US2538087A - Electron discharge device of the magnetron type - Google Patents

Description

Jam 16, 1951 P. P. DERBY ELECTRON DISCHARGE DEVICE 0F' THE MAGNETRON TYPE Filed Dec. 26, 1944 Patented Jan. 16, 1951 UNITED STATES PATENT OFFICE4 Application December 26, 1944, Serial No. 569,873

The present invention relates to electron discharge devices, such as magnetrons for example, and more particularly to tuning means for such devices.

One of the objects of the present invention is to provide an electron discharge device of the aforesaid general type having electronic tuning means.

Another object of the present invention is to provide an electron discharge device of the general type referred to having means for modulating the frequency more especially for transmission purposes.

These objects and such other objects and aims of the present invention as may hereinafter appear will be best understood from the following description, taken in connection with the accompanying drawing of one embodiment of the invention herein presented for illustrative purposes.

' In the drawing:

Fig. 1 is a vertical section on line l-I of Fig. 2 showing a magnetron embodying one illustrative embodiment of the present invention;

Fig. 2 is a horizontal section on line 2 2 of Fig. 1 of the illustrative embodiment of the invention shown in Fig. l;

Fig. 3 shows the various circuits of the device; and

line 4-4 of Fig. 2.

Referring to the drawing the invention is herein illustratively shown in its application to an electron discharge device of the magnetron type, herein comprising a cylindrical member 2 closed at both ends by caps 4 and E, respectively, soldered to the edges of said member 2 to form an hermetically sealed envelope or enclosure. Said cylindrical member 2 and said caps 4 and E may be made of copper or other suitable electrically conductive material. Said cylindrical member 2 has formed upon its inner surface a central, annular projection 8 to which are soldered a plurality of suitably spaced, radially disposed plates or arms Ill. Said arms ID, cylindrical member 2 and caps 4 and 6 constitute the anode structure, and the inner ends of said arms il) form anode faces for receiving electrons from a cathode l2 supported substantially centrally of said anode faces. Said plates or arms ID are preferably made of highly conductive copper, and may conveniently` be stamped from a plate of such copper.

The cathode l2 is preferably of the indirectly heated, oxide-coated, thermionic type', provided with an outer electrically conductive sleeve I4, and an internal heater wire of which the end conductors IE and I3 project centrally from the opposite ends of the cathode I2. One of said conductors, the conductor I6, for example, may be connectedy to said outer conductive cathode sleeve I4, while the other conductor I3 is insulated from said sleeve. Light, conductive shields 20, 22, herein conveniently integral with' said cathode sleeve `I4 lat opposite ends of theA latter,

Fig. 4 is a top plan view of a sectional detail on 3 Claims. (Cl. 315-540) 2 Q prevent electrons beams from being projected outwardly toward said end caps 4 and 6. The cathode I2 is preferably supported by a cathode and heater wire lead-in conductor 24 welded to the end of conductor I6 which, as previously stated, is electrically connected to said conductive cathode sleeve I4 and to one end of said cathode heater wire. A second lead-in conductor 2li has its inner end welded to the free end of said Vheater wire conductor I8. Said two lead-in conductors are connected to a suitable source of voltage, such as a battery, for example, not shown, and are sealed in well-known, conventional manner through glass seals mounted at the outer ends of conducting pipes, one of which is shown at 23 in Fig. 2, which extend through the wall of; the cylindrical member 2 and are hermetically secured therein adjacent the two ends, respectively, of said cylindrical member 2. Said glass seals and conducting pipes are all of well-known, identical, conventional construction and arrangement and therefore only one is shown, as above stated, Vso as not needlessly to increase the number of the figures.' Y Y If such an electron discharge device be placed betweenisuitable magnet pole pieces 28 and 3U to produce a longitudinal magnetic eld within the device and the device be energized, oscillations will be generated which may be led out of said device by a coupling loop 32, see Figs. 1 and 2, extending into the space between two ofl said anode arms I0. One end of said couplingloop 32 is connected to the inner end of a conducting pipe 34, 'hermetically sealed through the wall of said cylindrical member 2, substantially midway between the ends of the latter, and its other end is connected to a conductor 36 whichextends through said pipe 34 and is sealed through a glass seal 38 mounted at the outer end of said pipe 34. An additional conducting pipe, not shown, may be electrically connected to said pipe 34 and. form with said conductor 3B a concentric line through which the high frequency oscillations generated by said device may be conducted to any suitable utilization circuit. l:

Each pair of anode arms l0 forms with the portion of the projection 8 between them an oscilalating cavity or cavity resonator 40. A capacif tance exists between the cathode l2 and the end faces, ofsaid anode arms I0 and also between the sidewalls of each resonator cavity. The conn ductive path around each cavity afforded by the side walls thereof and the portion of said projection 8 -between them constitutes an inductance. The anode, therefore, is so designed and spaced relatively to the cathode that Asaid inductances and capacitances constitute tunedcircuits. It is desired that the circuits shall be'resonant at de.- finite,l predetermined frequencies at which the deviceistobe operated. Electrically conductive straps 44| and l43 may be providedat opposite ends respectively-of said anode to prevent spurious oscillations, thestrap 4| connectingralternate anode varms at one end of the anode, and the strap 43 at the other end of the anode connecting the intervening anode arms.

Referring to Figs. 1 and 2, a conducting pipe .32 extends through the wall of said cylindrical member 2 and is hermetically sealed in said wall, its inner end opening into one oi the resonant cavities 40. At its outer end said pipe 4Z is connected to a glass seal 413 through which are sealed three lead-in conductors t6, :i3 and 5D. The conductor 46 is welded to and supports an electrically .conductive .tubular .member 52 vhaving yan out- -wardly iiaring 'inner end 54 and surrounding a cathode 55 closed at its inner end 5l, the outer :surface of said end being preferably coated with .an ielectron-emissive surface, vsuch as barium or 'member 52. At its other end said cathode iscon- .1

nected by Wires 5. to the inner wall of said itu- 'bular member 252 'by which it is supported, said tubular member being suitably spaced from said ca-thodeand acting as a shield for said cathode 56 to prevent undue cooling of the latter. The .third :lead-in .conductor 553 is welded toand supports ain-#electrically conductive circular cap 52 which 2surrounds the inner end 'sill of said tubular mernber 52 and is spaced from the latter and from said vpipe-'12, The `endWall of said cap 52 is provided with a `circular, central aperture @d kfacing the inner end y5l oi said cathode 56 and tted with a fine mesh accelerator grid 66, see Fig. 4. lThe anode voltage, the gridrvoltage and voltage for 'the cathode 54 and its heater wire 53 'may be supplied from suitable sources, such as '55, 12 and "14, respectively, as diagrammatically represented 'inFig 3. A resistance 76 maybe inserted .in the `grid circuit to limit the voltage thereof.

If the cathode 56 be energized, it will emitan elect-ron beam of which the electrons will be attractedby'the accelerator grid 66, and, guided by `the flaring end walls of the inner end 5d of said ltubular member 52, will pass through said grid 6e and into the resonant cavity between the two 'anode arms Hl at each side oi the latter.

`In accordance with my present understanding of the operations of the present invention, the injection of the electron beam or cathode ray into the space between two anode arms changes the eiective dielectric constant between said two arms and thus varies the capacitances of the anode structure, without affecting the inductance thereof tothe same degree. Therefore, injection of an electron beam into a space between twooi said anode arms will `vary the tuning of the magnetron. The frequency will be varied in accordance with the intensity of the cathode ray. By controlling the voltage of the accelerator grid 6B, the frequency of the magnetron can thus'be controlled, an increase of the grid voltage increasing the frequency of the magnetron and vice versa. The electrons projected into said resonant cavity 'between said two anode arms lwill'be dispersed Wit-hin said cavity and captured before kpenetrating the region of the main discharge of the magnetron. Varying the grid volt` age may be effected in any suitable manner, manually or automatically. For example, in the illustrative embodiment of the invention shown,

the grid, responsive to any vmodulated signal re* ceived through said transformer 8, will vary the 'intensity of the electron beam emitted by the 4 cathode 56, and thus will modulate the frequency of the magnetron in accordance with the modulated signal received.

The Ypresent invention is a distinct advance in the art. It provides a device for electronic tun- The great rapidity of operation of the device makes it particularly valuable for tuning Where ultra-high frequencies are involved, for which mechanical means are wholly inadequate.

Wherever the expression a plurality occurs it is to be construed as meaning two or more.

I am aware that the present invention can be embodied in other specicforms without departing from the Yspirit or essential attributes thereof, .and I .therefore desire the present description to be considered in all respects as illustrative and not restrictive, reference being had to the `appended claims rather than to the aforesaid description to indicate the scope oi the invention-:

What is claimed is:

1. A tunable electron-discharge device comprising: a cathode; an anode structure .spaced from said cathode, and incorporating a Acavity resonator in which radio-frequency oscillations are adapted to be generated; means adjacent Vsaid cavity resonator for establishing a magnetic Aield therethrough; means, cooperable with the electric-field component of said radio-frequency oscillations, and with said magnetic eld, for setting up a space charge in said cavity resonator; and means, coupled between said cavity resonator and said last-named means, for varying the density of Ysaid space charge.

A tunable electron dscharge device com'- prising: a first cathode; an envelope spaced from said rst cathode; a pair of anode arms extendn ing inward from said envelope and, together with that portion of said envelope lying therebetween, defining a cavity resonator; means adjacent. said cavity resonator for establishing a magnetic ii'eld therethrough; and a second. cathode, communieating with said cavity resonator through .said portion of said envelope lying between said anode arms, for setting up a space charge in said cavity resonator.

3. A tunable electron discharge device comlprising: a cathode; an envelope spaced `from said cathode; a pair of anode arms extending inward `from said envelope and, together with that portion of said envelope lying therebetween, deiining a cavity resonator; means adjacent said cavity resonator for establishing a magnetic field therethrough, and a metallic sleeve, closed at one end and electron-emissively coated at said end, projecting into said cavity resonator through said portion of said envelope lying between said anode arms, with its longitudinal axis in a direction substantially perpendicular to the direction Aoff said magnetic iieldjfor setting up a space charge in said cavity resonator.

PALMER P. DERBY.

REFERENES CTED ri'he following references are of record in the le of this patent: l"

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