US2517726A - Ultra high frequency electron tube - Google Patents

Description

Aug. 8, 1950 A. M. SKELLETT ULTRA HIGH FREQUENCY ELECTRON TUBE Filed July 17, 1946 2 Sheets-Sheet 1 at 7g I I 7/ --4|||||| a I r I 0,

6 INVENTOR. Azamr m /raurr BY 4J fi I I flTTO/FA [V Aug. 8, 1950 A. M. SKELLETT ULTRA HIGH FREQUENCY ELECTRON TUBE Filed July 17, 1946 2 Sheets-Sheet 2 INVENTOR. $945597" /7 5AAZLE7'7' Patented Aug. 8, 1950 2,517,726 ULTRA HIGH FREQUENCY ELECTRON. TUBE Albert M. Skellett, Ma

dison, N. J., assignor, by

mesne assignments, to Philco Corporation, Philadelphia, Pa., a corporation of Pennsyl vania Application July 17, 1946, Serial No. 684,113

'7 Claims.

I This invention relates to electron tubes and more especially to improvements in tubes for generating, detectin or modulating at ultrahigh frequencies.

A principal object of the invention is to im prove and simplify the construction of ultra high frequency oscillator-generator tubes of the type employing a cavity resonator as a composite part of the electron control system.

Another object is to provide an ultra high frequency oscillator-generator tube of the cavity resonator type with an anode which forms one of the cavity surfaces and is specially treated to act as a copious source of secondary electron emission.

A. further object is to provide a novel high frequency generator tube embodying a cavity resonator control for the electron stream and wherein the electrondensity or distribution is a function of the dynatron characteristics of the anode which also forms part of the cavity resonator per se.

A feature of the invention relates to an improved dynatron oscillator tube having a specially designed cavity resonator for enabling the dynatron action to be usefully employed at very high frequencies.

Another feature relates to an electron tube having a cathode, grid, and anode so energized as to produce a negative resistance characteristic between the anode and grid; in conjunction with a special bi-part cavity resonator constituted in part of the anode and grid for extending the usefulness of the tube to the ultra high frequency range.

A still further feature relates to the novel organization, arrangement and relative interconnection of parts which cooperate to provide a simplified ultra high frequency electron tube.

Other features and advantages not particularly enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

While the inventive concept will be illustrated and explained as embodied in an oscillator-generator tube, it will be understood that the tube is capable of use also as a detector or modulator as will be apparent to those familiar with these respective arts.

In the drawing,

Fig. l is a top-plan view of a tube embodying the invention.

Fig. 2 is a composite tube and circuit diagram, with the tube shown as a crosssection taken along the line 2--2 of Fig. l, and viewed in the direction of the arrows.

Fig. 3 is a sectional view of Fig. 1, taken along theline 3--3 thereof. Fig. 4 is a modified em-- bodiment.

Referring to the drawing, there is shown an enclosin envelope ll] ofglass or other suitable dielectric material which has the usual reen' trant header or stem ll, terminating in a press I2, through which the lead-inand support wires 13-48 are vacuum-tight sealed. It will be understood that the invention is not limited to this particular type of header, and other well-known types such as disc-type headers, button-type headers and the like may be employed. Attached to the ends of support wires 13 and I5 is an electron-emitting cathode ll in the form of a circular fine wire carrying a coating of electron-emissive material such as a mixture of alkaline earth oxides. If desired, this cathode may be of the thoriated tungsten type. The invention is not limited to a cathode of the fila mentary type, and therefore any well-known indirectly heated cathode may be employed. Surrounding the cathode and in suitable spaced relation thereto is an emission shield [8 which may be inthe form of an inverted metal cup attached to wire IB, and having a central opening IS. The annular portion 20 of member 18 therefore directly overlies the cathode I1 and prevents sputtering of the emissive material on to the remaining electrodes, while permitting the electrons to flow to these electrodes in trajectoriesrepresented by the arrows.

Sealed in a vacuum-tight manner through wall it is a dish-shaped metal member having an annular flat flange 21, and a truncated conical portion 22 with a central opening across which is fastened the foraminous electrode or grid 23. Likewise, sealed to the open rim of envelope in is a similar dish-shaped member comprising a flat annular flange 24, a truncated conical portion 25 and an unperforated flat central portion 26,

the latter acting as the anode of the tube. In tegrally united to the external face of anode 26 is a heat radiator comprising a block 21 of brass. or other high heat conducting metal, and

carrying a series of heat radiator fins 28.

It will be observed that the annular flanges 2! and 24 extend outwardly of the envelope l0 and their respective margins are bent and abut against corresponding bent margins on respective chan nel- shaped metal members 29, 30. Each of these latter members has a fiat annular flange 3|, 32, between which is sandwiched an annular ring 33 of suitable dielectric material. The elements 2|, 22, 29, 3| and 24, 25, 30, 32, when united as shown, constitute a cavity resonator, the physical dimensions and shape of which are properly designed, as well-known in the cavity resonator art, so as to resonate at the particular frequency at which the tube is to be operated. It will be understood of course, that if desired the portion may be circularly corrugated or in the form of a bellows so that it has sufiicient flexibility to enable it to be adjusted to vary the space relation between the grid 23 and the anode 26. The elements 21 and 2 1 can be sealed into the glass of envelope It in the well-known disc type of seal as is clear to those familiar with the glass sealing art.

Supported on the wire M interiorly of the envelope is a ring type getter 34 which carries any well-known gettering material, for example a magnesium compound or even magnesium itself. This ring is adapted to be raised to a sufficiently high temperature so as to flash magnesium therefrom on to the anode 26. The envelope I9 and all the metal parts are subjected to the usual cleaning and outgassing operations and the envelope in is subjected to the usual pumping or evacuating schedule. Durin this schedule, and after the various parts have been degassified and cleaned, the getter 34 is flashed causing magnesium to be deposited on the surface of anode 26. Oxygen is then admitted into the tube resulting in the formation on the anode surface 25 of magnesium oxide which acts as a copious source of secondary electrons when born barded by the primary electrons from the cathode l1. It will be understood of course that the invention is not limited to this particular 'second-ary emission coating or to the method of applying the secondary emission coating to the anode 26. This coating may be applied to the said anode prior to sealing-in of the various parts.

The portion of the cavity resonator is pro-- vided with a circular opening to the margin of l which is connected the outer conductor of a coaxial transmission line whose central conductor is indicated as 36. A small inductive pick-up loop 3'! conveys the high frequency energy from the cavity resonator to a suitable load circuit (not shown). It will be understood that a capacitive probe may be used instead of the inductive pick-up 31.

In accordance with the invention, the anode 26 is connected to a positive potential tap 38 on the D. C. power supply which tap is however of a lower potential than the positive potential tap 39 to which the grid 23 is connected. It will be observed that by forming the cavity resonator as a bi-part structure with the intervening dielectric as, it is possible to apply these different potentials respectively to the anode and grid. The filament or cathode ll is raised to emitting temperature from a suitable heater current supply indicated by the filament power transformer 40.

When the tube is in operation, the primary electrons from cathode I1 strike the anode 26 with sufficient velocity to release therefrom a copious supply of secondary electrons which travel towards the positive grid 23, thus imparting by well-known dynatron action, a negative resistance characteristic to the space between grid 23 and anode 25. By reason of the dimensional configuration of the cavity resonator and this negative resistance characteristic, the cavity will be subjected to charging oscillations at a frequency determined by the various electric and dimensional parameters. The cavity continues to oscillate at its resonant frequency secondary electron emission material, and by having different D. C. potentials applied to members 23 and 26, the dynatron action provides a negative resistance which balances out the conventional shunt resistance, thus facilitating the generation and sustaining of ultra-high frequenucy oscillations.

While one particular cross-sectional configuration is shown for the cavity resonator, it will be understood that any other suitable shape may be employed, and various changes and modifications may be made in the disclosed embodiment without departing from the spirit and. scope of the invention. For example, while Fig. 2

of the drawing shows an apertured shield [8 for preventing contamination of the anode surface by undesired emanations from the oathode, there is shown in Fig. 4 another preferred way of shielding the anode surface from this undesired emanation. In this embodiment the parts which correspond with those of Fig. 2 bear the same designation numerals. The source of electrons for the tube is derived from any 'well-known form of electron gun M which is inclined with respect to the central longitudinal axis of the electrode system 23, 26 so that the electrons from the gun ll are emitted towards the side walls of the elongated neck portion 42 of the enclosing bulb. Cooperating with the gun is electromagnetic field producing member or winding which acts on the electrons from the gun ll so as to restore their trajectory in a direction away from the wall 42 and towards the electrodes 23, 25. By this arrangement heavy ions or particles of emissive material leaving the emissive cathode of the gun 4| strike the wall 42, whereas the electrons from the cathode are allowed to proceed towards the electrodes 23 and 2E. For a more detailed description of this manner of segregating the electrons from undesired emanation of the cathode, reference may be had to U. S. Patent No. 2,274,586, n d February 24, 1942. There are disclosed in said patent three different arrangements for segregating the electrons from other undesired emanations, and it will be understood that any one of these arrangements can be used in the tube of Fig. l. Thus, instead of having the neck portion 52 straight, and the gun 4| inclined, the neck portion 42 may be inclined with respect to the remainder of the envelope and the gun may be concentric with this inclined neck portion as disclosed in Fig. 5 of said Patent #2374586. Likewise, instead of using an inclined gun or inclined neck to achieve the electron segregation, this segregation can be achieved as disclosed in Figs. 1 and 3 of said Patent #2274586.

What is claimed is:

1. An electron tube of the dynatron oscillator type, comprising a thermionic cathode for emitting primary electrons, an anode to be bombarded by said primary electrons and having a surface which acts as a copious source of secondar electrons in response to said bombardment, a grid electrode located between the cathode and anode, a closed cavity resonator having one resonator wall formed in part of said anode and the opposite resonator wall formed in part of said grid, the dimensions of said cavity resonator being proportioned so that the resonance of the cavity determines the dynatron frequency of the tube oscillation while maintaining a negative resistance characteristic between the anode and grid, said cavity resonator being a bi-part metal structure with one part electrically connected to the grid and the other part electrically connected to the anode, and separate connections are provided for the two parts of said resonator to apply different potentials thereto.

2. A high frequency tube of the dynatron oscillator type, comprising an enclosing envelope, a primary electron emitter, a grid, an anode, said anode having its surface treated to act as a copious secondary electron emitter in response to impinging primary electrons, first and second dishshaped metal members sealed vacuum-tight to the envelope wall and each having a flange extending exteriorly and interiorly of said wall, two channel-shaped metal members having flanges united by a dielectric material said channelshaped metal members being connected to the exterior flanges of the dish-shaped metal members to define a resonant cavity with the boundary walls of the cavity direct-current-insulated from each other, the central section of one dish-shaped member being foraminous and planar to act as said grid, and the central section of the other dish-shaped member also being planar and acting as the anode, and means to apply different potentials to said dish-shaped metal members and thence respectively to said grid and anode to provide a negative resistance characteristic in the space between the grid and anode.

3. A high frequency tube comprising an enclosing envelope, an electron-emitting cathode, a reentrant metal member closing off said envelope and sealed thereto in a vacuum-tight manner, said reentrant metal member having a central flat section acting as the anode of the tube, the internal face of said flat section having a coating of secondary emission material, an inverted dish-shaped metal member having its outer margin sealed vacuum-tight through the wall of said envelope and having its central portion in the form of a foraminous fiat section substantially parallel to the flat section of said reentrant member, a perforated shield surrounding said cathode to protect said anode sputtering from said cathode while allowing electron emission towards the anode, and means external of said envelope and connected to the rims of said metal members to form therewith a cavity resonator with the boundary walls thereof D. C. insulated from each other and separate connections for said boundary walls for applying thereto different positive potentials with respect to the cathode.

4. A tube according to claim 3 in which said means external to said envelope forming said cavity resonator consists of bi-part channel metal members having outwardly extending flanges which are joined by an intervening dielectric.

5. Apparatus for generating ultra high frequency oscillations comprising an enclosing envelope having one end closed by a metal member sealed vacuum-tight thereto, the central section of said metal member on the interior of said envelope being coated with secondary electronemission material and serving as a dynatron anode, an electron-emitting cathode supported within said envelope, another metal member having a central foraminous section acting as a dynatron grid between said cathode and anode and having its margin sealed vacuum-tight through said envelope wall, a bi-part metal member forming with the said first and second metal members a cavity resonator, said oi-part metal member having the two parts thereof joined by a dielectric, means coupled to one of said bi-part metal members to apply a positive D. C. potential to one of said bi-part metal members and thence to said grid, and means coupled to the other of said bi-part metal members to apply a D. C. positive potential lower than the first-mentioned potential to the other of said bi-part metal members and thence to said anode to cause the space between said anode and grid to have negative resistance characteristics.

6. An electron tube of the dynatron oscillator type, comprising a thermionic cathode for emitting primary electrons, an anode to be bombarded by said primary electrons and having a surface which acts as a copious source of secondary electrons in response to said bombardment, a grid electrode located between the cathode and anodefa closed cavity resonator having one resonator wall formed in part of said anode and the opposite resonator wall formed in part of said grid, the dimensions of said cavity resonator being proportioned so that the resonance of the cavity determines the dynatron frequency of the tube oscillation while maintaining a negative resistance characteristic between the anode and grid, said grid and anode being substantially planar and parallel to each other, said closed cavity having a portion of its resonating space internal of the tube and another portion external of the tube.

7. An electron tube of the dynatron oscillator type, comprising a thermionic cathode for emitting primary electrons, an anode to be bombarded by said primary electrons and having a surface which acts as a copious source of secondary electrons in response to said bombardment, a grid electrode located between the cathode and anode, a closed cavity resonator having one resonator wall formed in part of said anode and the opposite resonator wall formed in part of said grid, the dimensions of said cavity resonator being proportioned so that the resonance of the cavity determines the dynatron frequency of the tube oscillation while maintaining a negative resistance characteristic between the anode and grid, the walls of the cavity resonator being insulated from each other for direct current.

ALBERT M. SKELLE'II.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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