DE2424679A1 - BROADBAND MULTI-CHAMBER KLYSTRON - Google Patents

Description

"Broadband multi-chamber Klys tron"

The invention relates to a broadband multi-chamber klystron.

Broadband multi-chamber klystrons for amplifying television video signals are required to have a bandwidth of the order of 6 to 8 MHz between the -1 dB in the frequency band for VHP television transmission (e.g. 470 MHz 890 MHz) Points. Since this bandwidth is more than 1 io of a reference frequency, the resonance frequencies of 4 or 5 chambers are normally staggered for this purpose and at the same time the perveance is determined in such a way that it is between 1.5 and 3.10 perv. lies, so that the value for Q of the individual chambers during operation, ie when a beam current is passed through them, can be reduced to a minimum by the beam loading of the electron beam.

In the UHF band, the wavelength is also longer than that in the GHz band, so that the construction of a klystron in the range of the chambers, which depends on the wavelength, becomes very large. Because of this, it is in order to have an excessive length of the tube

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To avoid it, it is necessary to choose a relatively high value for the perveance. On the other hand, it has a high level of perveance the disadvantage that the efficiency of converting energy from an electron beam to a microwave circuit decreases an alternating effect gap assigned to the exit chamber becomes correspondingly lower.

It has been reported (Walder / Mclsaac, "Experimental Analysis of Biased Gap Klystron", IEEE Trans. ED, Vol. 13, 1966, pp.950-955) that when an accelerating bias is applied across the drift tube interaction gap in the penultimate Chamber achieved an efficiency of $ 66>. The achievement of a broadband characteristic was, however, unpredictable. In this connection it was also reported that when an acceleration voltage was applied across the interaction gap of a drift tube in the second chamber, no improvement in the efficiency could be observed.

It has also been reported (Mihran, "Design and Demonstration of a Klystron with 62 percent Efficiency", IEEE Trans. ED, Vol. 18, No.2, Feb. 1971, p.124-133) that if a broadband characteristic A perveance of approx. 0.5- is disregarded with regard to the degree of efficiency. 10 perv. is more advantageous.

The object of the invention is to create a multi-chamber klystron with a large bandwidth, high efficiency and high gain, However, its structural design is shorter than that of known klystrons of this type.

According to the invention this is achieved in that in a preliminary stage formed by one or more chambers, the excitation a broad frequency band is used, at least one chamber is coupled to an external reactance circuit and at least at the last drift tube interaction gap of the chambers of the preliminary stage, a voltage to accelerate the electron beam and one final stage of chambers in which the electron beam is concentrated, one or more chambers,

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which is one to several percent higher than the middle one Frequency of the frequency band lying frequency are tuned, as well as an output chamber, which is essentially on the middle Frequency of the frequency band is set, has.

Ausftihrungsbeispiele the invention are based on the following of the accompanying drawings. They represent:

Fig. 1 a first embodiment} Fig. 2 shows a second embodiment.

The embodiment of FIG. 1 has a cathode 2, an acceleration electrode 3, a yoke 10 for direct current Isolation of an input drift tube 4 from the first chamber 9 (input chamber) and an outer reactance circuit 7. the Input chamber 9 forms, if necessary with further chambers, a preliminary stage group of broadband exciter chambers. In the exemplary embodiment a second chamber 13 is also provided, belonging to the same preliminary stage group. A third chamber 17 also forms if necessary further chambers a final group of chambers that are used for bunching. Furthermore, there is an exit chamber 20 intended. The embodiment also has a drift tube interaction gap 11 in the input chamber 9 »a clamping part for the direct current insulation of a first Drift tube 12 from the second chamber 13, as well as another Drift tube interaction gap 15 in the second chamber 13. The acceleration voltage E i lies at the drift tube interaction gap 11 in the input chamber 9, the accelerating voltage E- at the second drift tube interaction gap 15.

The embodiment according to FIG. 1 is therefore a multi-chamber klystron with four chambers. Between cathode 2 and the accelerating electrode 3 becomes a perveance of, for example, 2.10 perv. set. The entrance drift tube 4-, between the and the first drift tube 12, the first interaction gap is provided, is provided with the clamping part 10, which, as

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mentioned, the input drift tube 4 isolated from the input chamber 9 in terms of direct current, but with regard to the microwaves shorts with her. The input drift tube 4 and input chamber 9 together have the puncture of the conventional cavity resonator. The clamping member 10 is conventional, i.e. it consists essentially of one Insulator, for example made of ceramic parts, which are arranged between metallic parts in such a way that the latter the ceramic Keep parts in their relative arrangement to each other and give them the necessary strength; the dimension of the yoke is 1/4 of the wavelength at the operating frequency of the klystron.

A signal emitted by an external signal generator 5 is fed into the input chamber 9 via a capacitance or an electrostatic one Coupling element 6 (to suppress the direct current component), the reactance circuit 7, which is used for broadband excitation, and a loop 8 are fed in. Men thus receives one Broadband velocity modulation of an electron beam 26 in the first drift tube interaction gap 11. The first Drift tube 12, which is the upper limit of the first drift tube interaction gap 11 is isolated from the second chamber by the yoke 14 in terms of direct current, but with it shorted with respect to microwaves. In this respect, the connection is similar to that of the entrance drift tube 4; However the drift tube 12 is directly connected to the input tube 9. As a result, the drift tube 12 acts as a whole as part of the cavity resonator, which is formed by the input chamber 9 and the chamber.

The second chamber 13 is in a conventional manner directly connected to a second drift tube 16, the third chamber 17 and one third drift tube 19 »as well as the exit chamber 20 and an exit drift tube 24 and forms with these components together the remaining part of the klystron. A load 22, for example an antenna, is coupled into the output tube via a loop 21. This output chamber 20, inter alia, is grounded in a conventional manner. Furthermore, a collector 25 is provided, which has a The ammeter is grounded. However, it can be used to increase the efficiency of a voltage source E, - with a potential that lower than earth potential.

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If one now assumes that the efficiency of the (energy) conversion from electron beam 26 to an external circuit, e.g. the load 22 applied to the interaction gap 23 associated with the exit chamber 20 is 66.6 $ that at the same Interaction gap an equivalent perveance of the electron beam 26 of 0.8.10 "perv. Is given, and that If an output power of approximately 9.3 W is delivered to the external load 22, it can then be deduced from this that the 6-light current power of the electron beam over this fourth interaction gap 23 14 KW associated with the power output, the beam voltage is 12.5 kV and the beam current is 1.12 A.

Since the perveance for the generation of the electron beam in the embodiment according to Pig. 1 to 2.10 perv. was chosen (see above), the acceleration voltage of the acceleration electrode 3 with respect to the cathode 2, which is applied to this with the aid of the voltage source Eg, is 6.85 kV.

Generally the entrance drift tube 4 is with the accelerating electrode 3 either short-circuited during manufacture or, although designed separately for current measurement purposes, but then subsequently short-circuited externally so that both have the same potential.

The difference voltage of 5.65 kV between the voltage of 12.5 kV (Beam voltage across the interaction gap 23, see above) and the Voltage of 6.85 kV (acceleration voltage at the acceleration electrode 3) is divided into two voltages, which are carried out by Voltage sources E, and E symbolize and, as in Pig. 1 can be seen, are created.

As a result, the electron beam 26 is additionally firstly above the first interaction gap 11 due to the voltage E, and also second, accelerated by the voltage E. via the second interaction gap 15.

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Although the acceleration across the first interaction gap 11 is related to a flattening of the frequency behavior in the case of broadband excitation under strong beam charging has a rather negative effect, was shown in the exemplary embodiment according to Fig. 1 the voltage of the voltage source E chosen to be 1 kV, to meet the requirements for the yoke 10 in terms of tension, which this component has to withstand on its own and to improve a focusing of the electron beam in that this collector accelerates increasingly (see below) and also to prevent feedback from back-wandering electrons.

Accordingly, in the exemplary embodiment according to FIG. 1, the equivalent perveance of the electron beam changes over the first interaction gap from 2.10 "perv. To 1.62.10" perv. ; If the voltage E. across the second interaction gap is selected to be 4.65 kV, it changes across the second interaction gap from 1.62.10 "perv. to 0.8.10""perv.

One can find the coupling coefficient between an electron beam and a circuit formed by a chamber over the interaction gap of a drift tube generally therethrough calculate that the structural dimensions are based on an equilibrium speed of the electron beam and an operating frequency can be normalized. Besides, one determines the density modulation, which increases as the electron beam travels through the drift tube, with the help of a reduced plasma wavelength Aq. This is obtained by using the plasma wavelength that is in turn derived from the beam voltage, the beam current and a beam radius are determined, multiplied by a reduction factor that takes into account the configuration, which is obtained from the diameter of the drift tube, the diameter of the electron beam, the operating frequency, etc.

The following calculation was based on the following dimensions and frequencies based on: operating frequency 500 MHz, drift tube radius 9 mm, electron beam radius 6 mm, width of the drift tube interaction column (the same for all chambers) 16 mm. From it

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were "calculated: the coupling coefficient IYL over the first interaction gap, the coupling coefficient Mp over the second interaction gap, the coupling coefficients M- = M over the third and fourth interaction gap, the effective plasma wavelength λ ₂ ⁼ ^ -z in the areas The results are shown in Table 1. In addition, the values for the beam loading Gb are given above the interaction gaps.

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Tabel

O CD OO -C- * CD

CD CD NJ QO

Coupling coefficient
above that
Interaction gap Effective plasma
wavelength beam
load First
Interaction gap 0.891 <M ₁
<0.905 Area of the first
Drift tube Λ q1 at 84.5 cm Second
Interaction gap 0.905 <M ₂
<0.945 Areas of the second
or third
Drift tube * ci2 => q3
= 146 cm Third or fourth
Interaction gap M ₅ = M ₄
= 0.945 Gb3 »Gb4

00 I.

When passing through the first and the second interaction gap 11 ″ and 15, there is between the opposite Drift tubes an acceleration voltage is applied, which Speed of the electron beam increased. Therefore, although the coupling coefficient is above the interaction gap increases, beam loading is reduced. In practice, the speed across the interaction gap decreases gradually so that these factors are between the values given in the table, which result from the speeds at the leading and trailing edges of the alternating effect column were calculated, intermediate values were run through.

As described, with a stress distribution according to fig. 1 the radiation load over the first interaction gap approximately 2.5 times as high as above the third and fourth interaction gap. That implies that the radiation exposure of the electron beam can in this case be made larger than in a case in which the initial equivalent perveance of the electron beam is chosen to be 0.8.10 "perv. and that the Q value of the entrance chamber can be lowered accordingly.

With such a low Q-value, one can o? 9 and the filter coupled to it (Reactance circuit 7) one of a signal emitted by the signal generator, the electron beam 26 at the first interaction gap achieve impressed speed modulation of the same, which has a very high bandwidth.

During its passage through the first drift tube 12, the electron beam 26 experiences a density modulation. It is customary to use an electrically correspondingly longer drift tube in the stage in which the microwave signal has an even lower level in order to achieve a certain gain (gain). If you choose L ₁ «0.2.λ., You get L ₁ « 17 cm, since X * is only (see Tab. 1) 84.5 cm. In contrast to the value of 29 cm, which results from an initial equivalent perveance of 0.8.10 "perv., This length can be shortened considerably.

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In order to increase the efficiency of the conversion of the electron stream, it is necessary to detune the second and third chambers by a few percent towards a higher frequency and to increase the density of the bunching in the electron beam by increasingly shortening the drift distance . For this reason, the length of the second drift tube becomes L ₂ = 0.115. ^ q ₂ = 17 cm and the length of the third drift tube chosen to be L, »0.09 Aq,» 13 cm. However, if the perveance of the electron beam in the area of the third drift tube is 2.10-6 perv., Then the extremely low value of Lz = 0.09 results for the length of the drift tube. ^ = 6.3 cm; this has the disadvantage that there is no longer any space left between the adjacent chambers to attach a cooling arrangement and that the interaction gap of the drift tube has to be arranged very close to the wall of the chamber, thereby necessarily lowering the impedance.

In the exemplary embodiment of the invention, however, the equivalent Perveance in the areas of the second and third drift tubes, in which the bunching in the electron beam is significantly reduced to 0.8.10 ". You can have such a Achieve agglomeration with a very low velocity dispersion and a high conversion efficiency.

In a klystron according to the invention, in the entrance chamber and in the region of the first drift tube, which are both regions of low level of the signal, the electron beam is subjected to broadband excitation in a state in which it has a large perveance, ie a low Q _T value in order to achieve sufficient gain (gain) over a mechanically short distance; However, in the second and third chambers, which largely influence the efficiency, a speed dispersion of the electron beam is suppressed by reducing the equivalent perveance, the restriction with regard to the distance between adjacent chambers is alleviated and the efficiency is fully increased. Since the Reaonnanzetellen of the second and the third chamber in the direction of § a higher

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Frequency are shifted outside the operating frequency range, In order to achieve higher efficiency, these chambers worsen the broadband characteristics of the previous stage not negative.

In a multi-chamber klystron according to the embodiment described, the distance from the first interaction gap to the fourth interaction gap is 0.2 λ -, + 0.115 A ₂ ⁺ 0.09 \ τ = 47 cm in contrast to the corresponding distance according to the state the technique, which is 0.405 A ^ = 59 cm. A high gain can therefore easily be achieved with a tubular body which is more than 10 cm shorter than a tubular body according to the state of the art; however, broadband characteristics and an efficiency of $ 60 or more are obtained and in this respect are equivalent to the prior art tubes.

The electron beam is focused by an electrostatic lens effect in the first and the second interaction gap, over which an acceleration voltage is applied in each case, so that magnetic focusing becomes easier. If one intends to improve the efficiency by lowering the collector potential, there is occasionally a feedback of energy to the input chamber by electrons that have _{been accelerated by the inverted voltage E 1} - and therefore migrate back out of the area of the collector in such a way that a Repeated interaction with the microwave circle in the interaction gaps of the drift tubes takes place in the reverse order as with the main beam. This gives rise to various unstable phenomena. Provided that the voltages satisfy the equation E - = Ej-, however, in the case of the described klystron, the electrons migrating backwards enter the drift tubes and others before they have returned to the first interaction gap. Disturbances caused by back-migrating electrons are then practically of no importance.

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Furthermore, it results that the voltage at the acceleration electrode, compared to the having a high operating temperature Cathode is arranged, is under low voltage, since a relatively high value is selected for the perveance has been. This has the advantage that the occurrence of spark interference is extremely reduced.

The yoke part 10 on the input chamber 9 and the yoke 14 on the second chamber 13 must have voltages of 1 kV and 4.65 kV or respectively can withstand more, as can be seen from the explanations above.

Although a multi-chamber klystron causes few problems in terms of safety at high voltages, since it generally does is used enclosed in a magnetic focusing device, it is desirable to use the first and second To connect the chamber to a structure whose potential is close to the earth potential, as shown in FIG.

Placed over the first and the second interaction gap Tensions on, then structures are very easy to implement, which isolate with respect to direct current but short with respect to microwaves because of the microwave power level of the associated chambers is low.

In the Pig. 1 are the drift tubes formed in the clamping parts; however, this is not absolutely necessary. You can use other trainings instead, in which the clamping parts are built into the upper and lower areas of the walls of the chambers.

From the point of view of safety, it is desirable to make the entrance chamber and the broadband reactance circuit uniform so that they are on the same potential.

Applying the voltages in Pig. 1 can also be modified.

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As the current at the accelerating electrode and the drift tube currents are small compared to the main beam current, the connections to the voltage source can be designed in such a way that that a voltage divider formed by a resistor is applied to a single voltage source, its voltage is equal to Ep + E ^ + E. and that the necessary potentials removed at the tap of this resistance and applied to the drift tubes, etc.

The reduction of the collector potential with the aid of the voltage source Ef serves in the exemplary embodiment to be a feature of the exemplary embodiment to explain. Of course, all other known techniques can also be used to lower the collector potential use without giving up the benefit and effects of this lowering.

The invention can apply not only to klystrons in which the chambers are formed internally, but also to klystrons with external ones arranged chambers are used.

In the embodiment according to FIG. 1, these are acceleration causing voltages applied across the first interaction gap 11 and the second interaction gap 15. in the The following describes an embodiment in which the voltages used for acceleration do not exceed the first or the second interaction gap "are created and in which the perveance to achieve a broadband characteristic is still is chosen, in which, however, the electron beam is accelerated abruptly over the third interaction gap in order to achieve a highly effective agglomeration.

Fig. 2 shows such an embodiment. A relatively high value has been chosen for the perveance. _{Accordingly, a low voltage E 6} is applied to the input drift tube 30, which is formed in one piece with an acceleration electrode, and also via a load wire 40 insulated with the aid of the insulator 39 to the first drift tube 38. The drift tubes 30 and are insulated from the chambers 31 and 43, respectively

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are designed as internal chambers, but on the other hand with the components 34 ″ or 41 for microwaves via clamping parts shorted.

A signal generator 37 reaches the input chamber 31 via an auxiliary chamber 36 and an input loop 35 Signal; a broadband velocity modulation of the electron beam over the first interaction gap 33 is thus obtained with strong radiation exposure.

The second chamber 43 is connected to an adapted load 47 via a loop 45 and a broadband circuit 46 such that that the impedance from the second interaction gap has broadband and low Q characteristics. In this way you see thus a broadband speed modulation of the electron beam also over the second interaction gap and at the same time an acceleration which corresponds to the direct voltage Εγ. The electron beam becomes one in the second drift tube 48 and in the components of the circuit arranged below Electron beam with low perveance, so that a concentration with a high efficiency in energy conversion is achieved.

Since in the embodiment according to Mg. 2 the walls of the chambers are completely at ground potential, there is no need to use the circuit elements provided for changing the frequency 32 and 34, the circuits 36 and 37 at the input and the circuits 46 and 47 representing the load for the second chamber in terms of direct current from the walls of the chambers. Because of this, this construction is safe and simple.

In FIG. 1, the individual values are used for the perveance in the area of the electron gun, for the equivalent perveance of the electron beam in the area of the chambers of the pre-stage, in which the broadband speed modulation with low signal level takes place, and the equivalent perveance of the electron beam im

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Area of the chambers of the output stage, in which the concentration at high signal level and the decoupling with high efficiency the output power takes place, for illustration only; they only represent exemplary information.

Claim;

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Claims (1)

Claim Broadband multi-chamber klystron, characterized in that in a preliminary stage formed by one or more chambers (9 »13), which is used to excite a wide frequency band, at least one chamber (9) with an outer reactance circuit (7) is coupled and at least at the last drift tube interaction gap (15) of the chambers (9,13) of the preliminary stage a voltage (E,) for accelerating the electron beam (26) and an end stage of chambers (17, 20) in which the electron beam (26) is concentrated, one or more Chambers (17) »the frequency one to several percent higher than the mean frequency of the frequency band are tuned, as well as an output chamber (20), which is set essentially to the middle frequency of the frequency band is, has. 4U98A9 / U928