US2222902A

US2222902A - High frequency apparatus

Info

Publication number: US2222902A
Application number: US276172A
Authority: US
Inventors: William C Hahn
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1937-07-14
Filing date: 1939-05-27
Publication date: 1940-11-26
Anticipated expiration: 1957-11-26
Also published as: US2220839A; GB518015A; FR50997E; BE429160A; CH222371A; GB533939A; FR51488E; GB555863A; US2266595A; FR840676A; GB555864A; GB533826A; US2200986A; GB553529A; US2220840A; FR51527E; CH231586A; US2276806A; FR51863E; BE442681A

Description

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The present invention relates to ultra-high frequency apparatus utilizing lthe principles of velocity modulation described in my copending application Serial No. 153,602 led July 14, 1937. 5 More speciiically, the invention relates to improvements in devices. of the general structural form described and claimed inmy copending application Serial No. 211,123.led June 1, 1938. Howevenwhile the devices disclosed in the latter lo application are described mainly as oscillators, the improved structures tof be described herein are considered to be useful not only. or gen-l erating oscillations, but also for purposes of ampliiication, etc.

It is a primary object of the invention to pro-= vide ultra-high frequency apparatus capable of realizing high power output. In this connection, an important feature of the invention consists the use of an arrangement in which an electron beam is caused to traverse an extended series of mutually spaced electrode elements which arev so dimensioned and spaced as to constitute in themselves the primary parts of a resonant electrical system and which are so correlated to the beam velocity as to assure the occurrence of cumulative eilects at the various inter-electrode gaps.

In a further aspect, the invention may also be viewed as comprising an improved method of operating high frequency electronic apparatus to obtain the results outlined in the preceding para- The features which I desire. to protect herein are pointed out with particularity in the appended claims. The invention itself, together i with further objects and advantages thereof, may

best be understoodby :reference to the following description taken in connection with the drawings in which Figs. 1 and `2 comprise imaginative representations useful in explaining the inven- 3.40 tion; Fig. 3 is a-schematic illustration of' an oscillator embodying the invention; Fig. 4 is a. graphical representation of potential distribution from point to point along the oscillator; Fig. 5 isja diagram of a circuit which is in some respects functionally equivalent to the structure of Fig. 3; Figs. 6 and 7 are graphical representations of L current'and longitudinal potential gradient distribution respectively; Fig. 8 illustrates the application of the invention in connection with a pracv tical oscillator construction; Fig. 9 is a sectional I- view taken online 9 9 of Fig. 8; Fig..10 is a. schematic illustration of an 'ampliner utilizing the invention; Figs. 11,13, 15 and 16 represent structural variations of the invention andFigs. 12 and William O. Hahn, Scotia, N.

eral Electric Com, a corporation o New a No. avai-az im. 25o-3e) 14 are graphical representations respectively ap plicable to the structures of Figs. 11 and 13.

Before proceeding to a detailed description of the invention it will be helpful to consider briefly the principles or velocity modulation as the same are set forth in my application Serial No. 153,602J above referred to. Y

In the said application, it is pointed out that if a uniform stream of electrons is caused to traverse a region which is subjected to cyclically variable potential gradients, the various elements velocity. That is to say, electrons which traverse the region when thegradient in itis positive, will be accelerated, while electrons which enter thev region during a period of negative4 potential of the beam will be differently affected as togradient wm be deeeiemted. 'rnus, ifI the pritential applied to the said region is of cyclically reversible character, the portion of the beam issuing from the region will be characterized by illustrated in Fig. 1 wherein the black dots a. may

the light dots b to represent relatively slow electrons. At the instant the beam emerges from the gradient-containing space, the charge density distribution in it may still be substantially uniform as shown. However, at a somewhat later time, if no further disturbance of the beam is permitted, a regrouping of electrons will occur as a. result of the. tendency of the faster electrons to catch up with the slower ones. Thus, Fig. 2 represents the condition of the beam of Fig. 1 after the same has traversed a drift space of substantial length; tha't is, after an appreciable time alternate components of high and low velocity. y The condition referred to in the foregoing is has'elapsed. It wili'be noted that in the condi- Vmodulation oi' an electron beam and thereafter.

converting the velocity modulation into charge -density modulation for the accomplishment of certain desired results.

y Referring particularly to Fig. 3 there is showt-rn'y in schematic form an exemplary embodiment of the-invention. Thisincludes an elongated discharge tube 9 having a cathode I0, two or-more high .voltage accelerating electrodes il and anA anode i2 for producing an electron beam through the tube. Outside. the tube there are provided a series of conductive electrode elements,l numbered ments are enabled to inuence the beam at vari-- Il to I8 inclusive. which are arranged along the beam path and' in juxtaposition thereto. In the particular arrangement illustrated, the said conductive elements are in the form of hollow tubular members which are mutually spaced to permit the establishment of potential gradients in the gaps between them. By this means, the eleous displaced points (2| to 2l) along its axis.

Outside the tubular elements I4 to Il, a further conductive structure is provided in the form of a tubular shell 26 which is concentric with' the elements. The shell 26 -is connected at its extremities to the elements I4 and I8 by means of wall parts 28 and 29.

In connection with my present invention, the structure so far described` may be viewed in two aspects. `In theirst, it comprises an electrode system for influencing the electron beam which traverses the tube 9. In the second the structure may be consideredas a. resonant feed-back system for assuring effective coupling between elements last traversed by the electron beam and those initially traversed by it. -(This latter statement applies especially; of course, when the apparatus as a whole isl to be employed as an oscillator.)V

ing of the system as a whole simulates that of a resonant circuit of the general form illustrated in Fis. 5. y v

In thegure last referred -to there is shown a .series ofV alternately positioned inductive elements 32 to 36 and capacitive elements 38 to 4I, these elements being assumed to be4A so matched as to produce resonance. In the relationship illustrated,` the Vinductive elements represent the electrodes I4 to I8,'viewed as components of an impedance network, and the capacitive elements represent the end-to-end capacitive coupling between adjacent electrodes. During resonant operation of either thenetwork of Fig. 3 or that of Fig. 5, there will be an alternate rise and fall of potential level as one proceeds from point to point along the network.

The representation of Fig. 5 is, of course, only an approximation to the arrangement of Fig. 3

since the elements I4 to Il may not properly be viewed as of purely inductive character. They are, on the contrary, more in the nature of short sections of transmission line having distributed constants. However. it may be shown that under a particular condition of resonance, to be specifled in -the following, the potential variation along the electrode structure (as measured to the shell 26) is 'in the general form noted in Fig.' 4. That is to say, as one proceeds` along the electrodestructure from the wall member 23, the potential rises 'continuouslyy until an interelectrode gap (2i) is reached. At the gap the. potential re- 'verses abruptly as a result of the presence of the lumped capacitance which couples the iuxtaposed electrode elements Il andgIl. This condition is repetitive for each combinationof electrode elementsand gaps. The corresponding' to Il tothe shell 2Basone: proceeds along the axis of the tube. If the condition illustrated actually prevails, the function- Ycaca-.90a

current distribution along the electrode structure is shown by curve B of Fig. 6, which indicates that the current attains a maximum value at the center of each electrode element and is a minimum in the interelectrode gaps.

Referring now more-particularly to the reaction of the electrode structure on the beam itself, it will be understood that with the potential relationship shown in Fig. 4 the gap gradients assume a form such as is indicated by the curve C of Fig. 7. In this connection it will be noted that there exists a sharp rise in gradient at the extremity of each element, which is followed by an abrupt drop as the edge of the next element is approached. At any given instantthe gradients in the variousgaps are similarly directed. They are reversed every half cycle and return to their original condition at the beginning of the next cycle.

An electron which traverses any one of the gaps 2i to 24 at a time when a potential gradient exists across it is obviously affected as to velocity. It is desired for the purposes of my present invention that any given electron shall be similarly affected as it traverses each of the sans. so that cumulative effects may be obtained.- T'hat is to say, it is desired that an electron which is accelerated in the rst gap shall be similarly accelerated in each of the remaining gaps, and, on

This result win obtain if the transit time of a' given electron through a single electrode element corresponds' approximately to somev integral number (including one) of complete cycles of the potential variation across the gaps. In order to meet this condition.' there must be appropriate correlation of the dimensional and electrical characteristics of the various parts. The means to be employed in securing this correlation are 'A brieflyoutlined in the following.

termine an appropriate length for the various elements II, I8 and I1 `(these'being each twice as an angle 0g, measured in such units that one complete wavelength (at the desired operating frequency) is equal to 360. 0g may be determined by thel following equation (which in turn is gerived from the more elementary known relationship between the beam velocity and the velocity ot propagation of an electromagnetic wave):

wherein V represents the d-c voltage of the beam and 0b represents the angularpart of a complete cycle which is required at such voltage for the transit of an electron'completely through one electrode element. l

It has previously been implied that 0b must be equal to `360 (2r radians) in order to bring about a desired cumulative action of the various inter- Tabe I Number of gaps lnasmuch as the output power tends to increase with the beam voltage, it is appropriate to choose the highest convenient value for V. In order to illustrate the method of calculation, let it be assumed that six gaps are to be employed. and that a d=c voltage or 8,000 volts is to be used. Using these values in Equation 1, 0g turns out to The length of the electrode elements being -thus tentatively xed, it is desirable next to determine the interelectrcde capacity required to enact resonant operation of the system (i. e., such operation asto produce the voltage distribution shown in Fig. 4). In this connection it may be noted from Fig. lthat the capacitive drop across a given gap must be equal'to twice the voltage appeing between either of the adjacent electrode extrem ities and the shell 2S. Furthermore. since the current now observed at the extremity of any electrode is identical with that across the contiguous gap, it may he reasoned that the gap.

capacitance should be made to equal twice the electrode-to-shell impedance at the gap boundary.

(It will be understood that the gap capa':aitance may be controlled` either by properly adjusting the form of the electrodes at their extremities or by providing capacitance increasing meansadjacent the gap, as will be later explained in connection with Irig. 8.)

ln order Ito determine the electrcde-to-sheli impedance, recourse must be had to transmission line theory, since as has been previously specied, the electrode elements tend to function as transmission line sections. Applying the relevant tormula in this connection we may write for the impedance at any'point:

Z=Zu, tan hhs-H6) (3) where Zo is the characteristic impedanceof the type of line under consideration; a is the attenuation constant; and 0 is the electrical angle measured from a current maximum. l

In the present case considerations of symmetry indicate the occurrence of .current mamma at the :enters of the various .electrode elements, as

pedance at the end of an element, therefore, the angle 0 may be taken as the length of a half element or,

Also, attenuation can bev neglected, so that Equation 3- may be rewritten:

z=z tan h "2-"=jz.tan setungthis quantity equal to one nur the capacitive impedance of the gap, we have where ).o is the desired wavelength of operation,

C is the gap capacitance, and c is the velocity of light.

For a practical construction. wherein the diameter of the discharge tube is 3A inch, that oi the electrode elements is I'inch and that of the shell is 2 inches, Zn is about 41.6 ohms. Therefore, using the previously calculated value oi-@g (59.2) and solving Equation 5, it appears that for an operating wavelength of 20 centimeters, C@ should be about 2.24 m. m. f.

. The discussion up to this point has been mainly` concerned with the operation of the apparatus of Fig. 3 viewed solely as a circuit network and without regard to the mode of its excitation. The latter factor will now be brought into the picture by investigating the cooperative reaction of the electrode elements with .the electron beam of the tube Q.

In considering the edect of the electrode structure on the beam let it be assumed that a radio frequency voltage of value" Vg is by some means impressed across the gap 2l. The velocity modulation produced by such voltage is then Vg B1, where Bi is a factor which takes into account the geometry of the aan, the operating wave length, and the average velocity of the beam.l

In accordance with the explanation given in connection with Figs. l and 2, the velocity modulation thus produced will cause at least some 'charge density modulation to exist in the beam issuing from the drift space dened by the electrode element l5. The amount of R. F. conduction cu1'rent.(I) thus developed will be a function of' the velocity modulation (VU B1), of the total beam current (Io), of the D. C. beam voltage (V),

and of the electrode length (0b) A complete ex.-

pression or this quantity may be `written as follows:

As the modulated beam traverses the second interelectrode gap 22 it will induce'in the elecV trede structure a radio frequency current corresponding to the conduction current I but opposite to it in sign.

ten

' r=ra (7) where B is a factor which takes into accon the lcharacteristics of the gap. For reasons which need not be elaborated here, B may be taken as equal to the `quantity B1 previously employed above. Consequently, the complete expression for l,the conduction current induced in the electrode structure is New. iet it be arruinar ed that thel gap 22 is also subjected to a radio frequency voltage l Vg, .similar in amplitude and' phase to the voltage predicated across the gap 2l. Under these conditions the apparent admittance of the gap.

'This equation may be simplined by grouping the quantities I L?? as G, v whereupon we have l A=jG.Q (10) The foregoing analysis peminsmalnu to the interaction .of the beam and 4electrode system The actual current thus induced may be. writ.- I

soA

where only twogaps are involved. It must be remembered, however, that kin the system under consideration the complete electrode structure involves the use of n gaps each spaced 0s" (in the beam) apart. Each part has a radio frequency voltage across it and tends to produce a modulating reaction on the beam. Furthermore, each of the Velectrode elements provides a drift space between two gaps. Thus, the total reaction of the beam on the electrode structure may be derived as follows:

As we have seen, the rst gap produces a velocity modulation VgBi which in turn results in an apparent admittance at the second gap of -iGmgr. that the gradient in the second gap is in the 'I same direction as in the first.) 'I'he admittance of the third gap, due to the voltage across the first, is 12GMQQ. Similarly, for the fourth gap, the admittance 'is -:i3Gm 3 9 b, etc.

Now, consider the effect of the voltage across the second gap. The admittance created across the third gap as a result of the modulation pro- 25' duced by this voltage is -jGm/; that across the fourth gap is -:2Gm 2 01 etc. Adding the admittances for all gaps, one obtains the total admittance as- For satisfactory oscillator operation, a condition desired to-be fulfilled is that the current required to initiate oscillation shall be a minimum. This condition provides a means of cal/- culating the preferred value of 0b.

-In this connection it will be noted'that in Equation 12 the quantity Gm, .as defined, conftains the beam current In as a factor. The quantity Gf may, therefore, be viewed -as being the product ,of two components, of which one, Gm, is mainly a function of the beam current Io and the other,

i G.. is mainly a function of the angle 0. Since the value of Gt required 'for oscillation is fixed by the consideration that it shall be equal to the internal losses of the device (such losses being fixed in turn by the physical characteristics of the system) we may determine the best value for the angle 0 approximately by plotting `the quantity 1 Qi G..

as a function of 0s .for a xed-value of n. For each value of n selected. the point of maximum of the quantity QL G., will define the value of 0s for which 'a minimum value of Gm, and consequently of In, will be' remarized by saying that most eective feedback action and consequently most satisfactory osciliator operation will` obtain when the beam volt- (Thisis on the postulated condition'4 1) sin (n-1)8b} (12)V age is adjusted to bring about a value of 0 corresponding to the values indicated in Table I. It will be appreciated, of course, that no change in results will occur if the value of 0 is increased by 360" or by some integral multiple of that angle. Thus, if a six gap System is to -be used and voltage considerations make it necessary tc employ an electrode length greater than. say, 500, satisfactory resultsmay be obtained by using 335 '(from Table I) plus 360, or 695. .It will be understood from a consideration of Table I, however, that in each case the electrode length is such that the average electron transit time through the electrode will be on the order of the time consumed by an integral number of complete cycles of potential. variation (at the desired operating frequency of the apparatus) and will depart therefrom by only a fraction of the period of a quarter-cycle of such variation.

The particular mode of operation described in 20 the .foregoing is that which is calculated to produce a voltage distribution along the electrode system of the character illustrated in Fig. 4. It will be understood, however, that a system of the type under consideration actually comprises 2i in no sense a departure from my invention to.

so modify the operating conditions of the apparatus as to procure operation in a mode of resonance different from the zero order mode and to produce a voltage distribution different from that shown in Fig. 4, as long as modulation,

effects are still obtained thereby.

'I'he discussion so far has been concerned mainly with the problem of assuring satisfactory operation of the apparatus as anoscillating system without regard to the ultimate disposition of the high frequency power thus realized. It will be'understood, however, that connection to an external utilization circuit, such as a'radiating antenna, may be accomplished by coupling to the electrode system in any appropriate manner. Thus, in the arrangement V'shown in Fig. 3, a plate-likeelement 48 is pomtionedadjacent to one extremity of the electrode element II so as to be capacity coupled thereto at a point fof voltage maximum. (The central electrode element ispreferably utilized for this purpose for the reason that its use tends to prevent operation of the system in any mode of oscillationI the various elements is very much simplified.. Furthermore, due to the method of 'design of the electrode system, one may avoid the use of inconveniently small electrode parts such as are V"usually required for ultra-short-wave operation.

(This is a consequence of Athe previously` described possibility of adding to the theoretically correct electrode length any desired number of 366 units without thereby altering the oper ating characteristics obtained.)

1n transmitting devices, the use of a plurality oi cascaded gaps, each subjected to a relatively moderate voltage, permits the attainment oi operating elciencies materially higher than can be obtained in previously available constructions without the use of unsafe voltage concentran tions.

in receiving devices, the same method oi cas-f cading greatly increases the effective voltage amplication which may be obtained and thus raise the limit of internal losses which can be tolerated. This latter factor is oi considerable importance in that it avoids the necessity o employing special low loss materials in all parts or" the apparatus. In particular, it permits certain glasses to be employed in place ci a more expensive dielectric such as quarta 'in the tube envelope where the occurrence oi high frequency dielectric losses would ordinarily require that the latter material be utilized.

The invention has so far been described solely by Yreference to a schematic represen-tation oi the same, but in Fig. 8 it is shown as being embodied in a practical structure. in the arrangement referred to there is illustrated an electron beam tube which comprises an evacuated envelope having an elongated shaft portion tti, and an enlarged anode-containing portion di". This envelope may be suitably constituted of quarta or of low-loss glass.

The shaft portion tu encloses means for producing an. electron beam, such as a known type oi electron gun. The combination shown com= prises a iil'amentary cathode Sil, which is indicated in dotted outline, and a cylinder @E which may be used for conning the electrons to a ooncentrated beam. This cylinder may be either cmnected directly to the cathode as shown or maintained at a few volts negative or positive with respect to it. In order to accelerate the electrons to a desired extent there is, provided an accelerating electrode et which is spaced from the cathode and which may be biased to a suitable positive potential, say, several hundred volts.

In order that the intermediateportion of the beam path may be maintained at a desired potential level there are provided a pair of intermediate electrodes di, which suitably comprise rings of conducting material such as colloidal graphite applied to the inner wall surface of the envelope. These are connected with external elements by means of appropriate lead-in connections 62. A number of magnetic focusing coils 65, distributed along the envelope, serve to maintain the beam in focus during its passage through the discharge space.

After traversing the envelope, the electron beam is collected by an anode 6d which is in the form of a hollow conical structure, suitably consisting of graphite. A tubular electrode E9 in the .nature of a suppressor grid serves to prevent secondary electrons emitted by the anode from returning to the discharge space.

In .the operation of the device, the intermediate electrodes 6| may be maintained at ground potential, the cathode 6d at one-thousand to sev- 70' eral-thousand volts below ground, and the anode 68 at one-thousand to several-thousand volts above the cathode. The suppressor 4grid 69 should be biased iifty to several hundred volts negative with respect to the anode 69. These potential relationships may be established by means of a suitable source oi potential, an exemplary such source being conveniently represented in the drawing as a battery lt. i

The combination oi elements so far described comprises means for producing a unidirectional electron beam ci substantially constant average intensity and velocity. Outside the envelope there is provided an electrode arrangement for 'ailecting the beam at radio frequencies. This arrangement includes'a series o tubular electrode elements (numbered lf3 to ll inclusive) which are disposed at spaced intervals along the axis of the envelope du. 'These elements, which should consist of a conductive material such as copper, are maintained in spaced relationship by means of a number oi intertting insulating rings, l@ to di. For use at ultra-high frequencies, these rings are preferably constituted oi a material which has relatively low dielectric losses, for example, cuarta,

The electrode elements referred to are concentrlcally enclosed within a conducting shell 83 which extends along substantially the entire length o the envelope shaft. A connection b'etween the end elements it and 'il and the shell at is provided by means o' circular metal diaphragms dd and @d which extend transversely to the axis ci the envelope. 'These diaphragrns may be made oi exible character to allow for heat efxpansion of the electrode parts. In the arrangement shown, the diaphragme et, ad are equipped with circular anges t8 and 8d which are adapted to interiit with the inner surface oi the shell In order to assure a/satisfactory engagement of parts, the anges are preferably out at various points (not illustrated) so as to be readily expansible and are respectively associated with'split rings ed, Qi, which can be spread by means ci tapered screws Q2, SS. By tightening these screws the anges can be forced outwardly into tight-fitting contact with the shell.

it will be understood that the electrode elements it to Ti and'tne shell dt correspond in nature and function with the similar items described in connection with Fig. 3. IEhat is to say, the elements 'i3 to il, considered alone, constitute electrodes for mutually reacting with the beam, while in cooperation with one another and with the shell 83, they form a feedback system for assuring oscillatory operation of the system as a. whole. The longitudinal dimensions of the electrode elements are so correlated with the average velocity of the electron. beam traversing the envelope shaft 6u as to assure effective reaction therewith at a' desired frequency of operation of the apparatus. 4

In accordance with the principles previously set forth, it is necessary, in order to obtain the desired operation of the system, that the end-toend capacities betwen the various electrode elements be so adjusted as to secure resonancey with the elements themselves. In order that this adjustment may be made with the desired neness, there are provided a series of conductive bands 95 to t@ which are slidingly supported on the insulating rings 'I8 to 8l in regions overlapping the gaps which separate the electrode elements. The gap capacity is obviously a function both of the size-and of the' position of theserings. Consequently, by making'the rings of 4appropriate longitudinal extent and by regulating their posi'- tion, it is possible toadjust the interelectrode capacity to any desired value within reasonable Under certain circumstances it may be desirable to change the normal frequency of operation of the'oscillating system. To this end the capacity-controlling rings 33 to 3l are mechanically connected with a movable rod (constituted of a suitable dielectric material, such as quartz) which can be moved longitudinally of the discharge envelope so assimultaneouslyto alter the position of the various rings. An externally accessible actuating element I0| makes such adjustment readily practicable. It will be understood that each adjustment of the gap capacity to alter the resonant frequency of the system requires a corresponding adjustment of the eifective electrode length (as referred to the beam). 'This latter adjustment is made by varying the beam velocity to an appropriate degree.

Radio frequency power may be taken from the oscillating system by means of a plate-like member |03 which provides capacity coupling to one extremity of the electrode element 15. This member is associated with concentric conductors |04 and |05 which constitute a transmission line system for connection to an externalcircuit.

The foregoing has included an explanation ofl In the arrangement illustrated, there is pro-' vided an electron-beam-producing means including an elongated envelope |I0 which encloses a cathode I||, high voltage accelerating electrodes I|2, and an anode |I3. (In a practical construction this may be replaced by a tube of the character shown in Fig. 8.) Surrounding the end of the beam path which is nearer the cathode there is provided an input system comprising an electrode arrangement of the general type previously described herein. This comprises a series of tubular elements 4, ||5 and H5, successively arranged along the beam axis and concentrically surrounded by a conductive shell ||3. The element I 5 is of such length that the electron transit time therethrough corresponds as nearly as possible to a complete cycle of potential variation at the desired operating frequency. A resonant condition oi' the system as a whole is obtained by balancing the capacitive coupling which exists between the ends of the element ||5 and the adjacent elements ||4 andfl|6 against the distributed. constants of the various elements.

Inorder to energize the electrode system thus described so as to produce a desired modulation of the electron beam, there is provided in proximity to one end of. the electrode element Ill, a plate-like member which serves as an input coupling means. The member |20 is connected through a pair of concentric conductors |2| and |22 to an exciting source such as an oscillator |23. T'he energy supplied by/the oscillator |23 serves to excite the electrode system to resonant voperation so that in-phase voltages are developed across the gaps |25 and |23 in accordance with the principles already explained.

' Inasmuchas the losses of the system are supplied externally from the power source |23, it is unnecessary that the electrode system itself exhibit negative conductance such as is required for oscillator operation. Consequently, the length of the electrode I I5 may be made precisely 360 (or as near thereto as is practical); AOf l course, if energy feedback is desired for any reaaaaaaoa 5 son, the electrode element' ||5 can be made somewhatlessthan 360 in length.

The effect of the electrode structure thus de- 5 characterized by variations in electron -velocity from point to point along its length.' In accordance with principles already explained, these Y velocity variations are converted into'charge density variations as the beam progresses along l the axis of the envelope ||0.

' At a point somewhat displaced from the input' electrode structure there is provided afurther electrode system adapted to serve for output purposes. Like the input structure.. this comprises a series of electrode elements |28 to |32 which are enclosed within a cylindrical conducting shell |33 and which are separated by a plurality of gaps |34 to |31.

The action of the charge density modulated beam in traversing any of the intereiectrode gaps is to induce a current flow in the electrode structures which bound the gaps. For present purposes it is desired that the currents inducedat the various gaps be unidirectional and additive at any given: instant, this end being best served when the length of the individual electrodes corresponds to the spacing between two adjacent charge density maxima in the beam. It will be found that this condition is fulfilled when the electrode length is 360 in terms of beam velocity so that the average electron transit time through the electrode corresponds to one full cycle of the potential variation. The effect of the beam in traversing the various gaps |34 to |31 will be4 stood that if the impedance oi.' the load circuit including the transmission line elements |4| and |42 is properly matched to the characteristics of the output electrode system, the current induced in the electrode system may be caused to develop a very high voltage across the load.

In the structures so far described the various high frequency electrodes have been shown as being all of'identical form. While this arrangement is preferred because ofthe higher operating emciency which it realizes, it is not an essential attribute 'of my invention, and in Fig. 11 I have shown an alternative embodiment in which it is not utilized.

In this case a'tube |50, shown broken away, is assumed to serve as a confining means for an electron beam (of which the source is not indicated). The beam' successively traverses a series of tubular electrode elements |52 to |55,v

these being in turn surrounded by a conducting shell |53.

" -The electrodes |53 and |55 are taken to be on the order of 360 in length (so that the electron transit time therethrough corresponds approximately to a full cycle of the operating potential), while the electrode |54 is onthe order of twice this length. The electrode sections |52 and |54 aaeaooa y Vlished and the system is operating in an excited condition as a result o the pressure of an electron beam therethrough, the instantaneous potential distribution along the electrode struc-- ture will be approximately as indicated by the irregular saw-tooth curve D of Fig. 12. Under these circumstances cumulative effects are obtained at the `various gaps, as previously explained.

The negative conductance which is requisite to oscillator operation can be secured by shortening the various electrodes to the necessary degree. As an alternative to shortening all the electrodes, certain electrodes only may be shortened. For example, the electrodes E53 and i563 may be made 36il in length and the electrodes H52, i5@ and' ISS shortened by the appropriate amount. With an' arrangement such as that last specified, the length oi. electrode ld is preferably set at about 360 and the length of electrodes 52 and i5@ at one half this value. Power may be taken from the system by means of a capacitive element l@ coupled to one extremity of electrode i.

A.still further possible variation of structure is that shown in Fig. 13. In this case the high frequency electrodes (numbered it@ to 635) are not terminally connected to the. outer shell (it) as in the arrangements previously described. On the contrary, terminal couplingis accomplished by providing the end electrodes it@ and 65 with extensions, measured from a to b and a' to h respectively, which constitute quarter wavelength transmission line sections or, alternatively, odd multiple quarter-wave sections.

Under these circumstances, standing waves may be established along the electrodes it and E65, which Waves have voltage minima at a and a respectively. The resultant voltage distribution along the electrode system is as indicated by the saw-tooth curve E of Fig. 14. It will be seen that as far as modulating action is concerned, the arrangement of Fig. 13 is substantially the same as that oi the construction of Fig. 3. However, some longitudinal potential gradients will exist at the open ends b and b of the quarterwave sections and will add to the mutual reaction of the beam and the electrode system. If calculations in a given case indicate'that this factor is of appreciable value, it should, of course, be taken into account in designing the system.

If desired for mechanical reasons, the construction of Fig. 13 may be' combined with that of Fig. 3 by utilizing the direct electrical connection of the former gure at one end of the electrode system and employing transmission line coupling at the other end. Also, the coupling means of .Fig. 13 may be further modified by providing some form of lumped capacitance at the electrode extremities to permit shortening of the quarter-wave sections.

An arrangement such as that of Fig. 13 may be variably tuned by the use of 'means for varying the eective length of the terminal electrode. This feature is illustrated in Fig. 15 in which the parts IBB', ISE', and |68' (shown broken away) correspond in nature and function with the similarly numbered elements of Fig. 13.

For the purpose stated in the preceding paragraph the extremity of the electrode |60' is provided with a sleeve which can be moved amally as desired. This sleeve may be used to adjust the dimensions of the quarter-wave transmissionl "line section to cause it to function effectively for a plurality of dierent frequencies at which itj is desired to operate the system as a Whole.

Another attribute ofthe construction of Fig.

13 is that it permits the high frequency electrodes to be placed within the discharge tube so as to be separated from the cooperating conductive shell by the Wall of the tube. This may be done,

for example, in the manner indicated in Fig` 16y wherein l'the electrodes are shown at i3d and it and the shell at ist". The Wall of the envelope is indicated at lli. This construction is especially advantageous when design considerations make it desirable to position the electrode surfaces relatively close to the beam.

While have described my invention by reference to particular embodiments thereof, it may be understood that numerous additional modifications may be made by those skilled in the art without departing from its principles. l, therefore, intend to cover in the appended claims all such variations as fall within the true spiritand scope oi' the foregoing disclosure. What I claim as new and desire to secure by Letters Patent of the United States is;

l. lin electronic apparatus having means for producing an electron beam, a resonant electrode system including a conductive structure surrounding the beam for an appreciable portion of its path length, a conductive tubular element posiltioned within said structure so as to `be axially traversed by the beam, the length of said element being so correlated to the beam velocity that the average electron transit time through the element is on the order of thetime consumed by an integral number of complete cycles of potential variation at the desired operating frequency of 2. In electronic apparatus having means for producing a beam of electrons, a resonant elec-` trode system including a series of tubular electrode elements arranged in mutually spaced relation to provide a plurality of gaps which are successively traversed by the beam, said elements being dimensionallyporrelated to the beam veiocity-so thatthe average electron transit time through each element is on the order of the time consumed by an integral number oi complete cycles of potential variation at the desired operating frequency of the apparatus and departs ,therefrom by no more than the period of a quarter cycle of such variation, and an elongated conductive structure concentrically surrounding the said tubular elements, the capacitance across each of the said gaps being matched to the distributed constants of the elements and the `conductive structure, 'whereby upon excitation of the said electrode system, the potential gradients -ocstant are similarly directed.

' curring across the various gaps at any given in- 3. An electronic apparatus having means for producing a beamof electrons, the combination which includes a series of .tubular electrode elements arranged in mutually spaced relation to provide a plurality of gaps which are successively traversed by the beam, said elements being dimensionally correlated to the beam velocity so that the average electron transit time through each element is onthe order of the time consumed by an integral number of complete cycles of potential variation at the desired operating frequency o f .the apparatus and departs therefrom -by no more thanA the period of a quarter cycle of such variation, an elongated conductive structure concentrlcally surrounding the said .tubular elements and means associated with .the said elements at said gaps for matching the capacitance of the gaps to the distributed constants of the elements and the conductive structure, whereby upon excitation of the resonant. electrode system which is formed by said elements and said conductive structure, the instantaneous potential gradients occurring across the various gaps are similarly directed.

4. Electronic -apparatus comprising an elongated tubular envelope, a series of tubular conductive elements surrounding the envelope at spaced points along its length, insulating means interposed between the various tubular elements so as to establish fixed gaps between them, a conductive structure concentrically surrounding the said tubular elements and forming therewith a resonant electrode system, means associated with each of said gaps for correlating the capacitance of the gaps to' the distributed constants of the tubular elements and conductive structure, thereby to permit resonant operation of the electrodesystem at a frequency corresponding to thedesired frequency'of operation ofthe apparatus,

means within the envelope forprojecting an electron beam axially thereof at a velocity which is so correlated to the dimensions of the tubular envelope as to assure the occurrence of cumulative effects at the various gaps as a result of the electrical interaction of the beam and the elements at such gaps and means coupled to the electrode system for abstracting energy therefrom upon passage of the electron beam therethrough.

5. In electronic apparatus having means for producing a beam of electrons, a series of tubular electrode elements arranged to be axially traversed by the Ibeam, the elements being mutually spaced to provide a plurality of gaps, and the axial dimensions of the elements being correlated to the average velocity of the beam and to the desired frequency of operation of the apparatus, a conductive structure surrounding the said tubular elements and forming in combination therewith a resonant system, means associated with each 'of said gaps for matching the capacitance of. the gaps to the distributed constants of said said tubular elementsand forming in combination therewith a resonant system, a series of conductive bands positioned coaxially with said tubular elements at points adjacent said gaps..

the said bands serving to match the capacitance of the gaps to the distributed constants of the said resonant system so as to facilitate operation of the apparatus at a desired frequency, and` means for producing axial adjustment of the bands to vary the operating frequency of the apparatus.

'1. In combination, means for producing a beam of electrons, a Vseries of tubular elements arranged to be axially traversed by the beam, said elements being mutually spaced to provide a plurality of gaps between them, a conductive structure surrounding the said elements and forming therewith a resonant standing wave system by virtue of the distributed constants of the elements and the structure, means for modulating the beam prior to its traversal of the said elements thereby to produce excitation of the said resonant system, and means coupled to the said resonant system for abstracting energy therefrom uponexcitation of the system.

8. A method of operating a high frequencyA electronic device having -a series of coaxially spaced tubular electrodes and a conductive structure forming with said electrode an electrical system which is adapted to resonate at a particular frequency; which method comprises projecting an electron beam axially through said electrodes atsuch velocity that the electron transit time through a single electrode is on the order of the time consumed by an integral number of complete cycles of potential variation at the said particular frequency but departs theremutual reaction of the beam and the resonant A system resulting in modulation of the former and excitation o f the latter at the said particular frequency.

9. A method of operating a high frequency electronic device having a series of dimensionally similar tubular electrodes arranged in axially spaced alignment to provide a plurality of interelectrode gaps and a conductive structure concentrically surrounding the electrodes so as to form therewith an electrical systemadapted to resonate at a particular frequency; which method by to procure mutual reaction ofthe beam and the resonant system resulting in excitation of the latter, and abstracting energy from the resonant system for utilization outside the system.

10. In hi'gh frequency apparatus, the combination which includes means for producing a beam of electrons, a series of tubularconductive elements which are arranged to be axially traversed by the beam and which are mutually spaced to provide a plurality of gaps between them, at least several of the successive intermediate elements being electrically isolated in the sense of having no direct electrical connection to any other conductive part of the appa-l ratus, a conductive structure surroundingv the said tubular elements and forming therewith a standing wave resonant system by virtue of the distributed constants of the structure and thek elements, the` said system being maintained in excited condition during operation' of the apparatus by mutual reaction with the beam at the lsaid gaps, and! means coupled to the said resonant system for abstracting energy therefrom for utilization outside the system.`

11. In high frequency apparatus, the combination which includes means for producing a beam of electrons, a series of tubular conductive elements which are arranged to be axially traversed by the beam and which are mutually spaced to provide va plurality or gaps between them, all of the said elements being electrically isolated in the sense of having no direct electrical connec-i tion to, any other conductive part of the apparatus. a conductive structure surrounding the said elements and forming therewith a standing wave resonant system by virtue ofthe distrlb uted constants oi' they structure and the elements, the said system being maintained in excited condition during operation of the apparatus byv mutual reaction with-the beam at the said gaps, and means coupled to the said resonant system for abstracting `energy therefrom for utilization outside Ithe system l12. In high frequency apparatus. the combination which includes means for producing a beam of electrons, a series of tubular conductive ele- 1 ments which are arranged to be axially traversed -by the beam and which are mutually spaced to provide a plurality oi gapsbetween them, all of the saidV elements being electrically isolated in the sense o f having no direct electrical connection to any other conductive part of the apparatus, a conductive structure surrounding-the said elements and forming therewith a standing wave. resonant systemwhich is maintained in excited condition by mutual reaction with the` beam at the said sans. capacitance-increasing' means associated with the end -ones oi.' the lsaid elements to provide a desiredterminal coupling 40gbetween the elements andthe said conductive 45 13. In high frequency electronic apparatus, the

structure without a direct electrical connection therebetween, and means' coupled to the said resonant system for abstracting energy therefrom for utilization outside the system.

combination which includes means for producing a beam of electrons, an elongated hollow structure surrounding the path of the said elec-A tron beam, a series of coaxial tubular conductive elements arranged concentrically within the said structure so as to be axially traversed by the beam, all of the said elements being electrically visolated in the sense of having no electrical connection to any other conductive part of the apparatus but, nevertheless, forming a standing wave resonant system with the said conductive structure by virtue of the distributed constants of the.

yelements and the structure, means supporting ductive structure without a direct electrical. conl' nection therebetween.

14. In high frequency electronic apparatus, the combination which includes meansy for producing a beam of electrons. a series of tubular conductive elements which are arranged to be stxially traversed by the beam and which are mutually spaced Ato providea plurality of gaps be-l tween them, all of the said elements being electrlcally isolated in the sense of having no direct `electrical connection to any other conductive part o! the apparatus, a conductive structure 35 surrounding the said elements and forming therewith a standing wave resonant system which is kmaintained in` excited condition by mutual reaction with the electron beam' at the said gaps, 'theend ones of the said elements being vlonger than the remaining elements so that they provide a desired terminal coupling between the elements and the said conductive .structure without a direct electrical connection between them.

- WILLIAM QHAHN.'