US2748279A - Magnetron amplifier - Google Patents

Description

y 9, 1956 D. A. WILBUR 2,748,279

MAGNETRON AMPLIFIER Filed July 25, 1952 our/ 07 m/Pur f a lnven'b'oh: Donald AWHbur',

His Attorney. 7

MAGNETRON AMPLIFIER Donald A. Wilbur, Albany, N. Y., assignor to General Electric Company, a corporation of New York Application July 25, 1952, Serial No. 300,929

Claims. (Cl. 250-36) This invention relates to frequency multiplying amplifiers of the magnetron type.

Discharge devices of the magnetron type have been extensively and successfully employed as high frequency generators. Their ability to deliver large amounts of high frequency power at relatively high efiiciencies are especially desirable characteristics for amplifiers as well as oscillators, and accordingly, various attempts have been made to utilize the magnetron type of discharge device advantageously in high frequency amplifiers. In magnetrons of the general type having a plurality of anode segments or vanes arranged about a centrally disposed cathode to define a cylindrical space charge chamber, input signals to be amplified have been applied to selected segments and output circuits have been coupled to the other segments for amplifier operation. Usually, feedback coupling from the output to the input anode segments occurs, due both to the geometry of the magnetron and t0 the electronic coupling which is characteristic of magnetron oscillators. Since feedback coupling is generally undesirable in amplifier arrangements, it is desirable to minimize such coupling while at the same time maintaining the advantages of the magetron type of structure.

Accordingly, it is a primary object of my invention to provide an improved discharge device of the magnetron type for amplifying the high frequency signals. It is a further object of my invention toprovide an improved magnetron amplifier in which feedback coupling to the input circuit is minimized.

It is a still further object of my invention toprovide an improved magnetron amplifier which also serves as a frequency multiplier.

' In accordance with my invention, amulti-vane' magnetron discharge device is employed as an amplifier in which a pair of input anode segments or vanes are spaced axially or end-to-end to provide balanced capacitance between the input system and the remainder of the anode segments, which are coupled to an output circuit tuned to the output frequency. Circuit coupling means between the input anode system and the output anode system is thus balanced out due to the symmetry of construction. To minimize electronic back-coupling whereby the reaction of the output vanes or segments upon the space charge in turn affect the input system, the magnetron is preferably operated as a frequency multiplier by making the angle subtended by the input anode segments with respect to the space charge chamber axis a multiple of that subtended by each of the output anode segments.

'The features of my invention which I believe to be novel are described with particularity in the appended claims. The invention itself, however, both as to its method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is a schematic representation of a magnetron amplifier circuit embodynited States Patento 2,748,279 Patented May 29, 1956 ing my invention and Fig. 2 is a sectional view of a magnetron discharge device used in the circuit of Fig. 1.

Reference is made to Fig. 1 where magnetron cathode and anode segments are shown connected in circuit to illustrate the amplifier'operationf As may be seen, an elongated thermionic cathode 1 which may suitably take the form of a tungsten wire helix, is surrounded by an anode structure 2 comprising a pair of axially spaced input or driving vanes 3 and 4 and two pairs laterally spaced of output vanes or segments 5, the output segments each having an axial length equal to the combined length of the input segments 3 and 4.

A tuned input circuit 6 schematically represented by lumped inductance and capacitive elements connected in parallel, is coupled to a source of input signals of a given frequency f to which the input circuit is tuned. The output circuit is represented similarly by a tuned crcuit 7 tuned to a frequency 2] and is suitably coupled to a desired load. The output circuit is conventionally coupled to the output vanes 5 for pi mode operation, alternate or non-adjacent vanes being connected in parallel to the respective output circuit terminals.

The midpoints of the input and output circuit inductances, which represent the alternating current neutral point of these circuits, are both grounded and the cathode is maintained at a negative voltage with. respect to ground by a source of voltage 8 conventionally represented as a battery. A radial electric field is thus provided between the cathode 1 and the anode assembly 2.

Current for maintaining the cathode 1 at an emitting temperature is suitably provided from a low voltage 10, although, of course, permanent magnet means may be substituted. V p

In omens provide the frequency multiplying action, the magnetron of Fig. l is arranged as a frequency doubler, the width of each anode segment 3. and 4 being twice that of each of the output segments 5. The width,

which is thclength of the space charge path under the segment may be also described in terms of the angle subtended by a segment with respect to the cathode or.

space charge chamber axis. Accordingly, in the illustrated arrangement, four output segments 5, each subtend an angle of substantially 60, or more accurately, an angle of'60' is subtended between the centers of the small interaction gaps on either side of any of the anode segments 5. The double-width input segments or vanes.

accordingly each subtend an angle of substantially For a given angular velocity of the space charge twice as much time is therefore required for the space charge to'pass under either input electrode'3 or 4 as under any one of the output electrodes 5. Since the space charge is axially distributed along the cathode only a portion of itpasses under theinput electrode 3, the other portion passing underthe other input electrode 4..

When the applied voltage betweenthe cathode and anode assembly is raised to a value just less than that required for generation of magnetron oscillations in a conventional manner, the magnetron will, upon the application of an additional voltage, produce a useful output in to produce the output change provides a measure of the amplification characteristics of the device. However, instead of applying the additional voltage as a static field the voltage is instead applied as a signal voltage of a given frequency between the input electrodes 3 and 4. The amplified power output is accordingly proportional to the input signal amplitude to provide the desired amplifier operation.

An analysis of the reaction of the alternating electric fields upon the electronic space charge explains the nature of the amplifier operation.

For example, at an instant when the alternating input voltage at the input vane 3 is positive, the electrons of the space charge passing underneath this vane are accelerated, thus tending to raise the angular velocity of the space charge above the velocity at which it is in synchronism with the alternating fields associated. with the anode segments. Assuming a clockwise direction of space charge rotation, electrons passing under one edge of segment 3 across the gap and under the adjacent edge of the adjacent output segment when the input segment 3 is still positive and the adjacent segment is negative, are in phase to maintain conventional pi mode excitation of the output anode system. In other words, in passing from under a positive segment to a negative segment, the electrons are in phase with the direction of the fringing electric field between them and must do work against that field, thus tending to decrease their velocity and to impart some of their kinetic energy to the output circuit associated with the output segments defining the gaps. This in-phase portion of the space charge, because of its decrease in velocity increases in radius to regain its velocity and thus forms what may be termed a space charge spoke analogous to an electronic commutator.

The same process occurs during the next half cycle at the input frequency f with respect to the other input segment 4. Since that half cycle is a full cycle for the output frequency 2 the adjacent segment 5 in the clock wise direction is again at a negative potential.

A space charge spoke from either segment 3 or 4 of the input system accordingly enters the output section comprising the anode segments 5 every half cycle at frequency f or every cycle at the output frequency 2). These spokes conventionally excite the output section, being in phase with the alternating fields of frequency 2 between the adjacent output segments. By virtue of the added energy imparted to the spokes under the input segments 3 and 4, energy is transferred to the output section for the required amplifier operation. The input circuit is not materially loaded by the induced spokes from the output section since it is tuned to a different frequency, the back induction effects tending to cancel out. In the particular arrangement of Fig. 1 three space charge spokes pass under each input segment for every space charge rotation. Each spoke rotates about the cathode once for every one and one-half cycles of the input frequency f, traversing an input anode segment or an output segment in one-half cycle of input or the output frequency respectively. In this manner the axially spaced input segments 3 and 4 alternately drive the space charge spokes so that periodic half-cycle excitation of the output system is maintained at the multiplied output frequency.

Other members of anode segments may also be employed in accordance with my invention, each axiallyspaced driving or input segment preferably subtending an angle which is the product of the desired frequency multiplier times the angle subtended by an output segment.

Fig. 2 illustrates a magnetron discharge device corresponding :to that semi-schematically shown in Fig. l. A cathode 11, the input anode segments 3 and 4, and the output anode segments 5 are enclosed in an envelope 12 which may be suitably made of glass. The electrodes are supported by a circular array of upright conductive rods 13 which are supported near their lower ends from the stem or base 14 of the envelope. and, hermetically sealed therethrough. The, upper ends; of the, support rods; 13

are suitably maintained in position by a mica spacer 15.

The cathode 11, which is shown for the purposes of illustration as taking the form of a tubular nickel sleeve coated with an electron emitting material such as barium oxide, is supported at its ends by relatively stiff wire segments welded between the cathode sleeve and to two of the support rods 13, one of which serves as the cathode terminal. Within the cathode is a suitable heater such as a wound wire helix having its end positions extending from the cathode sleeve and connected between two of the support rods 13. The input electrodes 3 and 4, also suitably made of sheet nickel material are provided with tabs welded to the external surface. The tabs are welded to separate support rods which serve as the input anode leads and also support the anode sections. As previously mentioned the input anode segments are axially spaced from each other and their combined length is preferably coextensive with that of each of the remaining anode output segments 5. To simplify construction each of the output anode segments 5 is suitably formed from a single rectangle of sheet nickel having one end portion bent over to form the active anode surface facing the cathode with the remaining tab or flange portion extending radially to a support rod 13 and welded thereto.

In accordance with conventional practice, suitable means for evacuating the envelope and protecting it from electron bombardment are employed. Accordingly, end shield 16 in the form of metallic disks of a diameter slightly greater than the overall anode diameter are positioned near the opposite ends of the cathode and supported from the support rods 13 to protect the envelope 11 from electrons leaving the space charge chamber. A getter assembly 17 is suitably mounted above the mica spacer 15 and supported from one of the support rods 13 the getter being flashed in a conventional manner to remove residual gases from the evacuated envelope.

Although the active surfaces of the various anode segments are preferably curved or arcuate to define a circular space charge chamber cross section, some departure from this configuration may be tolerated, especialy in small and inexpensive discharge devices of the type shown in Fig. 2. Accordingly, the active surfaces of the output electrodes 5 may be plane rather than curved since they are relatively narrow, each subtending an angle somewhat less than 60 to the space charge chamber axis. As in usual magnetron construction the axial interaction gaps between the adjacent segments are relatively small so that a radial electric field throughout the space charge chamber may be maintained, the minimum spacing between being determined by convenience of construction and the extent of capacitive coupling which can be tolerated. Similar considerations control the axial spacing of the input electrodes 3 and 4. It should be understood, of course, that the specific construction illustrated is exemplary of the types of discharge devices which can be employed in magnetron amplifiers utilizing my invention.

While the present invention has been described by reference to a particular embodiment thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

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

1. A magnetron discharge device comprising an elongated cathode extending along a given axis and an anode assembly surrounding said cathode in a cylindrical array comprising a pair of anode segments spaced along an axis parallel to said axis and a plurality of anode segments laterally spaced with respect to each other and said pair of segments, the length of each of said plurality of segment being substantially equal to the combined length of said axial spaced pair of segments, all of said J) segments lying on substantially the same cylindrical surface and defining a reentrant annular space charge region.

2. A magnetron discharge device comprising an elongated cathode extending along a given axis and an anode assembly of a given length surrounding said cathode in a cylindrical array coaxial therewith, said anode assembly including a plurality of laterally spaced anode segments of said length and a pair of axially spaced anode segments having a combined length equal to said length, the width of each of said pair of segments being equal to an integral multiple of the width of each of said plurality of said segments, said segments all lying on substantially the same cylindrical surface and defining a reentrant annular space charge region between said segments and said cathode.

3. A high frequency amplifier including a magnetron discharge device comprising an elongated cathode extending along a given axis and an anode assembly of a given length surrounding said cathode in a cylindrical array coaxial and coextensive therewith, said anode assembly including a plurality of laterally spaced segments and a pair of axially spaced anode segments, all of said segments lying on substantially the same cylindrical surface and defining an annular reentrant space charge region between said segments and said cathode, means coupling said pair of segments to a source of input signals and maintaining them at a positive voltage with respect to said cathode, and means coupling said plurality of segments to an output circuit.

4. A frequency multiplying amplifier including a magnetron discharge device comprising an elongated cathode extending along a given axis and an anode assembly of a given length surrounding said cathode in a cylindrical array coaxial therewith, said anode assembly including a plurality of laterally spaced segments each of said length and a pair of axially spaced anode segments having a combined length equal to said length, the width of each of said pair of segments being equal to an integral multiple of the Width of each of said plurality of said segments, all of said segments lying on substantially the same cylindrical surface and defining an annular reentrant space charge region between said segments and said cathode, means coupling said pair of segments to a source of input signals of a given frenquency and maintaining them at a positive voltage with respect to said cathode, and means coupling said plurality of segments to an output circuit tuned to a frequency equal to the product of said multiple times said given frequency.

5. A frequency doubling amplifier including a magnetron discharge device comprising an elongated cathode extending along a given axis and an anode assembly of a given length surrounding said cathode in a cylindrical array coaxial therewith, said anode assembly including a plurality of laterially spaced segments each of said length and a pair of axially spaced anode segments having a combined length equal to said length, the width of each of said pair of segments being substantially equal to twice the width of each of said plurality of said segments, all of said segments lying on substantially the same cylindrical surface and defining an annular reentrant space charge region between said segments and said cathode, means coupling said pair of segments to a source of input signals of a given frequency and maintaining them at a positive voltage with respect to said cathode, and means coupling said plurality of segments to an output circuit tuned to a frequency equal to twice said given frenquency.

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 a1. Aug. 1, 1939 2,168,296 De Vriet et a1 Aug. 1, 1939 2,187,149 Fritz Jan. 16, 1940 2,198,334 Fritz Apr. 23, 1940 2,250,698 Berline July 29, 1941 2,293,798 Braden Aug. 25, 1942

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