US2511899A - Antenna system - Google Patents

Description

June 20, 1950 cs. H. BROWN ANTENNA SYSTEM Filed Dec. 30, 1944 IN VEN TOR. aliflmzm Patented June 20, 1950 ANTENNA SYSTEM George H. Brown, Princeton, N. J., assignoifljflj Radio Corporation of America, a corporation of Delaware Application December 30, 1944, Serial No. sides;

This invention relates to radio frequency power networks wherein two independent sources, which must be electrically isolated from one another, are'required to supply energy simultaneously to a "common load device. Networks of the described type find application; for example, in television broadcast systems, wherein it is desired to transmit a picture signal and an accompanying sound signal from a single antenna. In order to prevent interchange of power between the sound and picture transmitters, it has been the practice to employ filters. Such filters require careful design, will operate only with sound and picture carrier frequencies for which they are designed,

introduce a certain'amount of loss, and introduce reactances in the system which make it difiicult to design the overall system for efiicient broad band operation which is necessary for high definition television.

It is the principal objectof the present invention to provide a radio frequency network which will substantially isolate two sources from each'other, while enabling them to supply a common load simultaneously.

Another object is toprovide a system of the described type which does not rely upon filters or equivalent means for the function of isolation, and thus introduces a minimum of undesirable reactance in the system.

Another object is to provide an isolation network coupling a single antennasystem to a transmitter and a receiver for operation independently of oneanother.

A furtherobject of this invention is to provide an isolation network which is readily adaptable to the requirements of combined sound and television broadcasting. 1

Still another object is to provide a network of the described type which is conveniently applicable to antennas of the type including two separately excited groups of radiators, such as the turnstile.

The invention will be described with reference to the accompanying drawings, of which Figure 1 is a schematic diagram of an isolation network according to the invention,

Figure 2 is a schematic diagram of a sound and television broadcast antenna system embodying an isolation network in accordance with the invention.

' The principle of the present invention is illustrated by Figure 1. A pair of identical loads, represented by equal resistors 5| and 53, are to be energized simultaneously and independently from sources '55 and 51. The lower end of each of the 8 Claims (Cl. 250*33') resistors 5i and 53 is grounded. The upper end of the resistor 5l is connected to' one side of the source 5i through a coaxial line section 59. The upper end of the other resistor 53 is connected" to the other side of the source'5l throug'li a second coaxial line sectioniil.

The line sections 58 and SI are equal in'length. The source 51 is electrically symmetrical or balanced with respect t0 ground, that is when one terminal is positive with respect to ground potential, the other terminal is negative by the same amount with respect'to ground potential. The source 55 is unbalanced to ground, with its lower terminal grounded. The upper end of the source 55' is connected through line sections 63 and 135 re M spectively to the upper ends of the resistorslil and 53. The linesections 63 and are equal in length.

The operation of the system of Figure 1 is as follows: The terminal voltage'oi the source 51 is applied to the loads 5| and"53 in series through the line'sections 59 and 61. The potentials at the upper ends of the resistors 5i and 53 are equal and opposite to each other,'referred to ground Thus the potential at the junction" point of the lines 63 and 65, at the upper end potential.

of the source 55, is zero, referred to ground and no voltage is produced across the source 55 by the source 51. At the same' time, the source '55 supplies the loads 5|, 53 in parallel with each other "through the lines 63, 65. The potentials produced at the upper ends of the loads 51 andv Therefore, no

53' by the source 55' are equal. voltage is produced across the source ill by the source 55. Thus it is apparent that each ofthe' loads5'l and 53 is supplied by both sourcesf55 and 51 without any interaction between the'two si'iurces; The source 51' feeds the loads 5| and 53 asymmetrically with respect to ground, while the so'u rce 55 feeds the loads symmetricallywith respect to ground.

Figure 2 shows the application of the system of Figurel to a sound and television broadcast arrtenna system. Theantenna in this instanceisf illustrated as a single layer turnstile, comprising four orthogonally disposed horizontal radiator elements N, E, S and W. Thetw'o pairs N-S and E-W are excited as doublets, in quadrature phase relationship to each other, in order to provide horizontally polarized radiation with a field in Each doublet is balanced to ground,v

3 radiator N) while an equal current flows out of the other radiator (S).

The radiators N, S, E and W are provided with separate coaxial feed lines I, 3, and 7 respectively. The lines 5 and I are made one-quarter wavelength longer than the lines I and 3 in order to provide the required quadrature relationship in excitation. of the dipoles N-S and E-W. Actually the two lines I and 3 are the conductors of a balanced line to the dipole N-S. and the lines ipol 5 and 'I constitute a balanced line to the E-W.

Line balance converters line sections IIand I3 disposed in parallel relationship. with each other and a cylindrical conductor I5, similar to the outer conductors of the line sections I I andl3. The outer conductors oi thelinesections II and I3 are connected to each; other, and to the conductor I5 by a conductivev plate I7, which acts. also as the bottom closure.

ojjya shield I9 surrounding the balance convertor.

linfeisections II and I3, which are connected togather at their lower ends at the point 2|. The;. sections II and I3 areapproximately one-half.

wavelength long over all, and the conductor: I5

is approximately one-quarter wavelengthlong.

The upper end oi the shield I9 is closed by a plate 23'into which the feed lines I and 3 extend.

Theouter conductors of the lines I and3. are

grounded to theshield plate 23. The inner conductororthe line I is connected to the end of the. cylindrical conductor 'I 5, and the inner conductor Qffthieline 3 is connected to the end of the outer conductor of the line section II. The inner conductor of the line section II is connected at 25 to theouter conductorof the line section I3, and the inner conductor of the line section I3 is con.

nected to the end of the conductor I5.

The radiators E and W, are connected through thelines iand 7 tea line balance convertor 9, identical with the convertor 9. The halt-wave lines .I I" and I3 of the convertor 9' areconnected together at the junction point 2|, whichcorre spends to the point 2I of the N-S circuit.

The points 2| and 2| are supplied with radio frequency power through a network described hereinafter. For the present, it is suincient to say, that points 2I and ill are unbalanced to ground; 1. e. the outer conductors are at ground potential and the radio frequency input voltage applied between the inner conductor and ground, Since the operation of the E-W balance convertor circuit is identical with that of the N-S' circuit only the latter will be described.-

Balance convertor operation The voltage appliedto thepointll reaches the. upper ends .of the linesections in phas e be cause the two sections are of equal lengths. The upper.quarterwavelength portions of the outer conductorsof the sections II and I3, being con-,

nectedtogether at the plate I'I, cooperate .to act asa quarter wave short-,circuited parallel line,

presenting a high impedance at the upper ends The plate I7 is approximately one-. quarter. wavelength fromv the upper ends of the 24 and 25. Each of the outer conductors of line sections II and I3 cooperates similarly with the conductor I5, so that the upper end 25 of the conductor I5 is effectivel isolated from ground.

' balance convertors, and comprises two coaxial.

as are the points 24 and 25. Since the voltages across the upper ends of the sections II and I3 are in phase, the voltages, referred to ground potential, of the outer conductor of the line II at the point 24 is 180 out of phase with that of the inner conductor of the line I3 at the point 25. The lines 3 and I are thus excited in opposite phases. The flow of current at a given instant may be traced up through the inner conductors of lines II, and I3,'the current on the inner conductor of line- II flowing back down the inside of the outer conductor of line I3 and that on the inner conductor of line I3 fiOWing up the line I to the radiator N. Current flowing down the line 3 from the radiator S goes down the inside of the.-

outer conductor of the line II.

Convertor circuit reactance compensation connected across the upper end of each otthe line.-

sections II and 13. These reactances are compensated throughout a very wide frequency band, by themethoddescribed and claimed in ,copending U. S. Patent application Ser. No. 551,247, filed August.25, 1944 byG. H. Brown, now U. S. Patent No. 2,419,985.1ssued May 6, 1947, and entitled Reactance compensation.

The lines I and 3 are assumed :to be. matched.

in impedance to the radiators N and S. Denoting.

theimpedance level asZo, the characteristic impedancesof the lines I and 3 are Z0 and the impedances-presented to theupper ends of the line sections II and .I3 are-also 20.. By making the surge impedances of the lines II and I3 somewhat higher thanZo'. in accordance'with the relationshipbetween the impedance level Z0 and the characteristic impedance of the equivalent shunt reactance element representing the characteristic of the convertor/S, the reactance may be balanced, by shuntingthe lower-ends of thelinc.

sections- H and I3 with a similar reactance. In accordance with the teachings of said U. S. application; Ser. No. 551,247, the quantity should lie between and percent of whereinZsis the surge impedance of the equivalent short-circuited, stub shunted across the upper end of each of the line sections II and. I3, andZc is the surgeimpedance of each of the line sections. II and I3... The balancingreactance.

of thedower ends of linesections II andISis providedby the elements of the isolation circuit. The reactance cancellation WOIkS both ways, i. e. the reactances of the isoladescribed below.

tio'n circuit are balanced by the eonvertor reactance, and vice versa. It will be apparent to those skilled in the art that the spacings of the sections II and I3 and the conductor l5 within the eonvertor 9 must be made such that the resulting shunt reactances are identical with the reactances presented by the isolation circuit.

Isolation network The feed points 2| and 2| of the N-S and E-W circuits respectively are connected through coaxial lines 21 and 21' to a junction point 23. Also connected to the point 29 is a coaxial line 3| which runs to a television picture transmitter, not shown. The lines 21 and 21 are each substantially one-quarter wavelength, or an odd integral number of quarter wavelengths long, and are of characteristic impedance Zo. They should be equal in length, or difier in length by an integral number of wavelengths. The feed points 2| and 2| are also connected through lines 33 and 33' to the balanced output terminals of a line balance convertor 35. The lines 33 and 33 are each one-half wavelength, or an integral number of half wavelengths long.

The line balance eonvertor 35 includes an unbalanced input line 31 which extends to a sound transmitter, not shown. This line, as well as the line 3| to the picture transmitter, may be of any required length. Both of the lines 3| and 31 are of Z0 characteristic impedance. The terminal quarter wavelength section of the line 33 is surrounded by a cylindrical conductor 33, closed at its end by disc 4| through which the line 33 extends. The outer conductor of the line 33 is connected to the disc 4|. The connections of the sound and picture transmitters to the network may be interchanged without substantially aiiecting the operation of the system. The inner conductor of the line 33 is connected to that of the line 33. The inner conductor of the line 31 is connected to the outer conductor of the line 33. The outer conductors of the lines 33 and 33, and 31 are connected to the sleeve 33.

The outer conductor of the line 33 cooperates with the sleeve 39 as a quarter wave coaxial line, short-circuited by the disc 4|, and presents a high impedance at the end of the line 33, eifectively isolating the end of the outer conductor from ground. Current flowing up on the inner conductor of the line 31 goes along the outer conductor of the line 33 to the disc 4|, inducing an equal and opposite current in the inner conductor of the line 33. This current flows down the inner conductor of the line 33 and up the inner conductor of the line 33. Thus the points 2| and 2| are fed 180 out of phase with each other from the input line 31. The lines 33 and 33' are in series with each other across the line 31. 7

Operation of isolation network pedances are transformed to (Line Z) Z Input ZQ- Z Z 02Z looking into the lines 21 and 21' from the junction 29. Sincethe lines 21 and 21' arecon'iiected in parallel to this point, the impedance there isZo, and is matched by the picture input linell.

The half wave lines 33 and 33' present the same impedances Zo/ 2 at their input ends at the convertorf35 as they look into at the points 2| and 2|. The input ends are connected in series in the eonvertor 35, presenting a total impedance Zo/2+Zo/2 or Z0 to the sound input line 31.

' As stated above the reactances of the convertors 9 and 9' are balanced by those presented to the points 2| and 2| by the isolation circuit. The latter reactances are principally comprised of the reactance presented at the points 2| and 2| by the half wave lines 33 and 33'.

The input from the picture input line 3| reaches the points 2| and 2| in phase because the lines 21 and 21' are of equal lengths. The

1 picture input will not travel down the sound input line 31, since it reaches the inner and outer conductors of the line 31 in phase, through the lines 33 and 33', and no voltage across the line 31 can be produced by the picture input.

The input from the sound input line 31, on the other hand, reaches the points 2| and 2| out of phase, and through the lines 21 and 21', the point 29. Since the voltages arriving at the point 23 from the sound transmitter are out of phase, the resultant voltage at the point 29 is zero and no energy from the sound transmitter flows into the line 3|. Thus the sound and picture input lines are eflectively isolated from each other, although each is coupled efiiciently to the antenna system.- The fact that the points 2| and 2| are in phase for the picture signal and out of phase for the sound signal is of substantially no importance. The only effect is that the turnstile phase rotation is clockwise for one signal and counter-clockwise for the other.

Summary The invention has been described as embodied in a combined television and sound broadcast antenna system, for transmitting both sound and picture signals from a common radiator system. It is to be noted, however, that the invention may find other applications in systems requiring a common load or common loads to be supplied by independent sources which must be isolated from one another, or conversely in systems wherein common sources supply independent loads. Briefly, two feed points are supplied in opposite phases by one source through a line balance eonvertor or the equivalent. The same two feed points are supplied in phase by the second source. Energy from one source will arrive through the feed points at the other source by two paths; the voltage transmitted through one path will be 180 out of phase with that transmitted through the other. Thus each source is balanced out with respect to the other, and no interchange of energy can occur between them. In the described arrangement, impedance matching is obtained by simple arrangement of transmission lines, and, unavoidable reactances presented by the line balance convertors are substantially neutralized, permitting efiicient broad-band operation of the system.

:I claim as my invention:

' 1. A radio antenna system for excitation from two independent input circuits simultaneously, including two groups of radiators, each electrically balanced to ground, two pairs of balanced 76 lines, one pair connected to each of saidradiatoi awa t? Z craps resn o ln two i e balance o rte s Qneeomgected; to; each of said; pairsofi balanced. nespectivelig, ,eachi of saidfbalancez-converters including two half Wavelength line sections, one; haying its, outer conductorconneoted at its upper to enact said balanced lines.and; the other hayin its inner-conductor connected at itsuppei'. and to theother-o-t said balancedilines the lower ends; o;f said half Wave linesections: being con nected in; parallel with] eaolriI other to, constitute, a feed point, means oonnecting the; outer; conductgrs of-said hali wavelengthlinc:sections together. app i nately, at their mid-points; wherebtptha upp r portionsof, said outer: conductors actlasa qaarter; waveparallellioe shunting said balanced; lines, quarterwavelengthzlines-tconneetedbetweem p t ircui s and! said feedpoints half; ave lines: connected at. one tosaid feed points a lineebalance; g its, balanced; terminals conneeted;bet\veen the other ends -.of said lastemene ti onedhaliwave es and its-unbalanced circuit, connected to-the other oflsaid input circuits, the design of sidl St: ioned balance converter being; such; tl iat the resonance; characteristics presentedflhereby atsaid'feed-points: are sub-; stantially the same- ;a s1those presentedwbyysaid firstrmen on di alan e,j cnvertorsat hei-rx lr anced terminals said firstementioned, half wave sections having ,;cha rac teristic impedancestdeteremined: in accordance with: said resonance charace. Y teristicsso as tosei iectsubstantial cancellation of tl e. reactanoes or said balance converters.

2,, Ari network for radioantenna systems including; a of. radio frequency feed points wtotbe s t neous y upplied witneen rsy froma pa tinda ndsct r dioe aencyfi puts a -w input cir cuits compnising coaxial transmission lines; haying inner. and A outer; conductora, two equal length transmission linesjconnecting said; feedl the lother-of ..said input circuitsto the outer con-.

ducton ofisaid additional, transmission line;: and; means arranged} to form 1 a transmission line'stub, to connect vthe outer conductor ,of.' the other. 20f- ,said linput circuits totheouterconductor oirsaidv further tr ns nission line:andtorthe outerncone ductor of saidf additional transmission clinesat'na,

pointa quart r-Wave length at the, "operating frequency from the end thereofjto, transfer energy from said other input circuit, tosaid feed-points,- .antiephas l atiO ls lQ V 3. A} net work ,for; radio frequency. systemsrinw eluding, a pai'r of; radio-frequency: ,outputs; to besimultaneou'sly supplied. with energy, from-a rpairs oijradio frequency inputs to, beisolated fromeachother, saidfinputs comprising coaxialltransmissionn sharingi ner douter conductors, tw qua lengthjtransmission lines connecting saidlout'putsa to enact said inputs to transfer- .energy to said, outputs'in the same phase relationship an taddi-s. tional coaxial transmission line connected to one of said outputs, a .further coaxial transmission lineof the same length as said additional trans-1 mission lineconnected to the other of said outputs, the-inner conductors of said additional and; saidjurther transmission lines being connected- 1 frequency from; the end together. at the. ends remote. from said 4 outputs, means to connect theirinerv conductor of'the other ofsaidinputs'tothe-outer conductor of said additionaltransmission line, and stub means ar-f ranged to connect the outer condnctor of the other-of said inputsto the outer conductor of-sai'd further transmission line and to the outer condoctor of said additional transmission line at a point a quarter wave length at the operating thereof to transfer energy from) said: other input-to said outputs in anti-phase:relationship. H a

4i AH-antennasystem including apair of radio frequency feed points; to foe simultaneously supplied. with energy, from: a pair of independent radio freq uency input-circuits; each of said inputcircuits: comprising a coaxial transmission linehavingian-outer. conductor maintained at-a given reference.- pntentiala and an inner conduoton. meanstoiprevent theetransier of energy from: one: oiisaidl inpnttcircuitsttoithe other comprising. two equal.- length transmission lines connecting. said feed points toioneof said:- input circuits'to transenergy therefrom tol-said feed points in the-- same phase relationship; an additional transmiwion lineac'onnectedto oneaof said feed points, a-fur-ther transmissioniline of the samelengtlras saidtadditional. transmission. lineconnectedto the other oftsaid:ieedxpoints,.theinner conductors cfi said additionali and said further transmission lines beings connected together at the ends re mot'e from said.feedmpoints meansto connect the inner conductor: of the other of= said-input: circuits. to the outer conductor of said 1 additional transmissionilinay and aconductor: surroundingv a. portion on said! additional. transmission line to connectttheouter conductor: of the-other of said input circuits to: the outer conductor of said further.- transmissionline and :the outer: conductor oi i said additional transmission line at a point a" quarter-Wave length'a from the end thereof to transfer-:energn from-said other input oircuitwtosaid feed points .in--antiephase relationsh-ip.

5; A-i radial antenna systemfor simultaneous excitation from two independent input circuits unbalanced with; respect tov a. givenreferen'ce potential. and. including two 7 groups of radiator elements comprising aepairi of transmission-fines eoupledztoeach-groupof radiator elements and" connected in parallelwith ea-ch other. to con stitu-te .aav feed point; quarter-wave length: linesi connectedbetweemone of. said input circuits and' said feed pointss respectively; ,haIfF'WH VB COHXiEI- transmission. lines connectedoat one end respfectiveiy; to .saidxfeedepoints; means'lto intercorm'ect the inner: conductors-'1' of said; halfewawee lin'es meansto-;interconnect the end 101" the iouter con ductor:ofithe..other-renrioofionetot said halfiiwave lines a'nd-zth'e tei'ininait otithe'ioth-er "of said input circuits-. remote from said g-iverr reference po tential, and a conductor coaxially arranged about said one ofsaidzhalfiewave'liries to forniia}quarter- Wavestub section, saidconductorbeing connected wtnerouter condfictor of the other-half-wave lineia't'th'e e'n hereof; to the-terminal. at-refer-- e'r'ice potential f "said ot herinput circuit and to: the ou'teilcoiiddctor oilt'hesfi rst saiduhalf-wave lines-substantially at its mid-point 6.1 Ai radio tantenna system for simultaneous: excitation from two .-i-ndependentvinp.ut tcircuits including two groups of radiators, transmission line sectionscoup'i'ed to said radiators and connected in parallel with each other to constitute a feed point, equal length lines connected between onetof said input circuits and saidlfeed pointsire-w spectively, further equal length lines connected at one end respectively to said feed points, and apparatus connected between the other ends of said further equal length lines and the other of said input circuits to induce equal and opposite currents in said further equal length lines in response to excitation in said other input circuit.

7. A radio antenna system for simultaneous excitation from two independent input circuits, including two groups of radiators, transmission lines coupled to each group of radiators and connected in parallel with each other to constitute a feed point, quarter-wave length lines connected between one of said input circuits and said feed points respectively, half-wave lines connected at one end respectively to said feed points, and apparatus connected between the other ends of said last-mentioned half-wave lines and the other of said input circuits to induce equal and opposite currents in said further equal length lines in response to excitation in said other input circuit.

8. A radio antenna system for simultaneous excitation from two independent input circuits,

having its inner conductor connected at its upper end to the other of said balanced lines, the lower 1 ends of said half-Wave line sections being connected in parallel with each other to constitute a feed point, means connecting the outer conductors of said half-wave length line sections to gether approximately at their mid points, whereby the upper portions of said outer conductors act as a quarter-Wave parallel line shunting said balanced lines, quarter-wave length lines connected between one of said input circuits and said feed points respectively, equal length lines connected at one end respectively to said feed points, a line balance converter having its balanced terminals connected between the other ends of said last-mentioned equal length lines, and its unbalanced circuit connected to the other of said input circuits.

GEORGE H. BROWN.

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

UNITED STATES PATENTS Number Name Date 2,252,062 Chireix Aug. 12, 1941. 2,267,550 Brown Dec. 23, 1941 2,283,897 Alford May 26, 1942 2,286,179 Lindenblad June 9, 1942 2,341,408 Lindenblad Feb. 8, 1944 2,416,790 Barrow Mar. 4. 1947

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