GB2243943A

GB2243943A - Electron beam tube with input cavity

Info

Publication number: GB2243943A
Application number: GB9104850A
Authority: GB
Inventors: Heinz Peter Bohlen; Edward Stanislaw Sobieradski; Mark Bridges; Steven Bardell
Original assignee: EEV Ltd
Current assignee: Teledyne UK Ltd
Priority date: 1990-03-09
Filing date: 1991-03-07
Publication date: 1991-11-13
Anticipated expiration: 2011-03-07
Also published as: FR2660796A1; JP3075753B2; DE4107552C2; GB2243943B; FR2660796B1; JPH0582034A; DE4107552A1; GB9104850D0

Abstract

An electron beam tube 10, 12, 14, 16, typically an inductive output tetrode device, includes an input resonant cavity 22 which is at least partially defined by an internal body portion 40 maintained at a high voltage with respect to an external body portion 42 at a relatively low voltage, said body portions having no electrically conductive connection therebetween. The body portions are joined by a moulded insulating material 52 which insulates the body portions while still allowing r.f. leakage. <IMAGE>

Description

- 1 Electron Beam Tube Arranqements The present invention relates to

electron beam tube arrangements and more particularly to input resonator cavities of such arrangements at which high frequency energy is applied.

The present invention is particularly applicable to an inductive output tetrode device (IOT) such as a KLYSTRODE (Registered Trade Mark, Varian Associates Inc). The advantages of inductive output tetrode devices (hereinafter referred to as 11IOTs") 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 is currently met by stagger tuning of the various cavities included along the electron beam path to give outputs at different frequencies which add to provide the required bandwidth. However, this is not possible with conventional IOT design.

1 Another problem which has been encountered results from P/8244/EEV - 2 the high voltages of the order of 30kV, which the cathode and grid must maintain, especially as the input cavity can define an external part of the IOT and so might be handled in normal usage.

The present invention arose from an attempt to provide a system which obviates or mitigates some or all of the problems associated with maintaining high cathode and grid voltages while providing an IOT suitable for television applications.

In accordance with the present invention, there is provided an electron beam tube arrangement comprising: an input resonant cavity at least partially defined by an internal body portion and an external body portion, the internal body portion being maintained at a high voltage with respect to the external body portion and said body portions having no electrically conductive connection therebetween.

By "high voltage" it is meant of the order of tens of kilovolts.

Although the invention arose from the consideration of IOT devices, it is envisaged that it may be applicable to h P/8244/EEV other forms of electron beam tube arrangements, such as klystrons, which have input resonant cavities.

The external body portion is typically at a very low voltage, usually earthed.

It is preferred that the body portions are physically joined together by a dielectric insulator portion, which advantageously is moulded. The. body portions can also be provided with mutually interengaging formations to assist in the joining of the two body portions. These formations are advantageously dimensioned so as to define a very high d.c. impedance path but a very low r.f. impedance path at the joint to inhibit r.f. leakage from the cavity whilst enabling the required voltage difference between the external and internal body portions to be maintained.

It may be preferred that an electrical connection be provided between the outside of the cavity and the internal body portion through the insulator material.

Advantageously, the input resonant cavity is a primary cavity and a secondary resonator cavity is included, being coupled to the primary cavity.

P/8244/EEV - 4 It is preferred that the cavities are tuned to respective different 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.

The volume of the primary cavity may be varied by means included in the external body portion to adjust the resonant frequency.

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 present invention (parts have been omitted for clarity); Figure 2 is a schematic drawing of an alternative form z P/8244/EEV - 5 of primary input cavity; and Figure 3 schematically illustrates another embodiment in accordance with the invention.

The IOT shown in Figure 1 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 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 primary input cavity 22 of the device shown in the drawing. An internal body portion 40 comprises upper and lower annular metal plates 70, 71 separated by a dielectric 1 P/8244/EEV material 73 so as to define an annular channel. The upper plate 70 is electrically connected to the cathode and the lower plate 71 is electrically connected to the grid. The open part of the channel faces outwardly and embraces the open part of a further annular channel comprising a metal external body portion 42, the input cavity 22 being defined by the portions 40 and 42.

Angled flanges 44, 46 are provided on either side of the external body portion 42 so as to define further annular channels 48, 50 into which the free edges of the internal body portion 40 project. However, there is no direct electrical contact between any part of the internal body portion 40 and any part of the external body portion 42 and the flanges 44, 46, a moulded insulating dielectric material 52 being provided therebetween. This serves to insulate the exterior body portion 42 from the interior body portion 40 and hence from the very high voltage encountered in use. While the use of the dielectric 52 insulates the body portions 40, 42 electrically, there is still a potential path for r.f. leakage through the dielectric 52.

Consequently, the dimensions of the overlapping paths of the portions 40, 42 are chosen to provide a very low r.f. impedance path and hence prevent as much r.f. leakage as possible.

1 P/8244/EEV The volume and hence the resonant frequency of the cavity 22 can be varied in a conventional manner, for example by using tuning doors as shown at 94.

An alternative form of primary input cavity 22 is shown in Figure 2. In this case, the external body portion 42 is extended in the axial direction so as to form an elongate annular region 90 which is defined by extended cylindrical walls 91, 92 of the body portion 42. The effective volume of the region 90 can be varied by means of a sliding plate 93 which can be moved axially by any suitable means.

In the accompanying drawing, the surfaces of the dielectric are shown as smooth but the voltage hold-off ability can be improved still further by providing a surface configured, say, as a crenellated form of ridges and grooves.

A power lead 54 is routed through the dielectric 52 in order to maintain the grid 14 at the appropriate bias voltage while maintaining the electrical insulation of the exterior body portion 42, the connection being made via the lead 54 and plate 71.

P/8244/EEV The interior of the primary input cavity 22 is linked to the secondary input cavity 24 by means of coupling loops 60, 62. The internal volume of the secondary input cavity 24, and hence its resonant frequency, is adjustable by means of a movable plunger 64 projecting from a bore member 66. In this embodiment of the invention the volumes of the primary cavity 22 and the secondary cavity 24 are independently variable, but they could be linked to move together. The primary and secondary cavities 22 and 24 are arranged to have respective different resonant frequencies.

At the output end of the IOT a primary output cavit surrounds the output section 16 and is tunable in conventional manner. The cavitv 28 is counled to y 28 the 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.

With reference to Figure 3, in another embodiment of the invention, only one input cavity is included in the arrangement. In this particular arrangement, the input cavity is similar to that illustrated in Figure 2.

P/8244/EEV 9

Claims

1. An electron beam tube arrangement comprising: an input resonant cavity at least partially defined by an internal body portion and an external body portion, the internal body portion being maintained at a high voltage with respect to the external body portion and said body portions having no electrically conductive connection therebetween.

2. An arrangement as claimed in claim 1 wherein the external body portion is at a relatively low voltage.

3. An arrangement as claimed in claim 2 wherein the external body portion is earthed.

4. An arrangement as claimed in any preceding claim wherei the body portions are physically joined together by dielectric insulator portion.

5. An arrangement as claimed in claim 4 wherein an electrical connection is provided between the outside of the cavity and the internal body portion through said insulator portion.

6. An arrangement as claimed in any preceding claim wherein the resonant cavity is of substantially annular cross P/8244/EEV - 10 section and surrounds an electron gun.

7. An arrangement as claimed in claim 6 wherein the resonant cavity has one part which is of greater radial extent than another part.

8. An arrangement as claimed in claim 7 wherein the said another part extends further in the direction normal to the annular radius than said part.

9. An arrangement as claimed in any preceding claim wherein the body portions have formations which are mutually interleaved and which are dimensioned so as to provide a very low r.f. impedance path at the joint between said body portions so as to inhibit r.f. leakage from the cavity.

10. An arrangement as claimed in claim 9 wherein mutually interleaved formations comprise a first annular disc extensive from the internal body portion and second and third annular discs extensive from the external body portions and overlapping the first annular disc, the regions between the second and first, and first and third discs being occupied by dielectric material capable of holding off said high voltage.

P/8244/EEV

11. An arrangement as claimed in claim 10 when dependent on claims 7 or 8 wherein the said another part is defined by the external body portion.

12. An arrangement as claimed in any preceding claim wherein the external body portion includes means for varying the volume of the cavity.

13. An arrangement as claimed in any preceding claim and wherein the said input resonant cavity is a primary cavity and including a secondary resonator cavity coupled to the said primary resonant cavity.

14. An arrangement as claimed in claim 13 wherein the cavities are tuned to respective different frequencies.

15. An arrangement as claimed in claim 13 or 14 wherein the primary and secondary cavities are coupled by means of a loop provided in each cavity, the loops being electrically connected together.

16. An arrangement as claimed in claim 15 wherein the loops are movable and the degree of coupling is controllable by movement of one or both loops.

P/8244/EEV

17. An arrangement as claimed in any of claims 13 to 16 wherein the resonant frequency of the primary cavity is tunable.

18. An arrangement as claimed in any of claims 13 to 17 wherein the resonant frequency of the secondary cavity is tunable.

19. An arrangement as claimed in claim 18 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.

20. An arrangement as claimed in claim 19 wherein the position of the plunger is adjusted by means of an adjusting screw.

21. An arrangement as claimed in any of claims 17 to 20 wherein the primary and secondary cavities are independently tunable.

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

23. An electron beam tube arrangement substantially as 1 P/8244/EEV - 13 illustrated in and described with reference to Figure or 3 of the accompanying drawings 1 ' 2 Published 1991 at The Patent Office, Concept House, Cardiff Road, Newport. Gwent NP9 lRH. Further copies may be obtained from Sales Brunch. Unit 6. Nine Mile Point, Cwmfelinfach, cross Keys. Newport. NP 1 7HZ. Printed by Multiplex techniques lid. St Mary Cray' Kent.