GB2237140A

GB2237140A - Magnetrons

Info

Publication number: GB2237140A
Application number: GB8923322A
Authority: GB
Inventors: Peter Lewis
Original assignee: EEV Ltd
Current assignee: Teledyne UK Ltd
Priority date: 1989-10-17
Filing date: 1989-10-17
Publication date: 1991-04-24
Also published as: FR2653267A1; JPH03179641A; GB8923322D0

Abstract

A magnetron includes a cathode 1 and a surrounding anode structure 2 having vanes 4 defining two sets of cavities 5 and 6 between them. The cavities 5 of one set are of a larger volume than those of the other set 6, the two sets being arranged alternately. The inner ends 8 of the vanes 4 are arranged equidistant around a circle defined by a radius b and their outer ends 7 are unequally spaced around a circle of radius a. The inner ends 8 of the vanes 4 are radiused to give a smooth curved surface without edges, enabling the vanes to be distributed symmetrically about the interaction space of the magnetron, even although the vanes 4 are not aligned radially with the centre of the cathode 1. <IMAGE>

Description

MAGNETRONS This invention relates to magnetrons.

One known type of magnetron has an anode, called a rising sun anode, which defines large and small resonant cavities arranged alternately around its circumference.

Such a structure enables stable oscillation in a single mode to be produced.

Conventionally, a rising sun anode is manufactured by machining a block of metal, usually copper, to produce a hollow cylinder having resonant cavities extending into the cylinder wall from its inner surface. For optimum performance, the sections of the inner wall between the cavities must be spaced equally apart, being of uniform width and radius so that they appear as symmetrical as possible to rotating electron streams in the interaction space between the anode and the magnetron cathode. In order to accommodate both large and small volume cavities whilst retaining this symmetrical configuration around the interaction space, the larger cavities must have a greater radial depth than the smaller cavities. The anode cylinder tends to be bulky as it must therefore be of a large enough diameter to accommodate the large cavities.Also, it is expensive to manufacture such an anode because of the accurate machining required.

According to a first aspect of the invention there is provided a magnetron comprising an anode having two sets of resonant cavities, the cavities of each set being of the same volume which is different from that of the other set, the cavities being arranged around the circumference of a circle and being partly defined by anode vanes having outer ends which are at substantially the same outer radial distance, and inner ends which are at substantially the same inner radial distance, from the centre of the circle, the inner ends being spaced substantially equidistant around a circle having a radius which is the inner radial distance. To implement the invention, the outer ends of the vanes are not equally spaced around the circumference of the circle defined by the outer radial distance.Thus, the vanes have different angular separations to produce the desired ratio of frequency of adjacent cavities, not being aligned along radii of the same circle. By ensuring that the inner ends of the vanes are symmetrically arranged about the interaction space, good performance of the magnetron may be achieved. Also, as both sizes of cavity have substantially the same radial depth, the resulting anode structure is less bulky than a conventional device in which the larger volume cavities extend further in a radial direction than the smaller ones.

It is preferred that the inner end of each vane is radiused. By "radiused" it is meant that the end of the vane is smoothly curved, such that there are no edges at the interaction space. Preferably, the radiused end of each vane is curved in a surface having a uniform radius from a point on the centre-line of the vane parallel to its two major surfaces. The advantage of using radiused inner ends of the vanes is that they may be arranged at equal spacings around the interaction space even though the vanes themselves are not aligned along radii of the same circle.

Advantageously, the anode comprises a hollow cylinder formed separately from the vanes and the vanes are fixed at their outer ends to slots in the inner surface of the cylinder. Alternatively, the anode may be machined as an integral structure. However, by using seperately manufactured vanes, a simple constructional technique may be used which can be inexpensively implemented.

The invention arose from the consideration of magnetron having a "rising sun" type anode in which large and small volume resonant cavities are alternately arranged around the anode. However, it is envisaged that other forms of anode which utilise different size resonant cavities may also be advantageously configured in accordance with the invention.

According to a second aspect of the invention a magnetron comprises an anode structure having vanes defining resonant cavities, wherein the inner ends of the vanes adjacent to the interaction space of the magnetron are radiused. The use of radiused ends is advantageous even for anode configurations in which all the resonant cavities are of the same volume, or where the cavities have different radial dimensions, as it enables tolerances to be increased whilst still ensuring that the part of the anode structure adjacent to the interaction space is symmetrical.

One way in which the invention may be performed is now described by way of example with reference to the accompanying drawings in which: Figure 1 is a transverse section of a magnetron in accordance with the invention; and Figure 2 is an enlarged view of part of Figure 1.

With reference to Figure 1, a magnetron comprises a central cylindrical cathode 1 surrounded by an anode structure 2 which consists of a copper cylinder 3 and anode vanes 4 projecting inwards from the inner surface of the cylinder 3 towards the cathode 1. The anode structure 2 defines two sets of resonant cavities arranged circumferentially about the cathode 1. The resonant cavities of one set 5 are of a large volume and are arranged alternately with cavities of the other set 6 to give a "rising sun" configuration. The outer ends 7 of the vanes 4 are located in slots in the cylinder wall 3 and are arranged on a circle having a radius a from the centre of the cathode 1. The inner ends 8 of the vanes 4 are also arranged at the same distance as each other from the centre of the cathode 1, this distance being shown as b in Figure 1.The inner ends 8 of the vanes 4 are arranged substantially equidistant around the circle of radius b as can be seen more clearly in Figure 2. Thus, the anode structure 2 is symmetrical about the interaction region of the magnetron between the anode vane ends 8 and the cathode 1. The outer ends 7 of the vanes 4 are spaced at unequal distances around the circle having radius a, as can be clearly seen from Figure 1. Thus, the vanes 4 are not aligned radially with respect to the centre of the cathode 1, as is demonstrated by the broken lines of Figure 1 along the centre-lines of some of the anode vanes 4.

The inner ends 8 of the vanes 4 are radiused, having smoothly curving surfaces. Thus, even though the vanes 4 are not aligned radially with the centre of the cathode 1, the part of the anode structure adjacent to the interaction space is symmetrical, giving good performance.

In an alternative embodiment of the invention, pairs of anode vanes may be located in such a way as to provide a set of cavities having parallel walls.

Claims

1. A magnetron comprising an anode having two sets of resonant cavities, the cavities of one set each being of the same volume which is different from that of the other set, the cavities being arranged around the circumference of a circle and being partly defined by anode vanes having outer ends which are at substantially the same outer radial distance, and inner ends which are at substantially the same inner radial distance, from the centre of the circle the inner ends being spaced substantially equidistant around a circle having a radius which is the inner radial distance.

2. A magnetron as claimed in claim 1 wherein the inner ends of each vane is radiused.

3. A magnetron as claimed in claim 2 wherein the radiused end of each vane is curved in a surface having a uniform radius from a point on the centre-line of the vane parallel to its two major surfaces.

4. A magnetron as claimed in claim 1, 2 or 3 wherein the anode comprises a hollow cylinder formed separately from the vanes and the vanes are fixed at their outer ends in slots in the inner surface of the cylinder.

5. A magnetron as claimed in any preceding claim wherein the cavities of one set are arranged alternately around the circumference with cavities of the other set.

6. A magnetron substantially as illustrated in and described with reference to the accompanying drawings.

7. A magnetron comprising an anode structure having vanes defining resonant cavities, wherein the inner ends of the vanes adjacent to the interaction space of the magnetron are radiused.