US3094643A - Frequency multiplier and wave signal generator - Google Patents

Description

G. WADE June 18; 1963 FREQUENCY MULTIPLIER AND WAVE SIGNAL GENERATOR L |.l: (n

Filed Oct. 1, 1959 IIVVENTOR G Zen Wade O moEmwzmw 22m mozwmmumm Un wd S a es P ten 3,094,643 L FREQUENCY MULTWLIER AND WAVE SIGNAL GENERATOR Glen Wade, Menlo Park, Calif., assignorto Zenith Radio Corporation, a corporation of Delaware Filed Octal, 1959, Ser. No. 843,663 2 Claims. (Cl. 315-3) V The. present invention is directed to a frequency multiplierandsi'gnal generator for developing millimeter, waves. It stemsfrorn research conducted on beam-type. transvers rnode parametric amplifiers and employs both structures and operating principles developed for such amplifiers. U

In:a bea;m type transverse-mode parametric amplifier, abeam is projected along a path to a collector and a condition of electron resonance is established in, the beam. That condition may onveniently be achievedby asolenoid arranged coaxially of the beam path and havinga selected 110. energization which provides a magnetic field cgrresponding to a desired electron or cyclotron resonance. A coupler to which an input signal is .applied effects deflection modulationof the electrons of the beam to the end that the electrons are placed into .orbital motion, that is, they arecaused to travel helical paths.- In this fashion, an electron wave representing the signal applied to the coupler is developed on the beam as it passes through the field of,that coupler; v

I he radius of the orbit 1 paths reflects theinstantaneous amplitude of the signal and, accordingly, to amplify the electron wave representing that signal it is necessary to increase the radius of orbital movement. Such increase in orbital motion is accomplished by what. is referred to as a modulation expander. Inone practical and effective form, the modulation expander is a quadrupole electrode structure which develops a non-homogeneous field that is symmetrical with respect to the beam path. The energy for this field, which is also the energy required for amplification, is delivered by a pump signal generator which, in one specific form of transverse-mode amplifier, has an operating frequency of approximately twice the cyclotron frequency. Such an expander is specifically described and claimedin a copending application, Serial No. 747,764, filed in the name of Glen Wade and assigned to the assignee of the present invention.

Another form of modulation expandenjdiifering from the quadrupole type in that it is a DC. structure, is the subject of still another application Serial No. 840,336 filed September 16, 1959, likewise filed in the name of Glen -Wade and assigned to the assignee of the present invention. it is a structure which, While energized by a D.C-.-potential,- simulates a-pumping field which appears to the electrons of the beamto be rotating in synchronism with these electrons as required to increase the radius of theirorbital motion. a I

As thus far described much of the parametric-amplifier structureis also employedin themillimeter-wave generator of this invention which takes advantage of the fact that a. multi-polar structure disposed in coupling relation to the beam, near the final portion of its travel, may accomplish frequency multiplication of the electron signal wave conveyed by the beam, Such a generator may supplya load inasmuch as the energy for driving a load maybe derived through themodulation expander andits driving or pump energy source. Consequently, the .arrangement comprehends a system which maybe characterized as a power source for millimeter .waves.

lt is accordingly an object of the invention toprovide a novel frequency multiplier and signal generator for producing millimeter waves.

It is a specific object of the invention to provide such 2 frequency multiplication and such signal. generation premised upon certainoper-ating principles which are characteristic of a beam type transverse-mode parametric amplifier.,--.

It-is still another specific object of the invention to provide a novel millimeterrwave signal generator which, in effect, develops the desired signal waves by effecting frequency .multiplicationaof. the. reference ,wave signal. 1

.A frequency multiplier andwave signal generator, embodying thesubject invention, comprises means for projecting an electron stream .along a given path and for establishing inthat stream orbital electron motion having a rotational component of a-predetennined frequency. A multi-polar structure is positioned coaxially. of the path and includes atleast two pairs of poles arranged symmetrically about the path in coupling relation to the stream...v There are means forderiving from the multipolar structure an output signal of N times'the aforesaid predetermined frequency, where N is the number of pairs of poles included in the multi-polar structure.

In accordance with. the invention, a modulation expander is positioned along, the beam path following an input couplernthrough which the electron stream. passes and as a consequence of which its electrons are caused to travel orbital paths. .Theexpander is of the DC. type, simulating a pumping ,field which appears to the electronsof the stream to be rotating in synchronism with electron motion. t

The features of. the present invention which are believed to be novel are set forth with particularity in the appended claims. The organization and-manner of operation of the invention, together withfurther objects and advantages thereof,-may best be understood by reference to the followingdescription taken in connection with the accompanying drawings, in the several figures. of which like reference numerals identify like elements, and in which: Y

-FIGURE 1 is ,a schematic representation one form of a millimeter-wave generator; 1

FIGURES. 2 and. 3 representaform of DC. modulation expander which vmayin accordance. with the invention be employed in place ,ofthe quadrupole or AC. modulation I expander included in the arrangement of FIGURE I; and,v

.-FIGURE 4 is an endview of a modified form of multipolar structure that may .be substituted for the multi-polar output coupler ofFIGURE 1.

The arrangement of FIGURE 1,. aside from the multipolar coupling structure to be described hereinafter, is similar to. the structure described and claimed in the aforementioned Wade application Serial -No. 747,764. Reference may be :had to that application for structural detailsof the .overall arrangemennincluding provisions for mounting its component parts other than signal sources within a tube envelope, and for a comprehensive explanation of the, operating principles of the modulation expandenemployed. to increase the amplitude of the electron orbits. These matters will, therefore, be treated in less detail in thisdescription. A I v The arrangement under consideration comprises means for projecting anelectron stream along a given path'l0 and for establishing in that stream orbital electron motion having a rotational component of a predetermined frequency More particularly, this-means is-comprised of the .followingprincipal components: an electron gun for projecting a stream of electrons, a field arrangement for establishing electron resonance in Tthe stream,- and a .deflectionmodulator or input coupler for developing an electron wave onthe beam-representinga reference signalof a predetermined frequency. These components will be considered seriatims v r a The electron gun 11 may be entirely conventional and preferably includes the usual indirectly heated cathode together with suitable focusing and accelerating electrodes for developing a well-defined beam or stream of electrons directed along path 10. For best operation the beam diameter should not exceed the dimension, measured in a circumferential direction, of the elemental electrodes constituting a multi-polar output coupler to be described hereinafter. The electrons travel this path toward a collector or anode 12 disposed transversely of the path and maintained at a suitable positive potential as indicated by the symbol +B.

This means for creating a condition of electron resonance in the beam may be of the magnetic or electrostatic type and, for convenience, is represented as a solenoid 14 surrounding the beam path to establish lines of magnetic flux parallel thereto. The solenoid is physically positioned externally of the tube envelope and is energized by a DO source (not shown) of adjustable magnitude for the purpose of establishing a desired cyclotron frequency which may be assumed to correspond to the frequency of the reference signal to be considered presently. In axial length, solenoid 14 is long enough to encompass a deflection modulator or input coupler, a modulation expander and a multi-polar output structure which are disposed in the recited order along path as will be made clear hereinafter. The focusing field established by the solenoid is designated symbolically by arrow H.

The deflection modulator or input coupler may take any of a variety of forms; it may for example comprise resonant cavities, transmission lines or deflection plates spaced alongside the beam for interaction therewith. As illustrated, the deflection modulator 15 includes a pair of deflector plates 16, 17 located on opposite sides of the beam path. A reference signal generator 18 is coupled to the modulator by means of a transmission line 19 which is short-circuited at one end and is coupled at its opposite end to deflectors 16, 17. A transmission link 21 is tapped as indicated onto transmission line 19 in a position adjusted to match [the impedance of generator 18 to that presented by the pair of deflectors. Transmission line 19 has an effective electrical length of one quarter wave length at the frequency of the reference signal supplied by generator 18.

Following deflection modulator 15 in the direction of collector 12 is a modulation expander for expanding the radius of the orbiting electrons to the end that the beam, in effect, sweeps a cylindrical path of such radius in relation to that of the multi-polar output structure as to attain a substantial coupling therebetween. This modulation expander is of the quadrupole type described and claimed in Wade application Serial No. 747,764. I-t comprises four electrodes 21, 22, 23, 24 symmetrically disposed circumferentially around beam path 10. Each electrode has the shape of an equilateral hyperbola and the electrodes are disposed with their intermediate portions facing the beam path and their terminal portions projecting outwardly therefrom with each terminal portion spaced generally parallel from the adjacent terminal portions of the neighboring electrodes. Oppositely disposed electrodes 21, 23 are coupled to one terminal of an alternating-current pump signal generator and the other pair of oppositely-spaced electrodes 22, 24 are coupled to the remaining terminal of generator 25. The operating frequency of pump generator 25 is approximately twice that of reference signal generator 18.

Positioned coaxially of beam path 10 beyond modulation expander 20 is a multi-polar output structure including a plurality of pairs of poles arranged symmetrically of path 10 for coupling relation to the electron stream. More specifically, this structure has an even number of pole pieces with the even-numbered ones interconnected and with the odd-numbered ones likewise interconnected so that the structure is restricted in excitation to the 1r mode. It is convenient in constructing the multi-polar device to make use of a pair of iterative combv11 into the held of input coupler 15.

type conductive structures bent into an annulus and posi' tioned so that the tines or electrode element of each such structure interlace with those of the other. The common band of one such structure is designated 31 and it sup ports odd-numbered electrode elements 33, 35, etc. The band for the companion structure is designated 32; it supports the even-numbered electrode elements such as 34 and 36. An inductor 40 is coupled across conductive bands 31, 32 and is tuned by a capacitance 41 to constitute a circuit resonant at the output frequency of the generator. Capacitor 41 is represented in broken-line construction since it may be constituted in whole or in part by the capacitance represented by the interlaced electrode structures comprising elements 31-36. While the lengths of the electrode elements are not critical, they preferably should be short compared to one-half the wave length of the output signal so that the interlaced structure represents predominantly a capacitance for resonating with inductor 40. Preferably, the internal diameter of the cylinder defined by interlaced electrode elements 33-36 is only slightly larger than the diameter of the cylinder enclosing or defined by the electron orbits of the beam as it emerges from modulation expander 20.

A load 42 to which the signal generated by the device may be applied is coupled to multi-polar structure 30 through an impedance-matching arrangement similar to that employed in coupling reference signal generator 18 to deflection modulator 15.

The potential sources designated E E and E coupled respectively to deflection modulator 15, modulation expander 20 and multi-polar structure 30 through choices, are sources of unidirectional potential employed to determine the drift velocity of electrons along beam path 10 and through modulation expander 20. It is practicable to have sources E and E of approximately equal values and slightly larger than source E The generator is housed in an evacuated envelope represented symbolically at 45. Techniques generally similar to those of copending application Serial No. 747,764, may be employed in securing the components of the structure within that envelope.

In the operation of the described millimeter-wave generator, a beam is projected along path 10 by electron gun As the beam traverses the coupler, it is subjected to deflection modulation because of the interaction of the beam with defiectors 16, 17. This deflection modulation causes the electrons of the beam to travel along orbital paths at the frequency of cyclotron resonance established by magnetic field H; for the illustrated case using simple lumped input coupler electrodes, the orbital frequency also corresponds to that of the reference signal supplied from generator 18 to the input coupler. The radius of the electron orbits is determined by the amplitude of the reference signal and for the case under consideration is small compared to the internal radius of multi-polar output coupler 30.

As the beam enters modulation expander 20, the electrons are subjected to'a non-homogeneous pumping field which, as explained in copending application Serial No.

747,764, causes a net increase in the radius of the electron orbits, the energy required for increasing the electron motion being supplied by pump signal generator 25. The drift velocity, which is determined by the applied operating potentials as noted above, and the axial length of the expander are so chosen that the radius of the electron orbits as the beam emerges from the modulation expander is nearly equal to the internal radius of output coupler 30. In other words, the beam which has been deflected off axis 10 in its passage through input coupler 15 rotates about that axis at a radius approaching that of the output coupler. Moreover, the electrons of the beam experience a phase-focusing effect as ff c exhibited byt c .expa riert ndsi o ad ce o remm 95 lec n o lt e be m wh n rin antintermediate phase condition causing them to shift toward the nearest optimum phasecondition in which their electron orbits are increased to a maximum. As a result of this phase-focusing or bunching effect, the beam crosssection is distorted from its original cylindrical shape, the electrons tending'to bunch about the position of optimum phase.

As the beam enters output coupler 30 rotating at the frequency of the reference signal from generator 18, it induces in this structure by means of space charge coupling effects a signal having a frequency of N times the frequency of the reference signal, where N is the number of pairs of poles in that structure. In other words, there is a multiplication of the input frequency by a factor corresponding to the pairs of poles in the output coupler which facilitates the generation of millimeter waves. The coupling from structure 30 to load 32. constitutes means for deriving and for supplying to the load an output signal harmonically related by the factor N to the reference frequency of source 1 8.

One restriction of the arrangement of FIGURE 1 is the need of a pump capable of supplying a signal of approximately twice the frequency of the reference signal delivered by generator 18 or at least of twice the cyclotron frequency. This restriction may be overcome by the use of a DC. modulation expander such as that represented in FIGURES 2. and 3. This structure is the subject of copending application Serial No. 840,336. In this case the modulation expander is a multi-filar arrangement of helical conductors. As represented, it includes four conductors 50, 51, 52 and 53 individually having the configuration of a helix and collectively interlaced to constitute a quadri-filar structure. The pitch of each helical conductor corresponds with or is matched to the pitch of the electron orbits of the beam traveling along path 10. This quadri-filar structure is energized from a DC, as distinguished from an A.C. source. The DC. source is designated 54 and has one terminal connected to opposed conductors 50, 52 whereas the remaining terminal connects to opposed conductors -1, 53 of the quadri-filar structure.

Obviously, the physical arrangement of conductors 5053 is to be such that each is insulated from its neighbors and this may be facilitated as a practical matter by providing the conductors with flanges defining channeh ways between the conductors, as appears from FIGURE 2, into which suitable insulating material (not shown) may be placed. It has also been found, as explained in copending application Serial No. 840,336, that there is a sufiicient approach to the ideal quadrupole field if the portions of the four conductors of the quadri-fil'ar structure which face beam path 10 outline a square.

The field established within the modulation expander in response to the DC. "excitation is a symmetrical nonhomogeneous pumping field which appears to the elec trons of the beam to be rotating in synchronism therewith. This condition accomplishes expansion of the radius of the electron orbits and phase focusing in a manner analogous to that of the quadrupole modulation expander of FIGURE 1.

The multi-polar coupling structure 30 may, if desired, be a multi-resonant cavity structure similar to that employed as the anode of a cavity magnetron. FIGURE 4 is an end view of such a structure having a series of resonant cavities 60-67. Strapping is resorted to, as in magnetron practice, to assure operation in only the 11' mode. Strapping is accomplished by a conductor 68 which is conduetively connected to the even-numbered poles of the structure and by a second conductor 69 which is conductively connected to the odd-numbered poles. An output may be derived from this multi-cavity structure by means of a coaxial connection 70 which terminates .ina probe, 71 located in one ofthe resonantcavities. The other end oi the coaxialv connector may. leaddirectly to the load. When such ratmultiecavitystructure idem: pioyed, the frequency of the output signal is once again N times the reference .ffequenc'y,".1N is then-umber sf P inc udss .Wil in ness 3% The described arrangements ude a modulatiomexpander in order that a significa amount of energy may be supplied" at a desiredf-requency. It the devices were to be used merely as a signal source as distinguished from a power source, the modulation expanders would be omitted. In such a case the signal applied to input coupler [15 would need be strong eough to deflect the beam away from axis .10 by a significant amount relative to the beam radius.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within true spirit and scope of the invention.

1 claim:

1. A frequency multiplier and wave signal generator comprising: means for projecting an electron stream along a given path; means tor creating in said path a field for establishing electron resonance in said stream; means for deflection modulating said stream in accordance with a modulating signal of a predetermined frequency to establish therein orbital electron motion having a rotational component of said predetermined frequency; an electron-motion expander positioned along said path for expanding the radius of the orbital motion of the electrons of said stream, said expander including a multi-filar arrangem-ent of interleaved helical conductors coaxial with said path and a source of unidirectional excitation potential connected across adjacent ones of said conductors for simulating within said expander a symmetrical, nonhomogeneous pumping field which appears to be rotating in synchronism with the electrons of said stream; a multipolar structure positioned coaxially of said path beyond said expander and including at least two pairs of poles arranged symmetrically about said path in electrostatic coupling relation to said stream; and means for deriving from said multi pol-ar structure an output signal of N times said predetermined frequency, where N is the number of pairs of poles included in said multi-polar structure.

2. A wave signal generator comprising means for projecting an electron stream along a given path; means for creating in said path a field fior establishing electron resonance in said stream; means for deflection modulating said stream in accordance with a modulating signal of a predetermined frequency to impart motion to electrons in said stream along a helical path of a predetermined pitch related to the strength of said field and with a radius representing the amplitude of said modulating signal; an electron-motion expander positioned along said given path for expanding the radius of the orbital motion of the electrons of said stream, said expander including means for subjecting said electrons to non-homogeneous pumping field forces, the strength of which vary linearly with distance from said given path which are uni-directional in a time domain, and which define a field pattern with a plurality of pairs of space-opposed poles disposed along interleaved helicoid-al loci which are coaxial of said helical path, are of the same pitch as and co-di-rectional with said helical path and which have a coaxial length corresponding to at least one convolution of said helical path, the even numbered ones of said pairs being of one polarity and the odd numbered pairs being of the other polarity; a multi-polar structure positioned coaxially of said given path beyond said expander and including at least two pairs of poles arranged symmetrically about said given path in electrostatic coupling relation to said stream; and means for deriving from said multi-polar 7 structure an output signal of N tirnes said predetermined 2,169,725 frequency, Where N is the number of pairs of poles in- 2,638,539 eluded in said multi-polar structure. 2,834,908 2,844,753

References Citedin the file of this patent UNITED STATES PATENTS De Vries et a1. Aug. 1, 1939 De Vries et a1 Aug. 1, 1939 Aug. 15, 1939 Cuccia May 12, 1953 Kompfuer May 13, 1958 Quate July 22, 1958 OTHER REFERENCES Amide by R. Adler et 211., pp. 1756-1757, Free. of the I.R.E. for Ootober 1958, No. 10, vol. 46.

Claims (1)

1. A FREQUENCY MULTIPLIER AND WAVE SIGNAL GENERATOR COMPRISING: MEANS FOR PROJECTING AN ELECTRON STREAM ALONG A GIVEN PATH; MEANS FOR CREATING IN SAID PATH A FIELD FOR ESTABLISHING ELECTRON RESONANCE IN SAID STREAM; MEANS FOR DEFLECTION MODULATING SAID STREAM IN ACCORDANCE WITH A MODULATING SIGNAL OF A PREDETERMINED FREQUENCY TO ESTABLISH THEREIN ORBITAL ELECTRON MOTION HAVING A ROTATIONAL COMPONENT OF SAID PREDETERMINED FREQUENCY; AN ELECTRON-MOTION EXPANDER POSITIONED ALONG SAID PATH FOR EXPANDING THE RADIUS OF THE ORBITAL MOTION OF THE ELECTRONS OF SAID STREAM, SAID EXPANDER INCLUDING A MULTI-FILAR ARRANGEMENT OF INTERLEAVED HELICAL CONDUCTORS COAXIAL WITH SAID PATH AND A SOURCE OF UNIDIRECTIONAL EXCITATION POTENTIAL CONNECTED ACROSS ADJACENT ONES OF SAID CONDUCTORS FOR SIMULATING WITHIN SAID EXPANDER A SYMMETRICAL, NONHOMOGENEOUS PUMPING FIELD WHICH APPEARS TO BE ROTATING IN SYNCHRONISM WITH THE ELECTRONS OF SAID STREAM; A MULTIPOLAR STRUCTURE POSITIONED COAXIALLY OF SAID PATH BEYOND SAID EXPANDER AND INCLUDING AT LEAST TWO PAIRS OF POLES ARRANGED SYMMETRICALLY ABOUT SAID PATH IN ELECTROSTATIC COUPLING RELATION TO SAID STREAM; AND MEANS FOR DERIVING FROM SAID MULTI-POLAR STRUCTURE AN OUTPUT SIGNAL OF N TIMES SAID PREDETERMINED FREQUENCY, WHERE N IS THE NUMBER OF PAIRS OF POLES INCLUDED IN SAID MULTI-POLAR STRUCTURE.

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