US2747031A - Magnetron amplifier - Google Patents

Description

2 Sheets-Sheet 1 D. A. WILBUR EFAL MAGNETRON AMPLIFIER Fig/a.

May 22. 1956 Filed May 10, 1950 Inventors: Donald A.Wilbun Pn H.PC1Y5,JY.

Their Attorney ANODE CUR RENT SOURCE OF DR! VING SIGNAL BUFFER AMPLIFIER y 22, 1956 D. A. WILBUR ETAL 2,747,031

MAGNETRON AMPLIFIER Filed May 10, 1950 2 Sheets-Sheet 2 y} l a! 44 3'2 as 3 4/ 36 27 27 27 38 15 37 57 fi 2e 30 J0 Invent, ors: Donaid A.Wilbu1;

Philip lipebersflr, by WW4 KM Their" Attorney.

United States Patent MAGNETRON AMPLIFIER Donald A. Wilbur, Albany, and Philip H. Peters, .lr., Schenectady, N. Y., assignors to General Electric Company, a corporation of New York Application May 10, 1950, Serial No. 161,052

1 Claim. (Cl. 179-171) This invention relates in general to method and apparatus for amplifying electromagnetic signals, and in particular relates to improvements in high frequency magnetron apparatus directed to the purpose of amplifying electromagnetic energy at the high frequency end of the electromagnetic spectrum.

Magnetrons are extensively used as generators of high frequency electromagnetic energy. They are used for this purpose because they are adapted to the generation of large amounts of power at high efficiencies at the high frequency end of the electromagnetic spectrum. Heretofore, apparatus for amplifying high frequency electromagnetic energy has not approached the power output and efiiciency capabilities of the magnetron apparatus functioning as a generator of high frequency electromagnetic oscillations. Amplifying apparatus for delivering large amounts of power at the high frequency end of the electromagnetic spectrum constitutes a real and pressing need in the art. Amplifying apparatus that can amplify to high power levels and at high efficiencies is even more welcome in the art.

Accordingly, it is an object of our invention to provide means for amplifying electromagnetic energy.

It is another object of our invention to provide a highly efficient amplifier of high frequency electromagnetic energy.

It is a further object of our invention to provide magnetron apparatus for amplifying high frequency signals to high power levels.

In an exemplary embodiment of the invention, shown in the drawings, magnetron apparatus is adapted for the purpose of amplifying electromagnetic energy by providing means for coupling energy into the magnetron apparatus and operating the magnetron in a manner so that energy is developed only When signals to be amplified are coupled into the magnetron apparatus.

The features of the invention desired to be protected herein are pointed out in the appended claims. The invention itself together with its further objects and advantages may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1:: shows a schematic representation of a magnetron useful in explaining the operation of the invention; Fig. lb shows a schematic diagram of a circuit useful in explaining the operation of the invention; Fig. 2 is a simplified anode voltage vs. anode current characteristic of a typical magnetron of the kind under discussion in this specification; Fig. 3 is a semischematic representation of apparatus by means of which the invention may be carried out; Fig. 4 shows diagrammatically another embodiment by means of which the invention may be carried out; Figs. 5a and 5b show the constructional details of the composite magnetron devices of the kind that may be used in the apparatus of Figs. 3 and 4 in carrying out the invention; Fig. 50 being a plan view and Fig. 5b being a side view.

A typical magnetron generator of electromagnetic oscillations comp-rises a cylindrical anode structure with resonant cavities symmetrically located around the periphery of the inner cylindrical surface of the anode, and a cathode located axially within the generally cylindrical chamber defined by the cylindrical anode structure. When a unidirectional magnetic field of proper magnitude and a unidirectional electric field of proper magnitude are applied to the aforementioned structure in a manner well known in the art, the magnetron develops useful high frequency electromagnetic energy.

Referring now to Fig. In, there is shown a developed view of a traveling wave type of magnetron such as was briefly described in the paragraph above. This view shows a series of anode segments, collectively designated by numeral in, and a cathode 2. Resonators or resonant circuits, collectively designated by the numeral 3, are connected between the anode segments 1a as shown. Of course, the space between the anode segments 1a and the cathode 2 is evacuated. By adjusting the axial magnetic field, symbolically designated by H, and the unidirectional electric field between the anode and cathode symbolically designated by E, to a value such that the average drift velocity of the electrons in the space between the anode and cathode corresponds to the frequency to which resonators 3 are tuned, the magnetron can be made to convert energy from the unidirectional power source supplying the electric field into useful high frequency electromagnetic energy.

The explanation of the manner in which the foregoing conversion of energy is effected is complicated; however. a simplified explanation may be advanced to give an appreciation of the nature of the effects involved. The high frequency electromagnetic fields existing in the resonators extend out and fringe the anode segments as schematically indicated by E. In the steady state operation these fields cause the moving electron space charge to assume a spoke shaped form, the number of spokes depending on the number of anode segment interaction gaps. When the spokes of space charge impelled by the unidirectional forces from the unidirectional magnetic and electric fields exerted on the electron space charge move against the high frequency fringing field E energy is developed in the resonators 3. It should be noted that the average drift velocity of the electrons should-correspond to the resonant frequency of the resonators connected to the anode segments. When the average drift velocity of the electrons corresponds to the resonant frequency of the resonators, the electron space charge is then said to be in synchronism. If the average drift velocity is less than this value there is no net interchange of energy from the elec trons to the high frequency fields associated with the resonator. The average drift velocity of the electrons is dependent upon the ratio E/H, where E is the electric field intensity and H is the magnetic field intensity of the unidirectional fields within the space charge chainber. Thus, if the value of unidirectional voltage between the anode segments and the cathode is reduced to such an extent that the average drift velocity of electrons is less than the value of drift velocity which corresponds to the frequency to which the resonators are tuned, then no high frequency energy will be developed in the resonators. It will be understood that the foregoing planation applies in particular to the operation of a travcling wave magnetron as an oscillator as distinct from magnetron operation at cyclotron frequency. It should be understood that since the above description applies to Fig. 1a which is a developed view of a cylindrically shaped magnetron, the term average angular velocity will be the appropriate expression to use in connection with the actual structure.

In Fig. 2 is shown, somewhat simplified, the unidirectional anode voltage versus the unidirectional anode current characteristics of a typical magnetron of the kind under discussion herein. V represents the magnitude of voltage applied between the anode segments 1a and the cathode 2. I represents the magnitude of the unidirectional current flowing between the cathode and anode or, in other words, the current supplied by the unidirectional power source. The voltage source V produces the electric field E. From Fig. 2 it can be seen generally the manner in which the voltage and current in a magnetron of the kind schematically shown in Fig. 1a varies. As the anode voltage is increased from zero magnitude the anode current increases without any energy being developed in the resonators. This is usually referred to as leakage current. A point 4 is eventually reached as the voltage is increased at which oscillations in the resonators start, and as the voltage is increased the amount of power developed in the resonators increases. As the voltage is raised it should be kept in mind that the E factor of the ratio E/H is changed to bring the angular velocity of the electrons up to the oscillation point. Below this point the E/H ratio was less than that required to sustain oscillations. Assume for the moment that the voltage applied to the magnetron the magnetic field of course being constant, corresponds to the value of point 5, that is, the voltage applied has a value below the oscillation point 4. This voltage may be applied, for example, by means of a fixed battery. Let a second battery be connected in series with the first battery so that the total applied unidirectional voltage corresponds to the value of point 6, the second battery contributing the increment of anode voltage delta V. It is readily appreciated from the foregoing discussion that this magnitude of voltage on the magnetron along with the effects of the high frequency voltages produced in the magnetron is sufficient to raise the E/H ratio to a value at which the average anuglar velocity of the electrons corresponds to the resonant frequency of the resonator. Oscillations are developed in the resonator in accordance with the preceding explanation and energy is converted from the unidirectional source into the high frequency field associated with the resonators. At this latter value the power supplied to the magnetron is measured by the product of (V+AV) I. The first battery contributes the magnitude of power represented by V I and the magnitude of power contributed by the second battery is represented by AVXI. The high frequency energy developed by the magnetron is (V+AV) XIx an efliciency factor. It should be noted that the magnitude of the power contributed by the second battery is much smaller than the total high frequency power delivered by the magnetron. This latter fact may readily be appreciated from the following numerical example. Assume that a magnetron develops high frequency power with an anode voltage of 1000 and draws anode current of 2 amperes. Assume further that this magnetron operates at an efficiency of 50%. The high frequency power output will be 1000 watts (1000 2 .50). Assume further that the second battery contributes 50 volts of the anode voltage. The power input into the magnetron of the second battery will be 100 watts (50x2). This indicates that by supplying an incremental energy of 100 watts to the magnetron, 1000 watts of high frequency energy can be obtained from the magnetron. The applicants have found that the incremental energy supplied by an external source of energy can be a high frequency source; and hence with reference to the example under considera tion by supplying 100 watts of high frequency energy, 1000 watts of high frequency energy can be obtained from the magnetron, that is, amplification of high frequency energy is achieved with a power amplification of 10. It should be understood that the above numerical calculations are given by way of example to facilitate understanding of the principle involved.

- In Fig. 1b there is shown a schematic representation of a split anode magnetron in which a batterysupplies the electrical field between the cathode 2 and anode 1b. While in the preceding description, for the purpose of simplicity of explanation, a second battery has been added to increase the electric field between anode and cathode, the high frequency energy is not supplied to the magnetron in this way, that is, it is not supplied in series between the cathode and anode, but rather it is supplied in series between the anodes as diagrammatically indicated by the arrow. The increment of high frequency voltage supplied between anode segments is designated AV in Fig. 1b. With the high frequency energy introduced in this manner, the electrical field in one-half of the split anode magnetron is alternately augmented as the high frequency energy passes through its periodic time variations; the effect is substantially the same as supplying the electrical field by means of a battery placed in series between the cathode and the anodes. The use of high frequency energy to supply the component of the electric field necessaryto raise the electric field to a value that will cause the magnetron to develop useful power does not in principle differ from the use of a battery for this purpose.

With reference to Fig. 2 is should be noted that the first battery may supply a value of potential varying between 0 and the value V and that the value V need not be a value just below the operating point 4.- If the point 5, corresponding to the potential suppliedby the first battery is appreciably below point 4, then an appreciable amount of input energy must be supplied before the magnetron starts amplifying. If the potential supplied by the first battery corresponds to point 4, then of course very little, if any, input energy need be supplied before the magnetron starts amplifying. If the potential supplied by the first battery is above the point 4, the magnetron will be in an oscillating condition when a signal is applied, yet the magnetron will still function to amplify the signal supplied. It has been found that even if a potential corresponding to the upper current cutoff potential of the magnetron is applied and the magnetron is delivering the maximum power it is capable of delivering as an oscillator, that additional power may be obtained from the magnetron by supplying high frequency energy to the magnetron and causing it to func tion as an amplifier. Even at the upper current cutofi point the magnetron will amplify high frequency energy input in proportion to the input.

It will be understood that for the sake of simplicity of explanation the above remarks apply to a magnetron operated in a particular mode, the ar-mode for instance. Assuming that the plot of Fig. 2 relates to a magnetron operating in the Ir-IIlOdE, it should be noted that at some value between 0 and V, other than at point 5, the magnetron may operate as an oscillator on some other mode besides the ar-mode. Of course, this condition should be avoided in selecting the operating point 5.

While in Fig. l resonators are shown connected by the anode segments, it will be understood that in general this figure describes an oscillator. It should be noted that in applicants magnetron amplifier a resonator need not be used but that any suitable high impedance may be used in place of a resonator. Further, in the case of an oscillator a resonant circuit establishes the frequency of oscillation in the magnetron. amplier the frequency is pre-determined by the frequency of the input signal. If a resonator is used to obtain a high impedance, then of course, the input signal should correspond to the resonant frequency of the resonator;

The exemplary embodiments shown and described in fication to high power levels of high frequency electro-l magnetic energy.

Referring now to Fig. 3 there is shown apparatus for carrying out the invention comprising a parallel wire type of traveling wave magnetron adapted to amplify electro-' In the case of the magnetron magnetic energy, and a source of signal to be amplified which is connected to the magnetron through a buffer amplifier. The parallel wire type of magnetron shown in this figure is used by way of illustration and it should be understood that generally any of the other types of traveling wave type of magnetrons including those having more than two anode segments may be utilized as amplifiers in applicants system. The buffer amplifier also may be eliminated and is included for the purpose of isolating the source of signal from the magnetron amplifier proper.

Referring now to the particularities of construction of the magnetron in this figure, there is shown a parallel wire transmission line 7 short-circuited at one end by the fixed connection 8 and at the other end by a movable connection 9 which is utilized for the purpose of tuning the resonant line 7. Intermediate the ends of this section of transmission line is connected a load 10 which may be adapted to slidably move along the transmission line 7. It should be understood that the load 10 may represent other apparatus to which power is coupled. It should further be understood that the load may have a substantial reactive component without disturbing the basic operation of the amplifier. Near the end of the transmission line 7 with the fixed short-circuited connection 8 are located a pair of anode blocks 11 and 12 connected to the transmission line. On their inward sides anode blocks 11 and 12 are shaped to form a generally cylindrical opening in which a cathode 13 is axially located as shown in the figure. Battery 14 is shown for energizing the cathode and a second battery 15 is shown for energizing the anodes 11 and 12. This source is connected, as is readily seen from the drawing, between the anode blocks 11 and 12 and the cathode 13. A unidirectional magnetic field is supplied by any of a variety of means schematically indicated by a coil 16 in the drawing. A slidable tap 17 is connected to a point on the transmission line 7 intermediate the short-circuited ends to couple electromagnetic energy into the resonant system. Preferably, tap 17 is adjusted in such a manner that there is a maximum power transfer from a buffer amplifier 18 to the resonator system. The driving signal, that is the signal to be amplified, is supplied to the magnetron apparatus through buffer amplifier 18 and through a section of coaxial transmission line 17a connecting the buffer amplifier to the magnetron. Various other ways of coupling power from the source of signal to be amplified into the magnetron amplifier may be used other than the direct sliding connection as shown. For instance, various well known inductive and capacitive coupling means may be used.

In utilizing the apparatus of Fig. 3 to amplify electromagnetic energy, cathode 13 of the magnetron is heated by means of battery 14 and the resonant frequency of the system is adjusted by means of tuner 9 to present a high impedance at the anode blocks at the frequency of the signal to be amplified. Anodes 11 and 12 are so energized that the ratio of the electric field intensity between the cathode and the anode to the magnetic field intensity axially directed through the cylindrical space in which the electrons move is of a proper magnitude so that the average angular velocity of the electrons in the inter-electrode space between cathode and anode is at or below the value required for the magnetron to function as an oscillator. When the signal to be amplified is supplied to the magnetron, the electric field in the inter-electrode space is increased to such a value that the magnetron delivers power to the load. The reason why the power delivered to the load is greater than the high frequency power supplied to the magnetron has been discussed in the preceding paragraphs. From the explanation therein contained, and particularly from a consideration of the linearity of the curve of Fig. 2, it is readily apparent that as the magnitude of the signal to be amplified is increased the power supplied to the load is proportionately increased.

In the discussion of Fig. 3, there has been described the manner in which a conventional magnetron oscillator may be adapted structurally and the operating parameters may be adjusted so thatthe high power and high efiiciency capabilities of magnetron type apparatus may be readily utilized for amplifying purposes. In such apparatus, the magnetron is completely controlled by the external source of electromagnetic energy to be amplified. With apparatus of this kind power gains of from 2 to 10 and output powers up to 1000 watts in the frequency range of 500 to 1000 megacycles have been obtained. These amplifiers operated with anode efiiciencies ranging from" 40 to depending upon the kind of magnetron discharge device used. It should be noted that since the input power to the magnetron amplifier is also applied to the load, and not lost, the over-all efficiencies are even higher than the above figures indicate.

Referring now to Fig. 4 wherein like numerals designate previously described parts, there is shown another embodiment of apparatus useful in carrying out applicants invention. The right-hand section of the apparatus is similar to the magnetron amplifier of Fig. 3 and performs the amplifying function. The left-hand section is utilized as a source of signal to be amplified, that is, as an oscillator. Coupling between the oscillator section and the amplifier section is achieved by means ofa common resonant line 7 short circuited at its ends by members 8 and 19, respectively. At the left end of the resonant line is formed the oscillator section and at the other end of the resonant line is formed the amplifier section. A load 10 similar to the load of Fig. 3 is connected intermediate the magnetron sections. A tuning section comprising a transmission line 20 and an adjustable tuner 21 connected to the resonant system at the point on transmission line 7 to which the load is connected is used for tuning the system to the frequency of operation. A battery 22 supplies heater power to the cathode of the oscillator section of the magnetron. A battery 23 supplies a voltage between anodes 11a, 12a and the cathode 13a of oscillator magnetron sufiicient to cause it to oscillate. The unidirectional magnetic field of the oscillator section of the apparatus may be supplied by any suitable means, such as a coil 24 through which a unidirectional current is adapted to flow or by means of a permanent magnet. The magnitude of the unidirectional anode voltage, the magnitude of the magnetic field, and the resonant frequency of the resonant system are mutually interrelated and are so adjusted that oscillations are developed by the oscillator section of the system. The amplifier section of this apparatus is adjusted in a manner similar to the apparatus of Fig. 3. If identical magnetrons are used for the oscillator and amplifier sections a power gain of two is obtained and as the magnitude of the power developed by the oscillator increases the power supplied to the load increases proportionately due to the contribution of the amplifier section.

Referring now to Figs. 5a and 5 b of the drawing, there is shown a magnetron device of the kind schematically shown in the systems of Figs. 3 and 4. It will be understood that in general our invention is applicable to all types of traveling wave magnetrons and particular kinds of traveling wave magnetrons are shown in this specification only by way of example. The magnetron device of Figs. 5a and 51) includes an envelope 25 formed of glass, within which is mounted a generally U-shaped conductor 26 which may to advantage be formed of copper tubing. The arms of the U-shaped tubing extend through the end wall of the envelope and are sealed thereto by suitable seal constructions including sleeves 27 and 28 which are joined, respectively, to the envelope and the arms of the U-shaped conductor and which may be made of any of a class of conventional compositions suitable for metal to glass sealing and comprising the elements of iron, nickel, and cobalt. The conductor 26 includes portions 29 and 30 which extend to the exterior of the envelope to provide a parallel wire transmission line corresponding to the parallel wire transmission line 7 of Figs. 3 and 4. Within the tube envelope a pair of anode members 30 and 31 corresponding to anode members 11 and 12 of Figs, 3 and 4, are supported in opposed relation from the opposite arms of U-shaped conductor 26. The anode members are spaced at the inner ends thereof and provided with arcuate surfaces 32 and 33 respectively, which cooperate to confine the space charge of the device supplied by an elongated cathode 34. The cathode 34, which may be a tungsten wire, is supported on the aXis of the generally cylindrical space defined by the curved face portions 32 and 33 of the'anode segments by resilient supporting conductors 35 and 36. These supporting conductors are secured to relatively rigid lead-in conductors 37 and 33 respectively, which are, in turn, sealed through the end wall of the envelope in any suitable manner. Circular shielding members 39 and 40 are supported respectively, from the flexible conductors 35 and 36 on opposite sides of the anode structure to prevent electrons escaping from the interelectrode space from impinging on the glass walls of the envelope. Also, a shield member 41 may be connected to the anode member 30 and extend over the gap 42 to collect electrons escaping therefrom. A suitable getter 43 is supported near the inner Wall of the envelope by a conductor 44 secured to the end of the loop conductor 26. While we have shown and described particular embodiments of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from our invention in its broader aspects and, we, therefore, aim in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of our invention.

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

A magnetron amplifier comprising a cathode, an anode including an array of spaced anode segments defining interaction gaps facing said cathode and spaced to sustain an oscillation at a traveling wave mode frequency, an output system coupled to said anode segments for sustaining an electromagnetic wave at said frequency traveling along the array, means for introducing an electron space charge between said cathode and said anode, means for establishing a static electric field between said anode segments and said cathode and means for establishing an applied static magnetic field perpendicular thereto, the ratio of the static electric field to the static magnetic field determining the average velocity of said space charge along said anode array, means coupling a source of high frequency signals to said output system to modify the electric field between said cathode and anode to cause high frequency energy to be generated through traveling wave mode operation by the electron space charge at the interaction gaps in excess of the .cou:- pled high frequency signals, said excess energy being obtained from said static electric field, and means for coupling said output system to a load.

References Cited in the file of this patent UNITED STATES PATENTS 2,087,737 Runge July 20, 1937 2,184,556 Linder Dec. 26, 1939 2,233,482 Linder Mar. 4, 1941 2,278,210 Morton Mar. 31, 1942 2,462,698 Wilbur Feb. 22, 1949 2,490,007 Peters Nov. 29, 1949 2,511,407 Kleen et al. June 13, 1950 2,528,241 Peters et al. Oct. 31, 1950 2,546,033 Knight Mar. 20, 1951 2,562,738 Ramo July 31, 1951 2,576,599 Hansel] Nov. 27,

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