US2348986A - Resonant cavity magnetron - Google Patents

Description

May 16, 1944. E. G. LINDER RESONANT CAVITY MAGNETRON Filed Oct. 24, 1940' TPHA/Skf/ZSE 41/5 of a multicavity magnetron Patented May 16, 1944 BESONANT CAVITY MAGNETBON Ernest c. Linder, Philadelphia, 2a., assignor to Radio Corporation of America, a corporation of Delaware Application October 24, 1940, Serial No. 362,487

3 Claims.

This invention relates to magnetrons and particularly to resonant cavity magnetrons in which the cavity acts as a tank circuit.

Magnetrons, using a plurality of arcuate shape anodes, are well known. The arcuate shape anodes are usually connected to tank circuits or in some devices the anodes themselves form the tank circuit as shown in Ernest G. Linders U. S. Patent No. 2,233,482 granted on March 4, 1941, for Anode tank circuit oscillators. In such devices electrons, under the influence of a magnetic field, travel along curved paths toward the anode. Some of the electrons give up their energy to initiate or reinforce oscillatory currents inthe tank circuit.

In the present invention the anode electrode of a magnetron includes a slit or a plurality of slits. A resonant cavity member also including a slit, is attached to the anode so that a slit in the anode substantially coincides with the slit in the resonant cavity member. As the electrons spiral past the slits, some of the electrons deliver energy to reinforce or, establish within the cavity standing electromagnetic waves.

It is an object of the invention to provide an improved means for detecting, amplifying or generating ultra high frequency electromagnetic waves. Another object is to provide means whereby a magnetron is provided with a resonant cavity tank circuit. Another object is to provide pecans whereby a plurality oi resonant cavity members are eiiectively connected to the anode electrode of a magnetron. An additional object is to provide means for adjusting the phase rela tions of standing waves established in aplurality of resonant cavities which are connected to a magnetron. 7

The invention will he described by reierring to the accompanying drawing in which Fig. l is a perspective view of one embodiment of the invention; Figures 2a and 2b are plan and elevational views, respectively, of the anode and resonant cavity members employed in said one embodiment; Figure 3 is a graph illustrating the field distribution of the device of Fig. 1; Figure 4 is a schematic diagram of the circuit of the invention as applied to a detector; and Figure 5 is a plan view of the electrode and cavity portion including phasing means,

Referring to Fig. 1 within an evacuated envelope l are mounted a substantially cylindrical anode 3 and a pair of substantially cylindrical members 5, i which each include a resonant cavity. The anode includes longitudinal slits 9, ll;

by soldering or the like to the anode so that their respective slits coincide. It should be un- 1 derstood that the anode and cavity members may be fabricated in any desired manner, and

the space within the anode may be considered as part of the resonant cavity. A cathode 17 extends along the axis of the anode. A magnetic field is established by a permanent magnet l5, eiectromagnet, or solenoid. If a permanent magnet is used, cylindrical or conical polepieces may be attached to increase the :dux which surrounds and is substantially parallel to the cathode.

The circuit connections are as follows: The cathode is connected to a battery 25 and rheostat 23. The anode is connected to the positive terminalof a battery 25 whose negative terminal is connected to the cathode circuit. A pickup loop 21 is inserted through a suitable aperture 29 in one of the resonant cavities. The pickup loop may be terminated in a load circuit, such as a dipole antenna.

Under the influence of the magnetic field electrons are liberated from the cathode spiral outwardly toward the anode. Some or these electrons passing the slits react upon the standing wave fields which are established within the cavities by electromotive iorces in the coupling loop or by a transient'edect oscillations are established within the cavities. This reaction reinforces the fields and maintains the electromagnetic standing waves within the cavities. The distribution of the fields is shown in Fig. 3 in which the abscissa represents the transverse ams through the cavities and anode, and the ordinate represents the electric intensity E. Since the .cathodeis perpendicular to the electric field, it

offers substantially no interference to the waves.

The device may be used as a detector by means of the circuit shown in Fig. 4. The pickup loop 3! is connected through a transmission line 33 to a dipole antenna 35. The anode is connected through a. transformer primary 3l and battery 39 to the cathode circuit ll. The secondary of the transformer is connected to a signal indi-v cator, such as telephone receivers 43.

The slitted anode arrangement may be used with a plurality of resonant cavity members as shownin Fig. 5. The anode electrode includes four slits 41. While the resonant cavities may be of any suitable shape, such as a rectangle cav ity, cuneiform members 49 may be used. The apex of each member is slitted so that the memby a coupling loop.

bers may be Jointed to the anode so that each of the slits of the anode coincide with aslit in the apex of an attached resonant cavity member.

The resonant cavity members may be coupled.

by an adjustable length of concentric line II to regulate the phases of the standing waves. The load circuit may be connected to a concentric line 53 which includes a coupling loop 55 terwhere x=2b and b equals the cavity width =wave length in free space L =the cavity length The foregoing formula applies to a rectangular cavity in which the height has a'negligible eifect on wave length. The'formula applies approximately to a wedge shape cavity in which the wedge angle is small. Furthermore the anode electrode is connected to the wedge shape cavity and effects its resonant wave length. In practice waves of varying length are applied to the cavity and their eflect determined by a p'robe inserted within the cavity. The probe is connected to a resonance indicator. The resonant wave length, or frequency, may be thus determined accurately. Since the foregoing formula does not apply to cavities of other shapes, such as a cylindrical cavity, the probe method of determining resonance is preferred. In any event the calculations are only a guide; the exact resonance is determined by any desired method of measurement.

Thus the invention has been described as a magnetron in which the anode includes longitudinal slits. Resonant cavity members, opening into the anode slits, are attached to the anode. The out-of-phase electrons moving past the slits give up energy to establish and maintain within the resonant cavities standing electromagnetic waves. The waves may be applied to a coupling loop, if the device is used as an oscillator or the currents in a load cricuit may be used to establish electric waves within the cavity. These waves are amplified or detected by the electrons spiralling within the anode electrode. The waves in a plurality of cavities may be phased The invention is not limited to any precise number of resonant cavities of any specific shape. Furthermore, it should be understood that the resonant cavity may be adjusted to respond to any desired frequency by employing means for adjusting the size or shape of the cavity as disclosed in U. S. Patent No.

2,233,263 which was granted on February 25, 1941 on an application Serial No. 243,211 filed November 30, 1938 by Ernest G. Linder. While the cavity members and anode have been described as included within an evacuated envelope, it should be understood that they may form their own envelope with the attendant advantages of cooling and the like.

I claim as my invention:

1. An ultra high frequency device including a cathode, a substantially cylindrical anode surrounding saici cathode and including longitudinal slits, a pair of members including in each a cylindraceous cavity resonator closed at its ends, said cavity resonator being effectively entirely closed to standing waves which are to be established therein, each of said members including a longitudinal slit opening into said cavity resonators respectively, and each of said members secured to said anode with one of said anode slits and one of the slits in said members substantially coinciding and said cavity resonator members mounted eccentrically with respect to said anode, and means adjacent said anode for creating a magnetic field having its lines of force substantially parallel to and surrounding the axis of said cylindrical anode.

2. An ultra high frequency device including a cathode, a substantially cylindrical anode surrounding said cathode and including longitudinal slits, a pair of cylindrical members including in each a cylind'raceous cavity resonator closed at its ends, said cavity resonator being effectively entirely closed to ultra high frequency standing waves which are to be established therein, each of said members including a longitudinal slit opening into said cavity resonator, and each of said members secured to said anode with one of said anode slits and one of the slits in said members coinciding and said anode and members mounted eccentrically, and means adjacent said anode for creating a magnetic field having its lines of force substantially parallel to and surrounding the axis of said cylindrical anode.

3. An ultra high frequency device including a cathode, a substantially cylindrical anode surrounding said cathode and including two diametrically opposed longitudinal slits, a pair of cylindrical members including in each a cylindraceous cavity resonator closed at its ends, said cavity resonator being effectively entirely closed to ultra high frequency standing waves which

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