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Патент USA US2408272

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Sept. 24, 1946.
w. w. RlGRoD ETAL
Filed Augf 12, 1942
Patented Sept. 24, 1946
William W. Rigrod, Bloomfield, and David Gordon
Clifford, Montclair, N. J., assignors to Westing
house Electric Corporation, East Pittsburgh,
ì ì Pa., a corporation of Pennsylvania
Application August 12, 1942, Serial No. 454,615
7 Claims. (Cl. 178-44)
This invention relates to coaxial terminal as
semblies, and while shown in direct connection
with an ultra high frequency device, is of a char
meral I!! designates generally the evacuated body
of an ultra high frequency generator of which
the above-mentioned “Klystron” is an example.
acter usable in any part of a coaxial line where a
From this generator body protrudes a hollow pipe
bead of dielectric is employed for spacing and/or
sealing the channel enclosed by the tubular part
or tube I I formingpart of a coaxial terminal.
This tube II is preferably of a material having
substantially the same coefficient of expansion
as borosilicate glass, such material being sold
in trade as “Kovan” One end of this “Kovar”
tube is silver soldered or otherwise mounted
vacuum tight on the body Il] and in communica
tion with the interior of said body. The other
of the coaxial line.
Presence of a dielectric bead in a coaxial line,
and more especially in a terminal structure pre
sents an impedance discontinuity. For instance,
in association with an ultra high frequency gen
erator sold under the trade name of “Klystron,”_
a bead oi' Corning '704 glass has been used at the
end of a short coaxial line, said line constituting
a “plug-in” terminal for attachment of a further
coaxial line leading to some other instrumen
tality. In that particular construction the bead
vacuum seals the parts of the coaxial line of the
terminal so that one end is under the Vacuum of
the generator whereas the otherl end of the ter
minal is open to the atmosphere. The speciiic
construction referred to utilizes a bead of ap
proximately one quarter inch in length and about
the same or somewhat greater diameter. It has
been determined that such a bead presents a
reñection factor of about 30% due to the irn- l
pedance discontinuity, thereby seriously impair
ing the eiiiciency of the available output of the
An object of the present invention is to over
end of said “Kovar” tube is sealed with a dielec
tric closure or bead I2, preferably of borosilicate
glass of the character just mentioned. Said clo
sure I2 is of a generally cylindrical formation
the outer cylindrical surface by preference con
stituting a continuation of the outside cylindrical
surface of the hollow pipe or tube II to which it
is sealed,
Axially of the tube I I and closure I2 is the cen
tral member or rod I3, the assembly of these
parts being known in the trade as a coaxial line.
The inner end of the rod forms a suitable loop
I4 Within the resonant cavity with the terminus
of the rod silver soldered or otherwise joined to
the inner terminus of the tube. The outer end
of the central member or rod I3 continues for
wardly through and beyond the dielectric clo
sure or bead I2, said bead making sealing con
tact therewith. As shown, said closure or bead
axial line bead.
is formed with a body portion I5 which is cylin
A further object is to overcome the reflection
drical at its outer face in continuation of the
loss of a vacuum-sealing bead in a coaxial line
cylindrical outer face of a collar portion I6 the
35 far end of which is the part sealed to the metallic
Another object of the invention is to provide a
tube I I. The body portion of the bead I2 iills
structure which is readily manufactured, strongly
the entire cross-sectional area from the said
built, conveniently assembled and applicable at
outer cylindrical surface to the coaxial or central
a later time to the concentric line portion previ
rod member I3, and it is this portion of the bead
ously sealed to the generator.
40 which heretofore has been troublesome in caus
Still further objects will appear to those skilled
ing wave energy reflection.
in the art both by direct reference thereto as the
In accordance with the present invention thisv
come the high percent reñection loss of a co
description proceeds and by implication from
the context.
impedance discontinuity may be overcome by
using with the said bead I2 a washer-like ring
Referring to the accompanying drawing in
' I7 of dielectric engirdling the body portion I5
which like numerals of reference indicate similar
of said bead. This ring is perhaps best made
parts throughout the several views; ~
Figure l is a longitudinal sectional view of a
of a material having a dielectric constant sub
stantially equal to that of the bead, but from a
practical constructional standpoint a substance
ultra high frequency generator device by way of 50 the dielectric constant of which differs consider
illustration; and
ably from that of glass may be employed. We
Figure 2 is a cross-sectional view on line II-II
have found, for instance, that polystyrene recom
of Fig. 1.
mends itself for use even though its dielectric
In the speciñc embodiment of the invention
constant at the wave length employed O\=l0 cm.)
illustrated in said drawing, the _reference nu 55 is only about half of the dielectric constant of
concentric line terminal applied in place on an
the particular glass (Corning '704) preferably
the same (case A) or different (case B) dielec
tric constant from the glass bead.
Let the radius of the rod or central member I3
be designated by the letter a; the radius of the
bead I5 by letter b; outer radius of the ring di
electric by letter c; and any radius between a and
Overlapping the “Kovar” tube and glass collar
butt joint is a metallic sleeve I8 of good conduc
tivity, such as copper, this sleeve being shown
as extending substantially from the mid-length
c ’by letter r.
of the tube, past the joint and to the near end
Let e1 and e2 designate the relative dielectric
of said collar. At the collar, the sleeve bends
-constants of bead and ring, respectively, and let:
outward forming an oiîsetting portion I 8 and
Z,=surge impedance, in ohms, of the coaxial
then bends again to provide a cuff portion 2U ..10
line at the seal.
extending backward with respect to fthe sleeve
Zo=surge impedance, in ohms, of the line in
portion and in spaced parallelism thereto. Said
cuff portion 20 is of less length ‘than the sleeve
vacuum preceding, and of the line in air follow
ing, the seal.
A general expression for Zl can be obtained
On the outside of the culi portion, in >surface .1.5
theoretically as follows: The units to be used are
contact therewith is an enlarged _cylindrical por
-in the Giorgi System `(M. K. S.--Coulomb), and
tion 2| of an outer tube which Vextends across the
the notation as adopted by Prof. Ernst Weber
peripheral edge of the ring I7 and shoulders in
of Brooklyn Polytechnic Institute:
ward, at 22, next the outer face of said ring. The
inwardly directed shoulder is preferably coexten 20 É-r=complex electric field intensity in radial di
sive .with the flat face of the ring and at its inner
rection (volts/m) at radius r.
periphery merges with an end tube section 23 of
Dr=complex displacement in coulombs/meter2
substantially `the diameter of the “Kovar” tube
at f.
I.I and is concentric with and around the end
A=absolute dielectric >constant of medium, and
portion of the rod member I3 and projects out 25
wardly substantially as far as said rod. Near
its outer end, the tube section 23 may have a cou
ezrelative dielectric constant.
pling boss 24 secured thereon, the outer periphery
Ao=absolute -dielectric constant vof freespace.
of .said boss being threaded for engagement by
a cooperating part of a coaxial cable or other in
strumentality (not shown).
It is now appropriate to call attention to the
fact that the enlarged cylindrical portion 2l ex
c=velocity of electric magnetic radiation in free
tends the full length of the cuiic portion 20 and is
secured thereto, the end of the enlarged cylindri
Ilo=absolute permeability of freeV space defined
cal portion being spun over the end of the culi at
as H0=41r><10-7 henry/meter.
25 for the purpose. Spot welding, silver solder
I‘0=propagation constant of line to TM (0, 1)
ing or like modes of attachment may be substi
tuted for or supplement 'the illustrated spun grip
C1, M, N--boundary-condition constants.
between the parts. Furthermore it is to be noted 40 e=distance along axis of line.
that end vof sleeve I8 overlapping tube II is soft
V=voltage measured between conductors `of line
soldered at its end to said tube, as at 2B, and that
at position z.
this soldering is done at a considerable distance
,azrelative permeability of medium.
from the `dielectric ring. Consequent -upon the
structure described, said dielectric ring may be 45 z`=current in amperes.
1J=velocity of propagation'of energy along line.
ofv a material of lower >melting point than that
C=capacitance per unit length of line in
of solder, a fact which is true `when said ring is
made of polystyrene. Inasmuch as said sleeve,
:inductance per unit length of line in henry/m.
cuff and overlapping tube are all of good con
ducting material, such as copper, brass or the 50 ln=usua1 abbreviation for logarithm.
like, no appreciable electrical losses are intro
Case ifir-Dielectric constant of ‘bead vand ring
are equal: e1=f2=e~
In process vof fabrication, the "Kovar” ítube,
Inasmuch vas only the principal 'TM-mode
concentric rod and glass beadv are assembled on
transmits energy inthe coaxial wave guide, the
the wave >generator or other device. The rest 55 electric ?leld strength for this mode assumes the
general form:
of -the connector parts may be separately assem
bled and then slid onto the bead and tube, and
soldered thereto, as described, at 26. The ysaid
dielectric ring »I1 is juxtaposed to the body por~
If at the position fz where the bead seal is
tion I5 vof the bead, both having approximately 60
the same length. In View ofthe lower melting
located a voltage V can -be 'measured between -the
conductors, then
point of‘ the dielectric ring, ’it may be melted
slightly, ~ar‘ter placement, by gentle torching and
thus effect close contact or virtual unification
between the bead and Vsaid ring.
It can be shown both theoretically and practi
cally that the 'dimensions of .the dielectric to outer
and inner peripheries thereof .have deñnite .rela
tion to the limpedance and that making‘the outer
diameter »of the dielectric greater, with all other
factors remaining the same, the impedance is in
creased. By mathematical calculation it is prac
tical to determine, therefore, proper diameter
for the dielectric ring either with the ring having
J'ufst as lin electrostatics.
The charge per unit length on the inner sur
ñeld distribution is the same, as in electrostatics.
face of a coaxial line is, by Gauss’ law
and, as
By Gauss’ law, as in Equation 3,
Then the Q_:
21I'a‘AEf r_a=21ra-A-a_]m
per unit length is
The voltage V between conductors becomes:
E _M_
17`1n c/a- C
The velocity of energy propagation along the
line is
en Ve
big fue
21TAU[L el 7* + b e3 T
_ q
_2T/Alexis b/a-teahi C/b
Then the current flowing past section z of the
line is
2 A
C: uf“,
if 1°
[an wal-_111 c/b]
'L =q-v=m-wfé- amperes
The capacitance per unit length of line is
Using, as explained above,
The characteristic impedance of the line at the
bead is
U z_ehu. x--=_=«-__.
Vg «A0110 \/€1
< )
The current flowing past the seal is
And the characteristic impedance of the line
at the bead is
In order that no electromagnetic energy be
reflected by the `head-ring combination, it is
necessary that
In order that there be no reilection of energy
at the seal,
Knowing numerical values of all quantities in
Equation 12 except radius c, we can solve this
equation for that numerical value, which is the
dimension desired.
Case B.-Dielectric constant of bead and ring
unequal; that is, e1¢e2~
The foregoing general treatment is applicable,
Knowing numerical values of all quantities in
Equation 20 except radius c, the equation can be
solved for this desired dimension.
Thus we have provided a practical and theo
retically correct means for overcoming the im
pedance discontinuity in a coaxial line of which
one part is sealed in vacuum and an outer part
is in air, by addition of a dielectric ring upon
with modiñcations as stated below.
60 the sealing dielectric bead, and enclosing the
Inasrnuch as the energy density is greatest in
ring Within the outer conductor. Whether the
the region of maximum ñeld strength, which in
said ring has the same dielectric constant as the
a coaxial line is in the vicinity of the central
bead or a different constant does not alter the
conductor, the energy transport takes place prin
invention here disclosed as it is then but a mat
cipally through the glass bead.
65 ter of calculation as to the necessary diameter for
This phenomenon permits the assumption that
the dielectric ring.
the propagation characteristics (I‘n and v)
Since the various details of construction, as
through the bead-ring combination are, to a
well as the precise relation and functioning of
close approximation, the same as through the
parts are subject to variation and change with
bead alone.
70 out departing from the inventive concept or
If all the wave energy suffers the same re
scope of the invention, it is intended that all
tardation in velocity and change in phase in
matter contained in ,fthe specification or illus
traversing the seal, it retains essentially its char
trated in the drawing, shall be interpreted as
acter of a plane electromagnetic wave of the TM
exemplary and not in a limiting sense. It is also
(0,1) mode. Then, as in case A, the transverse 75 to |be understood that the following claims are
intended ‘to cover all rof the generic and specific
lfeatures of the invention herein 'shown vand de
scribed and all statements of the scope of the
invention herein >set forth as a matter of language
which might'be said to fall therebetween.
We claim:
1. A coaxial terminal assembly comprising a
dielectric means, tubular coaxial line portions ap
proaching the dielectric means at opposite ends, a
central rod through the dielectric means axially
diameter than said tubular .coaxial line portions,
and a sleeve secured to one 'of said coaxial ‘line
portions, said sleeve having a turned back cuñ
.portion and the other-coaxial line portion having
an enlarged cylindrical portion overlying said
5. A coaxial terminal assembly having a tubu
lar portion and a coaxial rod, a bead vacuum
sealing said tube portion with the rod project
ing through `said bead and providing therewith a
surge impedance in the coaxial line, and a di
disposed with respect to both said coaxial line
electric ycollar outside theV vacuum seal :of 'the
portions, said dielectric means having one part
bead increasing the elfective diameter of the
thereof sealing one of the coaxial line portions
fbead and surge impedance to substantially equal
and having a part of -greater diameter than said
one part, and conductive means overlying said 1.5 surge impedance between the tubular pontion and
rod adjacent said bead and collar.
dielectric means and »connecting said tubular
6. A coaxial terminal assembly comprising a
coaxial line portions, said dielectric means with
said overlying conductive means and portion of
pair of alined 'tubular portions and a coaxial
rod therein having a surge impedance substan
tially equal to the surge impedance of the co
axial line portion adjacent said Ádielectric means.
2. A coaxial terminal assembly having a tubu
lar portion and a coaxial rod, a bead sealing said
tube portion with the rod projecting through said
rod, a bead vacuum sealing a iirst one of said
tubular portions with said rod projecting through
the bea-d and into the second Vone of said tubu
lar portions, the ñrst one of said tubular portions
and bead having substantially equal outside di
ameters, the second one of said tubular portions
having an enlarged cylindrical portion overlying
bead, and providing therewith a surge impedance
discontinuity in the line, and means for increas
ing the eiTective diameter of the bead and surge
said bead, a dielectric ring. included between
impedance to substantially equal the surge im
pedance between :the-tubular portion and rod ad
jacent said bead.
3. A coaxial terminal assembly having a tubu
and conductive means connecting the two tubu
lar portions and having a pant thereof in sur-V
face contact with the surfaces of equal diameter
lar portion and a coaxial rod, a bead sealing said
tubular portion with said rod projecting through
the bead, said tubular portion and bead having
said bead and -'said enlarged cylindrical portion,
of said iirst tubular portion and bead.
7. A coaxial terminal assembly comprising a
pair of alined tubular portions and a coaxial
rod, a ibead vacuum sealing a first one of said
substantially equal outside diameters, a sleeve
tubular Portions with said rod projecting through
constituting a continuation of said tubular por
the bead and into »the second one of said tubu
lar portions, the first one'of îsaid tubular por
tion and slid thereon, a dielectric ring juxtaposed
on said bead and abutting said sleeve, and a sec
ond tubular portion in axial alinement with the
ñrst said tubular portion and abutting said ring
and having an enlargement overlying said ring
peripherally, thereby obtaining electrical con
tinuity of the tubular portions and vmechanical
connection therebetween.
4. A coaxial terminal assembly comprising a 45
tions and bead having substantially equal out
side diameters, a sleeve slipped over the adjoin
ing parts of said bead and ñrst tubular portion, a
dielectric ring girdling anotherv part of said bead
and in endwise engagement with said sleeve, Isa-idv
sleeve having a turned back cuff portion the out
side diameter Whereof is substantially that of
the ring, and said second vtubular portion hav
ing an enlarged portion overlying 'said ring and
dielectric means, tubular coaxial line portions ap
proaching the dielectric means at opposite ends,
a central rod through the dielectric means axially
disposed With respect to both said coaxial line
portions, said dielectric means >having a :greater 50
2,408,271.--Willf¿am W. Rigrod, Bloomfield, and David Gordon Olißord, Montclair,
N. J. COAXIAL TERMINAL ASSEMBLY. Patent dated Sept. 24, 1946.
Disclaimer filed Aug. 27, 1949, by the assignee, Westinghouse Eleotrz'o
Hereby enters this disclaimer t0 claims 1 and 2 in said specification.
[Oficial Gazette October 4, 1949.]
2,408,271.--William W." Rigrod, Bloomfield, and David Gordon Olijïord, Montclair,
N. J. COAXIAL TERMINAL ASSEMBLY. Patent dated Sept. 24, 1946.
Disclaimer filed Aug. 27, 1949, by the assignee, Westinghouse Electric
Hereby enters thisdisclaimer to claims 1 and 2 in said speciñcatíon.
[O_?ïcial Gazette October 4, 1949.]
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