US1768239A - Directive antenna system - Google Patents

Description

June 24,- 1930. 7 c. R. ENGLUND 4 1,768,239

DIRECTIVE ANTENNA SYSTEM Filed July 8, 1925 p Patented June 24, 1930 ATE'r FFEQE CARL R. ENG-LUND, 0F FREEI-IOLD, NEW JERSEY, ASSIGNOR T0 WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK DIRECTIVE ANTENNA SYSTEM Application filed July 8,

To approach as closely as possible the ideal, so far not closely approximated inpractice, of a unidirectional receiving system;

To elficiently receive radio signals from a desired direction to the substantial exclusion of signals coming from a predetermined undesired direction.

To efliciently receive at a station of a two- Way radio communication system, signals from a cooperating distant station Without interference from Waves radiated from the local transmitting station.

To achieve each and all of the above objects Without sacrifice of protection against strays or, in a somewhat broader sense, to achieve each and all of the above objects and concomitantly to substantially prevent interference due to strays both from the desired direction and from other directions.

The Word strays is used here and throughout the specification and claims, as in approved modern texts, to comprehend all signal simulating phenomena not falling Within the category of signals, and therefore to include phenomena having artificial, as Well as natural origin. It is intended specifically to include both static and atmospheric.

An embodiment of the present invention is incidentally disclosed but not claimed in U. S. Patent 1,668,?57, granted May 8, 1928, and assigned to the American Telephone and Telegraph Company.

A specific object of the invention is to improve the operation of long antennae known as Beverage or Wave antenna, and in particular to improve the methods of eliminating one or more of the minor lobes of its polar reception diagram, the presence of which lobes tends to cause the antenna to be merely preponderantly, instead of strictly, unidirectional.

By the improved means of this invention, the elimination is accomplished Without 1925. Serial No. 42,128.

adding, to a harmful extent, new areas to the reception diagram. The presence of these additional areas Would connote an increased susceptibility to the influence of strays, a susceptibility that is measured both by the size of the area and its angular extent. In accordance With prior practice, as represented by the practice of the Radiov Corporation which developed this type of antenna and is its principal user, the Wave antenna is in effect arranged for simultaneous operation in the two opposite axial directions, so as to have similar but relatively reversed reception diagrams. After adjustment to provide the proper equality relation of the ordinates of the respective diagrams corresponding to a certain direction of interfering Waves, the currents due to Waves incident upon the antenna are superposed in the receiving circuit. It is apparent that this prior method is inherently adapted for the elimination of the axial minor lobe only since the reception diagrams must be unvaryingly 180 degrees apart. The lateral lobes, or certain of them, can be eliminated only by relatively enormously increasing the size of the reception diagram representing the compensating circuits With the production of a corresponding enormously increased additional reception area along the reverse axis.

By the method of the present invention, any selected lobe Whatever can be eliminated with the same facility as the axial or any other lobe, and with no sacrifice of protection against strays.

Specifically, in the method of the present invention, the compensating Wave is picked up by an entirely independent antenna, the reception diagram of Which has sucha configuration as to readily lend itself to combination With the corresponding diagram of the principal antenna, if superposed in a particular angular relation, to produce the desired resultant diagram. This independent or aux- 9 "inthe appended claims.

equal and opposed over the region of the lobe to be eliminated.

Because the Wave antenna is normally so.

nearly unidirectional, the auxiliary antenna 'may be relatively small, since the area of its reception diagram is of the order of that of the particular minor lobe 'tobecompe'nsated or eliminated. Although perhaps a substantially unidirectional auxiliary antenna tvouldfoln theoretical chnsiderations, be preferr'edfit has been found that a-simple-dirigible loop, having a bidirectional reception diagram resembling the shapeofa'figure's Well answers every practical purpose. By means of thisinvention any one of the minor "lobes'of the receptiondiagram'of the principal antenna 'may be substantially Wholly eliminated. Withith'e production of a'very small additional reception area which 'Will be distributed partly in the general direction of that lobe and partly in substantially the reverse'direction. lf under special conditrons, the'add tronal expense would be gust1fiecl,the ordinary dirigible loop could be re placed by a dirigiblevantenna having a uniand method of operation Will best be understood by reference'to the following descrip- 'tion' taken in connection with the adcon1panyingdrawings in which:

Fig. lisa circuit'di'agram of one embodiment of the system of'the invention.

Figy2is apo-lar reception-diagram illustrating the operating characteristics "of the Wave "antenna which constitutes a portion of "the-system of Fig. 1.

='Fig.3-is'"a:p'olar reception diagram illustrating the operating characteristics of the loop-antenna Whichc'onstitutes another portion of the system of Fig. 1; and

I Fig. iis a polar reception diagram illustratin'g'the operating characteristics of the system of Fig. l as a Whole including both an a ei 7 Before entering on the description of the specific arrangement of the invention, Which make useof any one of several forms of Wave" antenna cir"c'uits,'the general theory of the operation of wave antennae will be delop'ed. This plan,"as providing a"b'aclrgroimdffor'the specific invention tliat'is to b'eclesci'i bed,'tvill tend to aid one inloolring back of the specific disclosure illustrated in the drawing to'determine the Teahnature and extent 'of the invention.

' he following references comprise in their disclosures substantially all of-the learning and practice in this art available to the public up to this time. They, or some of them, may be studied to advantage in connection With this specification:

(1) A paper by Beverage, Rice, and Kello rinted in three arts in the Journal 7, 1921, 1,434,984., November 7," 1922, 1,434,-

985, November 7, 1922 and 1,43%,986, Novem-- bel' 7, 1922.

I Kellogg U. S. Patent 1,387,339, March rrwvave' antenna'may be simplyany substantially straight current conducting circuit,'having a lengthof the'ord'er of the Wave length -'of' the ether Wave, extending 'substantially horizontally, along which Wave energy impressed" upon it may be p'ropagated at a velocity comparable with that of the same Wave in ether. lhe last requirement maybe satisfied by inserting condensers in seri'esiat uniform intervals'throughoutthe length of the antenna, which may otherwisehave the form of an ordinary transmission line of one or more conductors grounded at each end. The same effect, that of increasedvelocity' of propagation, may be se'cured'by inserting inductances betweaentheantenna and ground. a I lnaccordance With the most easily explainable theory of 01 eration,a Wave generated at one end of the antenna,.hereinafter called the near end, by an ethervvave'which travels in the direction of extension of the antenna, is propagated along tl e antenna. The ether Wave also generates awave in each of the other elemental lengths into which the antenna may be considered divided, and theseWaves are similarly propagated along the antenna. The efiect,'pra ctically, is that the Wavev generated at the end of the antenna absorbs energy from'theaccompanying ether Wave and therefore increases i-n amplitude as it progresses along the antenna, attaining a maximum at the opposite end, hereinafter called theremote end, Where the receiver is locatec. By parity of reasoning there WOlllCl'lOG no energy at the receiving end absorbed from a Wave proceeding in the opposite direction, although an additional receiver at the opposite end could'efi'ectively'receive sucha Wave. In order that the above operation may not be complicated by reflection effects, and accordingly so that the unidirectional character of the antenna may be preserved, the ground lead at the end opposi'te to the receiver, and thereforeat bothends if two receivers are to be used, maybe caused to have'an impedance F equal to the surge impedance of the antenna. Meanssuch asthis have, 1n practice, been sufi icient to nearly but not quite eliminate the axial 'minor' lobe. Instead of placing the receiver at the remote end, as in the ground lead, a reflection transformer can be placed in this ground lead 1f a t wconductor antenna 1s used and the antenna can then be used like an ordinary transmission line (current flow ing in opposite directions in the two conductors) to transmit the energy back to the near end where the receiver may be placed. This permits the element which determines the surge impedance to be placed near the re-' ceiver where the impedance of the element can antenna continues to build up until limited only by the antenna losses, that is, the benefits of an extra long antenna can be secured by high velocity (so long as it is not higher than that of light) and low attenuation. if the two velocities are not the same, there will be a cyclical variation of amplitude of the wave along the antenna as the relative phases of the two waves vary .through successive conditions of coincidence and opposition, and an extra long antenna is not of advantage, so far as it affects the maximum signal strength. It has been found that, in general, the directivity as determined principally by the area of the axial minorlobe increases as the velocity of propagation approaches the velocity of light (compare Figs. 35, 36, and 39 of the above mentioned American Institute paper). The decrease in the width of the major lobe as the propagation velocity decreases is favorable but is not suiiicient to compensate for the more important efiect of change of area of the axial minor lobe. Also, as appears from a comparison of Figs. 35, 37 and 38 of the same paper the directivity improves somewhat as the length of antenna increases princip ally on account of the decrease in the width of the major lobe. In practice, it has been found that in order to obtain maximum strength of signals the length of the antenna should be at least half the length of the ether wave and preferably several times this length.

It should be noted that, if the antenna design is such that the propagation velocity is not equal to the velocity of light, the antenna necessarily must have a certain frequencyvelocity characteristic. Practical use can be made of this characteristic in order to obtain frequency, as well as directional, selectivity. This may be done by positioning receivers, intended'for reception of waves of different frequencies, at different positions along the antenna. Similarly this method of positioning the receivers may be used to avoid the effect of systematic stray interference. F or the purposes of this invention the velocity should be as nearly that of light as possible and the attenuation should be assmall as possible.

The above discussion treats of the mode of operation when an ether wave is incident on the antenna in the direction of its axis. The described mode of operation accounts for the presence of a pronounced major lobe of the reception diagram. Considering now the effects of ether waves incident on the antenna at an angle to its axis, it is evident that one of the effects is to shorten the distance the ether wave has to travel between its incidence on successive elemental lengths as compared with the case where the wave travels in a cothese differences in distance, translated into differences in phase, have simple integral multiple relations that result in a reenforcenientsubstantially like that where the ether waves and antenna waves are travelling along the antenna in parallel. This at least qualitatively explains the existence of the lateral minor lobes.

The number, size and angular relation of these lobes can be caused to diifer greatly by adjustments of the length, propagation velocity, and attenuation of the antenna. For example if the antenna is an integral multiple of half the wave length and if the propagation velocity equals that of light (a coincidence of conditions diflicult to realize in practice) the axial minor lobe Will be absent; The polar diagram illustrated in Fig. 2 is as nearly typical as any and is the one assumed to result from the operation of the system of Fig. 1 now to be described. Except perhaps as to the relative values of the ordinates, it is the same as Fig. of the American Institute paper above mentioned.

The foregoing explanation should bekept in mind in considering the following description of a specific embodiment. Referring to Fig. l, the antenna 1 is of thewave type and, as used in this system, receives most efiiciently waves coming from the right. The antenna comprises a two-conductor line extending from the near end (near with respect to the ether waves) to the reflection transformer 2.

The ground circuit at the near end contains. impedance 3 adjusted to equal the surge impedance of the antenna to prevent reflection of waves propagated along the antenna from the other (the remote) end. These waves, if reflected, would be superposedonan'd be indistinguishable from, the desired waves. The other end is grounded through the reflection transformer 2 which transduces the energy there received back to the antenna which ac cordingly serves as an ordinary transmission line (currents flowing in" opposite directions in the two conductors) ttT-hTHHSHHhtllQ'11- ergy to'the-near' end! If the antenna were not so used, the receiver could, and conven ie'ntlywould, be placed inthe" ground leadat the remote end This ground lead does not contain an element the primary function of whichis to match the surge inipedance,since the'refiection transformer is designed toeffectthis result. 7 a

The disclosure of the antenna itse'ltis diagrammatic only.

7 may actually consist simply of a two-conductional forms now known and may be'causedtor line, if the'distributed ind'uctanceand capacity'are small enough to give apropagation'velocity comparable with thatoflight, or such a line varied by the inclusion ofseries-condei'isers or shunt inductances, or both, asha's been explained.

At the near end, the desired energy is again transducedi by transformer 4 to circuit 5.

The two halves of the'primary of transformera are related to the secondary winding,

and to each other, in such a manner tliatma gnetic-efifects resulting from undesired wavespropagatedsimultaneously along both wires of the 'an'tenna from the remote to the near end; are balanced out 111 43116 secondary winding. That is, this balanced circuit arrange mentpreve'ntssuch-undesired waves from directly affecting the receiving circuits connected tocircuit 5,-whil'e the surge impedance element 3- prevents these waves from being reflected and thereby later entering circuit 5' through-transformer 4:. v I

The receiving circuits connected to the circuit 5 include an amplifier AM- and a radioreceiver RR. The amplifier, of course, may

be om-itted on occasion, andthe transformers 6 and 7, whereby energy is transferred to the relatedcircuits, may be replaced by well known equivalents The radio receiver may comprise any one of the well known circuit arrangements in which the impressed modulated carrier wave is demodulated to reproduce the low frequency modulatingcomponent, as radio telephony,- or rectified to reproduce radio telegraphic signals. The demodulated component is impressed on low frequency circuit 8. Tllfi'ftidlO receiver include a filter, to eliminate the undesired frequency components resulting from demodulation so that only the low frequency signal currents are transmitted to circuit 8. V A; loop antenna 9, here diagrammatically illustrated, may be of any one of the convento be dirigible also in accordance with conventional practice, .as by a simple rotatable mounting. Fig. 3 illustrates-the polar rec'eption diagram or a loop antenna, the axis drawn through thediameter of the two lobes corresponding to the direction of the plane of the loop. Since this direction can be va- Accordingly the antennajust the phase of the wavesderived from'the loop antenna sothat they are in opposite. phase to those derived from the waveanenna, withrespect toth-e-waves incident on the system frointhe directio'n corresponding to-tlielobe which isto beelim'ina tedl The pe t'eiitionicter functions to equate the amplitudes ot-the two waves for-this direction.

In order that the function-of the-loop-antenna system" as related to the wave antenna system may be better understood, reference is made to Fig. i. In'thisfigure, polar di'agrams corresponding to Figs. 2- and 3 are shown respectively in-light full; an-dbrolren lines. The heavy full lines illustrate there.- sultant polar reception diagram.-- This re sultant diagram indicates the current im pressed upon the input of the radio receiver resulting from the superposition of: the two component currents. The resultant diagram may be plotted, as it was in drawing this fig-- ure, by superposing the two component dia grams, dividing the field into as manylines representing directions as is practically pos-- sible adding the ordina-tesof thetwo di'a grams for each line while taking into account the differences in phase laying oifthese difference values from the origin and along the same directions, and" connecting thepointsthusobtained. I

It is mentioned above that account must be tal'renof differences in phase. This results flOIIl' the tact that the phase of the current, at the input of the radio receiver, derive'd froin the wave antenna progressively varies with a corresponding variation of the angle of the incident waves with respect to thata-ntenna.

This variation of ph'a se is indicated directly by the quantities in the last column of table HI or" the above" mentioned America-n Institute paper, which assumes a set of conditions similar to those assumed here. There is no corresponding phase Variation for the loop antenna except where the rotating vector passes from an angle corresponding t'oone side ofthe plane of the loop to an angle corresponding'to the other side. The relations of the two superposed currents can be" ob' tained very easily by merely superposing a curve taken from the last column o'litable' III on a rectangular curve for the loop antenna, adjusting these curves as is practically'accomplished by phase shifting device= 10) u ntil there is opposition of phase at thecent'er of the lobe to be eliminated and picking 011' the corresponding diflerences of phase for the other angles. The details of this method are not disclosed in the drawing since they would tend to unnecessarily complicate it and because the qualitative relations, which are all that required to teach th essential principles of the invention, are thought to be sufiiciently apparent without recourse to rigid geometrical methods of proof. The important thing to notice is that, beginning with the central line of the minor lobe there are four substantially equally spaced angles at which there is exact phase opposition and four symmetrically located intermediate angles at which there is phase coincidence.

For the assumed case, it was desired to eliminate the lobe indicated in Fig. 2 as a. For example, this lobe might point in the general direction of the local transmitting circuit of a two-way radio telephone station, of which the circuits of Fig. 1 constitute the receiving circuits.

The loop antenna would be accordingly oriented to a position such that the combination of currents in accordance with the method explained in the above paragraph results in as complete an elimination of this lobe as possible. The position of the polar diagram for the loop antenna in Fig. 4 indicates the best position of this antenna to satisfy this condition.

The potentiometer 11 would also be adjusted so as to contribute to the satisfaction of this condition. That it has been so adjusted in the assumed case is indicated by the equality of the ordinates of the two component diagrams of Fig. i for a direction corresponding to the center of the lobe. The resultant heavy full line diagram indicates that the lobe has been substantially eliminated.

The resultant diagram also indicates that very little additional area has been produced. This area is indicated by that part or" the resultant diagram outside of the diagram for the wave antenna, i. e. light full line diagram.

In accordance with prior practice, the compensating wave would be obtained from the ground lead at the near end of the wave antenna instead of from a separate dirigible antenna. The compensating wave would therefore be the wave resulting from the use of the antenna for waves oppositely directed relatively to those called the desired waves in the description of this invention. The polar diagram for the compensating wave would be similar to that of Fig. 2 but relatively reversed. It would be invariable in position with relation to the diagram for the desired waves. Accordingly, such a diagram could be superposed on that of Fig. 2 in such a manner as to substantially eliminate the axial lobe b of Fig. 2, and this is its normally intended function. However, if it were attempted to eliminate the lobe a, as by greatly increasing the size of the compensating wave diagram, a stray area of relatively large dimensions would be added to the polar diagram for the antenna system.

l Vhat is claimed is:

l. A radio receiving circuit comprising in combination, a preponderantly unidirectional receiving antenna, a directive dirigible antenna, said antennae being of types such that the axes of their polar reception diagrams are relatively displaced as the dirigible antenna is moved, receiving apparatus, and means whereby electrical variations produced in said antennae when adjusted so that the axes of their polar diagrams are relatively displaced are superposed on said apparatus.

2. The combination recited in claim 1.in which the dirigible antenna is ofthe unidirectional type.

3. The combination recited in claim 1 in which the dirigible antenna comprises a loop aerial, and means for rotating said loop about a vertical axis.

4-. The combination recited in claim 1 in which'the unidirectional antenna is a horizontal wave antenna.

5. The combination recited in claim 1 in which the unidirectional antenna comprises a substantially horizontal wave conducting circuit grounded at each end, having a substantially aperiodiccharacteristic, a length oi the order of the wave length of the waves incident thereon and a propagation velocity comparable with that oi ether waves, and in that the dirigible antenna comprises a loop aerial and means for rotating it about a vertical axis.

6. In a directive radio receiving circuit, in combination, a wave antenna, comprising a substantially horizontal wave conducting circuit extending in the general direction of the source of radio waves which it is desired to receive, said circuit being substantially aperiodic, having a wave length of the order of the waves incident thereon and a propagation velocity comparable with that of ether waves, a circuit connecting the end nearest the distantsource with ground and having an impedancesubstantially equal to the surge impedance of the conducting circuit; a radio receiving apparatus; means for impressing on said apparatus the waves propagated to the end of the wave antenna remote from said source; adirigible antenna comprising an aerial loop and means for rotating it about a vertical axis; and means for impressing the waves receivedby said loop on sald apparatus in any desired phase relation with respect to the propagated waves.

7. The method of eliminating a selected minor lobe of a polar reception diagram of a horizontal aperiodic antenna, using a horizontal aperiodic antenna and a rotatable loop antenna, which comprises rotating said loop antenna until the axis of its polar reception diagram substantially coincides With the axis of said minor lobe, receiving radio Waves jointly with said antennae and super-posing the resultant Waves.

v8. The method using a directive horizontal aperiodic antenna and a dirigible loop antenna, of receiving desired Waves from a direction corresponding to the major lobe of the polar reception diagram of said horizontal aperiodic antenna, to the substantial exclusion of interfering Waves from a directionycorresponding to a selected minor lobe of said diagram, Which comprises orienting said loop antenna so as to most efficiently receive Waves from a direction corresponding to said minor lobe, receiving the desired and interfering aves on said horizontal aperiodic antenna and compensating Waves on said loop antenna, and superposing all'of said Waves in such phase relation that the interfering Waves are substantially balanced out by said compensating aves. 7

9. A radio receiving circuit comprising incombination, a fixed, preponderantly unidirectional, receiving antenna, a "directive dirigible antenna, said antennae being of types such that the axes oftheir polar reception diagrams are relatively displaced as the dirigible antenna is 1noved,.receiving apparatus, and means whereby the electrical variations produced in said antennae are superposed on said apparatus. p

10. The combination recited in' claim 9, in Which'the dirigible antenna is of a unidirectional type.

11. The combination recited in claim 9, in which the dirigible antenna comprises a loop aerial, and means for rotating said loop about a vertical a'xi 12. The method of improving the directive receivingquali JlQS of an antenna which is pre ponderantly unidirectional, using a rotatable loopantenna, which comprises rotating said loop antenna until the axis of its polar 'rece'ption dia ram substantially coincides With a region or the polar reception diagram of said unidirectional antenna which it is desired to at least partially eliminate, receiving radio Waves jointly With said antennae, and superposing the resultant Waves.

In witness whereof, I hereunto subscribe my name this 7th day of -July, All). 1925. CARL R. ENGLUN D.

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