US2106769A - Transmission of guided waves - Google Patents

Description

Feb- 1, 1938- G. cfsoUTHwom-H 2,106,769

TRANSMSSON OF GUIDED WVESv Filed Aug. 25, 1955 www INVENTOR v 6: C. Souad/00kt BY MQ ATTORNEY *Patented Feh. 1,1938

2,106,169 TRANSMISSION or GUIDED wAvEs George C. Southworth, Red Bank, N. J., assignor to American Telephone and Telegraph Company, a' corporation of New York Application August 23, 1935, Serial No. 37,557

21 Claims.

secure an impedance match between the inputv and the output. All these objects and other objects and advantages of my invention will become apparent on consideration of a limited -number of examples of practice in accordance with the invention which I have chosen for present-ation in the following specification. It will be e0 understood that this specification relates principally to these particular vembodiments of the invention and that the scope of the invention will be indicated in the appended claims.

Referring to the accompanying drawing, Figure l is anaxial section of impedance matching apparatus at the input end of a dielectric guide; Fig. lais a detailed cross-section on the corresponding line of Fig. 1; Fig. 2 is a sectional elevation of a structural d-etail which is indicated diagrammatically in Fig. 1; Fig. 3 is an axial section showing a modication as compared with Fig. 1; Fig. 4 is an axial section of impedance matching apparatus which may be interposed between two. dielectric guides of different char- ;,5 acteristcs; Fig. 5 is a curve diagram corresponding to Fig. 4, which will be referred to in explaining the operation of Fig. 5; and Fig. 6 is a longitudinal section of a further modification.

This application is in part a continuation of my application, Serial No. 745,457, filed September 25, 1934, on a Filter system for high frequency` electric waves.

In my pending application, supra, and also in my pending applications Serial No. 661,154 .15 filed March 16, 1933 and Serial No. 701,711 filed December 9, 1933 are disclosed systems for the guided transmission of electromagnetic waves of unusual character. The wave guiding structure may take a variety of forms;typical is a guide consisting of a rod of dielectric material having a high dielectric coefficient relative to unity. Another typical guide comprises a metallic pipe, containing only a dielectric medium, such as air, for specific example. In these typical dielectric guides, as in all the others disclosed, there is a dielectric medium and an enclosing boundary which denes a discontinuity in electromagnetic properties and within which electromagnetic waves may be propagated.

A specific dielectric guide which may be considered is a cylinder of vceramic material having rutile (titanium dioxide) as its principal. constituent. This prepared material may be made to have a dielectric constant of about 70 to 90, and a low dielectric loss factor, and it has the favorable property that its loss factor decreases with increasing frequency. The specific gravity is about 4 and its bending strength and other physical properties are favorable for practical use in. dielectric guides. Forthis purpose a cylinder of this ceramic material 'may or may not have a metallic sheath. l

Aside from the structure of the guide, the systems disclosed in my pending. applications, supra, are. unique in respect of the character of the wave transmission. The field pattern of the waves transmitted through a dielectric guide may take a great variety of forms, but in each instance thus far observed all forms have certainA characteristics in common. Thus, it has been 25 Cil ' shown that for each form the dielectric guide guide and the index of refraction of the dielectric metallic sheath around the dielectric medium.

presents the attenuation characteristic of a highpass filter. I'he criticalor cut-oft' frequency is dependent on the transverse dimensions of the medium comprising it, and it may be more or less distinct depending on the resistivity of the metallic portions of the guide and other factors that may influence energy dissipation along the guide. The phase velocity, too, is dependent on the transverse dimensions of the guide, and it is ordinarily either greater or less than that characteristic of light in the dielectric medium, depending on whether there is or there is not a The absence of the go-and-return flow of conduction current is another characteristic common to many dielectric guide systems. Y The expression dielectrically guided waves, as used in this specification, denotes the unique waves discussed hereinbefore and all other guided electromagnetic waves of equivalent character.' Dielectric guide denotes a wave guide adapted for the transmission of dielectrically guided Waves. 50

Referring to Fig. l, the metal pipe 2 which extends to the right and is shown broken oi may be taken as the input end of 'a dielectric guide, the dielectric I consisting of empty space or v its equivalent, air. This guide |-2 may be thought of as extending a considerable distance to the right from the input terminal apparatus shown in Fig. 1.

'I'he input end of the dielectric guide |-2 of Fig. 1 is connected to a side opening in a transverse cylindrical chamber 35. This chamber 35 and the associated apparatus constitute an adjustable impedance matching device for matching impedances between the alternating current generator 3 and the dielectric guide |2. The output connections for the source 3 are shown at 4 and 5 in Fig. 1a in the form of opposite terminal conductors from the generator 3, with sliding connections against the side walls of the chamber 35 so that the source 3 may be adjusted longitudinally in relation to the chamber 35. This chamber 35 is of conductive material and the source 3 is mounted on the insulatedend of an axial carrier rod 36 which is adjustable along the axis of the chamber 35 by means of the pinion 31 engaging its Acorresponding rack. The opposite end wall 38 is adjustable by another pinion 39 engaging its rack; and the end wall 40 behind the source 3 is similarly adjustable by the pinion 4| engaging its rack. It will be seen that both end walls 38 and 40 and the source 3 are adjustable longitudinally in relation to the'opening from the chamber 35 into the guidev |-2. Across this opening is an adjustable iris 43, which is indicated diagrammatically in Fig. 1. It may be constructed like a camera shutter, or a slide 44 may be provided as in Fig. 2, with diierent sized openings 43 along its length.

For any given frequency, a resonant adjustment may be established by shifting the end walls 38 and 40 and thereby determining the character of y the reactance of the load presented to the source 3. On the other hand, the magnitude of the energy dissipation component will be determined by the size of the opening of the iris 43.

At sumciently high frequencies the source 3 will generate lines of electric force within the cylinder lying in transverse planes and approximately parallel to the conductor system 4--5 of Fig. 1a. Waves of such lines will travel back and forth along the length of the cylinder 35, being reflected at its end walls 38 and 40, and on proper adjustment of these end walls, a system of standing waves will be established within the chamber 35. To some extent the wave energy will pass out through the adjustable iris 43 and be propagated along the interior of the dielectric guide |2. A wave of the type that has just been described, I call an asymmetric magnetic wave. l

'Ihe modification shown in Fig. 3 is adapted to generate and propagate waves of the type which I callsymmetric electric waves. These have their lines of magnetic force in circles centered on the axis and lying in planes perpendicular thereto. 'I'he dielectric guide |-2 comprising the air core I and the metallic sheath 2 is terminated at the left by the end wall 40 which is adjustable by means of the pinion 4| and its corresponding rack. The rod 36 of conductive material carries the source 3 and the piston 42 of conductive material, both adjustable by the pinion 3l engaging the corresponding rack. The resonant chamberl between the wall 40 and the piston 42 i's adjusted in suitable relation to the frequency of the source 3. The two output conductors from the source 3 are respectively a and fe;,and the complete circuit of the generator 3 is along the conductors a, b, then across the annular gap bc, and then along the conductive path c, d, e, f. The

energy in the form of symmetric type waves escapes through the annular opening bc between the edge of the piston 42 and the side wall 45. The volume of energy going into the guide |-2 may be adjusted by varying the width of the annular opening around the piston 42 or by means of the iris 43.

Referring to Fig. 1 it will be seenthat in relation to the guide chamber 35 with its end walls 38 and 40 there is an energy input at 3 and an output at the place of connection with the guide |-2. The place of the input and the place of the output are relatively adjustable along the length of the chamber. The same general principle and the samegeneral relation of parts are shown in Fig. 4, which represents two guides 98 and 9| of different diameters, between which it is desired to match their impedances. For example, the guide may be of diameter 10.2 centimeters, and we may consider the transmission oi asymmetric magnetic waves at a frequency of 2,000 megacycles per second. It is desired to pass these waves into the guide 9| whose diameter is assumed to be 12.7 centimeters, and to accomv plish this transfer without substantial reflection loss. With these dimensions and at the frequency stated, the characteristic impedance in the output guide 9| will be about 1.84 times that in the input guide 90.

The transverse cylindrical chamber 88 is interposed with two adjustable ends 89. This cylindrical chamber 88 is made in the form of two half cylinders meeting along the diametrically epposite longitudinallines 92. The chamber within the casing 88 between the pistons 89 can be adjusted to any desired length, and the place along the length where the input is connected and the place along the length where the output is connected are. independently adjustable. The diameter of the chamber 88 is 12.7 centimeters, the same as that of the output guide 9|, and the end plungers 89 are adjusted so .that its length is 21.5 centimeters. In this way it is secured that the length of the chamber is such as to give about one standing wave length. This is diagrammed in Fig. 5 where the curve E represents the magnitude of the electric force vectorof the wave and the curve H represents the magnitude of the magnetic force vector of the same wave. It will be understood that these Vectors are at a right angle to each other and thatfor the asymmetric magnetic wave which is assumed to be involved-in this case, the magnetic vector has a component along the axis of the chamber 88 and the electric vector is at `a right angle with this axis.

The standing waves set up in the chamber 88 provide the impedances against which the impedances of the two guides 90 and 9| will be matched. Referring to the diagram in Fig. 5, this shows that the electric force component of the standing wave in the chamber 88 is at zero at each end and in the middle and is a maximum at the two quarter points. The magnetic component is a maximum at the ends and also at the midpoint, and zero at the two quarter points.

Looking into the chamber 88 at various points along its length, it appears as a low impedance at points where the magnetic field is a maximum and as a high impedance where the electric field is a maximum. Accordingly, to match the impedances of the two wave guides 90 and 9| we connect each of .them at the particular point along the chamber 88 where the impedances are appropriate.

If the waves being propagated are of thesymsymmetric magnetic waves are being propagated,

then the guides 90 and 9| may have a high characteristic impedance and should be connected into the resonant chamber 88, each near a voltage maximum. After making these adjustments to a rst degree of approximation, a further final adjustment for optimum conditions may be effected by' again shifting the two movable plungers 89.

When it is desired to match two guides 90 and 9| of different diameters for a certain frequency and with certain other` conditions established once for all, the system of Fig.`6 may be employed. The guide section |0| is interposed in coaxial alignment with the guides 90 and 9|, having its length equal to an odd multiple of a quarter wave length, its diameter xed at the proper intermediate value in relation to the diameters of the guides 90 and 9|. Between the discontinuities at |02 and |03 a standing wavewill be set up, which will afford the necessary impedance match at each end so that the energy-now from the one guide 90 or 9| to the other will be without reflection into the one whence such ow occurs. The proper diameter of the intermediate section |0| may be determined experimentally or by a computation based on general principles. The

characteristic impedance of the intermediate part |0| should be a geometric mean between the characteristic impedances of the, two guides 90 and 3|.

Referring to Fig. 1 this shows the transmitting end for the dielectric guide |-2. 'Ihe high fre-` quency generator 3 generates asymmetric mag- Vnetic waves which are propagated as such within the guide |-2 from left to right. It is well known that, in general, the arrangement of apparatus which is appropriate at the sending end for dielectric wave energy may be reversibly appropriate at the receiving end. Accordingly, Fig. 1 correctly represents suitable receiving apparatus for connection to the distant end of the dielectric guide |--2, provided that a suitable sensitive receiver is placed where the element 3 is represented. In the more general aspect of a source or a receiver, the device 3 may be called an electromagnetic energy translator.

Similarly, if the element 3 of Fig. 3 were taken to represent such a receiver, then this gure would represent the entire receiving end for reception along a dielectric guide whose transmit- 'ting end is that which is actually shown in Fig. 3.

Fig. 4 represents an intermediate assembly of parts by which an impedance match may be made for transmission from a'dielectric guide of certain type into a dielectric guide of a different type. It Will be seen that in principle, Figs. 1 and 4 are similar. In relation to the transverse cylindrical chamber there is an energy input at 3 in Fig. 1 and at 90 in Fig. 4 and there is an energy output at the iris 43 in Fig. 1 and at the branch guide connection 9| in Fig. 4. yIn both figures the relative spacing between the end walls and the places of application of the energy input and the energy output are adjustable.

In accordance with the principles which have been explained heretofore, Fig. 4 may be regarded impedance matching device in that 90 may be an input dielectric guide, or be replaced by a source, such as 3 of Fig. 1; and 9| may be an output dielectric guide or be replaced by a receiver or 'other energy absorbing device.

With regard to the combination disclosed in Fig. 3, a novel and useful adjustment and manner of operation of that combination is claimed in my copending application Serial No. 73,940, filed April 11, 1936.

I claim:

1. A metal sheathed wave guide, a source of electromagnetic waves. a metallic-walled chamber enclosing said source and connected with said guide to establish dielectrically guided waves therein, the impedance of said guide being matched with the impedance presented by said source.

2. A metal sheathed wave guide, a source` of electromagnetic waves, a cylindrical chamber with an adjustable end wall enclosing said source, said chamber being connected with said guide for the generation of dielectrically guided waves therein, and said end wall being adjusted to fa position for which said chamber is resonant at the frequency of said source.

3. A device for coupling two dielectric guides for the transfer of dielectrically guided waves consisting of a transverse metal sheathed guide section interposed between the two guides and connected therewith at dierent places along its length.

4. Two dielectric guides of different impedance and an adjustable impedance matching connection between them consisting of a hollow metal cylinder with transverse axis, and adjustable end .walls therefor, said guides being connected to said cylinder at different places along its length.

5. The method of transferring electromagnetic wave energy from an input element to an output element, at least one of such elements being a dielectric guide carrying dielectrically guided waves', which consists in setting up a standing Wave with the input element connected to sustain it and with the output element connected to draw energy from said wave, and adjusting the places of connection of said elements along the length of said standing wave to establish an impedance match between the said two elements.

6. The method of transferring electromagnetic wave energy from an input element to an output element, at least one Iof such elements being a dielectric guide Iin which said energy is in the form of dielectrically guided waves, which consists in setting up a standing wave with the input element connected to sustain it and with the output -element connected to draw energy from said wave, adjusting the places of connection of said elements along the length of the wave so as to establish an impedance match between the said two elements, and' adjusting the volume iiow of wave energy at some place between the input and the output.

7. In combination, a cylindrical metallic pipe of limited length, respective reflectors across its ends, an electric Wave translating means at an intermediate place along its length, and a dielectric guide opening into said pipe at an intery mediate place along its length, said reflectors and said two places being relatively adjustable lengthwise and being adjusted so that said translating means operates at its optimum effectiveness.

8. The method of matching the impedances of two elements, one of which is a wave guide carrying dielectrically guided waves, which consists in establishing a standing electromagnetic wave and connecting the said two elements into it at respective places positioned along its length so as to attain the desired proper impedance match.

9. A device for coupling two wave guides carrying dielectrically guided waves consisting of an intermediatemetal sheathed guide section interposed between the two guides and connected therewith at different places along its length, said intermediate guide section being proportioned to effect an impedance match between said two guides.

10. In combination, an input element for electromagnetic wave energy and a corresponding output element, at least one of them`\being a di electric guide consisting essentially of\ a metallic pipe, and an intermediate element adapted to yhave standing waves set up therein from the said input element, the said output element being connected 'to receive wave energy therefrom, said input and 'output elements being so positioned along the length of the standing waves as to match their impedances.

11 A metal sheathed wave guide carrying dielectrically guided waves, an electromagnetic wave energy translator, and a chamber enclosing said ltranslator and connected with said guide, said chamber being so dimensioned and so related physically to said vguide and said translator as to eiect an impedance match between said guide and translator.

12. In combination, two dielectric guides of different characteristic impedance values, and an interposed dielectric guide section of quarter wave length and of geometric mean impedance value.

13. In combination, for the transmission of dielectrically guided waves of a certain mean wave length, two metal sheathed, air core dielectric guides of different diameters and in axial alignment, an interposed metal sheathed, air core dielectricguide section in the same alignment and of quarter wave length. and having an intermediate diameter such that its characteristic impedance is the geometric mean of the impedances of the two rst mentioned guides.

14. In combination, two metal sheathed dielectric guides of diierent characteristic impedance values for dielectrically guided waves and an interposed tandem-connected section of dielectric guide substantially an odd number of quarterwaves in length having a characteristic impedance intermediate the characteristic impedance values of said guides whereby said guides are coupled in efilcient energy transfer relation.

15. In combination, two dielectric guides of unlike characteristic impedance and section of dielectric guide interconnecting them, the transverse dimensions of said section being such as to minimize reflection in the transfer of dielectrically guided wave energy from one of said guides tothe other, said section of guide being substantially axially-resonant at an operating frequency of the combination.

16. In combinationftwo dielectric guides andA means for conveying dielectrically guided wave energy from one of said guides to the other comprising a section of dielectric guide connected laterally to the ends thereof. v

17. Two dielectric guides of unlike characteristic impedance and means coupling them for the transfer of dielectrically guided waves comprising a section of dielectric guide that is s ubstantially resonant at the frequency ofsaid waves, at least one of said guides being connected to lateral point of said section of guide.

18. Means for interconnecting two metal sheathed dielectric guides the proximate ends of which are out of axial alignment comprising a metallic chamber connected to the ends of both of said guides, the length of said chamber and the points at which it is connectedto said guides being such that dielectrically guided wave energy is efciently transmitted from one of said guides to the other.

19. In combination, a metallically bounded chamber, two wave guides, each consisting essentially of a metallic pipe containing only a dielectric medium, connected to said chamber` at respective points along an axis thereof, and means for transmitting dielectrically guided waves through said guidesthe frequency of said waves, the length of said chamber along said axis and the points at which said guides are connected to said chamber being so correlated that wave energy is eillciently transmitted from one of said guides to the other.

20. A metal sheathed wave guide carrying dielectrically guided waves, an electromagnetic lenergy translator and a metallic-walled chamber enclosing said translator and connected with said guide for the interchange of electromagnetic energy, the dimensions of vsaid chamber being such that said chamber is resonant at the frequency of said waves, and the impedance of said translator and its position within said chamber being soA correlated that the impedance of saidv guide and the impedance of said translator are matched to each other.

21. In combination in a system for the transmission of dielectrically guided Waves, an input element and an output element, a metallic-walled chamber enclosing one of said elements, the other of said elements being a metal sheathed wave guide opening into said chamber, said chamber being resonant at the frequency of said waves and the said element enclosed by said chamber being so positioned therein that its impedance is matched to the impedance of said guide, and an apertured barrier -near the mouth of said guide for controlling the volume ow of wave energy.

GEORGE C. SOUTHWORTH.

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