DE955610C - Traveling field pipes for spatially harmonious operation - Google Patents

Description

ISSUED JANUARY 3, 1957

W 12596 VIIIa / 21 a *

has been named as the inventor

The invention relates to microwave transmission devices, especially on so-called traveling wave tubes.

The main object of the invention is to provide a wave propagating gravel for at extreme To create traveling wave tubes operating at short wavelengths, which are relatively easy to manufacture and is particularly suitable for the use of circular electron beams.

Another task is that of traveling wave tubes operating at ultra-high frequencies broadband amplification without loss of load capacity and simplicity of construction to reach.

The amplification usually takes place in traveling wave tubes with helical delay lines of electromagnetic waves held by an electron beam from a wire helix is surrounded, which forwards the waves at an axial speed which is essentially the same as the speed of the electron beam, so that the wave is kinetic to the electrons Drains energy. Such a tube is designed to operate at frequencies below e.g. ioooo MHz excellent suitable because it combines a very large bandwidth with good gain and at the same time is easy to manufacture. However, if the operating frequency is increased, the radiation will of the wave propagating circle very large, if not the size of this element mechanically proportionally reduced. At one frequency of 50000MHz e.g. the wire has one

conventional wire helix a diameter approximately that of a fine pencil line, and it is difficult, if not impossible, to see the individual turns of wire with the naked eye to distinguish. As a result, such a helix is not only very difficult to manufacture, but also very difficult to manufacture their resilience is also very limited. A solution to many of the at these high frequencies Problems that arise are discussed in an essay, “A Spatial Harmony Traveling Wave Amplifier for Six Millimeters Wavelength "by S. Millman, in the" Proceedings of the Institute of Radio Engineers', Vol. 39, p. 1040, (September 1951), is given. For one more complete explanation of the principle of working with spatial harmonics than that the reader is referred to this article. However, since this principle applies to the present Invention is used, a brief explanation is given here.

If an electron beam is alternately shielded and exposed to a component of the electric field strength of an advancing electromagnetic wave traveling in the same direction, the wave can extract energy from the beam even if the wave travels at a higher speed, provided that the alternating shielding is arranged in suitable spaces. This is done by letting the electrons pass in the vicinity of a number of discontinuities which are at regular intervals in the beam direction and which are selected so that in their areas a component of the electric wave field parallel to the direction of the electron beam is present and that no such component is present exists in the area between the discontinuities. By adjusting the speed of the electron beam, a given electron can be made to reach each successive discontinuity region at a time when the electric field strength is the same as in the previous discontinuity region when that electron was there. The electrons can thus be synchronized in phase with a wave that progresses along these discontinuities with a component of the phase velocity parallel to the electron beam direction, which is equal to the electron velocity increased by such a high velocity that the electric wave field increases by any multiple of + 360 ⁰ rotates between successive discontinuities.

Tubes, which until today have been built according to the spatial harmonic principle, represent a remarkable one Improvement over the usual helical tubes for millimeter wavelengths, there they are more robust and provide a better product of gain and bandwidth. However is no such tube to manufacture as easily as would be desired; a task of the present The invention is therefore to eliminate this disadvantage.

According to one feature of the invention, a wire helix is in connection with a conductively limited Waveguide intended as a wave transmission circuit to be used using the spatial harmonic principle. Such an arrangement has many advantages usual helical circle and offers some additional advantages. The invention is accordingly based on a traveling wave tube for spatially harmonious operation using a waveguide for the Wave transmission which contains a delay line arranged parallel to its longitudinal axis and in which the delay line assumes an asymmetrical position from; their peculiarity consists in that the delay line consists of a tubular conductor of circular Cross section consists of a multitude of periodic in the direction of propagation of the electromagnetic Wave successive and arranged essentially transversely to the direction of propagation Has openings, which as an annular or annular arc-shaped slots or as the Axis of the conductor helically surrounding recesses are formed.

A clearer understanding of this embodiment and other specific embodiments shown herein can be obtained, along with a better one In order to appreciate the general nature and objects of the invention, best by reviewing the Drawings and the following detailed explanation.

General explanation of the drawings:

Fig. Ι shows the perspective view of an embodiment of a wave-propagating circle for spatially harmonious operation, in which the spatial harmonic discontinuities through a Large number of transverse slot-like openings are formed in a thin-walled tube, the axis of which with the direction of wave propagation collapses within a rectangular waveguide;

Fig. 2 shows a cross section through the middle part of a second embodiment of a wave transmission circuit, in which a rectangular waveguide surrounds a helix of wire which is in line with the waveguide and from a its walls are separated by a sheet of dielectric no material;

Fig. 3 shows a longitudinal section of a reverse wave oscillator in which the wave transmission circuit is a rectangular waveguide which contains a wire helix inside, which runs along the Center line of the upper wall of the waveguide rests.

The drawings will now be discussed in detail.

Fig. Ι shows an example of the explanation of a wave transmission circuit 10 for spatial harmonic operation, which consists of a rectangular waveguide 11 in which a hollow cylindrical Rail or tube 12 is arranged asymmetrically. There is one in the wall of this rail A large number of slot-like openings 13

sections that are arranged at regular intervals in the direction of wave propagation and together with the part of the pipe section lying between them a number of slot resonators form. These slot-like openings serve to keep the electrons coming through the hollow interior the rail 12, repeated the electric field of a progressing through the circle 10 to expose electromagnetic wave so that an amplification of the wave takes place in the manner described above. This is because of this causes the electric field within the circle to be so distorted that one in the transverse basic electrical shape advancing wave in the areas of the slot-like openings has a component of the electric field lying parallel to the electron beam.

The internal dimensions of the waveguide 11 are preferably chosen so that a trans-

ao versale electric wave (TE wave) propagates through it in its basic form, whereby the electric Field is perpendicular to the broad walls of the waveguide. The stretched middle part of this Waveguide surrounds the rail or tube 12, which is wider along the center line of the lower one Wall can be welded. The wall thickness of the rail is not critical, but it should be repeated several times as thick as the penetration depth of the electromagnetic waves at the working frequency, but still be thin compared to the diameter of the splint. The length of the slot incisions the circumference of this wall should be roughly equal to half a wavelength in free space at the top Be the cutoff frequency of the wave transmission circuit.

Because of the mechanical strength of the rail with the openings shown in FIG. 1, the The circumference of the splint should be slightly larger than its length from incision to incision. ' By request the rail 12 can be replaced by an equivalent wire helix be replaced with a suitable pitch and suitable diameter. At both ends of the Rail 12 is bent upward in Fig. 1 of the waveguide to provide an impedance match between the center piece of the wave transmission circuit and the input and output ports create the z. B. waveguides with the same cross section as the waveguide 11 and directly be connected to the ends 14 and 15 can, openings in the curved parts of the lower wall of the waveguide 11 create space for inserting the rail 12 into the waveguide when assembling the circuit. You allow also the conduction of the electron beam through the hollow interior of this rail, if the Circle is in operation. The electron gun 17 and the collecting electrode 18 are aligned (with respect to circle 10) in such a way that the electron-

beam axially through the rail 12. Identically constructed Coverings 19 surround these electrodes -65 and together with the (not shown) windows in the two ends of the waveguide 11 and with its metallic walls an airtight housing that surrounds the electron beam. A magnetic field generated by means not shown, the magnets shown in FIG same can be generated, runs parallel to the axis of the electron beam to the electrons to a small area around the beam axis. The conducting elements of the wave transmission circuit 10 should be non-magnetic so as not to distort the magnetic field, and they should preferably have the same coefficient of expansion in order to avoid the effects of heating to prevent. So

The wave energy is preferably applied to the circle by any suitable means so as to that the electric field of the wave perpendicular to the upper wide wall of the conductor 11 through the Circle advances. When this wave (in Fig. 1) progresses from the input 14 of the circuit to the output 15, it becomes through spatial 'harmonious interaction with that through the center of the Rail 12 guided electron beam amplified. This spatial harmonic process was go above briefly, however, a better understanding will be obtained by considering the brief ones below achieved mathematical investigation carried out specifically for the arrangement shown in FIG is, however, applicable to spatial harmonic operation in general.

If ζ is the direction of the wave velocity in the waveguide, the 0 component of a progressing wave can be written in the vicinity of the recurring discontinuities in the conductor:

j did

E _z = F {z) e>
where ω is the angular frequency and

η == το / \

F (z) = 2 ^A n exp I— j (2πη + θ) ~) (2)

η— —οο \ <* /

is. Here, d is the distance between successive discontinuities, which are the slots 13 in the rail 12 here, η is an integer and Θ is the phase shift in angular measure from one discontinuity to the next and given by

2nd

(3)

where X _{g is} the guide wavelength of the fundamental wave corresponding to n = 0 in equation (2). With the assumption that the amplitude of E _z at the edges of the discontinuities or slots is constant and is denoted by B ₀ , ^ "can be written:

/ (2 π η +

■ H- 2 πη

sin I (2 π η +

w \

Yd)

(4)

where w is the width of a slot in the rail 12. Insertion into equation (1) gives:

»= 00 2 π sin ((2

E = E

² °

From the latter equation it can be seen that close to the slot continuities in the waveguide an unlimited number of spatial harmonic components of the fundamental wave exist appears to be, each of which progresses at a different phase rate, the

is given by - -, where η is a whole

\ 2 TCVI -} ~ CJ

Number is between - · 00 and + 00. If one sets η = O, one sees that the fundamental wave in the positive 2-direction with a phase velocity

age

cod

progresses. For η = 1 one appears

so wave in the positive ^ direction at one speed from

to hike the lower

is than the speed of the fundamental wave. The same is true for other positive values of n. For

a ₅ % = —ι seems one in the positive, s-direction

with a phase velocity - ~ r away-

passing wave, the velocity being negative, since the fundamental phase shift Θ between successive slots is less than 2 π. Thus, every negative integer η corresponds to a wave with a negative phase velocity or, in other words, a wave running backwards. As is well known, the group velocity of all spatial harmonic waves is always in the direction of power propagation and is the same for all waves, including waves with negative phase velocity.

By considering Fig. 1, it will be apparent that somewhere between the state in which the slit pitch d is zero, in which case there is essentially no interaction between the electromagnetic wave and the electron beam, and the state in which the width w in the slot opening is zero, in which case the interaction is also zero, there must be a ratio of slot width to slot spacing which gives an optimal interaction if pure gain is to be present. Now it can easily be shown that the electron speed V _e required for synchronism is given by

(2 π η

where α) is the angular frequency, d is the distance from slot center to slot center and Θ is the fundamental phase shift between the slots, usually ■ - to -. It can also be shown that the gain with the electrons in exp I j I ω t - (2πη +

(5)

Interaction occurring electromagnetic wave proportionally

Ampl. = K

. _% ((2 πη + Θ) w)

(2 π η + 2, i.e.

(7)

where K is a constant of proportionality and w is the width of a slot opening. By differentiating the last equation by - ^ - and equating the result with zero, one sees that the gain is a maximum when

2.33

(2 π η

(8th)

is; as mentioned above, can have practical values

from 0 to approximately between - «9 <-. Thus can

3.2 °

w can be easily determined from equations (6) and (8) for a given electron velocity V _e , a given value of η, and a given operating frequency.

The optimal slot spacing and slot width of an arrangement intended for a particular form of spatial harmonic operation are given by equations (6) and (8), but of course the same arrangement can be used for operation with other shapes , albeit with a somewhat reduced degree of efficiency. The number of slots used depends on the gain desired, but a hundred slots are usually sufficient. The following dimensions serve to indicate the proportions of the various elements of the arrangement shown in FIG. 1. Although these demarcations have been found to be satisfactory on a circle which was essentially the same as that shown in Fig. 1, and which was built and tested, they are not limited to them, they are only used to explain the possible values. These dimensions are chosen for optimal interaction between the first spatial harmonic of a wave with an electron beam having a speed corresponding to 1300 volts. The inner width and the inner height of the waveguide 11 are 0.83 X ₀ and 0.41 X ₀ , the length of the slot 13 is 0.46 X ₀ , the width w is 0.027 K ^ ^he distance d is 0.086 X ₀ , where X _{0 is} the wavelength in free space at the frequency of operation.

Fig. 2 shows the cross section of a center piece of a wave transmission circuit 30, which in operation the one drawn in Fig. 1 is the same. The circle

consists of a rectangular waveguide 31, which can be constructed in the same way as the waveguide 11 in FIG. 1, but does not have to, and which surrounds the wire helix 32. This helix, which is separated from a broad wall of the waveguide 31, which corresponds to the lower wall of the conductor 11, by a dielectric disk 33, can be regarded as equivalent to the rail 12 in FIG. The pitch between the turns of the helix 32 corresponds to the distance d, the width of the openings between the turns corresponds to the width w of the openings in the rail 12. The presence of the dielectric material 33, the z. B. mica, allows the diameter of the coil 32 to be about twice as large as the diameter of the rail 12 can be made at a given operating frequency. The thickness t of this dielectric, which is preferably uniform over the length of the waveguide, so that the helix 32 can be aligned parallel to its axis, can be selected within a range with wide limits, but a value of approximately one tenth of the diameter of the Wendel 32 proved to be satisfactory.

A decrease in thickness t results in a decrease in the operating frequency for a given helix and waveguide. The wire windings which form the helix 32, together with their interspaces, result in a series of slot resonators which are essentially the same as the resonators in FIG. It is therefore evident that the helix 32 can be replaced by a plurality of wire loops which lie transversely to the direction of wave propagation and have a regular spacing d in this direction.

In operation, an electron beam can be passed through the center of the coil 32, and one transverse electrical wave can be applied to circuit 30 by any suitable means, e.g. B. through the curved end of the waveguide 11 in Fig.-i .. At the output end 15 of the circle can then Wave energy removed by a suitable means: be.

The wire helix shown in Fig. 2 as well as the arrangement with parallel loops is particularly suitable for operation with spatial backward harmonics, since the ratio of the distance w between the wire to the wire pitch d can easily be carried out in such a way that it corresponds to equations (6) and ( 8) for negative integers

enough. A ratio of - = - has turned out to be

such an arrangement for synchronizing the electron beam with the first reverse wave proved suitable. A smaller ratio

about - ^ - = -, should be Λ · 3 on the first forward wave

be used.

Of course, none of the waveguide circuits described above have any effect on the amplification spatial harmonic waves are limited, as each of these arrangements produce Wave energy can be used either in the usual way or by reverse wave operation, if it has the required dimensions. The usual vibrations can occur with any amplifier can simply be obtained by the fact that 'a sufficiently large part of the output energy to the Input of the amplifier is fed back. How such an arrangement works is so well known that further explanation is superfluous. The generation of backward wave vibrations on the other hand is a recent development in technology, so considering the importance of the present Invention in this regard, a brief description of a reverse wave oscillator is appropriate.

In Fig. 3 the side section of a backward wave oscillator is shown, in which the circle 40 forms the wave-propagating element. This circle is related to the electron gun 41 and the collection cavity 42 aligned so that the electron beam 43 through the Center of helix 44 goes which runs along the center of the top broad wall of the rectangular waveguide 45 can be welded on. At the collecting electrode end of the circle is within of the waveguide 45 surrounding the helix 44 resistive material 46 in order to reduce the reflection of To bring wave energy to a minimum at this point. Any wave energy coming from the output port 52 (at the electron beam system end) of the circle thrown back due to impedance mismatch is thereby substantially reduced, and their undesirable interference with energy advancing in the opposite direction is for the most part eliminated. At the exit From 52 of the circle, vibrational energy is extracted through a continuation of waveguide 45; this is curved downwards to match the impedance. In the curved part of the upper The wall of this waveguide is a suitable opening for the passage of the electron beam 43 -intended. The waveguide 45 is fused into the piston 47. This piston forms together with the window 48 in the waveguide and the magnetic poles 50 and 51 an airtight housing, that surrounds the electron beam. The opening 42 in the pole piece 51 is shaped approximately as it is drawn is to reduce the secondary emission from this part. The pole piece also serves as a collecting electrode. All elements in the area between the pole pieces should be non-magnetic so that the magnetic field moves the electron beam along an axis with which the field is in lies in a line, can focus.

When the current density of the electron beam 43 in the arrangement of FIG. 3 a certain exceeding the critical value can suddenly occur at a frequency determined by the speed of the jet is intended to use vibrations. Wave energy at the collecting electrode end of the circle 40 arises, flows to the output end of the circuit where it passes through window 48 to a suitable output port is fed. When this energy

passes along the helix within the waveguide 45, it is due to interaction between the backward wandering spatial harmonics that synchronize with the electron beam is, and amplified the electron beam. This interaction also causes a Focusing the electron beam. This bundling in turn causes an increase in the wave energy, which in turn results in a bundling of the electron beam, etc. Thus, the the necessary feedback energy to maintain the vibrations returned the electron beam to the circle. Since, for a given waveguide arrangement, the frequency of the oscillations is mainly determined by the electron speed and since this speed can be easily changed electrically over a wide range the frequency can be modulated to a large extent and with a very wide bandwidth.

The invention described here is not limited to the embodiments shown and described, since it can also include waveguides with other than rectangular cross-sections. aside from that may use the input and output connections described above in connection with the drawings be replaced by equivalent means without changing the nature of the invention. Finally, it will be clear to those skilled in the art that the dimensions selected in a large area of the waveguide circles shown in the drawings without deviating from the essence and aim of the invention.

Claims (6)

Patent claims: i. Traveling wave tube for spatially harmonious operation using a waveguide for wave transmission, which has a delay line arranged parallel to its longitudinal axis - Contains and in which the delay line has an asymmetrical position occupies, characterized in that the delay line consists of a tubular conductor of circular cross-section consisting of a multitude of periodic in the direction of propagation the electromagnetic wave successive and substantially transverse to the direction of propagation arranged openings has, which as an annular or annular arc-shaped slots or as the axis of the Conductors are formed helically surrounding recesses. 2. Traveling wave tube according to claim 1, characterized in that the tubular Head is connected in the longitudinal direction to a wall of the waveguide. 3. Traveling wave tube according to claim 1, characterized in that the tubular Conductor separated from a wall of the waveguide by a disk of dielectric material is, 4. Traveling wave tube according to claim 3, characterized in that the thickness of the disc of dielectric material about one tenth the diameter of the tubular conductor is equivalent to. 5. Traveling wave tube according to one of the preceding claims, characterized in that that the tubular conductor consists of a tube which has a plurality of transverse to Has wave propagation direction lying slot-like openings. 6. Traveling wave tube according to one of the preceding claims, characterized in that that the end portions of the waveguide are bent out of the straight direction of the electron beam path are. 80 Publications Considered: Bell Lab. Record, Jan. 1951, p. 14 ff; Nov. 1952, p. 413 ff; Proc. of the I. R. E., Sept. 1951, pp. 1035 ff. For this purpose i sheet of drawings © 609 546/305 6.56 (609 726 12. 56)