US2755415A - Malter - Google Patents

Description

July 17, 1956 L. MALTER ELECTRON DISCHARGE DEVICES, INCLUDING CAVITY REsoNAToRs Original Filed Oct. 5. 1948 INI/ENTOR.

I DUIS MEIJER Z L: d /f Z A\\- 1 a @l .IAM 4 4 HM- 7MB. P 4 l H .H\ C. llll -M-- 0, anni; ITI L. wn P 7 w27 .f//4 .DIMM 6 r|h|| u /W... uuu lll Z A, if Z/ United States Patent O ELECTRON DISCHARGE DEVICES, INCLUDING CAVITY RESONATORS Louis Malter, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Original application October 5, 1948, Serial No. 52,908,

now Patent No. 2,637,604, dated April 28, 1953. Divided and this application May 16, 1952, Serial No. 288,283

12 Claims. (Cl. S15-39.75)

This invention relates to improvements in electron discharge devices including cavity resonators, and particularly, `such devices of the multi-cavity magnetron type.

The anode Structure of a conventional multi-cavity magnetron is formed wi-th an annular array of identica-1 anode cavities which are open toward .a central cathode and closed at the outer end and two sides to form substantially separate cavity resonators. The resonators are usually coupled together to some extent at the other -two sides to form a single resonant system. It is well known that conventional multi-cavity magnetron oscillators with similar cavity resonators operate in any one of a number of different modes. Each of the different modes of operation involves a different instantaneous phase differ- -ence between the oscillations generated in adjacent resonators. It has been found that as a rule the most eilicient and desirable mode of operation is that referred to as the 1r-mode, in which the oscillations in adjacent resonators of the magnetron oscillator are 180 or 1r radians out of phase with each other, or, in -other Words, one yset of alternate anode elements coupled Ito the resonators is at the maximum positive potential when the other or intermediate set of alternate anode elements is at the maximum negative potential. In order to achieve 1r-mode operation in conventional multi-cavity magnetrons, it is customary to electrically connect alternate anode elements together by means of low impedance conductors or straps, to lock alternate anode elements and alternate resonators together into lthe same phase. One effect of these .straps is to shift the oscillation frequencies of the various undesirable modes away from the frequency of the qr-mode without -alecting 4the latter, thus facilitating the elimination of the undesirable modes by causing the electric and magnetic field condi-tions suitable for the generation of the undesirable modes to lie far away from those which favor the 1r-mode. While the provision of such straps results in improved operation, it involves a considerable increase in the complexities of the device and in its mode of construction.

The primary object of my invention is to provide a multi-cavity magnetron with an improved struc-ture for favoring 1r-mode operation.

`Another object is to provide such a structure in which strapping is not required.

A further object is to provide a magnetron anode structure favorable to vr-mode operation which is simple and easy to manufacture.

In accordance with my invention, the magnetron anode structures forming the cavities, instead of being alike, are constructed of two dissimilar forms arranged alternately along .the periphery of the anode. The desired 1r-mode operation is achieved in cavity magnetrons having the cavities -either closed on all sides or open on two sides by terminating alternate vanes short of the rear walls of the cavities, thus providing communication between adjacent cavities in pairs. Each pair of communicating cavities oscillates as a single cavity resonator.

The novel features which I believe to be character- ICC s 2 istie of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connect-ion with the accompanying drawing, in which:

Figure l is a top sect-ion View, taken on the line 1--1 of Figure 2, of a multi-cavity electron discharge device incorporating one embodiment of my invention; and

Figures 2 and 3 are axial section views taken on the lines 2-2 and 3-3, respectively, of Figure l.

Referring to Figures 1 to 3, I have shown a multi-cavity magnetron having an anode structure composed of a hollow cylinder 1 in the interior of which are mounted by suitable means an even number of radially-extending anode vanes 2 and 3. The vanes are uniformly distributed around the inner periphery of the cylinder 1 and terminate short of the central axis. The inner edges of the vanes 2 and 3 provide an annular series of anode elements surrounding a central cathode space. A disc 4 having a central aperture of approximately the same diameter as the cathode space is provided in each end of the cylinder 1 in contact with the adjacent side edges of the vanes 2, 3 and seated on annular shoulders S in the cylinder wall.

A conventional indirectly-heated cylindrical cathode 6, having end shields or hats 7, is axially mounted within the cathode space, to supply electrons therein for exciting the anode cavities during operation of the device. The vacuum envelope is completed by end plates 8 sealed to the ends of the cylinder 1. The cylinder 1, vanes 2 and 3 and discs 4 are made of good conducting metal, such as copper. Suitable means for maintaining a constant magnetic field parallel to the cathode within the cathode space are provided. Such means may consist of permanent magnet poles P, P positioned closely adjacent the outer faces of the end plates 8, as shown in Fig. 2, or an electromagnet coil coaxially disposed with reh spect to the cathode axis. High frequency energy may be taken out of the magnetron by any suitable means, such as a coupling loop 9 linked with the axial magnetic ux of the electromagnetic eld set up in one of the cavities and forming a continuation of the center conductor of a coaxial transmission line 10, as shown in Figure l.

In operation, the anode structure and the cathode are connected to the positive and negativeterminals, respectively, of a source of direct current potential and the radical electric field thus produced cooperates with the axial magnetic eld to cause the electrons supplied by the cathode to form a rotating space charge within the cathode-anode space in the usual magnetron fashion. This space charge sweeps past the anode elements formed by the inner edges of the vanes 2 and 3 inducing high frequency voltages therein and setting up high frequency fields in the cavities. v

Ordinarily, in an anode structure in which the cavities are closed on all sides the cavities are not coupled together except through the central cathode space into which the cavities open. According to my invention, alternate vanes 2 extend outwardly to the inner wall ofthe cylinder 1 and the intermediate vanes 3 terminate short of this wall, as shown, to form coupling aperturesfbetween adjacent cavities. As a result the cavities between adjacent vanes oscillate in'pairs and adjacent pairs of cavities are out of phase at every instant.

Each pair of adjacent anode vanes 2 and 3 and the portions of the discs 4 and cylinder 1 connected between the vanes constitute conducting walls defining or forming one of an annular sei-'ies of anode cavities of equal radial length or depth, each cavity being closed on all sides except for the opening between the vane tips facing the cathode space and for the coupling aperture in one vane adjacent to the cylinder 1.`

Due to the apertures thus provided between the coupling cavities at their rear or outer ends, the continuity of electric and magnetic components of the electromagnetic field set up in the cavities is such that the currents along the vane surfaces and the electric fields in the cavities must be directed as shown by the solid and dotted arrows 11 and l2, respectively, in Figure l. This structure results in the interesting property of this magnetron that the electric fields at the anode elements formed by the inner edges of the vanes, where they are coupled to the rotating space charge in the cathode space, are similarly directed in pairs. Each pair of adjacent cavities on each side of the short vanes 3 oscillate together as a single cavity resonator and the pairs of cavities on each side of each long vane 2 oscillate 180 out of phase. Whereas conventional magnetrons in which adjacent cavities oscillate 180 out of phase in the desired 1rmode require an even number of cavities, or 211 cavities, where n is an integer, in the form of magnetron shown in Figures l to 3 the condition that when one has made a complete circuit around the anode one must return to the same phase requires that for 1r-mode operation there must be an even number or" pairs of cavities, or 411 cavities. These cavities form 2n cavity resonators.

It is apparent that the structure of my invention achieves substantially the same results as conventional strapping in favoring 1r mode operation, in a structure that is obviously much simpler and easier to manufacture than a strapped magnetron.

`The present application is a division of my copending application Serial No. 52,908, filed October 5, 1948, now Patent No. 2,637,004, dated April 28, 1953, assigned to the same assignee.

While I have indicated only two embodiments of my invention, it will be apparent that my invention is by no means limited to the exact form illustrated or use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What is claimed is:

l. An electron discharge device anode structure comprising conducting wall means defining a series of adjacent cavities of equal depth, each cavity having a closed end and an open end and being closed on all sides except for said open en d and for a coupling aperture in one side only located adjacent to said closed end and opening into the next cavity, the number of said cavities being 4n, where n is an integer, whereby said anode structure can be excited in a mode with each pair of adjacent coupled cavities oscillating as a single cavity resonator.

2. An electron discharge device anode structure providing a series of cavities closed at one end and open at the other end and separated by conducting side walls, alternate separating side walls only being apertured adjacent to said closed ends only to couple said cavities together in pairs, and other conducting side walls connected between said separating side walls and closing the other sides of said cavities, the number of said cavities being 4n, where n is an integer, whereby said anode structure can be excited in a mode with each pair of adjacent coupled cavities oscillating as a single cavity resonator.

3. An electron discharge device anode structure comprising an annular series of spaced parallel anode elements of equal length defining a central cathode space, the number of anode elements being 411, where n is an integer, and cavity resonators connected between alternate anode elements only, each of said cavity resonators including conducting Wall means closing the outer end and atleast two sides thereof.

4. An electron discharge device anode structure according to claim `3, including conducting wall means entirely closing said cavity Vresonators except for the spacers between said anode elements opening into said cathode space.

5. An electron discharge device anode structure comprising conducting wall means defining an annular series of cavities closed at one end and opening into a central cathode space at the other end, said conducting wall means including radially-extending separating side wall portions of which alternate ones only are provided with apertures adjacent to said closed ends only for coupling adjacent cavities together in pairs and other radiallyextending side wall portions closing the other sides of said cavities, the number of said cavities being 411, where n is an integer, whereby said anode structure can be excited in a mode with each pair of adjacent coupled cavities oscillating as a single cavity resonator.

6. A magnetron anode structure comprising a cylindrical conducting wall, an annular series of spaced parallel anode elements concentrically arranged within said cylindrical wall and defining a central cathode space, radially-extending conducting walls connecting alternate anode elements with said cylindrical wall, other radiallyextending conducting walls extending from the other alternate anode elements toward but spaced from said cylindrical wall, and other conducting walls connected bctween adjacent radially-extending walls and closing the spaces therebetween, said walls defining a series of cavities open toward said cathode space and coupled together in pairs at the outer ends, the number of said cavities being 411, where n is an integer, whereby said anode structure can be excited in a mode with each pair of adjacent coupled cavities oscillating as a single cavity resonator.

7. A magnetron anode structure comprising an annular series of radially-extending conducting walls surrounding a central cathode space, a conducting wall surrounding said radially-extending walls and joined to alternate ones thereof and spaced from the other alternate ones, and other conducting walls joined to said radially-extending walls and closing the spaces therebetween, said walls defining a series of cavities open toward said cathode space and coupled together in pairs, the number of said cavities being 411, where n is an integer, whereby said anode structure can be excited in a mode with each pair of adjacent coupled cavities oscillating as a single cavity resonator.

8. A magnetron anode structure comprising an annular series of radially-extending conducting vanes surrounding a central cathode space, a cylindrical conducting wall surrounding said varies and joined to the outer ends of alternate vanes, the outer ends of the other alternate vanes being spaced from said wall, and other conducting walls joined to the radially-extending edges of said vanes and closing the spaces between said vanes, said vanes and said walls defining an annular series of cavities open toward the cathode space and coupled together in pairs at their outer ends, the number of said cavities being 411, where n is an integer, whereby said anode structure can be excited in a mode with each pair of adjacent coupled cavities oscillating as a single cavity resonator.

9. A magnetron including: a anode structure comprising conducting wall means defining a series of adjacent cavities of equal depth, each cavity having a closed end and an open end and being closed on all sides except for said open end and for a coupling aperture in one side only located adjacent to said closed end and opening 'into the next cavity, the number of said cavities being 4:1, where 11 is an integer, whereby said anode structure can be excited in a mode with each pair of adjacent coupled cavities oscillating as a single cavity resonator; a cathode disposed adjacent to the open ends of said cavities; and means for establishing a constant magnetic field in the space between said cathode and said anode structure normal to the paths of electrons therebetween.

10. ,A magnetron including: an anode structure comprising an annular series of spaced parallel anode elements of equal length dening a central cathode space, the number of anode elements being 4n, where n is an integer, and cavity resonators connected between alternate anode elements only, each of said cavity resonators including conducting wall means closing the outer end and at least two sides thereof; an elongated cathode axially disposed in said cathode space; and means for establishing an axial constant magnetic field in said cathode space.

11. A magnetron according to claim 10, including conducting wall means entirely closing said cavity resonators except for the spaces between said anode elements opening into said cathode space.

12. A magnetron including: an anode structure comprising an annular series of radially-extending conducting vanes surrounding a central cathode space, a cylindrical Wall surrounding said vanes and joined to the outer ends of alternate vanes, the outer ends of the other alternate vanes being spaced from said wall, and other conducting walls joined to the radially-extending edges of said vanes and closing the spaces between said vanes, said vanes and said Walls defining an annular series of cavities open toward the cathode space and coupled together in pairs at their outer ends, the number of said cavities being 4n, where n is an integer, whereby said anode structure can be excited in a mode with each pair of adjacent coupled cavities oscillating as a single cavity resonator; an elongated cathode axially disposed in said cathode space; and means for establishing an axial constant magnetic field in said cathode space.

References Cited in the le of this patent UNITED STATES PATENTS 2,450,629 Bondley Oct. 5, 1948 2,497,831 De Vore Feb. 14, 1950 2,501,196 Spencer Mar. 21, 1950 2,637,004 Malter Apr. 18, 1953

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