US3775635A

US3775635A - Power amplifier klystrons operating in wide frequency bands

Info

Publication number: US3775635A
Application number: US00281272A
Authority: US
Inventors: G Faillon; G Firmain
Original assignee: Thomson CSF SA
Current assignee: Thales SA
Priority date: 1971-09-16
Filing date: 1972-08-17
Publication date: 1973-11-27
Anticipated expiration: 1990-11-27
Also published as: GB1366741A; FR2153585A5; DE2245220A1

Abstract

Klystrons of the invention comprise resonant cavities tuned to frequencies higher than the maximum frequency of the frequency band B of operating in order to improve the efficiency at frequencies higher than the centre frequency Fo of the band B, and harmonic cavities tuned to frequencies slightly below the frequency 2 Fo - B, in order to improve the efficiency at frequencies of less than Fo. Wide-band improved klystrons of this kind can be used for operation within wide power ranges and even at relatively low powers, for example some few hundreds of killowatts.

Description

United States Patent Faillon et a1.

11] -3,775,635 [451 Nov. 27, 1973 1 POWER AMPLIFIER KLYSTRONS OPERATING IN WIDE FREQUENCY BANDS [75] Inventors: Georges Faillon; Grard Firmain,

both of Paris, France [73] Assignee: Thomson-CS1", Paris, France [22] Filed: Aug. 17, 1972 [21] Appl. No.: 281,272

[30] Foreign Application Priority Data Sept. 16, 1971 France 7133392 [52] U.S. Cl 3l5/5.43, 3l5/5.39, 315/5.52 [51] Int. Cl. l-l0lj 25/10 [58] Field of Search 3l5/5.39, 5.43, 5.52

[56] References Cited UNITED STATES PATENTS 3,594,606 7/1971 Lien 315/5.43

3,622,834 11/1971 Lien 315/5.52 3,483,420 12/1969 Lien et al.... 3l5/5.52 X 3,453,483 7/1969 Leidigh 315/5.39

Watson et al 3l5/5.43

2,591,910 4/1952 Braford 2,579,480 12/1951 Feenberg 315/5.43 3,249,794 5/1966 Staprans et a1. 3.l5/5.43

Primary Examiner-Rudolph V. Rolinec Assistant Examiner-Saxfield Chatmon, Jr. Att0meyCushman, Darby et a1.

[5 7 ABSTRACT Wide-band improved klystrons of this kind can be used for operation within wide power ranges and even at relatively low powers, for example some few hundreds of killowatts.

2 Claims, 4 Drawing Figures POWER AMPLIFIER KLYSTRONS OPERATING IN WIDE FREQUENCY BANDS The present invention relates to improvements in widebandklystron power amplifiers. It relates more particularly to klystrons improved to give them high efficiency throughout the whole of the working frequency band, this even in the case of relatively lowpower klystrons producing outputs in the order of some few hundreds of kilowatts for example.

It is well known that the combination of conditions of this kind, namely wide passband and relatively low power, makes it extremely difficult to produce klystrons which have satisfactory efficiency throughout the band.

In other words, although it is relatively straightforwardto improve the efiiciency of a narrow-band'klystron by utilising harmonic cavities tuned substantially to twice the centre frequency of the working band, it is equally well known that this method leads to an efficiency/frequency curve which is more peakedand only produces satisfactory efficiency in a relatively narrow band; there is no question of utilising this artifice for wide-band klystrons.

Generally speaking, to improve the efficiency of wide-band klystrons, another method is used; this consists in optimising the efficiency at the centre of thepassband by tuning the last two or three-cavities-of that section of the klystron often referred to as the amplifier" section, to frequencies which are higher than the operating frequencies.

This amplifier section, also often known as the large signal section, comprises a certain numberof cavities where the effective high-frequency power (HF) is generated.

It is generally preceded by a' pre-amplifier" or small signal section, to the input of which the HF signal for amplification is applied and which comprises a certain number of cavities where the gain isbuilt up; a judicious choice of the number of these cavities, their arrangement and their tuned frequencies which are staggered in relation to one another in accordance with a known technique, makes it possible to achieve a suitable gain'and passband in this pre-amplifier section.

This section is followed by a circuit for picking off' the amplified HF power, which in the conventional way and depending upon the type of klystron, comprises one or more cavities, possibly followed by filters, a resonant spiral, etc.

Although this optimising of the band centre efficiency leads to very small variations in the band as a whole, talking at any rate of very high-power klystrons producing for example some megawatts, this unfortunately not the case in klystrons of lower power, producing for example some few kilowatts or even some few hundreds of kilowatts.

At these relatively lower powers, the procedure outlined here leads to an efficiency curve which peaks at the centre of the passband and decreases very rapidly as the frequency progresses to either side of the centre frequency. It is difficult if not impossible to obtain klystrons which will operate properly in wide passbands, that is to say ones having widths in the order of percent of the centre frequency in band S for example.

The object of the present invention is to produce klystron amplifiers which will operate properly and in particular with a high and substantially constant efficiency,

quency (or frequencies) which is/are higher than the maximum frequency F of said frequency band'Band such that the frequency of the high=frequencysignal,.

within wide frequency bands, even at relatively low output powers.

In accordance with the invention; a klystron; for

power amplification of a highfrequency signal; which: klystron can be operated'within a-wide frequency band" B centred on a frequency F 0 comprises, within an evac-' uated enclosure, an electron-gunemitting anelectron beam, a first set of resonant cavities known'as the preamplifier section, a second set of resonant cavities known as the amplifier" section, a high frequency cir cuit for picking off the amplified-high frequency signal;

anda collector, one/several of the resonant cavity/ies in the said amplifier" section'beingtunedto a frefor which the klystron has a maximum efficiency is higher than the centre frequency F0 and lower than said'maximum frequency F and said amplifier section furthermore comprising one/several harmonic cavity/ies tuned to a frequency 2Fo B twice the-minimum frequency of the'band B and less than said'2Fo-B frequency by an amount such'that an increase inthe klystron efficiency is achieved by this/these'cavity/ies in respect of high frequency signal'shavinga frequency less than the centre frequency and greater than the minimum frequency F 1 of the frequency band B.

This novel combination of cavities tuned specially andin particular in such a fashionthat each of them promotes efficient operation of the klystron not at the centre F0 of the band Bas was the case hitherto, but at each side thereof, makes it possible to achieve'high efficiencies which vary very little throughout wide frequency bands.

Other objects, features and results of the inventionwill become apparent from the ensuing description, given by way of non-limitative exampleand illustrated by the attached figures where FIGS. 1 and 2 are graphs indicatingthe'behaviour. of the variation, as a function of frequency, in the efficiency of wide-band conventional klystrons for high (FIG. I) and low (FIG. 2) power'2) power outputs FIG. 3 is a graph indicating the behaviour of thevariation, as a function of frequency, in'the efficiency of a klystron improved in accordance with the invention FIG. 4 is a highly schematic representationof anembodiment of part of a klystron in accordance with the invention.

FIG. 1 illustrates the behaviour of a curveplottingefficiency r as a function of frequency F, in aconventional klystron power amplifier. We are concerned'here with a klystron having a wide operating band Band' a high power output. The efficiency of this klystron or, to put it another way, its fundamental beam current at the output circuit, is a maximum at the centre Fo of the frequency band B.

In accordance with a prior art'technique, referred to hereinbefore, this efficiency r is brought to a maximum through the band B, by utilisingin the amplifier section of the klystron, cavities tuned. to frequencies higher than the frequency Fo.

If frequency shifts of this kind, in the last two-or three cavities of the amplifier section, make'it possible to obtain relatively constant efficiency curves, such as that of FIG. 1, in high-power klystrons, this is certainly not he case with klystrons of lower power.

FIG. 2 illustrates the behaviour of the efficiency curve in this kind of lower power klystron, the klystron having a passband B identical to that of FIG. 1. Although it is possible, in this case, to obtain at the centre F,, of the band, an efficiency r which is quite high, as in the case of FIG. 1, it is not possible to maintain this efficiency at values anywhere near r in the remainder of the band.

FIG. 3 illustrates the behaviour of the efficiency curve r as a function of frequency F, in a klystron improved in accordance with the invention, FIG. 4 schematically illustrating a sectional view of such a klystron.

The klystron shown in FIG. 4 contains an evacuated enclosure 1 of approximately cylindrical general shape, this enclosure exhibiting at one end an electron-gun symbolically represented by the emissive cathode 2, and at the other end a collector electrode 3. The beam of electrons emitted by the cathode 2 and directed towards the collector 3, passes through the drift tube formed by the succession of drift spaces where electron bunching takes place and between which there are interposed resonators which constitute the different cavities 4 to 10.

The first cavity, through a coupler device schematically marked 11, receives the high-frequency signal for amplification. This signal, transposed to the electron beam emitted by the cathode and modulated in the input cavity 4, is preamplified in known fashion in the first section I of the klystron, where the gain is developed. In the figure, this first section comprises two socalled fundamental" cavities, that is to say which are tuned within the operating frequency band B of the klystron this section, in a manner known per se, can comprise more than two such cavities.

The third section III of the klystron, schematically represented here by a fundamental" output cavity, with which there is associated a coupler device 12 picking off the amplified HF signal, is the section in which the HF power is extracted and, as stated hereinbefore, is in fact constituted in a manner known per se, by any suitable system for extracting the maximum power within the working frequency band, for example two coupled cavities, a cavity associated with a filter, a resonant spiral, etc.

The second section II, the power amplifier proper, here comprises four cavities 6, 7, 8, 9, one of which is a harmonic" cavity 7.

It goes without saying that this arrangement is purely an example and could differ both in terms of the total number of cavities, in terms of their tuned frequencies (and consequently their dimensions), and in terms of their arrangement along the length of the drift tube.

In all the embodiments, a klystron in accordance with the invention comprises, in its amplifier section II, on the one hand cavities tuned to frequencies higher than the maximum frequency F F 8/2 of the working band, and on the other hand harmonic cavities tuned to frequencies close to twice the minimum band frequency, namely 2F 2 (F 8/2) 2F B.

The diameter d and length l of these harmonic cavities, are respectively equal substantially to half the diameter D and half the length L, of the fundamental cavities.

To obtain an efficiency curve of the kind shown in full line in FIG. 3, the cavities tuned to the frequencies higher than the mean frequency F are so tuned in such a way that the efficiency curve which would be obtained in the absence of the harmonic cavities (curve ABC), is not symmetrical in relation to F,,, but has its peak M located between F, and the maximum frequency F of the band B. This result is achieved by tuning these cavities to frequencies higher than those which would produce a curve symmetrical in relation to F in the manner adopted in conventional klystrons.

As far as the harmonic cavities are concerned, these are tuned to a little below the frequency 2R, B, in order to reinforce the efficiency of the klystron between the minimum frequency F, of the band B and the frequency F The effect of these harmonic cavities upon the section AB of the curve of FIG. 3, is such that the efficiency curve of the thus improved klystrons, has the form of the curve DBC.

To obtain this kind of result, a variety of embodiments are possible the klystron can have one or more harmonic cavities and one or more cavities tuned to frequencies higher than F,,. In addition, the location of these cavities in relation to one another, in the amplifier section II, can vary.

In the example illustrated in FIG. 4, the amplifier section II comprises a fundamental cavity 6 tuned in the working frequency band B, then a harmonic cavity 7 tuned to a frequency slight lower than (2 F B), 1.88 F for example for a bandwidth B equal to 10 percent of F,,, then two cavities 8 and 9 tuned to frequencies higher than the frequency F,,; the cavity 8 is for example tuned to 1.05 F, and the cavity 9 to 1.07 F,,, it being understood of course that these values are given purely by way of example.

Thus, assuming that the outputs of the klystrons in question are in all cases taken to an optimised load, and if we consider klystrons operating in the S band (from 1,500 MC/s to 5,200 MC/s), with bandwidths B equal to 10 percent of the centre frequency F these klystrons producing output powers peaking at around 200 kW, then klystrons in accordance with the invention will have efficiencies varying for example between 50 and percent for the whole of the bandwidth B prior art klystrons operating under the same conditions of power, frequency and bandwidth, will have efficiency variations ranging from 44 to 60 percent.

We claim:

1. A klystron for power amplification of a high frequency signal, which klystron can be operated within a wide frequency band B centred on a frequency Fo, comprising, within an evacuated enclosure, an electron-gun emitting an electron beam, a first set of resonant cavities known as the preamplifier" section, a second set of resonant cavities known as the amplifier section, a high frequency circuit for picking off the amplified high frequency signal and a collector, at least one of the resonant cavities in the said amplifier section being tuned to a frequency which is higher than the maximum frequency band B such that the frequency of the high frequency signal, for which the klystron has a maximum efficiency, is higher than the centre frequency F0 and lower than said maximum frequency F and said amplifier" section furthermore comprising at least one harmonic" cavity tuned to a so-called harmonic frequency close to a frequency (2 Fo-B) twice the minimum frequency of the band B, said so-called harmonic frequency being less than said 2Fo-B frequency by an amount such that an increase in the klystron efficiency is achieved by this cavity in respect of high fequency signals having a frequency less least one cavity of the amplifier section which is than the centre frequency F and greater than the minituned to a frequency higher than the centre frequency mum frequency F of the frequency band B. F0 is the last cavity of said amplifier section.

2. A klystron according to claim 1 wherein the at

Claims

1. A klystron for power amplification of a high frequency signal, which klystron can be operated within a wide frequency band B centred on a frequency Fo, comprising, within an evacuated enclosure, an electron-gun emitting an electron beam, a first set of resonant cavities known as the ''''preamplifier'''' section, a second set of resonant cavities known as the ''''amplifier'''' section, a high frequency circuit for picking off the amplified high frequency signal and a collector, at least one of the resonant cavities in the said ''''amplifier'''' section being tuned to a frequency which is higher than the maximum frequency band B such that the frequency of the high frequency signal, for which the klystron has a maximum efficiency, is higher than the centre frequency Fo and lower than said maximum frequency F2, and said ''''amplifier'''' section furthermore comprising at least one ''''harmonic'''' cavity tuned to a so-called harmonic frequency close to a frequency (2 Fo-B) twice the minimum frequency of the band B, said so-called harmonic frequency being less than said 2Fo-B frequency by an amount such that an increase in the klystron efficiency is achieved by this cavity in respect of high fequency signals having a frequency less than the centre frequency Fo and greater than the minimum frequency F1 of the frequency band B.

2. A klystron according to claim 1 wherein the at least one cavity of the ''''amplifier'''' section which is tuned to a frequency higher than the centre frequency Fo is the last cavity of said ''''amplifier'''' section.