US3760223A

US3760223A - Single conductor multi-coil multi-beam microwave device

Info

Publication number: US3760223A
Application number: US00279592A
Authority: US
Inventors: L Jasper
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1972-08-10
Filing date: 1972-08-10
Publication date: 1973-09-18
Anticipated expiration: 1990-09-18

Abstract

A traveling wave tube is provided with a low-wave, electron beam interaction means in the form of a single wire conductor coiled into at least two parallel series of aligned turns; in each series, the turns are of identical size and configuration. In one form, all the turns have rectilinear stretches of equal length that are in a common plane; an electron beam source, a collector, a sole electrode and electric and magnetic fields direct a sheet beam alongside the rectilinear stretches outside the turns. In another form, the turns of the single wire conductor are almost entirely circular and in figure-eight configuration viewed endwise; electron beams are directed through either one or both series of turns. In still other forms of the invention, the slowwave means viewed endwise has more than two turns and the axes are coplanar or in a circular distribution.

Description

United States Patent 1191 Jasper, Jr.

[ 1 Sept. 18, i973 1 SINGLE CONDUCTOR MULTI-COIL MULTI-BEAM MICROWAVE DEVICE [75] inventor: Louis J. Jasper, Jr., Neptune City,

221 Filed: Aug. 10, 1972 211 Appl. No.: 279,592

[52] U.S. Cl. ..31S/3.6, 315/35 1,168,573 4/l964 Germany 3l5/3.5

Primary ExaminerEli Lieberman Assistant ExaminerSaxfield Chatmon, Jr.

Attorney-Harry M. Saragovitz et al.

[ 57] ABSTRACT A traveling wave tube is provided with a lowwave, electron beam interaction means in the form ofa single wire conductor coiled into at least two parallel series of aligned turns; in each series, the turns are of identical [51] Int Cl H01 j 25/34 size and configuration. In one form, all the turns have [58] Field 3 5 X 3 5 rectilinear stretches of equal length that are in a common plane; an electron beam source, a collector, a sole [56] References Cited electrode and electric and magnetic fields direct a sheet beam alongside the rectilinear stretches outside UNITED STATES PATENTS the turns. in another form, the turns of the single wire I Kompfner conductor are almost entirely circular and in figure. 21925567 2/1960 f 5/35 X eight configuration viewed endwise; electron beams are directed through either one or both series of turns. In 3273081 9/1966 ltzkan 5"5 6 still other forms of the invention, the slow-wave means 3413512 11/1968 Buck..:::::: .11: 315/316 x Viewed endwise has than and the axes OREIGN PATENTS OR APPLICATIONS are coplanar or in a circular distribution. 856,013 12/1960 Great Britain 3l5/3.5 1 Claim, 4 Drawing Figures 82 RF SOURCE 34 LOAD e it...

86 W K 62 l ELECTRON BEAM SOURCE l o ELECTRON t BEAM GG/jv SOURCE /ff/ [1 I l I [II I I,

PAIEHIEUSEP I 8I975 I SIIEEI 1 If 2 FIG. 1 (Prior An) WITH ONE wAvE-BEAM' INTERACTION SPACE RF OUTPUT COLLECTOR ELECTRON BEAM SOURCE ELECTRICAL MEANS PROVIDING CONVENTIONAL DC VOLTAGES AND CURRENTS FIG. 2

RF OUTPUT RF INPUT 46I SLOW-WAVE ELECTRON BEAM SOURCE SWITCH COLLECTOR PROPAGATION COIL if? WITH Two WAVE-BEAM ELECTRON BEAM INTERACTION SPACES SOURCE ELECTRICAL MEANS PROVIDING CONVENTIONAL DC VOLTAGES AND CURRENTS PATENTED 3.760.223

SHI 2 BF 2 /82 FIG 3 RF SOURCE v 34 LOAD ELECTRON BEAM 64 SOURCE ELECTRON A/ EAM 66 SOURCE RF OUTPUT SINGLE CONDUCTOR MULTI-COIL MULTI-BEAM MICROWAVE DEVICE BACKGROUND OF THE INVENTION The most common form of slow wave means for a traveling wave tube is the wire conductor coil of identical aligned turns with a constant pitch, though coils may be designed with a pitch that changes along its length to compensate for slowing of the electrons in the beam as they give up energy. The geometry of the coil as seen endwise is related to whether the traveling wave tube is designed for O-type linear operation or for M- type crossed field operation. For O-type operation, the geometry of the slow-wave means, viewed endwise is a circle; for M-type operation, the geometry of the slowwave means viewed endwise is a loop that includes a rectilinear stretch. Regardless of the type of operation, the coil has been formed as a single series of aligned loops. In O-type operation, the electron beam is projected through the wire helix and the focusing field resists spreading of the beam eletrons laterally beyond the interaction space. In crossed field operation, a high current beam is projected and then redirected by a perpendicular magnetic field to a course that runs between a sole electrode and the coplanar rectilinear stretches of the coil for wave-beam interaction proximate to the rectilinear stretches of the coil. If the traveling wave tube is designed for as much power amplification as is practical, the beam voltage and beam current are made as high as is feasible, the focusing current is high, the wire'size of the coil must be large enough to carry the amplified RF and the collector must be designed for very high heat dissipation and the electron beam source must be designed to emit the high density beam.

Phase velocity of a propagated RF wave is related to the helix design i.e. the helix diameter and pitch. In the interaction space, the electron beam must have a velocity somewhat greater than the phase velocity to transfer energy to the RF wave. The electron beam accelerating voltage level is set to impart the correct velocity to the beam electrons for interaction and energy transfer to the RF wave. Beam current may be adjusted but the DC focusing field needs to be adjusted too for the resultant change in beam current density. If the tube needs to be operated at much higher power level during one time interval compared to that during another time interval, the tube needs to be designed to operate with the higher beam current though it may be operated at the lower beam current most of the time. Also, a traveling wave tube amplifier may have to operate in continuous-wave and pulse modes sequentially. Each time mode is switched, the power level at which the tube operates needs to be switched; in order that there be no loss in data which would occur during switching, the shift in power level needs to be essentially instantaneous. However, the DC focusing field and the beam voltage cannot be switched between widely different levels of operation at a rate fast enough for widely different levels of dual power operation. One problem is that the beam current does not continue in close proximity to the helical structure during and immediately following switching; there is degradation in gain and efficiency. It is well known that a 2:1- change in power level is about the maximum that can be tolerated with out adversely affecting efficiency to an unacceptable degree.

If two traveling wave tubes are connected in parallel to meet the above requirements, not only is the cost high but sophisticated phasing techniques are needed particularly for operation over a wide frequency band. If a traveling wave tube is made with two slow-wave helices connected in parallel and with two electron beam sources that can be energized singly or in combination, sophisticated phasing techniques are still required; additionally the input RF energy divides between the two paralleLmounted helices, a 3db drop prior to amplification.

SUMMARY OF THE INVENTION Instead of providing a traveling wave tube with a slow-wave coil of one continuous wire conductor having identical turns that are coaxial, this invention provides the traveling wave tube with a slow-wave multicoil of one continuous wire conductor that forms one complete element of the multi-coil by looping alternately clockwise and counterclockwise crossing over itself at least once to form two or more turns side-byside, e.g. a figure-eight or a chain of three or more turns side-by-side; the looping repeats to form a series of identical such elements in line and with a predetermined pitch. The geometry of the novel multi-coil viewed endwise may be a plurality of almost circular loops; the circles are incomplete to a minor extent at the crossovers. A multi-coil with circular loops may be operated with one beam projected through one of the sub-coils or with a plurality of beams up to the number of sub-coils projected through the respective sub-coils. For crossed field operation, the loops of the novel coil include rectilinear stretches that are of equal length and coplanar. The multi-coil with the rectilinear stretches is used with a single beam source.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. I is a block diagram of a conventional prior-art traveling wave tube and power supply;

FIG. 2 is a block diagram of a travelingwave tube and power supply, showing the primary feature of this invention;

FIG. 3 shows partly in perspective and partly in section, a traveling wave tube corresponding to FIG. 2 but with structural detail of the invention; and

FIG. 4 is a perspective showing of another embodi-.

ment of the invention in a crossed field device wherein the basic elements shown are without detail or electrical connections.

In FIG. I there is shown a conventional traveling wave tube in having. an elongated evacuated envelope 12 that supports therein an electron beam source I4 near one end of the envelope 12., a collector 16 near the other end of the envelope l2, and a slow-wave propagation coil 18 e.g. a helix. between the beam source 14 and the collector 16'. The slow-wave coil l8 has an input 20 for RF and an output 22 for coupling amplified RF to a load. The tube I'll has one wave-beam interaction space. Input RF traversing the slow wave coil 18 is accompanied by an electromagnetic wave field having a phase velocity in the beam direction which is a very small fraction of the free space velocity of the input RF. Electron beam 24 projected by beam source 14 has an average velocity somewhat greater than the phase velocity of the propagated electromagnetic wave whereby energy is transferred from the projected stream of electrons to the electromagnetic wave. A substantially uniform longitudinal magnetic field H is provided in the envelope between the beam source and the collector by a coil, periodic permanent magnet, etc. All conventional DC voltages and DC currents required for operating the tube are provided by electrical means 26.

In FIG. 2 there is shown a traveling wave tube 30 in an envelope 32 that differs from the prior art exemplified by FIG. 1 in that it includes two

electron beam sources

34, 36 and a slow-wavepropagation coil 38 with two wave-beam interaction spaces but having one RF path between input 40 and output 42 that produces the same electromagnetic wave in both ineraction spaces. One collector 44 is provided for the

beams

46, 48 emitted by the two electron beam sources. If necessary, the two beams may be of different powers. A switch 50 is provided to turn on or off, separately or together, the

electron beams

46 and 48. Electrical means 52 for providing conventional DC voltages and currents is coupled to collector 44 and slow-wave coil 38 as shown in FIG. 1 and in addition is connected to

electron beam sources

34 and 36 through switch 50. In its simplest form, switch 50 is a manual switch for connecting electrical means 52 either to one or to both

electron beam sources

34, 36. While only one connection is shown extending between each electron beam source andjelectrical means 52 via switch 50, each of the connections shown represent the several conductors that connect to the several elements of each electron beam source. The switch 52 may be connected so as to be operable to connect or disconnect the heater element of each electron beam source or to connect or disconnect cutoff bias to each electron beam source or to otherwise control the beams, between any current levels. Either

beam

46, 48 or both beams simultaneously, interact with the wave'propagated by the slowwave means 38 to amplify the RF. One advantage realized by using this arrangement is that the RF can be raised by any one of a plurality of multipower levels depending on the magnitude of the beam currents and the number of beams used or depending upon operational requirements. There are obvious advantages in this flexibility. If a traveling wave tube is fabricated to use two beams instead'of one beam of the same poweras the power of the two beams, beam voltage and beam current is lower, backward wave oscillations are minimized, and design factors are generally simplified. If the tube is fabricated so that each of the two beams is of equal power to what the power of one beam would have been, high power output can be obtained by operating both beams at the same time. The latter design also lends itself to push-pull operation, e.g. by using an 'Eccles-Jordan type circuit for switch to operate the two I beams alternately.v Push-pull operation avoids overheating any one of the elements.

In FIG. 3 there is showna traveling wave tube having an envelope 62 that supports therein, near one end, a pair of

electron beam sources

64, 66, a figure-eight multi-coil slow-wave circuit 68 and a collector 70 near the other end of the envelope. Dielectric ceramic rods 72 support the multi-coil in place in the conventional manner and also serve to dissipate heat during high power operation. The ends of the rods 72 are nested in or secured to support elements, not shown, that would be fixed in place in the envelope; the rods may be provided with an aquadag layer for attenuating backward wave energy. If the coil is viewed endwise, the wire of the multi-coil describes a figure-eight with identical loops almost all the way around except in the vicinity of the crossover. While it is not essential, it is preferable for the multi-coilloops to be essentially planar and for the crossovers to provide the pitch. The dominant mode supported by the figure-eight structure is characterized by large longitudinal electric fields similar to the characteristics of a TM mode. The multi-coil68 is aligned with the two electron beam sources so that focused beams projected by the respective beam sources and represented by the

broken lines

74, 76 are properly aligned with the interaction spaces of the multi-coil. The ends of the multi-coil are connected to conventional

RF coupling devices

78, 80. A source 82 of RF to be amplified is coupled to the beam source end of the coil and a load 84 is coupled to the other end of the coil. A focusing structure 86 surrounds the envelope 62. The traveling wave tube shown in FIG. 3 requires confined focusing because the two electron beams are not axial; the coil type focusing structure in FIG. 3 needs to extend over the beam source region, even though it means greater weight, in order that the projected beams shall be in an essentially longitudinal magnetic field. Periodic permanent magnet (PPM) focusing can be employed if the entrance conditions for the electron beams are adjusted for proper focusing. Also electrostatic focusing techniques may be substituted for the focusing structure if beam current density is low.

The multi-coil 68 may be fonned with three, four or more sub-coils rather than two as in the figure-eight to have the approximate appearance endwise of three-leaf or four-leaf clovers, etc. Also the sub-coils can be fabricated so that their axes are coplanar, a predetermined distance apart, or their axes can be arranged in an arcuate or circular distribution, a predetermined distance apart. The beam focusing problem is more complicated for an increased number of beams and is more complicated for smaller distances between beams.

It is within the scope of this invention for any of the described multi-coils to be formed without crossovers between adjacent turns.

In FIG. 4 there is shown a figure-eight multi-coil of a single conductor wire but having different geome- I try than the figure-eight multi-coil shown in FIG. 3. Each of the series of aligned loops 102 and 104 include

rectilinear stretches

106 and 108 respectively that are arrangement of electron emitter 114 and anode .116

oriented normal to and near one end of the slow-wave coil 100, a sole electrode 118 having a planar surface 1 19 parallel to the plane of the

rectilinear stretches

106 and 108 andcoextensive therewith, and a collector adjacent the other ends of the coil 100 and sole elec-' node 118. A magnetic field providing means, not shown, directs a magnetic field H normal to the direction between electron emitter 114 and anode 116 to bend the paths of electrons projected by emitter 114 into the space between the sole electrode 118 and the coil 100. The DC electric field is normal to the H field and in the sense to project the electrons toward the collector. The emitted electrons move in a sheet beam parallel to but outside the figure-eight coil. With the coil 100 wound in the manner described, the electron beam interacts with an essentially symmetrical RF structure. RF is coupled into the end 122 of the coil and an RF load is coupled to the other end 124 of the coil. All DC operating parameters are omitted since they do not constitute part of the invention; one skilled in this art can readily select a set of operating voltages and currents for a particular design of the elements described.

The geometry of the coil shown in FIG. 4 requires the coplanar rectilinear stretches but the rest of each loop need not be rectilinear with corners as shown on the drawing but may be curvilinear. Ease of fabrication governs the choice of geometry; however, all the loops must have the same geometry.

1 wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

What is claimed is:

1. ma traveling wave tube amplifier a slow-wave multi-coil of a single conductor that loops'alternat'ely.

clockwise and counterclockwise and from the longitudinal aspect intersects and crosses over itself between loops to form a plurality of series of aligned essentially circular loops wherein the number of loops in each of the plurality of series of loops is the same, and provid ing an equal plurality of interaction spaces, whereby RF conducted through the wire is accompanied by an electromagnetic wave .that traverses the plurality of interaction spaces in unison,

an evacuated envelope confining said coil therein, means supporting said coil in said envelope and being operable to attenuate backward wave energy, means for coupling one end of said wire to an RF source, means for coupling the otherendof said wire to an RF load, electron beam source means being operable to project an electron beam through each of the plurality of series of aligned loops respectively, switch means controlling the electron beam source means to project any one or combination of beams, collector means for said beams, and field means for flowing projected electrons along said coil for interaction with an electromagnetic wave traversing said coil.

0 I. i i i

Claims

1. In a traveling wave tube amplifier a slow-wave multi-coil of a single conductor that loops alternately clockwise and counterclockwise and from the longitudinal aspect intersects and crosses over itself between loops to form a plurality of series of aligned essentially circular loops wherein the number of loops in each of the plurality of series of loops is the same, and providing an equal plurality of interaction spaces, whereby RF conducted through the wire is accompanied by an electromagnetic wave that traverses the plurality of interaction spaces in unison, an evacuated envelope confining said coil therein, means supporting said coil in said envelope and being operable to attenuate backward wave energy, means for coupling one end of said wire to an RF source, means for coupling the other end of said wire to an RF load, electron beam source means being operable to project an electron beam through each of the plurality of series of aligned loops respectively, switch means controlling the electron beam source means to project any one or combination of beams, collector means for said beams, and field means for flowing projected electrons along said coil for interaction with an electromagnetic wave traversing said coil.