US2604610A - Magnetron - Google Patents

Description

H. GUTTON July 22, 1952 v MAGNETRON Filed May 1, 194'? N II I N I II I [NYC- IN TOR.

I GUT TON Patented July 22, 1952 vi .pagni'e Generale deTelegraiphie-jsansji l,acorporation of France 1 ApplicationiMa'y 1,1947, staiisogaigaz 1 r In France December ,17, 1940 3'.

section 1, Public Law seolj'augusts, 1946f ,1 Liz? Patentexpires December'jn, '1

6.0laims. (01.315 40 This invention relates to'magnetrons and magnetron circuit arrangements.

In United States Patent No. 2,147,159 is described a magnetron which can'maintain ultrashort waves on a wave length ranging-between a few cms. and about 25 cm.

Figure l representsdiagrammatically the circuit formed by the aforementioned known tube.

Figs. 2 and 3 represent in cut perspective two variants of the tube according to the invention.

The distinguishing feature of the tube described in Patent 2,147,159 is that it sustains oscillations in a circuit entirely built on an anode cylinder. This circuit consists of two parts each containinga certain number of electrodes arranged parallel with the axis ofthe cylinder and all joined together atone end by a ring, whilst the other ends are free. The parts are interleaved in one another as described,

A circuit so constructed may be diagrammatically represented'by a series of lines A1 B1, A2 B2, Fig. 1, all the ends 131 B2 being joined together so that the high frequency potential of these points is zero, whilst A1 A2 are, on the contrary, at 'maximum high frequency potentials. A1 is at a positive potential, whilst A: is at a negative potential. Such a circuit canresonate at a wave length defined by the dimensions A1 B1 and'Az 132.

It is found by experience that for such system to give a good output, it is'necessary that the'potential of all the points B1 and B2 shouldbe zero. It is therefore necessary to connect all the extremities B1 and B2, on onering and to join the ring B1 to the ring Bzthrough the shortest possible connection. The aforementioned patent describes one arrangement" of this nature. The power of the tube is limited by the dissipation of the anode.

This invention seeks to increase the power dissipated whilst still retaining optimum output conditions. c

To this end, in accordance with the invention,

the surface of the anode is increased by altering its diameter only so that a greater power dissipation is obtained without altering the lateral dimension of the cylinder which determines the value of the wave length. In addition to thus increasing the anode diameter, the'invention also envisages the introduction of a large diameter cathode and the replacing of the ringsby'discs as a means for connecting the extremities ofthe anode elements. In order to obtain'maximum output, it is necessary that the magnetic'field should be of a high value associated with the frequency sustaining the oscillations. -With anode cylinders of'large diameter anda cathode of-small diameter, such as have been used generally hitherto, this results irij-a necessity'forthetube to be'operated at very high; voltage, since the magnetic field required is proportional to-the square'root of the applied voltag'eJ' In accordance with this;invention,'this difficulty is overcome by using a cathode of large diameter, for instance, an oxide cathode indirectly heated. The cut-off magnetic field is then related to the anode potential by the ratio:

Where: I

H is the magnetic field, I

the ratio of the charge tothe mass of the elecron, t

Rthe anode radius,- a To the cathode radius. v

The coeificient E M may be made as large as desired, thereby enabling the obtaining of a satisfactory ratio of voltage to magnet field facilitating sustention of oscillations under maximum output conditions. In this way it is possible to cause magnetrons of a cathode diameterfof-IO mm. to oscillate with ultra-short waves oflthe order of 10 cm. The cathode has a diameter at least equal to a quarter of the anode diameter. v

The increase, of thanode diameter leads to another difliculty, which is as follows:

The oscillating circuit is entirely on the anodic cylinder, and it is necessary that the potential at the extremities B1 and B2 ofthe circuit should be the same for all electrodes. In proportion as the anodic diameter increases, the rings connecting the points B1 and B2 assume dimensions which are no longer negligible, with relation to the .wave length. The result is that the extremities B1 and B2 are no longer all at the same high frequency potential, that the circuit no longer functions under the conditions above described with reference to Fig. 1 and that it again becomes necessary to reduce the length of the electrodes for a given frequency. With large anode diameters, oscillations might not be sustained.

I In accordance with this invention, this defect is avoided by using, instead of rings connecting the electrodes together, solid discs. This arrangement of the invention is shown in Fig. 2 which represents mounted on. a base P, a system of electrodes comprising a cathode C of large diameter,

same references.

heated bya filament? and surrounded by an anode A composed of alternately interleaved segments. 'I'heopposite'ehds of the two sets of segments are connected by full discs D1, D2. That is to say all odd segments are connected together and connected to one circuit and all even seg-' ments are connected together and connected to 1 another circuit. The electrode systemris contained in the envelope T and a magnetic field in the direction of the cathode C is produced by the'poles NS. This makes it possible clearly to define the potential of the extremities of the electrodes connected with the discs, and to retain perfect symmetry. It is then possible to connect It ssoinetimes advantageous to obtain the same result luv-mounting the anode electrodes on two discs arranged in a crown or ring D1 D: as shown in Fig. 3. of an outer diameter larger than the anode, and of an inner diameter equal to the anode diameter. Fig.6 represents the same assembly of elements as Fig. 2 using the Two screens E1 and E2 of the same outer diameter as D1 D2 are put at zero high frequency potential, the potential of the cathode; for instance. The space between Di and E1 and D2 and E2 is so small thatthe capacity resulting therefrom is large-enough to prevent any oscillation of the discs D1 D2.

If desired the screens E1 and Ed can be subjected to variable potentials of low frequency in order to modulate the .anode current of the magnetron, and consequently the high frequency:

Furthermore; since the circumference of the anodel is increased, itisnecessary in order to maintain"good-conditions of oscillation to increase 'theinumb'er of electrodes so that the space between twoelectrodes shalhnot be too great,

for-this -spacefi V I tions for 'sustain'ing'oscillation. e e 7 Finally, it is to beobserved that theinvention allows the use of powerful cathode with high saturation eurrentf'a very great advantage as regards the production of high peakpowers in impulse working; 7 r

The advantagesof the invention are clearly shown in: the example given in the table below:

a factor determining condi- V V r t Mag- Mag- Dimensions and operating conditions netron netron 'f r r No.1 No.2

Workingwave length cm 12 l6 Cathode: g

'outerdimm 6 v 6 length mm 28 Anode:

' diameter lmm 18 18 I' number of segments. l6 7 16 ll ,lengthoiisegmcnts-n mm l7 -22 "Iypel..';'. Fig.3 Fig.6 lffitte 120 150 usefuLQ. w 20 25 eak. (1400 .w 800 1, 000 Ma netic field; 60 600 7 Voltage (Qontinueus r 1 509 l, 500

be clearlyunderstood by considering that tubes made as known :prior to this invention and with a thread like cathode,'would'have given useful power of 7 watts only in telegraphic working.

and from 80-100 watts peak. 1 What I claim is:

1. A magnetron comprising means for generatinga magnetic'field, a cathode and an anode,

the." said cathode extending parallel to said field and having a diameter at least equal to a quarter of the .anode diameter, the said anode surrounding the saidcathode and being divided into odd and even. sets of segments, all odd segments and ali'e'ven'. segments being respectively joined together by an end piece and the respective end pieces of the two sets being on opposite sides anode surrounding the .said' cathode and beingof the anode. V l

1 A. ma netron. ompris nsm an Q i. erating a magnetic-flelda eathode and an node, .thei'sai .ca h d .ei endi parall l to aidlfield..and ,hav ei m te at ea t equal to agquartepof; the anode diameter, the said anode surrounding the said cathode and being ivi eddnto oddan r e sei O Segments, all oddc eements and a l i ea em being 1 p ptive i in oaet erh n nd ec n the res ec iv T n s e o th w t b in n. r q t side 19 th anode, the m t n n th Qfth amd fi nsp th s m O der offx c aseitnde-v 3- A masns mn e s e me o se at n ma neti l ne-cat d and an asa d aat oae e ndinap e tdsaid l aaslh ivi laadiam er a vleast e u l to a quarter ofthe ;anode diameter, the said anode surrounding the said cathode' a nd being divided Odd and e e s ts 9f. assai n 2i11 Odd segments and 1 all even segments being respectively jcined; together by .an{ end disc and the respe.ctive';end discs reat we sets being on opposite sides of 'tl e anode, and two screens connected. to the two. ends of -the cathode and 4jAl'mag'netifon' comprising means .for generating a Tina'gnetic Ifield, a cathode and an a'nOdeQth'e' s'aid' cathode 'eiite'nding parallel to said'liiel'd and having a diameter at least equal to a quarter of the anodei'diamete'r, the said dividedliiitooddand even sets ofsegments all oddsegmentsand all even segments'being respectively fjo'ned together by an end ring and the re'spective' fend rings of the twosets being on opposite-sides ofthe anode, and two screens connected to the two ends of the cathode and iacing said. rings, thereby forming withsaid rihgs'respectively two'by-pass capacities forhigh frequency. Y

5.- A. magnetron comprising. means "for" generatingaiinagnetic field, a cathode and an anode, the said cathode extending par'allelto said field and having adiameter at leastequal. to a quarter of theanofde diameter, the said anode surrounding'the said cathode andf diyidedihto odd-and even setskoi segments, all odd segments and all even segments being respectively joined to getheii py'ari end piece and the respective end p eces of-the. two sets being on opposite sides of the anode, and means individual to each of said end pieces for protecting said end pieces against-electronic bombardment from the catho.e.-.f.., f

..-6-.;A;Lmaehtrn ram in m an e erat ng a magneti field, a cathodeand an anode,

h said-ba ted? axt nai pa i el to s i fiel mounted between said cathode and said discs.

5 and having a. diameter at least equal to a quarter of the'anode diameter, the said anode surrounding the said cathode and divided into odd and even sets of segments, all odd segments and all even segments being respectively joined together by an end piece and the respective end pieces of the two sets being on opposite sides of the anode,

and means individually to each of said end pieces for preventing self-oscillation of the said end pieces; v

HENRI GU'ITON.

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

Number Number UNITED STATES PATENTS Name Date Fritz et a1. Apr. 26, 1938 Hollmann Jan. 17, 1939 Gutton et a1 Feb. 14, 1939 Samuel June 20, 1939 McArthur et a1. June 3, 1947 Hansell July 29, 1947 Spencer Mar. 9, 1948 FOREIGN PATENTS Country Date Great Britain July 1, 1940

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