Casper W. Barnes, Jr., Palo Alto, Calif., assignor to. A. B. Dick Company .... trodes (not shown), a focusing electrode 42 focuses the electrons from the cathode ...
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April 19, 1960
P. M. LALLY FREQUENCY SHIFTING APPARATUS Filed Dec. 6, 1956
United States> Patent Ótiice 1
2,933,639 Patented Apr. 19, 1950 Z
It is a further object of this invention to provide a fre
quency selective frequency changing device.
2,933,639 FREQUENCY SHIF’I‘ING APPARATUS Philip M. Lally, Huntington, N.Y., assignor to Sperry
In accordance with the principles of the present inven tion there is provided an electron discharge device em ploying a novel type of interaction between an electron stream and a slow electromagnetic wave. The device em
ploys a pair of slow wave structures disposed in tandem and provided with axial apertures for passage there through by an electron stream. The slow wave structures Application December 6, 1956, Serial No. 626,707 10 are adapted to propagate waves with substantially trans 1 Claim. (Cl. S15-3.6) verse electric fields. A magnetic focusing field is pro vided along and directed parallel to the axes of the slow wave structures. An electron drift tube interconnects the slow wave structures. An input electromagnetic wave is This invention relates to apparatus providing for inter coupled to the first slow wave structure and propagates change of energy between a stream of charged particles tberealong. An electron beam is projected through the and a traveling electromagnetic wave and more particu apertures of the slow wave structures. The beam velocity larly to a device for transmitting an electromagnetic wave in the first structure is adjusted to a particular value sub differing in frequency from and responsive to a received stantially different from that of the slow wave. The elec electromagnetic wave. trons move in helical paths of increasing radii about the In a frequency changing device a wave is received at 20Y axis at the cyclotron frequency, continually absorbing a first frequency and retransmitted at a second frequency energy from the input electromagnetic wave. The elec differing from said first frequency by a predetermined tronA beam then passes through the drift tube, which pre amount. In prior art frequency changing devices, such as vents passage of the input wave, and enters the second those used in microwave relays, it is customary to provide slow wave structure rotating about the axis thereof at the an interaction process between the received microwave cyclotron frequency. In the second structure the axial
Rand Corporation, a corporation of Delaware
signal and the signal produced by an auxiliary oscillator located at the relay point. One sideband is selected from the output signal of the. interaction process Yfor retrans
mission, the frequency of the sideband diifering from that of the received _signal by an amount equal to the fre quency of the local signal or an harmonic thereof. Two types of interaction processes are commonly employed,
one of which employs nonlinear mixing of the received
velocity of the electrons is changed, thereby changing the frequency of the slow wave with which they can interact. The spiraling electrons induce a wave on the second slow wave structure whose frequency differs from that of the
input wave by an amount determined by the velocity dif ference of the electron beam in the two slow Wave struc tures. Means is provided forpremoving the induced wave from the second slow wave structure.
signal and the local signal by methods well known in the This invention will be described with reference to the art, and the other of which employs the synchrodyne 35 following drawings wherein: principle as disclosed in U.S. Patent No. 2,519,369l'to Fig. l is a cross-sectional drawing of the preferred em W. W. Hansen and J. R. Woodyard and assigned to the bodiment of the invention; same assignee as the instant invention. In the latter proc Fig. 2 is a sectional drawing taken on line 2_2 of ess an electron beam velocity modulated by the> received Fig. 1; 40 signal is also phase modulated by the local signal, one Fig. 3 is a sectional drawing taken on line 3-3 of sideband of the process being selected for retransmission. Fig. 1; Frequency changers of the types described require com Fig. 4 is a drawing showing the electron ñeld configura plex electronic circuitry and include'as a necessary ele tion of a wave traveling along a slow wave structure of ment the aforementioned auxiliary oscillator. Further the type employed in the embodiment of Fig. l; and more, such prior art devices had no inherent selectivity, 45 Fig. 5 is a drawing showing the transverse motion of but would act to shift the frequency of all received sig electrons within the electron stream of the embodiment of
nals. Selectivity could only be achieved by applying the received or output signals to a frequency selective device, such as a resonant cavity.
It was desired therefore to
provide a frequency changing device simple in operation, having no auxiliary oscillator, and one which rejected un desired received signals.
It is therefore a principal object of this invention to provide an improved'frequency changing device. `
Fig. 1. 'I‘he preferred embodiment of this frequency changing
50 device comprises a pair of wave transmission structures
10 and 11 disposed in tandem and having a drift tube 12
interposed between them, as shown in Fig. l. Structures 10 and 11 each comprise a rectangular waveguide section
13 (Fig. 2) and a plurality of inwardly extending conduc
tive members 14. Structures 10 and 11 are each adapted It is a further object of this invention to provide a more 55 to propagate an electromagnetic wave with a substan
reliable frequency changing device simple in circuitry and
It is a further object of this invention to provide a fre quency changing means employing but one electron dis
It is a further object of this invention to provide a fre
tially transverse electric field at a velocity substantially less than that of the velocity of light; for example, of the order of M0 the velocity of light. Structures of this type 60 are termed slow wave structures and are described in
U.S. patent application Ser. No. 253,343 by L. M. Field,
now Patent No. 2,808,532. Drift tube 12 (Fig. 3) is aper tured to permit passage of an electron beam. However, It is a further object of this invention to provide a the aperture 16 in drift tube 12 is not suñicient in trans novel electron discharge device to> effect an interchange of verse extent to permit passage of the electromagnetic energy between a stream of charged particles and a travel 65 waves which propagate in structures 10 and 11. In this ing electromagnetic wave. regard, drift tube =12 functions as a waveguide beyond It is a further object of this invention to provide a cutoff. novel electron discharge device to effect an interchange of ` An input signal comprising electromagnetic energy of energy between a -stream of charged particles and an frequency f1 is coupled into the device by means of an 70 electromagnetic wave traveling at substantially different input waveguide section 18. The «input signal is coupled velocities with respect to eachother. from input section 18 through a waveguide bend section
quency changing circuit employing no auxiliary oscillator.
The electron is moving along the z-'axis with a velocity
19, through a waveguide transition 20, and into the left
u1, so that in Equation 1
end of slow wave structure 10. Electromagnetic energy of frequency f2 _induced in slow wave structure 11 is cou
pled out from the right end thereof, through a waveguide transition 22, through a waveguide bend section 23, and into an output waveguide section 24. Energycoupled to output waveguide section 24 is termed the output signal. The output signal is delivered at a frequency f2 which dif
Therefore, the electron is subjected to a transverse elec
fers from the frequency f1 of the input signal by a pre#` 10 tric Afield of frequency determined frequency shift. A stream of electrons is generated in an electron gun
comprising an indirectly heated cathode 28, a focusing cylinder 29, and an apertured anode 30. The electron stream is accelerated to a velocity u1 determined by the voltage V1 of a ñrst direct voltage source 31 connected between cathode 28 and anode 30. lThe electron stream travels toward the right in the figure through an aperture
The frequency indicated in Equation 4`is that “seen” by the electrons as they pass wavefronts of constant phase or
are passed by such wavefronts. Simultaneously with being acted on by the transverse electric ñelds, the electrons are subjected to the axially
32 in anode 30, and along the respective axes of wave‘- .
Y directed‘magnetic íield of magnetic ñux density B.
guide transition 2i), slow wave structure 10, drift tube 12„ field would normally accomplish focusing (holding the slowY wave structure 11, andy waveguide transition 22. 20 beam together) by inducing electrons having transverse The electron stream finally passes through an aperture 33 velocity components to describe helical paths as they in waveguide bend section 23 and impinges on a conduc traveled along the z-axis. In the transverse (x-`-y) plane tive collector 34. A second direct voltage source 36 of the electrons would describe circles Vofconstant radius in voltage V2 is connected between cathode 28 and collector the absence of the transverse electric fields. The fre 34, which is electrically connected to structure 11, and 25 quency of rotation of an electron in a uniform magnetic serves to operate the structure 11 at a potential different
iield is independent of the electron’s velocity, being given
from that of structure 10. An apertured insulator 38 electrically isolates slow wave structure 11 from drift tube 12. An evacuated dielectric envelope 40 encloses and
supports the portions of the device through which the 30 electron stream must travel. Electrodes extend through envelope 40 in vacuum sealed relation thereto to couple voltages to the elements therein for heating the cathode
Where e/m is the charge to mass ratio of the electron.
The frequency fc of Equation 5 is'known as the cyclotron frequency Yof the electrons in the magnetic field B.
and accelerating the electron stream. Y A plurality of solef
The y-component of velocity of the spiraling electrons
-noids 42, 43, 44 provide a steady magnetic field along the axis of the structure and directed parallel thereto for im
is .therefore given by
mersing the electron stream. The magnetic ñeld provides
for focusing the electron stream ad for exciting interaction between the electrons and waves traveling on the slow wave structures.
The electron stream 46 originates at the electron gun end of the device as a thin, sharply deñned beam. As the beam travels toward the right through slow wave structure 10, it interacts with the transverse electric field
where um is a'reference value of y-directed velocity. Maximum energy will be absorbed by the electron from
40 the transverse electric lield if the force of the field on the
electron is always accelerating. This can only be so if the
transverse lvelocity of the electron is in synchronism with the transverse electric ñeld; Le., if the exponential terms in Equations 3 and 6 are equal
components of the wave of frequency f1 traveling therein. 45
The resultant interaction increases the ,tangential velocity
nef-.(174 ' t7) of the individual electrons of the stream, thereby enlarg-> ing thecross-section of the beam.k The enlarged beam Therefore, Equation 7 expresses the condition for inter-v then passes through drift tube 12 and enters slow wave action between the electron stream and the transverse structureV 11, where its axial velocity is changed’due to 50 electric field components of the traveling wave. For a direct voltage source 36. As the electron stream travels given magnetic field, B, the electron stream can be made to the right in slow wave structure 11, it induces a wave to absorb energy from the wave due tothe input signal of frequency f2 to travel along said structure in syn-V by adjusting the >strearnrvelocity u1 to satisfy Equation 7. v
chronism, this wave gradually absorbing energy from the ‘ Equation 7 may be modified toelectron stream. This absorption of energy decreases the 55 .
tangential velocity of the individual electrons of the The electron stream terminates in collector 34.
Where )t1 is the guided wavelength of the wave of fre
rrstream, thereby reducing its cross-sectional area. The in duced wave is delivered to output waveguide section 24.
Y quency f1.
Thus, for a particular value _141, the electron
stream will interact with> but one frequency component of
. The theory of operation of this invention may be 60 explained as follows: Consider. an electron traveling to
the input signal.
the right (-l-z direction) in the slow Wave structure 10l of Fig. 4. The particular electromagnetic wave of in terest has substantially transverse electricñelds, as shown.
travel in'helical paths of increasingY radius; rlv‘he value of um) increases but the cyclotron frequency,` fc, remains
As the electrons absorb energy from the wave, they.
constant. An end ortransverse picture offtypical` elec-.
The transverse electric field of a wave due to the inputV 65 tron paths is shownin -Fig.r5-. The small loopk A is the path of an electron rotating at cyclotron frequency as signal acting on the electron located at any point z along it travels along the tube axisv and not subjectedv to any the z-axis of the slow wave structure is given by ~
where Eloy is a reference value of transverse electric field;
w1=21rf1, where f1 is the frequency Aof the input signal; and v1 is the phase velocity along'the z-axis of the par ticular wave in slow wave structure 1t).
transverse electric fields.V 'I_'he dat spiral/is the path of a corresponding electron moving in synchronism with a traveling transverse Velectric iieldmand subject to successive
Y acceleration forces atV points B,_C; A1¿),-E_, F; The ac
celerating electricltieldr. at these successive points, and its direction is shown b'ylthe dotted lin'es¿_in¿ Fig. 5_. An elec-. tronV subject to but- not in synchronism .with a traveling transversev electric field be'¿ subjected .to random ac->
vcele?atiêui and‘deceleration- forces, will not absorb energy from the- Wave, and will continue to move in a helical
path of small radius. The radius of the helical path is a measure of the energy the electron has absorbed from
the `field. The electron stream nowl passes through the drift tube
12 of Fig. 1, where it is shielded- from interaction with the traveling waves. The input signal f1 cannot pass
jacent the path of the stream.Y Waves having substantial transverse electric field components propagate along the structure parallel to the stream path. The velocity of the stream is adjusted by the first voltage source so that thel electrons interact with one component of the input wave, and travel in helices of increasing radius as they absorb energy from the synchronous wave. The electron stream
then passes through a field-free region, retaining the en
through the drift tube to slow wave structure 11. The ergy absorbed from the particular waves as tangential electrons continue to move in the helical paths of rela 10 velocity of the individual electrons; ' However, the stream tively large radii that they assumed after interaction with retains no “memory” of the‘frequencyof the wave from
the input signal traveling wave` These electrons are now accelerated to -a different axial velocity u2, and enter slow wave structure 11. The transverse velocity of the spiral
which it absorbed the energy, the electrons spiralling at the cyclotron frequency. The stream is then further ac celerated or decelerated and projected into a path op
ing electrons continues to be that given by Equation 6. 15 posite a second slow Wave structure. A wave is induced Noise and shock excitation will excite slow wave struc on this structure, the frequency of which is that neces
ture 11 at all frequencies. However, one of these waves will build up because it operates in synchronism with the
spiraling electrons. This wave, of frequency f2, will sub
sary to cause synchronous interaction with the rotating electrons. The amount of additional acceleration given the beam determines the value of this new frequency and,
ject an electron moving with velocity ug to a transverse 20 consequently, the frequency shift of the device.
Although this invention has been described, as employ ing different electron stream velocities in slow wave struc
tures 10 and 11, it is within the spirit of this invention to achieve frequency shifting by variation of other par where v2 is the phase velocity along the z-axis of this 25 ameters. For example, the magnetic‘ñeld may have wave. different magnitudes along the axes of respective slow Maximum energy will be absorbed by the wave from wave structures 10 and 11. The output frequency would the spiraling electron if the force of the transverse ñeld then diifer from the input frequency by an amount de on the electron is always retarding. This can only be so pendent on the relative magnitudes of two magnetic iields. if the transverse velocity of the electron and the trans 30 In a similar manner, the two slow wave structures may verse electric field of the wave are in synchronism, i.e. if be designed with different electrical or physical charac the exponential terms in Equations 6 and 9 are equal teristics so that the velocity vs. frequency characteristics of the two structures dilîer. 1In such device although the
Therefore, with -an electron beam adjusted to interact with the wave of frequency f1 traveling on slow wave structure 10, a Wave of frequency f2 will be induced on
magnetic fields and electron stream velocities are the
35 same in both structures the output frequency will differ
from the input frequency. The invention has been described as employing a novel
interaction of an electron stream and a traveling elec slow wave structure 11. By combining Equations 7 and tromagnetic wave. It is within the scope of this inven 10 the relationship between f1 and f3 can be obtained 40 tion that the traveling electromagnetic wave may be one traveling wave component of a standing electromagnetic __î‘l wave of the type which occurs in periodically loaded ¿L U1
fì- 1_ ïz
wave transmission devices.
While the invention has been described in its preferred
If the slow Wave structures are identical and broadband; 45 embodiment, it is to be understood that the words which have been used are words of description rather than of that is, they propagate waves of a broad frequency range
at constant velocity, Equation 11 can be simplified to
limitation and that changes within the purview of the appended claim may be made without departing from
the true scope and spirit of the invention in its broader 50 aspects.
What is claimed is:
A frequency changing device comprising means for projecting an electron stream along an axis, first and IIn this instance the frequency shift between input and second wave transmission structures disposed adjacent output signals is dependent solely on the electron beam 55 said axis and in tandem along said axis, each of said struc velocities, or upon the ratio of accelerating voltage V2 tures being adapted to propagate respectively along said to accelerating voltage V1. .ln operation, the value of V1 axis first and second waves having electric ñeld com and correspondingly u1 must be adjusted for synchronism ponents perpendicular to said axis, said first and second with an¿input wave of the frequency to be passed (Equa waves each being of different frequency f1, means for tion 7), and then the value of V2 and correspondingly providing a steady magnetic iield along said axis and u2 is adjusted to obtain the desired frequency shift for directed parallel thereto in each of said first and second the output signal. wave transmission structures, said steady magnetic field In these equations, the presence of an apparent nega in each of said structures immersing said electron stream
tive sign if u is greater than v may be ignored. 'I'he equa and thereby imparting to said electron stream a helical tions were «arbitrarily set up to give a positive sign with 65 motion about said axis, said helically moving electron v greater than u. In the event u is greater than v, the stream having a frequency of rotation about said axis of parenthetical terms should read fc, wherein the velocity u1 of said electron stream along
said axis in each of said wave transmission structures is related to the phase velocity v1 and the frequency f1 of a 70 respective one of said'ñrst and second Waves substantially 'In summary, the theory of operation of this invention in accordance with the expression
is as follows: A stream of electrons is accelerated by a
first voltage source and directed along a path parallel to the direction of an applied magnetic field. An input Signal is applied to a slow wave structure disposed ad 75 means for accelerating said electron stream to a iii-st
velocity adjacent ’said ñrst wave transmission structure; and means to aœçlerate Said eleçtron Stream toa Second. velocity adjacent said seçond wave transmission structure, said ñrst and second velocities being diíîerent.
References Cited inv theñle of this patent UNITED STATES PATENTS 2,424,965 2,584,308 2,584,597