GB2132008A - A method of altering the frequency tuning range of a klystron - Google Patents

Abstract

By providing an external cavity klystron with two sets of end plates 14,15 and 13,16 located about an interaction gap 12, the frequency range of the klystron may be altered by clamping either of two cavity-forming members 18 and 22 to a respective pair of the end plates. <IMAGE>

Description

SPECIFICATION A method of altering the frequency tuning range of a klystron This invention relates to a method of altering the frequency tuning range of an external cavity type klystron.

A conventional external cavity type klystron, as illustrated by a longitudinal section shown in Figure 1, includes an evacuated electron drift tube 1 along which an electron beam travels. A resonant cavity 2 is coupled to the drift tube 1 via an interaction gap 3.

R.f. frequency oscillations are set up in the resonant cavity 2 and a voltage is generated across the interaction gap. The electron beam interacts with the oscillations and becomes velocity modulated. There are generally a number of resonant cavities and corresponding interaction gaps along the drift tube 1 at which the process is repeated, causing further velocity modulation, r.f. energy then being coupled from the beam.

The resonant cavity 2 comprises two annular end plates 4 and 5, located at the drift tube 1 on respective sides of the gap 3, and an external cavity forming member 6. Cavity forming member 6 comprises two halves which are clamped together around the plates 4 and 5. The inner edge of the member 6 in contact with the plates 4 and 5 is circular and the outer edge is rectangular in shape. A ceramic cylinder 7 surrounds the drift tube 1 and is positioned between the two plates 4 and 5. The cylinder 7 is part of the vacuum envelope of the klystron so that the cavity forming member 6 surrounds the part of the klystron under vacuum but is not itself evacuated.

The frequency at which the klystron operates is varied by moving a tuning door 8 to different positions in the resonant cavity 2 by way of a shaft 9.

The minimum frequency may be obtained when the door is in the position illustrated by a continuous line and the maximum when it is in the position shown as a broken line at 10.

These positions determine the limits ofthefre- quencytuning range at the klystron.

According to this invention a method of altering the frequency tuning range of an external cavity klystron includes: selecting one of a plurality of differently dimensioned cavity forming members and forming a resonant cavity by arranging the selected member to co-operate with fixing means located at an interaction gap of an electron drift tube of the klystron, the fixing means being able to co-operate with each of the plurality of members.

By employing this invention it is possible to extend the tuning range of the klystron since each cavity will form a resonant cavity having different dimensions to those formed by the other cavities.

The klystron is one which has a number of resonant cavities along a drift tube.

Preferably the frequency range of a resonant cavity including one selected cavity forming member overlaps that of another resonant cavity including a different selected cavity forming member, the tuning range of the klystron then tending to be continuous between maximum and minimum operating frequencies.

Preferably, the fixing means includes a plurality of end plates attached to the drift tube at its outer surface, spaced from each other and extending normal to its longitudinal axis, there being at least one end plate located on each side of the interaction gap. There may be only two end plates, which are usually annular, to which each of the plurality of cavity forming members may be clamped in its turn, or there may be more, each cavity being provided to be fixed to different end plates. In practice two cavity forming members are provided for selection.

According to a feature of the invention an external cavity klystron arrangement comprises a klystron, and at least two selectable cavity forming members, there being provided means whereby any one or either of said members may be employed to form a resonant cavity for said klystron in accordance with the method described above.

According to another feature an external cavity type klystron includes: an electron drift tube having an interaction gap, and a plurality of end plates attached to the tube at its outer surface, spaced from each other and extending normal to its longitudinal axis, there being at least two end plates located at each side of the gap. Different cavity forming members may then be attached to the end plates to form respective resonant cavities.

The invention will now be further described by way of example with reference to Figure 2 of the accompanying drawings which illustrates part of one external cavity klystron in accordance with the invention in longitudinal section.

An external cavity type klystron has a number of sections, one of which is illustrated, where an electron beam travelling along a drifttube 11 interacts with r.f. oscillations at an interaction gap region 12. The drift tube 11 has first, second, third and fourth annular end plates 13,14, 15 and 16 respectively attached to its outer surface. They are arranged parallel to and spaced from each other, the first and second 13 and 14 being located on one side of the gap 12 and the third and fourth 15 and 16 being located on the other side.

A ceramic cylinder 17, which forms part of the vacuum envelope of the klystron, is positioned between the second and third end plates 14 and 15 located on either side of and nearest to the interaction gap 12.

A first cavity forming member 18 is clamped to the second and third end plates 14 and 15 to form resonant cavity 19. This has a frequency range which is determined by the movement of a tuning door 20, its minimum frequency position being shown as a continuous line and its maximum as a broken line at 21.

To obtain frequencies of less tham the minimum achieved with the first cavity forming member 18, it is removed and a second annular cavity forming member 22 selected.

The second cavity forming member (shown by a chain dotted line) is clamped to the first and fourth end plate 13 and 16forming another resonant cavity 23. There is also a second tuning door 24 which may be arranged at various positions to give a range of frequencies. The maximum frequency is obtained when the second tuning door 24 is at 25 (as indicated by a broken line). This maximum frequency is such that it is greater than the minimum frequency obtainable with the first cavity 22.

Thus the klystron has an overall greater range of operating frequencies than would be available using a conventional klystron.

Claims (1)

1. A method of altering the frequency tuning range of an external cavity klystron including: selecting one of a plurality of differently dimensioned cavity forming members, and forming members, and forming a resonant cavity by arranging the selected member to co-operate with fixing means located at an interaction gap of an electron drift tube of the klystron, the fixing means being able to co-operate with each of the plurality of members.

2. A method as claimed in claim 1 and wherein the frequency range of a resonant cavity including one selected cavity forming member overlaps that of another resonant cavity including a different selected cavity forming member.

3. A method as claimed in claim 1 or 2 and wherein the fixing means includes a plurality of end plates attached to the drift tube at its outer surface, spaced from each other and extending normal to its longitudinal axis, there being at least one end plate located on each side of the interaction gap.

4. An external cavity klystron arrangement comprising a klystron and at least two selectable cavity forming members, there being provided means whereby any one or-either of said members may be employed to form a resonant cavity for said klystron in accordance with the method claimed in any preceding claim.

5. An external cavity type klystron including: an electron drift tube having an interaction gap, and a plurality of end plates attached to the tube at its outer surface, spaced from each other and extending normal to its longitudinal axis, there being at least two end plates located at each side of the gap.

7. A method as illustrated in and described with reference to Figure 2 of the accompanying drawings,

8. A klystron as illustrated in and described with reference to Figure 2 of the accompanying drawings.

Superseded claims 1 to 8 New or amended claims:

1. A method of altering the frequency tuning range of an external cavity klystron including: selecting one of a plurality of differently dimensioned cavity forming members, and forming a resonant cavity by arranging the selected member to co-operate with a respective one of a plurality of fixing means located at an interaction gap of an electron drift tube of the klystron, each fixing means being extensive over a length, in a direction parallel to the tube axis, which increases from fixing means to fixing means.

2. A method as claimed in claim 1 and wherein the frequency range of a resonant cavity including one selected cavity forming member overlaps that of another resonant cavity including a different selected cavity forming member.

3. An external cavity type klystron including: an electron drift tube having an interaction gap, and a plurality of fixing means, each of which is selectively able to co-operate with a respective one of a plurality of differently dimensioned cavity forming members to form a resonant cavity at the interaction gap, each fixing means being extensive over a length, in a direction parallel to the tube axis, which increases from fixing means to fixing means.

4. A klystron as claimed in claim 3 and wherein each fixing means comprises a pair of end plates attached to the drift tube at its outer surface and extending substantially normal to its longitudinal axis, one plate of each pair being disposed on one side of the interaction gap and the other on the other.

5. An external cavity klystron arrangement comprising a klystron as claimed in claim 3 or 4 and at least two cavity forming members from which a selection may be made.

6. A klystron arrangement as claimed in claim 5 and wherein one of said cavity forming members is attached to its respective fixing means.

7. A method as illustrated in and described with reference to Figure 2 of the accompanying drawings.

8. A klystron as illustrated in and described with reference to Figure 2 of the accompanying drawings.