US2409913A

US2409913A - Wave guide structure

Info

Publication number: US2409913A
Application number: US522241A
Authority: US
Inventors: Tonks Lewi
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1944-02-14
Filing date: 1944-02-14
Publication date: 1946-10-22
Anticipated expiration: 1963-10-22
Also published as: FR962864A; BE482709A; GB585290A

Description

Oct. 22, 1946.l L -TONKS WAVE GUIDE STRUCTURE Filed Feb. 14, 1944 3 Sheets-Sheet 1 Figi.

ff 'I Lew Ton k s.

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OCL 22, 1946. TQNKS WAVE GUIDE STRUCTURE Filed Feb. 14, 1944 3 Sheets-Sheet 2 Inventor` Lew Tonk; bg IIL-l His Attorney.

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IAVE GUIDE sTnUcTURE Filed Feb. 14, 1944 3 SheBtS-Sheet 3 Fig. X Figa N l if' FigJO. Figli.

w /82 *8l 8 N "82 Figlz. 1 m* Figli ,imm ai* bg #v7/M His Attorneg.

Patented ct. 1946 WAVE GUIDE s'raUc'rUm; Lew: Tonks, Schenectady, N. Y., signor-'tc Gem' eral York Electric Company. a corporation of New Application February 14, 1944, No. 522,241

l 1s claims.

My invention relates to ultra high frequency c systemsvand, in particular. to apparatus for coupling an ultra high frequency generatorto a wave guide of the hollow pipe type. It is an object of my invention to provide an improved electric discharge device to wave guide coupling.

It is an object of my invention to provide a coupling arrangement between a magnetron generator and a wave guide of the hollow pipe type which is particularly'suited for the transmission of a large amount of power at a very short wave length.

same cut-oil frequency, said cut-off frequency being the same as that of the uniform wave guide fed by said tapered section. Moreover, the crosssectional area at longitudinally positioned points is dimensioned to effect a gradual transition in impedance between the magnetron generator and the output wave guide.

The features of the invention desired t0 be protected herein are pointed out in the appended claims. The invention itself, together with its further objects and advantages, may best be understood by the following description taken in connection with the drawings in which Fig. 1 is a vertical section of a magnetron device and a coupling arrangement suitably embodying the invention; Fig. 2 is an end view serving to illustrate the magnetron structure employed in the device of Fig. l; Fig. 3 is an end view of the coupling arrangement of Fig. 1; Fig. 4 is a longitudinal section taken along the axis of one of the apertures of the coupling arrangement; Fig. 5 is another view of the anode employed in the magnetron of Fig. 1 showing the output arrangement; Fig. 6 is a view of a uniform wave guide having a cross 2 section similar to that of the wave guide coupling; Fig. 'Lis a curve illustrating certain characteristics of the wave guide shown in Fig. 6; and Figs. 8-14 illustrate other configurations of the cross section of the tapered coupling arrangement of my invention.

Referring particularly to Fig. 1,' thereis shown an ultra high frequency generator I0 of the magnetron type which provides electromagnetic waves of a predetermined frequency and mode to a dielectric wave guide I l of the hollow pipe type. 'I'he electromagnetic waves from the generator I0 are transmitted to the waveguide II through a wave guide coupling I2 which is dimensioned to aiford the same cut-oil' frequency to electromagnetic waves at longitudinally positioned points, as well as to provide a gradual transition in impedance between the magnetron output and the wave guide I While my improved coupling arrangement may be employed with any suitable ultra high frequency generator, one suitable device is shown in Fig. 1 as the magnetron III which comprises an elongated cylindrical container. the lateral wall structure of which is provided by a single metallic tube I3 consisting of ferromagnetic material, such as cold rolled steel or the like. Opposite ends of the container are similar in construction and are closed by flanged members I4 which are welded or otherwise hermetically joined to the inner surface of the part I'Il. Within the container and approximately at its central region, there is provided an anode structure I5 shown in plan view in Fig. 2. This anode structure comprises a circular metallic member which has a relatively large central opening i6 and a series of v smaller openings Il arranged symmetrically about the central opening, and the central opening i8 is joined to the openings II by means of laterally extending slotsl. Alternate ones of the metallicv walls or anode posts between the slots I8 are electrically connected together by means of conductive `straps I9.

Within the opening I6 of the anode structure, as shown in Fig. l, there is provided anindirectly heated cathode comprising a sleeve 2i of nickel cor. other suitable material having flanges 22 spun up at its extremities. 'Ihis sleeve, which may be coated externally ,with a suitable activating material such as barium oxide. contains a la- 3 Y mentary heater 2l by which it may be maintained at an emissive temperature. Que end of the cathode sleeve is closed by a metal disk 25, while an apertured disk 26 partially closes its other extremity.

In the operation of the device. a space charge is assumed to be developed in the space between the cathode sleeve 2l and the surrounding anode structure by the application of a suitable potential impressed between the cathode lead-in wire 28 and the container I to which the anode structure is directly conductively connected. The electrons which compose this space charge :are given a spiral or orbital motion by a magnetic field produced by means to be described hereinaiter, and their resultant gyrations about the cathode produce excitation of the anode structure at its resonant frequency. The functioning oi the anode structure inthe latter connection may be explained from one point of View by consid ering that it 'ls made up of a plurality of mutually coupled resonant units, in each of which induct-l ance is provided by the wall surface bounding one of the circular openings l'l and capacitance is provided by the opposing surfaces of one oi the slots iii. Taking this viewpoint, it is seen that the operating frequency is determined in a large measure by the dimensions of the openings i1.

For the purpose of providing a magnetic field of suicient intensity to permit the apparatus to function in its intended fashion, there are provided within the container I3 tapered magnetic pole pieces dit and 3i which are directed axially of the container and which extend in close proximity to the upper and lower surfaces of the anode structure i5. These pole pieces are permanently magnetized in such sense that the north pole of one faces the south 'pole of the other. in order to assure the existence of a magnetic held of the required intensity, the pole pieces at, 3i are constituted of a magnetizable substance having a high coercive force and a high energy factor. one material which may 4be used in this connection is that known as Alnico, a name designating a particular class of alloys of aluminum, nickel, and cobalt. .As an alternative structure, instead of using permanent magnets for pole pieces 30, 3i, soft iron pole pieces may be used and may be magnetized by means of an external winding (not shown).

In order to provide a low reluctance connection between the basic extremities of the respective pole pieces and the lateral wall of the container I3, the pole pieces may be respectively seated upon relatively thick disk-like members 33 consisting of ferromagnetic material, such as steel, and may be secured to these members by means of a clamping ring 34 slipped over the pole pieces andwelded to themembers 33. The base member 33 is of such diameter as to lit snugly within the tubular container I3 so as to provide a low reluctance connection with that partc and is welded to the associated closure member I4.

Accurate spacing of the pole pieces 30, 3i with reference to the anode structure I5 may be obtained by the use vof spacing rings 36 interposed between anode structure i5 and the sur-v face ci an apertured disk 31.

The Vwave, guide li is illustrated as a hollow pipe having a rectangular cross section and defined by conductive .side walls dii and conductive top and bottom walls 4I, 42. It is well known that ultra high frequency electromagnetic waves may be propagated dielectrically through such a hollow-pipe type wave guide Where the frequencyof the eaciting electromagnetic waves is' greater than Aa critical minimum frequency guides. These waves have been generally -indicated heretofore as being of the TE and TM types. The TM type waves have both a longivtudinal and transverse component of electric ileld but only a transverse component of magnetic held, whereas the TE type waves have both a longitudinal and transverse component oi.' magnetic field but only atransverse component of electric ileld. Electromagnetic waves of this type may be extracted from a magnetron, such as the' -illustrated magnetron ld. Although my invention is applicable to systems for transmitting a greater variety of waves, in describing my invention hereinafter reference will be made particularly to the TEm type of wave.

In order to provide means for directly coupling electromagnetic waves generated in the magnetron ill to the wave guide il the transition coupling section l2 is interposed between the wave guide il and the magnetron I0. The tapered transition section I2, as seen in Fig. 3, comprises a metallic member 44 whose cross section has two substantially circular aperturer 45, therein connected together by a rectangular slot 4l. The size of the holes 45, 56 and of the slot 41 increases uniformly from the end of the member i2 connected to the magnetron to its point of connection with the wave guide II.

The transition section- I2 may be constructed by forming two semi-circles at the wave guide end of metallic member 44, each semi-circle being tangent substantially to three sides of the rectangular wave guide II. The two semi-circles are connected together by two .straight edges 49, 5U, as shown in Fig. 4. At its opposite end the member 44 isvr provided with an oriiice comprising two symmetrically positioned holes 5I, l2 joined together by a rectangular slot 53, as shown in Fig. 3. The member M may then be bored with two conical holes which nt the large semi-circles at the Wave guide end of the member and the circles 5I, 52 at the magnetron end of vthe member. The partition between the hollow cones is then out away so that every cross section is of dumb-bell shape and of such proportions that a uniformguide of that same cross section would have a cut-oh' frequency substantially equal to the wave guide cut-oft frequency. At the same time, the coupling member I2 eiects a gradual change in impedance between the impedance at its magnetron end, whereits value is such that it provides optimum couplingA with the cavity resonator of the magnetron, and the impedance at its wave guide end, where its 'value matches that of the wave guide II.V

For purposes of transmitting electromagnetic energy from the magnetron into' the coupling section i2, the anode I5 is flattened at one point to provide a at wall 55,l as shown in Fig. 5, against which the left-hand end of the cou-V pling section i2 abuts. The at wall 55 of the anode is provided with an output oriiice of dumb-bell shape which comprises two circular openings 56, El equal in diameter to the openings 5i, 52 of coupling l2 and connected by a rectangular slot 58 which coincides with the slot 53 of coupling member l2. The cylindrical tank I3 may be provided with an aperture overlying the wall 55 of anode Il'through which a constricted portion 66 of coupling member I2 projects. The coupling member l2 may be secured to tank I3 of the magnetron in any suitable el-cobalt alloy. to facilitate sealing of the window i thereto. Wall 62 is interposed between the abut-- ting end's of coupling member I2 and wave guide I I, being brazed or welded to member I2. A conductive strap 63 welded or brazed to both members II and I2 strengthens the joint.-

into a corresponding shoulder in wall 62 on the high pressure side thereof, to strengthen the glass to metal seal. After the window 6I is sealed in Iplace. the magnetron and the coupling unit I2v may be evacuated through an exhaust tubulation 69 connected to the bottom of the magnetron structure.

The operation of -thewave guide coupling unit I2, as well 'as its dimensioning, may be better understood from the following description of the propagation characteristics of the dumb-bell cross section wave guide, which. in tapered form, constitutes the coupling unit. To assist in this explanation, reference is made to Fig. 6 of the drawing wherein the circular openings 5I, 52 are shown as having a diameter d. The distance between the centers of the circular openings 5I, 52 is designated as the dimension l. The length of the slot 53 is shown as equal to 2b and the height of this slot as having a value t. 'I'he angle subtended by half of the gap 53 at the center of one of the holes 5I, 52 is equal to a.

I'he curves in Fig. 7 have been derived by the suitable application of Maxwells equations to the propagation space of the wave guide shown in Fig. 6. These curves give the dimensions of cross sections which produce a cut-ofi wave length of 10.0 centimeters. 'For example, a cross section in which t=.018 inch, l=0.5 inch, and d=0.2 inch, has its cut-oil' at 10 centimeters, because for it d/l=0.4, and following the d/l=0.4 line 70 on Fig. 7 to its intersection with the l=0.50 curve. it is seen that that intersection lies also on the :.018 inch line.

Certain approximations have to be made in the mathematical theory leading to Fig. 7, with the consequence that the curves are substantially valid over a limited region which is defined by the dashed curves labelled l=0.5 radian and t=l-d. It is well known that to apply a set of curves, such as those of Fig. 7, to a structure having a cut-ofi wave length of l centimeters, diierent from 10 centimeters. it is only necessary to multiply the actual dimensions by 10/7l thereby obtaining scaled values to which Fig. 7 is applicable.

By way of illustrating the procedure of obtaining from Fig. 7 the dimensions for a tapered wave guide coupling section, consider an actual example in which the wave guide I1, of Fig. 1 is 1.44

vinches x 2.84 inches, inside dimensions, the tapered section I2 is 4 inches long from magnetron block I5 to wave guide II, and the oriilce 56, 51, 56 at the small end is approximately 1 inch long over all.

The 2.84 inch dimension of the wave guide immediately xes the cut-oil wavelength A@ as 14.5

Window 6| is provided with a shoulder yportion 6l, which ilts centimeters. If we assume a given slot thickness for slot ,58 and a value for the dimension l,

the curves of Fig. 7 enable us to calculate thedimension d. Assumption of a sequence of values for t and l enables us to reach the following set of values which are consistent with Fig. 7 and which are primed to distinguish them from actual dimensions: I

When multiplied by the ratio 14.5/10, the desired values are given as .1

l1= .725 di 276 0174 li-l-di =1. 001

Sinceithe circular arcs at the large and small ends are joined by conical surfaces, it follows that for any cross-section a fractional distance .f (shown in Fig. 4) from small to large end It is then possible to construct the following table:

The values of f in horizontal row 1 are chosen conveniently and arbitrarily. Rows 2 and 3 are calculated by Equations 1 and 2. Row 4 follows from rows 2 and 3. Row 5 is obtained by multiplying row.3 by the ratio explained. Row 6 is taken from Fig. 7 using rows 4 and 5, except in vertical column 8 which applies to the rectangular wave guide. Row 7 is row 6 multiplied by 14.5/ 10.

Thus the dimensions of the coupling section are complete up to half the distance from the small or magnetron end to the wave guide end. It is seen, however, that Fig. 7 does notapply beyond l=0.5 so that another consideration has to -be used. The 4curve of t against f in Fig. 4 is continued as a smooth curve to t=1.44 at; f=1, that is, at the wave' guide junction, as indicated in Fig. 4.

In connection with the foregoing illustration,v

the wave` length or the electromagnetic wave 10/14.5 as previously section, that is. the cut-oi! wave length of a uniform wave guide having this particular cross section, must be greater than the wave length ot the wave being propagated. Another important advantage of the coupling arrangement is that the gradually tapered section provides an essentially smooth transition in impedance so that the coupling section is substantially reilectionless at all points beyond approximately 11s of a wave length from the point 'of connection to the ultra high frequency generator.

While in the illustrations and discussion thus far the cross section of the coupling member I2 has beenI described as being substantially dumbbell in shape, the cross section of the section I2 need not be limited to this particular shape and 8 What I `claim. as new and desire to secure by Letters Patent of the United States is:

1. A wave guide of the hollow pipe type defined by a block of metal provided with a tapered longil tudinal opening, every cross section of ,said opening taken at .longitudinally positioned points thereof comprising a narrowed central portionv and being dimensioned so that al uniform wave guide of said cross section would ailord the same cut-oi! frequency to electromagnetic waves.

2. A couplingl device for an ultra high irequency transmission system comprising a conductive member defining'therein a tapered longitudinal opening the cross-sectional arca of which at longitudinal points comprises a'. narrowed central portion and is dimensioned to have a predetermined variation in impedance along Ithe any other suitable cross section may be employed, l

the apertures in the member tapering from the point of connection to the ultra high frequency device to the end connected to the wave guide I I..

In Figs. `8l2, there are shown other coniiguras tions of cross sections for the coupling member I2, all of which employ a pair of apertures 80, 8I

, connected by a slot 82. Each of the apertures and the slot are tapered between the two ends of the coupling member I2. Fig. l1, for example, shows a cross section which is rectangular in form and Fig. 12, one which is octagonal in form. t

In Fig. 13, there is shown a cross section for the couplingmember I2 in which the two tapered apertures 80, Stare not of the same size so that the symmetry oi' form illustrated in the preceding cross section views of the coupling member I2 is not present in this particular form oi' coupling member. A similar asymmetrical condition may ibe employed in coupling members using circular apertures, as well as members using rectangular apertures, as in Fig 13. In Fig. 14. the slot connecting the tapered apertures 80, SI is of a sinuous type and consists of a pair of parallel passages 33, 84 and a connecting passage 85. Congurations in the cross section of a coupling unit of this type are especially desirable where the cut-off frequency oi the wave being propagated' is relatively low so that extremely large wave guide sections would :be required.

It is apparent, moreover, that, while the wave guide II is illustrated as of the rectangular type, 'the coupling member I 2 may-be employed to connect the output 'of an ultra high frequency device to a wave guide of any given configuration, the criteria'being that the cut-off wave length at every cross section must be greater than the wave v length of the electromagnetic wave being propagated and that a gradual transition impedance be effected between the two ends ,of the couplim unit to effect a match with the impedanceof the wave guide connected thereto. Such a coupling is particularly suited for the transmission of large amounts of energy of relatively short wave length. r

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since various modifications may be made, and I contemplate fby the appended claims to cover any such modications as fall within the true spirit and -scope of my invention.

longitudinal axis.

3. A coupling 'device for use in an ultra high frequency transmission system comprising a conductive member having a tapered longitudinal opening extending therethrough the cross section of which at one end is deilned by an elongated central opening terminated at each end in an enlarged opening the last mentioned open- -ings progressivelyy increasing in cross-sectional area in the longitudinal direction.

4. A dielectric wave guide of the hollow-pipe type comprising a block of metal having tlierein a tapered longitudinal opening the cross sectional area of which at one end includes a central elongated slot terminatedat each end thereof in` an enlarged circular opening, the last mentioned openings progressively increasing in cross secltional area in the longitudinal direction.

5. In combination, a dielectric wave guide of` the hollow-pipe type comprising a conductive member of'rectangular cross sectionan ultra high frequency generator. comprising a cavity resonator, and means. for coupling said Wave guide and said cavity resonator comprising a conductive member having therein a tapered longitudinal opening the cross sectional area of whichl at longitudinal points comprises a narrowed central portion and is dimensioned to effect a gradual transition in impedance. 'f

6. In combination, a waveguide of the hollow pipe type, an Yultra, high frequency generator comprising'a cavity resonator, and means for coupling said wave guide and said cavity resonator comprising a conductive member having a length greater than 1x5 of afree space wave length of area of which at longitudinal pointsvcomprises,

onator, said member being provided with an aperture through which high frequency',y energy may be extracted, a dielectric wave guide of the hollow pipe type, and coupling means for `connecting said generator to said Wave guide comprising a metallic vmember Ahaving' therein a tapered longitudinal opening the cross sectional a constricted central portion and is dimensioned to have a substantially uniform cut-off`characteristic and having at one end adjacent said generator a geometry similar to said aperture.

8. In combination, an ultra high frequency magnetron of the space'resonant type comprism ing a plurality of electrodes including an anode structure for defining a. cavity resonator, said anode structure being provided with an aperture comprising a central slot terminated at the ends in circular openings, a dielectric wave guide of the hollow pipe type having a rectangular cross section, and coupling means between said anode structure and said wave guide comprising a conductive member having a tapered longitudinal opening the cross sectional area of which is dimensioned at one end adjacent said anode structure for optimum coupling to said cavity resonator and dimensioned at the other end to match the impedance of said guide.

9. In combination, an ultra high frequency magnetron of the space resonant type comprising a plurality of electrodes including anuanode structure for defining a cavity resonator, said anode structure being provided with an aperture, a dielectric wave guide of the hollow pipe type, and coupling means between said anode structure and said guide comprising a conductive member having a tapered longitudinal opening the cross sectional area of which comprises a narrowed central portion and is dimensioned to have a transitional impedance which provides optimum coupling to said cavity resonator and impedance matching with said guide.

10. In combination, an ultra high frequency generator of the space resonant type including a structure for deiining a, cavity resonator, said structure being provided with an aperture through which the energy of said cavity resonator may be extracted, a, dielectric Wave guide of the hollow pipe type, and coupling means between said structure and said wave guide comprising a conductive member having a tapered longitudinal opening the cross sectional area of which comprises a narrowed central portion and is dimensioned to aord a transitional impedance which provides optimum coupling to said cavity resonator and impedance matching with said wave guide.

11. A dielectric wave guide of the hollow pipe type defined by a block of metal having a longitudinal opening comprising a pair of longitudinal tapered openings joined by an intermediate slot, the separation of opposing faces of said slot increasing with the cross sectional area of said tapered opening.

12. A dielectric wave guide of the hollow pipe type defined by a block of metal having a longitudinal opening comprising a pair of longitudinal conical openings joined by an intermediate slot the separation of opposing faces of which increases in accordance with the cross sectional area of said conical openings.

13. A discharge device for an ultra high frequency transmission system comprising a conductive member deiining therein a tapered longitudinal opening comprising a pair of longitudinal conical openings joined by an intermediate slot the separation of opposing faces of which increases in accordance with the longitudinal cross sectional area of the conical openings to produce at one end a substantially rectangular opening for connection to a dielectric wave guide of the hollow pipe type.

LEWI TONKS.