US2803773A - High frequency diode magnetron - Google Patents

Description

Zq, 1957 D. A. WILBUR Em 2,803,773

HIGH FREQUENCY DIODE MAGNETRON Filed Oct. 28, 1952 A lr wve ntors Donald A.Wi Ibur,

I H. PeteraJh, Their- Attorney.

HIGH FREQUENCY DIODE MAGNETRON Donald A. Wilbur, Albany, and Philip H. Peters, Jr.,

Schenectady, N. Y., assignors to General Electric Company, a corporation of New York Application October 28, 1952, Serial No. 317,272

7 Claims. (Cl. 313-457) This invention relates to high frequency discharge devices of the magnetron type and has particular reference to magnetron diodes in which the anode is a single electrode.

In a magnetron diode discharge device, the only electrodes are a cathode and a concentric anode, the anode being a single electrode. Such a device operates as a magnetron oscillator due to an applied radial electric field and axial magnetic field which react upon an electronic space charge. Historically, the first magnetron was a diode utilized to provide audio frequency oscillations through feedback coupling from the anode circuit to the magnetic field-producing means. Magnetron oscillators were subsequently used in higher frequency ranges by splitting the anode into two or more segments so that different segments of the anode could be maintained at different alternating potentials. High frequency split anode magnetrons are generally classified as three typesthe negative resistance, the cyclotron frequency, and the traveling wave magnetron oscillators. The third type, the traveling wave magnetron oscillator, has had wide and extensive use as a high frequency, high power oscillator, almost to the exclusion of the other types. In the traveling wave magnetron, resonant circuit means coupled between selected anode segments are used to facilitate extraction of energy from the rotating electronic space charge passing under the anode segments. In some such magnetrons circuit connections external to the discharge device envelope are employed while in others the interconnecting circuit or circuits may be incorporated in an internal anode assembly or anode block, the choice of lumped or distributed circuit components depending to'a large extent upon the frequency range involved. One general trend of the development of the art, however, has been toward greater complexity and smaller component parts, with a resultant increase in the cost of fabrication and assembly. Obviously, simplification or elimination of the anode segment array would provide structural economies.

It is an object of our invention to provide a high frequency magnetron diode.

It is another object of our invention to provide an improved magnetron diode oscillator.

It is a further object of our invention to provide a simple and improved magnetron construction.

In accordance with our invention, a magnetron diode is provided having a tubular cathode and a single tubular anode, these electrodes being concentric to provide a space charge chamber between them. The cross section of the anode, or of both the anode and cathode, depart from a circular form to define a discrete number of sides. For example, in a preferred embodiment described herein the anode cross section is that of a regular polygon coaxial with the cathode so that the mid region of each side of the polygon corresponds to an active anode vane or segment. With such a construction, both the anode segments and the means for interconnecting them in a nited States Patent high frequency traveling wave operation are easily provided in a unitary anode structure.

The features of our invention which we believe to be novel are set forth with particularity in the appended claims. Our invention itself, however, both as to its organization and 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 drawings in which Fig. 1 is a schematic representation of a magnetron oscillator apparatus embodying our invention; Figs. 2a, 2b, and 2c are a schematic representation by successive steps of a possible evolution of a magnetron construction em bodying our invention from a conventional multivane magnetron; Fig. 3 is a perspective view of a magnetron discharge device corresponding to the device schematically shown in Fig. 2; Figs. 4a, 4b, 4c, and 4d illustrate alternative anode cross sections; Figs. 5a, 5b, 5c, and 5d are modifications of the arrangements of Fig. 4; and Fig. 6 represents a modification of the oscillator apparatus of Fig. 1.

Referring now to Fig. 1, the magnetron diode 1 schematically represented therein is connected in circuit as a high frequency oscillator. The cathode 2 is a tubular member extending along a given axis, the cathode preferably having a triangular cross section so as to provide three sides of equal width. A tubular anode concentric with the cathode is also provided with an equilateral triangular cross section having each side parallel to the facing side of the cathode. An output circuit or tank 4 is connected to the anode 3 and through a unidirectional voltage source 5 to the cathode. The generalized output circuit is schematically represented as having parallel inductive, capacitive, and resistive elements. When the resistance is very high, the reactive components provide a sharply tuned circuit. The bandwidth of the circuit may be increased by decreasing the resistance. The direct voltage source 5 is preferably bypassed for output frequencies by a capacitor 6, and is connected to place a positive potential on the anode 3, thus establishing a radial electric field in the space charge chamber between the cathode and anode. Means for producing an axial magnetic field in the space charge chamber is schematically represented as a solenoid coil 7.

Electrons emitted from the cathode 2 are acted upon by the orthogonal electric and magnetic fields with the result that an average angular velocity about the cathode is imparted to the electronic space charge. As in conventional traveling wave multi-vane magnetrons, oscillations are established in the output circuit, which in this case is coupled between the anode and cathode, when the applied voltage from the source 5 reaches a certain value. These oscillations are usually considered as established by space charge spokes spaced about the cathode, each spoke extending along the cathode length and representing a region of bunched electrons in which the average distance of the electrons from the cathode is greater than in the space charge regions between the spokes. The space charge spokes travel in synchronism with the high frequency traveling wave circulating around the anode, whose active portions in Fig. l are the mid-regions of the three sides. A simplified but descriptive concept for explaining the transfer of energy from the voltage source 5 to the high frequency output circuit 4 is to consider the rotating space charge current spokes as a generator rotor commutating the mid-regions of the three anode sides at a frequency corresponding to the number of spokes times the rate of revolution of the space charge. in the apparatus of Fig. 1 the mos-t readily established mode of oscillation produces three such space charge spokes. This corresponds to the space charge configuration of a conventional six' vanemagnetron excited in the pi mode in which alternate segments are of opposite polarity. The output frequency may be controlled by the applied anode voltage as described and claimed in our application Serial No. 169,712, filed June 22, 1950, now Patent No. 2,774,039 and assigned to the assignee of the present invention. The tuning range is to some extent governed by the impedance of the output circuit 4, but is much less dependent in cathode emission and heavy tank loading than for a voltage tuned magnetron of conventional structure.

For better understanding of our invention and its relation to conventional traveling wave magne-tr-ons, reference is made to Figs. 2a, 2.), and 20. In Fig. 2a, a conventional six vane traveling wave magnetron oscillator is represented in simplified schematic form. The six anode vanes or segments surround an elongated cathode to define a cylindrical space charge chamber coaxial therewith, and the vanes are spaced from each other to provide interaction gaps between them. In such multivane magnetrons the vanes are usually coupled for pi mode oscillation by externally connecting a resonant output circuit between two sets of alternately positioned vanes. An equivalent output circuit arrangement for the purpose of illustration here concerned is shown in Fig. 2a, in which two similarly tuned output circuits Zr: and Zb are substituted for the single resonant output circuit conventionally employed. Three alternate anode segments 3a are connected in parallel by external conductors and an.

output circuit Za is connected between their common terminal and the cathode 2. Similarly the other three alternate segments 3b are connected together and the other output circuit Zb is connected between their crnmon terminal and cathode. The effect of dividing the output circuit is much the same as connecting the alternating current midpoints of a single output circuit to the cathode.

The formation of the usual space charge spokes may be readily visualized in the arrangement of Fig. 2a, the adjacent anode segments being out of phase with each other upon initial excitation of the output circuits at the output frequency so that three space charge spokes are formed. As previously mentioned, such space charge spokes or bunches comprise electrons in synchronism with the advancing wave traveling around the anode segment array. To the extent that the average velocity of the rotating electronic space charge tends to exceed the phase velocity of the traveling wave, energy is transferred from the space charge to the propagated wave. This action maintains the space charge spokes or bunched configuration since any loss of rotational energy by the in-phase electrons is compensated for by their radial displacement toward the anodes, where they are ultimately collected. Accordingly, the electron current may be considered as flowing from the cathode alternately to the two sets of vanes 3a and 311, or intermittently to any one set of vanes. Each set of vanes thus alternates in polarity or phase wit-h respect to the cathode as well as to each other.

Referring now to Fig. 2!), if one set of three alternate vanes 31) is left floating, the remaining three vanes 3a are still spaced for a conventional six gap operation. Accordingly, the vanes 3b and the output circuit Zb may be omitted altogether, leaving the vanes 3a to alternate in polarity with respect to the cathode at the same frequency as before.

These vanes may be connected more conveniently from the fabrication standpoint as shown in Fig. 20 by extending each of the vanes in a direction parallel to its midpoint tangent until the extended vane portions meet, thus forming an anode assembly of generally triangular cross section. Again, since the vanes are still arranged in a manner corresponding to conventional six vane operation and since the output circuit is connected between the triangular anode electrode and the cathode, each of the three sides of the triangle will be contacted by the three space charge spokes once during each space charge rotation. The corners of the triangle, which are relatively far away from the cathode, as normally would be the external intersegment connections of a conventional magnetron, do not therefore serve as anode segments and are not contacted by the space charge spokes. Oscillation in other modes has been observed with such diode magnetrons, but the foregoing explanation is believed sufficient to illustrate the mechanism by which the space charge drives the output system so far as is necessary for the design of magnetrons embodying our invention.

While in Fig. 2c the portion of each side of the triangular a-node corresponding to the segments 3a is an arc concentric with a cylindrical cathode, the anode may be more readily fabricated with plane sides as shown in Fig. 1. The cathode is preferably also provided with plane sides parallel to the facing anode portions as shown in Fig. 1 for improved mode stability. It is not essential, however, that the cathode depart from the conventional cylindrical cross section.

Referring now to Figs 3 and 4, a magnetron discharge device 1 corresponding to that schematically shown in Fig. 1 is illustrated. The triangular cross section cathode 2 and the triangular cross section anode 3 surround ing the cathode are shown enclosed within an envelope 8, which is made of glass or other suitable non-magnetic material. An array of base pins 10, each of which may suitably consist of a rigid metal rod or wire, is provided in the base or header 9 of the envelope, each pin being sealed through the header so as to provide external terminals for circuit connections at one end thereof and conductive support means at the inner ends for the tube elements. The cathode 2 is suitably formed from a sheet of relatively thin nickel folded to provide the triangular cross section. The cathode triangular cross section may also be conveniently provided by deforming a section of hollow cylindrical tubing. A heater coil 11 is positioned within the cathode sleeve and is supported thereby, the ends of the heater coil being connected to two of the pins 10. The outer surface of the cathode 2 is coated with a suitable thermionic emitting material, such as barium oxide. The cathode itself is supported at each end by rigid conductive extensions of two of the support pins 10. The anode 3 is similarly formed as is the cathode from a thin sheet of nickel. The anode is also supported by conductive extensions of selected base pins 10.

The envelope 9 is suitably evacuated, the tubulation 12 at the top of the envelope being pinched when the evacuation is complete. A getter loop 13 within the envelope is also supported from one of the base pins 10 and the getter is flashed in a conventional manner to remove any residual gases.

As may be seen, the magnetron diode is very simply fabricated, the construction illustrated being especially adapted for small and inexpensive devices. The tuned circuit is entirely external to the magnetron diode and there are no cavity resonators in or forming a portion of the anode structure. In operation, the circuit connections corresponding to those in Fig. 1 are connected to terminal pins corresponding to the cathode and anode connections and a source of heater voltage is supplied between the heater terminal pins. If voltage tuning is desired as described and claimed in our copending application, Serial No. 169,712, filed June 22, 1950, and assigned to the assignee of the present invention, the oathode emission may be limited, such as by limiting the area of the cathode 2 which is provided with an emissive coat- Referring now to Figs. 4a to 4d, several of the useful anode cross sections for magnetrons incorporating our invention are illustrated. In each of these the cathode may be assumed to be entirely conventional, having the generally circular cross section of the usual cathode sleeve or close-wound helix. Thus, as shown in Fig. 4a, the anode cross section is an elipse or oval in which two opposite sides are closer than the other portions of the elipse to provide the magnetron action corresponding to the conventional split anode. In Fig. 4b, a rectangular anode is shown in which one pair of opposite sides is relatively long with respect to the other pair so as to again provide essentially split anode operation since only the portions of the long sides which are relatively close to the centrally disposed cathode form the active portions of the anode segments. The manner of connecting the portions which are distant from the cathode, whether by rectilinear portions as in Fig. 4b or as by curved portions as in Fig. 4a is immaterial to the magnetron operation so long as the active sides are distinctly defined.

Referring next to Fig. 40, a square anode cross section is illustrated in which the magnetron oscillator operation corresponds to an eight section conventional magnetron. Similarly, in Fig. 4d, a pentagonal cross section anode corresponds in operation to a conventional ten vane magnetron. It is apparent that the anode cross section is not limited to the regular polygons illustrated here. The cross section may depart somewhat from a strictly polygonal shape as in Fig. 4a, where the conductive regions connecting the relatively close active portions of the diode anode are curved. Here the curved portions are relatively remote from the cathode. However, the ability to maintain discrete anode portions is decreased as the number of polygonal sides is increased, making it dilficult to maintain a single mode of oscillation during the magnetron oscillator operation. It should also be noted that since the effective sides of the diode anode correspond to only half of the segments of the conventional segment or multivane magnetron, the number of sides of the polygon cross section may be either an odd or even integer.

In order to stabilize the mode of operation the anode cross sections illustrated in Figs. 4a-4d may be provided with corresponding cathode sections as was illustrated in Figs. 1 and 3 where both the anode and the cathode are triangular in cross section. Accordingly, in Figs. 5a to 5d in which the anode configurations correspond to those in Figs. 4a to 4d, the cathode cross sections conform to those of the anode, the anode being concentric with the cathode in each case.

Fig. 6 illustrates schematically an inverted magnetron diode embodying our invention in which the cathode 14 surrounds the anode 15. According to our invention the anode has a triangular cross section. The cathode is shown as having a circular cross section. A noninductive heater 16, schematically indicated as a winding on the cathode 14, provides means for heating a conventional thermionic emitting coating on the inside surface of the cathode and is shown connected to a heater current source 17. An output circuit 18, generally represented as an impedance Z and a source of unidirectional voltage 19 are connected between the anode and cathode. Since the relative cathode and anode positions are the converse of the usual arrangement, adaptation of such a diode for coupling to concentric transmission line sections is facilitated as the cathode heater leads are on outside of the magnetron structure.

In accordance with our invention, the anode of the magnetron of Fig. 6 may have other cross sections as discussed in connection with the anode cross sections of Figs. 4a-4d. Similarly, the cathode cross section need not be circular but may, for greater mode stability, conform to the cathode cross sections described with respect to Figs. 5a to 5d.

It should be understood that, in the foregoing description of our invention, the specification of the cross sections of the anode and cathode refers to the boundaries of their facing surfaces. Thus in the arrangement of Fig. 3, the triangular cross section of the anode refers primarily to the shape of the inner boundaries of the hollow anode since the outer surface configuration does not affeet the magnetron characteristics.

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: I

l. A magnetron diode oscillator system comprising a single tubular anode membersurrounding an elongated cathode member and concentric therewith, the cross section of said anode electrode and said cathode member providing regularly positioned portions of said anode around its cross sectional perimeter which are spaced substantially closer to corresponding angular-portions of said cathode than the intervening portions of the anode, means for establishing a radial electric field and an axial magnetic field in the space between said anode and cathode members, and a high frequency output circuit coupled between said anode and cathode with respect to high frequency voltages.

2. A magnetron oscillator system diode comprising a single tubular anode member having substantially flat continuous surface portions and being concentric with an elongated cathode member and surrounded thereby, the cross section of said anode electrode and said cathode member providing regularly positioned portions of said anode around its cross sectional perimeter which are spaced substantially closer to corresponding angular portions of said cathode than the intervening portions of the anode, means for establishing a radial electric field and an axial magnetic field in a space between said anode and cathode members, and a high frequency output circuit coupled between said anode and cathode with respect to high frequency voltages.

3. A high frequency magnetron system comprising a diode discharge device having a single tubular anode formed of substantially fiat continuous surface portions coaxial with an elongated cathode, the cross section of said anode providing regularly positioned portions of said anode around its cross-sectional perimeter which are spaced substantially closer to said cathode than other portions of the anode; means for establishing a radial electric field and an axial magnetic field in the space between said anode and cathode, and a high frequency output circuit coupled between said anode and cathode with respect to high frequency voltages.

4. A high frequency magnetron oscillator system comprising a diode discharge device having a single tubular anode coaxial with an elongated cylindrical cathode, the cross section of said anode formed in the shape of a polygon; means for establishing a radial electric field and an axial magnetic field in the space between said anode and cathode, and a high frequency output circuit coupled between said anode and cathode with respect to high frequency voltages.

5. A high frequency magnetron oscillator system comprising a diode discharge device having a single tubular anode coaxial with an elongated cylindrical cathode, the cross section of said anode formed in the shape of a regular polygon; means for establishing a radial electric field and an axial magnetic field in the space between said anode and cathode, and a high frequency output circuit coupled between said anode and cathode with respect to high frequency voltages.

6. A high frequency magnetron oscillator system comprising a diode discharge device having a single tubular anode having substantially fiat continuous surface portions coaxial with an elongated cylindrical cathode, the cross section of said anode formed in the shape of a polygon; means for establishing a radial electric field and an axial magnetic field in the space between said anode and cathode and a high frequency output circuit. coupled between said anode and cathode with respect to high frequency voltages.

7. A high frequency magnetron oscillator system comprising a diode discharge device having an elongated cathode and an anode surrounding said cathode, said 7 8 anode and said cathode having corresponding regular 2,217,745 Hansell Oct. 15, 1940 polygonal cross sections, means establishing a radial elec- 2,454,337 Okress Nov. 23, 1948 tric field and an axial magnetic field in a space between 2,512,618 Edwards et a1 June 27, 1950 said anode and cathode with respect to high frequency 2,617,968 Gutton et a1. Nov. 11, 1952 voltages and an output circuit coupled between said 5 FOREIGN PATENTS Cathode and sand anode 407,477 Germany Dec, 22, 1924 References Cited in the file of this patent UNITED STATES PATENTS 1,645,904 Gavin Oct. 18, 1927

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