UJNCLASSI F[ED4 01 9,6 8

AD

DEFENSE DOCUMENTATION CENTERFOR

SCIENTIFIC AND TECHN11CAL INFORMATION

CAMERON STATION, ALEXANDRIA, VIRGINIA

U N C]LA S S I F H E D

NOTICE: When government or other drawings, speci-fications or other data are used for any purposeother than in connection with a definitely relatedgovernment procurement operation, the U. S.Government thereby incurs no responsibility, nor anyobligation whatsoever; and the fact that the Govern-ment may have formulated, furnished, or in any waysupplied the said drawings, specifications, or otherdata is not to be regarded by implication or other-wise as in any manner licensing the holder or anyother person or corporation, or conveying any rightsor permission to manufacture, use or sell anypatented invention that may in any way be relatedthereto.

OFFICE OF NAVAL RESEARCH

CONTRACT Nonr (G)-Oool6-61

-- 0

Technical Reporton

THE OSAKA TUBE AS AN OSCILLATOR IN THE SHORT MILLIMETER WAVES

by

A. Murai and S. Mito

May 30, 1963

The research reported in this document was supported bySGrant Nonr (G) -00016-61 of the Office of Naval Research..

Department of Applied PhysicsFaculty of Engineering, Osaka City University

-1-

THE OSAKA TUBE AS AN OSCILLATOR IN THE

SHORT MILLIMETER WAVES

Akira Murai* and Sanai Mito**

Department of Applied Physics,Faculty of Engineering, Osaka City University

Synopsis

A Barkhausen-Kurz type electron tube with a confining d.c. mag-netic field, the so-called Osaka Tube, was designed and fabricated tooperate at 2.5 mm wave length with a purpose to study the possibilityof its practical fabricability. Oscillation was detected at a wave-length of 2.5 mm at a magnetic field of 4,000 gauss and an anode vol-tage of 800 volts. No special precision machining was adopted, andtherefore the output and efficiency were not the prime purpose of thisexperiment other than to find the possibility of oscillation. Owingto the restricted cathode area of 0.1 mm2 , it was anticipated that atbest an emission current of 1 mA would be drawn. However, actually,an emission current of 4 mA resulted, which indicates that furtherreduction of operating wave length may be possible. Problems stillremain in the mechanical tuning construction and also in the improve-ment of efficiency, the solution of which lies in the precision of themachining process.

Design Procedure

This work is a continuation of our previous studies(1)-(3)on OsakaTube in the longer millimeter wave region. The present work was aimedat designing an Osaka Tube in the shorter millimeter waves capable ofoperating at comparatively low anode voltage and magnetic field.These requirements necessitates the reduction of the electrode dimen-sions. Thus, a choice of 0.5 mm for the distance between the cathodeand re6peller necessarily results in a distance of 0.1 mm between therepeller and the anode where the spacing becomes closest, since theanode comprising the cavity resonator must be located between the ca-thode and repeller.

The cavity resonator was machined from a copper disc. (Fig. 1 & 2).Here, it Was noticed that the precision of welding to ensure the conduc-tivity of the internal wall of the cavity poses a problem.

The basic relation that governs the electrode dimensions and theoperating parameters with regard to the operation frequency is given inFig. 3 together with the computed results. Here, the computed curveshows the relation between the anode voltage and the magnetic field withrespect to the operating frequency. The letter n in the formula andfigure denotes the order of the dwarfT2),(3)wave. Frequencies of 100GC, 120 GC and 150 GO represent the central frequencies of the cavityresonators which are to be determined by the designated dimension of thecavity, other dimension as Dx, Dr, etc. being kept constant.

* Lecturer• Professor

-2-

Experimental Results

Figs. '4, 5 and 6 illustrate the anode current ye:,>ersus anode voltagecharacteristics-uxider constant magnetic field with h, Me hea- ter input as aparameter.

Fig. 7 shows the current versus voltage charaqe.9,risti -s at constantheater input of 1.10 amp. with the magnetic field aparýseter. Fromthese figures it is inferred that the electrons ar~fjLfairly well formedinto bunches that describe to-and-fro oscillations e as expe.-ted. Eowever,while oscillations readily result with tubes of lalge:eer diensions designedfor lower frequencies, the range of oscillation inth:-ihs ex-tremely shortwave region is seen to be small.

An example of the oscillating characteristicsi saas follows.

VP = 800 volts Order of dwarf w4e e, n = 15B =4000 gauss Heater power, Ph=- 8 wattsIp = 200 i amp. Wavelength, X = 2.6 mm

Output power, P0= 10 watts.

The descrepancy of the operating wavelength aj - the designed valuemay have resulted from the expansion of the cathodý.tj,-ttvrepiller distanceduring mounting of the electrode parts.

The efficiency and output are expected to be ilptqproved if more precisemachining is adopted, as well as higher voltage and~ali•etir field areapplied for lower n value operation. These aspect~rv.remain to be comparedwith conventional millimeter tubes.

A NEW DESIGN OF OSAKA TUBE IN, THE 3OoGC CANGE

The conception of Design

The possibility of fabricating an Osaka Tube iI 1 the 120 GC sand wasverified in the foregoing report. Although elabortioj00 n of machining pro-cess to improve the output and efficiency for the 0 CD GC tube is necessary,a design of the Osaka Tube in the 300 GC band will ýe s proposed.

An axial symmetrical reentrant type cavity rema-neator was adopted forthe Osaka Tube up to 120 GC, which proved to be a co06ce8s. However, thereseems to be a limitation with this type of cavity i t the machining processas well as in the effective coupling between the el~ci-tron wurrent and thecavity,, which seems to be around 150 GC. As a coulez~rmeasuare, a sort ofslow wave structure will be proposed to replace thhvweentrant type cavity,whereby forced oscillation due to electron currentqf Xhigh4r order dwarfwaves will, be excited, which in turn, through feedl0o1k, for-ms the electroncurrent into more discrete higher order dwarf wave nhin•.

The interaction of electron beam and the fiel•o:f the resonant structurewas analyzed and reported (4). According to the al1flypis, the fundamentalcomponent of dible'radiation from an electron bean '&-•ith square wave confi-guration of bunching may be expressed as,

-- o = ý7 AU. (qodl)2 -= I-c(Ne d-d )ý - 2

12nc q0 12noc

where, N number of electrons that constitute t• • dipoledg = interaction gap dimensionVp= anode voltage

Dx= cathode-to-repeller distancee t electron chargem. = electron mass

Since the effective dipole moment and the effýi*zive arxgular frequencyfor the n th order dwarf wave are 1/n and n folds o0t~zhe fuadamental radia-

tion, respectively, the radiation power of the nthi6.der dwarf wave becomes,

-3-

Ti =1 (Nedg/n)2(2eVD)2dn-12nc (•x n4 = n2dPo

Actually, formation of sharp bunching may be hindered by the spacecharge effect and therefore the output may not reach the above value.

As a rough estimate, assuming an electron current of 1 mA at an angu-lar frequency of 2n.3.10ll rad./sec.. we have N : 3"103. If d = 0.1 mmand w= 2n.3. 1 0 10, we have d-Pn -l-01 0 watts. If there are 5 sfots alonga total length of lmm, the radiation power is estimated to be about lO-

watts.Infra-red radiation may be possible with similar construction, though

the radiation may not be ideally coherent.In Fig. 8 are illustrated the construction of the proposed Osaka Tube.

Conclusion

An Osaka Tube was designed and fabricated in the short millimeterregion for the purpose to study the practical limitation in. fabrication.Preliminary experiments indicated that it was still possible to reducethe wavelength below 2 millimeters. Difficulties of fabrication at thiswavelength compares favorably with those encountered with klystrons.However, actual precision machining problems remain to be solved if theabsolute output power and efficiency are to be questioned. These will bebest solved with the cooperation of manufacturing companies excelling inthe field of micro wave electron tubes.

Acknowledgement

This work was partly supported by the ONR Grant and material aid andadvices were given by the Oki Electric Industry Co., to whom the authorswish to reveal their gratitude. Thanks are also due to Miss Y. Saito,Messers Y. Yamada and Y. Yamazaki who, as students, had undertaken mostof the experimental measurements.

References

(1) "The Osaka Tube", by S. Mito & K. Baba, Memoirs of the Faculty ofEngineering, Osaka City University, Vol. 1, Dec.,1959.

"(2) "Experimental Results with Osaka Tube", by S. Mito & A. Mura±,ditto,Vol. 3, Dec., 1961.

(3) "Millimeter Osaka Tube", by S. Mito & A. Murai, ditto, Vol. 4, Dec.,1962.

(4) "Millimeter Osaka Tube", by S. lito & A. Murai, Report of the ResearchCommittee on Millimeter Waves in Japan, 1960 (in Japanese)

-4-

Output ~--Waveguide

/Y

MatchingSection [ ahd

Insula~tor -

- InsulatorRepeller -

CavityResonatorHae

Chamber

Anode

<--62 .5--

Fig. 1. Construction and dimensions of the 2.5 mmn waveOsaka Tube(unit in mm.)

-5-

Matching section

S - 6- /

• Fi g. 2.

Vt

S____=_•Configuration and dimensionof the anode block with

S•° cavity resonator.

_• o (unit in. ram.)

fI;~ iT 74

t T.1 1 lit r

& -1~~ t-It ~

> 4 r4;tYfn4l4T

U 4- I 0

JI-r~:o OJO 12. ~-Pj

0 M,

""Y' 4 4 4 1 t,1g

4-)f

9 0~04 0

o ~ 0~~:j-

4* 0 0d 40

(1) 0xi 0

4- 00

4 -) -

to 0*0 P1m

(vu~) quaanii apouv-.____

P4 P4 %P4 P4

0C00

P4 0

coc4-4 H aS CU 0

H Ht

() H 0 4

A )j41) +)04-) 0) C. 4) 0 04 ,p 0' 4-H H'0 ~-HO -:4 4)40

4.) 0)~d

w boPIL bC 4 0

0. c D1

0

0H 4)4 4)0"

U) C) C) C

(Vul) d I~ .... 4 a.. D.U

P, P;44-)4 Ei 0

(D4 V, P4 1 4

01C co 1~44)H H 00 Hi

0 H HH 0

cof4 0 H*Hi Hc4-4-P 4) 4-1 Q) 0 4)(a ýd 4.) (0 0 ba

*dOO40 ) (0j (U

4-) 0

C 0)

o 4-1Ll4ý- 0 4-)

UCd 00

-P 4 to~ kU Hq

(VMf1) di 4uegxano apourv

-8-

I -I "

Fig. 7 Anode Current vs. Anode Voltage

il-i

Heater Current 1.10 Amp

9.0 K.Gauss

31

. i y'81.0 K. Gauss

S, •1ý'.L K.Gauss

" 6.2 K.Gauss

aL~~ / I. , " -,

0 .4.0 K.Gauss

./,,, t

i;,

•--. Anode Voltage (volt) r0 000 2000 3010

!±g. 8 Eectrode Cdonistruc-tio~n of 300-GC OsakaTube.'

ýB,

$ Repeller S'e,&f ace,Antenna Surface'

Terermnal

a. Vetical0 Center~ Cross,' (Positive power. supply connect-ýe tioi ':(i o the Anode, Cathode Surface

arid one Heater connect to theearth potential.)

c.L Side View (1)

OutputCathode -Weid

AoeSurface 4

Antenna part Rplefor Output Srfaele

Surrface

b. Horizo~ntal, Center Cross Section (xl) d. Under half of AntennaSurface (Overlooked)

0.25mm

S01mm

t.Anode Block (xl) /'%Interaction Slot

f., Anode ýBlock-(XlO)