US2493842A - Wave guide with phase compensating paired bends - Google Patents

Description

Patented Jan. 10, 1950 WAVE GUIDE WITH PHASE COMPENSATING PAIRED BENDS Warren A. Tyrrell, Fail-haven, N. J assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application January 25, 1944, Serial No. 519,595

Claims.

The present invention relates to the guided transmission of ultra-high frequency electromagnetic waves, and it has as its principal objective the elimination or substantial reduction of .undesirable efiects that are incident to changes in the direction of the wave guiding structure.

In accordance with a feature of the invention a desired change in the direction of the wave guide is effected, not by means of a single bend, but by a succession of differently oriented bends. In one embodiment, for example, a change of 90 degrees in the course of a hollow-pipe guide is provided by a pair of successive right angle bends disposed in mutually perpendicular planes.

The nature of the invention and its various features, objects and advantages will appear more fully from a consideration of the following detailed description of the embodiments that are illustrated in the accompanying drawing. In the latter, Figs. 1 to 3 illustrate how a 90-degree change in direction may be accomplished in accordance with the invention, and Fig. 4 shows diagrammatically a radio system embodying the invention.

In the arrangement illustrated in Fig. 1, the wave guiding structure is a hollow-pipe guide of circular cross-section. The guide comprises a tubular shell of copper or other conducting material enclosing a low loss dielectric medium, which may be air, for specific example, or any other suitable non-conducting material. It is well known that electromagnetic waves can be propagated through the interior of such a guide provided the wave frequency exceeds a-critical or cut-off frequency that is dependent on the internal diameter of the pipe, the dielectric coeflicient of the dielectric medium, and the type or field configuration of the waves. It may be assumed, in the interest of a complete disclosure, of a specific embodiment, that the internal diam-;

eter of the pipe is 2% inches, thatthe dielectric medium is air, and that the free-space wavelength of the guided waves is 9.80 centimeters, corresponding to a wave frequency of somewhat more than 3000 megacycles per second. Under these circumstances the guide will support waves of the dominant or H11 type, that is, a non-symmetric type of transverse electric wave in which the lines of electromotive force extend across the interior of the pipe approximately parallel to a diameter.

The guide is represented in Fig. 1 as having a pair of adjacent -degree arcuate bends. The

lower bend l0 connects a guide section II, which leads to a source of H11 waves, not shown, and

a short guide section I 2. The latter is connected in turn by the upper bend l3 to a guide section l4 which leads to a wave receiver, antenna or other utilization means, not shown. Referring to the indicated axes of a system of rectangular coordinates, bend l0 and the guide sections connected thereto lie in the YZ plane, while bend l3 and the guide sections connected thereto lie in a plane XY that is normal to the other. The two main guide sections II and I4, it will be noted, are offset from each other by the distance L.

One of the undesirable effects that is introduced by a bend in a pipe guide of circular crosssection is ellipticity of polarization of the transmitted waves. of dominant type transmitted through a bend in the guide is generally split into two mutually perpendicular components, one component lying in the plane of the bend and the other component perpendicular thereto, and that the two components travel with unequal velocities. Hence, upon emerging from the bend, one component lags the other by an appreciable part of a wavelength, or, in other words, the two are displaced in phase angle. Excepting then for the possibility that the phase displacement may be degrees or a multiple thereof, the emergent waves are elliptically polarized. The usual wave receiver or other utilization means is ill adapted for elliptically polarized waves but is designed rather to utilize eificiently only plane polarized Waves having a predetermined fixed orientation. A typical receiver of H11 waves, for example, comprises a diametral pick-up conductor so oriented in the guide that it is in registry with the electric field of the incident waves, the latter being a condition that cannot be maintained if the incident waves are elliptically polarized. In addition to, or aside from, loss of efficiency other eflects produced by elliptical polarization of the transmitted waves may be regarded as deleterious in particular systems.

Fig. 2 represents diagrammatically two wave components appearing in the intermediate guide section l2 as a result of the effect of bend I0- on plane polarized waves of dominant type applied through guide section II. The larger component a lies in the YZ plane and the smaller component b lies at right angles thereto in the XY plane. Experimental studies indicate that if the electric vector of the applied waves lies in the YZ plane, i. e., in the plane of the bend,

component b is zero, and that if the electric Y I vector is rotated 90 degrees, component a is zero,

It has been found that a wave is not represented in the drawing. In the specific. .10

embodiment described with reference to Fig. 1 in which, it may be further specified;thersmean; radius of curvature of the bends is 3 inchesgxar. phase displacement of 25 degrees has been.found.

In another embodiment in Whichlitheradius-0165 5;,

phaseropposing relation to the waves reflected from the other.

curvature of the bends was 4 inches,- .all..'other. conditions being the same, the measured phase displacement was degrees. *Iir-beth 'cases the' plane of polarization of the incident waveswas at-- an angle of 45 degrees to the YZ plane. Inasmuch as the diiierenceinphase is attributable to the difierence in the velocity with which the two components are propagated throughthe"' bend, it is recognized that by proper'choice .of.

operating frequency and/or dimensions, the phase v -a multiple thereof.

displacement may be made 180' degrees or.a multiple thereof. In such case,. the 'plane of polarization of the emergent waves might be. displacedbut it would'be invariable and elliptical polarization would be avoided. This condition" o in'a hollow pipe gu1d'e'of rectangular cross-sec would obtain, however, only for a particular operating frequency andnot for any considerable range of frequencies, and itwould impose a re.- striction on the radius of curvature or length'of the bend; It. is to .be noted,-too,. that. if a bend' ss.

causes'elliptical. polarization, the effectis;no.t"' cancelled, but doubled, by refiectingthe emergent; waves or otherwise vcausingthem to traverse the same bend in the oppositedirection:

I'have discoveredlithat' the second bend I3" 40 largely compensates for. the deleterious effects introduced by the first bend I I7. lvioreparticularly I have found that" with. the. two bends arranged": in'the manner herein described; a plane polarized H11 wave enteringthroughguide section I I at'any section-and 1t 1s associated witlrn'reans; *notillu'sangle of'polarizationemerges through guide section 14 with substantially no evidence of "elliptical? polarization. This .is .ta'kento mean that the" I phase displacement introducedi'by the second bend. issubstantially equaliandopposit'e to the phase displacement. introduced lbythe first bend; The, two bends may thereiorebe said toshave' substantially the, same phase length; In explanation. of' these observationsit'imaybe noted that if the wave passing through guide-section II is polarized at an angle of 45Tdegrees with respect to the YZplane, it may be regarded. as comprising. two equal components, one in the plane of the..bend and'oneat right angles thereto, and" that the two components are Subjected to sub-. 60,

stantiallythe same treatment in passing through. the pair. of. bends; That; is, each component". passes through one bend with its. electric. vector in the plane of the bend and it passes through theother bend withitsele'ctric. vector normalto;

the .plane thereoflj Inv short, the ele'ctricalflengthif of the pair. of bends appears thesame .t'o the two:

components and they. emerge withjno phasedif-L' ference between them. .Forptheir'angls of'polarization of the appliedxwaves the. ttvocompo- 7o, p

' a wave-tight 'rotary'jointor 'swivel, which 'may"' nents are not so nearly equal and -the efifct.de scribed therefore obtains. to alesser extent; but" with the v.electridvector. =more nearly. coincident v with. or. normalto the .plane..of;.the bends,..the latter. have alessertende'ncy .to split. theappliedgm waves into phase displaced components. In view of the foregoing explanation it will be understood that the phase compensation obtaining in the Fig. 1 system is not critically dependent on the operating frequency and that the arrangement is efiective to suppress elliptical polarization over a wide range of frequencies- Partial reflection" of the-transmitted waves is another undesirable effect that is attributable to asingle Wave guide bend, for the bend tends to introduce an impedance discontinuity in the thatfthe waves reflected from the one are in The two bends in Fig. 1 constitute a pair 'of =sucli discontinuities, and they ,may. be advantageously spaced apart in reflection-canceling relation. In the specific embodiment described with reference to Fig. 1, a spacing Lofabout'l incheswas foundt'dyi'eldminimum reflection losses. Theoretical considerations'im dicate that the optimum spacing isapproximatel'y 1' one-half of" the wavelength "within" the: guide; or

Fig. 3 is a cross-sectional view of one-'of'the bends I0; I3 taken in the planeof the bend? The radius R indicates themean radius'of' curvature. Fig. 3 is equally illustrative of "an" arcuate-bend tion. The amount of reflectionloss that'occurs" within such a bend is marked-lrdepen'dent on the arcuate length of the bendor, in other wordsy'on" the mean-radiusofcurvature R: It'is found=that" 'the'opti'mum arcua'te length 1rR/2-fo'r minimum internal reflection losses iscriticalIy' dependent on'the wave-'fi' 'equency'andis approximately equal to a half wavelength'or multiple'thereof'.

Fig. 4 illustrates diagrammatically a" radio "transmitting and/or receiving system embodying? the present invention; The-system comprisesv a horizontally-aimed paraboloidal reflector 2D "that is fixedly attached to" the vertically disposed-hot low pipe guide I I. The guide is of circular-cross tratedffor' rotating'it about its-axis. At it'supper" extremityguide I I is terminated "by the" double bend structure-'ofFig. 1} the latter being-disposed with guide section I2 norma'l to-the-axis" of theparaboloid and-with guide section I4 aligned with the-*axis of the-reflector 20." The en'd of guide section "l'd 'is open and it is disposed" at' the; principal focus of 'the parab'oloid. In transmitting -guided waves issuing from-theopen end of section I4 strike the--refiector wand form an'axiallydirected radio beam'." Fig.3'1" of U. S. Patent No; 2",'206,-92'3,--'issued'- July 9; 1940, to G; C. Southworth illustrates a 1 device which can be employed-forthis purpose when the "transceiver 23 is to-be'used 'to'launcl'i waves-intothe guidefor transmission therethr0ug-h:- In receiving, radio wavesincident'upon the reflector aredirected to the open end-and" give rise-to guided waves inthe hollow 'pipeguide I I". Fig. -'12:"of-"Uf SiP'atenir No." 2,257,783, issued October 71194-1; to A? E? Bowen illustrates a 1 device'- which can" be-employed for" this purpose whenthe transceiver 23 istobe used to receive'waves incident upon theguide."

The lower end of guide-'1 I "is connected through be of the known type represented schematically. by ya-.pair .of spaced conductive flanges .2 I to a. stationary hollow. nipes uide'. 22;..th'at; leads .to... .,transceiver..2.3 Theetransceiverjfiiis.adapted launch waves of the H11 type into the lower end of guide 22 or to receive waves of that type from the guide, and in either case the orientation of the waves relative to the guide is fixed or predetermined. The Fig. 4 system is adapted primarily for radio echo ranging or object locating and for this field of use the transceiver 23 may be assumed to transmit the waves in the form of short spaced pulses and to receive selectively the pulse echoes that result from reflection of the waves at a distant object. Continuous rotation of the guide H and reflector 20 permits the entire horizon to be kept under observation.

It is to be noted that in the normal operation of the Fig. 4 system, as above described, the electric vector of the transmitted waves in guide ll rotates continuously relative to the guide as the structure rotates about the vertical axis, or inasmuch as the field is non-symmetric it suffices to say that the waves so rotate. Hence, if the vertical guide I l and guide section M were joined by a single 90-degree bend, the direction of the electric vector would continuously vary with respect to the plane of the bend and, intermittently, the waves would become elliptically polarized, that is, whenever the rotating structure passed through certain angular positions. The double bend provided in Fig. 4, however, substantially suppresses elliptical polarization as described with reference to Fig. 1 and by virtue of the spacing of the bends minimum reflection losses are obtained regardless of the angular position of the rotating structure. It may be noted also that the direction of polarization of the radiated waves depends on the azimuthal angle of the rotating structure, and more particularly that with continuous rotation the radiated waves vary cyclically between horizontal and vertical polarization. The direction of polarization of the received reflected waves varies in the same manner, but. the orientation of the waves appearing in guide 22 is nevertheless invariable. Where two distant stations differ on azimuth by 90 degrees, it is accordingly possible to employ vertically polarized waves for communicating with the one station and, merely by rotating the antenna system, to shift to horizontal polarization for communication with the other.

A feature of the Fig. 4 system is that with ellipticity of polarization substantially eliminated in the manner described, it is possible to employ a swivel joint of the simplest time. It is not necessary, for example, to employ a joint that is adapted to convert the H11 wave to a symmetric type of wave for the purpose of coupling the stationary and rotating guide sections.

Although the present invention has been described with reference to specific embodiments thereof, it will be appreciated that the invention is susceptible of embodiment in other forms within the spirit and scope of the appended claims.

What is claimed is:

1. A microwave transmission system comprising a hollow-pipe guide and means for transmitting waves of non-symmetric type through said guide, said guide having two adjacent, substantially identical bends fixed in mutually perpendicular planes.

2. A microwave transmission system comprising a hollow-pipe guide of substantially circular cross-section and means for transmitting waves of dominant type through said guide, said guide having a pair of adjacent arcuate right angle bends that are of substantially equal phase length and are fixed in mutually perpendicular planes whereby said bends have similar but opposite effects with respect to the production of elliptical polarization of said waves.

3. A microwave transmission system comprising a hollow-pipe guide of substantially circular cross-section and means for transmitting waves of dominant type through said guide, said guide having a pair of similar right angle bends spaced apart an approximately integral multiple of half wavelengths in reflection cancelling relation to each other, the respective planes of said bends being mutually perpendicular.

4. In combination, a hollow-pipe guide for the transmission of ultra-high frequency electromagnetic waves, said guide being of substantially circular cross-section and having a first smoothly curving bend therein, means for applying to said bend for transmission therethrough polarized waves the field of which is subject to rotation relative to the guide, said guide having a second similar bend of substantially the same phase length adjacent the first bend, and said second bend being fixed in a plane that is substantially perpendicular to the plane of the first bend.

5. In combination, a hollow-pipe guide for the transmission of ultra-high frequency electromagnetic waves, said guide being of substantially circular cross-section and having a first substantially arcuate right angle bend therein, means for transmitting through said guide electromagnetic waves the polarization of which is subject to variation with reference to the plane of said bend, said guide having a second substantially identical bend adjacent the first bend, and the two bends being fixed in planes that are sub stantially perpendicular to each other.

6. In combination, a hollow-pipe guide of substantially circular cross-section for the transmission of ultra-high frequency electromagnetic waves, said guide having a bend therein such as to produce elliptical polarization of the transmitted waves, means continually changing the orientation of the transmitted waves with reference to the plane of said bend whereby the degree of ellipticity introduced by said bend continually changes, and means for substantially neutralizing the variable effect of said bend on the transmitted waves comprising a second bend in said guide adjacent said first-mentioned bend, said second bend being of substantially the same phase length as the first-mentioned bend but disposed in a different plane.

7. In combination, a hollow-pipe guide, means for rotating said guide about a longitudinal axis, means at one end of said guide for launching plane polarized waves into said guide for transmission therethrough or for receiving such waves from said guide, a pair of substantially equal arcuate bends of substantially the same phase length adjacent each other near the other end of said guide, said other end being open for the radiation or interception of radio waves and said bends being fixed in mutually perpendicular planes.

8. In combination, a vertically disposed hollowpipe guide 'of substantially circular cross-section, said guide having at its upper end a pair of substantially identical right angle curving bends fixed in mutually perpendicular planes and an opening for the radiation or interception of radio waves, means for rotating said guide about a vertical axis, and means at the lower end of said guide for launching therein or receiving therefrom guided electromagnetic waves of the dominant type.

- 1 t 9; .In* combination, ae'section of: :hollowepipe V iguidein therformiof"twozsuccessive :curved' bends of substantially equallphase length: fixedzinrsubstantially; mutually perpendiculariplanes, transiceiver. means forexciting:electromagnetic waves inrsaid guide for transmission throughisaid bends in succession 'or forereceiving electromagnetic of similar adjacent bends in respective'planes that aresubstantially perpendicular" to each other; said bends being spaced aapartvan approximately integral multiple of half Wavelengths in substantially refiectiomcancelling relation to each other.

13; A microwave transmissionsystem comprising atubular uniconductor' wave guidingpassage having a pair of similar adjacent bends of substantially equal phase lengthifixed in respective planes "that are substantially perpendicular" to each othenand .means'for exciting in one end i of said pair of bends a non-symmetric plane polarized wave the orientation of'which is variable relative to the plane of the bend nearestsaid :one

end. V

14. A'microwave transmission system compris iing a tubular uniconductor wave guiding passage .-:having a pair of adjacent bends of' substantially .equal phaselength; fixed'in planes ithat are substantiallyperpendicularto each other, means including a:wave transceiver for. applying to or receiving from one end of saidupair of bends a nonsymmetricplaneupolarized electromagnetic wave, and means forrotating said passage about a'lonigitudinal axis-passinglthrougn said one end.

. 15. A microwave transmission system comprising a tubular:.uniconductor Wave-guiding pasisagehavinga-pair'of adjacent, substantially identical bends of substantially"equalphase length fixed in respective "planes 1 that are substantially perpendicular to *each other, and transceiver means ior applyingtto ortreceivin'g from one end of said pair of bends a non-symmetric plane polarized .wave that rotates :continuously with respect to the said end.

-=WARREN A. TYRRELL.

: REFERENCES CITED "Thefollowingreferencesare of record inthe file of this patent:

UNITED STATES PATENTS Number Name Date 2,129,669 I Bowen Sept. 13, 1938 2,129,712 Southworth Sept. 13, 1938 2,206,923 Southworth July 9', 1940 2,398,095 7 Katzin "Apr. 9, 1946 2,407,305 Langstroth "Sept. 10, 1946 2,410,827 Langstroth Nov. 12, 1946 "2,412,320 Carter Dec. 10, 1946 2,416,675 Beck et a1 Mar. 4, 1947 I OTHERREFERENCES "Proceedings of The Institute of Radio Engineers, vo1. 24,-"No'2-10, October 1936 (pages 1325- 1328).

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