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Патент USA US3037183

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May 29, 1962
c. L. RUTHROFF
3,037,173
HYBRID NETWORK
Filed Jan. 23, 1959
FIG. /
,V I D
INVENTOR
C. L. RUTHROFF
BY 1%)”. ?é%
ATTORNEY
United States Patent O?ice
3,037,173
Patented May 29, 1962
2
1
the other end of the second coil, that is, by joining non
adjacent ends of the two coils. Utilizing means are con
3,037,173
nected from each of the remaining free ends and from
HYBRID NETWORK
Clyde L. Ruthrotf, Fair Haven, N.J., assignor to Bell Tele
the interconnection to a common terminal. Additional
utilizing means are connected either between the free ends
or between the interconnection and one of the free ends,
phone Laboratories, Incorporated, New York, N.Y., a
corporation of New York
Filed Jan. 23, 1959, Ser. No. 788,648
5 Claims. (Cl. 333-11)
depending upon the impedance match desired.
These and other objects and advantages, the nature of
the present invention, and its various features, will ap
This invention relates to wave transmission systems,
and, in particular, to broad-band coupling arrangements 10 pear more fully upon consideration of the various illus
trative embodiments now to be described in detail in con
commonly known as hybrid networks for use in such sys
nection with the accompanying drawings, in which:
tems.
FIG. 1 shows diagrammatically a hybrid network con—
One of the more useful circuit arrangements employed
nected in accordance with the principles of the invention;
in communications networks is the so-called hybrid net
work. This type of network is of particular importance 15 FIG. 2 is a schematic illustration of the network of
FIG. 1;
in that it makes possible the two-way operation of a
FIG. 3 is a schematic illustration of a hybrid network
telephone line. However, because of its nature, the
modi?ed for impedance matching purposes, and
ordinary hybrid coil is not adaptable to the higher fre
FIG. 4 is a schematic illustration of a hybrid network _\
quencies. Thus, as the range of operating frequencies is
extended, as is the current trend, the problems of distor 20 modi?ed to accommodate single ended utilization means.
Referring to the accompanying drawings, and more
tion and unbalance in hybrid networks have become more
speci?cally to FIG. 1, there is diagrammatically shown
acute. For example, in order to supply gain and to
a ?rst embodiment of a broad-band hybrid network con
transmit pulses of millimicrosecond duration, ampli?ers
nected in accordance with the present invention. The
and coupling networks with bandwidths of hundreds of
megacycles are needed. While the problem of extending 25 transformer T comprises a pair of insulated conductive
?laments 11 and 12, wound together in a substantially
the frequency range of hybrid networks has received the
helical form over coil form 10. Insulated ?laments 11
and 12 are arranged so that their insulated coverings are
attention of many investigators, current circuit arrange- .
ments still fall far short of ful?lling the bandwidth re
quirements presently encountered in the communications
art.
30
in close juxtaposition substantially throughout their entire
lengths. The juxtaposition or contiguous arrangement of
these two wires is such as to produce substantially unity
coupling between the two windings and, in addition, to
produce the equivalent of a uniform parallel wire trans
are described which have bandwidth ratios as high as
mission line from one end of the coil to the other ‘end
20,000 to 1 in the frequency range of a few tens of kilo
cycles to over a thousand megacycles. It is therein in 35 thereof. The double threaded spiral or helical coils de
scribed above are known in the art as bi?lar coils and
dicated that the frequency limitations in a conventional
will be referred to as such hereinafter. The actual spac
transformer of a type which might be used in a hybrid
ing of the conductive portions of members 11 and 12,
network are in great part due to the series self-inductance
and the diameter of said conductors, will be considered
and parasitic interwinding capacitance of the transformer
windings themselves. For example, in a conventionally 40 in greater detail below.
The bi?lar coil is mounted upon a coil form 10 which
wound transformer, the upper end of the pass~band is gen
may be composed of any suitable high permeability, low
erally determined by the large interwinding capacity
loss core material. For example, a number of trans
which resonates at some relatively low frequency, while
formers using nickel-zinc ferrite cores have been con
the low frequency end of the pass-band is limited by a
structed and have given very satisfactory results. While
relatively small coil inductance which appears as a low
coil form 10 has been shown as a toroidal member, it
impedance in parallel with the signal source. While these
may assume any convenient shape consistent ‘with the elec
limitations have been somewhat overcome by the use of
trical requirements of the transformer windings.
miniature construction and new and improved magnetic
Coils 11 and 12 are serially connected by joining non
core materials, this type of approach to the problem has
enjoyed only limited success.
50 adjacent ends 2 and 3 to form an internal interconnec
tion. The latter is brought out as terminal 5.
It is, therefore, an object of this invention to produce
In my copending application Serial No. 734,751, ?led
May 12, 1958, broad-band bi?lar wound transformers
Connected to coils 11 and 12 are the two pairs of con
broad-band hybrid network arrangements using a single
jugate impedances 13 and 14 ‘and 15 and 16. One pair
bi?lar wound coil.
of conjugate impedances 15 and 16 connects between ter
By applying transmission line theory to the transformer
art, broad-band transformers of the type described in my 55 minals 1 and 4, respectively, and the common terminal 6.
Impedance 14, of the second pair of conjugate impedances
copending application are now available. It has been
13 and 14, connects between the common junction 6 and
recognized in accordance with the present invention that
the interconnection 5. The other impedance, 13, is con
bi?lar transformers of this type may be adapted and
nected across terminals 3 and 4.
utilized to produce broad-band hybrid networks by the
appropriate interconnection of the bi?lar transformers 60
In FIG. 2 there is shown a schematic diagram of the
and the external utilization networks. As will be shown
network of FIG. 1 in which impedance 13 of FIG. 11
hereinafter, transformers utilized in this manner preserve
more speci?cally comprises a signal generator 20 and its
their broadband characteristics and produce hybrid cou
equivalent internal impedance R1, and impedance 14 com;
pling properties.
prises a resistor R4. The conjugate impedances 15 and
A broad-band hybrid network constructed in accordance 65 16 are represented by the two equal resistors R2 and R3.
with the invention comprises a pair of insulated conduc
The hybrid operation of the network and its frequency
tive wires, uniformly spaced from each other and wound
response, may be demonstrated by considering the cur
together in a substantially helical form. A coil so wound
has the distributed properties of a uniform transmission
rents produced as a result of a signal E impressed upon
line and the corresponding broad-band capabilities when 70 the circuit by signal [generator 20. Assuming that the
reactance of each winding is much larger than the ter
The two coils thus formed are
minating resistances and that the coupling coefficient k
serially connected by joining one end of one of them to
used as a transformer.
3,0 0 7,173
3
4
is equal to unity, the network equations may be written
Solving fOtl‘ Z0, the characteristic impedance of the trans
as:
former, gives
Zo=\/2R
The transmission T3 to load R3 may also be calculated
and is found to be
T3:
11:12 cos ?l-l-JJZLZ0 sin til
where l is the equivalent length of transmission line
formed by the bi?lar windings 11 and 12, B is the phase
constant of this line, and Z0 is the characteristic impedance
of the line. Solving for the currents gives
2
‘ (1+7
m
10
. - 2 ?l [a
212
cos Bl) 2 +-ls1n
R+ZO
It will be noted that both T2 and T3 at low frequencies
(Blz?) are equal to 1/2, as expected.
15
Letting Z0=\/iI€ and solving for the ratio of the trans
mission to loads R2 and R3, gives
T3_(1+3 cos BZ)2+2 sing at
At low frequencies 51:0 and T2/T3=1, or, equal power
is delivered to each of the load resistors R2 and R3. At
Bl=1r/ 4, or at a frequency -for which the transformer has
an equivalent length equal to one-quarter wavelength, the
ratio of the power delivered to the two load resistors R2
and R3 is 1.218, or the power split is unequal by about 1
, decibel.
Miriam-R1123] 00s al+iZ0 Sin HZIRIJFRSJFR‘]
+j slgflmlmwRlRzRsJrRlRsRd
At half a wavelength, the ratio of power de
livered to the two resistors is 3:1.
The ratio of power delivered to the conjugate resistor
R4 to the available power is given as
30
For balanced loads and matched conditions,
T
_4(cos Bl-1)Z+2 sin2 Bl
“(1+7 cos Bl)2+32 sing at
At 18l:0, T4 is equal to zero. At ?l=1r/4, T4=.O332 or
or the insertion loss from R1 to R4 is about 30 decibels.
Ideally, of course, the insertion loss should be in?nite
Under these conditions,
R1=R4=Rtheand
currents can be written as
, at all frequencies or T4 should equal zero.
In the embodiment of FIG. 1 and FIG. 2, the con
jugate resistors R1 and R4 are equal. In some applica
tions, however, these resistors are more conveniently made
unequal. In particular, for those applications in which
R1=4R4, the circuit is modi?ed as shown in FIG. 3,
wherein resistor R1 is connected across both of the serially
connected coils ‘11 and ‘12. As shown, resistor R1 con
nects from the terminal 1 to terminal 4, all other con
nections being the same as in FIG. 1.
In either arrangement, however, the characteristic im
pedance of the transmission line formed by the bi?lar
wound coils 11 and 12 is given as Z0=\/_27€. In terms of
the Wire size and spacing,
Ideally, the current in R4 should be zero. Actually, this
current is
50
However, at low frequencies, when the wavelength is
large compared to the winding length, BI is small and
the current (Ia-I2) approaches Zero in amplitude.
The transmission T is given as the power delivered to
the load resistors R2 and R3, divided by the available
power,
E2
4R
where
n is the effective permeability;
e is the effective dielectric constant;
b is the distance between wire centers, and
a is the wire diameter.
An examination of the hybrid networks shown in FIGS.
60 1 and 3, discloses that at best only three of the four loads
For load resistor ‘R2,
can be grounded simultaneously. In FIG. 2, the common
terminal 6 for resistors R2, R3 and R4 is grounded, where
as the generator, 20, is double-ended, or balanced with
X1?
respect to ground. This arrangement may be modi?ed,
65 and all four load resistors operated single-ended, by using
or
an additional bi?lar transformer as shown in FIG. 4. In
T2:
2(3-l-cos (Bl)2
FIG. 4, generator 20 and resistor R1 are connected to
2
transformer I‘; through the second transformer T2 which
(1+7 cos sz)2+4 sin” al<-Z—“+-2la
R Z0
acts as a simple balanced-to-unbalanced transformer. Be
cause of the broad-band properties of this type of trans
The transmission is a maximum when the coe?icient of
sin2 pl is a minimum or where
dZ02R2
217, n+2; =0
'
former there is no appreciable degradation in frequency
response. The characteristic impedance of transformer T2
is either R or 4R depending upon whether the arrange‘
ment of FIG. 1 or FIG. 3 is used. In either arrangement,
75 however, all four loads may be operated single-ended, with
3,037,173
5
the grounds as shown in FIG. 4 as a typical arrangement.
In all ‘cases it is understood that the above-described
arrangements are illustrative of a small number of the
fourth circuit is connected between said free ends and has
many possible speci?c embodiments which can represent
applications of the principles of the invention. Numerous
and varied other arrangements can readily ‘be devised in
accordance with these principles by those skilled in the
art without departing from the spirit and scope of the
invention.
fourth circuit is connected between one of said free ends
and said interconnection and has an impedance R.
4. The combination according to claim 1 wherein said
common terminal is grounded and said fourth circuit is
having a characteristic impedance Z, comprising two
which is unbalanced with respect to ground.
an impedance 4R.
3. The combination according to claim 1 wherein said
balanced with respect to ground.
5. The combination according to claim 1 wherein said
What is claimed is:
10 common terminal is grounded and said fourth circuit com~
prises an unbalanced-to-balanced transformer and a load
1. In combination, a two-element transmission line
insulated conductive wires wound together in a substan
tially helical form to form a pair of coils, said wires being
contiguous and parallel from the ?rst end of each to the 15
second end of each, said coils being serially intercon
nected ‘with said ?rst end of one being connected directly
to the second end of the other, first and second external
circuits each having an impedance 2R connected from
each of the remaining free ends of said coils to a common
terminal, a third external circuit having an impedance R
connected from said interconnection to said common
terminal, and a fourth external circuit connected between
a pair of ends of said coils wherein said characteristic
impedance and said external circuit impedances are re- 25
larted by z,=\/2_RT
2. The combination according to claim 1 wherein said
References Cited in the ?le of this patent
UNITED STATES PATENTS
1,755,243
2,229,078
2,654,836
2,735,988
2,736,864
2,875,283
Crisson ______________ __ Apr. 22, 1930
Hansell ______________ __ Jan. 21, 1941
Beck __________________ __ Oct. 6, 1953
Fyler ________________ __. Feb. 21, 1956
Sinclair ______________ .__ Feb. 28, 1956
Maione ______________ __ Feb. 24, 1959
OTHER REFERENCES
Article, “The Hybrid Coil,” from. Electrical Communi
cation by Arthur L. Albert, 2nd ed., John Wiley & Sons,
Inc. (1940), page 434 relied upon.
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