US2947988A - Traveling wave antenna - Google Patents

Description

Aug. 2, 1960 Filed March 29, 1955 R. W. MASTERS TRAVELING WAVE ANTENNA 8 Sheets-Sheet 1 INVENT OR BY a M d ATTORNEY A g' 1960 R. w. MASTERS 2,947,988

TRAVELING WAVE ANTENNA Filed March-29, 1955 8 Sheets-Sheet 2 o/ zsxie :5; (400A r50 A r 6800410 aw-4 NVENTOR 4(9 (306mm WW 912M141,

PIC 70/?! Aug. 2, 1960 R. w. MASTERS TRAVELING WAVE ANTENNA Filed March 29, 1955 8 Sheets-Sheet 3 E L m BY L dirt I AT'IORNE Aug. 2, 1960 R. w. MASTERS 2,947,938

TRAVELING WAVE ANTENNA Filed March 29, 1955 8 Sheets-heet 4 Ira--11 Attenuation In db Per Turn O 940 960 980 I000 I020 I040 I060 I080 IIOO Frequency In Megucycles INVENT OR BY d'rfix Q ATTORNEY Aug. 2, 1960 R. w. MASTERS TRAVELING WAVE ANTENNA 8 Sheets-Sheet 5 Filed March 29, 1955 INVENTOR 913a Aliza 3 d A'ITOR R. W. MASTERS TRAVELING WAVE ANTENNA Aug. 2, 1960 s Sheets-Sheet s INVENTOR .3! I :3- I I: l d

Filed March 29, 1955 I II IIII [Ill-Ill lull-ll 80$! WA 912M144 ATTORNEY Aug. 2, 1960 R. w. MASTERS TRAVELING WAVE ANTENNA Filed March 29, 1955 8 Sheets-Sheet 8 m m i l 9% m w M wfl m N 9 x W i W 3 M m am N I'M MMNHU *w in NH UH nwwuwmwwmwmmwwm www H RN mm, m )nu m 1 w 11 v 1 & "Wm 2 A ORNEY Un t e a s t O" 2,947,988 TRAVELING WAVE ANTENNA Robert Wayne Masters, Columbus, Ohio, assignor to The Filed Mar. 29, 19 s, Ser. No. 497,693 22 Claims- (Cl. 343-742 My invention relates broadly to traveling wave antennas and more particularly to an antenna particularly suited for high frequency transmission.

One of the objects of my invention is to provide a construction of traveling wave antennawhich may be readily predesigned to radiate an omnidirectional high power radio frequency field pattern.

Another object of my invention is to provide a construction for traveling wave antenna which will produce a highly directive toroidal beam whose shape and direction are substantially independent of the frequency over an appreciable range.

Still another object of my invention is to provide a construction of traveling wave antenna for producing predetermined horizontal or vertical polarized radiation in a predetermined pattern for facilitating :operation of television broadcast stations within the separation limits prescribed by the regulations of the Federal Communications Commission, and yet provide television service for maximum population in various geographical areas,

A further object of my invention is to provide a construction of traveling wave antenna having an envelope delay, whose envelope delay distortion or phase distortion is exceedingly small and welldwithin the very close tolerances set by the standards of the Federal Communications Commission for color television.

A still further object of my invention is to provide a construction of traveling wave antenna including a lineal radiating element which may be excited at both ends simultaneously by two transmitters within relatively close frequencies for facilitating visual and aural transmission in television broadcasting without the necessity for separate diplexing networks for preventing objectionable cross-modulation.

Still another object of my invention is to provide a construction of traveling wave antenna including a lineal element which may be fed or excited at some pointin- =termcdiate the two ends for achieving directivities greatly exceeding those obtainable with an end-fed embodiment having equal stability of beam in shape and direction.

Other and further objects of my invention reside in a construction of traveling wave antenna whose characteristics may be reliably predetermined to meet particular operational problems as set forth more fully in the specification hereinafter following by reference to'the accompanying drawings, in which:

Fig. 1 is a theoretical diagram explaining the principles of operation of the antenna structure of my invention;

Fig. 2 is an explanatory diagram illustrating the circuit system of the antenna structure of my invention, shown in Figs. 4, 16 and 18;

Fig. 3 is a schematic circuit arrangement explaining the theory of the antenna structure of my invention, shown in Figs. 4, 16 and 18;

Fig. 4 is a fragmentary verticalsectional view illustrat- A 2,941,988 Patented Aug. 2,

ice

ing an antenna structure in accordance with one embodiment of my invention, and showing particularly connections for both visual and aural transmission and connections for diplexerless operation;

Fig. 5 is a view of another form of antenna structure embodying my invention and illustrating an arrangement for diplex operation;

Fig. .6 shows a modified arrangement for absorbing residual energy at the remote end of the antenna;

Fig. 7. isa side elevational view of the external tubular conductor forming part of the antenna structure according .to one form of my invention, the view being fore-shortened in order to more clearly illustrate the slots which are formed therein, the external conductor being shown in assembled relation to the internal condnctor;

Fig. 8 is a side elevational view of the internal tubular conductor forming part of the antenna structure of my invention for coaction with the external conductor of Fi t Fig. 9 is a transverse sectional view taken on line 979 of Fig.7 on an enlarged scale;

Fig. 10 is an enlarged cross sectional view of one form of the adjustable probe coupler employed in the antenna st ctu e of my nv t Fig. 11 shows characteristic curves representing beam orientation andattenuation functions for three difie rent tuning settings of the antenna structure of my invention; Fig. 12 is a chart showing a beam cluster from which beam orientation, with respect to frequency, in the structure of my invention is determined;

.1.Fig..13 is an. elevational .view of a modified form of antenna structure embodying my invention, the view showingthe assembly of the outer conductor associated with three folded unipole types of radiators;

Fig. 14 is an elevational view of the inner conductor which; is associated with the outer conductor of 13; Fig. 15 is a transverse sectional view on line 15-15 of Fig. 13, showing the relationship of the folded unipole radiators shown in Fig. 13;

Fig. :16 is a vertical sectional view on line 16-16 of Fig. 15 showing .the relationship of the folded unipole the slots in the surface of the external conductor provided i the r an eme o i s 0;

Fig. 0 is a horizontal sectional view taken online ai 2m ns 9;

Fig. 2.1 is a theoretical diagram explaining the application of the circuit structure of Fig. 17;

Fig. 22 schematically shows the electrical characteristics of the antenna of Fig. 17;

Fig. 23 shows schematically the method of applying the teaching of my invention to a center or intermediate tieedantennasystem;

Fig. 24 is an enlarged cross sectional view of :Fig'. -23

illustrating the radiator means of Fig. 18 associated thaw Fig. 25 is a plan View of the assembly shown in Fig. but illustrating the balanced pair of probe-coupled anti-resonant. loops of Fig. 18 schematically for purposes of more clearly explaining the assembly, and

.;Fig..:26 is :a section substantially on line 26-26 of .Fig.r24.

My. invention provides anomnidirectional, high power,

i of application.

radio frequency antenna isimple construction and high directive gain, having the primary objective of applicatlon in television broadcasting. Feasible solutions to the problems of custom-shapingand gap-filling the radiation beam pattern are additional objectives.

spiral plan along the line so that a wave initiated at the input will be largely, if not entirely, dissipated in radiated energy in the desired pattern as it approaches the remote end of the radiating system. A well known property of such systems is that the beam produced has an inherent tendency to change direction with changes in the frequency. This property has heretofore limited the application of traveling wave antennas to single frequency transmission or to situations where beam direction is relatively non-critical.

A particular novelty of the present improvement as compared to prior traveling wave type antennas lies in the arrangement of the system details so as to preserve the radiation beam characteristics essentially invariant in 'shape and direction with respect to frequency over a discrete range or band, thus greatly broadening its scope Beamstability in these respects is of prime importance in certain applications such as television broadcasting which require the antenna to operate over a band. A second novelty is that the variation in. the input impedance of the invention with respect to frequency may be made negligible in the operating range.

The antenna structure of my invention secures both beam pattern control and input impedance stability over an appreciable band of frequencies.

Physical properties One embodiment of my invention employs a transmission line constituted by a coaxial line of suificient mechanical strength to comprise a free standing antenna mast. The radiating elements are pairs of short, diametrically opposed probe-excited, axial slots in the outer cylinder Wall. These elements are spaced approximately one-quarter wavelength apart on centers along the transmission line at the design frequency. The azimuthal orientation of the slot pairs, relative, say, to the first one of the antenna apertures follows a generally spiral plan prescribed by the requirements of the application. For the simplest possible arrangement which will produce exact broadside beaming of the radiation as required for example in some television transmitting applications, the spiral is a uniform one winding at the rate of one turn per nominal internal electrical wavelength, and the geometry at any cross section containing the centers of a pair of slots is identical in every respect with that at any other similar cross section.

In order to produce a given radiation pattern characteristic the spiral rate, or the element spacing for a design having a fixed number of pairs per turn, the coupling factor (i.e., the relative strength of excitation of the elements), and the eifective Q of the radiators, are highly important design parameters which may be pre-assigned at will to depend functionally upon distance along the aperture as the required complex aperture distribution of the excitation may dictate.

One of the many important advantages of my antenna structure is that it is completely reproducible once the designer has a certain minimum basic information at his disposal. In the slotted cylinder embodiment, for example, one needs only to know the effective radiator Q, the shunt capacitance introduced into the line by the probe coupler as a function of probe depth, and the peak attenuation of the typical antenna sections for one probe setting. Practically all the antennas presently used in television broadcasting today are realized only after extensive and exceedingly costly experimental development. In direct contrast, my' antenna structure can be specified,

built, and depended upon for performance as intended,

' after applying a relatively simple paper design procedure based on a laboratory determination of the above mentioned parameters.

Another superior advantage of my antenna structure is that the antenna is capable of handling all the power that can practically be delivered to it because of the large dimensions of the coaxial transmission line comprised by it. Branch transmission lines, which have become a severe limitation in one sense or anotherin many existing antennas designed for television broadcasting, are completely absent, and the construction of my antenna is strikingly simple by comparison. The embodiment using slot radiators is ideally shielded from the induction of high amplitude current or voltage surges by lightning strokes which sometimes cause extensive damage in systems not adequately shielded.

Other embodiments of my invention employ a-winding ladder arrangement of radiating elements; an anti-resonant probe-coupled folded unipole; a balanced pair of loopcoupled series resonant unipoles; and a balanced pair of probe-coupledanti-resonant loops for producing horizontally polarized radiation. The probe-coupled antiresonant loops produce vertically polarized radiation when oriented in planes containing the cylinder ax-is.

Pattern consideratio ns Referring to the drawings in more detail there are certain pattern considerations which must be considered. When the elements are closely spaced (of the order of one-quarter wave length) the spiral excitation, which is admittedly discontinuous, may be treated quite successfully as if it were continuous. Consider the coordinate system of Fig. l in which the antenna aperture originates at z=0, and the antenna axis lies along the positive z-axis. Electrical Waves travel along the antenna on the positive z direction, and the residual, unradiated energy is absorbed at the remote end by a matched terminating resistor. Let A(z) represent the amplitude distribution of the aperture excitation, B(z) the phase of the excita- 'tion relative to zero at the origin, and C(z) the angular displacement in the direction of increasing through which the spiral generatrix mustrotate in arriving at a given point z starting from coincidence with the x-axis at z=0. The spiral generatrix is a line which, at any point z on the positive z-axis, is perpendicular to the z-axis and passes through the null regions of the elementary pattern associated with the cross-section of the antenna at that point.

Assuming that the space pattern of a pair of slots is represented approximately by a tangent pair of identical spheres whose line of centers is perpendicular to the z-axis, it can be shown that with very good accuracy the remote relative field of an antenna aperture of length h is E =zero everywhere (1) 'and where 5 is thefree space phase propagation constant.

Unfortunately, the number of functions A, B, and C, which render Eq. 2 analytically integrable are exceedingly limited. One fortunate and especially feasible set is By considering an identical, orthogonal, spiral excited simultaneously in time quadrature with the first it is possible to obtain a very simple expression for the pattern which is exceedingly close to that of the single spiral a one. O e h s n s A careful consideration of this result for u O reveals that the resultant field is a figure of revolution having progressive azimuthal phase. The beam pattern is quite directive with no nulls except along the z-axis, which is a highly desirable property. The generally conical toroidal beam points in a direction given by cos reference is I 1l=l rl In non-uniform designs the exponent is an integral. In any case it is twice the overall insertion loss of the antenna in nepers. It will be shown in a subsequent section that the Z' of the antenna is essentially constant in the operating range of frequencies, hence Eq. 8 accurately indicates the variation which may be expected in the input impedance. The variation in input impedance may be suppressed as strongly as desired either by reducing the magnitude of K or by increasing a, or both.

The reflected residual wave on a uniform antenna travels backwards along the antenna and produces a similar beam pointing in the direction 1rand having a progressive azimuthal phase variation in the reverse sense. If fi=v (broadside case), the beams add in two opposite directions and subtract in two other (orthogonal) directions in the azimuthal plane, thus causing the pattern to become elliptical. The max/min. ratio of the fields in this principal plane is The directivity, D, of an antenna is defined as the ratio of the maximum energy flow density to the average energy flow density at a fixed remote distance in free space from the antenna. Let S(0) represent the power A pattern of the antenna, and 6 be the beam direction. Then the directivity is precisely Lsnndc where the differential surface area dit is in steradians, and A is the surface of a large sphere. For the exponential distribution which exists on an end-fed uniform a1i= tenna such as that hypothesized above, S (6) is the squared amplitude of E (0) from Eq. 4, and the directivity is closely approximated by.

D (1e (end-fed case) 11 where a is in nepers per nominal guide wavelength and h is in nominal guide wavelengths, provided that a fl and e 1, which will usually be the case in practice. An exact closed analytical expression cannot be obtained.

Various combinations of end-fed sections may be visualized. In particular, two which are identical, except that the senses of their spirals are opposite, may be ar ranged end to end on a common axis and excited with equal waves traveling in opposite directions fi'om a c0mmon generator at the junction. The sections need not necessarily be uniform, but this arrangement produces a symmetrical antenna. If the sections are uniform and h is taken to mean the overall aperture length, and at the net overall wave attenuation, the directivity becomes D (1e g) (center-fed case) (12) This appears to have roughly twice the directivity of the end-fed aperture until it is realized that for equal overall wave attenuation, 0c is just twice as great as it would be for an end-fed structure. Hence uniform apertures of equal length have essentially the same directivity whether they are end-fed or center-fed. The slight differences in .directivity which would arise in using various types of elementary radiator are entirely negligible. The important conclusion is that the antenna structure in its simplest possible form is inherently very directive and devoid of diffraction nulls.

Network considerations One of the important advantages of my antenna structure resides in the arrangement of the network details, which is accomplished in such a way as to minimize the variationin the phase propagation function over the op crating frequency range. The result of this in that the inherent tendency of the radiation beam to change direction with variations in the frequency is suppressed in the range. The supporting theory is as follows:

Assume a uniform dissipationless transmisison line loaded continuously and uniformly with a dissipative anisotropic material of specifiable properties. The complex propagation constant of such a line, as almost any good text on the subject reveals (e.g., Schellrunofi, Electromagnetic Waves,"1943, p. 196), is

where Z is the total series impedance per unit length including the added loading, and Y is the corresponding shunt admittance, both being specifiable functions of the frequency. If R and G are much, much smaller respectively than X and B, one has the accurate approximations 1 B Y M pa e] and fiiVBX (15) The phase propagation function, [3, is obviously stabilized with respect to variations in frequency if B and X are such that their product is constant, which situation can be approximated physically in a limited frequency range.

'Assume the hypothetical loading material is such that it does not alter the series line constants when it is introduced into the line. Then R=O and X =wL. To achieve the desired stabilization of [3, B must then vary as 1/0). Itwould. be especially desirableto have B;C/w, where 7 -C is the capacitance of the unperturbed line' per unit length corresponding to L. The result would be A physical realization of the required B could be obtained approximately in a limited range about resonance by shunt loading the line discretely at short intervals with series RLC triplets having the proper Q. The attenuation function would be determined by the resultant C.

A precisely analogous situation exists for the case of pure series loading. The physical realization is achieved by introducing parallel RLC triplets, having the proper Q, in series with the line at regular, closely-spaced intervals.

It is appropriate here, as well as important, to observe that compensation, i.e., suppression of variation of the phase propagation function as compared to the unperturbed line, occurs to some degree whenever the added series reactance or shunt susceptance function has negative slope. This is the reason for specifying so carefully the type of loading. Practical radiators exist which possess the required impedance properties, and in order to use them efficiently it is helpful to extend the analysis to include wide spacings.

Consider now the case of pure shunt loading on a dissipationless transmission line of characteristic admittance .Y and let the loads be represented by 2Y at regular intervals at along the line. Assuming the loads concentrated at their respective cross sections rather than somewhat distributed thereabouts, one can draw the following network diagram of atypical single iterated section of the structure; represented in Fig. 2.

An analysis of the four-pole network of Fig. 2 reveals that the complex propagation constant, a=a+j/3, per section is determined by cosh 0E cos B d-I sin B d (17) and the characteristic admittance, Y is Y Y Z Y b i 1 o )1 2 cot {3 d+( 8) where ,8 is the phase propagation constant inside the unperturbed section of line and which is assumed here to be equal to that of free space merely for purposes of simplification. Identical forms are found for the case of pure series loading by 2Z To obtain them one simply replace Y with Z Y with Z and Y with Z in Eqs. 17 and 18.

One can manipulate the pair of equations implied in (17) to obtain cos B= [c0s [i d:.'; sin d] (19) which appears to be fundamental in the analysis of the antenna. If a is very small compared with unity, as will be the case in most practical applications, then cosh a l. The variation with respect to frequency of the first term inside the bracket is opposed by that of the second in the neighborhood of a zero of B so long as the slope of B is negative. By properly adjusting the slope of B at the peak attenuation frequency (approximate resonance), which amounts practically to prescribing Q and the peak attenuation rate per section, it is possible to stabilize B about any desired value. It maybe said further that the net phase variation across any given frequency range is less for the loaded than for the unloaded line if B has negative slope throughout that range. The negative slope range of B is then identified very closely with the compensation range.

Fig. 3 represents an equivalent network which may be shown to represent the loading introduced into a transmission line by one of a balanced, out-of-phase pair of short, probe-coupled, anti-resonant slots or half that of a single, short, radial, folded, probe-coupled, anti-resonant unipole if Q is relatively high. The capacitance between 8 the probe and the inner conductor of a coaxial line is represented by C while the anti-resonant character of the radiator is accounted for by the RLC triplet. The conductance and susceptance of this network may be If lightly coupled loads (i.e., |Y Y are spaced nominally one-quarter wavelength apart along the transmission line, it is evident from Eq. 18 that Y =Y with the result that the frequency at which maximum attenuation occurs will coincide very, very nearly with the frequency at which G reaches its maximum. This normalized fre- It can also be shown that the inflection point of the phase function is practically identical with the inflection point F of B. This normalized frequency is it F-[1+ (24) v :k A further exploration locates the center, F, of the negative slope range at u A o the deslred workrng range, and since F rs by far the simplest reference for deducing practical design formula,

A e I F 1s selected as the nominal design frequency.

A consequence of this selection, upon due examination of Equation 19, is a practical design equation for the radiator spacing required to produce a prescribed g per section once C Q, a, and Y are stated. If D=,8 d and D=FD, then sinh Q AAA D r- 5 It can also be shown through a consideration of Eq. 19

that

A A A m=p2uQ (29) A where m is the slope, m, of the phase propagation func- A -tion at F.

"entirely overcomes this deficiency. tapered asymmetrically, the antenna directivity will differ The effective Q of the radiators in a uniform array may be obtained by measuring the attenuation functionof the antenna as a lossy section of transmission line. If AF is the normalized frequency difference between equal values of a, then If thecoupling of the radiators to the internal traveling wave is properly tapered, the external amplitude distribution may be made nearly uniform, thus effectively maximizing the directivity for a given. aperture, while the in ternal attenuation remains very high. Almost any desired amplitude distribution, directive or not, may be obtained, and the required internal attenuation function in terms of the distance from the input end of the aperture is:

1ftheinsertion loss of the antenna is of the order of 25 'db, which is anticipated in practice, it is at once evident lthattrans'mitters could operate into both ends of the antenna simultaneously without serious danger of objectionable cross modulation. An embodiment of my invention for accomplishing this is shown in Fig. 4, and 6-10. Since two isolated transmitters not differing greatly in frequency are required in television broadcasting, an ideal situation exists whereby the usual mutually isolating,

combining network (diplexer) is unnecessary. Hereto- 'fore television antennas have required an explicit diplexing unit to achieve proper operation of two transmitters into the same antenna. The structure of my invention If the coupling is at the two inputs thus requiring a consideration of. the

operating power levels of the two transmitters to achieve the desired remote signal level.

. Fig. 11 shows typical experimental results using the "form of myinvention shown in Figs. 4-10, which were measured on a high-frequency scale model representing a typical uniform section of a channel 7 television antenna structure, and which show the beam direction and attenuation functions in terms of the frequency, and indicates that the phase propagation function is compensated essentially as predicted by the theory. Fig. 12shows a typical null-free beam pattern for an antenna according to my invention having only about 14 db taper in the amplitude distribution along the aperture. The figure shows a beam icluster from which beam orientation with respect to frequency is determined. Nulls are absent in the complete ,pattern.

Other considerations of the theory show that the attenuation rate varies directly as the square of C Tuning of the radiators is not afiected markedly by changing C since C C Thus the radiator spacing plan is relatively insensitive to changes which might be required to alter the amplitude distribution moderately.

The question willhave arisen as to why a wider radia- "torspacing should not be used, thereby decreasing the manufacturing cost, inasmuch as compensation of the "phasepropagation function can'be achievedfor any size spacing. Thisis answered bypointingout that unless the radiatorsbecome more and more directive as they are {separatedfithe dir'ectivity of the array-' wiill eventually de- 'crease too'far below-the optimum value. lhe variation 10 in input impedance has been found theoretically to increase with the spacing for a uniform antenna, as the distance exceeds one-quarter wavelength.

There appears to be, a very practical way to reduce the radiator multiplicity, and that is to omit the 3rd and 4th slot pairs, represented in the form of my invention shown in Figs. 4-10, for example, from each turn of the array spiral. The dominant effect is to decrease the overall attenuation rate by a factor of two for a. given coupler probe setting, and this may be overcome completely by increasing the coupling of the remaining radiators. If radial unipoles are used, only three of them per turn are necessary. A difficulty connected with the use of such radiators has been the excitation of a strong spurious mode on the outer surface of the antenna which gives rise tosignificant power losses in cross-polarized radiation.

In Fig. 4 I have shown one embodiment of the traveling wave antenna consisting of the external tubular lineal conductor 1,-erected in a vertical position and supported 'by means of a collar or stop indicated at 2, supported by the top 3 of mast 4. Collar 2 may be metal welded to the conductor 1 and conductively in contact with the tower. The conductor 1 terminates at 10: below the conductive stop 12 suitable to the mechanical requirements. The external tubular lineal'conductor 1 carries a beacon light 5 at the upper extremity thereof which is powered through a suitable power line. The external tubular lineal conductor 1 is provided with a transmission line connection 6 intermediate the ends thereof which encloses ,a transmission line 7 through which the aural portion of the television program is conducted to the internal tubular member 8 which extends concentrically within the external tubular member 1 and is spaced therefrom by means of the'conductivestop shown at 12. The conductive stop 12 is located below the connection of transmission line 7 to the internal tubular member 8 for a distance equal to one-quarter wave length with which the antenna is adjusted to operate. The internal tubular member 8 terminates at its upper end in a position spaced from the conductive stop 10 inthe upper end of the external tubular member 1 as represented at 11. An innermost conductor 9 is disposed'concentrically within the internal tubular member 8 which connects with the conductive stop 10. The radiating system is that portion of the lineal tubular conductor includedbetween the extremes of the first and last slots. The television picture signal is applied to conductor 9. "{I-he'sound line connection 7 is made at a point bel'ow this portion. Thus the same antenna system oper- -ates by excitation of two transmitters. Diplexerless oper- -ation is thus secured. The external tubular lineal con- -=ductor-=1 is provided with longitudinally extending slots 14 and 15 spirally arranged around the surface of the externalconductor.

In Fig. 5 -'I "show an embodiment of my invention in which the antenna system is fed from two transmitters -from'the same end of the antenna. In this arrangement an external tubular lineal conductor 16 is erected verticall-y -by-meansof 'collar 17 on the support 3 at the top of mast 4 and is provided with an external taperlfia, as shown, leading to aconnection to the diplexer *18, docated at-groundlevel The taper shown is illustrative only and is not intended to indicate relative sizes. The diameterof the tubular outer conductor 16 is not an acutely critical dimension, and it may be tapered or steppedto'minimize-mechanical stresses at thebase. The -operation of the antenna is unimpaired by such tapering,

"and that tapering is permissible is a distinct advantage inherent in my invention when it comes to considering the-economic aspects of comparable designs. An approximate minimum outer cylinder diameter of the slotted variety-is of the-order of one-sixth wave length, the exact {value depending upon the required radiator Q; and an approximate upper' limitis of the order of one-half to three-quarters of a wavelength, depending upon-various design factors. The limits on the size of the support- 11 ing cylinder are even less restrictive when other types of radiator are used. Limits are virtually non-existent in this case. The transmitter for the aural broadcast'is connected to transmission line 19 while the television transmitter is connected to transmission line 20 and both species of signalling energy are conducted upwardly along the tubular inner conductor 21 and the external tubular conductor 16. The internal tubular conductor 21 terminates at the resistive material absorptive stop 22 which connects with the periphery of the external tubular cor1-- ductor 16. The resistive material 22 may absorb residual energy or a conductive stop maybe used for total reflection. The external tubular conductor 16 contains spirally arranged longitudinally disposed slots shown at 23 and 24.

Fig. 6 shows a modified arrangement for absorbing,

residual energy at the remote end of the antenna where .the inner tubular conductor 8 terminates short of the outer tubular conductor 1 as in the arrangement of Fig. 4,

-but wherein a conductivestop 35 is positioned across the internal section of the inner tubular conductor 8 and connected through resistor '36 with central pin 37 projecting in an axial direction from the conductive-stop of the outer tubularconductor 1.

In Figs. 7-10 I have shown a form of my invention employing'outer conductor 25 and inner concentrically I related tubular conductor 34. Slots 28 are formed in the surface of the external conductor 25 and disposed in a spiral course around the surface of the conductor as shown more clearly in the development diagrams of Figs. 20 and 21. The slots 28 are arranged in 90 positions about the transverse axis of the tubular member.

Across each slot is connected a tuning capacitor which in one form of my invention is constituted by parts 29 and 30 of Fig. 9 by means of which the slot is brought to the proper condition of resonance at the nominal oper ating frequency. At the proper side of each slot, 'in accordance with either a rightor left-hand spiral arrangement, a probe 32 is provided as shown more clearly in Fig. 10 for coupling energy out of the line. While the drawing shows a uniform construction of outer conductor having a six turn spiral with four slot-pairs per turn,

7 plus an additional pair to close the last turn, it is understood that there may be any desired number of turns with non-uniform radiator spacing and coupling. That is, the turn length and the coupling may be made 'to vary according to a particular design requirement. The inner conductor 34 is accurately aligned coaxially with the external tubular conductor 25 by means of non-con- I ducting supports 33 at suitable intervals. These supports 33 may take the form of a disc insulator as shown in Figs. 7- and 9. The capacitor or trimmer 31 coacts with path or turn length is one of the principal design param eters of the antenna.

One can locate the radiators virtually anywhere on the spiral and, by properly adjusting their excitation to the required level, obtain a predetermined radiation pattern. In the form of my invention shown in Figs. 13-16 the radiators are folded unipoles, represented at 40, consisting of conductive rods bent upon themselves and supported at one end by a screw-threaded connection 41 with the outside wall of the outer tubular conductor 38 and locked therein by asuitable nut 42, and carrying at the opposite end, which projects through aperture 43 and outer conductor 38, the adjustable probe 44 which is capacitively coupled with the inner tubular conductor 39.

. The folded unipole 40 includes tuning means such as the circular conductive disc 45 attached to one turn of the folded unipole with respect to which the circular conductivedisc 46 is adjustable by means of screw-threaded shank 47 which extends through the opposite portion of the folded dipole and which may be anchored in a selected position with the disc 46 capacitively related to the disc 45 by means of lock nut 48. All of the folded unipoles are similarly constructed, and in Figs. 13 and 15 I have indicated other unipoles at 40 and 40", each of which are separately selectively tunable. The cylinder constituting the outer conductor 38 concentricallysurrounds the inner cylindrical conductor 39. Thus, radiators may be located at selective positions along the traveling wave antenna and separately tuned for determining the radiation pattern for particular geographical areas.

Fig. 15 is a transverse sectional view taken on line 15-15 of Fig. .13, for purposes of more clearly illustrating the manner in which the folded unipole types of radiators are coupled with the inner and outer tubular conductors 38 and 39.

In Fig. 17 I have shown a balanced pair of loop coupled series resonant unipoles associated at spaced intervals with the traveling wave antenna where the series resonant unipoles are shown at 69 and 70 connected through the loop coupled wire forms 71 and 72, terminating at diagonally opposite positions on the interior of the outer conductor 65. A shield wire 73 and 74 is connectedto the inside of the external conductor 65 and associated with each of the loop couplings 71 and 72, respectively.

In Fig. 18 I have shown a further form of traveling wave antenna in which a balanced pair of anti-resonant loops 75 and 76 are probe-coupled with the traveling wave antenna. The probes are shown at 77 and78 coupled with the inner conductor 67 and connected with the anti-resonant loops 75 and 76. The loops and 76 are each separately tunable by condensers 79 and 80. The loops 75 and 76 connect at one side to outer conductor 6-5 and at the other side thereof to the probes 77 and 78.

The forms of my invention shown in Figs. 16-18 may be used as alternate methods to the slot-pair radiators heretofore described for producing horizontally polarized radiation. The arrangement shown in Fig. 18 can be used for producing vertically polarized radiation by orienting the loops so as to lie in planes containing the cylinder axis.

Figs. 19 and 20 more clearly represent in plan lay-out the development of the cylindrical surface of the outer conductor 25 of the form of my invention illustrated in Figs. 7-10. In this arrangement the cylinder is assumed to be unwrapped into a flat plane, respresented at 25, and the elongated radiation slots are represented at 28 with the apertures 29 and 30 located at each side thereoffor receiving the adjustable coupling probe and the tuning noted that the elongated slots 28 are arranged in spiral paths represented at 8-1, 82, 83 and 84. The spiral paths may be in either direction, that is, to the right or left. The adjustment means intermediate each of the slots 28 may be constituted by a number of modifications the form of the adjustable probe and tuning capacitor of Figs. 7-10. The tuning is effected intermediate the length of the slots.

Fig. 11 shows a series of curves illustrating the characteristics of the antenna system of my invention and particularly the beam orientation and attenuation functions for three different tunings, the characteristic curves being plotted with frequency in megacycles as abscissa and attenuation in db per turn and beam angle in degrees from array normal as ordinates.

In Fig. 12 I have shown a measured set of fragmentary beam patterns using the antenna system of my invention from which beam orientation with respect to frequency is determined. The absence of a null-point in a typical complete pattern is to be particularly noted. The cluster of measured beam patterns is intimately associated with a particular adjustment of the embodiment of Figs. 4, 5,6,

garage (measurement.

Fig. 21 is a theoretical diagram explaining the application of the circuit structure of Fig. 18, wherein the distribution of the impedance in the structure of Fig. 18, is

represented by impedances Z connected in series at each end of alength d of dissipationness transmission line of -characterktic impedance Z Fig. 22 indicates schematically the electric characteristics of the antenna of Fig. 18 where the impedance Z, ind icated in Fig. 21 is obtained by coupling a series resonant radiator having an equivalent representation in the RLC load circuit into the transmission line through the mutual. inductance M. The transformer action may be realized, for example, by a loop coupler such as that shown inFig.17. A s

There are occasions when the principles of my invention must be applied to a center or intermediate feed system as schematically represented in Fig. 23. In this case an outer tubular conductor 49 is provided with apertures on the external surface thereof which are arranged in opposite spiral senses, that is, the outer tubular conductor 49 is divided into two parts designated I and from the center 50 thereof. The apertures, that is, either slots in the form of my invention shown in Figs. 4-l0,

. or. apertures as in the form of my invention shown in Figs. 13-16, in the parts 1 and Z are arranged, one ina right-hand direction as represented by spiral path 51, and the other in a left-hand direction represented by the left spiral 52. The inner tubular conductor is divided into two sections shown at 53 and 54. A transmission line 55 extends through the section 54 in spaced electrical insulated relation thereto and connects with the end oft he inner tubular section 53. .The sections 53 and 54 are supported concentrically within the outer tubular conductor 49 by means of annular members56 and 57 which may be conductive or absorptive, or which may be nonconductive stops at 'the end of the tubular conductors asrequired by the particular application intended for the system. The transmission line 55 connects to a diplexer. .Wave directions established by the radiator are indicated by arrows 5,8. The current direction is indicated by arrows i and the potential stress is indicated by arrows e. The arrangement of the radiating means, such as slots, apertures and associated probe-coupled folded unipoles -in opposite spiral senses as shown in Figs. 24 and 25 insures the establishment of an omnidirectional fieldpattern. If the slots in this particular formof my invention are maintained in the same spiral path throughout the length of the outer conductor, a directional pattern will be obtained. Such an arrangement is applicable for ex- ;ample in a situation where two identical, broadside, spiral structures oriented base to base on a common coaxial axis are used. When driven equally at their common juncture, they produce identical patterns except that one is upside-down with respect to the other. The senses of the progressivephase of the two individual patterns in azimuthal directions are opposite so that in the equatorial plane the resultant field is Zero in one direction and double that of one antenna alone in the opposite direction. A cardioid type of directional pattern is thus *produced in the equatorial plane. Strong back lobes are ae s tadr ai he .sraelrfitfl just below and n above the equatorial plane which contain just as much energy as the main lobe wouldhave, 'liad'the separate antennas h nr s e S iral f q i s The traveling wave antenna fmy invention is essenitially impervious to damage 'by lightning strokes either cdi e or as lr 1 4 plurality of loops in the operating frequency range "as would be the case if the phase function were not Stabilized. The design parameters are readilycontrollable enabling various beam shapes to be specified, Even in the simplest basic form, my traveling wave antenna "construction produces a null free beam. The radiation field strength in the neighborhood of the beam nose is substantially independent of variations in azimuthal angle and the phase of the radiation beam is initially progressive with azimuthal angle for substantially traverses in the beam. The structure is such that by selection of the radiating elements the traveling wave antenna can be made to produce a circularly polarized omnidirectional broadside radiation beam. 7 p 4 As heretofore pointed out, the antenna maybe excited at both ends simultaneouslyby two transmittersfnotdifferiuggreatly in frequency as, for example, by the visual and aural transmitters in television broadcasting 'without the use or necessity for a separate diplexing network or isolation network to prevent objectionable crossmodulation. The traveling wave antenna structure is such that excitation may be applied from, either end through separate 'transmission lines by a single transmitter, thus providing reasonable assurance against operational failures in the event of a breakdown in one transmission line. The antenna may be fed or excitedat some point intermediate the two ends, for example, the center, and with an antenna of double symmetricallength on each sidefof the center it is possible to achievea directivity which greatly exceeds that of an end-fed antenna having equal stability of beam inshape and direction. V

The operation of the traveling wave antenna does not depend critically upon the lateral physical dimensionsof the su orting mass. s r

The envelope delay distortion or phase distortionof the remote signal is exceedingly small in the antenna of my invention and well within the close tolerances established by the standards of the Federal Communications Commission for color television. The remote signal amplitude response variation of the antenna structure may be made very small. Other very satisfactory attributes have been discovered in the operation of the antenna system of myinvention. I I

While I have described my invention in certain ofits embodiments I realize that modifications may be made,

and I desire that it be understood "that no limitations upon my inventionare intended other than may be-imposed by the scope of the appended claims. I What I claim'as new and desire to secure by "Letters Patent of the United States is as follows:

1. A traveling Wave antennacomprising la ipair'of concentric tubular conductors disposed substantially coextensively, means for exciting said conductors to establish a traveling wave internalto saidantenna, and a plui ality of radiator means spaced other than integral multiples of one half wavelength apart arranged in a spiral path around theouter one of said conductors, means for coupling said radiatorstosaidtraveling wave, said radiators operating under excitation of the traveling wave to maintain the input impedance constant and to preserve the radiation "beam substantially invariant in shape anddirection 'with respectto frequency over a discrete range of frequencies.

2. A traveling wave' antenna as set forth in claim 1 wherein said spiral uniformly winds 'atthe rate of one turn per nominal internal electrical wavelength.

3. A traveling wave antenna as set forth inelaim 1 wherein said plurality of radiator means comprises at least three Iiadiat'ors per wave length.

4. Atravelingwalve antennaas setforth 'in claim 1 wherein said spiral uniformly winds several times around the said outer conductor at the rate of one turn per nominal internal electrical wavelength and the geometry at any cross section containing the centers of a pair of radiators is identical with that. atv any other similar cross section.

T ,5. traveling wave antenna as set forth in claim 1 wherein said plurality of radiator means are spaced a ,quarter wavelength apart at the longitudinal axis of said outer conductor and perumetrically spaced 90 accord- .ing to the transverse dimension of said outer conductor.

6. A traveling wave antenna as set forth in claim 1 wherein said plurality of radiator means are elongated slots extending in a direction lineally of said outer conductor.

7. A traveling wave antenna as set forth in claim 1 wherein said plurality of radiator means are paired slots formed in the wall of said outer conductor extending in spaced radially extending planes passing through the longitudinal axis of said conductors.

8. A traveling wave antenna as set forth in claim 1 [wherein said plurality of radiator means comprises folded unipoleradiators projecting radially outward from the .outer conductor and probe coupling means capacitively connecting said radiators to the inner conductor.

9. A traveling wave antenna as set forth in claim -1 wherein said radiator means are individually tunable along 1 the length of said conductors.

. 1.0. A traveling wave antenna as set forth in claim 1 wherein said inner conductor of said pair of concentric tubular conductors is a solid electrically conductive member and wherein said plurality of radiators comprise lineally extending slots in said outer conductor and means intermediate the length of said slots for electrically tuning the same, said means comprising a tuning capacitor capacitatively aligned with respect to the inner conductor,

and probe coupling means electrically connecting said radiator to said inner conductor.

11. A traveling wave antenna as set forth in claim 1 wherein said inner conductor of said pair of concentric tubular conductors is a solid electrically conductive membeer and wherein said radiators comprise lineally extending slots in said outer conductor and means intermediate .the length of said slots for electrically tuning the same,

said means comprising a probe and trimmer plate, and means for adjusting said trimmer plate capacitatively with respect to the solid wall of said inner conductor.

12. A traveling wave antenna as set forth in claim 1 wherein said radiator means comprises an anti-resonant, probe-coupled, folded unipole.

13. A traveling wave antenna as set forth in claim 1 wherein said radiator means comprises a balanced pair of loop-coupled series-resonant unipoles.

' 14. A traveling wave antenna as set forth in claim 1 wherein said radiator means comprises a balanced pair ,of probe-coupled anti-resonant loops.

15. A traveling wave antenna comprising inner and outer tubular conductors, means for supporting said inner tubular conductor concentrically within said outer tubular conductor forming an antenna, said inner tubular conductor being separated into two segments spaced end to 1 end, and a power transmission line extending concentrically through one of the segments of said inner tubular conductor and connected with the end of the other segment thereof, said outer tubular conductor containing 4 radiator means spaced other than integral multiples of a half wave apart arranged in the surface thereof adjacerit the'segments of said inner tubular conductor, the

radiatormeans adjacent one segment extending in a spiral path directed clockwise and the radiator means adjacent the other segment extending in a spiral path directed 1 counter clockwise and contiguous with the aforesaid spiral path.

16. A traveling wave antenna as set forth in claim 15 in: which the means supporting said inner tubular conductor concentrically Within said outer tubular conductor are annular end members constituting conductive wave stops and spacers for separating said outer conductor from said inner conductor.

17. A traveling wave antenna as set forth in claim 15 in which the means supporting said inner tubular conductor concentrically within said outer tubular conductor are fiat annular end plate members of wave energy absorbing material and forming spacers for separating said outer conductor from said inner conductor.

18. A traveling wave antenna as set forth in claim 15 in which the means supporting said inner tubular conductor concentrically within said outer tubular conductor are flat annular members of nonconductive material and constituting end closures and spacers for separating said outer conductor from said inner conductor.

19. .A traveling wave, antenna as set forth in claim 1 wherein said plurality of radiator means comprises a pair of loops disposed in diametrically opposite positions with respect-to said inner of said conductors, one end of each of said loops being grounded to said inner conductor and lthe other end of each of said loops being individually connected to a probe extending through said inner conductor'to a position spaced from the outer of said pair of conductors on diametrically opposite sides thereof.

20. A traveling wave antenna as set forth in claim .1 wherein said plurality of radiator means comprises a pair of loops disposed in diametrically opposite positions with respect to said inner of said conductors, one end of each of said loops being grounded to said inner conductor and the other end of each of said loops being individually connected to a probe extending through said inner conductor to a position spaced from the outer of said pair of conductors on diametrically opposite sides thereof, and an individual variable condenser connected across each of said probes and the grounded end of each of said loops for shunting each loop.

22. A non-resonant traveling wave antenna structure comprising a pair of tubular concentrically related conductive members, means for exciting said members to establish a traveling wave internal to said antenna at a substantially uniform rate of time delay, a plurality of radiator members spaced less than a half wave apart arranged in a spiral path around the outer one of said conductors, said radiators providing controlled'phase and amplitude distribution of external excitation, and means for coupling said radiator means to said traveling wave.

References Cited in the file of this patent UNITED STATES PATENTS 2,385,783 Alford et al. Oct. 2, 1945 2,408,435 Mason Oct. 1, 1946 2,503,952 Laport Apr. 11, 1950 2,512,511 Weighton June 20, 1950 2,574,433 Clapp Nov. 6, 1951 2,658,143 Fiet et al. Nov. 3, 1953 2,724,774 Fiet Nov. 22, 1955 2,744,249 Shively May 1, 1956 2,803,008 Lindenblad Aug. 13, 1957

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