US2399114A - Oscillator circuit - Google Patents

Description

April 23, 1946.

c. w. HANsr-:LL

oscILLAToR CIRCUIT Filed April 24', 1941 lNvENToR uf ATTORNEY Patented Apr. 23, 1946 roFFlcE oscligta'ron omcurr Clarence W; Hansell, Port Jefferson, N. Y., assignor to Radio Corporation ofAmerca, a corporation of Delaware Application April 24', 1941, serial No. 390,039

eclaim's. (clase-21.5)

The present invention relates to a.` nlagnetronv oscillator electron discharge device, and particul'arly` to such a device adapted for the generation of Very short waves.

An object of the present invention is to provide asimplied mechanical arrangement for the anode electrode of the magnetron by means. of which the anode itself forms a tuned circuit located entirely within the envelope of the magnetron tube.

A further object is to provide a compact yand eici'ent magnetron tube for use at. ultra 'short' waves which is characterizedby reducedlosses in the anode circuit.

Another object is to provide in "a magnetrona compact and completely enclosed vanode tuned circuit whose natural frequency corresponds 'to the electron oscillation frequency.k

In the magnetron electronic oscillators of the. prior art, the velocities of electrons taking part in the oscillation have usually ranged lup to a maximum of only about 10% ofthe velocity of light, corresponding to anode to cathodepotentials up to about 3,000 volts.k The average velocitiesof electrons around their orbits from the cathode out to the vicinity of the anode' and backA to the cathode have been somewhat less than 10% of the velocity of light. As a consequence, the frequency of the .electronic oscillations has usually been much lower than would be the resonant frequency of a slotted cylindrical anode for oscillations in a circumferential direction around the cathode, and heretofore it has not been recognized that the anode mightI be made resonant circumferentially to thev *frequency 3.

of the electronic oscillations.

The present invention recognizes-this possibib:

ity and provides the means to accomplish it.

In accordance with thepresentinvention', there is employed electronic oscillator in which the.

anode itself forms a tuned ycircuit and is in the form cfa spiral coil of sheet metal extending circumferentially about the cathode for a distance of more than one turn- The ends, or turns ofthe coil are made to overlap in physically spaced relation, so that only the innermost turn receives the electrons emitted from the cathode. By employing a coil of predetermined dimensions, the anode becomes a half wave roscillator with oscillations taking place circumferentially around the anode. Putting it another way, the anode is constructed to have such inductance and such capacitance that it forms a circuit resonant to the electron oscillation. frequency or a harmonic thereof. Theterm electronic oscillator i's used herein -to designate an oscillator in which the transit time ofthe electrons is' coordinated with the frequency of oscillations.

By constructing the anode-in accordance withf the invention, the current-in ltheanode circuit has available 'la -verywide current path, as a consequenceof which there are less losses thanwould be the case if there were employed the customary externally located tuned circuit with its asso.

Referring now to the drawing, the magnetrons shown in Figsl and 2 comprise' an enclosing glass envelope l, having therein' a' lamentary cathode 2, andv surrounding the cathode a coiled anode indicated as 3 in Fig. 1 and as 4 in Fig. 2. The cathode 2 is disposed within the anode and may be a linear ',lament of suitable construction having leading-in conductors (not shown) secured at itsv ends. The glass envelope I may be encompassed by a field coil 5 which is coaxial with the filament 2 and may be utilized toproduce a magneticfield parallel to the iilament and at right angles to the vcross sections shown in the figures.' vA positive potential is maintained on thev y By suitable choice of the dimensions of the anode and the amount of overlap andv spacing at X and Y, there is obtained a desired circumferential" natural period for the Aanode which tunes the anode to the electron oscillation frequency;

or, if desired,to'a harmonic of the electron oscillation frequency. In effect, the anode is thus made to Ybe a one-half Wave oscillator upon which oscillations take place circumferentially.

The ceiling or curving ofthe anode strip or sheet, and the combining of the functions of anode and resonant circuit in a single element results in a very compact electron discharge device oscillator whose dimensions are considerably smaller than those of conventional magnetron oscillators.

Assuming that oscillations are taking place,

there willbe a radio frequency current flowing around the anode which periodically adds to or opposes the magnetic field set up by the external ,field coil.` The periodic fluctuation in magnetic Vfield will tend to. vary the paths Vof the electrons JuStasthe iiuctuations in external eld cur-r sible for oscillation which are present in ordinary magnetron tubes. In fact, if the anode oscillating current is great enouglnthje fluctuating magnetic field `may become a primary factor in the production of oscillations. In this case the frequency of the oscillations will become less dependent upon electron transit time andwill de-V pend more upon the circumferential natural period of the anode.

The circulating current around the anode will not be uniform but will be maximum at the point marked Z in Fig. 1. Point Z is substantially half Way between the two ends of the anode. Also, the current and magnetic field uctuations will be 90 out of phase with the voltage diierence between X and Y. To explain-one reason for oscillation, let us assume that at a given instant the current at Z is a maximum and is care ried by electrons in the direction of X as indicated by the arrow immediately beneath Z. 'Ihen electrons moving from the lament to the anode, starting toward Z, will have their paths bent relatively little and will tend to follow some such path as that marked B. When the current at Z is a maximum in the reversed direction toward Y, then the electron' path will follow one like that marked A. Electrons leaving the fila` ment when the current at Z is maximum, or a little before, will be passing X perhaps `threequarters cycle later when Xis most positive.

The positive potential of X will then tend also to pull out the path of the electron. The combination of fluctuations in magnetic eld and potential on X will then vary the current flow to` point Y Vwith such aphase relation as to produce oscillation.

Fig. 2 shows an `arrangement of a magnetron electron discharge device in which there .is obtained circumferential oscillations of lower frequency, obtainable with lower anode to cathode direct current potentials. The system of Fig. 2 uses an anode in the form of a spiral coil of considerably more than one turn. The individual turns are suitably spaced from one another and are composed of a ribbon or sheet of metal suitably dimensioned to give the desired tuning effect in relation to the electron oscillation frequency. Such a construction permits designing the magnetron with much less spacing from cathode to anode, for a given wavelength, and decreases the magnetrons of Figs. l and 2, one may utilize radioV wave radiation coming directly` from the oscillating anode, or, preferably, connections may be made either directly, or by induction, to the anode by means of conductors over which wave power may be transferred to a point of utilization. In Fig. 2, I have shown conductors 8 con-'- nected to the anode which may be used to modify the anode resonant frequency. In practice, these conductors are likely to range above and below a quarter wave in length. They may -be coupled to a transmission line 1, or any other'load circuit, as shown. Bridged across leads 8, there is shown an adjustable position bypass condenser 9 composed of a pair of spaced loops coupled together and which are slidable on the leads 8.

Although I prefer utilizing a single anode made of one piece of metal, I may also employ Atwo, or more overlapping pieces, each tuned to the oscillating frequency, taking into account the mutual effects between them.

What is claimed 1. A magnetron electronic oscillator having a linear cathode and an anode in the form of a cyllndrically shaped sheetor -ribb'o'no'f metal of more than one turn and having overlapping portions, the dimensions and arrangement of said anode being such that its circumferential natural period corresponds to the electron oscillation frequency or a. multiple thereof.

2. A magnetron electronic oscillator having a linear cathode, and an anode in the form of a coiled sheet of metal of more than one turn and having overlapping portions, the dimensions and spacing between turns of said anode being such that it is resonant in a circumferential direction to the electron oscillation frequency orv a multiple thereof. .Y

3. A magnetron electronic oscillator'having a linear Vcathode and a singlepart anode in the form of a substantially cylindrically shaped sheet or ribbon of -metal with overlapping, though spaced ends, said overlapping being in a circumferential direction, the dimensions of said anode and the degree of overlap being such that the anode is tuned to a circumferential natural period which corresponds to the electron oscillation frequency or a multiple thereof, and a coil surrounding said anode for producing a magnetic iield parallel to said cathode.

4.`An electronic oscillator having a cathode and an integral anode structure surrounding said cathode, said anode comprising a coiled metallic ribbon of more than one turn and having overlapping portions, the dimensions of said anode and its arrangement being such that its cir, cumferential natural'period corresponds to the electron oscillation frequency.

5.l A magnetron electronic `oscillator havinga cathode and a single part anode structure surf rounding said cathode, said anode comprising a'A coiled metallic ribbon of more than one turn and having overlapping portions, the dimensions of said anode and. its arrangement beingv such that its circumferential naturall period corresponds tothe electron oscillation frequencyor a multiple thereof. A

6. A magnetron oscillator having a linear cathode and a single part anode structure surrounding said cathode, said anode comprisinga'spiral metallic coil of two overlapping turns, the dimenjsions and spacing between'turns being such that` the circumferential natural 4period of saidV anode corresponds to the electron oscillation frequency or a multiple thereof.

7. Electron discharge device apparatus having. a cathode and asingle part anodev structure sur.- rounding said cathode, said anode comprising a, coiled metallic ribbon of more than one turn and having overlapping portions, the dimensions of said anode and its arrangement beingsuch that its circumferential natural period corresponds to the electron oscillation frequencey. y j

8. An electronic oscillator having an anode in. the form of a coiled sheet of metal having' over,- lapping portions circumferentially, the dimensions and spacing between turns of said anode being such that it is resonant in a circumferential, direction to the electron oscillation frequency or a multiple thereof.

9. In an electronic oscillator, a cathode, and an anodesubstantially one-half wave length long'` circumferentially at the operating frequencysurrounding said cathode, said anode comprisingay coiled metallic ribbon of more than one turn and vhaving overlapping portions. t v

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