DE1041169B - Low-noise traveling wave tubes for amplifying weak high-frequency signals - Google Patents

Description

GERMAN

On the properties of electron tubes used to amplify weak high-frequency signals self-noise is of great importance. Time-of-flight tubes, such as traveling wave tubes, generally have a particularly high level of self-noise. For traveling wave tubes the Noise factor under normal conditions a size of about 200. It is therefore necessary to take action to be taken in order to reduce the self-noise as far as possible, if time-of-flight tubes are used as initial stage amplifiers Should apply.

It is already known to improve the noise factor in a traveling wave tube in that the Electron beam before entering the delay line a suitably detuned Cavity resonator passes through. Due to the noise current density modulation of the electron beam Noise voltages caused in the cavity resonator, which in turn re-energize the electron beam modulate the speed so that two coherent noise modulations in the electron beam exist. By appropriately detuning the cavity resonator, it can be achieved that at the tube output the noise voltages originating from the two modulation components wisely compensate each other. The disadvantage of such an arrangement is, among other things, above all in that, because of the selectivity of the cavity resonator, a noise compensation only in a very small way narrow frequency band can be achieved.

It is already a traveling wave tube with a continuous one Delay line has been proposed in which no or only one in a central section decreased interaction between electron beam and high frequency signal wave occurs while there is an interaction along the initial and main sections, the noise fluctuations cause a noise wave on the electron beam, the component of which is becoming larger along the initial section practically synchronous with the corresponding noise fluctuations of the electron beam advances while in the middle section the noise wave is attenuated and with With regard to noise fluctuations in the electron beam, a phase shift is experienced by the greater component of the noise wave at the beginning of the main section, which is generated by noise modulation of the Electron beam is caused to compensate. The proposed traveling wave tube is a complete noise compensation is not possible, since this in the best case only under non-feasible idealized conditions could arise.

The invention relates to a low-noise traveling wave tube for amplifying weak high-frequency

to reinforce weaker ones

High frequency signals

Applicant:

Dr. rer. nat. Dieter Weber,
Darmstadt, Oppenheimer Str. 2

Dr. rer. nat. Dieter Weber, Darmstadt,
has been named as the inventor

signals with several one behind the other in the electron beam direction and delay lines operated at different operating points with regard to the interaction with the electron beam, of which at least the delay line that interacts with the electron beam first the noise reduction is used (preliminary line) and in which the preliminary line with that in the electron beam direction subsequent, the signal amplification serving delay line (main line) high frequency is only electronically coupled via the electron beam. According to the invention is the The front line is dimensioned and operated at such an operating point that one at the input noise current density modulation or noise current density and noise velocity modulation present in the electron beam is changed by the interaction of the electron beam with the preliminary line so that at the entrance the main line both a noise-speed modulation and a coherent noise-current density modulation is present, which are so oriented to each other in terms of amount and phase that this is due to the original noise modulation of the electron beam noise at the exit of the main line is as small as possible.

There are already electron beam amplifier tubes with a pre-circuit to reduce noise known, in which a waveguide coupled with the electron beam (delay line) whose gain is negative in the frequency range of interest. With these known tubes is sought through the action of the waveguide, for example helix Pre-circuit (pre-delay line) to reduce the noise modulation of the electron beam

Ä09 65 & / S3S

to reduce the noise power induced by the electron beam in the amplifier delay line. The \ ^ RECONDITIONS, under which such \ ^r ermin alteration of the noise modulation of the electron beam can be achieved by the Vorverzögerungsleitung are not easy to implement. In contrast, the arrangement according to the invention is characterized by a completely different mode of operation. The prerequisites under which noise compensation occurs in the traveling wave tube according to the invention can be calculated in advance on the basis of the known theories for all cases under consideration and also easily implemented.

The subject matter of the invention is shown in the following with reference to the figures in a schematic manner illustrated embodiments explained in more detail.

In the arrangement according to FIG. 1, the traveling wave tube contains an electron gun 1 for generating an electron beam 2. The noise modulation of the electron beam 2 present at the input 6 of the pre-coil 3 is changed by the interaction with the pre-coil 3 in such a way that at the input 7 of the main coil 4 there is such a noise modulation of the electron beam that the noise power influenced in the main coil 4 - and thus the noise power occurring at the output of the main helix - becomes a minimum. From the theory of traveling wave tubes, e.g. B. from that of Pierce, the modulation state of the electron beam 2 at the input 7, for which this minimum occurs, can be calculated in advance. If present at the input 7-noise current density modulation with i ₀₂ and the existing there to i ₀₂ coherent noise-speed modulation V ₀₂ called, then let two conditions for V ₀₂ and? ' _{Formulate O2} , which must be fulfilled if a compensation of the two noise voltages caused by i ₀₂ and V _{02 is to} occur at the output 8 of the main coil 4:

= k ₂ -

^T2 (k ₂ real)

(1)

45

95 ° O / ₂ <180 °, (2)

preferably HO ⁰ O / ;, <145 ° and k ₂ = 0.4 ... 2. In equations (1) and (2) means

_{Ug 9} = equal velocity of electrons in electron beam 2,

I _e . ₂ ~ direct current beam,

C ₂ = gain parameter of the main helix 4 according to Pierce according to equation (3),

η ₂ - phase angle between the noise speed modulation and the noise current density modulation at the input of the main coil 4.

Entrance 6 of the Vorwendel. In the case of the tube according to the invention, only the ratio of the two noise modulations in electron beam 2 and their phase relationships to one another are decisive and not, as in the known traveling wave tubes with pre-delay line, the absolute size of the noise modulation at input 7 Equations (1) and (2) specified noise modulation state can be implemented in the traveling wave tube according to the invention in various ways. It is Z. B. possible to dimension the electron gun in such a way that the noise current density modulation at the input 6 of the pre-coil 3 is considerably greater than it corresponds approximately to the value k ₂ according to equation (2). In this case, the inequality exists for input 6

* el

HxI ¹ B

C ₁ .

If this condition is met and the main helix 4 is in an operating point that is approximately corresponds to that greatest interaction, then the desired noise modulation state is established at input 7 of the electron beam 2 approximately when the pre-helix 3 is at an operating point which is within the following Limits lies:

0.26
+ 2.2

0.46
+ 4.3

In equation (5), the parameters b _t and C ₁ N _{1 have} the same meaning as in Pierce (P ₁ = speed parameter of the pre-spiral), that is, it is:

v _el -v _{dl = 2VC} . ₍₆₎

dl

IV ₁ =

L ₁ -C

-u _e

k-there • -'e2

4 · V _t9

(3)

60

In the equation (3) means
/ Q ₂ = coupling resistance of main helix 4,
V _e9 = DC beam voltage of the main coil 4.

As can be seen directly from equations (1) and (2) , the absolute size of V ₀₂ and i _{02 is} not specified, so it is not necessary, for example, that the noise modulation at input 7 is less than that at In means the latter equations
L ₁ = length of pre-spiral 3,
/. = Wavelength (in vacuum),
c = speed of light,
V _d j = propagation voltage of the pre-coil 3.

The latter is defined by the speed of an electron passing through this voltage has, just the size of the natural axial phase velocity of the wave along the relevant Has delay line.

Corresponding operating points of the can also be used for other modulation states at input 6 Find Vorwendel, for which approximately that characterized by the equations (1) and (2) Sets the modulation status at input 7.

In Fig. 2, another embodiment of the traveling wave tubes according to the invention is shown. In this case, the signal to be amplified is fed to the input 6 of the delay line 3 and the amplified signal at the output 8 of the delay line 4 is removed. While at the Traveling wave tube according to Fig. 1 Input 6 and output 9 of the pre-spiral 3 closed without reflection are, in the case of the traveling wave tube according to Fig. 2, output 9 is the pre-coil 3 and input 7 is the main coil 4 completed without reflection. This arrangement is characterized in that on this Way in some cases a more favorable reinforcement can be achieved with the same tube length, since the pre-spiral is used for reinforcement. in the

otherwise the noise factor to be achieved in the best case scenario is considerably lower than in these cases in the case of the traveling wave tube according to Fig. 1.

In some cases it has proven advantageous in the arrangement according to the invention to provide a running space between the two delay lines, which is almost or completely free of High frequency fields.

Another embodiment of the subject matter of the invention is shown in FIG. In In this case, the two delay lines are connected to one another in terms of direct current and in terms of high frequency decoupled by a damping 10, which is reflection-free on both sides, in such a way that the field-free running space is damped by the Part of the delay lines is formed. Preferably the delay lines formed by coils 3 and 4 with different slopes. The non-reflective on both sides Damping can be gradually increased in its effective strength in a known manner by one to both sides decreasing damping layer can be realized according to Fig. 3 on the outer surface of the Coil containing tube made of dielectric material is applied. But the topping can also be applied to the inner surface of the pipe.

Claims (11)

Patent claims: 1. Low-noise traveling wave tube for amplifying weak high-frequency signals with several one behind the other in the electron beam direction and with regard to the interaction with the Electron beam delay lines operated at different operating points, one of which at least the delay line that interacts with the electron beam first the noise reduction is used (preliminary line) and in which the preliminary line with that in the electron beam direction Subsequent delay line (main line) used for signal amplification is coupled in terms of high frequency only electronically via the electron beam, characterized in that that the foreline is dimensioned and operated at such an operating point that a noise current density modulation present at the entrance of the preliminary line in the electron beam or noise current density and noise velocity modulation through the interaction of the electron beam with the foreline is changed so that at the entrance of the main line both a noise speed modulation and a noise current density modulation coherent therewith is present, which are so oriented to each other in terms of amount and phase that this is due to the original noise modulation of the electron beam at the exit of the main line is as small as possible. 2. Traveling wave tube according to claim 1, characterized in that only two in the beam direction delay lines arranged one behind the other are provided. 3. Traveling wave tube according to claim 2, characterized in that the at the entrance of the main line existing noise speed and noise current density modulation the condition = A ₂ -C ₂ with A ₂ = 0.4 ... 2 "Ό2, JIe Modulation is phase-shifted by an angle <p ₂ with respect to the noise-speed modulation present there, which is the condition 95 ° <> ₂ <180 °, preferably 110 ° <ζρ ₂ <145 °. 4. traveling wave tube according to claim 2 or 3, characterized in that the main line is on an operating point is operated which at least approximately the maximum interaction with corresponds to the electron beam. 5. traveling wave tube according to claim 2 and 4, characterized in that the at the entrance of the Preliminary existing noise velocity and noise current density modulation the condition y ^ ii «e U ₁ ■ C ₁ with A ₁ = 0.4 .. .2 fulfilled and that, in addition, the preliminary line is dimensioned and operated in such a working point that the parameters b _v C ₁ and N ₁ defining this working point correspond to the relationships 0.1 <CiN ₁ S 0.26 + 1.5 < h <+ 2.2 suffice. 6. traveling wave tube according to claim 2 and 4, characterized in that the at the entrance of the Preliminary existing noise velocity and noise current density modulation the condition * el llh with A ₁ = 0.4 ... 2 fulfilled and that also fulfilled the noise current density present at the input of the main line and that also the preliminary line is dimensioned and operated in such an operating point that the parameters b _v C ₁ and N ₁ defining this operating point correspond to the relationships 0.2 ^ C ₁ N ₁ S 0.46 + 3.0 <Ö! <+ 4.3 suffice. 7. traveling wave tube according to claim 2 or one of the following, characterized in that the to amplifying signal fed to the input of the foreline and the amplified signal at the output the main line is removed and that the free ends of the delay lines are closed without reflection (Fig. 2). 8. traveling wave tube according to claim 2 or one of the following, characterized in that the Delay lines are dimensioned such that the desired operating points of the delay lines occur at practically the same operating voltages. 9. traveling wave tube according to claim 2 or one of the following, characterized in that a space is switched on between the delay lines for the beam electrons, which is at least almost free of high frequency fields. 10. Traveling wave tube according to claim 9, characterized in that the delay lines connected to one another in terms of direct current and in terms of high frequency by one to both sides reflection-free damping are decoupled in such a way that the field-free running space through the damped Part of the delay lines is formed. 11. Traveling wave tube according to claim 10, characterized in that the delay lines of coils with different slopes are formed and that the attenuation is reflection-free on both sides by one on both sides Sides in its effective strength gradually decreasing damping layer is caused on the inner or outer surface of the made of dielectric Helix containing tube material is applied. Considered publications: German patent application Sch 299 VIII a / 21 a ⁴ (published on September 28, 1950). Older patents considered: German Patent No. 966 835. For this purpose I sheet drawings © «0 & 658 '.' 338i 10.58