symmetrically surrounding said interior element and lying in more than one planeV andconnected at their endsV to said interior element,V all 'of said elements having al length vslightly less than half the Wave length o'f a frequency near the center of the Y band for which said antenna vis designed, said exterior elements being spaced throughout their length from said interior element more than the diameter of said interior element but only a very smallV fraction of said wavelength.

10. A directional antenna having a cage-like active section andat least one parasitic section.V said active section comprising an interior rod like element having electrically spaced portions and a plurality of electrically continuous exterior rod-like elements symmetrically surrounding said interior element and lying in more. .than one plane and connected at their ends to said interior .ele-

Anien't,"al1cfisaid elements having a length slightly 'less than `half the :wave 'lengthl of a frequency nearthe :center of the band'for which'said antenna is designed.

.11..A1directional antenna having -a cage-like active section and at least oneparasitic section, said active section comprising an interior rod-like di-pole element and a plurality of electrically continuous exterior vrod-like elements lying in more than 'one plane and connected at their ends to said interior elementadjacent its ends,V said exterior elements symmetrically surrounding said interior element. and all of said elements being parallel and having a length slightly less than vhalf the wave length of a frequency near the center of the Aband forwhich said antenna is designed.

12. A Vdirectional antenna having a cage-like active section and at least one parasitic section, said active section comprising an interior rod-like di-pole element connected to an external circuit intermediateits ends `and a plurality of electrically continuous exterior rod-likeelements .surrounding said di-pole and lying in more than one plane and connectedat their ends to said interior element at thev ends thereof, all of said elements having a length slightly less thanhalf the wave length of a, .frequency near the center ofthe band ffor which 'said antennais designed, said .exteriorv elements being spaced 'from said interior element morethan'the diameter 'of said interior elementbut only a very small fraction of said wave length.V ,Y f

13. A directiona1 antenna structure `ccinprlsinga pair of similary portions spaced half arwave length apart, each portion having ja cagelike active section and at least fone, parasitic section, each .active section comprising an interior rodlike element and a plurality of exterior rodlike elements lying in more thanoneplane and connected at Ytheir ends to said interiorfelement, said exterior elements being symmetrically spaced `about said interior velement and Vall of said elements being` parallel and having a length slightly less than half the wave length oi a frequency near 'theeenter of the band f orwhich said antenna is designed, said interior elementbeing a di-pcle and said exterior elements being continuous, a reversed connection between said active sections, Iand a lead-in Vattached to said'connection at a point where the currents are additive.

1 4. Apparatus of thecharacter claimed in y'claim Vlgywherein each di-pol e' has` electrically spaced portions andthe reversed `connection is between the di`polesintermediate their ends, and

Vwherein said intermediate connection is provided by a parallel wire transmission line having a propagation velocity factorgof substantially 32% of thatin free space, and-wherein saidv peint is substantially 9% of the distance from one dilp'ole.

' GERSHOM N. CARMICHAEL.

REFERENCES 'CITED v,The following references are of record in the filepoi this patent:

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