US 2404086 A
Description (OCR text may contain errors)
Patented July 16, 1946 COUPLING DEVICE Ernest Carl Okress, Montclair, Donald Eric Nelson, East Orange, and Robert Curtis ford, Newark, N. J., assigner-s .to
Rother- Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania.
Application October 7, 1942, Serial No. 461,134
This invention relates to coupling devices and more particularly to a coupling device for microwave energy, as, for instance, from the source of generation of the energy to a wave guide or other means of transmission of the energy from such source to effectuate its use. The coupling device is in effect a short length of coaxial line with a loop terminal for introduction into the generator, and the present invention is an improvement upon that of the copending application of E. C. Okress and Polykarp Kusch, S. N. 440,274, iled April 24, 1942, entitled Coaxial lines and the copending application of E. C. Ok-ress and Polykarp Kusch, S. N. 457,024, filed Sept. 2, 1942, entitled Coupling device and assigned to the same assignee as the present invention.
Interpositioning of a dielectric, under ordinary conditions, in the path of wave propagation, introduces an impedance discontinuity and consequently a disruption or partial loss of transmitted energy. Yet a dielectric has to be employed in connection with the output means from an evacuated generator to maintain the generator vacnum and at the same time have the voutput means not under vacuum. The desideratum is to transier the full derivable wave energy from an evacuated chamber to a transmission line or means not under vacuum, and this desideratu-m constitutes the primary object of the present invention.
Another object of the invention ,is to accomplish the stated desideratum by a coupling means of improved construction.
A further object of the invention iis to transfer the wave energy, with negligible loss, Afrom an evacuated ,generator to a wave guide Ynot under vacuum.
Again, object of the invention is to provide a .coupling device wherein the wave energy lfrom the generator to the output vline is along good conductors.
Yet another object is to provide a coupling device wherein an 'impedance matched electrical mirror is provided for the wave energy from the generator in its travel to the far wall of the coupling structure and wave guide away from the generator.
Still further objects of the invention are simplicity of parts, ease and permanence of assembly, mechanical ruggedness and adaptability to known generators and wave guides.
Additional objects will appear to those skilled in the art both by direct reference thereto as the description proceeds and by implication from the context.
Referring to the accompanying drawing in which like numerals of reference indicate similar rsion greater 'than Athe `other for parts throughout the several views,
Figure 1 is a longitudinal sectional view of a coupling device embodying the present invention and shown in associated relationship to a `generator and a wave guide;
Figures 2 and 3 are cross sections of said device taken on lines II-II and III-III of Fig. 1 respectively;
Figure 4 is a sectional elevation similar to Fig. l and showing a modified construction; and
Figure 5 is a diagrammatic View for purposes of mathematical reference.
In the specific embodiment of the invention illustrated in said drawing, and `giving `attention initially to Figures 1, 2 and 3, the reference numeral l Adesignates a part of a known ultra-high frequency generator from which wave energy is derivable through an output provided with a loop il situated within a cavity I2 of Athe generator. The interior of said generator, inclusive of said cavity, is evacuated and it is, of course, essential to maintain the vacuum throughout the useful life of said generator. Normally the loop H is exposed directly to the vacuum space. `According to the present invention external sealing of the coaxialline of the coupling device is accomplished with a minimum of energy transfer occurring. It should be borne in mind that the immediate desideratum is ecient transfer or conduct of the Wave energy from the evacuated cavity vof the generator to a hollow waveguide I3 that is not evacuated.
Generally dened, a waveguide is a hollow pipe by means of which electro-magnetic energy is propagated from one place to another before its ultimate transmission in free space or utilization in some other instrumentality. A wave guide is characterized by presence of a dielectric, `such as air, `within a metallic pipe engirdling the dielectric. The cross-sectional dimensions of the guide have a denite relation to the character of the wave transmitted thereby. Usually waveguides are rectangular in cross section with one dimennpurposes of obtaining the desired mode of oscillation and polarization of the wave that may be transmitted. Accordingly, the wave guide I3 shown is of rectangular cross section, and for convenience of description the longer dimension will be referred to as horizontal and the shorter dimension as vertical, but it is to be understood such Vdesignations are arbitrary and not in any sense limitations.
The coupling device per se comprises, in addition to loop H above mentioned, a coaxial line of which the center rod ld is in continuation of one leg of the loop, is of tungsten or copper and projects from the generator to and vertically through'the wave guide medially between the side walls thereof. The cooperating tubular portion of the coaxial guide is constituted by a conductive base or mounting thimble l5, as of copper,
and by a tube i6, which preferably is also copper, axially alined and projecting upwardly therefrom, both the thimble and the tube having central passages Il, I8, respectively, of which one is a continuation of the other. The upper end of said tube i6 is substantially at the level of the lower horizontal wall of the wave guide but does not have any contact therewith.
Also projecting from the upper end of said thimble, preferably coaxial with the said tube l, but of less length than said tube, is a sleeve is the upper end of which is sealed vacuum tight toy an end margin of a long glass envelope 2! of substantially the same diameter throughout its length-as said sleeve. The sleeve and glass envelope are of materials having substantially the same coeiilcient of expansion, and by preference the glass is borosilicate glass and the sleeve is an'alloy of nickel, cobalt, manganese and iron in accordance with disclosure of Patent 2,052,335 of December l, 1936 to Howard Scott, said material being sold under the trade name of Kovar- This alloy and glass obtain a very rugged seal both because the coefficients of expansion are substantially the same and because of the tenacious adhesion and for the further reason that a ne featheredge is not required. In the microwave art here involved, Kovar has been found inadequate as a conductor under certain conditions, as Ait is not only highly dissipative, but if a large quantity of energy is permitted to flow through the Kovar-glass seal there is a likelihood of failure of the seal and consequent loss of vacuum at the wavelength band of present concern. The construction employed in the present invention requires no now of micro-wave energy in the Kovar or next to the surface thereof. The flow of the micro-wave energy is within the passages Il. i3 between the coaxial rod and its engirdling thimble and sleeve.
As shown, the upper end of thimble l5 is provided with stepped-down sockets the outer-upper one receiving the end margin of the Kovar sleeve, and the inner-lower one receiving the end margin of the coaxial line tube I6. Both the sleeve and tube are soldered in place in their respective sockets in the thimble, preferably with the use of a gold-copper-eutectic solder indicated applied at 2l, 2i.
Glass envelope 2i) extends upwardly through the wave guide and is sealed to the downwardly directed rim of an inverted cup 22 preferably also of Kovarf The central rod lli in this showing projects axially to and is soldered to the closed top wall of said cup above the envelope. Overlying and engirdling said Kovar cup 22 is another, but larger, inverted cup constituting an upper metallic housing 23 having its lower edge engaging and secured to the top wall of the wave guide I3. rhere is no direct mechanical contact between the two cups, the outer one being spaced from the inner one by an air space 2li. The lower edges of both the Kovar and the overlying housing cups are preferably at the same level, namely', at the plane wave guide, and as close to each other as practi- 25 of the upper wall ofthe cal without injurious engagement of the glass of envelope 2t sealed to the Kovar cup, since said glass extends somewhat up the side of that cup and between the two cups. For convenience of reference, the particular part of gap or air space 2li at the level o said bottoms of the cups and plane 25 of the upper wall of the wave guide will be identified as gap 25C Similarly the portion of the gap 2d at the plane of the top wall of the Kovar cup between the side walls of the two cups will be identified as gap 24". The side wall of the Kovar cup has a depth equal to an odd quarter wave length in vacuum or air, and the odd wave length selected is preferably one-quarter wave length. The Kovar cup accordingly forms a quarter-wave length shorted line section which gives an impedance at its lower end or opening 25 which closely approximates the impedance across gap 2li', and acts as an electrical mirror, further explanation of which is given hereinafter.
Iell the impedance matching for output tuning between the coupling device and the wave guide, is accomplished by provision of an appropriate closure for one end of the said wave guide. Preierablysaid closure comprises a piston 2G having a head next the outer end of the wave guide which fits snugly therein. On the end of said head 'El toward the coupling device is a piston skirt 25 forming a cavity 29 the end wall 3l or" which constitutes the end wall for the wave guide. This skirt portion 28 is dimensioned to iit freely in the wave guide and the cavity is made a quarter wave length deep, thus forming at the plane 2d an electrical mirror. The piston can be moved longitudinaliy until maximum output from the wave guide is recorded provided the guide was first matched to the load or free space and the piston may then be soldered in place.
For accomplishing purposes of the present invention electrical continuity between the upper end of coaxial tube l@ and the adjacent wave guide bottom wall is obtained, as set forth in said application of E. C. Okress and P. Kusch for Coupling device, namely, by means avoiding physical engagement of those parts thereat. The structure employed comprises radially enlarging a definite length of the coaxial tube It, as at 3l, next the upper end of said tube so that the outer peripheral face of the enlargement is almost in contact with the glassl of the envelope. On the outside of the envelope directly opposed to said enlargement, and of equal length, is a metallic ring 32 which is likewise almost in contact with the glass of the envelope but on the outside thereof. Engirdling the metallic ring 32 is a ring 33 of glass or other material having the same dielectric constant as the glass of the envelope. Mention may be made at this time that while necessity o exaggeration of thicknesses seems to make the axial length of said glass ring noticeably shorter than the enlargement Si, in actual practice the metal of ring 32 overlying upper end of glass ring 33` is sufficiently thin so that the difference in lengths is accounted for in compensation for end effects. The common length of said enlargement, metal ring and glass ring is equal to a quarter wave length, as measured in the dielectric, of the wave energy being promulgated. Observation is made at this time, that the wave-length in a dielectric such as glass is materially shorter than in air, and in the present showing, represents a single quarter-wave length for the glass dielectric as compared with the depth of the heretofore described piston cavity 2S) which length of the enlargement and rings y'5 represents 4a single quarter wave length in air. The upper ends ofenlargement 3l and ring 32 are in a common plane 'dil `with the lower wall of the wave `guide I3.
Outside of the glass ring is a lower housing 34 of 'metal coaxial with the several parts within and extending from the wave guide I3 to the mounting thimble I5 and secured to both, as .by sof-t solder 35, 35. The space below the glass ring Iwithin the said lower housing 34 is noncritical, the housing'only forming 'that `space incidental to its function of maintaining proper relationship of generator and wave guide.
vIn operation, micro-wave energy is picked up by loop II from the Vgenerator or other source, and is guided along the `passage formed between tube I6 and center rod I4 forming the coaxial line. At the gap 31 at .the upper end of tube I5 avery low impedance is encountered as contrasted with a high impedance at the gap 38 at Athe lower end of enlargement 3| by virtue of the -quarter wavelength vannular chamber 33. The resulting effect, by virtue `of this operation of fthe impedance section constituted by said enlargement, rings and associated part of the envelope, is eiect of electrical continuity between the upper end 40 of the said tube I6 and the encircling part of the metallic .ring 32 and wave guide wall at 31. Thus the low imepdance at 31 is `utilized to obtain Vfull power coupling from :1x
the concentric line of the coupling device to the wave guide. Then,.as explained above, the plane 25-o`f the cup 2.2 acts as an electrical mirror of substantially 100% efficiency and is adjusted so that a suitable impedance .level is established and .by matching at the end of the wave guide the energy is promulgated with substantially little loss along the wave guide for use as desired.
"The position of the cup 22, in Athe cup 23, determines the distribution of the kcurrent on the lead I4 between planes 25 and 43. `In other wordsit controls the impedance into which the tube I6 looks. only .decrease the impedance established bythe position of cup 22, .into which the generator looks. That is, its function is to adjust the position of the electric intensity maximum with regard to the probe I4, between .the surfaces 25, 40 of the guide.
The cup 22 represents a quarter wavelength line section whose .impedance at the open end is represented .by the compound vproduct Where Q represents the merit factor of the line and Zu the characteristic or surge impedance of the line section. Parameters and materials are chosen such that Q is large and such that the resulting impedance at 25 is high (of the order of a Vhundred thousand ohms). The `impedance at the annular gap 24 is almost equal to this as will be shown mathematically presently.
This means that practically no current iiows in the Kovar glass seal. The surface currents are high at the bottom of the cup, so that this surface up to the glass seal should be silver plated and polished as indicated by layer 39 shown. The underlying mathematical Vdevelopment substantiating the theory as basis for the present application is given herewith in conjunction with diagram of Fig. l5 wherein the several impedances at the areas involved have been identiedwith distinguished quantum Z charac- The position of piston 3U can ters in addition to :the referencev numeralsllfor those areas. i lScientific investigation and literature are authorities for the fundamental formula applicable to the present conditions of a shorted concentric lineas formed Vby cup 22 and rod I4, asfollows: v
.ZF-Zo1 tank (aafjp (.1)
The relationship 'further `exists atresonance and for a shorted line that (or odd multiple) but since 27W 221| or T by its definition, the Asubstitution of Vthis value gves'the'result of Under these premise conditions, .expansion-ofthe fundamental yFormula 1 obtains a differently expressed .equivalent fZvl Z1 *rauh al (2) Furthermore the value of al is always small, and sinceit is'known that a small angle is approximately the same 4as its tangent, the value may be substitutedin place of the hyperbolic tangent in the formula, which becomes 'where r is resistance of the lineV per unitlength and g is the transverse leakage conductance per unit length. The value inthe `present instance of is .so smallin comparison 'with `the value of L 2Z01 that lfor all practical purposes it `may be disregarded and lomitted, wherefore it may be stated that The value of a in Equation 6 may be substituted for inforegoing Equation 4 from which it follows 7 and this value substituted for n in equation rI which gives y SZm2 i Zi---fm-TZOIQM Since Zai, Zoz, and l are known from the assumed parameters of the lines and wavelength one can readily obtain Z1, Z2 and Z3. In all cases Zoz should be a minimum consistent with physical limitations, and Zni a maximum. The potential difference between the surfaces of Zoz, decreases as Zoz decreases for a given current flow.
Compactness and certain savings in manufacturing cost at the expense of a degree of efciency, may be obtained by a structure embodying the present invention and shown in Figure 4. In this showing coaxial rod Ili is present as before, passing through a copper nipple a to the generator and soldered at its outer end to the middle of the end wall of inverted cup 22 as before. Said rod i4 passes medially through wave guide I3 as in the preceding figures and has its lower edge in the plane of the upper wall of said guide and of the lower edge of upper housing 23. Secured to the lower edge of inverted cup 22 in this instance is a short length of glass envelope 23a substantially entirely within the wave guide. The lower end edge of the glass envelope is sealed to a sleeve IBa the lower end of which has an outwardly directed flange |917 which rests upon and is sealed to the upper edge of said nipple. Said sleeve l9a and cup 22 are preferably both Kovar and envelope Za is preferably borosilicate glass. Y
Engirdling the Kovar sleeve 19a above the flange Igb thereof, is a metallic ring 32a, preferably of copper, and next outwardly is a glass ring 33a and outside of that is a lower housing 34a secured to the bottom wall of the wave guide and through attachment tcthe rim of the ange 19h i5 thereby supported from nipple 15a. Metallic ring 32a provides a top flange 32h overlying the upper edge of the glass ring and glass ring 33a provides a bottom flange 33h underlying the lower rim edge of the metallic ring. The length and other characteristics' of these two rings conform to the preceding description and provide a quarter-wave shorted section. The wave guide has one end closed by piston 29 as previously described. Micro-wave energy owing from the generator arrives at the plane of the upper edge of the sleeve ISa (which is the planev of the upper edge of ring 32a and of the bottom wall of the wave guide also) and by means of the quarter wave shorted section provided thereat passes the 'gap at that plane as if the sleeve and ring were mechanically in-contact, said sleeve in this respect functioning as described with respect to tube l@ in the preceding form of the invention.
Both constructions above described with inverted cup 22 located and spaced as described at .the upper end of the coaxial line form electrical reflectors. Likewise both constructions with the quarter-wave shorted section at the lower wall of the wave guide provide'energy transfer means across a gap as if that gap did not exist. The structures are therefore rugged and not subject to any imposition of strain upon the glass sealing from extraneous forces resulting from assembly or use with the wave guide.
Since the various details of construction as well as the precise relation and functioning of parts are subject to variation and change without departing from the inventive concept or scope of the invention, it is intended that all matter contained in the specification or illustrated in the drawing, shall be interpreted as exemplary and not in a limiting sense. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein shown and described and all statements of the scope of the invention herein set forth as a matter of language which might be said to fall therebetween.
l. A coupling device comprising a coaxial line having electrical energy pick-up means at one end and having a fixed electrical reflector of infinite impedance next the other end effective at a plane transverse to said coaxial line, and an inverted cup overlying said coaxial line at the end thereof having the electrical reflector, the edge of said cup being substantially in the effective plane of said electrical reflector` and constituting a conductor of radio frequency current from and out of contact with said coaxial line.
2. A coupling device comprising a coaxial line having electrical energy pick-up means at one end and having an electrical series reactance reflector of high impedance next the other end effective at a plane transverse to said coaxial line, an inverted cup overlying said coaxial line at the end thereof having the electrical reector, the edge of said cup being substantially in the effective plane of said electrical reflector and elsewhere beyond said plane and constituting a conductor of radio frequency current from and out of contact with said coainal line, and electrical energy transfer means intermediate' said ends.
3. AV coupling device comprising a coaxial line having a metallic hollow structure and a rod member axially thereof and projecting from both ends thereof, means for mounting one end of said metallic hollow structure for use upon and in communication with an evacuated generator, an inverted cup over the end of said rod member re-mote from said mounting means, and an envelope of insulating material extending from and sealed to both said cup and said hollow structure.
4. A coupling device comprising a coaxial line having a metallic hollow structure and a rod member axially thereof and projecting from both ends thereof, said hollow structure having a thimble constituting one end thereof and having an envelope projecting from the other end thereof; a wave guide, said coupling device projecting through said wave guide and having the upper end of said hollow structure terminating in the plane of one wall of said wave guide, an inverted cup at the other end of said coupling device, said cup having its marginal edge terminating in the plane of an opposite wall of said wave guide, and a housing between said wave guide and cou pling device exterior of said hollow structure and vextending from adjacent the upper part of said thimble to the wave guide and constituting the supporting mechanical connection between the coupling device ,and the wave guide.
5. A coupling device for electrical energy from a generator to a wave guide, comprising a coaxial line having electrical energy pick-up means from the generator and having a-xed planar electrical reflector` substantially in the plane of one wall of said wave guide, and having a quarter wave impedance section presenting substantially a continuity of electrical connection and a mechanical separation between another'wall of said wave 9 guide and said coaxial line thereby confining transfer of energy within the region within the Wave guide.
6. A coupling device comprising a coaxial line having inner and outer conductors of which the outer conductor is divided transversely and prcvides separated end sections, one end section next an end of the inner conductor being insulated from the other section and joined to the end of said inner conductor and having a quarter wave length depth for constituting a quarter wave length shorted line section open toward the other section, and means out of Contact from said quarter Wave length shorted line section overlyingr the same and cooperating therewith to produce high impedance next the said shorted line section at the said open end thereof.
'7. A coupling device comprising a coaxial line having inner and outer conductors of which the outer conductor is divided transversely and provides separated end sections, one end section next an end of the inner conductor being insulated from the other section and joined to the end of said inner conductor and having a quarter wave length depth for constituting a quarter Wave length shorted line section for obtaining desired reactance, and the other said section having a quarter Wave length enlargement for effecting radio frequency current ow from the coaxial line, and a Wave guide having metallic portions girdling the said quarter wave length portions of said coaxial line outer conductor sections.
8. A coupling device comprising a coaxial line having inner and outer conductors of Whichthe outer conductor is divided transversely and provides separated end sections, one end section next an end of the inner conductor being insulated from the other section and joined to the end of said inner conductor and having a quarter wave length depth for constituting a quarter wave length shorted line section for obtaining desired reactance, and the other said section having a quarter Wave length enlargement for effecting radiofrequency current flow from the coaxial line, and a wave guide having metallic portions girdling the said quarter wave length portions of said coaxial line outer conductor sections, said inner conductor passing through the Wave guide, at the part of said inner conductor exposed between the end sections of the outer conductor.
ERNEST CARL OKRESS. DONALD ERIC NELSON. ROBERT CURTIS RETHERFORD.