US2573190A - Ultra high-frequency electron tube - Google Patents

Description

Oct. 30, 1951 w. w. ElTl-:L ET A1.

ULTRAHIGH-FREQUENCY ELECTRON TUBE 4 Sheets-Sheet l Filed April 8, 1949 Oct. 30, 1951 w. w. EITEL ETAL ULTRAHIGH-FRQUENCY ELECTRON TUBE 4 Sheets-Sheet 2 Filed April 8, 1949 Oct. 30,' 1951 w. w. EITEL ET AL. 2,573Q190 ULTRAHIGH-FREQUENCY ELECTRON TUBE 4 Sheets-Sheet 3 Filed April a, 1949 NL 'ENTORS Oct. 30, 1951 w. w. EITEL r-:T A1.

ULTRAHIGH-FREQUENCY ELECTRON TUBE] 4 Sheets-Sheet 4 Filed April 8, 1949 Lc1q5 Eli INVENTORS WILL/AM W. E/TEL JACK AMECULLOUGH HAROLD E. 50H6 ATTORNEY Patented Oct. 30, 1951 ULTRA HIGH-FREQUENCY ELECTRON TUBE William W. Eitel, Woodside, Jack A. McCullough, Millbrae, and Harold E. Sorg, Redwood City, Calif., assignors to Eitel-McCulloughlInc., San Bruno, Calif., a corporation of California Application April 8, 1949, Serial No. 86,232

8 Claims.

Our invention relates to a radio-frequency generator including an improved electron tube and associated circuitry for operation at ultrahigh frequencies.

Tubes of the negative grid type, either triodes or tetrodes, have in the past been made in tubular shapes, this conventional design having grown out of the old lamp industry. These tubes have served a good purpose at the lower frequencies, and, if more power output was desired it was only necessary to make the tube larger to take care of the additional heat dissipation because the lower frequencies did not place dimensional limitations on the tube. This increase in the tube size is not possible at the higher frequencies, however, and therefore a high frequency tube of the conventional type is seriously limited as to its power output capabilities.

The broad object of our invention is to provide a radio-frequency generator embodying an improved tube of annular shape which satisfies the dimensional limitations imposed by the higher frequencies and yet has sufficient heat dissipation capabilities to give a relatively large power output.

Another object is to provide an annular cavitytype resonator for operation in conjunction with the annular tube, which cavity circuitry is suited for use as an amplifier or an oscillator at the ultra-high frequencies.

Still another object is to provide a tube having planar type electrodes in which an improved electrode *design and supporting structure is provided for such electrodes, particularly for the grid."

A further object is to provide an improved method of assembling a tube having planar electrodes to facilitate establishing and maintaining close and accurate spacings between the electrodes.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of our invention. It is to be understood that we do not limit ourselves to this disclosure of species of our invention, as we may adopt variant embodiments thereof within the scope of the claims.

Referring to the drawings:

Figure 1 is a vertical sectional view of a triode embodying the improvements of our invention; and

Figure 2 is a bottom view of the same.

Figure 3 is a horizontal sectional view taken in a plane indicated by line 3-3 of Figure 1.

Figure 4 is a diagrammatic sectional view showing a radio-frequency generator incorporating the tube of our invention.

Figures 5 and 6 are exploded fragmentary sectional views illustrating the envelope structure and method of assembling the tube, these views showing only half of the tube structure.

Figure 7 is a sectional view, similar to Figure 1 but showing only half of a tube, illustrating a tetrode structure.

In terms of broad inclusion our improved radiofrequency generator comprises an electron tube having an annular envelope, a plurality ofringshaped electrodes including an anode and grid and cathode, the opposing surfaces of the electrodes preferably lying in planes transverse to the tube axis, and terminals for the electrodes concentric with the axis. The envelope preferably has concentric inner and outer side walls with the anode supported at one end and the cathode at the opposite end, and with the flat ring-shaped grid supported by terminal rings interposed in the side walls. In our improved tube the concentric side walls preferably comprise cylindrical sections of vitreous material extending vbetween the electrode supports, which sections are preferably sized to establish predetermined spacings between the electrodes. The tube is preferably constructed and assembled so that the nal seals are made at optical-flat abutting surfaces. The improved circuitry embodied in our radio-frequency generator comprises a reso'nator having annular cavities concentric with the axis ofthe annular tube, the conductors defining the cavities being coaxial with the electrode terminals on the tube. The ring-shaped electrodes of the annular tube are thus coupled across the ends of the annular cavities sothat the width and not the circumferential length of the electrodes becomes the important dimensional factor determining the upper frequency limit. A tube with relatively large electrode areas and consequently large power output capabilities is therefore provided, while at the same time satisfying the dimensions necessary for eiiicient operation at the ultra-high frequencies.

In greater detail, and referring rst to Figures 1, 2 and 3 of the drawings, the triode version of our improved high frequency tube comprises an annular or doughnut-shaped envelope, having concentric inner and outer side walls providing an evacuated closure for a plurality of ring-shaped electrodes including an anode 2, cathode 3 and control grid l. In order to allow close spacings between the electrodes and to provide other advantages in the annular tube structure, the electrodes are preferably of the planar type having opposed surfaces lying in parallel planes transverse to the tube axis. These electrodes have terminals on the envelope, preerably including a pair of anode terminals 6, a pair of grid terminals l and a pair of cathode terminals 8, which electrode terminals are also ring-shaped and concentric with the tube axis. In the interest of illustrating the structure most clearly the tube of Figure l is shown with fairly wide electrodes. In actual practice for high frequency operation the effective electrode width measured across the section rof the ringshaped electrodes would be considerably less than that shown, say about inch for a UHF' tube. 'I'he overall diameter of the tube maybe of any desirable size, depending upon the total active electrode area required for the power output desired.

Ring-shaped anode 2 is preferably of the external anode type and forms the upper part of the tube envelope, supported 'between the side walls. This circular anode may bemachined from any suitable metal, preferably copper for good heat conduction, and has an inner portion terminating at a flat face providing the active surface of the anode and an outer portion projecting from the upper end of the envelope carrying a cooler 9. For a forced air cooled tube, as illustrated, the cooler preferably comprises two circular cooler sections securedk to opposite sides of the anode, each section comprising radial fins II held by retaining sleeves I2. A ring-shaped cap I3 across the sections completes the cooler structure. If desired suitable jackets may be used `on the anode for water cooling.

At one point in the circle defined by the anode avertical passage Il is provided communicating with the interior of the envelope through a transverse passage I6. A metal exhausttubulation I1 is secured in the outer end of passage Il which tubulation, after evacuation of the envelope,is pinched off at tip I8. In the completed tube this tubulation is housed and protected by the cooler structure.

'I'he lower end of the envelope opposite the anode comprises a circular metal header I! shaped to form the downwardly extending cathode terminals 8 and the radial sealing flanges 2l, the bottom wall of the header being preferably made reentrant for added rigidity. The pair of concentric ring-shaped cathode terminals 8 are thus formed as an integral part of the header. Anodeterminalsl 6 have integrally formed circular sealing flanges 22 which have lips brazed to the anode, the flanges 22 being located above the sealing flanges 2l of the header I9. Grid terminal rings 'I likewise have integrally formed sealing flanges 23 located between the flanges 2| and 22.

The inner side/wall of the envelope comprises a pair of cylindrical vitreous sections, including an upper section 24 sealed between flanges 22 and 23 and a lower section 26 sealed between ilanges 2| and 23. In a like manner the outer side wall comprises a pair of cylindrical vitreous sections, including an upper section 21 sealed between the flanges 2Iand23 and a lower section 28 sealed between the flanges v2| and 23. The vitreous or glass envelope sections may be sealed along their edges to the metal flanges by ordinary glass-tometal sealing techniques using flames to fuse the glass at the sealing areas, but we prefer to use an .has good heat dissipation properties.-

improved method of tube assembly as will hereinafter be described.

As shown in Figure 1 the fiat ring-shaped grid 4 is supported along both of its circular edges by the inwardly extending anges 29 which are formed integrallyv with the grid terminal rings l. The ring-shaped grid may be fabricated in any suitable manner, as by wires bonded or woven together and stretched Y,across a pair of retaining rings 3I which are in turn secured to the flanges 23. Instead of being fabricated from wire or mesh the grid may be made of a perforated sheet metal ring. In any case, several advantages are gainedby the ring-like shape and mounting arrangement of the grid in our tube because the grid, although of large total effective area, is amply held by supports which extend along the entire length of its inner and outer peripheral edges. Since the grid is inherently narrow compared to its circumferential length, the active part of the grid has the necessary support and rigidity to insure accurate maintenance of the close spacings between it and the adjacent electrodes. This is very important in high frequency tubes where any change inthe already close electrode spacings results in a wide shift of the operating frequency.

Much trouble has been occasioned by such grid movement in the conventional tubular type tubes because of the oil-canning 'or diaphragm-like movement of the disk-shaped grids involved inv such tubes. The ring shape ofv our grid together with the support along both peripheral edges provides a great improvement in that respect as well as providing a grid of much larger effective electrode area. Still another advantage is that our grid, being circular and narrow, is ideally shaped and supported for maximum heat removal from the effective grid area, which means greater heat dissipation capabilities of the grid and hence more power output from the tube. 'I'his will be apparent when it is realized that heat from the grid can flow radially in both directions out through the adjacent grid terminal rings. It should also be understood that electrode widths in the tube shown in Figure l are much greater than would be'the case in an actual tube, the

larger widths shown being for purposes of illustrating the structure more clearly. In an actual tube for ultra-high frequency operation the electrode widths for example may be not over inch or less. -A ring-shaped grid of that narrow width and supported along both edges, regardless of its circumferential length, obviously is very rigid and These advantages with respect to the grid in our improved tube are emphasized because grid dissipation and grid stability are usually the limiting factors in the high .frequency operation of transmitting tubes.

The vcathode 3 preferably comprises a cupped or channel shaped ring, say of nickel, with a flat upper face carrying a thermionic electron emitting material such as the conventional bariumstrontium foxide coating. This cathode ring is Vsupported by a pair of skirts or ring-like flanges 32, preferably of thin sheet metal to thermally isolate lthe cathode. Flanges 32 are in turn preferably supported on another channel-shaped ring 33 whichis fitted between the cathode terminal portions 8 of the header I3. Ring 33 also functions as a heat baille to conserve heat within the cathode structure.

.The cathode is heated indirectly, preferably by a pancake heater coil 34 embedded in an insulating layer 36 disposed between the cathode ring and a backing plate 31 fitted between the anges so that the cathode and its heater may be fabricated as a unit prior to assembly in the tube. One end 38 of the heatercoil is brought out and connected to the cathode structure as at the baille plate 33, and the other end 39 is connected to a lead 4| projecting out of the envelope between cathode terminals 8 and sealed in place by a glass bead 42. Heater current for the cathode may thus be applied by making external connections to a cathode terminal and the lead 4|.

Figure 4 illustrates diagrammatically an improved RF generator embodying the annular tube, the view being in vertical section and the tube being in sectional outline to show the terminal lconnections. ItA will be noted -that the generator comprises annular cavity resonators associated with the annular tube, which circuitry is ideally suited for ultra-high frequency. The generator shown comprises an annular output resonator 43 and annular input resonator 44 made up of pairs of coaxial metal conductors 46, 41 and 48, the conductors 46 beingconnected to anode terminal 6, conductors 41 being connected to grid terminals 1, -and conductors 48 being connected to cathode terminals 8.' The annular cavities and annular tube are thus all concentric about the central axis of the tube, which is possible because the electrode terminals and cavity conductors are all coaxial.

The input and output resonators may be tuned by annular plungers 49 and 5| for adjusting the axial length of the cavities, and which may have built-in blocking condensers as illustrated for isolating the D. C. plate and grid bias voltages.

The D. C. connections are not sho-wn since such will be obvious to those skilled in the art. it being understood that oneof the heater connections may be brought up through the space between the cathode conductors 48 and connected to the lead 4|. Any conventional means (not shown) such as probes or loops may be provided for coupling RF power into and out of the resonators, which in the case of an amplifier would involve feeding the driving power into the input resonator 44 and taking power out of the output resonator 43. In the case of an oscillator, suitable feedback loops or probes would be arranged to feed energy from the outputI resonator back to the input resonator, as will be readily understood. l

It will be noted that. annular or ring-shaped electrodes of the tube are bridged across the ends of the annular cavities so that the critical electrode dimension with respect to frequency is the width and not the length of the electrodes. That is a very important factor in our improved RF generator because it makes possible the generation of very large orders of RF power in the upper frequency ranges. This advantage stems directly from the improved tube and circuit relationship, wherein the ring-shaped electrodes are coupled across the ends of the annular cavities. 'I'hus in the amplifier version of the generator shown in Figure 4, which is a common-grid type of triode operation, the cathode and gridare coupled across the end of the annular input cavity 44 and the anode and grid are coupled across the annular output cavity 43, the annular cavities and ring-shaped electrodes all being concentric with the central axis of the annular tube.

As hereinbefore mentioned we have also provided an improved method of assembling av tube having planar type electrodes, which method is ideally suited for making the annular tube herein disclosed. In describing the tube structure of Figure 1 it was pointed out that 'the vitreous or glass sections 24, 26. 21 and 28 may be sealed along the edges to the sealing flanges in accordance with ordinary glass-to-metal sealing practice using flames to melt the glass at the sealing surfaces. While this old practice may be employed, we prefer to use an improved method which results in.more accurate electrode spacings and permits the achievement of much closer spacings, it being understood that as the frequency of operation is increased a closer spacing is required between the electrodes. Our new method involves sizing the vitreous envelope sections to establish predetermmed spacings between the electrodes. Thus. the upper envelope sections 24 and 21 are cut and ground to a precise length so that when these sections are inserted between the flanges 22 and 23 the desired predetermined spacing is established between the anode 2 and control grid 4. Likewise, the lower envelope sections 26 and 28 are cut and ground to a precise length to establish the desired predetermined spacing between the control grid and cathode 3. Figure 5 shows an exploded view of the tube with the envelope sections cut to precise length and ready for insertion between the respective sealing flanges. In other words, the tube is made in three parts: the upper anode part carrying the sealing flanges 22, the middle lgrid part carrying the sealing flanges 23, and the lower cathode part carrying the sealing flanges 2|. These three parts are all first completed as sub-assemblies l and checked for accurate dimensions before the nal assembly is made. The three parts are then put together with the cylindrical envelope sections interposed between as spacers. Thus the envelope sections serve the dual purpose of forming the envelope walls and establishing the spacings between the electrodes.

In Figure 5 the envelope sections 24, 26, 21 and 28 are preferably of glass extending the full length between the flanges, and the final vacuum-tight seal is insured by grinding and polishing the opposed surfaces of the glass and metal to a degree known in the glass art as an optical-fiat. The parts so prepared and assembled are temporarily clamped together and put on the vacuum pump. The tube may then vbe faces, which forms a permanent and durable seal. Since the time and temperature required for such knitting is below the melting or softening point of the materials involved, no deformation takes place which would destroy the spacer function of the envelope sections. Ceramic as well as glass` may be used for the vitreous envelope sections.'\

An alternative procedure shown in Figure 6 involves forming each of the glass envelope sections in two halves and first sealing each half to the respective flanges. This initial sealing may conveniently be done by ordinary 'glass-tometal sealing techniques using llames. Opposing glass flanges are thus provided on the metal flanges as shown by the condition of the parts in Figure 6. The opposing edges of the halfsections are then ground and polished to provide optical-flat surfaces which when brought together form the vacuum-tight seals. These glass-to-glass flats` are particularly well adapted for knitting or coalescing together at relatively low temperatures and the procedure illustrated by Figure 6 is therefore preferred in some cases. VAs was the case with the one-piece sections shown in Figure 5, the two-piece sections of Figure 6 are ground and.polishedto precise dimensions for establishing the predetermined spacings between the electrodes. Instead of using glass cylinders which are sealed to the metal flanges. the half-sections may be formed by molding powdered glass in the proper cylindrical shapes directly to the metal flanges, using suitable molds and-powdered glass molding techniques known in the art. I

which is subject to precisely controlled tolerances and therefore enables tubes to be made with exceedingly close electrode spacings. After the 'subassemblies and parts have been accurately prepared and checked lfor dimensions, the job of final tubeassembly is merely a question of stacking the parts together which does not require skilled operators, therefore eliminating the type of skill in the final assembly of a tube which has always been'the bottle-neck inA` production operations. With our improved *tube it is not at all diillcult to achieve and maintain electrode spacings of a few thousandths of an inch.

Our annular tube structure is also well adapted for tetrodes and other multi-grid tubes as well as for triodes. Figure 'I shows a tetrode having electrode terminals. The assembly procedures described above in` connection with the triode (Figures and 6) are ideally adapted` for assembling the tetrode as will readily be appreciated. Likewise, the annular tetrode tube flts well into cavity type circuitry for ultra-high frequency operation, in a manner similar to that shown in Figure 4 for the triode, as will also be appreciated by those skilled in the art.` f

The particular advantage of our annular type planar electrode tube, whether constructed as a triodel or as a tetrode, is that large electrode area and electrode supporting mass is y provided to handle large currents in the tube and take care of the heat dissipation necessary for high power operation, yetclose electrode spacings are attainable and the width across a given section of the tube may be kept small to provide good eillcient operation in the ultra-high frequency range. This matter of suitability for high frequency operation will be apparent from inspection of Figure ,4, where it is seen that the annular `or ring-shaped electrodes are connected acro the adjacent the lower ends of said walls, a flatl the electrodes described `in connection with 'l 8 may be kept to a small dimension in our tube, it is possible to provide efficient operation in the upper UHF region, say above 2000 mc. Furthermore, since the circumferential length of the electrodes does not limit the frequency in our RF generator it is clear that the overall diameier of the tube may be increased indefinitely to provide the needed electrode areas, depending upon the output power required. We have thus provided an RF generator, using a single negative grid type of tube, for generating very large orders of power in the upper frequency ranges. If desired the electrodes may be of different shapes than that shown, such as electrodes of arcuate or dome-shape in cross section. The planar type electrodes are preferred, however, because of the simplicity of construction and the ease of establishing close electrode spacings.

We claim:

1. Anvelectron tube comprising an annular envelope having concentric inner and outeriside walls of insulating material, a ring-shaped externa] anode supported v'adjacent the upper ends of said walls, a ring-shaped cathode supported adjacent the lower ends of said walls, and a ilat ring-shaped grid between the anode and cathode and suported at the intermediate portions of said walls.

2. An electron tube comprising an annular envelope having concentric inner and outer side walls of insulating material, a ring-shapedexternal anode supported adjacent the upper ends of said walls, a ring-shaped cathode supported ring-shaped control grid between the anode and cathode and supported at the intermediate portions of said walls, and a flat ring-shaped screen grid between the control grid and anode and supported at the intermediate portions of said walls.-

3. An electron tube comprisng an annular envelope having concentric inner and outer side walls, a pair of concentric grid terminal rings interposed in said walls, a pair of concentric cathode terminal rings on theenvelope adjacent the lower ends of said walls, a pair of concentric anode terminal rings on the envelope adjacent the upper ends of said walls, a ring-shaped anode supported by the anode terminal rings, a ringshaped cathode supported by the cathode terminal rings, and a. flat ring-shaped grid between the anode and cathode` and-supported by said gridterminal rings.

4. An electron tube comprising an annular envelope having concentric innerfan outer side walls, a pair of grid terminal rings interposed in said walls, a pair of concentric cathode terminal rings projecting from the envelope adjaends of the annular resonant cavities. Thus the width and not the length of the electrodes is the cent the lower ends of said walls, a ring-shaped anode supported adjacent the upper ends of said walls, a ring-shaped cathode having supporting flanges connected to the cathode terminal rings, a heater below the cathode, a lead for the heater projecting from the envelope between said cath- 0de terminal rings, and a flat ring-shaped grid between the anode and cathode and supported by said grid terminal rings.

5. An electron tube comprising an annular envelope having concentric inner and outer walls, a plurality of ring-shaped electrodes having opposed active surfaces including an external anode and grid and cathode, ring-shaped metallic supports on the envelope for the electrodes, and rings of insulating material sealed between the electrode supports and forming said side walls.

6. An electron tube comprising an annular envelope having concentric inner and outer walls.

a. plurality of ring-shaped electrodes having op- REFERNCES CITED The following references are of record in the file ot this patenti UNITED STATES PATENTS Number l5 Nuinber Name Date Rosell et al July 7, 1925 Gossel et al May 28, 1940 Laico Nov. 24, 1942 Lavoie Sept. 7, 1943 Hartley et al Sept. l0, 1946 Beggs Feb. 25, 194'?l Kane Feb. 24, 1948 DeWalt June l5, 1948 Law May 24, 1949 Despois Apr. 18, 1950 FOREIGN PATENTS Country Date Great Britain July 21, 1947

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