US3727098A - Magnetron filter box - Google Patents

Magnetron filter box Download PDF

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Publication number
US3727098A
US3727098A US00165113A US16511371A US3727098A US 3727098 A US3727098 A US 3727098A US 00165113 A US00165113 A US 00165113A US 16511371 A US16511371 A US 16511371A US 3727098 A US3727098 A US 3727098A
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microwave
cavity
magnetron
dissipative material
portions
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P Crapuchettes
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Northrop Grumman Guidance and Electronics Co Inc
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Litton Systems Inc
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Priority to DE19722229743 priority patent/DE2229743B2/de
Priority to JP7272662A priority patent/JPS5412034B1/ja
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00—Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/14—Leading-in arrangements; Seals therefor
    • H01J23/15—Means for preventing wave energy leakage structurally associated with tube leading-in arrangements, e.g. filters, chokes, attenuating devices
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/20—Frequency-selective devices, e.g. filters

Definitions

  • MAGNETRON FILTER BOX Inventor: Paul Wythe Crapuchettes, Woodside, Calif.
  • a magnetron filter box of novel construction serves to dissipate and filter out spurious signals appearing at the filament terminals of a magnetron.
  • the filter box includes: two (or more) elongated electrical conduc tors spaced and insulated from one another which are provided with adjacent end portions of each adapted for connection to a respective one of the filament terminals of the magnetron which provide a current carrying path to the filament; microwave dissipative material of a predetermined volume is placed about and surrounds the electrical conductors minimally all along a portion of the lengths; and a metal container of predetermined dimension and volume encloses the microwave dissipative material and underlying conductors and is adapted to enclose additionally the stem or terminal end of the magnetron either with or without the metal pole piece as part of the container combination.
  • the relative geometry between the dissipative material and the metal enclosure is such as to form a microwave cavity of a lowQ factor, suitably less than 100, and adjacent portions of the metal enclosure and the dissipative material is such as to define by analogy a transmission line with a lossy characteristic impedance, suitably less than 50 ohms.
  • This invention relates to a magnetron filter box and, more particularly, to a dissipative filter which is adapted to be used in conjunction with the filament leads of a magnetron.
  • Microwave vacuum tubes have heretofore been used as generators of microwave frequency energy, microwave sources or, as variously termed, microwave oscillators, and as such are found in common use in many electronic systems.
  • One such microwave tube is the magnetron.
  • the magnetron is, essentially, a selfcontained device in that the elements which cooperate to generate the microwave frequency energy are internal of the envelope. Terminals for connection of various electrical circuitry, including filament terminals, which permit current to be applied to the magnetron filaments, a cathode terminal, an anode terminal, and an output terminal or window are provided outside the tube envelope.
  • the magnetron In magnetrons, as with all utilitarian devices, there is always some degree of imperfection, however slight, which requires correction, compensation, minimization, or adjustment.
  • the magnetron by design provides the predetermined microwave frequency at. the designed power level.
  • spurious there are in fact other frequencies generated in varying degrees in varying levels, usually substantially less than the predominating output signal, such as harmonics of the fundamental frequency, and these signals may be termed spurious.” Included in this definition of spurious signals are any portions. of the fundamental frequency which leak out through other than the output window.
  • spurious signals in practice have either been so small as to be disregarded or were reduced to acceptable levels by conventional electrical filters, electrical devices which filter out or eliminate, ideally, the undesired spurious signals.
  • the magnetron has found a prime commercial application as the source of microwave energy used in microwave cooking appliances or ovens. And it is in connection with this appliance-that the magnetron and spurious signals is next considered as background of my invention.
  • the microwave oven provides the means by which one can cook or heat food by exposure to microwave radiation. In this manner food is heated or cooked very, very rapidly in comparison to cookingwith conventional ovens and such a decrease in cooking time is an advantage and represents a significant convenience for many people.
  • microwave radiation is of utility in cooking food, it is not to be exposed to humans or interfere with other electronic equipment in any significant degree.
  • the Federal'Communications Commission another Government agency, prescribes and allocates the frequencies which may be used for various purposes and has assigned the frequency of 2,450 MHz for microwave cooking.
  • the FCC requires the radiating unit to be of such a construction that intensity of radiation leakage at frequencies outside of a percent bandwidth of the assigned frequency range of 2,400 to 2,500 MHz must be less than 25 microvolts per meter measured at a distance 'of1000 feet per 500 watts of output.
  • the purpose of this limit is to prevent signals from the microwave oven from interfering with other forms of radio communications and television.
  • the filament terminals on the magnetron physically appear as bands of conductive material on a stemlike projection at one end of the magnetron.
  • the stem is actually divided into'electrically insulated parts separated by aluminum oxide, an insulating material, with the tip of the stem comprising a pinched-off copper tube.
  • This stem end of the tube was inserted within or surrounded by a large metal or large shielding enclosure referredto as the choke box or magnetron filter box, and this latter unit'was added during assembly of the magnetron into the equipment.
  • a large metal or large shielding enclosure referredto as the choke box or magnetron filter box
  • the openings in the enclosure are, however, of such dimension as to prevent the passage of any spurious signals above a predetermined intensity from the vicinityof the cathode stem.
  • the power supply leads including the high voltage cathode supply and the two leads through which filament current was coupled to thefilament ter-' such sources considered, the normal level of spurious radiation in present ovens is below the FCC limits.
  • a second source of spurious signals are subharmoriics. These are microwave-signals of some submultiple 'of the fundamental frequency of 2,450 MHz which are inherently generated in the tube but in very, very low' levels. A prime objection to such subharrnonic signals is that they may fall within the television frequencies and thus could potentially interfere with normal television reception during operation of the magnetron.
  • the filter box typically included wire inductors and capacitors.
  • the inductors were placed in series with the respective filament leads and the capacitors were placed between a filament lead and electrical ground to form a low pass filter.
  • Such a filter prevented beyond permissible limits any high frequency signals which might leak from the cathode to the filament terminals from traveling along the electrical leads to the outside of the oven enclosure, and the capacitors served to shortcircuit to ground as much high frequency energy as was possible.
  • beads of lossy" or dissipative microwave material such as ferrites were included in such a filter box to positively absorb and dissipate any microwave energy in that vicinity. While such constructions proved acceptable in the past, costs must be reduced and the recent reduction in level of permissible radiation leakage requires reevaluation of design and manufacturing procedures.
  • a third form of spurious signal derives from the multiplicity of resonant modes of the multi-segment anode found withinthe magnetron tube. If the anode has N resonators there will be N resonant-modes of the first order, second order, etc. Since the normal mode of operation, called 1' mode, has been optimized for impedance all other signals are comparatively lower. Since these other resonant modes will always be outside of the allotted frequency range band allotted fro microwave cooking and heating, care must be exer- I cised to assure that energy produced and radiated is less than the permissible level.
  • a fourth form of spurious signal derives from an electronic interaction between the impedances associated with the normal 41" mode and unintended systematic impedances.
  • signals if generated, are within 2,415 and 2,485 MHz where their magnitude can exceed 25 uv/meter, as described above.
  • At least two elongated electrical conductors are spaced from one another and have adjacent end portions adapted for connection to filament terminals of a magnetron and form a portion of the electrical path by which filament current is supplied to such magnetron.
  • Microwave dissipative material is located along the length and substantially surrounds the two conductors.
  • a microwave cavity comprising metal walls surrounds and contains within the loss material and underlying conductor portion, the conductor ends and the magnetron filament terminals.
  • an opening is provided in this metal cavity into which a magnetron stern portion containing the filament and high voltage terminals can bev inserted for connection to the respective end portions of said electrical conductors and a passage is provided in a remote end portion of the cavityto permit suitable connections to be made with said conductors.
  • the microwave cavity is of a low Q factor, suitably less than 100.
  • the ratio of the volume defined by the microwave cavity to the volume of the loss material is a number of fraction greater than I and lesser, approximately, than 20.
  • the outer cavity walls and the elongated conductive wires and attached loss material are considered analogous to a coaxial transmission line and the geometry of such line is defined to have a characteristic impedance Z, preferably less than 50 ohms.
  • one wall of the microwave cavity may comprise the flat pole piece section of the magnetron.
  • FIG. 6 illustrates a top view of another embodiment of the invention with the upper container wall removed;
  • FIG. 7 and 8 illustrate side and end views of the embodiment of FIG. 6;
  • FIG. 9 illustrates still another embodiment of the invention.
  • FIG. 10a represents in cross section the conductors and loss material of FIG. 9.
  • FIG. 10b represents a modified form of the conductors and loss material suitable for the embodiment of FIG. 9.
  • FIG. 1 illustrates, symbolically, the elements of my invention in a magnetron filter box and its relationship to a magnetron, symbolically illustrated, used in microwave oven.
  • the magnetron is of the type L- 5260A sold by Litton Industries, Electron Tube Division, illustrated in greater detail in U.S. Pat. No. D- 212,758 and U.S. Pat. No. 3,493,810.
  • the magnetron includes a body portion I, typically a hollow copper cylinder, containing therewithin in a vacuum the elements of the magnetron that are necessary for the generation of microwave energy including cathode, anode, filament, and magnetic pole piece extensions, which details are not illustrated or otherwise explained since they form no part of the instant invention and are available elsewhere in the prior art.
  • a body portion I typically a hollow copper cylinder, containing therewithin in a vacuum the elements of the magnetron that are necessary for the generation of microwave energy including cathode, anode, filament, and magnetic pole piece extensions, which details are not illustrated or otherwise explained since they form no part of the instant invention and are available elsewhere in the prior art.
  • window 3 At one end of the magnetron body is an output terminal of window 3 which is the exit for the microwave energy generated within body 1.
  • a stem portion 5 extends from the body 1 and includes spaced metal portions or terminals 7 and 9 which internally complete a circuit to the magnetron filament winding.
  • the terminals are insulated from one
  • Both stem 5 and window 3 protrude through openings provided in pole pieces 13 and 15.
  • the pole pieces are of a flat rectangular shape and consist of ferromagnetic material, typically annealed iron, and function as part of the magnetic circuit necessary to the operation of the magnetron.
  • a first permanent magnet 17 is located between and at one end of pole pieces 13 and 15, and a like second permanent magnet 19 is located at the left end and between the same pole pieces. Both magnet 17 and magnet 19 have their North Poles facing pole piece 13.
  • the magnets provide the magnetic flux which is carried through the magnetic path formed by the pole pieces and by means of magnetic material connected at the front and back ends of magnetron body 1', and internal pole pieces (not illustrated) present the magnetic flux internally of the tube where such forms a necessary ingredient to the generation of microwave energy.
  • the horizontal lines 21 are symbolic of the metal, suitably aluminum, cooling fins which are stacked in between the pole pieces in a heat conducting relationship with the body 1.
  • the cooling fins contain suitable openings to permit them'to be fitted over the magnetron body 1 and magnets 17 and 19. Obviously in the variation of the magnetron illustrated in U.S. Pat. No. D-2l8,l69 the cooling fins would be arranged vertically and radially outward from body portion 1.
  • a pair of elongated electrical conductors or wires 31 and 33 are illustrated spaced from one another above pole piece 13.
  • Electrical conductors 31 and 33 include respective end portions 35 and 37 located proximate one another and connected, respectively, to filament terminals 7 and 9. These conductors extend through passages in and support three bodies of a dissipative or loss material 39. The passages, not Clearly illustrated in 1 this figure, permit the loss material to be mounted so that it surrounds all, portions of each conductor and at the same time serves to maintain the predetermined spacing between conductors 31 and 33.
  • Dashed line- 41 represents the walls of a compact metal container which encloses the ferrite material and a portion of the wires 31 and 33 including the end portions 35 and 37 thereof.
  • Thecontainer covers, also, and
  • one wall of the metal container 41 is effectively formed by the flat surface of pole piece 13.
  • the relationship between the metal, can or cover and the dissipative material will be discussed hereinafter in greater detail.
  • Loss material in addition to 39 is included in the metal cover.
  • An additional slab of microwave loss material 40 is attached to an end wall of the container.
  • An insulator 43 is inserted in a passage in an end wall of the container.
  • the insulator contains two passages spaced from one another through which wires 31 and 33 extend, and the insulator serves to prevent the wires from contacting the metal walls of container 41.
  • the particular conductors 31 and 33 need not be made so long as to extend beyond the confines of container 41 but instead may he -terminated at a socket fixed at the end wall.
  • the extension of electrical circuitry would require theinclusion of a plug fitted to be received with such a socket so as to permit anextension of the electricalpath through the containers beyond the walls of container 41 to the appropriate source of filament current.
  • the magnetron filter box is formed in a small and convenient package. suitably mounted integral with the magnetron.
  • the magnetron filter box is formed in a small and convenient package. suitably mounted integral with the magnetron.
  • FIG. 2 The top view of the preferred embodiment of the magnetron filter box is illustrated in FIG. 2 with a top wall or sideremoved inorder to provide better illustration of the contentsrA container or box which forms a microwave cavity is of an elongated narrow construction and is formed of metal, suitably aluminum or stainless steel.
  • This includes a pair of end walls 50 and 51, a front wall 53,'a back wall 54, a bottom wall 57 and a top wall (removed 55 in FIG. 3).
  • End wall 51 includes a v passage in which is mounted an insulator, 43 in FIG. 1.
  • Conductor 33 is mounted spaced from and generally parallel with the first conductor 31.
  • Conductor 33 includes a front end portion 37 proximate end portion 35 of conductor 31.
  • conductors 31 and 33 used are Teflon insulated, as made by Gore Industries, to eliminate corona. End portions'35 and 37 are bent so as to engage or contact satisfactorily the filament ter- I minals of the magnetron stem, represented by the dashed lines 9 and 7.
  • conductors 31 and 33 are of such a length as to extend through wall 51 and the insulator 43, mounted in wall 51, so that they are maintained spaced at thatend and insulated from electrical contact with the metal container walls.
  • Beads 39a, 39b and 390, of microwave dissipative or loss material, suitably ferrite, are mounted on conductors 31 and 33 along the straight elongated portion thereof within the metal container.
  • Each of the ferrite beads is a standard material,- usually grade 9 or 11, and has an elliptical cylindrical geometry and the consistency of a solid sintered pressed powder body.
  • Each of the beads has two spaced passages therethrough through which conductors 31 and 33 extend. In this way the conductors 31 and 33 support the ferrite beads and, in turn the ferrite beads assist to maintain the conductors spaced apart.
  • the ferrite A sheath 4 2 of heat shrinkable tubing suitably irradiated polyvinyl tubing, such as that sold by Raychem Company, which may include additional loss material, covers the beads 39a, 39b and 39c.
  • cover tubing is represented solely by dashed lines.
  • a standard size slab of ferrite microwave loss material 38 is attached to end wall 50, suitably with epoxy.
  • Bottom wall 57 represented by a dashed line in FIG. 3, of the filter box. in the preferred embodiment is in fact a portion-of the flat iron pole piece of the magnetron, such as illustrated in FIG. 1.
  • An opening 59 represents the opening in the pole piece through which the magnetron stern containing'the filament terminals and cathode terminals extends.
  • the side walls 50, 51, 53 and 54 are simply joined to the metal pole piece in a manner which eliminates any gaps or vcracks therebetween. This is suitably accomplished by welding or by electrically conductive epoxy material.
  • the magnetron pole piece thus serves to provide an electrically conductive body or wall to the metal container with an opening adapted to receive the end of the magnetron.
  • a'metal wall can be provided to close the bottom of the container before the box is placed atop the magnetron pole piece.
  • a suitable opening or passage such as 59 would be formed at the location in the figure to permit the insertion therethrough of the magnetronstem.
  • the bottom wall is fastened to the magnetron pole piece and the pole piece serves only to support the filter and, eliminates its function as an ele.ctrically conductive boundary.
  • FIG. 3 illustrates the filter boxfrom one side facing wall 53 but with side wall 53 and attached ferrite removed, the embodiment of FIG. 2.
  • the conductors are also shown extending through the ferrite beads 39a, 39b and 390, and the ferrite beads are enclosed in tubing 42.
  • ferrite slab 38 is shown attached to the end wall 50, and air openings 56 are visible in back wall 54.
  • Bottom wall 57 in this view is represented by dashed lines since in the preferred embodiment the electrically conductive wall is formed by a portion of the surface of the pole piece of the magnetron and in the alternative construction, discussed in connection with FIG. 2, may be a separate metal wall.
  • the stem portion of the magnetron is represented by the dashed lines and includes a pinch off tube and filament terminals 7 and 9 shown extendingthrough the opening59 in this bottom wall.
  • the top wall 55 of the container includes a raised portion, bulge, or dome 60 at the end of the container adjacent end wall 50 and over the opening 59.
  • This raised portion forms a dome over the end of the stem of the magnetron and serves to maintain a proper insulating space between the metal parts and the end of the magnetron stem while otherwise permitting a smaller dimension or height to the container elsewhere than at this location, thus reducing cavity Q.
  • the dome portion 60 of top wall 55 includes several holes or passages therethrough, such as 61a, 61b and 610, visible in this figure. These openings are generally less than 1/ 10th of the wavelength of the fundamental microwave frequency of 2,450 MHz so as to preclude any leakage of microwave frequency therethrough and at the same time permitting a passage for air to cool the magnetron stem.
  • top wall 55 and bottom wall 57 are enlarged at the right hand ends in FIGS. 2 and 3, primarily to make the container large enough in volume at that end to receive the stem of the magnetron and allow sufficient clearance therebetween so as to provide appropriate high voltage insulation and prevent corona or high voltage breakdown therebetween.
  • the width of the wall is significantly more narrow so as to provide a slender appearance, preferably with a slight spacing between the end walls and the ferrite beads.
  • Overall the top view of the top and bottom walls is seen to resemble in shape paddles with handles.
  • the front and back walls, 53 and 54 are bent in shape so as to conform to edge of the top and bottom walls.
  • End front wall 50 is rectangular in shape but of a larger area than the other end wall 51.
  • FIG. 4 The end view of 'FIG. 4 illustrates the filter box with end wall 51 and insulator 43 removed. Viewing the filter box from that end, electrical conductors 31 and 33 are visible and extend through passages in ferrite bead 39a. For clarity, sheath tubing 42 and ferrite slab 38 illustrated in FIGS. 2 and 3 is omitted. Top wall 55 is seen to include the dome portion 60 and in this view an additional hole, 61d, is visible, in addition to the holes 61a and 61b visible from theview of FIG. 3.
  • the metal walls of the container form essentially a closed microwave cavity in which any microwave energy is confined.
  • the microwave cavity in the filter box of the invention is of a low Q, 0 representing the quality factor of the cavity, and thus is considerably smaller in size than the shielding cavities of the prior art constructions.
  • the ferrite material installed within the cavity occupies a predetermined volume, represented by V,.
  • the volume of the cavity is of a predetermined volume, represented as V,.
  • the relationship or ratio between V and V, or V /V is such as to be a number, including any fraction thereof, approximately less than 20 andat least slightly greater than the number 1 (one).
  • FIGS. 2 through 4 A second factor used to determine the relative geometry and actual dimension of the metal container and ferrite of the preferred embodiment, FIGS. 2 through 4, is best illustrated in connection with FIG. 4.
  • an approximate characteristic impedance 2 can be assigned.
  • this characteristic impedance is as low as feasible, preferably less than 50 ohms.
  • An approximation in obtaining such impedance is that there is a mean perimeter such as represented by the dashed lines P in FIG. 4.
  • This means perimeter is the average between the perimeter of the ferrite material and the perimeter of the inner surface of the metal container.
  • a mean or average spacing s between the ferrite material and inner surface of the walls of the metal container is defined, disregarding the end ferrite slab 38 which is not a part of the cross-section. Accordingly, the impedance characteristic Z is approximated as 377 (S P). It is noted that in the instance where the metal container is formed such as to directly contact theenclosed ferrite material, then S reduces to approximately 0 and the perimeters of the ferrite, the container, and the mean perimeter P approach a common value for which there is no limiting impedance 2,. The addition of ferrite such as 38 at the end wall 50 reduces further 0,, or quality factor of the entire enclosed cavity.
  • top and bottom walls 55 and 57 of the filter box are 1% inches wide; at their narrow end these walls are /8 inch wide.
  • transition between wide to narrow width occurs at a location 1% inches from either end, and the length of the top and side walls is 3 inch overall.
  • the height of the front and back walls is of an inch.
  • one prior art construction had a filter box 1% inches deep by 4 inches in width and 5 inches in length.
  • Such prior art filter box contained four 1 inch balun coils and two filter capacitors.
  • the costs were high and the results were barely equivalent to that obtained in the filter box of the invention.
  • the filter box was 1% inches deep by 4 inches in length and 3 inches in width, and incorporated therewithin inductive components. Not only is this of a larger size and of a relatively more expensive cost of manufacture, but the results were poorer by some 20 dbs, which increased the possibility of television interference and required the power supply enclosure to be very tight.
  • Head 39 cross-section is /16" X 9/16" so that its perimeter, P,, is [5/16 1r 5/16) I X 2] which reduces to 1,605 inches
  • the height of the box is inches and its width is "/a of. an inch so its perimeter, P,,, is "/s "/a] or'3.25 inches.
  • the volume, V of the enclosed ferrite material is first determined and equals the sum of volumes of the three ferrites' 39a,
  • a suitable source of filament current is supplied to electrical leads 3] and 33 and the latter conductors carry this current to the filament terminals of the magnetron.
  • any microwave frequency energy be coupled from the cathode terminal into the stem area it is ideally absorbed by the ferrite material 39a through 39c and 38.
  • the ferrite material thus serves to eliminate any high frequency energy which couples from the cathode to the filament leads 31 and ,33.
  • the entire combination of metal cavity and ferrite material constructed according to the preceding teachings present a load to both the fundamentaL'to any. harmonics of the fundamental, and to any subharmonics of the fundamental energy. This essentially loads down the tube and inasmuch as the characteristic impedance Z, of the unit considered as a transmission line is low,'.suitably below 50 ohms, any
  • the volume of the container, V is according to the exemplary dimensions previously I V,,V, z 2.657/O.470 5.6
  • the measured attenuation for this unit was 60 dbm and the measured attenuation for the FCC limit on the same scale was 54 dbm.
  • the exploded view of the filter box illustrated in FIG. Sillustrates one method of assembly of the filter box of FIGS. 2-4.
  • the insulation coated electrical conductors 31 and 33 are relatively rigid and their end portions 35 and 37 may be first formed to the desired shape.
  • the ferrite beads 39a, 39b, and 39s, are thereupon slipped over the insulated conductors.
  • the ferrite slab 38 is cemented in place to the end wall of the can or metal container.
  • the heat shrinkable tubing is placed over the ferrite beads and shrunk in place to I form a good fit.
  • the ends'of the wires 35 and 37 are attached to the ends of the magnetron, suitably by soldering, to form a firm electrical path and mechanical joint therewith.
  • the can is moved down and the wires 31 and 33 slipped into the passage in the can and the can is then placed over the entire assemblyand in abutment with the pole piece, not illustrated, of the magnetron. Subsequently, insulator 43 is slipped over the ends of electrical leads 3] and 33 and pushed into position within the opening in the can. Subsequently the can is welded to the pole piece of the magnetron to form a complete unit.
  • FIGS. 6, 7 and 8 Another embodiment of the invention is illustrated in FIGS. 6, 7 and 8 showing the magnetron filter box from various views.
  • elements in FIGS. 6, 7, and'8, which find a corresponding element in the preceding'embodiment of the invention of FIGS. 2 through 5, are similarly identified with a corresponding numeral which is primed.
  • each of those'elements has been discussed in connection with the preceding preferred embodiment of the invention and have the same'function and purpose, it would appear-redundant to repeat in detail that description which is already in the readers understanding.
  • the container walls are essentially rectangular in shape. Accordingly, that portion of the metal container surrounding the ferrite beads, 39a through 39c, is spaced fromthose beads by a slightly larger distance and in this forms a basic transmission line, analogously, of a lossy characteristic impedance Z, slightly larger than that of the embodiment of FIGS. 2-4.
  • slabs of ferrite material, 40a, 40b, 40c and 40d are installed within the metal container and provide additional loss material. Ferrite slabs 40a and 40b are cemented or epoxied to front walls 53', and ferrite slabs 40c and 40d are cemented or epoxied to back wall 54'.
  • the length overall is 3 inches and the height is it of an inch.
  • the results obtained with this embodiment are comparable with that of the preferred embodiment although numerically a larger number of elements are required and the overall volume of the box is larger with this construction.
  • the ferrite pieces 40a, 40b, 40cand 40d located on the walls 53 and 54' are approximately 5/16 inches in thickness while the dimensions of ferrite beads 39 are the same as in the preceding example.
  • the wall separation is actually greater than in the preceding example, and is 1 inches in width, the distance or spacing is the same.
  • LS" 2 (5/ I6) of an inch.
  • the 0, in this example is determined as in the preceding case: V, volume of 7 ferrite beads 0.740 cubic inches. V 3" X 1%" X 54" 3.37 cubic inches. Thus Q V lV, 3.37/0.740 4.6. The measured value of attenuation was 59 dbm.
  • FIG. 9 represents a special case I stantially the same as the inner perimeter of the metal cavity.
  • This embodiment includes the two spaced electrical conductors 61 and 63 which are insulated from one another and are adapted to be connected to a suitable supply of filament current and high voltage.
  • the conductors are first surrounded or packed with a lossy dielectric material such as Eccosorb CR8 or FDS, illustrated as element 65.
  • the lossy dielectric is covered by a metal wrapping 67 which may be in the form of a metal tape.
  • a metal container 69 is fitted over the ends of conductors 61 and 63and in electrical contact with the metal tape 67.
  • Metal container 69 forms a dome which covers the stem section of the magnetron and serves a shielding function.
  • the magnetron filter box is mounted on a section of the pole .piece 71 of the magnetron, the pole piece serving as one of the electrically conductive walls of the filter box in the cavity otherwise formed by the domelike member 69.
  • this wall effectively has a passage through which the magnetron stem portion is inserted and introduced within the filter box.
  • FIG. 10a shows in cross-section a portion of the filter box which includes the conductors 61 and 63, the packing 65 of electrically lossy dielectric material, and the underlying layer of metal tape 67.
  • FIG. 10b shows in cross-section a portion of the filter box which includes the conductors 61 and 63, the packing 65 of electrically lossy dielectric material, and the underlying layer of metal tape 67.
  • FIG. 10b A modification of the foregoing is illustrated in FIG. 10b in which conductors 61' and 63' are first ens
  • this material is in turn covered by a heat shrinkable tube consisting of lossy material such as ferrite powder or both, within a large shielding metal enclosure, but no attempt was made to integrate the shielding enclosure with the dissipative networks to form a compact and more efficient magnetron filter box that comprised a fewer number of lower cost parts;
  • the shielding is integrated into the simple compact arrangement of the I drawings with the dissipative material so as to form structure analogous both to a low Q microwave cavity and a lossy transmission line, and in this more efficiently eliminates the leakage of the fundamental frequency, leakage of subharmonics, and any fast modes which in the prior art structures were capable of circulating between the filament lines and the large cavity.
  • a combination of a magnetron and magnetron filter box comprising:
  • a magnetron which includes a body portion, said body portion having an elongated stemlike end, and said stemlike end containing cathode and filament terminals, a pole piece of ferrous material, said pole piece containing an opening therethrough, said body portion positioned with said stemlike end extending through said opening and projecting outward from the surface of said pole piece, and means preventing microwave energy leakage through said pole piece opening between said body portion and said pole piece;
  • first and second elongated electrical conductor means for carrying electrical filament current and a high cathode electrical voltage, said electrical conductor means being insulated electrically from one another and having first respective end portions adjacent one another and each connected to a respective one of the cathode and filament terminals of said microwave tube;
  • microwave dissipative material for dissipating microwave energy and comprising a predetermined volume, V, said microwave dissipative material surrounding said first and second conductor means and extending therealong a major portion of the length thereof each to a point proximate said end portions of said conductor means;
  • microwave cavity means defining a predetermined region of volume V, for confining microwave energy therewithin, said cavity comprising walls of electrically conductive material and including as one wall thereof a portion of said pole piece surface, said microwave cavity including therein said electrical conductor means, said stemlike ends of said magnetron body and said microwave dissipative material;
  • a predetermined impedance Z is defined as approximately equal to 377 (S P) ohms, wherein said relationship of S and P being such that said Z is equal to or less than 50 ohms, where S is defined as an average spacing distance between the outer surface of said dissipative material and the inner wall surfaces of said cavity means and where P is defined as amean perimeter length about the space between said dissipative material and said cavity walls,
  • the invention as defined in claim 1 further com-' prising a slab of microwave dissipative material located on a wall of said microwave cavity at a location adjacent said st'emlike end of said magnetron body portion.
  • the invention as defined in claim 2 further comprising a plurality of small holes less than 1/ th A in diameter located, in at least some walls of said microwave cavity to provide a path out of and into said cavity for air.
  • An; electromagnetic energy filter means comprismg: g
  • first and second elongated electrical conductor means forcarrying electrical filament current and a high cathode electrical voltage, said electrical conductor means being spaced and having end portions adjacent one another for connection to the respective terminals of a microwave tube; microwave dissipative 7 material for dissipating microwave energy, said microwave dissipative material surrounding said first and second conduc-- tor means and extending along a predetermined length thereof upto 'a point proximate said end portions of said conductor means, said dissipative 7 material further comprising a predetermined volume V,;
  • microwave cavity means for confining microwave energy within a predetermined region of volume V', said cavity comprising walls of electrically conductive material, said cavity means including therewithin said microwave dissipative material, and said first and second conductor means, including said end portion of each said conductor means;
  • the ratio of cavity. volume, V,,, to dissipative material volume,,V, comprises a quantity equal to or less than 100 to define a low Q cavity
  • first opening in a first wall of said cavity means, said first opening being-of sufficient size to permit positioning within saidcavity means of a terminal socket end of a microwave tube for permitting connection within said cavity means between terminals on said socket and the corresponding end portions of said conductor means and to permit I said microwave tube to close said first opening;
  • an average spacing'distance is defined between the outer surface of said dissipative material and an inner surface of said cavity means which comprises a predetermined lengthS, and wherein a mean perimeter length, P, is defined about the space between said. dissipative material and said cavity walls, and wherein a predetermined impedance, Z,, is defined as approximately equal to the quantity 377 8/? ohms, said relationship of S and P being such that said Z, is equal to or less than ohms.
  • said cavity means comprises the metal box open along one side, and a metal pole piece of a microwave tube closes said open side to complete said metal cavity, and wherein said tube socket extends through said pole piece into said cavity,
  • dissipative material further comprises a plurality of discrete portions arranged in side by side relationship
  • each of' said portions having a passage therethrough and wherein said conductor extends through said passages for supporting said portions, and a single sheath of heat shrinkable polyvinyl tubing material extending over and covering all said portions to retain said discreet-portions in said side by side relationship.
  • a magnetron microwave tube for generating microwave frequency energy of a wavelength A; said magnetron microwave tube including a tube body, microwave passage means for permitting passage of generated microwave energy from said tube bodyto a load, and filament and high voltage terminal means'for coupling filament current and high voltage to within said tube body; low Q microwave cavity of a predetermined volume, V,, covering saidterminal means, said low Q microwave cavity including therewithin elongated electrical conductor means adapted for connection to an external source of filament current and high voltage for providing an electrically conductive path to said'terminals, and microwave dissipative material of a predetermined volume, V surrounding said conductor means along a substantial portion of the length of said conductor means for dissipating microwave energy exiting from said magnetron tube via said terminals, and wherein the outer surface of said-dissipative material'and the inner surface of said microwave cavity is separated by an average spacing distance of a predetermined length, S, and wherein a mean perimeter length, P, is defined about said space between said dissi
  • dissipative material further comprises a'plurality of discreet portions arranged in side by side relationship
  • each of said portions having a passage therethrough and wherein said conductor extends through said passages for supporting said portions, and a single sheath of heat shrinkable polyvinyl tubing material extending over and covering all said portions to retain said discreet portions in said side by side relationship.
  • microwave cavity means includes a plurality of openings through the walls thereof to permit passage of cooling air into said cavity, each of said passages having as its longest dimension a length less than 1/1 0th A.

Landscapes

  • Constitution Of High-Frequency Heating (AREA)
  • Microwave Tubes (AREA)
  • Control Of High-Frequency Heating Circuits (AREA)
US00165113A 1971-07-22 1971-07-22 Magnetron filter box Expired - Lifetime US3727098A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US00165113A US3727098A (en) 1971-07-22 1971-07-22 Magnetron filter box
DE19722229743 DE2229743B2 (de) 1971-07-22 1972-06-19 Mikrowellendichtung fuer eine magnetronanordnung
JP7272662A JPS5412034B1 (enrdf_load_stackoverflow) 1971-07-22 1972-07-21

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US00165113A US3727098A (en) 1971-07-22 1971-07-22 Magnetron filter box

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US3727098A true US3727098A (en) 1973-04-10

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US (1) US3727098A (enrdf_load_stackoverflow)
JP (1) JPS5412034B1 (enrdf_load_stackoverflow)
DE (1) DE2229743B2 (enrdf_load_stackoverflow)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3859558A (en) * 1972-09-01 1975-01-07 Hitachi Ltd Magnetron having spurious signal suppression means
JPS50104559U (enrdf_load_stackoverflow) * 1974-01-31 1975-08-28
US3922612A (en) * 1972-06-30 1975-11-25 Tokyo Shibaura Electric Co Magnetron device
US4163175A (en) * 1977-01-21 1979-07-31 Tokyo Shibaura Electric Co., Ltd. Magnetron for which leakage of H.F. noise is minimized
US4164685A (en) * 1976-09-14 1979-08-14 Tokyo Shibaura Electric Co., Ltd. Magnetron device
EP0141833A4 (en) * 1983-05-05 1985-08-20 Commw Of Australia TRANSMISSION LINES.
US5149929A (en) * 1990-03-30 1992-09-22 Sharp Kabushiki Kaisha Microwave oven with inverter controlled power source
EP0658913A1 (de) * 1993-12-18 1995-06-21 Philips Patentverwaltung GmbH Elektronenstrahlröhre mit einem Eingangsresonatorhohlraum
US5977713A (en) * 1996-03-27 1999-11-02 Matsushita Electronics Corporation High voltage noise filter and magnetron device using it
USD446499S1 (en) 2000-07-17 2001-08-14 Apple Computer, Inc. Power amplifier
USD588545S1 (en) 2007-01-05 2009-03-17 Apple Inc. Connectors
US9019044B2 (en) 2011-02-11 2015-04-28 E2V Technologies (Uk) Limited Filter for a magnetron power supply lead

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Publication number Priority date Publication date Assignee Title
US3020447A (en) * 1958-10-27 1962-02-06 Raytheon Co Magnetron systems
US3458753A (en) * 1965-08-30 1969-07-29 Gen Electric Crossed-field discharge devices and couplers therefor and oscillators and amplifiers incorporating the same
US3531613A (en) * 1968-08-22 1970-09-29 Raytheon Co Capacitive filter for suppression of spurious electrical radiation
US3543082A (en) * 1968-08-23 1970-11-24 Technology Instr Corp Of Calif Magnetron
US3551735A (en) * 1965-08-30 1970-12-29 Gen Electric Crossed-field discharge devices and oscillators and amplifiers incorporating the same
US3551858A (en) * 1967-06-14 1970-12-29 Ibm High current feed-through filter system

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3020447A (en) * 1958-10-27 1962-02-06 Raytheon Co Magnetron systems
US3458753A (en) * 1965-08-30 1969-07-29 Gen Electric Crossed-field discharge devices and couplers therefor and oscillators and amplifiers incorporating the same
US3551735A (en) * 1965-08-30 1970-12-29 Gen Electric Crossed-field discharge devices and oscillators and amplifiers incorporating the same
US3551858A (en) * 1967-06-14 1970-12-29 Ibm High current feed-through filter system
US3531613A (en) * 1968-08-22 1970-09-29 Raytheon Co Capacitive filter for suppression of spurious electrical radiation
US3543082A (en) * 1968-08-23 1970-11-24 Technology Instr Corp Of Calif Magnetron

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3922612A (en) * 1972-06-30 1975-11-25 Tokyo Shibaura Electric Co Magnetron device
US3859558A (en) * 1972-09-01 1975-01-07 Hitachi Ltd Magnetron having spurious signal suppression means
JPS50104559U (enrdf_load_stackoverflow) * 1974-01-31 1975-08-28
US4164685A (en) * 1976-09-14 1979-08-14 Tokyo Shibaura Electric Co., Ltd. Magnetron device
US4163175A (en) * 1977-01-21 1979-07-31 Tokyo Shibaura Electric Co., Ltd. Magnetron for which leakage of H.F. noise is minimized
EP0141833A4 (en) * 1983-05-05 1985-08-20 Commw Of Australia TRANSMISSION LINES.
US5149929A (en) * 1990-03-30 1992-09-22 Sharp Kabushiki Kaisha Microwave oven with inverter controlled power source
EP0658913A1 (de) * 1993-12-18 1995-06-21 Philips Patentverwaltung GmbH Elektronenstrahlröhre mit einem Eingangsresonatorhohlraum
US6304033B1 (en) 1993-12-18 2001-10-16 U.S. Philips Corporation Electron beam tube having a DC power lead with a damping structure
US5977713A (en) * 1996-03-27 1999-11-02 Matsushita Electronics Corporation High voltage noise filter and magnetron device using it
USD446499S1 (en) 2000-07-17 2001-08-14 Apple Computer, Inc. Power amplifier
USD588545S1 (en) 2007-01-05 2009-03-17 Apple Inc. Connectors
US9019044B2 (en) 2011-02-11 2015-04-28 E2V Technologies (Uk) Limited Filter for a magnetron power supply lead

Also Published As

Publication number Publication date
DE2229743A1 (de) 1973-02-15
DE2229743B2 (de) 1977-09-15
JPS5412034B1 (enrdf_load_stackoverflow) 1979-05-19

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