US3248593A

US3248593A - Multiple beam radio frequency apparatus having cooperating resonators and mode suppression means

Info

Publication number: US3248593A
Application number: US173725A
Authority: US
Inventors: Theodore G Mihran; Malcolm R Boyd
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1962-02-16
Filing date: 1962-02-16
Publication date: 1966-04-26
Anticipated expiration: 1983-04-26
Also published as: US3248594A

Description

April 1965 T. ca. MIHRAN ETAL 3,248,593

MULTIPLE BEAM RADIO FREQUENCY APPARATUS HAVING COOPERATING RESONATORS AND MODE SUPPRESSION MEANS Filed Feb. 16, 1962 2 Sheets-Sheet 1 E PO ER 8 HEATER JUPPLY [nverv tor-s,-

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PHASE SH/FT PER SECTION A n Aplll 1966 T. G. MIHRAN ETAL 3,248,593

MULTIPLE BEAM RADIO FREQUENCY APPARATUS HAVING COOPERATING RESONATORS AND MODE SUPPRESSION MEANS Filed Feb. 16, 1962 2 Sheets-Sheet 2 MAX [r7 ventor's: Theodore G: M/hr-dn,

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United States Patent MULTIPLE BEAM RADIO FREQUENCY APPARA- This invention relates to multiple-beam radio frequency (r.f.) apparatus adapted for generating and handling relatively 'high electromagnetic wave power at relatively high frequencies and more particularly to the suppression of undesired modes of operation in such apparatus.

In copending US. application S.N. 173,724 of M. R. Boyd et al. filed concurrently herewith and assigned to the same assignee as the present invention, there is disclosed and claimed multiple-beam radio frequency apparatus which is adapted for generating and handling substantially high electromagnetic wave power at microwave frequencies and in a manner effective for attaining maximum-etficiency energy exchange between the beams and electromagnetic waves in cooperating resonators and for minimizing mode interference problems of the type theretofore encountered in multiple-beam devices. lieved that by following the teachings of Boyd et al. power output increases of one order of magnitude can be obtained over prior microwave power generating devices. However, it is also believed that an attempt to increase the output to two or more orders of magnitude, which would involve the use of a hundred electron beams or more, would lead to interference between adjacent modes.

The present invention contemplates the provision of multiple beam radio frequency apparatus constructed according to the mentioned Boyd et a1. invention and further constructed to include new and improved means for suppressing undesired modes and thus is adapted for making realizable power increases of more than one magniude.

Accordingly, it is an object of this invention to provide new and improved multiple-beam radio frequency apparatus adapted for increased microwave energy generating and handling capacities.

Another object of this invention is to provide multiplebeam radio frequency apparatus including new and improved means for suppressing operation thereof in undesired modes.

Another object of this invention is to provide multiplebeam radio frequency apparatus adapted for maximumefliciency energy exchange between the beams and electromagnetic waves in cooperating resonators thereof and means whereby undesirable modes are attenuated without adversely affecting such maximum efliciency energy exchange.

Another object of this invention is to provide multiplebeam radio frequency apparatus adapted for attenuating undesired modes without adversely affecting the desired mode of operation or the amount of frequency separation between that mode and adjacent undesired modes.

Other objects and advantages of this invention will become apparent as the following description proceeds and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of this invention, and according to one embodiment thereof, there is provided mul tiple-beam radio frequency apparatus comprising input, output and preferably at least one intermediate, longitudinally-resonant waveguides supported in spaced parallel relation. Extending perpendicular to and in cooperative association with the waveguides are a plurality It is be-' of parallel klystron-like beam devices. Each such device includes a plurality of axially-spaced drift tubes defining input, output, and one or more intermediate, interaction gaps each located in a respective one of the mentioned waveguides, an electron gun for projecting a beam of electrons through the drift tubes past the interaction gap and a collector for collecting electrons emerging from the last drift tube. In each waveguide the interaction gaps, defined by the opposed ends of adjacent drift tubes, comprise equally-spaced active capacitive elements, and interposed midway between each pair of active elements therein is a passive, or dummy, capacitive element having a capacitance value substantially equal to that of an active element. Further, the periodic electrical spacing between adjacent capacitive elements and between the outermost capacitive element and adjacent end walls in each waveguide is made equal to one quarter of the loaded guide wavelength at a predetermined operating frequency. Suitable means is provided for exciting the input waveguide to establish therein a standing electromagnetic wave of the aforementioned frequency which results in the occurrence therein of an electric field maximum at each active capacitive element in the input waveguide and a voltage node at each passive capacitive element. Thusly, and in accordance with the invention of the above-mentioned Boyd et a1. application, the apparatus is adapted for cooperative maximum-efficiency energy exchange between the wave in the input section and all of the beams passing therethrough for effecting velocity modulation of the electrons in the beams which results in the electrons becoming density modulated in the subsequent field-free drift regions. The density-modulated electrons coopera tively excite similar standing waves in the intermediate waveguides which results in further density modulation of electrons in subsequent drift regions and, finally, the density-modulated electrons cooperatively, and with maximum-efiiciency energy exchange, induce a corresponding amplified electromagnetic wave in the output waveguide wherein the electric field maxima occur at the active gaps and the voltage nodes at the passive elements. The electromagnetic wave energy is extracted from the output waveguide by any suitable means. When the device is operated so that the mentioned field maxima and minirna occur, respectively, at the active and passive gaps the device is adapted for 1r/ 2 mode which is desirable in that in such operation the mentioned maximum-efficiency energy exchange and maximum mode separation are attained. In order to attenuate any undesired modes without adversely affecting the advantages obtainable in 1r/2 mode there is provided, according to the present invention, resistive elements at the same locations as the passive capacitive elements. Thus, at such location there is provided impedance means, each constituting a combination of a capacitive reactance and a resistance; and when the apparatus operates in the desired 1r/2 mode, a voltage node occurs at the passive impedance means and the resistance element will have no effect on the standing waves and resonators. However, if the apparatus should tend to operate in an adjacent undesired mode, or one other than 1r/2, the undesired mode will have electric field components occurring at each of the passive impedance means and the resistive elements thereof will attenuate the electric field components, whereby the undesired mode will be effectively attenuated without adversely affecting the desired rr/ 2 mode of operation. The passive impedance means, whereby combined resistance and capacitance components are provided, can assume various alternative forms according to the present invention. For a better understanding of the invention reference may be had to the accompanying drawing in which:

FIGURE 1 is a sectional view of a multiple-beam electric discharge device constructed according to one embodiment of the invention;

FIGURE 2 is a sectional view taken along the lines 22 in FIGURE 1 and looking in the direction of the arrows;

FIGURE 3 is a sectional view taken along the lines 3--3 in FIGURE 1 and looking in the direction of the arrows;

FIGURE 4 is an W-B diagram illustrating the maximum mode separation attainable in 1r/ 2 operation;

FIGURE 5 is a schematic illustration of the electric field distribution in the apparatus of FIGURE 1 in 1r/ 2 operation;

FIGURE 6 is a schematic illustration adapted to show the attenuating effects of the periodic passive impedance means in the present structure when the apparatus tends to operate in other than 7r/ 2 mode;

FIGURE 7 is a detailed illustration of a specific form of combined resistance and capacitive reactance impedance means employable according to the present invention; and

FIGURE 8 is a modified form of combined resistance and capacitive reactance impedance means also employable in the present invention.

Referring now to FIGURE 1, there is shown multiplebeam radio frequency amplifying apparatus constructed in accordance with the invention. More specifically, the arrangement of FIGURE 1 is an electric discharge device in which D.C. energy from four electron beams is converted into electromagnetic wave energy to afford a multiple-beam device having substantially four times the power generating and handling capacities as a single-beam klystron of comparable beam. dimensions and which is, according to the present invention, adapted for attenuating or suppressing other than 1r/2 modes. However, from the outset, it is to be understood that the modesuppressing means to be disclosed in detail hereinafter can be used with multiple-beam devices having more or less than four electron beams.

The device of FIGURE 1 is constructed as a unitary evacuated envelope comprising four longitudinally resonant waveguides designated 1-4 arranged in spaced parallel relation and a plurality of transversely extending, equally-spaced cooperating klystron-like beam devices designated 58. In this arrangement, and according to the invention of the above-referenced Boyd et a1. application, each of the waveguides 1-4 is a short-circuited or longitudinally resonant section of a periodically-loaded waveguide. The waveguides are preferably rectangular in cross-section as shown; however, it is to be understood and it will be appreciated from the following disclosure, that the invention is not limited to use of waveguides of this particular cross-sectional configuration and, in fact, in some applications resonant sections of other forms of transmission lines, such, for example, as line-over-groundplane transmission lines, are employable.

The lowermost waveguide 1 in FIGURE 1 constitutes an input resonator and is adapted to be excited for having a standing electromagnetic wave established therein by any suitable radio frequency input coupling means, such as an inductive coupling loop 11 seen in FIGURES 2 and 3. In a manner generally similar to that well known in the klystron art, the input resonator is effectively employed to velocity modulate the electrons in the beams of the devices 5-8. The uppermost Waveguide 4 in FIGURE 1 constitutes an output resonator and is adapted for having an amplified electromagnetic wave induced therein through the cooperative interaction of all of the beams and the wave established in the output resonator. Energy is extracted from the output resonator by any suitable radio frequency output means such as an inductive coupling loop 12 (FIG. 3). Interposed between the input and output resonators 1 and 4 are

intermediate resonators

2 and 3 which are shown as two in number but which can be employed in any desired number. The

intermediate resonators serve to increase beam modulation and bunching efiiciency in generally the same wellknown manner as intermediate resonators found in the klystron art.

The frequency characteristics of each of the resonators is selectively variable to some extent by adjustable short circuits in the form of sliding conductive end members 15 which, as seen in FIGURE 1, can be located at both opposed ends of each waveguide and can be provided with flexible hermetic sealing means 16 to maintain a vacuum in the structure.

In accordance with the above-mentioned invention of Boyd et al., the waveguides 1-4 are each periodicallyloaded with alternate active and passive capacitive elements. More specifically, the beam devices 5-8 each include a plurality of axially-spaced and aligned tubular sections 17 each having at least one end thereof sealed and extending reentrantly in one of the waveguides. In the waveguides the opposed ends of sections 17 define active capacitive gaps 20 and the ones of the sections extending between waveguides constitute drift tubes. An emitter generally designated 18 in each of the gun sections of the devices 5-8 projects a beam of electrons through the aligned section 17 and across the several interaction gaps 20, which electrons are finally collected in a collector 21 sealed to the endmost tubular section 17. The resonator assemblies are surrounded by solenoid coil 22 to provide a collimating magnetic field for focussing the electron beam. The coil 22 is enclosed in a casing 23 formed of a material of low reluctance, such, for example, as soft iron, to provide a uniform axial magnetic field within the region through which the electron beams pass. The electron guns 18, which can be positioned outside the casing 23, can be supplied with operating potentials by any suitable means known to those skilled in the art and generally indicated in FIGURE 1.

The active gaps 20 have uniform capacitance values across each waveguide and, as seen in the drawing, are periodically, or uniformly equally spaced, along each waveguide. Also in accordance with the mentioned Boyd et al. invention there is provided midway between each pair of adjacent active gaps in each resonator a passive, or dummy, capacitance 24 as hereinafter described having a value substantially the same as the capacitance value of one of the active gaps 20, and the outermost ones of the gaps 20 are spaced from the effective end walls of the resonators by amounts equal to the spacing between adjacent active and passive gaps. Thus, the present device is adapted for affording the operating advantages obtainable with the structure disclosed and claimed in the Boyd et al. application when that structure is operated in 1r/2 mode. More specifically, in 1r/2 operation the field maxima and minima occur, respectively, at the active and passive gaps in each waveguide which results in maximum-efficiency energy exchange between the electron beams traversing the active gaps and waves in the waveguides. Also, and as shown in FIGURE 4, in 1r/ 2 operation there is maximum frequency separation between the 1r/2 mode and adjacent modes which is desirable in that it minimizes any tendency for the apparatus to operate in adjacent undesired modes. Expressed in another manner, while the 1r/ 2 mode of operation provides maximum frequency separation of adjacent modes, the frequency separation of these adjacent modes in devices having large numbers of beams may be undesirably close. For example, a beam circuit will have 100 possible modes of operation spaced only 1% or less apart in frequency. Inasmuch as the output cavity for such klystrons may typically have a loaded Q in the hundreds, the half power point of the desired 1r/2 mode may well correspond with the half power point of an adjacent mode and the device may tend to operate in this adjacent mode. The present structure is adapted for attenuating and suppressing modes other than 1r/2 mode and thus further minimizing any tendency for the apparatus to operate in the mentioned adjacent modes and thereby enabling use of greater numbers of electron beams. This is accomplished by providing at the points midway between the active gaps passive impedance means generally designated 24 in FIGURE 1 and adapted for providing both a resistive element as Well as the capacitance required for the practice of the invention of Boyd et al. More specifically, and according to the present invention, each of the impedance means 24 constitutes a parallel combination of a capacitive reactance, or the passive capacitive gap referenced above, substantially equal in capacitance value to the capacitance of the active gaps and a resistance element adapted for high electrical loosiness.

In ordinary operation in the desired 1r/2 mode the mode pattern in each waveguide 1-4 is as illustrated in FIGURE 5 and the field maxima and minima occur, respectively, at the active gaps 20 and the impedance means 24. includes capacitive reactance substantially equal to that of the active gaps 20, the apparatus is adapted for operating so as to attain the advantages of the Boyd et al. invention. However, should the apparatus tend, for example, to operate in the next adjacent mode, such as the 31/8 mode, in the manner shown in FIGURE 6, the voltage nodes will not coincide with impedance means 24 with the result that currents will flow across the resistive elements thereof and thereby introduce losses at these points. As seen in FIGURE 6, the losses introduced by the resistive elements causes the voltage wave form to be attenuated substantially in the 31r/8 mode. The same would occur at the 51r/8 mode or any mode other than 1r/2.

Thus, in 1r/2 operation of the presently disclosed structure the resistive elements of the impedance means 24 have no effect on the above-discussed desired operation of the apparatus in view of the appearance of voltage node-s at these points. However, should the apparatus tend to operate in other than 1r/ 2 mode the voltage nodes and resistive elements will not coincide, with the desired result that electrical losses will be introduced which will have the desired efiect of attenuating, 'or damping, the other than 1r/ 2 mode. Also, and as indicated above, this desired attenuation is attained without subtracting from the capabilities of the apparatus in realizing the advantages discussed above and obtainable with the Boyd et al. invention.

In FIGURE 1 the means 24 are generally indicated and, according to the present invention, any suitable means effective for providing the required parallel combination of resistance and capacitive reactance can be employed as the mentioned passive impedance means. However, in FIGURE 7 is illustrated a waveguide res-onator incorporating a particular embodiment of impedance means employ-able in the present invention and effective for providing the desired combination of electrical characteristics. In this embodiment a waveguide, which can be any one or more of those designated 1-4 in FIGURE 1, is periodically loaded with alternate active capacitive gaps 20 and impedance mean-s generally designated 25. The passive impedance means in this form each comprise a conductive member 26 having a relatively high resistance conductive member 27 interposed between each end thereof and the adjacent walls of the waveguide. If desired, the members 26 can comprise copper posts and the members 27 can comprise ceramic disks impregnated with a high-resistance conductive material. The conductive members 26 and the spaces between the ends thereof and the waveguide walls are such as to provide the desired passive capacitance which is substantially equal to the capacitance of active gap 20. Additionally, the combined resistance provided by the

members

26 and 27 in each passive impedance means is such as to satisfy the requirements for an electrically lossy element located midway between each adjacent pair of active gaps.

Inasmuch as the impedance means 24 each It will be understood from the foregoing that, if desired, the two resistive members 27 can be replaced by a single member disposed between one end of each of the members 26 and one wall of the waveguide providing'the resistance characteristic aiiorded thereby is satisfactory for introducing the proper amount of lossiness to modes other than 1r/2. Also, if desired, the disk-like members can, if appropriately dimensioned, define the capacity gap and have a high-resistance conductive member extending therebetween to provide the required resistance interconnection.

Illustrated in FIGURE 8 is another form of the present invention adapted for providing the required combined resistance and capacitive characteristics at the locations midway between the active gaps. In this embodiment the waveguide which also can be any one or more of those designated 1-4 in FIGURE 1, is periodically loaded with alternate active gaps 20 and impedance means generally designated 30. The impedance means 30 each comprise a pair of opposed cylindrical conductive members 31 which cooperate to provide a passive capacitive gap having substantially the same capacitance value as one of the active gaps 20. Extending coaxially in the members 31 and electrically interconnecting the opposed the active gaps and, for example, can comprise the same material of which the disks 27 in FIGURE 7 are formed. In this embodiment each of the impedance means 30 can, if desired, comprise only one cylindrical member 31 provided the latter extends an appropriate distance from the active waveguide wall and is of appropriate dimensions to aiford the required capacitance value. Also, it will .be appreciated, that if desired, the members 32 can be tubular with one or more of the members 31 extending therein.

It is to be understood from the foregoing that the present invention is not limited to unitary evacuated devices such as that illustrated in the drawing. The invention is equally applicable to apparatus such as that disclosed as the second embodiment of the mentioned Boyd et al. application and wherein the beam devices and wave-' guide resonators comprise discrete subassemblies with the beam devices detachably mounted in or coupled to external resonant transmission line or waveguide sections. In such an arrangement the tuning members and the passive impedance means would be mounted in the external waveguide or transmission line sections.

Further, the present invention is not limited to apparatus wherein the active capacitive gaps comprise the interaction gaps of beam-type devices. The present concept of periodically loading a resonant section of transmission line with alternate active and passive impedance means and wherein the passive impedance means includes resistive elements for attenuating undesired modes is applicable also to apparatus wherein other types of active gaps are employed, such, forexample, as the apparatus disclosed and claimed in the copending US. application S.N. 173,703 of R. A. Dehn, filed concurrently herewith and assigned to the same assignee as the present invention and wherein space-charge controlled devices are employed.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A multiple beam radio frequency apparatus comprising at least one longitudinally resonant section of transmission line periodically loaded by a longitudinally extending array of alternate active and passive impedance means of substantially equal capacitance values at the operating frequency of said apparatus, said active impedance means constituting interaction gaps, said impedance means being electrically spaced M4 length of wave energy in said waveguide when said waveguide is loaded for effective 1r/2 mode operation, means directing electrons across said interaction gaps for enabling energy exchange between said elements and an electromagnetic wave on said line, and said passive impedance means each including means providing a capacitive reactance substantially equal in value to the capacitance of said interaction gaps and an adjacent high resistivity conductive path across said line said passive impedance means acting as mode suppression means in said apparatus for other than the 11/ 2 mode.

2. A multiple beam radio frequency apparatus comprising at least a pair of spaced longitudinally-resonant waveguides each periodically loaded by a longitudinallyextending array of alternate equally-spaced active and passive impedance means said means being electrically spaced /4 the length of wave energy in said waveguide when said waveguides are loaded at a predetermined operating frequency at the 1r/2 mode, the active impedance means of each waveguide constituting interaction gaps and being aligned with respective gaps of the other waveguide, means directing electrons successively across the respective gaps of first said one and then the other waveguide, and said passive impedance means in at least one of said waveguides each comprising an adjacent parallel combination of a capacitive reactance equal in capacitance value to one of said interaction gaps at the operating frequency of said apparatus and a high-resistivity conductive path between opposed sides of said waveguide.

3. Multiple-beam radio frequency apparatus comprising at least a pair of spaced longitudinally-resonant waveguides each periodically loaded by a longitudinally extending array of alternate equally-spaced active and pas sive impedance means being spaced A, the length of wave energy in said waveguide when said waveguides are loaded at a predetermined operating frequency in the 1r/2 mode, said active impedance means of each waveguide constituting interaction gaps of substantially equal capacitance values and being aligned with respective gaps of the other waveguide, said passive impedance means each including a capacitive element having a value substantially equal to the capacitance value of one of said interaction gaps at the operating frequency of said apparatus, means for establishing in one said waveguides a standing electromagnetic wave having electric field maxima and minima occurring, respectively, at said active and passive impedance means, means for projecting a plurality of discrete electron beams across said interaction gaps in first said one and then the other said waveguides and including drift-space-defining means located along said beams between said interaction gaps, whereby an amplified electromagnetic wave is induced in said other waveguide corresponding to said wave in said one waveguide and having electric field maxirna and miniina occurring, respectively, at said active and passive impedance means, said passive impedance means each further including an adjacent relatively high-resistivity conduction path extending across said waveguide, whereby said passive impedance means are effective for attenuating modes having voltage minima occurring other than at said passive means, and means for extracting radio frequency energy from said other waveguide.

4. In a multiple-beam radio frequency apparatus comprising a longitudinally resonant waveguide, said waveguide being periodically loaded by equally-spaced means defining alternate active and passive capacitive gaps between opposed walls of said Waveguide, said gaps being electrically spaced the length of wave energy in said waveguide when said Waveguide is loaded at a predetermined 1r/2 mode, said gaps having a capacitive value essentially equal at the operating frequency of said apparatus, said active gaps constituting interaction gaps adapted for having discrete electron beams projected thereacross in energy-exchanging relation with an electromagnetic wave in said waveguide, the improvement which comprises means in parallel with each said passive gaps providing a high-resistivity conduction path between said opposed walls of said waveguide and effective for attenuating and suppressing radio frequency energy of all modes except that having voltage nodes occurring at said passive gaps.

5. In a multiple-beam radio frequency apparatus comprising a longitudinally resonant waveguide, said waveguide being periodically loaded with equally-spaced active and passive impedance means between opposed walls of said waveguide, said means being electrically spaced along said waveguide A1 length of wave energy in said waveguide when said waveguide is loaded for operation in the 1r/2 mode, said active means constituting intermediate gaps adapted for having discrete electron beams projected thereacross in energy-exchanging relation with an electromagnetic wave in said waveguide, the improvement which comprises said passive means each comprising a conductive member extending between said opposed walls of said waveguide and separated therefrom by at least one intermediate relatively high-resistivity conductive member, whereby a capacitive gap and a highresistivity conduction path are provided, the capacitance of said capacitive gap being substantially equal to the capacitance of said active impedance means at the operating frequency of said apparatus.

6. In a multiple-beam radio frequency apparatus comrising a longitudinally resonant waveguide, said waveguide being periodically loaded by equally-spaced alternate active and passive impedance means between opposed walls of said waveguide, said means being electrically spaced At length of Wave energy in said waveguide when said waveguide is loaded for operation in the rr/Z mode, said active means constituting interaction gaps adapted for having discrete electron beams projected thereacross in energy-exchanging relation with anrelectromagnetic wave in said waveguide, the improvement which comprises said passive means each comprising a conductive member extending between said opposed walls of said waveguide and having each end thereof separated from said Waveguide by an intermediate relatively high-resistivity conductive member, whereby capacitive gaps and a high-resistivity conduction path are provided, the capacitance of said capacitive gaps being substantially equal to the capacitance of said active impedance means at the operating frequency of said apparatus.

7. in a multiple-beam radio frequency apparatus comprising a longitudinally resonant waveguide, said Waveguide being periodically loaded by equally-spaced alternate active and passive impedance means between opposed walls of said waveguide, said means being electrically spaced A length of wave energy in said waveguide when said waveguide is loaded for operating at a predetermined 1r/ 2 mode, said active means constituting interaction gaps adapted for having discrete electron beams projected thereacross in energy-exchanging relation with an electromagnetic wave-in said waveguide, the improvement which comprises said passive means each comprising at least one conductive member extending from one said opposed walls of said waveguide toward the other for defining therewith a capacitive gap having a capacitance substantially equal to the capacitance of said active impedance means at the operating frequency of said apparatus, and a cooperating relatively high-resistivity conductive member electrically interconnecting said opposed walls.

8. In a multiple-beam radio frequency apparatus comprising a longitudinally resonant waveguide, said waveguide being periodically loaded by equally-spaced alternate active and passive impedance means between opposed walls of said waveguide, said means being electrically spaced At length of wave energy in said waveguide when said wave uide is loaded for operation in the 7r/2 mode, said active means constituting interaction gaps adapted for having discrete electron beams projected thereacross in energy-exchanging relation with an electromagnetic wave in said Waveguide, the improvement which comprises said passive means each comprising at least one tubular conductive member extending from one said opposed walls of said waveguide toward the other for defining therewith a capacitive gap having a capacitance substantially equal to the capacitance of said active impedance means at the operating frequency of said apparatus, and a coaxial relatively high-resistivity conductive member electrically interconnecting said opposed walls.

9. In a multiple-beam radio frequency apparatus comprising a longitudinally resonant waveguide, said wave guide being periodically loaded by equally-spaced alternate active and passive impedance means between opposed walls of said waveguide, said means being electrically spaced in said waveguide 4 length of wave energy in said waveguide when said waveguide is loaded for operation in the 1r/2 mode, said active means constituting interaction gaps adapted for having discrete electron beams projected thereacross in energy-exchanging relation with anelectromagnetic wave in said waveguide, the improvement of said passive means each comprising a pair of coaxial conductive members extending from said opposed walls of said waveguide and defining a capacity gap having a capacitance substantially equal to the capitance of said active impedance means, at the operating 10 frequency of said apparatus, and a coaxial relatively highresistivity conductive member electrically interconnecting said opposed walls.

References Cited by the Examiner UNITED STATES PATENTS 2,458,556 1/1949 Bowen 3155.46 X 2,515,225 7/1950 Holst et al. 33383 X 2,682,641 6/1954 Sensiper 33383 X 2,745,910 5/1956 Dehn 33383 X 2,830,224 4/1958 Jenny 33383 X 2,875,376 2/1959 Havstad 33383 X 2,899,647 8/1959 Willwacher 33383 X 2,901,660 8/1959 Pearce et al 333-83 X 2,910,614 10/1959 Bondley 333-83 X 2,920,229 1/1960 Clarke 3155.16 2,934,672 4/1960 Pollack et al 333-83 X 2,944,233 7/1960 Fong 33383 X FOREIGN PATENTS 686,830 2/1905 Great Britain.

HERMAN KARL SAALBACH, Primary Examiner. ARTHUR GAUSS, Examiner.

c.o. GARDNER, s. CHATMON, ]R.,

Assistant Examiners.

Claims

1. A MULTIPLE BEAM RADIO FREQUENCY APPARATUS COMPRISING AT LEAST ONE LONGITUDINALLY RESONANT SECTION OF TRANSMISSION LINE PERIODICALLY LOADED BY A LONGITUDINALLY EXENDING ARRAY OF ALTERNATE ACTIVE AND PASSIVE IMPEDANCE MEANS OF SUBSTANTIALLY EQUAL CAPACITANCE VALUES AT THE OPERATING FREQUENCY OF SAID APPARATUS, SAID ACTIVE IMPEDANCE MEANS CONSTITUTING INTERACTION GAPS, SAID IMPEDANCE MEANS BEING ELECTRICALLY SPACED 1/4 LENGTH OF WAVE ENERGY IN SAID WAVEGUIDE WHEN SAID WAVEVGUIDE IS LOADED FOR EFFECTIVE /2 MODE OPERATION, MEANS DIRECTING ELECTRONS ACROSS SAID INTERACTION GAPS FOR ENABLING ENERGY EX-