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Патент USA US3089984

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May 14, 1963
R. c. HERGENROTHER
3,089,974
LOW DISPERSION INTERDIGITAL DELAY LINES
Filed Dec. 18, 1959
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RUDOLF 0. HER65NRO THEI?
By Maw/M
A TTORNEY
United States
C
1
3,089,974
Patented May 14, 1963
2
portions. By reason of this con?guration of the ?ngers
3 089,974
I;
LGW DISPERSION INTERDIGITAL DELAY LINES
Rudolf C. Hergenrother, West Newton, Mass, assignor to
Raytheon Company, Lexington, Mass, a corporation of
Delaware
successive wave paths are displaced in a direction per
pendicular to the wave and perpendicular to the electron
?ow. As a result a single electron ‘beam couples strongly
5
to only every other Wave passage, thus in successive en
counters with the electron beam only waves traveling in
the same direction are coupled therewith. This results
in a non or low dispersive fundamental mode similar, for
' This invention relates to traveling wave tubes and more
example, to that of the helix and a delay line having the
particularly to a low dispersion interdigital delay line for 10 most desirable characteristics of the helix and interdigital
use in traveling wave tubes and the like wherein ampli
type delay lines without their undesirable characteristics.
?cation of wave energy is effected by interaction between
The above-mentioned and other features, advantages,
a traveling wave and a stream of electrons.
and objects of the present invention will become more
For successful operation of such tubes, it is necessary
apparent by reference to the following description taken
that the electron velocity and the phase velocity of the 15 in conjunction with the accompanying drawing in which:
Wave to be ampli?ed be approximately the same. The
FIG. 1 is a longitudinal cross section of a traveling
Filed Dec. 18, 1959, Ser. No. 860,426
5 Claims. (Cl. SIS-3.6)
electron velocity depends upon the magnitude of the volt
wave tube illustrating the principles of the invention; and
age used to accelerate the stream. Owing to the increase
FIG. 2 is a perspective view with parts broken away of
in mass with velocity, the additional voltage required to
a portion of the improved delay line to more clearly show
produce a given additional electron velocity will increase 20 the delay line structure.
more and more rapidly as the velocity of light is ap
Referring now to FIG. 1 which shows an 0 type for
proached. For this reason it is impracticable at present
ward wave ampli?er, a delay line 11 constructed in ac
in tubes of the described type to use electron velocities
cordance with the invention and more thoroughly de
greater than one quarter the velocity of light. Conse
scribed hereinafter is shown extending substantially
quently, some means is required for propagating the wave 25 throughout the major portion of the tube envelope 12.
at a correspondingly low velocity with respect to that of
The tube envelope 12 is fabricated of a non-magnetic
light. A typical prior art structure for this purpose com
metallic material and is provided with insulative seals at
prises a helix which is supplied at one end with the input
convenient locations through which electrical connections
energy in such a manner as to carry a slowly traveling
are made ‘to elements housed in the envelope. The delay
wave along its axis. The electron stream is directed along 30 line 11 is shown as an interdigital line. A volt-age source,
the longitudinal axis of the helix in the form of a beam,
here indicated by battery 13, establishes an electric ?eld
and ampli?ed energy appears at the output end of the
in the interaction spaces bounded by the delay line and
helix.
the adjacent opposite Walls of the enclosure. A magnetic
Another typical prior art structure for the same pur
?eld is established in the enclosure 12 to prevent spread
pose comprises an interdigital delay line which is also 35 ing of the electron beam or ‘beams by any convenient
supplied at one end with the input energy in such a man
means, such as, for example, a magnetic ?eld produced
ner as to carry a slowly traveling wave. The electron
by coil 14 surrounding the enclosure 12. Current is sup
stream is directed along one or more sides of the delay
plied to the coil by a suitable source, such as, for exam
line in the form of a beam, and ampli?ed energy may in
ple, battery 15. At one end of the tube there are posi
certain embodiments be taken at the output end of the 40 tioned dual electron guns symbolized by electron emitting
line. However, inasmuch as the conventional interdigital
cathodes 16 and accelerating electrodes 17 which are
delay line has a high dispersion it is most suitable for use
‘biased positively in conventional manner with respect to
in a backward wave oscillator since the wave travels in
opposite directions in successive encounters with the elec
tron beam thus resulting in a backward wave fundamen
tal. For a forward wave ampli?er it is desirable to have
a non-dispersive delay line for a large bandwidth such as,
the cathodes 16 by the battery 18. A wall 19 having suit
able apertures 21 is disposed between the accelerating
electrodes 17 and the delay line 11. The cathodes 16 each
enclose a heating element 22 which is connected to a suit
able source of energy such as battery 23. Collector elec
for example, a helix. However, the helix ordinarily con
trodes 24 are situated at the end of the ‘tube opposite from
sists ‘of many turns of relatively ?ne wire and must be
the electron source. Input energy to the delay line 11 is
supported to maintain its shape and pitch. On the other 50 provided by input coupling 25 connected to the delay line
hand a tube utilizing an interdigital delay line has im
adjacent the gun end of the tube and the output of the
proved power handling capability but as pointed out here
tube is obtained from an output coupling 26 connected to
inabove it is not generally suitable for use in a forward
the delay line adjacent the collector end of the tube.
wave ampli?er.
Although a. dual electron gun has been shown it is to
55
The present invention has for its object to provide an
be understood that a dual gun of other construction or a
improved delay line or the like suitable for use in a for
single gun may be used with either an 0 type or M type
ward wave ampli?er.
tube construction.
In accordance with the invention, oppositely disposed
With particular reference now to the delay line as
and electrically connected portions of adjacent delay ele
ments or ?ngers comprising a delay line are displaced or
60 shown in FIGS. 1 and 2 {and as more clearly shown in
FIG. 2, successive ?ngers of the delay line 11 are electri
distorted toward each other along the longitudinal axis
cally connected at one end to opposite walls of the'en
of the line whereby as between any two adjacent ?ngers
velope 12 perpendicular to the electron ?ow and are of
oppositely disposed portions of each ?nger are in closer
such length that their free ends are spaced from the wall
spatial relationship than the other two oppositely disposed 65 adjacent thereto by a predetermined distance determinable
3,089,974
3
4
step in the direction of the longitudinal axis of said line,
in well-known and conventional manner. However,
where the entire oppositely disposed surfaces transverse
to the electron beam of the ?ngers of conventional inter
one pair of oppositely disposed portions of adjacent delay
elements being displaced toward each other with respect
to the other portions of said ‘adjacent delay elements.
digital lines lie in parallel planes, portions of adjacent
2. In a traveling wave electron discharge device the
combination comprising: an electron source and electron
beam forming means de?ning at least two paths of elec
tron ?ow, one on each side of an elongate delay line com
?ngers contemplated by the present invention are sym~
metrically equal and offset or staggered in opposite direc
tions to form an abrupt step whereby as between any two
adjacent ?ngers such as, for example, ?ngers Bil-32 two
oppositely disposed portions 33-64 forming a part of
prised of geometrically periodic structure having delay
elements disposed in coupling relationship with said path
one side of the line are spaced apart the required distance
' of electron ?ow, each of said delay elements being com
“a” but the remaining oppositely disposed end portions
prised of two portions transverse to said path of electron
35-—36 on the other side of the line are symmetrically
spaced apart a greater distance “b” which is equal to the
flow and displaced one from another in the direction of
the longitudinal axis of said line to form an abrupt step,
distance “a” plus twice the ?nger thickness. This in
one pair of the oppositely disposed portions of adjacent
delay elements being displaced toward each other with
respect to the other pair of oppositely disposed portions
of said adjacent delay elements, each of said other pairs
creased spacing “b” results in a spacing as between either
one of the aforementioned adjacent ?ngers and the next
adjacent ?nger of the required distance “a” on the side of
the line opposite from that ?rst referred to immediately
of portions being respectively displaced toward the delay
hereinabove. As may now be apparent, the required or
desired spacing of the ?ngers occur consecutively but on 20 elements next adjacent thereto.
3. In a traveling wave electron discharge device the
opposite sides of the line. Stating it another way, on
combination comprising: an electron source and electron
each side of the delay line, all parts of which are sym
beam forming means de?ning at least two paths of elec
metrically equal, the desired- distance “a” between con
tron ?ow, one on each side of an elongate delay line com
secutive but separate sets of ?ngers, for satisfactory cou
pling, is separated by a greater distance “11” such that 25 prised of geometrically periodic structure having delay
elements disposed in coupling relationship with said path
little or no coupling between the wave and the electron
of electron ?ow, each of said delay elements being com
beam occur at the point of increased separation. The
prised of two electrically connected portions transverse
distance “a” is determined in conventional manner for
to said path of electron ?ow and offset one from another
optimum coupling between the wave and the electron
beam, the closeness of spacing controlling impedance and 30 in the direction of the longitudinal axis of said line, a
?rst pair of oppositely disposed portions of adjacent delay
the con?guration of the ?ngers controlling the relation
elements being offset toward each other with respect to
between frequency and voltage. It will now be apparent
that in accordance with the invention there are alternately
provided weak and strong coupling between the wave and
the second pair of oppositely disposed portions of said
adjacent delay elements to form abrupt steps with said
the electron beam, i.e., the appropriate electron beam is 35 econd pair, said ?rst pair of oppositely disposed portions
‘ eing spaced apart a predetermined distance for maximum
effectively coupled to every other wave passage and only
waves traveling in the same direction successively en
coupling, each of said second pair of oppositely disposed
portions being respectively offset toward the delay ele
counter and are coupled to the electron beam as is shown
ments next adjacent thereto for minimum coupling be
in FIG. 1 where the circles with dot-s represent waves
coming out of the drawing and the circles with a cross 40 tween said second pair and maximum coupling between
each of said second pair and the delay element next adja
represent waves going into the drawing. It is this char
cent thereto.
acteristic which results in a non or low dispersive funda
4. A traveling wave electron discharge device compris
mental mode and which permits utilization of an im
ing: an evacuated housing; at least one electron source
proved interdigital delay line in a forward wave ampli
?er and incorporates all of the advantages inherent in 45 and electron beam forming means located in said housing
de?ning at least two paths of electron ?ow, one path on
this and equivalent types of delay lines.
each side of an elongate interdigital delay line located
Although the invention has been shown in combination
with an 0 type tube it will be readily appreciated by those
skilled in the art that it may be applied to an M type tube
and that the invention is not limited to the speci?c appli- r
cation or delay line shown and described. For example,
either a single or dual electron beam may be used in M
in said housing comprised of geometrically periodic struc
ture having delay elements to enable interaction between
a radio frequency wave traveling therealong and said
electron ?ow, each of said delay elements being com
prised of two electrically connected portions transverse
to said path of electron ?ow and offset one from another
in the direction of the longitudinal axis of said line to
or 0 type tubes, the con?guration of the ?ngers may vary
from that shown and described so long as the ?ngers are
symmetrically equal and the opposite portions are in elec 55 form an abrupt step a ?rst pair of oppositely disposed
portions of adjacent delay elements being offset toward
trical contact one with another, or the ?ngers may be
each other with respect to the second pair of oppositely
formed with one or more axial passages through which
disposed portions of said adjacent delay elements, said
an electron beam may be projected.
?rst pair of oppositely disposed portions being spaced
Since many changes could be made in the above
described construction and many apparently widely dif 60 apart a predetermined distance for maximum coupling,
each of said second pair of oppositely disposed portions
ferent embodiments of the invention could be made with
being respectively offset toward the delay elements next
out departing from the scope thereof it is intended that
adjacent thereto for minimum coupling between said sec
all matter contained in the above description or shown
ond pair and maximum coupling etween each of said
in the accompanying drawing shall be interpreted as
illustrative and not in a limiting sense.
65
second pair and the delay element next adjacent thereto;
What is claimed is:
1. In a traveling wave electron discharge device the
means for applying wave energy to one end of said delay
combination comprising: an electron source and electron
line in the direction of electron travel; and means for
beam forming means de?ning at least two paths of elec
extracting said wave from the other end of said delay line.
5. An elongate delay line comprising: a geometrically
periodic structure having delay elements disposed in cou
pling relationship with at least two paths of electron ?ow,
one of said paths on each side of said structure, said delay
elements being comprised of a ?rst group and a second
group, each of said second group being interposed be~
tron ?ow, one on each side at an elongate delay line com
prised of geometrically periodic structure having delay
elements disposed in coupling relationship with said path
of electron ?ow, each of said delay elements being com
prised of two portions transverse to said path of electron
?ow and displaced one from another to form an abrupt
line to induce propagation of said wave along said delay
3,089,974
tween each of said ?rst group, each of said delay elements
spatial relationship de?ning an energy storage gap there
being comprised of two symmetrical and electrically con-
between whereby successive wave paths between adjacent
nected portions offset one from another in the direction
of the longitudinal axis of said line ‘to form an abrupt
delay elements are displaced in a direction transverse to
the Wave and coplanar with the wave.
step, one portion of each of said delay elements of said 5
_
_
?rst group being in closer spatial relationship than its
References Cited In the ?le of this Patel?!t
other portion to the next succeeding adjacent delay ele—
UNITED STATES PATENTS
ment of said second grou , and one portion of said next
succeeding delay element ilacing in closer spatial relation-
21888595
Warnecke et a1 -------- —— May 26’ 19§9
ship than its other portion to the aforementioned delay 10
element in said ?rst group, the portions in said closer
2’889’486
219161656
Guenard et a1 —————————— —— June 2: 1939
Moms et a1 ———————————— —4 Dec- 8: 1959
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