US2578973A - Antenna array - Google Patents

Description

E. G. HILLS ANTENNA ARRAY Dec. 18, 1951 3 Sheets-Sheet l Filed Dec. ll, 1946 f Affornev E. G. HILLS 2,578,973

ANTENNA ARRAY 3 Sheets-Sheet 2 Dec. 18, 1951 Filed Deo. 11, 1946 91 AVION IT@ INVENToR. Elmer G. Hi//s BY Affornev E. G. HILLS'/ ANTENNA ARRAY Dec. 18, 1951 3 Sheecs-Sheetl I5 Filed Dec. l1, 1946 m .DE

INVENTOR. Elmer G H//s QN. OR

1 o nuo N 2 lojiouog aAnM uipumg bij pluamalg nuualuv lo; ouog @ADM ugpumg Attorney Patented Dec. 18, 1951 STTES TE FFICE ANTENNA ARRAY Elmer G. Hills, Chicago, Ill., assignor to Belmont Radio Corporation, Chicago, Ill., a. corporation of Illinois 13 claims. 1

connection with frequency modulation and tele'- vision circuits.

For both frequency modulation and television circuits, it is becoming increasingly important to employ directional antennas to concentrate transmitted power in the desired directions in the case of transmitting antennas and to receive radio frequency energy from the desired directions in the case of receiving antennas. It is a well known fact that to obtain a directive antenna arrangement, it is necessary to provide an antenna array so that the fields radiated from the elements making up the array add in some preferred direction and cancel in other directions. Heretofore Whether the array has been of the broadside, end-fire, or other types, a definite limitation was involved since the directional patterns of such arrays were confined to a narrow frequency band. This is a serious limitation due to the wide bands allocated to frequency modulation and television. The reason for this limitation of existing antenna arrays which limitation causes deterioration of the array reception pattern in the case of a receiving antenna when the frequency changes is due to three factors. First, a change in frequency causes a change in the relative electrical lengths of the radiator feed transmission lines to the elements of the array. Second, a change in frequency causes a change in radiator feed point impedances of the array elements assuming the elements are isolated from each other; and third, a change in frequency causes a change in mutual impedances between radiators when placed in an array, although the effect of such change may be negligible if the spacing between the elements is relatively large.

The reasons for the deterioration of the array reception pattern set forth above can be better understood by considering a typical array such for example as a broadside array of equal currents in which the different elements which are generally dipoles or modified forms of dipoles are fed from a common transmission line junction through transmission lines, the lengths of which differ by integral multiple wave lengths. Since the open circuit voltages at the ends of these transmission lines would all be in phase if the radiating or receiving elements were disconnected, it is necessary that all of the elements present the same complex impedances to their respective lines when connected to these lines in order that equal in-phase currents flow in the radiators. In order that the radiator impedances be equal when arranged in the array, the elements must, of course, be in generaldiferent from each other because if they had identical impedances when isolated from the other elements, the mutual impedances between the elements when placed in the array would alter the element input impedances so that they would not in general be identical. As the frequency of operation of the array is changed, the electrical lengths of the various transmission lines change such that they no longer differ by integral multiples of wave lengths even if at the new frequency the element or dipole input impedances were still identical. Consequently, the currents would have changed because of this change in relative electrical lengths of the transmission lines with the resulting deterioration of the array reception pattern. Actually, however, the radiator input impedances do change as a result of -two effects with resulting aggravation of the radiator current non-uniformity. As was mentioned above, one effect is that the impedances of the radiators if isolated in general change with frequency, and the other is that the mutual irnpedances between the radiators when placed in the array change with frequency.

With reference to the change in electrical lengths of the various transmission lines connected to the elements of the array, it will be understood that if the total electrical length of the composite paths that the signal must travel from the distant transmitting source through free space to the various elements of the receiving antenna array and then to the receiver, which path includes free space as well as the transmission lines, are made the same regardless of what path the signal is considered as traveling by way of, then the change in relative electrical lengths of the radiator feed transmission lines with frequency will exactly compensate for the change of relative phase of voltage induced in different dipoles by the arriving wave such that all voltages arrive at the receiver in phase for maximum signal. For the case of a broadside array where the signal path through free space is the same for all of the elements of the array this would merely mean the making of all of the transmission lines from the receiver input terminals to each element of the array of the same electrical length, that is, signal length as contrasted with phase length. Heretofore it was common practice to make the phase lengths the same so that different paths varied by integral wave lengths. It is obvious that for different frequencies the wave lengths will vary so that by maintaining the same phase lengths would make it work properly only at one frequency and for all other frequencies the phase lengths would vary. The distance the signal travels or in other words the length of the signal path should be the same foreach element of the array, when the composite path of the signal through free space and through the transmission line is converted to a constant velocity path.

Antennas have been constructed wherein the feed point impedance of the isolated elements remains constant with changes in frequencies. AExamples of such antennas are those usingconical elements. As has been pointed out above, however, even if the feed point impedances of :theisolated elements of the array remain constant with changes in frequency, when these elements Yare placed in the array, the ymutual impedances between the elements of thearray'change vwith fre quency. It has been suggested that the effect of the mutual impedances between the elementsfof the array changing withfrequency can Lbe'minimized by placing vthe `elementsof the array so far apart in'space A'that ythe mutual lirnpedances existing between them are'negligible. This spacing would 'have to 'be of Athe order of three-wave lengths at the lowest operating Afrequency'of the array and obviouslythis'wouldbe very'wasteful cf space with the result that anentirely 'impractical antenna'for general use would obtain.

It is an object ofth'e'present'invention to Yprovide a new and improved antenna arrangement for use in connection with Ytelevision or frequency modulationcircuits in which'a directional reception pattern is obtainable which'does not substantially change over a wideband offrequencies.

It is another object of the present inventionto provide a receiving antenna array in which the directive reception pattern does not substantially change with changes in frequency.

Still another object of the present invention is to provide a new and improved omnifrequency directional antenna array'for radio receivers in which changes in rfrequency have substantially no effect on either the mutual 'impedances 'of the elements of the array, or the impedances of the feed points of the array elements considered in an isolated condition, and the changes in relative electrical lengths of the transmissionlines connecting each array element with the receiver or transmitter compensate exactly for the change of relative phase of the voltages induced-in the elements of the array by the arriving wave so that all voltages arrive at the receiver in phase.

It is a feature of the present invention to provide an antenna array which has a desirable directive characteristic over a wide band of frequencies wherein the currents flowing in the various elements of the array are reduced to such low amplitudes that the effect of mutual vimpedances is substantially eliminated without re ducing the effective'efliciency of the power'transmission from the receiving elementto its transmission line.

It is another feature of the present invention to provide an omnifrequency directional antenna array in which a cathode follower device is associated with each element of the array, whereby the currents flowing in each element of the array may be reducedto such a low value that 'the effects of vmutual impedances are completely eliminated and yet whereby the radio frequency energy in the case of a receiving antenna is amplied in the cathode follower circuit so that a satisfactory signal is obtained at the receiver.

It is a further object of the present invention to provide an antenna array in which the signal supplied to the receiver includes power from a suitable source other than that supplied by the -electromagnetic radio wave.

Still a further object of the present invention is to provide a new and improved antenna comprising a modified dipole.

It is another object of the present invention to provide a modified dipole antenna which is inductive overa wide range of frequencies, which has a substantially constant resistance over a Wide frequency range, and which radiates normal toits `length with a directive pattern which has only a single lobe on each side regardless of the frequency.

Further objects and advantages of the present invention will 'become apparent as the following description proceeds and the features of novelty which characterize 4kthis invention `will be 'pointed out with particularity in the claims annexed'to and forming a'part of `this specification.

For a better understanding of the vvpresent invention, referencel maybe had to the accompanying drawings in which:

Fig. 1 isa schematic diagram of-a typical-endfire antenna array embodying the present invention;

Fig. 2 is a view of one elementfof lthe array of Fig. 1, showing its connection inthe circuit;

4Fig.`3 is a circuit KVdiagram of the'antenna shown in Fig. 2 ybringing outtthe'details of the cathode follower associated therewith;

"Fig 4 is a circuit diagram `Vsimilar to Fig. 3 illustrating a modification ofthe arrangement of Fig. 3;

Fig. 5 is a curve diagram indicating the standing wave ratio with various'frequencies ofthe antenna array of Fig.` 1;

Fig. 6 is a curve diagram similar to Fig. 5 indicating the standing wave ratio with variousv frequencies of the antenna element ofFig. 2; and

Figs. 7, 8 and 9 are polar diagrams showing the strength of field radiated in various directions from an ordinary dipole antenna at different fre quencies.

In practicing the present invention, there is provided an antenna. array made up of a plurality of elements each essentially a modified 'folded dipole. Associated with 4each dipole is a cathode follower circuit having its input connected to the feed point of fthe dipole. The outputs of the cathode followers vof the various antenna elements are interconnected in suitable series, parallel, or series parallel arrangement so as to match a transmission line such as a 300 ohm transmission line connected to the receiver. A

Vsuitable source of` pow-er which may be either 60 cycle or a relatively high frequency alternating current is supplied to each cathode follower circuit throughthe transmission line. The cathode follower circuits which have a constant output impedance regardless of frequency prevent the feed point impedance of the elements ofthe array when consideredto be isolated from each other from varying with frequency. By virtue of the arrangement, low input currents flow so that the e'ect of the change in mutual impedances with frequency are negligible. The alternating current power supplied through the transmission line to the cathode followers furnishes part of the signal Aenergyreceived atthe receiver.

vFor the purpose of simplifying the disclosure and the description, the omnifrequency directional antenna array of the present invention has been illustrated specifically in connection with an end-lire array connected to a television or frequency modulation receiver. It should be understood that the invention is equally applicable to various other types of antenna arrays such, for example, as the broadside, colinear and the like arrays and the particular disclosures and descriptions are by way of example only. Furthermore, each modified dipole element of the antenna array may be used separately as an antenna either with or without the cathode follower device described hereinafter.

Referring now to Fig. l, there is illustrated an end-fire array comprising twelve modified dipole elements, each designated by the reference numeral I0 with appropriate subscripts a, b, c, etc. and arranged in two rows, one above the other with six in each row. The elements Illa, ib, I |30, Id, Ille and Ilj are arranged in the upper rower of Fig. l while the elements IIlg, IIlh, Iz', |07', IOIc and IGZ are arranged in the lower row. These elements Ill may be connected in series, parallel, or in a series parallel arrangement. To illustrate the invention, it is assumed by` way of example that the array comprising the elements Il! is connected through a 300 ohm transmission line II to a receiver I2. As illustrated in Fig. l of the drawings the 300 ohm transmission line II connects the receiver I2 with a junction point I3. in order to relate the 300 ohm transmission line to the twelve element array, the elements are divided into four groups Ida, Mb, Ilic and Md of three elements each. The groups I d are connected in series with each other at the junction pointI I3 through a connection of substantially zero length and to match the 300 ohm impedance of the transmission line II each group is connected to the series connection point I3 through a 75 ohm transmission line I5 designated by the appropriate subscript corresponding with the associated group. These '75 ohm transmission lines Ia, |51), I5c and ldr interconnect the junction points ISa, I6b, IEc and |611 of each group I4 of three elements with the series junction point I3. It will be apparent from Fig. 1 that a plurality of parallel connected transmission lines 2G interconnect the elements I Il of each group I4 with the junction points lua, Ib, IGc and Id which must provide an impedance of 225 ohms each to match the 75 ohm transmission lines I5. These transmission lines 2t of each group are designated specifically as 2da, 20h and 20c respectively. Consequently, each antenna element I0 for the arrangement disclosed in Fig. 1 of the drawings must have a feed point impedance of 225 ohms to match the 225 ohm transmission lines 20. It should be understood that the specific values described are for the specific arrangement to match the 300 ohm transmission line II.l Various other combinations of the elements of the array might equally well be employed in which case the impedances of the transmission lines and the input impedances of the antenna elements would be different. It will be understood that the electrical path lengths must be identical between the transmitter and the receiver. The particular element of the array closest to the transmitter must have a longer transmission line path than the element farthest from the transmitter since the path of the signal through free Space for the former is shorter. The diiferences in length of the transmission line will not be the same as the differences inlength of thepaths `through free space since the velocity of travel of .the signa1 through air dilers from the velocity of travel through the transmission line. As illustrated in Fig, l, the antenna element Illa is closer to the oncoming signal wave than the element IIlb so that the transmission line 2Gb must be shorter than the transmission line 20a. Similarly the group Ma is closer to the oncoming signal wave than the group Illb so that the transmission line I5a must be longer than the transmission line I5b.

In accordance with the present invention, each element IIl of the antenna array comprises a modied folded dipole constructed in a particular manner so as to afford an inductive impedance, the purpose of which will become apparent as the following description proceeds. Referring now to Fig. 2 of the drawings, where there is illustrated the element Illa identical with all the other elements of the array comprising a pair of parallel conductors 2| and 22 supported in spaced parallel relationship by interconnecting conducting members 23 and 24. The conductor 22 is illustrated as made up of two sections 22a and 2219 arranged in spaced coaxial end-to-end relation- Ship with the adjacent ends separated slightly as indicated at 25 to provide the feed point for the folded dipole. As illustrated, the feed point 25 is opposite the mid-point of the conductor 2|, and the conductor 22 comprising the two parts 22a and 22h is twice as long as the conductor 2|.

Consequently, the supporting members 23 and 24 which are illustrated as comprising a one-turn loop are connected between the respective ends of the conductor 2| and the mid-points of the conductors 22a and 22h. The sizes of the conductors 2|, 22, 23. and 24 are not all the same, the reason for which will become apparent as the following description proceeds. For a particular embodiment of the present'invention, the conductor 22 comprises a pair of 1/4 inch brass rods having an over-all length when positioned as in Fig. 2 of the drawings of 'I1/ feet which is twice the length of the conductor 2| which for a particular embodiment comprises a l inch outside diameter brass tube. The supporting conductors 23 and 24 for the particular embodiment mentioned above comprised 1A inch brass rods each including a 3 inch diameter one-turn loop. The feed point 25 of the modified folded dipole described is in accordance with the present invention connected by suitable means to the input of a cathode follower circuit generally indicated at 26 and to be described in greater detail hereinafter in connection with Figs. 3 and 4 of the f drawings. Preferably, the cathode follower circuit of the present invention is contained within a suitable metal container 2'I supported from the conductor 2| in any suitable manner. If desired the vconductor 2| may be grounded as indicated at 28 so long as the ground is at the center thereof. This provides a simple means for supporting the antenna elements I0. Each one of the transmission lines 2U described in connection with Fig. 1 is connected to the output of its associated cathode follower circuit 26 within container 2l in a manner which will be described in greater detail.

'The electrical path from the antenna element Illa of Fig. 2 to the receiver I2 includes the transmission line 20a, junction point Ia, transmission line i|505, junction point I3 and the transmission line I.

For the purpose of maintaining the currents flowing in each of the elements Ill of the antenna array at` such low amplitudes that there is no appreciablevoltageinduced in any one element known` fact that the-input impedance -'of fafcath'e ode follower is very high while its-output-irn'- pedance is-relati-vely-low; Accordingly;the input 'impedance' of* the cathode 'follower device* 23,'shown in Fig; 3 ofthe drawings; -is extremely f high compared to the feedpoint impedanceat so long as the transit tirn'e loading does-not enter-l into the picture.4 Asafresult/al' verylow' current iowsin the'dipole or-antenna element' lll-sincerthedipole orantenna eleinentrl' 'is-eie'ctivelyf open circuitedV at" 25"'when1the cathode mfollower 26 is inserted in the1 circuit. Consequently nor ill effects of -change in mutual impedances-fwith change in frequency-result'andino deterioration* of the -directivity pattern Aofthearray'rnade'up of the cathodefollowerY antennaelements occurs` Since a transmission line'isalways'a' pure resistance it is desirablefor the-antenna'connected' to the transmission line -to also Apresent-a 'pure'y resistance for an accurate Ymatch'v therewith.

Actually the impedancev of thev input" orY grid circuitof the cathode-follo`wer device'26itobe" described in greater detail hereinafter is i capaci-v tive and it is for this reason,` as `wasroentioned abofraithatthe antenna element `lil is `a-rnodiedv folded dipole of4 ythe-form *described in4 order vto'I have an' inductive input impedance which is'inade possible at allfrequencies'in-the-40 to 220 megacycle band by the Supports23`and 26"; Yeach containing theone-turn loop; Thus," an antenna element'having an 'accurate match with-"a vpure resistance transmission line can vbe obtained.

'hesupports 23- and 2Q' alsov provide the folded dipole construction 'whereby Athe radiation 'resiste ance by-virtue'of the folded constructionwith the conductors-2l" and A22"of different diameters" is greatly increasedy thusincreasingconsiderably thevoltage applied to" the cathode'followerVv 26;

The 'input `impedance of the cathode`Y` follower docs not match the'feedpoint impedance of the dipoleitself but is substantially aninnite im'- pedanceto the line'and this mismatchtfurther produces substantially twice the voltage Yinput tothe cathode follower 'device'26 that wouldbel applied if its input impedance`Iriatclredthat'ofU the dipole.'

Referring now to Fig. 3 of the drawingsy'there is illustrated a 'cathode 'followerdevice 2G' which actually comprises two cathode followers although it will be understood vthat an arrange# ment employing a single cathode follower'crcuit could be used to advantagewith a coaxial transmission line. As illustrated in Fig; 3, the cathode follower device 23VV comprises. a pair of triodes 316,' and lea'ch having an'anode 32', a cathode 33 and a control electrode 34. Each Ymay also be supplied with a heater elementf35'. The control electrodes 34 offeach electron discharge valve 39 and 3l are connected respectively to the adjacent ends of the divided conductor portions 22a and 22h, this-connection being at the socalled feed point 25 of the modified folded` dipole of the fpresentlinvention. The-cathodes 33 of each of ftheelectron discharge .fvalvesf30V and 3 vI--rare each connected? .to suitable-'cathode re-` sistersA ttfA and 31,;respectivelywhich resistorsl are connected to a'cornmonterminal 38." The output of thecatho'de follower circuit 26`is obl tained'across the serially arranged resistors'v36 and 37 by meansof the transmissionfline'' comprising two conductors, each of'- which includes a suitable coupling'capacitor 39. Essentiallyl the two cathode followers are connected in series and each of the anodes '32 of electron discharge valves 36 and 3l is connected to a common terminalll' throughY a suitable resistorlll for decreasing the effect of plateeto-c'athode capacity in the tubes 30 and 3 l. A suitable plate supply filter capacitor 3lis preferably connected across the' plate-to-cathode circuits', as 'g illus-- trated, interconnecting Yterminals@Sand 43. A1'' so, a suitable gr'idFto-cathode resistor 44 may be provided for each lelectron discharge valve 30 and In accordance with the-present invention,` the f vtransmission line 2B which has been mentioned above'as a 225 ohm transmissionl line in' addition to providing a path for the signal is also employed to supply power to the plate circuits of the cathode follower circuits 23'.- In accordance with a preferred embodiment of the present insociated4 with the receiver I2soiasto'rsupply' power to the cathode followers 2131associatedwith f all of the antenna elements-making up the ari ray. Alternating electrical* energy of two'hundred kilocycle frequency is chosen since this` energyv can readily be rectified lto a direct current Y potential without any filter problem and in addition, any transformer requiredifor stepping up thevoltage is relatively small and inexpensive" compared to what would be the case if 60 cycle power were employed. y

In accordancel with the present invention the 200 kilocycle alternating current'en a pair of radio frequency choke'coi-ls-l; which readily pass 290 kiiocycleenergy 'but prevent the signal energy frompassingyto'r an auto-transe former l'having input terminals d8a rand and'outputterniinals'd8a'and 43e." The` output terminals [58a and lliicare vconnected to' asuit-v ablerectile'r 5l' illustrated' 'as a trio'de" havingits` plate' n52" and its control "electrode connected" l in parallel.` The cathode 5d' is connected through a suitable"capacitor'55- and a chokecoil tothe terminal 38' of the cathode follower Vdevice 2t? whilethe other terminal of thecapacitor"55"'is" connected to the terminal liti'. ln other word the direct current Voltage appearing "across cae pacitor E5 is supplied to the "plateito-cathode" circuits of the cathode' iollower'devic'e 26""coni2' prising the electron discharge valves Strand' 3i".

arranged in series. A suitable capacitor lmay be connected across the output terminals 48a" and 38C of the auto transformer 43 vif desired.'

charge valve El suitabletaps may be provided 4 on auto transformer l8`. Asillustrated in Figl 3,

y suppliednv to' the Y'transmission'line dis'cond-ucted through this power is obtained from taps 48a and 48h and the heaters 35 and 58 are preferably connected in series with suitably interspersed radio frequency choke coils 59.

It will be understood that the constants of the cathode follower circuit 26 will determine the magnitude of the current which must be supplied thereto from the 200 kilocycle source. In accordance with the present invention, the voltage of the 200 kilocycle source is then chosen such that with reference to the current supplied to the cathode follower circuit 26 there is an impedance presented which matches the irnpedance of the transmission line Il, or in other words, for the values referred to above has an impedance value of 300 oms. Because of this, the transmission line is matched and it will not de-tune the source no matter what length of 300 ohm transmission line the user of the antenna .sees fit to connect between the antenna and his receiver. In other words, the 300 ohm transmission line is matched at the antenna, both for the signal frequency and for the 200 kilocycle power frequency.

From the above discussion, it will be apparent that with the arrangement described a high voltage is obtained from the cathode follower which is fed to a transmission line of lower impedance than the dipole impedance so actually more power or signal energy is supplied from the antenna elements to the transmission line Il than was taken out of the radio wave received at the antenna. Part of this power is supplied by the 200 kilocycle generator 46. 'I'he voltage maintained at the output of the cathode follower circuit 26 is substantially the same or perhaps slightly lower than the voltage at the input thereof. It will furthermore be apparent that the cathode follower circuit 26 associated with each antenna element Il! will present a constant impedance. It is well established that the internal or source impedance presented by a cathode follower circuit is the reciprocal of the transconductance of the tube or tubes employed which is independent of frequency. The varying impedances of the modified folded dipole elements connected to the cathode follower devices 26 have no effect and essentially a constant output impedance for all frequencies intercepted by the antenna is provided with the result that the antenna is a very satisfactory directional antenna for all frequencies.

The operation of the antenna array of the present invention will be apparent in view of the detailed description included above. By virtue of the use of the cathode follower device 26 the output impedance of all the cathode follower circuits remains constant and independent of frequency. Actually, as was mentioned above, the output impedance of a cathode follower is equal to the reciprocal of the transconductance of the tube employed and preferably a tube of relatively high transconductance is employed such as the 604 or the like. Due to the fact that the high input impedance of the cathode follower causes very low currents to flow in the antenna, the effect of mutual impedances is negligible even at close spacing of the antenna elements. The signal power supplied to the receiver through the transmission line is partially the signal intercepted by the antenna amplified by the power supplied to the cathode follower circuit from the 200 kilocycle generator.

At frequencies in the 1'76 to 216 megacycle television band, the input loading of the electron discharge valves 30 and 3| becomes appreciable l and in this case, it is necessary partially to match the impedance of the modified folded dipole to the cathode follower input impedance in order to increase the voltage on the grid of the tube while still having the impedance of the modified folded dipole low enough with respect to the tube input impedance that large enough dipole currents do not flow to cause changes in the mutual impedances of the elements in the array. In the lower television band, this factor is unimportant, i. e., the 44 to 83 megacycle band.

Although in the arrangement described thus far 200 kilocycle Yalternating current energy is supplied through the transmission line to the antenna elements, it will be understood that ordinary 60 cycle energy might be supplied to the cathode follower circuits of each antenna element. In Fig. 4 of the drawings, there is illustrated an antenna ela-:ment similar to Fig. 3

' wherein the power supplied to the cathode follower -circuit 26' is 60 cycle energy. The corresame reference numerals as in Fig. 3. The electron tubes 36 and 3l are identical in the two arrangements but the 60 cycle energy is supplied from a source 46' through the choke coils 41 to a voltage doubler generally indicated at 60. Such a voltage doubler is required since the Underwriters have limited fthe 60 cycle voltage that can be supplied to antenna apparatus which is to be connected up by members of the public to 25 volts. The voltage doubler circuit comprises preferably a twin diode 6! having a pair -of anodes 62 and 63, respectively, a pair of cathodes 64 and 65, respectively, and a pair of heaters 66. The two rectifying paths through the twin diodes 6| are connected so that the path including anode 63 is in series with a capacitor 61, while the path including the anode 62 is in series with a capacitor 68. The output of the voltage doubler rectiiier arrangement is obtained across the capacitors 61 and 68 in series thus producing the voltage doubling action. The input circuit designated at 10 includes the choke coil 1| and the two rectifying paths referred to above which will alternately pass the alternate half cycles of fthe alternating current wave. plied through the choke coils 41 is also supplied directly to the heater elements 35 and 66 connected in series with suitable choke coils 59 interposed therebetween. The operation of the arrangement diselosed in Fig. 4 of the drawings will be obvious to those skilled in the art and no further discussion thereof will be included herewith.

It will be understood that a source of direct current potential may be fed directly to the cathode follower circuits in any suitable manner or a separate supply line for the power to the cathode followers may be employed rather than using the transmission line itself. However, the arrangements described above are believed to be preferable for reasons which are obvious.

It will be understood by those skilled in the art that the standing wave ratio of an antenna is effectively a measure of mismatch between the antenna and the associated transmission line connected thereto. In Fig. 5 of the drawings there is shown the standing wave ratio for the antenna array of Fig. 1 showing that it is very satisfactory particularly over the television band. In Fig. 6 there is illustrated the standing wave ratio for one antenna element of the array as The 60 cycle power sup-- l l for, example the antenna element of Fig. 2' of the drawings.

It is a well known -factthat Ythe reception pat tern of the ordinary dipole antenna varies greatly with frequency. In Figs. 7, 8 and 9 are shown the reception patterns lof a dipole antenna with the various frequencies specifically indicated at 50 megacycles, 100 megacycles, and 200 megacycles, respectively. Such a change in the recepe tion pattern of the modied dipole of the present invention with frequency does not'occur and for all frequencies the polar diagrams of the reception pattern are substantially identical and comprise a single lobe on each side of. a line each lobe. being. substantially a circle .tangentto said line, `and vthe direction of radiation of 'said modiiieddipole being normal to its length.

While theA circuit. parameters and fthe type of electron discharge Valves employed. in thea-ntenna circuits of the present invention may be chosen to meet` the requirements of` any particular installation, the; following. circuit specifications havebeen found. entirely satisfactory for use ina typical installation operableover the television bandirom .40 c0216. megacycles.

Circuit Component Description Transmission Line ll Transmission Lines 14. Transmission Lines 20 Conductor 2l Conductor 22 Supports 23 and 24 300 ohm-coaxial line.

73 ohm coaxial lines.

225 ohm'coaxial lines.

1 outside diameter brass tubing 3% ft. long.

M'brass rod 7%, ft. long with grip in the middle.

lwbrass'rod including 3" one-turn l loop. Electron discharge valves 30 6C4.

and 31. Resistors 36 and 37 300 ohms. Capacitors 39 100# ,if inFig. 3; 1500# i in Fig. 4. Resistors 4l.' 300 ohms in Fgxfi/ 200 ohms in Fig. 4. Capacitor 43 001 In View of the description included above', it will be apparent that there has been provided an antenna array which is directional in character and which directivity pattern will not vary with changes in frequency so that it is satisfactory over a wide range such as is employed in the frequency. modulation and television bands. By employing the cathode v'follower arrangement describedabove, the impedances of each element of the array remain constant regardless of frequency changes.. In addition to that, the high input impedances of the cathode followers cause relatively low dipole currents to flow so that the effects of mutual impedances with change in frequency is negligible and a Very compact antenna with close spacing of the elements ofthe array may be obtained. Since. the antenna andthe transmission line can be perfectly matched with the arrangement proposed above to provide perfect termination, the transmission. line acts as a 1:1 transformer and is wholly independent of frequency so the lengths ofthetransmission line are immaterial.

Also with the modied dipole of the present invention there is provided an antenna. which is inductive over a wide range of Afrequencies and which radiates normal to its length with a directive pattern which has onlyv asingle lobe. on ach side regardless of frequency.

While the present invention has been shown and described in connection with certain specific embodiments, it will, of course, be understood that the invention is not limited thereto since it is apparent that the principles herein disclosed are susceptible of numerous other applications. and modifications may be made in the circuit arrangement and in the instrumentalities employed without departing from the spirit and scope of the present invention as set forth in the ap pended claims.

What is desired to be secured by Letters Patent of the United States is:

1. In combination with an antenna, for a wave signal receiver Whichhas a constant impedance regardless of changes in frequency of the. received signalcomprising a radiatingelernent, a cathode follower circuitincluding a pairof electron discharge valves having input and outputcircuits, means for.` connecting said inputy circuit ,to said. element, a transmission line interconnecting said outputcircuit with .said receiver, a source. ofhigh frequency alternating current electrical energy1 for. the output circuittof said electron -discharge valves, and means including. said transmission line forinterconnecting. said source and said output circuit; said transmission line beingv matched: with said antenna for the wave signal energlffas well as said high frequency electrical energy.-

2. Any antenna for a wave signal receiverJ which has a constant impedance regardless of changes in frequency of the received signal lcorruirising--a radiating element, a cathode'follower circuit-have ing an input andan output circuit, means for connecting said input circuit to said element, a

transmission line connected to said output cir cuit, a sourceof low. frequency alternating current electrical energy for said output circuit, means including said transmission line for interconnectingr saidf source and said output circuit, and means for stepping up the potential of said source at said cathode follower circuit whereby said transmissionk line may be maintained at a low potential. Y I

3. A folded dipole antenna comprising a first relatively short'conductor, a second relatively, long conductor including two colinear parts` spaced from each other, and supporting means connected to the ends of said first conductor and said parts of said secondA conductor, said supl porting means having loopedconductor portions therein .to aiford reactive impedance connections between said conductors, each ofsuch loopedcognf ductor portions having extremities which are pov sitioned close to eachother substantiallyl in alignment with saidshort and. long conductors, andy having parts immediately adjoining such eXtremities which diverge from each other respectively, to pointsof maximum separation on opposite sides of the loop.

4. A folded dipole antenna comprising a. rst conductor adapted to be supported on a mast, a. second conductor includingV two colinear. parts spaced from each other, and .supporting.,means, secured to theends of said rst .conductonandto saidV 'partsof said second conductor. for. support-Y ingsaid. parts, saidsupporting means being single. turn loops; whichform. reactive impedance connections. between? said conductors, each'of. said. loops,havingextremitieswhich are postioned close to each other. substantially in alignmentwithsaid. first and ysecond conductors, and havingparts immediately adjoining such extremitiesdiverging; from'. each other respectively to pointsV of. maxil mum separation on opposite sides of the loop.`

13 5. A folded dipole antenna comprising dilrst conductor of relatively large diameter, a second conductor comprising two colinear parts of relatively small diameter spaced from each other,

and supporting means secured to the ends of said first; conductor and to said parts of said first conductor for supporting said parts from said. rst conductor, said supporting means being in the form of single turn loops which provide reactiveD impedance connections between said conductors.;

each of said loops having extremities Which are positioned close to each other and parts immediately adjoining such extremities which diverge from each other respectively to points of maximum separation on opposite sides of the loop.

6. An antenna which has a directional pattern substantially independent of frequency throughout a wide range of frequencies, such antenna comprising a folded dipole having a pair of substantially parallel spaced conductors, and a pair of conductors positioned in proximity to and interconnecting said spaced conductors, each of said interconnecting conductors having a continuous loop therein of such configuration that the two extremities of the loop are positioned close to each other substantially in alignment with said spaced conductors, while the portions of the loop immediately adjoining such extremities diverge from each other respectively to points of maximum separation on opposite sides of the loop.

7. An antenna which has a directional pattern substantially independent of frequency throughout a Wide range of frequencies, such antenna comprising a folded dipole having a pair of substantially parallel spaced conductors, and a pair of rigid conductors positioned in proximity to and interconnecting said spaced conductors, each of said interconnecting conductors having a loop therein Which is inductive over at least a large portion of said wide range of frequencies, with the opposite extremities of said loops being disposed close to each other in alignment with said spaced conductors, While the portions of the loop immediately adjoining such extremities diverge from each other respectively to points of maximum separation on opposite sides of the loop.

8. An antenna which is inductive throughout a wide range of frequencies, such antenna comprising a folded dipole having a pair of substantially parallel spaced conductors, and a pair of conductors interconnecting said spaced conductors, each of said interconnecting conductors having a length substantially greater than the spacing between said parallel spaced conductors and including an inductive loop positioned in proximity to said spaced conductors for determining in part the directional characteristics of said dipole, said loop having a substantial amount of inductive reactance over at least a large portion of said wide range of frequencies.

9. An antenna which has a directional pattern substantially independent of frequency throughout a wide range of frequencies, such antenna comprising a folded dipole having a pair of substantially parallel spaced conductors, one of said conductors being longer than the other of said conductors, and a pair of conductors interconnecting said spaced conductors at the ends of the s shorter conductor and intermediate the ends of said longer conductor, each of said interconnecting conductors having a loop therein which is primarily inductive over at least a large portion of said wide range of frequencies and which is 14 positioned in close proximity to said spaced conductors to determine in part the directional characteristics of said dipole.

10. An antenna which has a directional pattern substantially independent of frequency throughout a wide range of frequencies, such antenna comprising a folded dipole having a pair of substantially parallel spaced conductors, one of said conductors comprising two colinear parts spacedr from each other, and a pair of conductors interconnecting said spaced conductors being connected intermediate the ends of said colinear parts and at the extremities of the other of said spaced conductors, each of said interconnecting conductors having a loop therein which is primarily inductive over at least a large portion of said wide range of frequencies and which is positioned in proximity to said spaced conductors to determine in part the directional characteristics of said dipole.

11. An antenna array for a wave signal receiver comprising a plurality of antenna elements, a plurality of transmission lines connected to said receiver, and means for individually connecting said antenna elements to said transmission lines having high impedance input circuits connected to said elements and low impedance output circuits connected to said transmission lines, said transmission lines being of unequal lengths, and said antenna elements being arranged at unequal distances from the wave signal source, the elements closer to the wave signal source having longer transmission lines than do the elements farther from the wave signal source, whereby the differences in the electrical lengths of said transmission lines compensate for the differences in the phases of the voltages induced in the various antenna elements by the arriving wave signal so that all wave signal voltages arriving at the receiver through the various transmission lines are substantially in phase.

12. An antenna which has a directional pattern substantially independent of frequency throughout a wide range of frequencies, such antenna comprising a folded dipole having a short relatively thick conductor and a long relatively thin conductor in parallel spaced relation to each other, said long conductor being interrupted at its mid-pjoint, and a pair of conductors being connected intermediate the ends of said long conductor and interconnecting said spaced conductors at opposite ends of said short conductor, each of said interconnecting conductors having a loop therein which is primarily inductive over at least a large portion of said wide range of frequencies and which is disposed in proximity to said spaced conductors to affect the directional characteristics of said dipole.

13. A folded dipole antenna comprising a pair of spaced conductors, and a pair of rigid conductors interconnecting said spaced conductors and maintaining the spacing thereof fixed, each of said interconnecting conductors having a 1 length substantially greater than the spacing of said pair of conductors and having formed therein a continuous loop which is inductive over a wide range of frequencies and which is disposed in proximity to said spaced conductors for determining in part the directional characteristics of the antenna at various frequencies.

ELMER G. HILLS.

(References on following page) l5 16 .REEERENCESITED Number Name VTDate 'The following @references aa-re T'of' aeuordffn: the 212872,20 Alford --i June 2341942 fue of this patent: 2,314,132 B01-'lefty Mar. 16, v1943 2,345,735 Douma v A1312 4,1944 .UH ED. TATESPATENTS ,5 Y2,379,168 ,McClellan June 2s,o1945 l T n s 2,380,333 .schelden July-10,1945 Number Name n Dat? 2,393,971 Busignies Feb. 5, 1946 `2,131,042 IAIfrlStefM --Spt 27, 1938 2,419,205 Feldman Apu- 22 1947 2,256,084 Goodale sept. 16,1941 H 2,275,646 Peterson Mar. 10,1942 m OTHER REFRENCES 2,278,660 Lehmannl Apr. '7, 1942 A. R. R. L. Handbook, pages 188, 189 (1942). 2,283,914 Carter May 26, 1942 Terman, Radio Engineers Handbook, -pages 2,286,179 Lindenblad June 9, 1942 800, 801 (1943)

Images