US2748280A - Magnetron amplifier - Google Patents

Description

May 29, 1956 R. B. NELSON ETAL MAGNETRON AMPLIFIER Filed July 25. 1952 Inventors: Ri chard BNelson,

DonaldAWilbuh, by fi k/ The ir- Attorney.

United States Patent MAGNETRON AMPLIFIER.

RichardaB. Nelson, Mountain View, Calif., and Donald A. Wilbur,- Albany, N. Y., assignors to General Electric Company, a corporation of New York.

Application July 25., 1952, Serial No. 300,928.

8.Claims. (Cl. 250-36) This invention relates to frequency multiplying amplifiers and has particular reference to magnetron. apparatus.

Discharge devices of. the magnetron. type. have. been extensively and successively employed as high frequency generators. Their ability to produce largeamounts of power at relatively high efliciencies suggests their particular desirability as amplifying devices, and various attempts have been made to so utilize. the magnetron type. of discharge device. in high frequency amplifying. circuits. Accordingly, intraveling wave. multivane magnetrons of the type having an anode assembly comprising a. plurality of anode vanes or segments arranged in a circular array about a.central cathode, input signals to be, amplifiedhave been applied'toselected segments, and a power output circuit has. been coupled tothe other segments. In order to prevent loading of the input. signal source,.. it is desirable. in such magnetron amplifiers that input and outputcircuit coupling dueto the geometry of the-magnetron device discharge be minimized while still retaining the magnetron characteristics useful. in amplifier. arrangements.

Accordingly, a primary object of. this invention is.v to provide a discharge device of .themagnetron type for amplifying high frequency electromagnetic. signals.

his afurther, object of thisinyention, to. provide an improved magnetron amplifier inzwhich, loading of, the input cricuit is minimized.

It isa stillfurther. object of thisinvention. to. provide a magnetron amplifier which also multiplies afrequency to beamplified.

V In accordance with an exemplary embodiment. of the invention described. herein, amagnetron discharge. device of the type-,having a plurality of spaced. anode. segments surroundinga centrally disposed cathodeto define a .cylin: drical'space charge chamber, coaxial with the. cathode has an input section comprising at least one anode vane. or segment to which an inputcircuit forsupplying inputv signals of a given frequency is coupledlandanoutput section comprising a plurality of vanes or segmentsto which is coupled an output circuit for producing amplififld signals atpa desired integral harmonic or multiple of the input fie,- quency. Each segment of the input sectionsubtendfsan angle with respect to the cathode whichis equal to the productof the desired multiple times the. angle subtended by each of thesegments of the output section. A radially directed static electric field and an axially directed static magnetic fieldare established in the space charge chamber to impart an average angular space charge velocity about the cathode slightly below the synchronous velocity requiredto maintain oscillation in the tuned circuits. This space charge is modulated by the applied input signal" on the-input section, in which the signal tendsto drive the useful portion ofjthe space charge at a. higher. tl1.a11..syn-. chronous velocity. Energy is. thus impartedlo, thespace charge for maintaining excitation of. the. output section through interaction with the alternating electric .field be-. tween the, anode segment. .gans. Since the-circuit. coupled to :the, input segmentsis not tuned to the output frequency, any voltages induced in the input circuit due to backice 2. modulation: of the space charge by the ontput'circuitare very small, thus minimizing back coupling. At'the same time, the. input. signal has. been both amplified in accordance. with the amplitude modulation of'the input signal and multipliedin frequency.

Thefeatures of the invention which are believed to be novel. are described with particularity in the appended claims. The invention itself, however, both as to its method ofoperation together with further objects and advan: tages thereof, may best be understood by reference to the following description taken in connection with the-accompanying drawing in which Fig. l is a semi-schematic representation-of a magnetron discharge devicetogether with circuit connections in accordance with our invention; Fig. 2 is a sectional side view of the magnetron apparatus corresponding to Fig; l; and Fig. 3 is a modification of the arrangement of.,Fig. 1.

Referringnow to Fig. 1, a frequency doubling amplifier embodying our invention is illustrated. The magnetron; L is typical. of .the multi-segment type of discharge device conventionally employed as a high frequency oscillator in so far. as a-plurality of spaced anode vanes or segments are arranged about an elongated cathode 2 to define between their inner surfaces a cylindrical space chargechamber 3v coaxial with the cathode. The input section ofthe anode assembly is a segment dhaving an inner surfaceqsubtsantially. semi-cylindrical in form so as to subtend. almost. 18.0 of arc with respectto the space charge. chamber... axis; The output, section is a pair. of adjacent. anode segments 5 and 6. which each: subtend alm0st.90., of arc,;the. three segmentsqbeing spacedfrom eachothertoprovide.smallihteraction gaps betweentherm An input circuit 7, schematically represented byalumped capacitance, andinductance circuit tuned to the frequency ofitheiuputsignalf is, connected between the inputanodc- 4i. and.the..-cath.o.de:- 2.thro.ugh. a direct voltage source 'such as-aQbattery. 8. Theoutput segments 5 and, 6- are con: ncctedto. an output circuit-:9 similarly schematically representedasin pntcircuitTand tuned, to the doubled'output frequencylj. The. output and input circuits are respectively coupled. to. a suitable signal, source and-.a load. Since the frequencies.- profitably; employed. in magnetron operation. are-inthe.veryhigh on ultraehigh frequencyranges, var-ioustuned circuit structures employing distributed reactance may be utilized.

A.highfrequency neutral point. of the output circuit 9,.shown schematically asa center tapon its inductance element is. also. connected" to thecathode through the battery 8, thus. establishing a-uniformv static radial electric field.between..thecatl1o.de and the. anode assembly. To.

provide electrons for themagnetron: space. charge,v the.

cathode is. suitablyconnected-to a source. of heater currentlil. When; anqaxialstatio-magnetic field, shown as establishedrby asolenoidll; is. directed through the. space charge,-- chamber, the; resulting; space charge is given a generally rotating motion, about thecathode. For purposes .of illustration, aclockwiserotation isassumed. Thesynchronousl angular velocity. of the space charge is the same for :either theinput or output section, despite: their diiferent operating frequencies, since their respective. anode segments are-of-v appropriately diiferent circumferential spondsato thatofa. two-vane magnetron for the-input sectiongandof afour-vane magnetron for the output-section;

W-hen the voltage of the source 8 is. raised to a3value just lessr than thatrequired for oscillation of either. the input or output circuit, which value may be considered as the oscillation; threshold, the. velocity of the space:

chargeis just: less than; that required fortransfercof energy from: the. direct current. source; 8 to the high frequency" sections. The driven input segment 4 becomes alternately positive-and negative at frequency 1, thus increasing the velocity of the space charged during positive half cycles. This accelerated portion of the space charge then passes interaction gaps between the segments in phase with the fringing fields established by initial excitation of the output circuit at frequency 2 giving up energy and so assuming a greater diameter to define a space charge spoke. The initial excitation may be assumed to be noise or random excitation in accordance with the prevailing concepts of conventional magnetron operation. Since the term spoke offers a simplified descriptive analysis of the magnetron amplifier operation and since such a configuration of space charge is believed to conform with the actual effect of the various interacting fields upon the magnetron space charge, use of this term is continued in the explanation.

While the input section at frequency 1 produces and drives only one spoke for each 360 rotation of the space charge, the output section at frequency 2 operates, because of its geometry, with two spokes for each rotation. The single driven spoke, accordingly, delivers pulses of energy to the output system at a rate equal to half the output frequency, which is sufiicient to maintain excitation of the output circuit since the spoke is relatively narrow and not of a full half wave duration. The spoke may be considered, therefore, as having a high second harmonic content. The induced electric field at frequency 21 in the output system tends to react upon the space charge and modulate it at double frequency so as to increase the size of the driven spoke and to provide an an additional space charge spoke 180 displaced from the driven spoke. However, the current tending to be induced at the doubled frequency in the input circuit is cancelled out since the input circuit is tuned and operated at the fundamental frequency. The frequency doubling arrangement of the amplifier thus effectively isolates the input circuit.

Referring now to Fig. 2, magnetron apparatus corresponding to the arrangement schematically shown in Fig. 1 is illustrated. Here the magnetron 1 has a cylindrical metallic envelope 12 made of a non-magnetic material. Within the envelope are the cathode 2, shown in end view, the input anode sgement 4 and the output segments 5 and 6. Input segment 4 is a conducting block sealed around its periphery to a glass sealing ring 13 which is in turn sealed to one end of the envelope cylinder 12. The output anode segments 5 and 6 are respectively connected to each of a pair of parallel conductors 14. The conductors 14 are separately sealed through a glass sealing disk 15 at the other end of the envelope cylinder 12.

The input circuit 7 is a tuned concentric conductor section having an outer conductor 16 of approximately the same diameter as the envelope 12 and conductively engaging the envelope at the end to which the input anode segment 4 is sealed. The inner tubular conductor 17 of the input circuit 7 suitably engages the exposed portion of the anode segment 4 as shown in the drawing. Spring fingers 18 at the end of the inner tubular conductor are biased due to their resiliency against the sides of a cylindrical bore 19 in the end of the anode segment 4 within which the inner conductor end is positioned. An annular short-circuiting plunger 20 is actually positioned along the length of the concentric conductor arrangement between the inner end and outer conductors to determine the transmission line section length and thus tune it to the desired input frequency. A concentric transmission line from the source of input signals is suitably coupled to the input circuit 7. As shown in the drawing, the outer conductor of the input coupling transmission line 21 is connected to the outer conductor 16 of the tuned input tuned parallel conductor transmission line section therewith, this tuned section corresponding to the output tuned circuit 9 of Fig. l. A cylindrical outer conductor 23, of approximately the same diameter as the envelope cylinder 12, is conductively coupled at one end to the output end of the envelope cylinder. A short-circuiting plunger 24 provides a short-circuiting termination between the parallel conductors, the axial position of the tuning plunger determining the tuning of the output circuit. The high frequency neutral point of the output circuit 9 is simultaneously coupled through the remaining portion of the plunger 24 to the series-connected outer cylinders 23, 12, and 16. An output coupling means for coupling power from the output circuit to a desired load suitably takes the form of a concentric conductor transmission line 25 having its outer conductor connected to the slider 24 and its inner conductor extending therethrough to define an inductive loop.

As may be seen, the mechanical arrangement simplifies application of the anode voltage since the voltage supply need merely be connected between the cathode 2 and the envelope 12 of the magnetron. Since the outer cylinders 16 and 23 of the input and output circuit arrangements respectively are in conductive relation with the envelope 12, both the input anode 4 and the output anodes 5 and 6 are maintained at the desired positive potential. The arrangement shown is both compact and relatively simple to maintain and adjust while providing for efiicient operation as an amplifier. For example, a device of the nature described has been operated with a power gain of 100 at doubled frequency and with reasonable efiiciency. Of course, it is obvious that other mechanical arrangements can be substituted since the principles of our invention are applicable to traveling wave magnetron amplifiers generally.

Referring now to Fig. 3, another magnetron arrangement embodying the invention is schematically shown in which the input circuit is balanced with respect to the cathode so that it need not be coupled thereto. This arrangement corresponds closely to that of Fig. l in so far as it is arranged for a frequency multiplying ratio of 2. Here again an electron emitting cathode 26 extends along a given axis with a plurality of anode segments surrounding the cathode to define between their inner surfaces a space charge cylinder 27 coaxial with the cathode. Two adjacent anode segments 28 and 29 define the input section and the remaining four segments 30, 31, 32, and 33 define the output section. Since the amplifier is arranged as a doubler each of the input segments subtends twice the are or angle with respect to the chamber axis as does each of the output segments. Hence with a total of 6 segments here involved the input segments each subtend substantially of arc and the output segments each subtend substantially 45 of arc.

The input circuit 34, schematically indicated, is tuned to the desired input frequency and its high frequency neutral point is connected to the cathode 26 through the anode voltage supply source 35. The terminals of the input circuit are respectively coupled to the input electrodes 28 and 29 so that the input voltage appears between them. Output circuit 36, also schematically represented, is tuned to twice the input frequency and its high frequency neutral point is also connected to the cathode through the anode voltage source 35. The four output segments 30, 31, 32, and 33 are connected for 1r mode operation, one of the output circuit terminals being connected to segments 30 and 32 and the other being connected to segments 31 and 33. The cathode is suitably heated by a heating current source 37 and a magnetic field, schematically represented as provided by a solenoid 38, is axially directed in the space charge chamber 27.

As in the operation of the amplifier of Fig. 1, the anode voltage 35 is increased to a value just less than that required for oscillation. The application of an input signal across the input anode section causes excitation of the Oil-taut c it t: the u d re u nc W th. he. r-

relatiyely narrow and hence do not cancel the double frequency excitation produced, The output anode section also-producestwo additional spokes, each displaced 90 .fmm; the. driving spokes, but this back-modulation of the spacechargedoes notdoad-the inputcircuit 34, since the inputcircuit is; tuned to only one-half of the output frequency. Accordingly, back excitation or reaction of the tlnllt sec i ny a m at ng pa e ha e a g. four spokes per complete rotation is relatively small since the ql ag sp dus y pa r of adjacen pokes. tend t 9?. 1 out similarly as, described in relation to the operan; of; he ir ui f Fis- An nalys s. d at sthat om a ti n. of the e tron stream upon the input system is-obtained. However, this reaction does not result in positive or resistive load ing of the input circuit, but instead, results in excitation at the input frequency. The generaleffect therefore is to increase the effective input impedance of the input circuit. Sincethis is generally desirable and quite the ppp it f, theundesiredefiec bt ine pon. direct reistiye.loading,.. h impedance. matching to he. ource of h np t ignals may be ccordi gly pr rmined and isifa i i at d in many ases.

It will bcunderstnodthat. heinyenticn is notlimited to frequency doubling and that for use of higher multiplying ratios, the ratio of the arc subtended by each of the driving segments to each of the driven segments is accordingly increased.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that modifications may be employed without in any way departing from the spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A frequency multiplying amplifier comprising an electron discharge device of the magnetron type having an elongated electron emitting cathode and a plurality of spaced anode segments surrounding said cathode with their inner surfaces defining a unitary cylindrical space charge chamber coaxial therewith; an input circuit tuned to a given frequency coupled to an input anode section comprising at least one of said segments, an output circuit substantially independent of said input circuit tuned to an integral multiple of said frequency and coupled to an output anode section comprising other segments of said plurality of said segments, said at least one segment of said input section subtending an angle with said axis substantially equal to the product of said multiple times the angle subtended by each of the segments of said output section, and means for establishing an axially directed magnetic field and a radially electric field within said space charge chamber, said means being adjusted to maintain the amplifier slightly below the oscillation threshold.

2. A frequency multiplying amplifier comprising an electron discharge device of the magnetron type having an elongated cathode for supplying an electron space charge and a plurality of spaced anode segments surrounding said cathode and having their inner surfaces defining a unitary cylindrical space charge chamber coaxial therewith; an input circuit tuned to a given frequency coupled to an input anode section comprising at least one of said segments, an output circuit substantially independent of said input circuit tuned to an integral multiple of said fr quen y and-coupled to an outpu lu Sfiction C0111- prising. t e segmentsof said plurality of i said: seg e t said at least onesegrnentofsaid. inputsection substendng an ng th said: xis substantially equal .to the prodn t f id m l ip e-timesthe. an le. subtended by each of the segment tsaidoutput-section, means for; establishing an axially directedf magnetic; field within said chamber; and, means for applying. a posi ive vol age to said'anode segments, with respectto said cathode whereby an average angular space charge. velocity about the cathode is provided, said; voltage, being. adjusted in intensity relative to said, magnetic fieldto. a. value slightly. below that requiredformaintenance of joscillations in either of said circuits, and means for; coupling saidinput circuit to a signal source.

3. A frequency doubling-amplifier comprising anelec- U011 discharge e e o the:magnet-ron type having an elongated electron emitting; cathode, and a. plurality of spaced anode segmentsi surrounding said cathode and having their inner surf ces; defining aunitary. cylindrical space charge chambe-r coaxial. therewith; an input circuit tuned to a given frequency coupledto; an input anode section comprising; atleast one ofsaid'segments, an.output circuit substantially:independentof said'input circuit tuned; toa frequency and twice that of said given frequency coupledgto an output;anode.- section comprising other segments; of? Said; plurality of said, segments, said at eas n gment ofi aid input section subtending an angle withsaid axis substantialllyctwice the angle. subtendedgby; each or the seg'mentsof said output section, means. for; establishing an; axially directed static magneticv field and; a,- ra d i,all.y directed-static. electric field within saidchamber, saidifieldsbeing adjusted in relative intensi y. t9: a value; slightly below: that, at which either of said circuits will oscillate, and means for coupling said input circuit to a signal source.

4. A frequency doubling amplifier comprising an electron discharge device of the magnetron type having an elongated electron emitting cathode, and a plurality of spaced anode segments surrounding said cathode and having their inner surfaces defining a unitary cylindrical space charge chamber coaxial therewith; an input circuit tuned to a given frequency coupled to an input anode section having a given number of said segments, an output circuit substantially independent of said input circuit tuned to a frequency twice that of said given frequency and coupled to an output anode section having a number of other segments of said plurality of said segments twice said given number, each segment of said input section subtending an angle with said axis substantially equal to twice the angle subtended by each of the segments of said output section, means for establishing an axially directed magnetic field within said chamber, means for applying a radially directed static electric field between said cathode and said anode segments, said electric field being adjusted in intensity relative to said magnetic field to a value slightly below that at which the amplifier oscillates, means for coupling said input circuit to a source of signals of the given frequency to be doubled, and means for coupling said output circuit to a load.

5. A frequency multiplier amplifier comprising a discharge device of the magnetron type containing an elongated electron emitting cathode and a plurality of spaced anode segments surrounding said cathode with their inner surfaces defining a unitary cylindrical space charge chamber coaxial therewith, an input circuit tuned to a given frequency coupled between one of said segments and said cathode, an output circuit substantially independent of said input circuit tuned to an integral multiple of said frequency and coupled to the other segments, said one segment subtending an angle with the axis substantially equal to the product of said multiple times the angle subtended by each of the other segments, means for establishing a radially directed electric field and an axially directed magnetic field within said space charge chamber,

' 7 said means being adjusted to maintain the amplifier slightly below the threshold of oscillation, and means for coupling said input circuit to a source of signals.

6. A frequency doubling amplifier comprising a discharge device of the magnetron type containing an elongated electron emitting cathode and three spaced anode segments surrounding said cathode with their inner surfaces defining a cylindrical space charge chamber coaxial therewith, an input circuit tuned to a given frequency coupled between one of said segments and said cathode, an output circuit substantially independent of said input circuit tuned to a frequency twice that of said given frequency and coupled to the other two segments, said one segment subtending substantially 180 of arc, each of the other segments subtending substantially 90 of are, means establishing a radially directed electric field and an axially directed magnetic field within said space charge chamber for imparting a rotating space charge motion about the cathode, said means being adjusted to maintain the amplifier slightly below the threshold of oscillation, and means for coupling a source of signals to be amplified to said input circuit.

7. A frequency multiplying amplifier comprising a discharge device of the magnetron type containing an elongated electron emitting cathode and a plurality of spaced anode segments surrounding said cathode with their inner surfaces defining a unitary cylindrical space charge chamber coaxial therewith, an input circuit tuned to a given frequency coupled to two of said segments, an output circuit substantially independent of said input circuit tuned to a multiple of said input frequencies and coupled to other segments of said plurality of segments, each of said two segments subtending an angle with said axis substantially equal to the product of said multiple times the angle subtended by each of the other segments, means for establishing a radially directed electric field and an axially directed magnetic field within said space charge chamber, said means being adjusted to maintain the amplifier slightly below the threshold of oscillation, and means for coupling said input circuit to a source of signals to be amplified.

8. A frequency doubling amplifier comprising a discharge device of the magnetron type containing an elongated electron emitting cathode and a plurality of spaced anode segments surrounding said cathode with their inner surfaces defining a unitary cylindrical space charge chamber coaxial therewith, an input circuit tuned to a given frequency coupled between two of said plurality of said segments, an output circuit tuned to twice said input frequency coupled to four other segments of said plurality of segments, each of said two segments subtending an angle with said axis substantially equal to twice the angle subtended by each of said four segments, means for establishing a radially directed electric field and an axially directed magnetic field within said space charge chamber, said means being adjusted to maintain the amplifier slightly below the threshold of oscillation, and means for coupling said input circuit to a source of signals to be amplified.

References Cited in the file of this patent UNITED STATES PATENTS 2,162,807 Fritz June 20, 1939 2,166,210 Fritz July 18, 1939 2,168,295 De Vries et al Aug. 1, 1939 2,168,296 De Vries et al. Aug. 1, 1939 2,198,334 Fritz Apr. 23, 1940

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