US2555349A

US2555349A - Variable ramp for magnetrons

Info

Publication number: US2555349A
Application number: US44869A
Authority: US
Inventors: Charles V Litton
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-08-18
Filing date: 1948-08-18
Publication date: 1951-06-05
Anticipated expiration: 1968-06-05
Also published as: NL69550C; GB687573A; NL147915B; FR993374A

Description

June 5, 1951 C, v, |TTQN l 2,555,349

VARIABLE RAMP FOR MAGNETRONS 2 Sheet's-Sheet l Filed Aug. 18, 1948 1N V EN TOR.

N m 7 L K w on Hh C June 5, 1951 Q v L11-TON 2,555,349

VARIABLE RAMP FOR MAGNETRONS l Filed Aug. 18, 1948 i 2 sheetssheen 2 QLLQ?.

Patented June 5, 1951 UNITED STATES PATENT CFFICE VARIABLE RAMP FOR MAGNETRONS Charles V. Litton, Redwood City, Calif.

Application August 18, 1948, Serial No. 44,869

7 Claims.

My invention relates to electron discharge devices and is particularly directed to improvements in construction of devices of the magnetron type.

In magnetrons and other centimeter-wave generators, the problem persists of efliciently coupling the generator to its load circuit. Generally the low impedance of a resonant cavity must be matched to the relatively high impedance of the connected transmission line, and in the centimeter wave range, where the line usually comprises a wave guide, the end of the wave guide must be terminated at a relatively narrow slit in the side of the cavity. Accordingly, the junction between the wave guide and the cavity must account for the difference in physical dimensions of the wave guide and cavity slit as well-as the difference in impedance of the two. Although the physical dimensions of a coupling circuit may be calculated for a particular set of operating parameters, any variation from those parameters, such as changes in frequency or changes in impedance of the wave guide, causes a mismatch and ineicient operation.

'I'he principal object of my invention is an electrically efficient adjustable coupling between the resonant cavity of a centimeter wave generator and the output or load circuit of the generator.

A more specific object of my invention is an improved coupling structure between a resonant cavity and a wave guide which will accommodate great diierences in physical dimensions and which will match the impedances of the cavity and wave guide.

A still more specic object of my invention is a coupling between a microwave generator Vand a load circuit, the impedance ratio of the coupling being adjustable.

According to the invention there is provided a two conductor transmission line or wave guide for interconnecting an opening in a resonator and a larger output window, in which at least one of the conductors is pivotally supported, to

vary the transfer impedance of the line or guide.

2 tube is a tapered transmission line or wave guide extending from opposite sides of the resonator opening to opposite sides of the window. The spacing between the conductors of the transmission line increases throughout the length of the line so that the inductance and capacity of the line varies with distance from the end of the line. Such a line presents different impedances, respectively, to the resonator at one end and to a connected wave guide at the other end and may be easily adjusted accurately to match the impedances for the efficient transfer of energy from the cavity to the wave guide. Adjustment of the ratio of impedance transformation is made by moving one conductor of the transmission line with respect to the other.

These and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood, by reference to the following description Vof an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a longitudinal sectional View of said one embodiment,

Fig. 2 is a cross sectional view of line I-l of Fig. l of said one embodiment of the invention,

Fig. 3 is a view in perspective, of the adjustable conductor of the transmission line of my invention, and taken on line 3-3 of Fig. 1,

Fig. 4 is an exploded view of the conductor of mig. 3. Y

The electron discharge device to which my invention applies comprises a microwave generator with a cavity resonator and withV an opening in the side Wall of said cavity. To the side wall is hermetically joined the end of a tube, the

The particular microwave generator chosen for illustrating my invention is a magnetron comprising, as shown in the drawing, a round solid metal anode structure I having a plurality of resonators formed by vanes 2 arranged symmetrically about the central bore 3 and forming uniformly spaced slots 4 communicating with the cavities. Electric oscillations are induced in the slots and the cavities by electrons spiraling about the cathode sleeve 5 supported along the center of the structure. The end structures including the magnet poles, seals and cathode and heater leads may be conventional and are not shown.

To remove high frequency energy from the magnetron, a slit 6 is made in the side of one of the resonators, and to the side of the anode structure is formed and hermetically joined one end of a drawn sheet metal tube l. The tube may be rectangular or round, depending on the cross sectional shape of the wave guide 8 to be connected thereto. Should the anode be smaller in outside diameter than the wave guide, the anode end of the tube must of necessity be drawn in to join with the anode. While the tube must be open for the longitudinal transfer of energy. it must be sealed hermetically to gas to permit evacuation of the discharge space within the anode structure. A non-metallic Window 9 of low-loss material, such as mica or hard glass, is sealed in the tube, preferably across the outer end. The sealing ring I0, after junction with the Window has been made, may be braZed to the end of the envelope. The shoulder II on the ring provides a snug sliding contact with the end of the wave guide into which my novel discharge device must feed high frequency energy.

To summarize, the principal function of the tube is merely to enclose the space between the magnetron and its wave guide, the size and shape of the tube being determined principally by the sizes and shapes of the magnetron and wave guide. The internal configuration of the tube is substantially independent, according to my invention, of the high frequency parameters of the system. Hence the tube may be inexpensively die drawn or otherwise fabricated from sheet metal without troublesome dimensional tolerances.

Now, according to an important feature of my invention, a tapered two-conductor transmission line is incorporated within the tube to conduct the high frequency energy from the slit in the resonator to the relatively widely spaced sides of the wave guide. The two conductors I2 and I3 of the line have opposed coextensive curved metal surfaces Iii and i5 which in width may be equal to or less than the length of the cavity slit 6. For reasons which will more fully hereinafter appear, the spacing between the curved surfaces of the conductors of the line varies with distance from one end of the line in such a way the inductance an-d capacity of the line is an exponential function of said distance. It can be shown, then, that the ratio of the impedance of the transmission line at one end to the impedance at the other end is equal to where Zz and Z1 are, respectively, the characteristic impedances of the line looking into the wide end and the close-spaced end of the line. The ratio of impedances are also equal to where e is the constant 2.718, l is the length of the line, and )l is the variable cut-off wave length at various points along the line.

Hence, since the ratio of impedances presented to the resonator and to the wave guide deponds upon the difference in spacing between conductors at the ends of the line, the ratio of impedances may be changed by varying the ratio spacings at the ends. According to a further and important feature of my invention this ratio of end spacings may be varied, without appreciably disturbing the exponential relationship, by pivoting one of the conductors about a point near the wide spaced end. By moving the other end toward or away from the second conductor, the desired impedance transformation is easily obtained` and the output impedance of my magnetron may be matched to the impedance of any wave guide.

As shown in the drawing, one transmission line conductor I3, is a solid block of metal secured 4 to one wall of the envelope, the inner face of the block being machined to the exponential curvature mentioned. The other conductor, I2, is similarly shaped and secured opposite the solid conductor, but is provided with a wide and relatively deep groove Iii, Fig. 4, throughout the length of the face of the conductor. Within the groove is fitted a rectangular metal bar Il the outer face being formed with the exponential curvature of the solid conductors. The bar is pivoted on pin I3 near the outer end by a pin driven through aligned holes in the block and bar. The position of the other end is xed by a link I9 hinged to a second pin 2c and extending to and through a flexible diaphragm 2|. The diaphragm is sealed by bra-zing to the link, and is seated in and joined gas tight around its periphery to the bell-shaped diaphragm support 22. The link and connected bar is moved against the yielding pressure of the diaphragm by the dial 23 which is screw threaded at 24 over the support. The root spacing of the conductors of the transmission line may thus be varied in such a way as to preserve the exponential characteristic, and a broadband variable ratio transformer is the result.

For electrical continuity between the grooved conductor and its bar, small coil springs 25 may be laid in slots in the sides of the bar and compressed laterally between the inside conductor walls and the bar.

While I have described above the principals of my invention in connection with specic apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention.

I claim: n

1. In a coupling device for an ultra high frequency transmission system comprising a tubular housing, a pair of elongated conductors disposed opposite each other within and lengthwise of said housing, the opposed surfaces of said conductors being spaced apart with the spacing increasing exponentially over at least a part of the length of said conductors, one of said conductors being provided with a movable part including at least a portion of the surface thereof which opposes the other conductor and means for adjusting said movable part to vary the spacing between the said opposing surfaces of said conductors.

2. In a coupling device according to claim 1, wherein said one conductor is provided with pivot means located adjacent one end thereof for pivotally connecting thereto said movable part.

3. In a coupling device according to claim 1 further including an adjustable stem extending through a side wall of said housing, the inner portion of said stem being connected to said movable part and the outer portion of said stem being provided with means for adjusting the position of said stem transversely of said housing, and means for pivoting said movable part at a point spaced from said stem.

4. In a coupling device according to claim 1, wherein said one conductor is channeled along the surface thereof facing said other conductor and said movable part is disposed in said channeled portion.

5. In an ultra high frequency transmission system having an ultra high frequency generator of the resonant cavity type with an output slit in a cavity wall thereof, a dielectric wave guide and a coupling device disposed between said output slit and said dielectric guide; said coupling device being characterized in that it comprises a tubular housing and a pair of oppositely disposed conductors disposed longitudinally of said housing from adjacent said slit to the input end of said guide, the opposing surfaces of said conductors being curved away from each other for at least part of the length thereof and means for varying the position of at least part of the said surface of one of said conductors relative to the opposed surface of the other conductor.

6. In an ultra high frequency transmission system according to claim 5, wherein the movable part of said one conductor is provided with a pivot connection adjacent the end of said dielectric guide and the means for varying the position of said part includes an adjustable member for eiecting pivotal movement of said part.

7. In a coupling deviceaccording to claim 5,

6 wherein said one conductor is channeled along the surface thereof facing said other conductor and said movable part is disposed in said channeled portion.

' CHARLES V. LITTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,200,023 Dallenbach May '7, 1940 2,409,913 Tonks Oct. 22, 1946 2,421,912 Spooner June 10, 1947 2,442,118 Donal, Jr., et al.- May 25, 1948 2,459,030 Jonas et al. Jan. 11, 1949