US3048802A - Microwave cavity - Google Patents

Description

Aug. 7, 1962 E. J. JuRcY MICROWAVE CAVITY 2 Sheets-Sheet 1 Filed Feb. 8, 1961 INVENTOR EDWARD J. Juncv Z1!- Add Aug. 7, 1962 E. J. JURCY MICROWAVE CAVITY 2 Sheets-Sheet 2 Filed Feb. 8, 1961 bun.

INVENTOR. EDWARD J. Juacv United States Patent 3,048,802 MKCRGWAVE CAVllTY Edward J. Jurcy, Western Springs, lll., assignor, by mesne assignments, to Fidclitone Microwave Incorporated, Chicago, lit, a corporation of Illinois Filed Feb. 8, 1961, Ser. No. 87,892 4 Claims. ((11. 333-83) The present invention relates to microwave cavities and more particularly to an improved cavity capable of use with lighthouse type tubes for a number of dif ferent purposes in microwave equipment.

It is an object of the present invention to provide a cavity having improved electrical characteristics and which is so constructed that it can be manufactured at a fraction of the cost of conventional cavities. It is another object to provide a cavity which in spite of its light, compact construction is nevertheless stable electrically and mechanically, capable of resisting the severe shock and vibration, which may be encountered in rough field usage, without any change in frequency or operating characteristics. Since the cavities constitute the heart of any microwave apparatus, use of the present cavity enables the entire equipment to perform more consistently and reliably than has been possible heretofore. It is, in short, an object to provide a cavity which is especially suited for use in military and commercial communication systems where absolute reliability is required and where space and weight are at a premium.

It is another object to provide a cavity which can be easily fabricated and assembled and which is therefore ideally suited to quantity production runs. it is a related object to provide a cavity in which the component parts may be produced by such inherently inexpensive techniques as drawing, punching, spinning and the like, making it possible to employ semi-automated production facilities with a minimum of expenditure of manhours per unit. It is still another object to provide a cavity which is much simpler than conventional cavities intended for the same purpose, consisting of a minimum number of novel yet simply formed parts which are easily fitted together to form the completed unit.

It is a further object to provide a cavity which is flexible in application and which may be used as an oscillator, amplifier, multiplier or for other purpose over a wide range of frequency with provision for adjustment to an exact frequency and in which such parameters as class of operation, applied voltages, band width, input and output impedance and the like may be chosen or optimized with only minor and easily made modification including change of length, type of feed, and configuration of auxiliary elements such as skirts or the like. It is an object of the invention in this connection to provide a cavity which, for its size, has a maximum amount of internal space available for accommodation of skirts or other auxiliary elements. It is a related object to provide a cavity which, although specially well suited for use as a pulsed oscillator employing a grounded grid, grounded cathode, and grounded filament, is, nevertheless, capable of use with one or more of such electrodes ungrounded for other applications and depending upon the required circuit connections, the internal space being clear and uncluttered for interposition of insulated electrodes where required.

It is another object related to the above to provide an improved design of cavity in which a wide range of frequency and operating characteristics may be achieved using components of standard size and shape in various predetermined combinations, making it possible to extrapolate on known data in the design of a cavity for a new application and shortening the lead time required in "ice the production of the final unit to a period of days rather than a period of months after receiving the order.

It is a more specific object of the invention to provide a cavity which provides highly consistent results from unit to unit in spite of the minor variations in the physical size and shape, e.g., as regards eccentricity of the terminals of the lighthouse type tubes forming a part of the complete unit. It is also a specific object of the invention to provide a cavity which may readily be sealed at the factory following an optimizing adjustment, which is substantially tamper proof, but which may nevertheless be adjusted by the user within the specific frequency range for which the unit has been designed.

Other objects and advantages of the invention will become apparent upon reading the attached detailed description and upon reference to the drawings in which:

FIGURE 1 is a side view of a microwave cavity constructed in accordance with the present invention.

FIG. 2 is a longitudinal section of the cavity in FIG. 1.

FIG. 3 is a transverse section taken along the line 3-3 in FIG. 2.

FIG. 4 is a perspective showing the cathode pedestal employed in the construction of FIG. 1.

FIG. 5 is a fragmentary section of a modified cathode pedestal including a reversely bent skirt portion.

FIG. 6 is a fragmentary section showing the tube of FIG. 1 modified for bringing out an ungrounded grid connect-ion.

While the invention has been described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to the illustrated embodiment, but, on the contrary, it is intended to cover the various alternative and equivalent constructions falling within the spirit and scope of the appended claims.

Turning now to FIGS. 1 and 2 there is shown a cavity 10 for use in microwaves and systems. While the cavity which has been illustrated is particularly suitable for use as a pulsed oscillator, it will be apparent as the discussion proceeds that the cavity may be modified in certain minor respects to permit use as a C-W oscillator, amplifier, mixer or multiplier. The device is capable, with minor dimensional modification, of operating within a broad frequency spectrum, for example, within the range of 220 to 4,500 megacycles.

Where the cavity is employed as an oscillator, the output is taken from an output terminal 11. When the device is used as an amplifier or mixer an input terminal 12 (shown dotted) may be used.

The present cavity is particularly suited for use with a tube 20 of the so-called lighthouse type having an anode terminal 21, a grid flange 22, a cathode terminal 23, an outer filament terminal 24 and an inner filament terminal 25. The anode terminal 21, the cathode terminal 26, and the outer filament terminal 24 are of cylindrical shape and are concentric with the axis of the tube. Tubes of the type shown are per se well known to those skilled in the art; cross reference is, however, made to the technical literature describing the characteristics of General Electric GL-6442 Triode which may be considered as representative.

The present cavity in its simplest aspect may be con sidered to consist of two cups, an anode cup and a cathode cup, telescoped together to form a closed cylinder having substantially constant diameter. Turning attention to the anode cup 30, it is preferably of integral, drawn construction having a cylindrical sidewall 31 and an endwall 32. Mounted axially within the anode cup 34) is an anode pedestal 33 of hollow cylindrical shape having a mounting flange 34 at its base. For the purpose of securing the pedestal 33 to the bottom of the cup, a central post 35 is provided having a head 36 at its inner end dimensioned to fit snugly within the base of the pedestal. The head 36 is, moreover, peripherally dimpled or grooved as indicated at 37 so that the post and pedestal may be permanently locked together to form a single unit. If desired the two portions may be brazed or silver soldered. In order to insulate the pedestal from the anode cup a first insulating disc 38, which may be formed of mica or the like, is interposed between the flange 34 and the bottom of the cup. At the outside of the cup an insulating centering disc 39 is used formed of molded insulating material such as Teflon. Secured to the outer end of the post 35, for example, by means of a threaded connection, is a terminal 40 which is used to apply voltage to the tube anode.

For the purpose of making contact with the anode terminal 21, the cylindrical wall of the pedestal 3-3 has a series of integral contact fingers 41 which are punched or struck out from the wall, each finger being connected to the wall by an anchoring portion 42. The fingers are preferably elongated as shown in order to extend substantially the entire length of the anode terminal 21. The pedestal is preferably formed of springy good conducting material such as beryllium copper or Phosphor bronze so that each of the fingers 41 is springy and makes good contact with the surface of the terminal 21. In a practical case the fingers 41 may be approximately 7 inch in length, having a width of inch, and with about eight fingers being equally spaced about the periphery of the pedestal. It is found that this provides a good electrical connection, insures self centering of the anode within the pedestal, and yet permits the anode terminal to be slid easily in and out during assembly or when replacement of the tube becomes necessary.

Turning attention next to the opposite end of the structure a cathode cup 50 is provided having a wall 51 and bottom portion 52. The inside lip of the cathode cup 50 is provided with an annular barrier member 53 which is grooved about its inner edge to provide seat 54 for seating the grid flange of the tube. To hold the grid flange on the seat, a retaining ring 55 is used which overlies the grid flange and which is held in place on the barrier by means of suitable machine screws '56 equally spaced about the periphery. It is one of the novel features of the present construction that the barrier 53 is permanently secured to the lip of the cathode cup, for example, by providing an internal seat 57 and by spinning over the edge as indicated at 58 to provide a low resistance electrical connection and simplifying the construction. Moreover, the bottom portion 52 of the cup may be separate and similarly spun into place as indicated at 59. In short, then, the cathode cup in its preferred form, is in fact in the shape of a tube having annular end members spun in place to provide a high degree of rigidity.

In accordance with the present invention the cathode cup is provided with a central pedestal of generally cylindrical shape but having adjacent portions of different diameter each including integral, struck fingers for simultaneously engaging the cathode and filament terminals of the tube and with the pedestal being outwardly flanged to form a support forcoupling rods which extend through the barrier and into the chamber surrounding the anode terminal. In the present embodiment the cathode pedestalindicated at 60 includes an end portion 61 surrounding the filament terminal and an intermediate portion 62 surrounding the cathode terminal of the tube. Taking the base portion 61 by way of example it includes a plurality of resilient contacts in the form of integral fingers which are struck inwardly from the sidewall and each of which has an anchoring portion 64 to provide cantilever anchoring and with each finger extending generally parallel to the sidewall of the pedestal. As in the case of the anode pedestal 33, the cathode pedestal is preferably formed of springy good conducting metal about .020 inch in thickness and each finger is biased inwardly toward the engaged tube terminal. The

fingers are struck by providing a grooved die of cylindrical shape within the pedestal cooperating with an outside punch having a profile of the desired shape and with the pedestal being rotatably indexed between the punching strokes. In a practical case the fingers 63 may have the length of & inch and a width of about inch and a total number of eight may be evenly distributed about the periphery. A similar contact arrangement is employed at the intermediate portion 62 of the pedestal. Here it will be seen that the pedestal includes cathode contact fingers 65 struck out of the wall of the pedestal and each having a cantilever anchoring portion 66. The fingers in this position have a width of about inch with a total of twelve being used. The fingers are adjusted to have a radial interference fit on the order of .005 inch. It will be apparent that this contact arrangement produces high contact efficiency while occupying minimum space so that the pedestal can be made of minimum diameter. Moreover, since snug area contact is made with the tube terminals at regions which are substantially spaced from one another, as measured along the axis, the tube and pedestal together become a rigid unit and mutually reinforce one another.

In order to anchor the base of the pedestal to the bottom wall of the cathode cup, both electrically and mechanically, the opening in the base portion 52 of the cup has a diameter which substantially coincides with the outer diameter of the end of the pedestal. The joint, indicated at 76, may be staked inside and out as indicated at '71, 72, or, if desired, the base of the pedestal may simply be brazed or silver soldered in the member 52.

In order to provide the necessary inductance and capacity within the cathode cup as well as coupling to the anode cavity, the cathode pedestal 60 has an integral, outwardly extending flange 80 mounting coupling rods indicated at 81, 82, 83 (see FIG. 3) which project through the barrier 53, being insulated from the latter insulating sleeves 84 made of Teflon or the like. The rods are preferably secured to the flange by riveting as shown at 85. Since the rods are rigid with respect to the pedestal 60 and since they are snugly received in the barrier member 53, a firm tripod support is provided at the lefthand end of the pedestal. It will be apparent that the integrated pedestal assembly, shown in perspective in FIG. 4, forms a strong and firmly anchored unit which performs all of the supporting and contacting functions as well as establishing the operating characteristics of the cavity. The simple structure of FIG. 4 takes the place of the separate, inherently more delicate and expensive, parts required in prior devices.

For the purpose of making contact with the inner filament terminal 25, an insulating abutment 90 may be secured within the outer, projecting end of the pedestal and mounting a filament terminal 91 having spring contact means 92 at its inner end. Or, if desired, the insulating abutment may be omitted and the spring contact 92, connected to a wire lead, may simply be inserted into the end of the tube when the cavity is installed.

For securing together the anode cup 30 and the cathode cup 50 while providing adjustment of frequency to Within the desired range, the anode cup 30 is preferably provided with a cylindrical spring lip which is of slightly greater diameter than the remainder of the anode cup and which defines an internal seat 101. The lip 100 is preferably slotted as indicated at 102 for a portion of its length so that it forms a series of inwardly pressed fingers which frictionally engage the outer wall of the cathode cup 50. If desired the cathode cup 50 may be fully inserted into the receptacle thus formed in the anode cup, for seating of the cathode cup on the seat 101. However, the joint between the two cups permits approximate adjustment of frequency, the cups being either telescoped toward or away from one another to an adjusted position to change the effective length of the anode cavity.

Where cavities are manufactured in quantity for a particular frequency range, such frequency adjustment may be readily effected by simply inserting the assembly between the opposed faces of a dimension-adjusting jig following which the cups are pulled apart so that the ends thereof seat on the faces. The unit may be clamped in such adjusted position by means of an encircling clamp 105 having a clamping screw 106. Or, if desired to prevent tampering, the cups may be soldered together. While the relative position of the two cups serves to establish a nominal frequency, which is preferably the center of a desired frequency range, precise adjustment on both sides the nominal frequency may be brought about by an adjusting screw 110 which is threaded into a nut 111 which is silver soldered or otherwise secured to the wall of the anode cavity, such final adjustment being well within the skill of the art.

It is one of the features of the present device that because of the clean and uncluttered internal construction maximum space is available for auxiliary elements. Thus a folded skirt 120 of a desired dimension may be added to the flange 80 of the pedestal as shown in FIG. 5. Such skirt may simply be spun on the end of the flange 8i) and trimmed to length or, if desired, it may be formed of a separate length of tubing of the proper diameter and simply brazed to the outer edge of the flange 30 as, for example, along a joint 121. Where a skirt 120 is used the rods 81, 82, 83, instead of being riveted in place, may be notched at their ends as shown in FIG. 5 and brazed or silver soldered to the outer surface of the skirt.

While the construction has been directed toward use with a circuit requiring a grounded grid, it will be apparent that the invention is not necessarily limited thereto and suflicient space is available within the cathode chamber for achieving an insulated grid terminal. As shown in FIG. 6 the barrier member which contacts the grid flange may be formed of a shallow cup 130 having an annular portion 131 and an axially extending flang 132. Interposed between the flange 132 and the wall 51 of the cathode cup is a layer of insulation 133 which may be Teflon or the like. In order to maintain the barrier 130 positively positioned, the insulating material 133 may be channel shaped in cross section and may be held in place by ears 135 inwardly struck from the wall of the cathode cup. It will be noted that the "additional space taken up by insulating the barrier member to provide the ungrounded grid connection does not preclude the use of the coupling rods.

The present construction has been found to be suitable wherever a high degree of stability is required and where eight and space are at a premium. The unit of the present design may, for example, have a weight of approximately six ounces compared to twenty-one ounces for conventional construction, seventy percent saving. The cups may be formed of Invar in order to insure minimum change in dimension upon change in temperature. Negligible drift is encountered even when the device is subjected to severe shock and vibration. It is believed that this is due to the fact that the cathode pedestal, being anchored at its ends and snugly embracing the tube at spaced points, is precluded from moving in any direction and holds the tube in a precise cradled position. The device is highly flexible in use permitting a wide range of frequency and operating requirements with only minor modification in construction. For example, to achieve a lower output frequency it will be apparent that the anode cup 36 may be replaced by one having a greater axial dimension. As a matter of fact it is one of the features of the present invention that anode cups and other components may be stocked in certain standard sizes, permitting a large number of combinations to satisfy a wide variety of operating requirements. When an order is received for a cavity having particular requirements it is readily possible to extrapolate upon known data relating to cavities for similar applications and to specify, with a high degree of initial accuracy, the particular components which would be used in the construction. Thus design of a cavity formerly requiring days of design effort and much cut and try may be achieved within a few hours time and with 'a minimum bench modification or adjustment. Contributing to reliability is extremely low contact resistance throughout the device particularly at the critical points of contact between pedestals and the terminals of the tube, contact being assured in spite of any incidental layer of oxide which may form at the tube terminals. The use of thin weather stripping made of springy material and employed in prior constructions is eliminated with its attendant risk of damage, the function being performed in the present construction by spring fingers 41, 63, 65 which are protectively located inside of cylindrical pedestal members. A high degree of consistency from unit to unit is attained.

Since the present construction may be achieved by members having a wall thickness of only a fraction of that previously required, the unit is not only light in weight but easily formed using techniques applicable to forming of thin metal such as deep drawing, punching, and spinning, all of which operations are inherently inexpensive with turned or screw machine parts being largely eliminated.

I claim as my invention:

1. In a cavity for use with a tube of the lighthouse type having a central grid flange with a cylindrical anode electrode at one end thereof and cylindrical cathode and filament electrodes at the other end thereof, the combination comprising a cup-shaped anode member, a cupshaped cathode member of substantially the same diameter as the anode member, an annular barrier plate permanently joined to the lip of the cathode member and having means for securing the grid flange thereto, the lip portion of the anode member being resilient and dimensioned to snugly telescope over the lip of the cathode member, an insulated pedestal axially arranged in said anode member and seated on the bottom thereof for making contact with the anode electrode of the tube, said cup-shaped cathode member having a cylindrical pedestal axially secured therein having portions of unlike diameter, each portion including a series of integral fingers struck inwardly from the wall of the pedestal and lying generally parallel to it for engagement with the cathode and filament electrodes respectively when the tube is inserted and with the grid flange secured to the barrier plate, said cathode pedestal member having an integral outwardly extending flange thereon, a plurality of rods secured to the flange and extending through the barrier member for providing coupling with the anode cavity, and means providing coupling to said anode cavity for feeding an output signal therefrom.

2. In a cavity for use with a tube of the lighthouse type having a central grid flange with a cylindrical anode electrode at one end thereof and cylindrical cathode and filament electrodes at the other end thereof, the combination comprising a cup-shaped anode member, a cupshaped cathode member of substantially the same diameter as the anode member, an annular barrier plate engaging the lip of the cathode member and having means for securing the grid flange thereto, the lip portion of the anode member being dimensioned to snugly telescope with respect to the lip of the cathode member, a clamp for encircling the telescoped member, an insulated pedestal axially arranged in said anode member and seated on the bottom thereof for making contact with the anode electrode of the tube, said cup shaped cathode member having a cylindrical pedestal axially secured therein having adjacent portions each including a series of integral fingers struck inwardly from the Wall of its pedestal and lying generally parallel to it to define cylindrical contacts of unlike radii for engagement with the cathode and filament electrodes respectively when the tube is inserted and with the grid flange secured to the barrier plate, said cathode pedestal member having an integral outwardly extending flange thereon, and means providing coupling to said anode cavity for feeding an output signal therefrom.

3. In a cavity for use with a tube of the lighthouse type having a central grid flange with a cylindrical anode electrode at one end thereof and cylindrical cathode and filament electrodes at the other end thereof, the combination comprising a cup-shaped anode member, a cupshaped cathode member of substantially the same diameter as the anode member, an annular barrier plate engaging the lip of the cathode member and having means for securing the grid flange thereto, the lip portion of the anode member being resilient and dimensioned to snugly telescope over the lip of the cathode member, clamping means for encircling the telescoped portions, an insulated pedestal axially arranged in said anode member and seated on the bottom thereof for making contact with the anode electrode of the tube, said cup-shaped cathode member having a cylindrical pedestal formed of a Single piece of metal axially secured therein having portions of unlike diameter following the contours of the cathode and filament terminals, each portion including a series of integral cantilevered fingers struck inwardly from the wall of its pedestal and lying generally parallel to it at a shallow depth for engagement with the cathode and filament electrodes respectively when the tube is inserted and with the grid flange secured to the barrier plate, said cathode pedestal member having an integral outwardly extending flange thereon, and means providing coupling to said anode cavity for feeding an output signal therefrom.

4. In a cavity for use with a tube of the lighthouse type having a central grid flange with a cylindrical anode electrode at one end thereof and cylindrical cathode and filament electrodes at the other end thereof, the combination comprising a cup-shaped anode member, a cupshaped cathode member of substantially the same diameter as the anode member, an annular barrier plate having means for securing the grid flange thereto and defining anode and cathode cavities, a telescoping connection between said cup-shaped members, an insulated pedestal axially arranged in said anode member and seated on the bottom thereof for making contact with the anode electrode of the tube, said cup-shaped cathode member having a cylindrical pedestal axially secured therein having adjacent portions of unlike diameter, each portion including a series of integral fingers struck inwardly from the wall of its pedestal and cantilevered generally parallel to it for engagement with the cathode and filament electrodes respectively when the tube is inserted and with the grid flange secured to the barrier plate, said cathode pedestal member having a skirt portion of larger diameter, and means providing coupling to said anode cavity for feeding an output signal therefrom.

References Cited in the file of this patent UNITED STATES PATENTS

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