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Патент USA US2406635

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Aug, 27, 1946.
S. RAMO
METHOD FOR AMPLIFKYING HIGH FREQUENCY SIGNALS
2,406,635
Filed March 27,‘ 1942
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Sirn'oh RamQ, “
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Patented Aug. 27, 1946
2,406,635
UNITED STATES’ PATENT OFFICE
METHOD Fon AMPLIFYING HIGH-V
FREQUENCY SIGNALS
Simon Ramo, Schenectady, N. Y., assignor to Gen
eral Electric Company, a corporation of New
York
Application March 27, 1942, Serial No. 436,444
4 Claims.
.
1
.
The present invention relates to an improved
method and means for obtaining ampli?cation
at ultra high frequencies.
It is well known that as one proceeds from
relatively long wave lengths to Wave lengths on
the order of a few centimeters, the process of
(Cl. 250——20)
2
agating characteristics of the line and in the
usual case, act to produce attenuation of the,
propagated wave as it progresses along the line.
The factor which determines the amount of such
attenuation is ordinarily referred to as the at
tenuation constant and. may be de?ned by the
ampli?cation with conventional amplifying de
following approximate relationship:
vices becomes increasingly di?icult, this being a
result of unfavorable properties exhibited by
such devices in the ultra high frequency range. 10
(1)
a (attenuation constant)=g§) 5128-0
It is a primary object of my present invention
to provide an amplifying arrangement which is
not adversely affected by increasing frequency .
where G represents shunt conductance per unit
length, R represents series resistance per unit
length and Z0 is the so-called characteristic im
pedance of the line. Neglecting losses
and which is capable of being operated satisfac
torily at even the shortest wave lengths.
15
In one of its aspects, the invention involves
the use of a wave propagating system which-has
the attribute of negative attenuation. This
The effect of the attenuation constant on the
property is realized by incorporating in the wave
propagation of a particular aspect (say the volt
propagating structure an agency which imparts
age‘ aspect) of a propagated wave may be ex
to the structure a negative conductance of ap
pressed by the following relationship:
'
propriate value. As will be explained more fully
in the following, this maybe accomplished by
, Er=E0f (6-0“)
(2)
the use in a particular manner of certain elec
Where Ex represents the value of voltage at an
tronic devices which are of such con?guration 25 arbitrary point, x, along the line and E0 repre
as to permit their integral incorporation in a I
sents voltage at the sending end of the line.
wave propagating system. The nature of such
From this relationship it will be seen that as
devices and certain further requirements with
long as a is positive, the normal effect of at;
respect to the termination of the wave propa
tenuation is to reduce the amplitude of the prop‘
gating system will be described in detail in the 30 agated Wave. It is equally apparent, however,
ensuing description of the invention.
A further important aspect of the invention
consists in the utilization of a negative conduct
that if a can be given a negative value, then the
amplitude of the Wave will increase rather than
decrease with increasing distance from its source.
ance wave propagating system as an essentially
Accordingly, if a Wave propagating structure hav,
self-contained superheterodyne converter for 35 ingnegative attenuation is terminated in such a
ultra-high frequency application.
Way as to prevent regenerative oscillations from
The speci?c features desired to be protected
occurring, a mechanism is provided by which
herein are pointed out in the appended claims.
useful ampli?cation effects may be obtained.
The invention,.itse1f, together with its further
Moreover, such effects can be obtained with equal
objects and advantages, may best be understood 40 facility at even the highest frequencies by ap
by reference to the following description taken
propriate choice of the propagating system.
in connection with the drawing, in which Fig. 1
In accordance with the present invention, the
represents a parallel conductor transmission line
concept of negative attenuation is realized in a
incorporating means for imparting negative con
practical way by the use of a propagating system
' ductance to the line, and Fig. 2 illustrates the 4.5
which is characterized by a distributed negative
use of such a, line as a superheterodyne con
verter.
As is well known, the properties of a wave
propagating system such as a coaxial conductor
conductance (see Equation 1, above) it being as
sumed that the absolute value of the conduct
ance G is ‘suincient to outweight the positive ef
fect of the series resistance R of the propagating
transmission line are determined by the dis 50 system involved. Speci?cally, negative conduct
tributed constants of the system, including its
ance is obtained by the use of certain electronic
effective series resistance and inductance per
devices which have heretofore been found usable
unit length and further including its shunt ca
as oscillators (and which therefore introduce the
pacitance and conductance per unit length.
aspect of negative resistance) and which are of
These factors serve to determine the wave prop 55
Such structural form as to permit their effective
2,406,635
3
A
propagating system which is electrically uniform
incorporation in a wave propagating system.
The magnetron oscillator provides one example
of such .a. device, while the Barkhausen-Kurz
oscillator is another example.
throughout. For example, because of the need
for providing ?lament wires, seals, leads for ob
taining bias, etc., it is difficult to avoid introduc
Fig. 1 represents schematically an amplifying
system which includes a split anode magnetron
I0 incorporated in a transmission line having
ing discontinuities into an arrangement such as
that of Fig. 1, which discontinuities have a tend
ency to produce some reflection of incident waves.
The eiiects of such discontinuities may be tuned
parallel conductors H and [2. The magnetron
out, or neutralized, for a particular frequency by
includes a pair of mutually spaced, semi-cylindri 10 the use of tuning means appropriately arranged
cal anode members l3 and M which are respec
with reference to the discontinuities in question.
tively connected in series with the conductors II
However, since available tuning means neces
and I2 so as to be, in effect, continuations of
sarily involve the use of reactance elements, their
them. Electrons are supplied to the space be
effects will obviously not be equally favorable for
tween the anode members by means of a cathode
all possible frequencies. On the contrary, a tun
l5 having lead-in conductors l6 and H by which
ing element which has the effect of preventing
it may be supplied with heating current from a
resonance at a particular frequency, may tend
source 18. Choke coils I9 and 20 are connected
to promote resonance and self-sustained oscilla
in series with the cathode so as to isolate the
tions of the system at some other frequency.
source l8 from the high frequency system formed
Whether oscillations actually occur at such other
by the magnetron, and unidirectional potential
frequencies depends upon whether the system as
is impressed between the cathode and the anode
a whole, including particularly the negative con
members l3 and M by means of a potential source
ductance element of the system, is in an operat
2| connected as shown. (The choke coil 22 al
ing condition which tends to favor the occurrence
lows the conductors H and I2 and the connected
of oscillations at the frequency in question. In
anode members to be at a common potential as 25 general, this is a factor which can be controlled
far as D. C. potentials are concerned, while being
by proper regulation of the operating conditions
effectively separated with respect to high fre
quency currents.) With a magnetic ?eld estab
lished parallel to the axis of the magnetron as
of the electronic device by which negative con
ductance is provided, so that oscillations at the
unneutralized frequency can be obtained or
indicated by the arrow H, the magnetron assumes 30 avoided as desired.
a negative resistance characteristic, which, with
The considerations stated in the foregoing par
the parts in the relationship shown, appears as
agraph may be employed for the attainment of
distributed negative conductance between the
useful objects by a construction of the character
conductors of the transmission line. Because of
illustrated in Fig. 2, which represents the appli
35
the negative attenuation thus imparted to the
cation of the invention to a superheterodyne con
section of the transmission line subtended by the
erter in which the local oscillator and mixer are
magnetron, a signal-bearing wave propagated
combined in a single agency.
'
along the line, say from a source at 23, tends to
In this case the wave propagating system com
increase in amplitude.
prises a coaxial conductor transmission line hav
In order that the ampli?cation effects thus 40 ing an outer conductor 29 and an inner conduc
realized may be usefully'employed, the section
of the transmission line formed by the anode
members l3 and 14 should possess the same char
acteristic impedance as the remaining portions
of the line, and the line should be terminated in
its characteristic impedance so as to avoid re
?ection effects and a consequent tendency to re
generative oscillation. The ?rst of these require
ments may be adequately ful?lled by making the
spacing of the conductors H and I2 somewhat
less than the average spacing of the members l3
and [4 so as to offset the otherwise excessive ca
pacitance attributable to the relatively larger
area of the members. The requirement of
proper termination of the line may be met by
connecting between the extremities of the con-'
ductors H and [2 a resistance 24 the value of
tor 35. The central portion of the line is given
a negative conductance characteristic by the use
of a three-element electron discharge device in
the nature of a Barkhausen-Kurz oscillator. This
comprises a cylindrical evacuated metal envelope
3| which is closed at its extremities by means of
sealed-in glass plugs 32 and 33. Within the tube
there is provided a central ?lament 35 and a
helically wound grid 38 which surrounds the ?la
ment. By means of lead-in connections carried
through the plugs 32 and 33 the grid 36 is made
electrically continuous with the inner transmis
sion line conductor Bil. The ?lament 35, on the
which is the same as that of the line impedance.
In a practical case the resistance 24 may be made
up in part of the input of a detector 25 or other 60
device for converting the ampli?ed wave received
at 24 into a more usable form.
I '
It is to be noted that the arrangement of Fig. 1
may be used, if desired, to amplify waves which
simultaneously traverse the region of negative
conductance in opposite directions. This re
quires that both extremities of the propagating
system be terminated in the characteristic im
pedance of the system in order to prevent oscilla
tions from being set up. When this condition is
ful?lled, no mutual interference of the oppositely
directed waves will occur provided sufficiently
small signals are used.
Because of' mechanical limitations it is not
possible under all circumstances to provide a 75
other hand, is supplied with heating current by
lead-in conductors 3S and 39 which are brought
out through the wall of the cylindrical envelope
3| by lead-in seals M and 152. A battery 44 which
is externally connected between the conductors
and 39 serves as an energizing source for the
?lament.
In the intended operation of the Barl<hausen~
Kurz tube the grid 36 is maintained at a positive
potential with respect to the ?lament 35, whereas
the anode, which consists of the wall of the metal
envelope 3! is maintained at a relatively nega
tive potential, these potentials being established
by means of a battery 48.
As is well known, this
mode of connection imparts a negative resistance
characteristic to the tube as a whole so that under
certain conditions oscillations may be set up due
to the gyrations of electrons in the interelectrode
spaces. For present purposes, however, the nega
tive resistance characteristic of the device is prin
cipally of interest in that it provides negative con
2,406,685
ductance between'thegrid 3i and the ‘anode-form
i-ng wall 3| As has been explained in connection
with Fig; '1, this negative resistancepermits ampli
The ‘intermediate frequency side band may be
abstracted by ahappropriate circuit connected
?cation of- a signal-‘bearing wave propagated
along. the transmission'line (say, from a ‘source
indicated at ‘it, this frequency component being
across-the terminals of the transmission line as
thereafter further ampli?ed or detected as de
49) provided the line is terminated in'its char
acteristic impedance Z0.
sired;
Such a termination is
-
'
While the invention has been described by
indicated in the presentcase at 50.
reference to particular embodiments thereof, it
As has been 'previouslysuggested, the necessity
will ‘be understood that numerous modi?cations
for including lead-in wires, seals, etc.-in an ar 10 may be made by those skiiled in the art without
rangement such as that of Fig. 2 introduces elec
departing frcmthe invention. 1, therefore, aim
' trical discontinuities-into the system which tend
in the appended claims to cover ail such equiva~
lent variations as come within the true spirit
to produce wave re?ectionrand consequent reso
V nance
‘ effects.
'
Such ‘discontinuities are intro
duced, for example, by the‘ ?lament lead-in1con— 15
ductors 38 and-39 and bylthe glass Vsealing'plugs
32T'and 33. ' ‘These discontinuities'fmay be tuned
out (i. e. e?ectively neutralized)‘ by the use of
compensating reactancel'elements properly ar
ranged.
and scope of the foregoing disclosure.
'
_ What I claim as new and desire to secure by
Letters Patent of the United States is:
‘
1. Iii-combination, a source of signal-bearing
waves, a system for propagating waves derived _
from said source, said system "including a pair
For ‘example, in connection with the 20 ofconcentric transmission lines each including
conductors 38 and 39 neutralization may be ac
an outer tubular conductorand an inner conduc
complished by the use of stub transmission line
tor interconnected by an electronic discharge de
sections formed by the combination of the con
vice incorporated in the said propagating sys
ductors 38 and 39 and laterally extending metal
tem for giving it a negative attenuation charac
tubes 59 and 5! which are respectively associated 25 teristic whereby waves propagated by the system
with the conductors. Slidable conductive plugs
are ampli?ed in intensity, said electronic dis
53, 54 are provided in‘ connection with each of ‘
charge device including dielectric means for de
the tubular members 50 and 5| for tuning pur
?ning an evacuated region containing an electric
poses. While these plugs should be insulated
discharge path, and means for terminating the
from the ?lament lead-in conductors 38 and 39 30 system in such fashion as to minimize reflection
as far as direct current flow is concerned, they
of said signal-bearing waves, said ‘last-named
may be assumed to be su?iciently capacitively
means including reactance components associ
coupled to these conductors to form adjustable
ated with said electronic discharge device which
short circuiting terminations for the respective
neutralize the re?ection incident to the presence
stub lines with respect to high frequency cur 35 of said last-mentioned means and which cause
rents.
,
said device to be self-oscillatory at a. frequency
Similar stub lines are provided in association
different from the frequency of said signal-bear
with the plugs 32 and 33, one such line being
ing waves, whereby the output of said device in
formed by'the combination of a transversely ex
cludes side-band components representing the
tending tube 56 and a concentrically arranged 40 sum and difference of said frequencies.
conductor 51, and the other by a similarly asso
2. In a system for propagating electromagnetic
ciated tube 59 and conductor Gil. The conductor
waves, the combination comprising a pair of con
51 may be incidentally employed as a terminal
centric transmission line sections each including,
means for connecting the spiral grid 36 to the
an outer tubular conductor and an inner conduc
positive terminal of battery 48. Sliding tuners
tor, means for exciting one vof said transmission
.62 and 53 are provided in connection with each
line sections at signal wave frequency, electronic
of the stub lines just referred to.
I discharge means interconnecting said transmis
By properly adjusting all the sliding tuning
sion line sections and comprising an outer tubu
elements the wave propagating system may be
lar conductor in electrical contact with the ?rst
caused to simulate a uniform line as far as waves 50 mentioned tubular conductors and a concentric
of the particular frequency propagated by the
inner conductor, said outer conductor and said
signal source 49 are concerned. However, since
inner conductor of said electronic discharge de
the tuning devices are, in effect, reactance ele
vice-constituting an anode and a cathode of an
ments, complete tuning in the sense speci?ed can
electric discharge path which in conjunction with
be assured only for a relatively limited frequency 55 a spaced grid produce distributed negative con
band. Accordingly, with appropriate adjustment
ductance whereby waves propagated by the sys
of the operating conditions of the tube there will
tem are ampli?ed in intensity, means for termi
be some frequency, materially displaced from
nating the other transmission line section to
that of the signal waves, at which reflection effects
minimize re?ection of signal-bearing waves, and
and self-sustained oscillations will occur as a 60 reactance means which cause said device to be
self-resonant for electromagnetic waves of a fre
result of the negative conductance characteristic
of the tube 3|.
-
Because of inevitable non-linearities in the
quency different from the signal frequency and
to serve both as a local oscillator and a mixer.
system. the occurrence of s "one self-sustained
3. In a system for the propagation of electro
oscillations at a time when waves are being 65 magnetic waves, the combination comprising a.
propagated down the transmission line from
the signal source 49 will produce mixing of the
signal and oscillatory frequencies with resultant
pair of concentric transmission line sections each
including an outer tubular conductor and an in
ner conductor, means for exciting one of said
superheterodyne action of the system as a
transmission line sections at signal frequency,
whole. Accordingly,‘ the‘signal received at the 70 means interconnecting said transmission line sec
right-hand extremity of the propagating system
tions comprising an electronic discharge device
will be not only of ampli?ed character but will
also contain side band components correspond
ing to the sum and difference frequencies of the
signal and the locally generated oscillations.
including an outer tubular conductor of sub
stantially the same diameter as the ?rst men
tioned tubular conductors and in electrical con
tact therewith and having a, central inner con
2,406,635
7
ductor and an electrostatic grid in spaced rela
tion with respect to said outer tubular conduc
tor and said inner conductor of said electronic
discharge device which constitute respectively an
anode and a cathode of an electric discharge path
which produces a distributed negative conduct
ance whereby waves propagated by the system are
ampli?ed in intensity, means for de?ning a local
ized region containing said electric discharge path
stants of component parts of the system,‘ said sys
tem comprising apair of concentric transmis
sion line sections each including an outer tubu
lar conductor and an inner conductor and com
prising means for producing distributed negative
conductance whereby waves propagated by the
system are ampli?ed in intensity, said last-men
tioned means comprising an electronic discharge
'device, means'intermediate said pair of trans
mission line sections for de?ning the region of
and including dielectric members located near 10 said discharge device, and impedance means for
the extremities of the outer conductor of said
terminating said system in such fashion as to
electronic discharge device, tuning means asso
minimize re?ection of said signal-bearing waves
ciated with said inner conductor for neutralizing
and for neutralizing the reflection effects of said
the re?ections incident to said last mentioned
last-mentioned
means, said impedance means in
15
7 means, and additional tuning means for render
cluding reactance components connected to said
ing said device self-resonant for waves of a fre
system and having a value such that said de
quency different from the signal frequency and
vice
oscillates at a frequency different from the
for causing said device to serve conjointly as a
frequency of said signal-bearing waves and. serves
local oscillator and a mixer.
4. In a system for propagating Waves derived 20 eonjointly as a local oscillator and mixer.
from a source of signal-bearing waves having
SIMON RAMO.
characteristics determined by the distributed con
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