US2402184A - Ultra high frequency electronic device contained within wave guides - Google Patents

Description

June 18, 1946. y A L SAMUEL 2,402,184

ULTRA-HIGH FREQUENCY ELECTRONIC DEVICE CONTAINED WITHIN A WAVE GUIDE Filed May 3, 1941 5 Sheets-Sheet 1 /NvE/vron A. L. .SAMUEL A TTORNEV ,Jun1s,194s.V I ALSAMUE. 2,402,134

`ULTRA-HIGH FREQUENCY ELECTRONIC DEVICE CONTAINED WITHIN A WAVE GUIDE Filed May s, 1941 l s sheets-sneeze FIG. /4-

/NVE/vroR By A LSAMUL VMM , ATTORNEY June 18, 1946. A. L. SAMUEL ULTRA-HIGH FREQUENCY ELECTRONIC DEVICE CONTAINED WITHIN A WAVE GUIDE Filed May 3, 1941 3 Sheets-Sheet 3 F/G. a

FIG/0 /A/VENTOR ALSA MUEL VWM A TTOR/VEV Patented June 18, q1946 ULTRA HIGH FREQUENCYELECTRONIC DE- VICE CONTAINED WITHIN WAVE v(HTIDES Arthur L. samuel, summa, N. J., assigner to Bell Telephone Laboratories, Incorporated,

New

York, N. Y., a corporation of New Yorkv Application May 3, 1941, Serial No. 391,658

(Ci. 17M@ Claims.

This invention relates to methods of and apparatus for utilizing the interaction between electron streams and electromagnetic waves within wave guides.

An object of the invention is to increase the eiliciency of coupling of electronic energizing systems to wave guides.

Another object of the invention is to cause a section of a wave guide to serve as a negative resistance with respect to Waves traversing it, whereby the wave guide section may function as an amplifier.

An additional object of the invention is to increase the effective wave-length inside c. wave guide by virtue of the properties of the guide in the frequency range near its cut-ofi frequency.

A feature-of the invention lies in the incorporation of an electronic device such as an amplifier 'handled may be uneconomically small at the higher frequencies. In accordance with the present invention, a sheet of electrons may be employed instead of a beam or pencil thereof. To

` avoid difcultles due to phase and amplitude difentirely within the compass 'of the wave guide.

The device so incorporated` is protected by the wall of the wave guide and if the wall is of cony ductive material, the device is shielded thereby tended cathode. By c onstricting the inner cavityof the wave guide immediately surrounding the cathode, advantage is taken of the natural variation of the velocity of wave propagations in a wave guide operating near the cut-off` frequency of the guide,` which velocity may greatly exceed the free-space velocity of waves at the. operating frequency. In accordance with this feature of the invention, a cathode may be extended through Aa length of several free-space wavelengths and still occupy a length only a quarter wave-length or less relative to the waves inside the guide.

Another feature ofthe invention isthe placing of the cathode structure and connecting leads substantially within an equipotential plane with respect to the electromagnetic field in the adjacent portion of the wave guide.

While the main advantages of the above features will immediately be evident to those familiar with the ultra-high frequency technique, it

should be noted that the feature involving a ferences in the electromagnetic wave from point to point along the length of the electron sheet, the stream is preferably limited to the order of a quarter Wave-length in the direction of its linear extension. By placing the electron stream in a restricted section of wave guide where the velocity of wave propagation is several times the freespace velocity, the actual length of` the cathode may be extended to several times what it would be if it were operating upon a wave in free space or in 'an unmodified section of the wave guide. The restricted section of the guide may be connected to the adjacent unmodified portion either by a transition section to minimize reflections or through an apertured partition or coupling iris to secure an optimum impedance transformation, or through any other suitable coupling means, or by a combination of such means.

In the drawings:

Figs. i and, 2 show, respectively, a longitudinal and a transverse section of a wave guide containing the elements of a. diode oscillator in a constricted portion of the guide; y

Fig. 3 isa diagram useful in explaining the reason for the particular design of crosssection V of a wave guide;

Fig. 5 is a diagram useful in selecting appropriate designs for the cross-sectional configuration of the device shown in Fig. 4;

Fig. 6 shows an arrangement for projecting an electron stream into a wave guide through a side opening;

Fig. 7 is a diagram useful in explaining the operation of the arrangement of Fig. 6;

Figs. 8, 9, 10 and 11 show various shapes of wave guides and appropriate types of electrovmagnetic eld distributions which may be advantageously used in connection with electronic energization Figs. l2 and 13 show, respectively, a longitudinal and a transverse section of an arrangement forcoupling two wave guides through an electronic amplifier; and Fig. 14 is a cross-sectional view of an arrangethe same general principles employed in the sysi tem of Figs. land 2, in this case arranged to operate as a magnetron rather than in the man- A rod mounted substantially on the axis of the guide i and supported at either end -by means of extensions which are hermetically sealed intol and pass through the closures Il and I5. A magnetizing coil 2i, coaxial with the cathode 20 isprovided to supply the held required for magnetron operation. This arrangement is particularly designed for a second order type of wave propagation, the electric eld configuration for which is shown approximately by the arrows in Fig. 5, corresponding generally with Fig. 9b of the Southworth Patent 2,129,712, above cited. The thickened wall section 4' of Fig. 4 encloses a cavity 3' which may have a cross-sectional shape such as one of those represented by equipotential lines 22, 23 and 2H, respectively, in Fig. 5.

The arrangement of Fig. 4 operates in essentially the same manner as a four-plate conventional magnetron, current iowing principally to four regions on the anode surface, which regions, however, need not be physically separated or insulated from one another. Due to the constricted cavity il', the axial length of the elements may i be long compared to the free-space wave-length in accordance with the same principle governing the case of the diode. As in the case of the arrangement of Figs. 1 and 2, the magnetron of Fig-t may be used as an oscillator, amplifier, modulator, etc.

An alternate arrangement for a diode in a wave guide is as shown in Fig. 6. This arrangement has the property of acting upona traveling wave in a wave guide but does not make use of a constricted section nor of a linear cathode. The guide l is provided with a side tube 25 fastened over a hole 2S in the wall of the guide i. An electron gun, designated generally at 21, enclosed in an insulating envelope 28 is aiiixed to the tube 25 by` means of a suitable vacuum-tight seal, and the vacuum chamber is closed by means of insulating windows 29 and 3U which offer substantially no obstruction to the passage of electromagnetic waves along the guide l. A wave of the H1 type is suitably employed, giving an electric held conguration as indicated diagrammaticallyv in Fig. 7. The electron stream indicated by a dash-line arrow 3l is injected into the main guide l substantially in the principall direction of the electric eld. 'I'he electrons of the stream 3l are accelerated by a suitable'biasing potential between the cathode of the electron gun and the` conductive walls of the guide i. By suitably controlling the transit time of electrons in traversing the interior of the guide I, the electron stream may be made to deliver energy -to the electromagnetic field of the guide. Accordingly, the' device may be employed as a negative resistance element to sustain the amplitude of a traveling wave passing along the guide. It will readily be appreciated that the arrangement may also be` used as an oscillator or modulator.

The arrangements shown in Figs. 1, 2 and 6 are all characterized by an electron beam interacting with an electromagnetic field, the electric component of which is substantially at all times in .the direction of the beam or in the reverse of that direction. It' will be evident that there are many modes of oscillation in wave guides which will set up electric neld coniigurai 6 tions suitable for interactionwith an electron beam in the manner above described. It will-iurther be noted that the guide need not be a. circular one but may be square or prismatic with a lvariety of different shapes, the main characteristie desired being that the electric eld have a considerable region in which it consists essentially of parallel straight lines. Anumber of suitable wave guide sections with appropriate electric iields indicated are shown in Figs. 8, '9, 13 and 11.

Fig. 8 shows cylindrical guides supporting a wave of the E0 type as in Figs. 6 and Gain Southworth Patent 2,129,712.

Fig. 9 shows how the circular guide ofV Fig. 3

may be modiiied into'various prismatic shapes;

all of which will support essentially the same configuration of electrical waves as shown in Fig. 3. The modifications include a square guide in which the electron stream is suitably introduced in the direction of a diagonal of the square cross section, and a triangular guide in which the electron stream may be introduced eitherat the right arc. In all these examples the electron path is substantially parallel to the electric field.

Fig. 10 shows a eld conguration generally similar to that shown in Fig. 5 but imposed upon a. cylindrical guide transversely to the axis of the cylinder instead of longitudinally.

For comparison a cylindrical guide supporting a wave in the manner of Fig. 5 is shown in perspective in Fig. 11.

In Figs. 8, 9, 10 and 1l the direction of the axis of the electron stream is indicated by an arrow.

'I'he electron stream in the form of a beam or pencil may be employed with any of thewave guides illustrated in Figs. 8, 9, 10 and 11 as well as in other configurations not shown. The arrangements of Figs.9 and 11 are particularly well adapted, in addition, tothe use of the extended linear cathode in connection with aconstricted portion of a guide, in accordance with the principles set down in connection with the description of Figs. 1 2 and 4. y

Figs. 12 and 13 show longitudinal and transverse sections, respectively, partially diagrammatic, of a triode arrangement coupling two wave guides. The arrangement operates as an ordinary triode ampliiier except that the cathode-grid space and the grid-anode space are isolated from each other by being included each in a separate wave guide interconnected only through the meshes of the grid. The arrangement is shown as an amplifier.

In Figs. 12 and l3. two partially overlapping wave guides 45 and 46 are shown with' a common wall portion 49. The guides are preferably rectangular in cross section and in the case of an amplifier both guides may well have the same transverse dimension or width W, as indicated in Fig. 13. .In `the common wall 49 there is situated an electron permeable region or grid li'opposite which in. the guide 45 is a thermionically active cathode sectionl 5I insulated from th'e wall of the guide by insulation Il or otherwise suitably mounted. Vacuum seals are provided, as at 6|, 62, 63 and 6l. The cathode may be heated by an external heating element 52 insulatedas at 65 and energized by a. battery 53. The 'cathode may be positively polarized with respect to the grid SII by means of a polarizing battery 54. Opposite the grid 50 in the guide 46- may be mounted an anode 55 insulated from the wall of the guide by insulation 48 and polarized positively with' respect to the grid 50 by means of a battery 5t. Each of the batteries above mentioned may be replaced by any suitable source of direct current electromotive force. Adjustable pistons or reflectors 5T and 58 are provided for controlling the establishment of standing wave patterns An incoming wave in the guide 45 serves to impress a control voltage between the cathode 5I and the grid Si@ thereby producing a Variable electron current in the region between the grid 50 and the anode 5E, the variations of which current serve to set up amplified electromagnetic waves in the guide Mi. The mode of operation of the device is generally similar to that described in U. S. Patent 2,153,728, issued April 11, 1939, to G. C. Southworth.

Fig. 14 is a cross-sectional view of a modification of the arrangement of Figs. 12 and 13 adapted for frequency conversion. In this arrangement the incoming wave guide, shown at the top, is of a suitable width (horizontal dimension) to support a wave of a desired fundamental' frequency. The output wave guide, shown below, is narrower so that it will not support s, wave of the fundamental frequency but it may be tuned to the harmonic frequency. The vertical dimensions of the respective guides in Figs. 12, 13 and .4 -may be determined by the relative spacings desired between the grid and the cathode on the one hand and the anode on the other.

In Fig. 14 the wave guidefor the fundamental frequency is designated 59 and the guide for the harmonic Sii, the widths of the respective guides being W1 and W2.

The arrangement of Fig. 14 is claimed in my copending application Serial No. 461,517, filed October l0. 1942. assigned tothe same assignee as g the present application.l

What is claimed is:

1. In an ultra-high frequency electronic device, a source of waves of a given operating frequency. a section of wave guide of such transverse dimensions as to have a cut-ofi frequency close to and slightly below said operating frequency` said wave guide section being so proportioned that its length is of the order of magnitude of a quarter wave-length referred to propagation of waves`within said guide, but relatively great compared to the free-space Wave-length corresponding to the operating frequency, a cath'- ode with its active portion extending substantially the full length of said wave guide section, and means for causing an electron stream emitted from said cathode to eiiect energy interchange with electromagnetic Waves from said source within said wave guide section. l

2. 11i a system for effecting exchange of energy between an electron stream and an electro-l magnetic wave,l a source of Waves of given operating frequency, a wave guide, means in said guide to increase the speed of propagation of waves from said source therein over the speed Aof propagation of a wave of the same frequency in free space, thereby multiplying the waveflength in said guide compared to the free-space wavelength, and a source of an electron stream, said source extending along and adjacent to the path of propagation of said wave within the connes of said speed increasing means in said guide, the length of said source in this extension being of the order of magnitude of a quarter wave-length referred to propagation within said speed increasing means and at the same time of the order of magnitude of several free-space Wavelengths.

3. In a system for energy interchange at ultrahigh frequencies, a' source of electromagnetic waves of a given operating frequency, a. source of an electron stream, means for constraining waves from said first-mentioned source to traverse a. restricted region in which the speed of propagation of the wave is increased with respect to the speed of propagation of a wave of the same frequency in free space, thereby multiplying the wave-length in said region compared to the free-space wave-length, said source of an electron stream being positioned within said region of increased speed of wave propagation and being extended in its dimensions along the path of propagation of said wave to a length which is ofl the order of magnitude of a quarter wave-length referred to propagation within said region of increased speed and at the same time of the order of magnitude of several free-space wave-lengths.

4. An extended length of wave guide, a source of Waves of a given frequency freely transmitted by said guide, a section of reduced internal crosssectional area in said guide having such .dimensions as to have a cut-orf frequency close to and slightly below said given .operating frequency, said section of reduced area being so proportioned that its length is a fraction of a wavelength referred to the speed of Wave propagation within said section and at the same time equal to several free-space wave-lengths of the operating frequency, and means for projecting electrons transversely to the guide Within said section of reduced area along a substantial portion of the entire length of said section to eiect energy interchange between electrons so projected and a `wave of the operating frequency within said section.

5. In an ultra-high frequency transmission system, a wave guide designed for the propagation of an electromagnetic wave of a given field configuration, a portion of said guide being modiiied in internal dimensions to form a section of reduced internal diameter, the cross section at all points of said guide being such as to conform substantially with equipotential contours of the given field conguration to secure a section of increased speed and propagation without causing 4 material distortion of the eld coniiguration, and

meansfor maintaining in said section of reduced internal diameter an electron stream having a dimension transverse to the direction of motion of the electrons which is substantially as great as the length of said reduced section. said means comprising a heated cathode located within the said section of reduced internal diameter, and said cathode having its electrical connections located substantially in a single equipotential plane of said given iield coniiguration.v

ARTHUR L. SAMUEL.'

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