US2721294A

US2721294A - Electron discharge devices

Info

Publication number: US2721294A
Application number: US214706A
Authority: US
Inventors: Earl J Shelton
Original assignee: Raytheon Manufacturing Co
Current assignee: Raytheon Co
Priority date: 1951-03-09
Filing date: 1951-03-09
Publication date: 1955-10-18
Anticipated expiration: 1972-10-18

Description

Oct. 18, 1955 Filed March 9 1951 E. J. SHELTON ELECTRON DISCHARGE DEVICES 2 Sheets-Sheet 1 Oct. 18, 1955 E. J. SHELTON ELECTRON DISCHARGE DEVICES 2 Sheets-Sheet 2 Filed March 9 1951 /n /A/T0/? [an .1 5/952 ro/v 19y 6'7- 0 may ilnited States Patent 1 2,721,294 ELECTRON DISCHARGE DEVICES Earl l. Shelton, Natick, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., at corporation of Delaware Application March 9, 1951, Serial No. 214,796 Claims. (Cl. 31539.53)

This invention relates to electron discharge devices, and more particularly to devices of the magnetron type.

In copending application, Serial No. 66,249, filed December 20, 1948, by William C. Brown, entitled Electron Discharge Device, there is disclosed a cavity magnetron structure wherein alternating anode members are connected by conductive strapping, and, in addition, groups of anode members have transmission lines connected in parallel with the strapping attached to said anode members, the transmission lines being connected to the strapping at the end points of each group of anode members. By this type of group strapping, increased mode separation may be obtained, in particular, separation of the fundamental or 11' mode from the adjacent mode.

This invention discloses another type of group strapping wherein the end points of the groups of anode members are connected to a common junction by means of transmission lines or conductors. Briefly, a structure embodying this type of group strapping may be made as follows. A magnetron-anode structure has alternate anode members thereof connected by a pair of conductive straps such that adjacent anode members are connected to different of said straps. At a plurality of equally-spaced points along one of said straps, connections are made to a first common junction. Similarly, at a plurality of points along a second strap, connections are made to a second common junction, points of connection on the first strap, and points of connection on the second strap being, respectively, adjacent, and the connectors connecting the points of said straps to the common junctions forming transmission lines. By this structure the overall phase shift, at a given percentage frequency deviation from the 1r or fundamental mode, along the straps connecting the anode members is substantially reduced.

In addition, this invention discloses that the output may be coupled to the common junctions, for example, by means of a coaxial cable attached thereto with the result that the anode structure will be substantially symmetrically loaded, thereby aiding in producing optimum operating conditions for the discharge device.

Other and further objects and advantages of this invention will be apparent as the description thereof progresses, reference being had to the accompanying drawings, wherein:

Fig. 1 illustrates a longitudinal, cross-sectional view of a magnetron embodying this invention;

Fig. 2 illustrates a transverse, cross-sectional view of the device shown in Fig. 1, taken along line 22 of Fig. 1; and

Figs. 3, 4 and 5 illustrate equivalent electrical circuits of portions of the discharge device shown in Figs. 1 and 2;

Referring now to Figs. 1 and 2, there is shown an anode structure comprising a metallic cylindrical member 11 which may be made, for example, of copper. Extending radially inwardly from the inner surface of cylinder 11 is a plurality of anode vane members 12, said vane members 12 being substantially equally spaced circumferentially around said cylinder 11 and being made of metallic substantially rectangular planar members whose planes are parallel to the axis of cylinder 11. At points near the inner ends of vanes 12, on the top and bottom edges thereof, conductive strapping 13 is connected between alternate anode members in a well-known manner such that adjacent anode members are connected to diiferent straps.

2,721,294 Patented Oct. 18, 1955 "ice The pair of straps 13 at the upper edge of the anode members 12 is connected to additional conductive means in the following manner. The innermost of the upper straps 13 is connected at three equally-spaced points to the central conductor 14 of a transmission line 15 by conductors 16. Similarly, at points adjacent the connecting points on the innermost of the upper straps 13, the outermost of the upper straps 13 is connected to the outer conductor 17 of the coaxial transmission line 15 by means of conductors 18. As is shown here, by way of example, the innermost and outermost of the upper straps 13 are each connected to the transmission line 15 at three equally-spaced points. However, it is to be clearly understood that any number of connecting points can be used.

The upper end of cylinder 11 is covered by a pole piece 19 of magnetizable material such as an iron or steel alloy, said pole piece extending inwardly and downwardly toward the inner edges of anode members 12, thereby forming a modified frustro conical shape. Holes 20 are provided in pole piece 19 to allow the passage of the

conductors

16 and 18 therethrough without touching said pole piece 19. A metallic plate member 21 is sealed to the top of pole piece 19, the central portion of member 21 being struck up to form a cylindrical member 22 which surrounds the transmission line 15 but is spaced therefrom. Cylindrical portion 22 is sealed to the outer conductor 17 of the transmission line 15 by means of a ceramic member 23, while the inner conductor 14 of the transmission line 15 is sealed to the outer conductor 17 thereof by a ceramic sealing member 24.

Inside the space defined by the inner edges of anode members 12 is positioned a cathode structure 25 of any desired type, for example, as shown here, a cylindrical member whose outer surface is covered with electronemissive material. End shields 26 are provided for said cathode, and are positioned slightly above and below the anode vane members 12 in a well-known manner. The lower end of the cylindrical cathode member 25 is attached to alead-in cylinder 27 which extends through an opening in a lower magnetic pole piece 28. Magnetic pole piece 28 is substantially similar to the upper magnetic pole piece 19 and is sealed to the lower end of the anode cylinder 11. A metallic cylinder 29 is attached to the hole in the magnetic pole piece 28 through which the cathode support 27 passes, said cylinder 29 surrounding support cylinder 27 but being spaced therefrom. Cylinder 29 is sealed to cylinder 27 by means of a ceramic sealing member 30. A conducting rod 31 extends up through the center of the support cylinder 27, and is connected to a heater coil positioned in the cathode 25, the other end of the heater coil being connected to the cathode cylinder 25, and hence to support cylinder 27 through cathode 25. Thus, by application of a potential between the conductor 31 and the support cylinder 27, current may be fed through the coil to heat the cathode 25. Inner conductor 31 is sealed to the support cylinder 27 by means of a ceramic seal 32.

An analysis of the group strapping action in this device will now be described, reference being had to Figs. 3 through 5. Fig. 3 illustrates the equivalent transmission line section of a group of anode members 12 and the portions of the straps 13 associated therewith. Each group of anode members and associated strap portions 13 between points of connection of the

straps

16 and 18 to the strapping 13 will be termed an anode section. As shown here, this anode section may be represented by a transmission line having a series impedance W and two equal shunt impedances X and X connecting each side of the impedance W to the opposite of the transmission line. If one end of the transmission line labeled E and F is at one point of connection on a pair of

conductors

16 and 18 to adjacent points on the strapping 13, and the other end 3 of the transmission line indicated. by points C and D indicates points of connection of another pair of

conductors

16 and 18 to points on the strapping 13 separated by an anode section, then the series impedance W is equal to:

W=jZm sin (N/3 13m) and X=-]'Zm cot (N/3 [rm/2) (2) where Zm is the characteristic impedance of the group anode section, [3m is the phase function or phase shift across one anode cavity defined by one pair of adjacent anode members 12, and N is the number of anode members.

In Fig. 4, there is shown an equivalent transmission line for each of the pairs of

straps

16 and 18 connecting adjacent points of the strapping 13 to transmission line 15, each pair of

straps

16 and 18 forming a susbtantially parallel wire transmission line. If one end of the transmission line, as indicated'by points E and F in Fig. 4, represents the points of connection of the

conductors

16 and 18 to the straps 13, and the points A and B at the other end of the line in Fig. 4 indicate the points of connection of. the

conductors

16 and 18 to inner and

outer conductors

14 and 17, respectively, of the transmission line 15, then the transmission

line comprising conductors

16 and 18, as indicated in Fig. 4, may be represented by an equivalent 1r section network having a series impedance Y and two shunt impedances Z connecting either end of series impedance Y to the other side of the transmission line. The values of Y and Z may be ascertained as follows: Y=jZz sin [32, Z: jZz cot ,82, where Z1 is the characteristic impedance of the transmission

line comprising conductors

16 and 18, and [31 is the phase shift per unit length along said transmission line.

In Fig. 5, there is shown the equivalent overall circuit of the group anode sections of the type illustrated in Fig. 3 and the connecting transmission line sections of the type illustrated in Fig. 4. At three points there are junctions between two adjacent anode sections and a transmission line section and consequently there are three impedances labeled a which represent the parallel combination of two Xs and Z. The upper line has three impedances d which arethe impedances W of Fig. 3. The common junction of all the points A and B of Fig. 3 has connected thereacross an impedance C which is the parallel combination of three Zs. The impedance of the transmission line 15 of Fig. 1 which is connected to this structure is omitted for the purposes of this analysis in the interest of simplification. However, it could be included, if desired, in a more rigorous analysis. The impedances b represent the series impedances of the transmission lines of Fig. 4, and are equal to the impedance Y therein. If six currents are assumed to flow in various meshes of the 'network illustrated in Fig. 5, said currents being numbered I1 through I6, inclusive, network equations may be written and solved in accordance with Kirchhoffs laws. These equations are written for convenience in matrix form as follows:

E a a 2a+d --a a 14 E5 0 a -a a 2a+d a 1.;

E a 0 a a -a 2a+d is The solution of this-matrixby means of determinants and the equating of the solution to Zero yield the natural resonant frequencies of the system. The solution of the determinate is:

Substitution of the impedance Formulas l and 2 in 4 and factoring yield the following significant formulae:

where A is a constant for a particular number of anode sections and is determined from the matrix. For three sections, A+l equals zero, for four sections, A (A+2) equals zero, and for five sections, A |A+1 equals zero. in these formulae, N equals the total number of anode vane members, and S equals the number of anode sections. Incorporation of this type of strapping into a twelve-anode member magnetron yielded the following results: a-lculationof the mode separation of the adjacent mode from the 7r mode produced an increase of mode separation from fifteen point five per cent to twentytwo point five per cent. Testing of this device indicated that the mode separation was actually increased to twentyfour point three per cent by this structure.

Thus,v it may be seen that, by the addition of group strapping by means of parallel wire transmission lines connected to a common junction, a distinct improvement in power-producing capabilities and hence the operating efficiency of the device may be achieved.

This completes the description of the embodiment of the invention described herein. However, many modifications thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. For example, any desired number of anode vane members andanode groups may be used. Any desired output may be attached to the common junctions as, for example, probes or loops for exciting waveguides, and, indeed, the output need not necessarily be taken from the common junctions but may be taken out of the anode members by a loop or probe coupling in a conventional manner. Accordingly, it is desired that this invention be not limited by the particular embodiment described-herein,-except as defined by the appended claims.

What iselaimed is:

1. An electron discharge device comprising a cathode and an anode structure radially spaced from said cathode, a pair ofconductive straps, each of said straps connecting, respectively, diiferent alternate anode members together, a coaxial energy outputcoupling structure, and separate conductors connecting a plurality of circumferentially spacedpoints on each of said straps to said output structure.

2. An electron discharge device comprising a cathode and an anode structure radially spaced from said cathode, a pair of conductive straps, each of said straps connecting, respectively, dififerent alternate anode members together, a coaxial energy output coupling structure, and separate conductors connecting a plurality of circumferentiall-y spaced points-on each of said straps to said output structure, each adjacent pair of said separate conductors forming transmission lines.

3. An electron discharge device comprising a cathode and an anode structure radially spaced from said cathode, a pair of conductive straps, each of said straps connecting, respectively, diiierent alternate anode members together, a coaxial energy output coupling structure, and separate conductors connecting aplurality of circumferent-ially spaced points on each of said straps to said output structure, the points of connection of said con-ductors to said straps being arranged in pairs of adjacent points, one of each of said pairs of points being on one of said straps and the other of each of said pairs of points beingon-an adjacent'strap.

4. An electron discharge device comprising a cathode and an anode structure radially spaced from said cathode, a pair of conductive straps, each of said straps connecting, respectively, different alternate anode members together, a coaxial energy output coupling structure, separate conductors connecting a plurality of circumferentially spaced points on each of said straps to said output structure, and means for producing a magnetic field substantially transverse to the direction of motion of electrons moving from said cathode to said anode structure.

5. An electron discharge device comprising a cathode and an anode structure radially spaced from said cathode, a pair of conductive straps, each of said straps connecting, respectively, difierent alternate anode members together, a coaxial energy output coupling structure, and separate conductors connecting a plurality of circumferentially spaced points on each of said straps to said output structure, the points of connection of said conductors to said References Cited in the file of this patent UNITED STATES PATENTS 1,558,120 Simpson Oct. 20, 1925 2,103,638 Posthumus Dec. 28, 1937 2,111,263 Fritz Mar. 15, 1938 2,169,725 Fritz Aug. 15, 1939 2,428,612 Blewett Oct. 7, 1947 2,478,534 Kather Aug. 9, 1949