GB2245414A

GB2245414A - Output cavity for electron beam tube

Info

Publication number: GB2245414A
Application number: GB9006938A
Authority: GB
Inventors: Roy Heppinstall; Heinz Peter Bohlen; David Mark Wilcox
Original assignee: EEV Ltd
Current assignee: Teledyne UK Ltd
Priority date: 1990-03-28
Filing date: 1990-03-28
Publication date: 1992-01-02
Anticipated expiration: 2010-03-28
Also published as: GB2245414B; GB9006938D0

Abstract

An electron beam tube such as an inductive output tetrode device includes an output cavity resonator circuit comprising a first output cavity 28 having a second output cavity 30 coupled thereto by means of a loop 80 projecting into said first cavity and being connected to a conductive body 82 positioned within the second cavity and spaced from a conductive portion 90 therein so as to define a gap therebetween. The conductive portion is typically a further conductive body 90 which may be attached to a wall of the cavity or the conductive portion can comprise a portion of the wall of the cavity itself. <IMAGE>

Description

Output Cavity for Electron Beam Tube The present invention relates to an electron beam tube including an output cavity resonator circuit and in particular to such a circuit including coupled output cavities.

The present invention is particularly applicable to an inductive output tetrode (IOT) device such as a KLYSTRODE (Registered Trade Mark, Varian Associates Inc). The advantages of inductive output tetrode devices (hereinafter "lOT") are well known but previously proposed designs have suffered from problems in that it has been necessary to provide a number of tubes each of which may require to be used with a number of different cavities in order to provide instantaneous bandwidth required (e.g. 8 MHz) over the entire television frequency range (e.g. 470-860 MHz). In klystrons, this requirement has been met by stagger tuning of the various cavities to give outputs at different frequencies which add to give the required bandwidth. However, this is not possible with conventional IOT design.

It has been previously proposed to provide coupled output cavities for IOTs in which coupling is achieved between the two cavities by means of an adjustable aperture in a common wall. Variations in the coupling are limited to those obtained by varying the size of the aperture. It is an object of the present invention to provide a coupling system in which such limitations are mitigated.

In accordance with the present invention, there is provided an electron beam tube including an output cavity resonator circuit comprising a first output cavity having a second output cavity coupled thereto by means of a loop projecting into said first cavity and being connected to a conductive body positioned within the second cavity and spaced from a conductive portion therein so as to define a gap therebetween.

The conductive portion is typically a further conductive body which may be attached to a wall of the cavity.

Alternatively, the conductive portion can comprise a portion of the wall of the cavity itself.

The loop in the first cavity and the conductive body are preferably linked on a conductive movable shaft such that the attitude of the loop can be adjusted by rotation of the shaft.

It is preferred that one or both cavities include means for adjusting the volume thereof in order to vary the resonant frequency of the respective cavities.

The present invention will now be described by way of example with reference to the accompanying drawing which shows a diagrammatic cross-section side view of an IOT incorporating one embodiment of the present invention (parts have been omitted for clarity).

The IOT shown in the drawing comprises an electron gun 10 incorporating a cathode 12 and grid 14, and an output section 16 incorporating drift tubes 18, 20. The input assembly including the electron gun 10, cathode 12 and grid 14 is surrounded by a primary input cavity 22 which is coupled to a secondary input cavity 24 having an input coupling 26. The output section 16 is surrounded by a primary output cavity 28 which is coupled to a secondary output cavity 30 having an output coupling 32.

In use, an r.f. voltage of a few 100 V is produced between the cathode and grid while both are maintained at about 30,000 V. It is also necessary that the grid 14 should be maintained at a nominal d.c. bias voltage of +/- a few tens of volts with respect to the cathode.

The present invention particularly relates to the output resonator circuits surrounding the output section 16. In this embodiment, a primary output cavity 28 is provided around the output section 16 in the usual manner and includes means (not shown) for varying the volume of the cavity 28 so as to adjust the resonant frequency thereof. A secondary output cavity 30 is provided adjacent to the primary cavity 28 and coupled thereto by means of a movable coupling loop 80 which is positioned within the cavity 28. The size of the loop 80 is selected to achieve the optimum coupling effect.

The loop 80 is connected to a first conductive body 82 within the secondary cavity by means of a conductive shaft 84. The walls of the cavities 28, 30 are separated by a dielectric bush 86 through which the shaft 84 passes. Means are provided (not shown) for rotating the bush 86 and shaft 84 so as to adjust the attitude of the loop 80 in the cavity 28. The first conductive body 82 is also caused to move but as the axial surface 88 of the body is flat, there is no effect on the behaviour thereof. A further conductive body 90 is fixed to the wall of the cavity 30 opposite the first conductive body 82 so as to define a gap D. The size of this gap D is selected to give the optimum tuning effect and is substantially constant. In certain circumstances, it may be appropriate to provide an insulating material between the bodies 82, 90 to define the gap D.The second conductive body 90 could be dome shaped or might be provided by a formation in the wall of the cavity 30 or as a tubular body depending upon requirements. A further coupling loop 32 is provided in the cavity 30 to allow power to be output therefrom. The use of the insulating material between the bodies 82, 90 can be used to provide a mechanical connection and the second body 90 can be connected to an adjusting knob for rotation of the loop instead of the mechanism shown.

The use of the loop and conductive bodies in the resonance circuit allows efficient and controllable coupling and smooth and efficient transition between the resonances of the cavities at the power levels created in an IOT.

At the input end of the IOT shown in the drawing, a primary input cavity 22 is defined by internal and external body portions 40, 42 which are insulated from each other.

The volume of the cavity 22 is variable in the conventional manner. The cavity 22 is coupled via loops 60, 62 to a secondary input cavity 24, the volume of which is variable by adjustment of a plunger 64 projecting from a bore member 66.

It will be appreciated that changes can be made while remaining within the scope of the invention.

Claims

1. An electron beam tube including an output cavity resonator circuit comprising a first output cavity having a second output cavity coupled thereto by means of a loop projecting into said first cavity and being connected to a conductive body positioned within the second cavity and spaced from a conductive portion therein so as to define a gap therebetween.

2. An electron beam tube as claimed in claim 1, wherein the conductive portion is a further conductive body which is attached to a wall of the cavity.

3. An electron beam tube as claimed in claim 1, wherein the conductive portion comprises a portion of the wall of the second cavity.

4. An electron beam tube as claimed in any preceding claim, wherein the loop in the first cavity and the conductive body are linked on a conductive movable shaft such that the attitude of the loop can be adjusted by rotation of the shaft.

5. An electron beam tube as claimed in claim 4 when appended to claim 2, wherein the further conductive body is provided with means for rotation thereof and an insulating portion is used to connect the conductive bodies so as to allow movement of the loop by rotation of the further conductive body.

6. An electron beam tube as claimed in any preceding claim, wherein one or both cavities include means for adjusting the volume thereof in order to vary the resonant frequency of the respective cavity.

7. An electron beam tube which is substantially as herein described in relation to the accompanying drawing.

8. An inductive output tetrode device comprising an electron beam tube as claimed in any preceding claim.