US2610309A - Magnetron tube for the transmission of ultrashort waves - Google Patents

Description

H. GUTTON 2,610,309

MAGNETRON TUBE FOR THE TRANSMISSION OF ULTRASHORT WAVES Sept. 9, 1952 2 SHEETSSHEET 1 Filed April 14, 1948 5 m aw MWM 1U.

AGENTS H GUTTON Sept. 9, 1952 MAGNETRON TUBE FOR THE TRANSMISSION OF ULTRASHORT WAVES 2 SHEETS-SHEET 2 Filed April 14, 1 48 Hav/ @UTTON' AGEN Patented Sept. 9, 1952 .MAGNETRON TUBE FOR THE TRANSMIS- SION'OF ULTRASHORT WAVES Henri Gutton, Paris, France, assignor to Compagnie Generale. de Telegraphic Sans Fil, a corporation of. France Application April 14, 1948, Serial No. 21,067 In France April 18, 1947 Claims. (01. 315-40) This invention relates to tubes serving for the generation or the amplification of electric oscillations of a ultrahigh frequency, in which it is desired, for the purpose of increasing the output, to favor'an. electromagnetic oscillation of aparticular order in comparison with the others, or even to completely eliminate the latter.

The invention relates more particularly to tubes oi'the type called magnetrons having a cylindrical anode slit parallel to. the longitudinal axis or generatrices of thecylind'er,and dividedinto a certain number of segments disposed about the cathode.

Heretofore, for the. purpose of obtaining the desired effect, segments, havebeenarranged twobyktwo in. short-circuited relation by means of conductor tabs, but these means. introduce considerable losses. due tohigh frequency circulation currents in the said connections; moreover, they complicate manufacture and production due to the fact that they have to be clamped or welded, which is difiicult to carry out under the conditions of the smallness of the elements concerned.

,The subject of the present invention consists in a process of manufacture and inthe construction of such tubes enabling elimination in an associated circuit of all the oscillation, except practically one, without resorting to the hereinbeiore mentioned short-circuiting arrangements, and thereby avoiding the losses and the complication in manufacture in connection with their employment'. The invention insures this resultby giving the-anodicsegments oi 'magnetrons a section approaching the form of equipotentiallines ofthe'electromagnetic oscillation of a particular order which is-th'e' only one to be selectively maintained in practice. In order: to obtain such an equipotential surface, the anodicsegment is constructed in a very characteristic rounddiorm which clearly distinguishes it from the sharpedge segments of' the anode of classical magnetrons, having edges formed by the notches al'ong the generatrices of the cylinder provided in, the. body-of the anode.

The invention is also directed. to a process which, for a certain number ofgiven parameters, such as the order of the oscillation to be flavored, the number of segments, the diameter of the cathode and that of the anode, enables, the tracingof" the desired equipotential' lines, andtheree by, the determination of the patterns for the cutting ,of the anodic segments. The latter will have a section resembling the form of a hairpin whose apex is directed toward the cathode, and whose branches diverge along the path of the rays is-' suing from the axis of the cathode.

My invention will be more fully understood from the following specification by reference to the accompanying drawings, which illustrate, byway of non-limiting examples, preferred forms of my invention and wherein:

Figure 1 is a diagram showing the manner of laying out the desired equipotential surfaces; Fig. 2 represents a fragmentary view of a magnetron whose segments have been prepared according to my invention,.and in which for the sake of simplicity'the anodic crown and the cathode which normally have a circular form have-been shown" in a straight" line; Figs. '3 and 4 show modified forms of elements of a magnetron constructed in accordance with my invention and in which there is shown the connection between the sectioned notches of resonant cavities of various forms ;'=Fig. 5 represents the application of the invention to magnetrons with overlapping anodic segments; Figure 511 represents a partial section of this magnetron along the line 511-511 in Figure 5; and, Fig. 6" represents theap'plication of the invention to magnetrons.

There will first be considered a classical magnetron operating at an ultrahigh frequency and having a cylindrical anode slit parallelly with the generatrices of the cylinder. Assume that the number of the said slots is n.

The energy producedbythe'work of the electrons radiates, through the intermediary of the said slots, to the interior of a connected cavity. The presence of slots produces, in the interval separating the cathode from the anode, a stationary electromagnetic field, which can be divided into two fields of waves, the one travelling in the one direction and the other in the other direction. The electric field inthis space has two components, the one radial and the other tangential. The radial component is maximum when the tangential component. is zero, and conversely.

The continuouszcurrent of the'anode, and the presence of .a magneticv field, createa movement of rotation ofv the electrons, whose. velocity depends onthe potential of the. anode, and. the

size of the magnetic'field. When the velocity til the moment at which the energy produced.

3 equals the sum of the energies radiated by the oscillator and lost by the Joule effect in the walls of the circuits.

In general, circuits which are all disposed in series on the path of the electromagnetic wave constitute an indefinite chain capable of transmitting an indefinite number of electromagnetic waves circulating at speeds of rotation, as follows:

r i 2.1 W 311T lnT nT in which T is the period of oscillation.

These different modes of propagation of the electromagnetic Wave furnish between the lips of a same slot differences in phase equal to It is of the greatest interest to retain only one of these modes of propagation of the electromagnetic field in such away that all the actions of the field are in phase with the movements of the electrons. There'is usually retained only the mode for which the electromagnetic output of the tube is the best. For the purpose of avoiding the othermodes of propagation there is a known method for arranging the electrodes into short-circuit two-by-two by means of strap connections.

It willnow be demonstrated that it is possible, by giving, according to the invention, the anodic segments a suitable form, to retain only the mode of oscillation of the order pi, without resorting to the short-circuit connections, thereby avoiding high frequency losses, and complications in manufacture.

Consider in effect the equation of the electromagnetic field in cylindrical coordinates T,a,Z (Fig. '1') and assume, as is usually the case, that the electric and magnetic vectors are independent of the coordinate along the axis of the cylinder. Assume, further, the period wave of pulsation'kc. The cathode may be assumed to be a perfect conductor and, under this assumption, the electric fieldhas no tangential components on the surface of radius 1'0 of the cathode.

The general solution for electric and magnetic vectors is of the following form:

to etc;

in which Er is the radial component of the electric vector; EC. is the tangential of the electric vector; Hz is the axial component of the magnetic field, the other components being zero.

K is a constant of integration; Z'pUcr) is a derivative of this function in relation to Icr; Ap is a coefiicient of amplitude; p represents the order of the mode propagation, which varies from for the pi to :0 for the mode corresponding to a cylindrical magnetron without slots. The sequence of the numbers p is Each solution of the order P must satisfy the condition E=0 on the cathode, from which it results that ,Zp(lcro)=0 for all the values of p, This condition determines the value of K.

The amplitudes Ap of each of the waves can be selected in such a Way that one of the equin 5 corresponding to the mode pi, and the other waves will'not be able to propagate themselves. Thus, by calculating the equipotential lines of the field corresponding to the order pi, and employing one of these equipotential lines as the surface of the anode, there is only retained the'mode pi, to the exclusion of all the other modes. It is this which constitutes the principle of my invention.

is usually a number sufliciently smaller than 1 that there is onlyretained the first term of the development in series of the function ZpUcr). The components of the electromagnetic field of order then became as follows: TE,={ L) (2) cos m mo:

.' To T V L E C .rE Km) SlIl p s These ,equations show'that, if [or always remains sufficiently'smaller than 1, that is, if the perimeter of the anodic circumference is small enough for the wave length, then the form and amplitude of the electromagnetic field are independent of the frequency.

The equipotential lines of, the electric field are represented by the equation:

I (a -e r 1' cos p and their forms areindependent of the frequency. Fig. 1 represents the application of this .equa--.

tion to the tracing of the equipotential in the case of a, magnetron with ten slots (11:10 and p=g=5 The cathode is designated by C; the reference E1 designatesa point on the equipotential, line defined by the coordinates a and r;. for the angle .1; equals zero cos 'pa becomes equal to 1; and 1' denotes the inside diameter R of theanode. This enables determination of the constant A. When the electric field E.

' anodeis; sufiiciently. great compared Withh diameter of: the; cathode.v then the term...

becomes ne l i e T uipc tia lines h come I c smand are practically independent of the diameter of the cathode. I

, Theforegoing equation enablesthe tracing of the. equipotential lines. E1, E2, etc., for any mag.- netronwith slots whose parameters are given, andior any single mode of propagation which it. is desired to, maintain, With the help of these linesas patterns it is. easily possible to trace and cutout the segments in the crown. of the anodic crown, While in'the classical magnetrons the faces of the segments. turned toward the cathode present a form of circonvolution bounded by sharp edges, the. magnetron according. to this invention presents. rounded edges and the section. oi segments-resembling the form of a hairpin whose rounded summit is turned toward the cathode and whose branches are directed toward the exterior along the asymptotes Y-Y of the equipotential lines as shown in Fig. l. ;Moreover, the magnetron according to my invention is characterized by the absence of shortcircuiting connections between the anodic-segments. If it-is desired forthe purpose of; eliminating all the waves-except one, particularly the wave pi, to give the anode. a section identical to the equipotential line, there arethereby already obtainedsatisfactcry results, enabling the shortcircuiting tabs to be dispensedwith, and giving, the said section a rounded form similar to that of the equipotential lines; Magnetrons-constructed in this way retain a highoutput, and do not require the employment of short-circuiting; .con-

nections,

.In the case of the above calculation the radial wave which" penetrates through the slot was assumed to be stationary. Itmaybe regarded'as the sum of two traveling waves. If the slot is terminated at ad by a purely reactive impedance Z, Fig. 2, it is possible wave in 'thezone which separates aa' fromthe cathode, and, for this purpose, it is sufficient for the impedance to have such a value that the current and the voltage between cm are identical with those prevailingin the electromagnetic field in this place. This impedance may be zero, in which case act is a short-circuit; in this case ca must be disposed at such a distance M that is zero, that is, if the following condition, between the above determined Bessel functions, is realized.

When kro is small J 'pUcT'o) is practically zero, in which case M'is calculated by the equation:

This relation determines the depth M of the radial slits which terminate where the field becomes zero.

For the purpose of simplifying the anode it is desirable to terminate the form of the slot at aa with a purely reactive self-impedance by cutting in the body of the anode a cylindrical cavity to avoid disturbing the 6. such as..is.,-representedin Fig, 3, in; which; in: dicates. the. magn tic coils. an V e ontain n vesseL;

Starting: at, aa, it would, be possible to connect attheend ofthe slot-any other form of cavity serving to give, a suitableself-impedance at an, Fig. 4. v

The invention is also applicable to magnetrons with resonant segments, in which there-are-employedtwo groups ofoverlapping. segments; the. one inside the other, and all of them rediating intopa single cavity surrounding the assembly. Such tubes have been particularly described in French Patent No. 835,305, filed March 16, 1938, and French Patent No. 839,690, filed December l937, to the present applicant. In the case of these magnetrons the slot terminates in the form of an opening at ac and radiates toward the exterior. The impedance occurring between cm is complex, and has a real part. The wave which. circulates in the slot is not stationary- The incidentxwave transports a greater energy than the reflected wave. The movement of the wave, can be. represented by a system consisting of; a stationary wave plus a fraction of a traveling wave circulating from theinterior toward the exterior; This fractionoi a progressive wave represents the useful energy.- This energy is furnished by the work of the electronic charges in the interval between the cathode and the anode. Fig. 5 shows such a magnetron, which isparticularly described in my patent application Serial No. 759,663, filed July 8, 1947. The segmentsPi belonging, to the one group overlap in the segments-P2 .of the .op

. posite. group presenting an imbricatedappear ance, and they surround'the cathode. C. Experh. ence shows that it is desirable to give. the; seg: meritsv a bevel in the direction of the cathode. The section of these segments is represented in- Fig. 5a.vv giving a partial view in section along 5a=-5.-a. It has been carried-out according to this invention, but instead of being solidthesesegmentsmay alsobehollow, and at; the same. time. be. given the rounded form. The inventionis of the greatest importance-in. this case, because with this type ofmagnetron. the expedient of shortc1rcuiting by means of tabs is entirelydispensed with, and-the modification of the section of the segments is all that is necessary. to r'eachxa high output: through the elimination of all the.oscil.. lations except one.

Fig. 6. represents another type. of, magnetron, the so-called fiat type, in which the cathode C is flattened instead of rounded, and is surrounded by the anodic segments P-P disposed along a contour which is also flattened. The latter are given a section according to my invention. The results obtained are highly important in that the ordinary method of short-circuiting by means of tabs becomes superfluous when the dimensions of the anodic plane are of the same order of magnitude of or greater than the wave length. The anodic slots may terminate either in a series of cavities connected as with the cylindrical magnetron, or, in the case of the magnetron with resonant segments, in the interior of a single cavity into which all of the slots radiate.

I desire that it be understood that the invention is not limited to the types of magnetrons herein described but that it is applicable to any magnetron or any tube, regardless of its function, in which it is desired to eliminate all the modes of propagation of the electromagnetic wave except one, in such a way that all the actions of the field are in phase with the movements of the electrons. The invention covers any tube serving for the transmission of short waves, and, more particularly, ultrashort waves, in which this result is obtained by giving a suitable form to particularelements, particularly the anodic segments in the case of the magnetron, which form is similar to or identical with the trace of the equipotential lines at the place of the said elements, in which the said lines correspond to the single wave which it is desired to maintain.

ing a magnetic field parallel to the axis of the cathode.

2. Magnetron comprising in the interior of an air-tight envelope, a single cathode, an anode surrounding said cathode and comprising a plurality of segments extending towards the cathode, having a section determined substantially by the equationin polar coordinates r and a! 7 I T A (n, (r cos p in which T0 and A are parameters, and p the mode of. .propagation of the .Wave produced by said magnetron, and means adjacent said magnetron for producing a magnetic field parallel to the axis of the cathode.

. 3. Magnetron of the type having cavity resonators .comprising, in the interior of a gas-tight envelope, a cathode, a single cylindrical anode coaxial with and surrounding saidcathode, a plurality of slits formed in the said anode, terminating on the one hand in said cavity resonators'and opening on .the other hand on to the cathode-anode space, said slits defining anodic segments whose section in a plane perpendicular to the cathode axis is substantially in the form of a hairpin whose apex is directed toward the cathode, and means adjacent said magnetron for producing a magnetic field parallel to the axis of the cathode.

.4. Magnetron of the type having interleaved segments comprisingjin the interiorofa' gastight envelope, a s'ingle'cyli'ndric'al cathode, two plane parallel supports perpendicular to the axis of said cathode, each support carrying a certain number of anodic elements extending parallel with the cathode and symmetrically arranged around it, the segments of the two supports being interlaced among themselves and having a'se'ction in a plane perpendicular to the cathode axis in the form of a hairpin whose apex is directed toward the cathode, and means adjacent said magnetron for producing a magnetic field parallel to the axis of the cathode.

5. Method of making a magnetron tube with split. anodes, said magnetron comprising a plurality of anodic segments arranged symmetrically around a single cylindrical cathode of radius re, the said magnetron being designed to oscillate in accordance with the mode 12, said method comprising placing a smooth curve of the section of said segment around a point in the axis 01 said anode taken as a pole, in accordance with the equation in polar coordinates 1' and a, 1- being the distance of a point of the curve to said pole and ,a the polar angle of said point with respect to the axis of symmetry of said sections:

Y-( A r r sin p in which A is a parameter, embodying the anodic sections substantially in accordance with said smooth curve, and arranging the cathode within the anode thus formed in section so as to make.

its axis coincide with that of the anode.

HENRI GUITON.

REFERENCES CITED The following references are of record inthe file of this patent:

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