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Патент USA US3083454

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April 2, 1963
Filed Nov. 30, 1959
United States Patent 0 M C6
Patented Apr. 2, 1963
ther plates of a different material with the further plates
Arthur George Mitchell and John Ralph Bagnali,
Cheiznsford, England, assignors to Engiish Electric
interspersed between the plates of said one metal; deposit
ing metal to a required thickness on at least one longi
.tudinal face of the stack, said metal being a material
different from that used for said further plates; removing
Valve Company Limited, London, England, a company
said stack a sheet of predetermined thickness includ
of Great Britain
ing portions of all the plates in the stack and deposited
Filed Nov. 30, 1959, Ser. No. 856,155
metal holding the same in their relative positions; and dis
Gaims priority, application Great Britain Feb. 10, 1959
solving away the portions of the further plates included
5 Claims. (Cl. 29-—155.5)
10 in said sheet.
This invention relates to the manufacture of delay lines
According to a feature of this invention a method of
manufacturing a comb-like member for an interdigital
and more speci?cally to the manufacture of so-called
interdigital delay lines such as are employed in travelling
delay line includes the steps of making a plurality of
wave tubes.
plates of predetermined thicknesses of one metal; making
As is well known travelling wave tubes operate by virtue 15 a plurality of further similar plates of pre-determined
of interaction produced between an electron stream and
thicknesses of a di?erent metal; assembling the plates and
further plates alternately and clamping them in a stack;
a travelling wave in a delay line adjacent said stream. In
machining the longitudinal faces of the stack to prede
some tubes the travelling wave travels in the same direc
termined dimensions; depositing metal other than that of
tion as the electrons of the stream, while in others, i.e.
in the so-called backward wave travelling wave tubes, the 20 which the further plates are made on at least one longi
interaction occurs between beam electrons travelling in
tudinal face of the stack; removing from the stack a sheet
one direction and a wave travelling along the delay line
of desired thickness between planes which are parallel to
a longitudinal stack face on which no metal has been
in the other opposite direction. A common form of delay
deposited; and dissolving away the portions of the further
line is the so-called interdigital form. In this form of
delay line there are two comb-like members (i.e. members 25 plates in the removed sheet. Preferably the longitudinal
consisting of spaced ?ngers extending from a back-piece)
faces of the stack are machined to be those. of a right
rectangular parallelepiped.
so assembled that the ?ngers of one lie in the spaces
between the ?ngers of the other.
In practice, it is convenient, when depositing metal, to
deposit it on all faces of the stack except one longitudinal
The invention is illustrated in and explained in connec
tion with the accompanying drawings in which FIG. 1, 30 face, and afterwards to cut off ‘from the removed sheet
metal not required in the ?nished comb.
which is provided for purposes of explanation shows part
of a typical known interdigital delay line such as might
The metal deposited is preferably deposited electro
lytically and the dissolving of the further plate portions
be used in a backward wave travelling tube and FIG. 2
illustrates one way of carrying out the present invention.
in the removed sheet is preferably effected by a solvent
Referring to FIG. 1 the delay line therein partly shown 35 which will dissolve the material of the further plates but
not the material of the ?rst mentioned plates or the de—
consists of two comb-like members A and B (shown
broken away) each consisting of a back-piece A1 or B1
posited metal. To quote preferred practice, the ?rst men
from which extend parallel rectangularly sectioned ?ngers
tioned plates and the deposited metal may be copper and
the further plates may be steel, hydrochloric acid being a
interleaved between and spaced from the ?ngers A2 of 40 suitable solvent in this case.
comb A.
If the comb member is required to have ?ngers all of
An interdigital delay line for use in a travelling wave
the same width the ?rst mentioned plates will be all of
tube has to be dimensioned with high precision in order
the same thickness and, similarly, if the ?ngers of each
comb are to be separated by the same spacings the further
that the tube is to have required characteristics and per
formance. This necessity for high precision leads to 45 plates will be all of the same thickness. However, it will
manufacturing dif?culties and known methods of manu
be apparent that by suitably choosing the thicknesses of
facturing interdigital delay lines are very expensive to
the plates assembled in the stack, combs with ?ngers of
A2 or B2. As will be seen the ?ngers B2 of comb B are
practice with the high degree of precision often required.
desired ditferent widths and/ or with desired different spac
The most important dimensions are shown in FIGURE 1
ings may be made.
and are (a) the ?nger length L, (b) the ?nger spacing S, 50
(c) the pitch P, i.e. the distance between the centre line
of one ?nger of one comb and the centre line of an
FIGURE 2 shows an intermediate stage in a preferred
method of manufacturing a comb member for a line such
as that shown in FIGURE 1.
Referring to FIGURE 2 two sets of plates 1 and 2
adjacent ?nger on the other comb, and (d) the thickness t.
In some tubes the pitch is constant, but in others, it
are made, the plates ‘1 being of copper and the plates 2 of
changes along the length of the line. To manufacture an 55 ‘some other material, for example, steel. These plates
interdigital line such as that shown in FIGURE 1 by
are all machined accurately to predetermined thicknesses.
machining the combs from the solid is an expensive proc
In the case of a comb having identical ?ngers throughout
ess and it is particularly di?icult and expensive to make, by
its length with identical spacings between them, the plates
such machining, a series of interdigital lines all precisely
1 are machined accurately to‘ be of a thickness equal to
of the same dimensions-as is required, of course, if a 60 the required ?nger width (the ?nger dimension at right
series of tubes of the same performance and characteristics
angles to the dimensions L and t of FIGURE 1) and the
is to be obtained. The present invention seeks to provide
plates 2 are accurately machined to a thickness equal to
improved methods of manufacturing interdigital lines
that required for the spacing between two adjacent
which will satisfy the onerous requirements as to precision
and be at the same time relatively economical and easy to
?ngers of the comb. The plates 1 and 2 are then assem
bled in a stack so that they alternate with each of the
practice under factory conditions.
plates 2 between a pair of plates ‘1.. The plates in the
According to this invention a method of manufacturing
stack are clamped ?rmly together in any convenient
a comb-like member for an interdigital delay line includes
way, for example, by one or more longitudinal studs pass
the steps of making a clamped stack of plates of prede
70 ing therethrough and carrying clamp nuts on their ends,
termined thicknesses and of the same shape and face
and the stack longitudinal faces are machined to form
areas, said plates including plates of one metal and fur
those of a right rectangular parallelepiped of desired
3 .
said plates including plates of one metal substantially in
soluble in a- predetermined solvent and havingthicknesses
equal to the widths of said ?ngers and further plates of
di?erent material soluble in said predetermined solvent
and having thicknesses equal to the spacing between said
?ngers with the further plates interspersed between the
plates of said one metal; depositingmetal'to a predeter
dimensions. One clamp stud is represented at 3 in FIG
URE 2, but obviously more than one'could‘ be provided
and .they may be placed in any convenient position
through the stack. The. required precise con?guration of
the stackis‘ preferably obtained, as sta.ted,-wby accurate
machining of its ‘four longitudinal faces after assembly,
though it is vpossible (though not preferred) to machine‘
the edges of the individual ‘platesbef-ore assembly.
mined thickness on all ‘outer faces of the stack except on
one longitudinal outer face of the stack, said predeter
‘ ‘One. longitudinal face, for example, therface 4 of the
stack, is now masked in any convenient’ known manner 10 mined thickness of the deposited metal being su?'icientto
cause said deposited metal mechanically and electrically
soasto make it resistive to plating depositionand the
to bond said deposited metal to the platesof said one
stack with its masked face is immersed in a copper electro
metal and to hold together and unite said stack of plates,
plating bath. Copper is then deposited to a required pre
said deposited metal being a material di?erent from that
determined thickness (say one quarter of an inch) over
thehnmasked‘faces of vthe stack, that is‘ on less than all of 15 used for‘ said further plates and being. substantially in
chanically and electrically bonded ‘to the copper of which‘
soluble. in said predetermined solvent;.ren1oving from said.
stack,-along aplane Whichds parallel to, said one longi-.
theplatesljare formed.‘ Such a predetermined thickness
of vth'edeposited metal is suf?cient to hold together and
unite the stackzof plates. The deposited'copper, shown
20 and deposited metalholding the. same in their relative
the longitudinal-faces of the stack, so asrto become me
tudinal out-er face of said stack, a sheet of predetermined
thickness including ‘portions of‘all 1the plates in. the stack
broken away in one. place in FIGURE 2, is represented
in thesaid ?gure at 5. n
The plated stack is now removed from the bath and
cleaned and a “slice”'or sheet is cut from the plated stack
alonga plane of cutting running parallel to. the unplated
face-4., This planeiof. cutting is represented by the broken
linev 6- in FIGURE 2 and is so chosen that the resultant
sheet cut away has a. thickness a little more than the
required thickness vt (FIGURE 1)}of the ?nished comb.
The sheet is then machined to the required thickness and
it will be seen that it wilconsist of portions of the plates
land 2 sideby side and held together and united by the
deposited copper 5. The machined cut-awaysheet is now
‘immersed in a predetermined solvent ‘in which the metal
of .theplateslis substantially insoluble and the material
of the plates 2_,is soluble The solvent may be, for ex
ampleHCl, which dissolves the steel plates 2 but leaves
the coppersubsta-ntially unchanged. The result will leave
positions; dissolving away the portions. of' the further
plates in saidisheetswith thc?predetermined solvent and.
machining the undissolved remaining. portion of said.
sheet to the required overall dimensions of the ?nished
2. A method of vmanufacturing a;comb-likewmember
having a-set of spaced’?nger-sextending from a back
plate for an interdigital. delayline, said method including
the steps of. :makinga plurality o£ ?rst plates of onemetal
substantiallyv insoluble. in. apredetermined solvent and
having thicknessesequal to.the. widths ofsaid ?ngers;
making a plurality of rfurthersimilarplates of a different
metal soluble in .said predetermined solvent and having
thicknesses-equal tothe spacing between said?ngers;
assembling the ?rstvplateseand'further plates alternately
and clamping-them in a stack; machining the longitudinal
faces ofsthe staclcto.v predetermined dimensions; deposit
ing metal other-than. that ofwhich the further plates are
the plates 1 spaced by spaces previouslyoccupied by the
made on at least one longitudinal faceand. less than .all
along-asplaneparallel to the,unplated face 4, using that
longitudinalstack face on which no metal has been de
‘steel plates 2 and it may then be cut oif at one edge, for 40 longitudinal-faces of.v the‘ outside of the. stack, said de
posited metal beingv substantially insoluble in said pre
example as .indicatedbythe chain line ,7 in FIGURE .2
determined solvent, and . mechanically and electrically
to. give a comb‘ with? ?ngers of a required length L‘. The
bondingsaid deposited metal to said ?rst plates, said de:
comb is then sintered and two such combs when ?tted
posited? metal being. deposited o-n..said one. longitudinal
together, .for exampleby-bolting on to a base plate (not
face in su?icient thickness to hold together and unite said
shown) ‘willhform. an i-nterdig'it-al linelikethat of FIG
stack 10f plates; removing frornthe. stacka sheet which
URE 1.. It will. be seen that great accuracy at relatively
includes depositedzmetal which has been. .depositedon
small'post can. be obtained with this ,method of‘manu
one of-isaid longitudinal facesand which sheet is of de
facture. Furthermore,.a-conside-rable‘number of sheets
siredthicknessbetween planeswhich areparallel to a
can, be cut from the same stack bytcutting each time
face as, a datum forcutting. (for the ?rst cut), and subse
quent parallel faces left by eachv cut as a, datum for the
next cut. All such sheets orslices will be. to a high‘ de
greeiof accuracy alike after being machined for thick
ness, so that two combs made- in. this way from the same
stack will interleave with great precision. In practice the
plates of the stack may be made. large enough to enable
a considerable number of ‘sheets, each of which will ulti
mately form a comb, to be cut therefrom. Furthermore,
by suitablychoosing the thickness of the individual plates
in the stack the method of manufacture may be. used for
making combs of desired varying pitches.
Of course, ‘the invention is not limited to the use of
copper and steel, but these materials are quite convenient 65
and practical.
We claim:
1. A method of manufacturing acomb-like member
havinga set of_ spaced ?ngers extending from a back
plate, for an interdigital delay line, said method including 70
the steps of making'a clamped stack of plates of predeter
mined-thicknesses and of the same shape and face areas,
posited; ‘dissolving away‘ thcportions of the further plates
‘in the removedsheet-With said. predetermined solvent;
and machining. said-sheet to the required overall dimen
sions of the ?nished comb.
3., Amethodas claimed in claim 1 wherein the longi
tudinal ‘faces'ofthe stack .are machined to be thoseof a
right rectangular parallelepiped.
4. A method-as claimed ill-‘Claim 1 wherein the. de
posited metal is deposited electrolytically.
'5.' Amethod as claimed in claim 1 wherein the ?rst
mentionedplates and the deposited metal are made of
copper and the further plates are made of steel.
References Cited in the ?le of this patent
Scott __..__'_ ___________ __ Mar.’ 7', 1950
Lines ________________ __ June 9, 1953
Dench ______________ __ May 13, 1958
2,866,727 '
Keegan____.e __________ __ Dec. 30,‘ 1958
Unger et al.‘ _.. _______ __ Apr. 21, 1959
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