GB2244173A - Electron beam tube arrangements - Google Patents

Abstract

An electron beam tube arrangement, typically an inductive output tetrode device includes an input resonator circuit having two resonant cavities 22, 24. The cavities are coupled, typically by means of linked loops 60, 62 and the second cavity can be tuned by a movable plunger 64. <IMAGE>

Description

Electron Beam Tube Arranvements The present invention relates to electron beam tube arrangements and more particularly to input cavity resonator cavities of such arrangements at which high frequency energy is applied.

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 referred to as '1IOTs") 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 the 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 included along the electron beam path to give outputs at different frequencies which add to give the required bandwidth.

However, this is not possible with conventional IOT design.

In accordance with the present invention, there is provided an electron beam tube arrangement comprising an input cavity resonator circuit including a primary resonator cavity having a secondary resonator cavity coupled thereto.

Although the invention arose from the consideration of IOT devices, it is envisaged that it may be applicable to other forms of electron beam tube arrangements, such as klystrons, which have input resonant cavities.

It is preferred that the cavities are tuned to respective different resonant frequencies, making a larger bandwidth available than would be the case if only one cavity were used.

Advantageously, the resonant frequencies of the primary and secondary cavities are tunable. The tuning may be carried out independently or could be linked, for example, so that a change made in the resonant frequency of one cavity results in a corresponding change in that of the other cavity.

It is preferred that the primary and secondary cavities are coupled by means of loops provided in each cavity which are electrically connected together, the degree of coupling being affected by moving one or both loops.

In one preferred embodiment of the invention, the resonant frequency of the secondary cavity is adjusted by means of a plunger arranged to project from a bore into the secondary cavity so as to vary the volume thereof. The plunger is typically adjusted by means of an adjusting screw.

Some ways in which the invention may be performed are now described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic cross-section side view of an IOT in accordance with the invention (parts have been omitted for clarity); and Figure 2 schematically illustrates part of another arrangement in accordance with the invention.

With reference to Figure 1, and IOT 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 of annular cross-section 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 kV. It is also necessary that the grid 14 should be maintained at a nominal d.c. bias voltage of the order of a hundred volts negative with respect to the cathode.

In particular the present invention relates to the input resonator circuit of the IOT shown in the drawing.

The primary cavity 22 is provided with means, which in this case are tuning doors 94, for varying its volume and hence its resonant frequency. The primary cavity 22 is coupled to the secondary cavity 24 by means of linked coupling loops 60, 62, the position of which can be adjusted to affect the coupling between the cavities 22, 24. It will be appreciated that other means could be provided to effect coupling, such as a variable aperture between the cavities.

The secondary cavity 24 is provided with a bore member 66 having a slidable plunger 64 therein. A screw thread device 68 is attached to the plunger 64 and can be operated to cause different amounts of the plunger 64 to project from the open end of the member 66 and in this manner the internal volume of the cavity 24 and consequently the resonant frequency thereof is varied. A seal 70 is provided around the plunger 64 to prevent r.f. leakage through the bore 66. The output from the secondary cavity 24 is taken from the output loop 26.

At the output end of the IOT a primary output cavity 28 surrounds the output section 16 and is tunable in the conventional manner. The cavity 28 is coupled to the secondary output cavity 30 by means of a coupling loop 80, the connection to the secondary cavity 30 including a domed formation 82 provided on an inner wall thereof. The tuning of the secondary cavity 30 can be achieved by conventional means.

An alternative form of primary input cavity 22 is shown in Figure 2. In this case the cavity 22 is extended in the axial direction so as to form an elongate annular region 90 which is defined by extended cylindrical walls 91, 92. The effective volume of the region 90 is varied by means of a sliding plate 93 which is axially movable. The coupling loop has been omitted for clarity.

Claims (14)

1. An electron beam tube arrangement comprising: an input cavity resonator circuit including a primary resonator cavity having a secondary resonator cavity coupled thereto.

2. An arrangement as claimed in claim 1 wherein the cavities are tuned to respective different resonant frequencies.

3. An arrangement as claimed in claim 1 or 2 wherein the primary and secondary cavities are coupled by means of a loop provided in each cavity, the loops being electrically connected together.

4. An arrangement as claimed in claim 3 wherein the loops are movable and the degree of coupling can be affected by movement of one or both loops.

5. An arrangement as claimed in any preceding claim wherein the resonant frequency of the primary cavity is tunable.

6. An arrangement as claimed in any preceding claim wherein the resonant frequency of the secondary cavity is tunable.

7. An arrangement as claimed in claim 6 wherein the resonant frequency of the secondary cavity is adjusted by means of a plunger arranged to project from a bore into the secondary cavity so as to vary the volume thereof.

8. A arrangement as claimed in claim 7 wherein the position of the plunger is adjusted by means of an adjusting screw.

9. An arrangement as claimed in any preceding claim wherein the primary and secondary cavities are independently tunable.

10. An arrangement as claimed in any preceding claim wherein the primary cavity is of substantially annular cross section and surrounds an electron gun.

11. An arrangement as claimed in claim 10 wherein the primary cavity has one part which is of greater radial extent than another part.

12. An arrangement as claimed in claim 11 wherein the said another part extends further in the direction normal to the annular radius than said part.

13. An arrangement as claimed in any preceding claim wherein the electron beam tube is an IOT (as herein defined).

14. An electron beam tube arrangement substantially as illustrated in and described with reference to Figure 1 or 2 of the accompanying drawings.