US2863092A - Magnetron oscillators - Google Patents

Description

Dec. 2, 1958 E. c. DENCH 2,863,092

MAGNETRON OSCILLATORS Filed Aug. 5, 1953 2 Sheets-Sheet 1 IMPEDANCE 52 MATCHE'D ANODE VOLTAGE S UPPLY so ANODE VOLTAGE SUPPLY FIG. 2 45 ourpur 44 LOAD IMPEDANCE MATCHED TERM/M770 IN VENTOR EDWARD C. DENCH ATTCR/VEY Dec. 2, 1958 E. c. DENCH 2, 3, 92

MAGNETRON OSCILLATORS' Filed Aug. 5, 1953 2 Sheets-Sheet 2 Iv s 5 N,

\N) 1 8 \M /NVENTOI2 g o EDWARD C. DENCH 5V gy ATTORNEY United States Patent MAGNETRON OSCILLATORS Edward C. Dench, Needham, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass, 21 corporation of Delaware Application August 5, 1953, Serial No. 372,522 3 Claims. 01. sis-39.3

This is a continuation-in-part of application, Serial No. 253,879, filed October 30,1951, by Edward C. Dench, now abandoned and application, Serial No. 268, 097, filed January 24, 1952, by Edward C. Dench.

This invention relates to electron discharge devices and more particularly to high frequency oscillation generating devices of the magnetron type.

In copending application, Serial No. 253,879, filed October 30, 1951, by Edward C. Dench, now abandoned, there is disclosed a microwave oscillator utilizing traveling waves in a magnetron amplifier device. The operating frequency of the device may be tuned over a relative ly wide range of frequencies by varying the reactance of the tuning structure, and the device may be made to operate at a plurality of difierent discrete frequencies for a given tuning structure setting by varying the velocity of the electron stream moving along paths adjacent the anode network. Preferably this variation of electron velocity is achieved by variation of the anode voltage.

This invention discloses that the frequency may be made to vary continuously over a relatively wide range of frequencies by terminating the end of the anode network toward which electrons are moving in an energy-absorbing medium, such as a resistive load, which is impedance matched to the characteristic impedance of the line over as wide a range of frequencies as is feasible. The output signal from the device is then coupled otf the anode structure adjacent the end away from which the electrons are moving. Such a device will oscillate at a frequency determined by the intensity of the electrostatic field in the space between the anode and the electrode member positioned adjacent thereto which may be the cathode or an auxiliary electrode. Variation of this electrostatic field is achieved by variation of the anode voltage, thereby varying the frequency as a continuous function of anode volt age.

This invention further discloses that a more nearly single velocity electron beam may be achieved by positioning a cathode adjacent one end of the anode structure and directing the beam by means of crossed electrostatic and magnetic fields along paths adjacent the network.

Other and further objects and advantages of this invention will become apparent as the description thereof progresses, reference being had to the accompanying drawing wherein:

Fig. 1 illustrates a transverse cross-sectional view of a first embodiment of this invention wherein the anode structure comprises a plurality of anode members alternately connected by conductive strapping;

Fig. 2 illustrates a partially broken away transverse cross-sectional view of the second embodiment of this invention wherein the signal transmission network comprises an unstrapped anode structure wherein lumped constants are connected between adjacent anode member's;

Fig. 3 illustrates a longitudinal cross-sectional view of a further modification of the invention; and

Fig. 4 illustrates a transverse cross-sectional view of the device shown in Fig. 3.

Referring now to Fig. 1, there is shown an anode structure 10 comprising a metallic cylinder 11. Extending radially inwardly from the. inner surface of anode cylinder 11 is a plurality of anode members 12 comprising substantially planar rectangular metallic conductors which are positioned substantially parallel to the axis of anode cylinder 11. Alternate anode members 12 are connected at points adjacent their inner ends on the upper andlower edges thereof by conductive straps 13 according to wellknown practice. At one point in the anode structure 10, the anode members 12 and strapping 13 are omitted, and a block of conductive material 14 is substituted therefor. Block 14 occupies the space of several anode members 12. Block 14 is rigidly attached to anode cylinder 11, and ex tends radially inwardly therefrom for substantially the same distance as the anode members 12. The inner face of block 14 has a slot 15 therein which extends radially outwardly toward anode cylinder 11. Slot 15 is appropriately dimensioned to cause the metallic block 14 to behave as a radio frequency choke at the desired operating frequency of the device. The purpose of the radio frequency choke is to effectively isolate signal waves in the anode structure on one side of the metallic block 14 from being fed through the choke to the anode structure on the other side thereof, Because of the break in the anode structure 10 and the presence of the slotted block 14, the signal wave transmission network 11, 12, 13 is nonreentrant.

Signal coupling devices 17 are connected to the ends of the signal wave transmission network by connecting one of the straps 13 to a lead-in member 18, which extends outwardly through anode cylinder 11 spaced therefrom. After lead-in member 18 passes outside cylinder 11 it is surrounded by an outer conductor 19 spaced therefrom and coaxial therewith, outer conductor 19 being sealed to the aperture in cylinder 11 through which lead-in member 18 passes. Outer conductor 19 is insulatedly sealed to lead-in member 18 by a glass seal 20 in a wellknown manner.

Positioned in the space defined by the inner ends of,

anode members 12 is a cathode structure 21 comprising a cathode cylinder 22 positioned concentric with anode cylinder 11. The outer surface of cathode cylinder 22 is coated with electron-emissive material, and is adapted to produce clouds of electrons in the space between the cathode cylinder 22 and the inner ends. of the anode,

members 12 when cathode cylinder 22 is heated by a heater coil, not shown, in a well-known manner. upper and lower ends of cathode cylinder 22 are covered by end shields 23 which tend to prevent movement of the electrons in a direction axial to the cathode cylinder 22.

It is to be clearly understood that the particular details of the cathode structure are disclosed herein by way of example only, and any desired cathode structure or electron source can be used. While the support and lead-in structure for the cathode is not disclosed in this embodiment of the invention, it may be, for example, of the type disclosed in copending application, Serial No. 81,804, filed March 16, 1949, by William C. Brown and Edward C. Dench, now Patent No. 2,673,306, issued March 23, 1954, to William C. Brown. A voltage is produced between the anode structure 10 and the cathode structure 21 by means of an anode voltage supply 24, which is made adjustable in order to select the particular frequency at which it is desired that the device shall operate.

An impedance-matched resistive termination 25 is connected to the signal coupling device 17 which is connected to the end of the line toward which electrons are moving. Termination 25 is preferably of the energy absorbing type which absorbs and dissipates any energy traveling along the anode network in the same direction as the electron beam. An output load 52 is connected The to the coupling device 17 attached to the end of the anode:

network away from which electrons are traveling along the anode network. The direction of electron motion the device of Fig. l is indicated by the arrow 53, being: clockwise about the cathode 2 3 for the particular view illustrated in Fig. 1.

Y Referring now to Fig. 2, there is shown a further embodiment of this invention wherein the signal transmis-- sion network comprises a plurality of adjacent anode: members connected together through lumped electrical. constants to form an equivalent unstrapped type of anode: structure. The anode structure comprises an anode cylin-- der 26, the ends of which are covered by upper and. lower end plates 27 and 28;, respectively. Positioned in.-

side anode cylinder 26 is a cathode structure 29 com-- 1 prising a cathode cylinder 30 whose outer surface is coated with electron-emissive material. The upper and, lower ends of cathode cylinder 30 are covered by end. shields 31 which extend outwardly beyond cathode cylinder 30. Cathode 29 is rigidly mounted with respect tothe anode cylinder 26 by a cathode support structure 32- comprising a cylindrical member 33 attached to one of the end shields 31, which member extends upwardly through an aperture in upper end plate 27, and is rigidly supported with respect thereto by being attached through. a cylindrical member 34 and a cup member 35 to a. ceramic sleeve 36 surrounding cylinder 33 and sealed to a recess in upper end plate 27. Extending downwardly through cylinder 33 into the cathode structure 29 is a lead-in member 37, which is connected to one end of a heater wire inside cathode cylinder 30, the other end of said heater wire being connected to cathode cylinder 30. Lead-in member 37 is insulatedly sealed to cathode cylinder 34 by an insulating seal 38 so that by application of a potential between lead-in wire 37 and cylinder 34, a current may be caused to pass through the cathode heater coil, thereby heating the cathode to the desired. electron emitting temperature.

Surrounding cathode structure 29 is a plurality of anode members 39 comprising elongated conductive mem bers which extend upwardly through upper end plate 27, and are insulatedly supported with respect thereto by insulating beads 40, sealed around anode rods 39, and. inside apertures in end plate 27. Extensions of anode members 39 extend upwardly above upper end plate 27 outside anode cylinder 26, said extensions forming terminal posts to which lumped constants may be connected to form with anode members 39 a signal wave transmission network. Specifically, inductors 4 1 are connected between each pair of adjacent anode members 39, and each anode member 39 is connected to a ground reference plane comprising upper end plate 27 through condensers 42. Inductors 41 are supported on rings 43 which are supported with respect to upper end plate 27 by means of rods 44. At one point in the anode structure, the inductor connecting a pair of adjacent anode members is omitted, said pair of adjacent anode mem bers forming respectively the ends of the signal wave transmission line.

One end of the transmission line is connected to an output load 45 by connecting the anode member 39 at this point directly to the output load, the other terminal of the output load being connected directly to the anode ground plane comprising upper end plate 27. The transmission line has the other end thereof connected by means of a lead-in member 4a to one side of an impedance-matched energy-absorbing termination 47, the other side of termination 47 being connected to the upper end plate 27.

A metallic plate 49 is rigidly attached to cathode cylinder 30, and extends radially outwardly therefrom to a point intermediate the anode members 39 which constitute the ends of the transmission line. Thus, electrons emitted from the cathode are prevented from passing completely around the anode structure from the output of the device to the input thereof. If desired, plate 49 embodiment of the invention illustrated in Fig. 1.

A variable anode supply 50 is connected between the cathode structure and the anode structure whereby the particular frequency at which the device will oscillate is controlled by adjustment of the anode-to-cathode voltage. A magnet coil 51 is positioned around anode cylinder 26 whereby the desired magnetic field may be produced in thespace between-theanode members 39 and the cathode cylinder 30 in a direction transverse to the direction of motion of the electrons.

It is to be clearly understood that any desired means, such as a permanent magnet, could be substituted for the magnet coil illustrated in the species of Figs. 1 and 2, and that either means for producing a magnetic field could be used with the species of Fig. 1.

Referring now to Figs. 3 and 4, there is shown another embodiment of the invention comprising anode structure which is fabricated to form a signal wave transmission network. Anode structure 110 comprises a backing support member 111 which is shown as a flat plate of conductive material such as copper. Extending downwardly from plate 111 is a plurality of anode members 112 which are shown here, for example, as substantially rectangular planar members. Anode members 112 are rigidly attached at their upper ends to support member 111 and are alternately connected at points on their edges adjacent their lower ends by conductive straps 113 according to well-known practice. Planar members 112 are positioned substantially perpendicular to support member 1 11 and to the conductive straps 1'13.

The anode members 112 are positioned within a conductive evacuated envelope of which the support member 111 is a part. The envelope comprises side walls 114 attached to support member 111, a lower wall 115 sealed to side members 114, and end walls 116 whichare sealed to the ends of the box-like structure made up of members 111, 114 and 115.

Positioned inside the envelope adjacent the lower ends of anode members 112 is a metallic trough-like member 117, the bottom of said trough-like member being positioned parallel to the lower edges of anode members 112, and the sides 118 of trough-like member 117' extending upwardly to a point slightly above, but spaced from, the lower corners of anode members 112. Trough 117 is supported by means of insulated supports 119, which provide electrical connection of trough 117 with circuits outside the envelope, but which prevent electrical contact of trough 117 with the envelope or the anode structure 110. Trough 117 and the insulated supports therefor are described in greater detail in my copending application, Serial No. 255,499, filed November 8, 1951, now U. S. Patent No. 2,809,328. i

A cathode structure 120 is positioned adjacent one end of the signal wave transmission network made up of anode members 112 while a catcher electrode 121 is positioned adjacent the other end of signal wave transmission network. The purpose of the cathode 120 is to emit electrons which, under the influence of the proper electrostatic and magnetic fields produced in the space between trough 117 and the lower ends of the anode member 112, will move along paths adjacent the anode members 112 and, after amplifying any signal present in the network through interaction therewith, the electrons will impinge on the catcher electrode 121, The particular details of the cathode 120 and catcher electrode 121, as well as the support and electrical connections thereto, is described in greater detail in the aforesaid copending application, Serial No. 255,499, now Pat. No. 2,809,328. The magnetic field may be produced by means of a magnet which is connected to magnetic pole pieces 122, positioned adja- ,cent the external sides of side members 114.

The anode members 112 do not extend all the way to the end members 116 but a spaceis left adjacent the end members 116 where the members 112 have been omitted. Signal coupling devices 123 are connected to the signal wave transmission network made up of the anode members 112. The coupling device 123 comprises a coaxial line, having an outer conductor 124 sealed through end plate 116, and terminating in the end anode member 112 at a point substantially halfway between the sets of straps 113 and adjacent the lower end of said anode member. Positioned inside conductor 124, and spaced therefrom, is a central conductor 125 which extends through an aperture in the end anode member 112 spaced therefrom and is connected to the anode member adjacent the end anode member. Inner and outer conductors 124 and 125, after passing outwardly through end plate 116, having a tapered transition section 126 designed to match the impedance of the device being coupled to the signal wave transmission network to the impedance of said network. There after, central conductor 125 is insulatedly sealed to the outer conductor 124 by means of an insulating seal, not shown. A signal coupling device 123 is coupled to each end of the transmission network. An output load 133 is coupled to the signal coupling device 123 connected to the end of the network adjacent the cathode 120 while an energy-absorbing impedance-matched termination 134 is coupled to the signal coupling device 123 at the other end of said network.

A variable anode voltage supply 135 is impressed between the electrode 117 and the anode 110. A voltage supply, not shown, is connected between the cathode 120 and the electrode 117 whereby the cathode 120 may be adjusted somewhat positive or negative with respect to the electrode 117 to adjust the position of the beam in the space between the electrode 117 and the anode 110.

It can be shown that a wave traveling along the network in a direction opposite to the direction of the electron stream will have a component which travels backward along the network in the same direction as the electron stream. If the velocity of the electron stream is made substantially equal to the velocity of th backward component of the wave, that is, the component which is traveling in the same direction as the electron stream, interaction will occur and a signal will build up in the network. The energy content of the signal, however, will travel in a direction opposite to the direction of the electron stream. If the end of the network toward which the electron beam is moving is terminated in a matched impedance over a wide range of frequencies and absorbs any energy impinging thereon, the device will generate oscillations whose frequency is dependent substantially entirely on the velocity of the electron stream. If the velocity of the backward component of the wave varies with frequency, as is the case with all the network structures described herein and as is the case with most network structures used in the microwave field, and since the electron velocity is determined by the intensity of the electrostatic field produced by the voltage applied between the anode and cathode or anode and substantially non-emissive electrode 117, variation of this voltage will vary the oscillation frequency of the device. The oscillation frequency may also be controlled or varied by variation of the transverse magnetic field.

This completes the description of the embodiments of the invention illustrated herein. However, many modifications thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. For example, many different types of anode structures could be used, other types of cathode structures could be used and the principles illustrated herein could be utilized in devices not employing a transverse magnetic field. In addition, output power may be varied by variation of the intensity of the electron stream. Accordingly, it is desired that this invention be not limited by the particular details illustrated herein except as defined by the appended claims.

What is claimed is:

1. An electron discharge oscillation generating device comprising a signal wave transmission network having first and second ends, means for electrically isolating said ends from each other at high frequencies, a source of electrons spaced from and substantially coextensive with said network, said means for isolating being spaced from said source substantially the same distance as said network, means for directing a stream of electrons from said source along paths adjacent said network, signal output means coupled to said device adjacent the end thereof away from which electrons move along said paths, and means coupled to said network adjacent the end toward which electrons move along said paths for absorbing incident energy over a wide range of fre quencies.

2. An electron discharge oscillation generating device comprising a signal wave transmission network including several spaced members, said network having first and second ends, means for electrically isolating said ends from each other at high frequencies, a source of electrons arranged substantially coextensive with said network, said means for isolating being spaced from said source substantially the same distance as said network, means for directing a stream of electrons from said source along paths adjacent said network, signal output means coupled to said device adjacent the end thereof away from which electrons move along said paths, and means coupled to said network adjacent the end toward which electrons move along said paths for absorbing incident energy over a wide range of frequencies.

3. An electron discharge oscillation generating device comprising a signal wave transmission network including a cylindrical member and several spaced members extending radially inward from said cylindrical member, a first electrically-conductive element interconnecting a nonalternate set of spaced members and a second electrically-conductive element interconnecting the other set of spaced members, said network having first and second ends, means for electrically isolating said. ends from each other at high frequencies, a source of electrons arranged substantially coextensive with said network, said means for isolating extending radially inward from said cylindrical member for substantially the same distance as said spaced members, said means for isolating further including a slot extending radially outward toward said cylindrical member and dimensioned to form a radio frequency choke at the desired operating frequency of said device,

means for directing a stream of electrons from said source along paths adjacent said network, signal output means coupled to said device adjacent the end thereof away from which electrons move along said paths, and means coupled to said network adjacent the end toward which electrons move along said paths for absorbing incident energy over a wide range of frequencies.

References Cited in the. file of this patent UNITED STATES PATENTS 2,511,407 Kleen et al. June 13, 1950 2,566,087 Lerbs Aug. 28, 1951 2,673,306 Brown Mar. 23, 1954 2,735,958 Brown Feb. 21, 1956 FOREIGN PATENTS 987,573 France Apr. 18, 1951 510,250 Belgium Apr. 15, 1952 699,893 Great Britain Nov. 18, 1953

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